Fight Aging!

At the end of 2022, we can reflect on the fact that we are steadily entering a new era of medicine, one in which mechanisms of aging are targeted rather than ignored. It is a profound change, one that will change the shape of a human life and ultimately the human condition by eliminating the greatest sources of suffering and death in the world. Year after year, we see increased funding, ongoing progress towards therapies capable of slowing aging or reversing aspects of aging, and a growing taxonomy of such potential therapies and their target mechanisms.

The view of aging in the medical community and public at large is changing, slowly, in the face of this, such as the recognition that the long-established practice of dividing aging into many different diseases and treating them one by one isn't working. To fight aging one must tackle the causes of aging, and each cause contributes to multiple conditions. One day in the not-so-distant future, the average person in the street will see aging the same way that he or she presently sees cancer, meaning that it is obviously a research priority, something that should be treated and cured.

The Longevity Industry and Associated Non-Profit Initiatives

The longevity industry continues to grow and diversify, and there are now far too many companies and too many venture funds for any one observer, and certainly not this one, to keep up with new teams, new funding, and new projects. Much the same could be said for the non-profit space. The organizer and volunteers at AgingBiotech.info are certainly doing their best to maintain a useful, up-to-date resource, however!

That said, I will note a few items, starting with one sizable fund, Kizoo Technology Ventures, that was profiled earlier this year. It is an important fund because its principals specifically focus on the SENS view of aging: the importance of molecular damage, and the point that rejuvenation will only be achieved by repairing that damage. The SENS Research Foundation released its annual reports a few months ago, and it is, as always, interesting reading for those interested in the science of rejuvenation. Aubrey de Grey has launched a new non-profit, the Longevity Escape Velocity Foundation that will focus on similar work to that conducted at the SENS Research Foundation, with an emphasis on repairing the cell and tissue damage that causes aging.

Fundraising activity was quite energetic prior to the recent market downturn. While many of these companies are actually working on drug discovery platforms or next generation dietary supplements or other low-hanging fruit rather than bold new therapies, there are nonetheless exciting biotechnologies under development as well, true means of rejuvenation. We'd always want to see a larger portion of the industry undertaking that sort of work, but it is what it is. As growth occurs, it is interesting to see the rush to moderation in messaging. It is a longevity industry, yes, but one in which the larger players are quick to reassure the world that they are not in fact trying to produce longevity.

Cellular Senescence

Cellular senescence is an important contributing cause of aging, in that the burden of senescent cells rises with age, and these cells disrupt tissue and organ function with their pro-growth, pro-inflammatory signaling. Researchers are optimistic regarding the potential of therapies targeting senescent cells, even the cautious types, and so is the popular science press. In just the last year, many studies have reported slowing or reversal of specific aspects of aging via clearance of senescent cells, or otherwise implicated senescent cells in disease progression. A partial list: neurogenesis; neuronal function; Alzheimer's disease, liver disease; kidney aging; T helper cell function; atrial fibrillation; reducing pain but not cartilage damage in osteoathritis; loss of microvasculature; atherosclerosis; fibrosis and inflammation in NASH; diabetic macular edema; particularly senescence in vascular smooth muscle; pulmonary fibrosis, amyotrophic lateral sclerosis; chronic obstructive pulmonary disease, and age-related loss of pulmonary function via a range of mechanisms; failure of organ transplants; loss of regenerative capacity in the heart; cardiovascular disease in general; cognitive function and brain aging in late life; amyloid aggregation in the vasculature; sarcopenia via reduced stem cell function; osteoporosis was frequently discussed; disc degeneration; vascular calcification; Parkinson's disease, such as via removing senescent microglia; improving ischemic stroke recovery; accelerated aging due to induction of cellular senescence by chemotherapy and radiotherapy; abdominal aortic aneurysm; immune function in the brain; gum disease.

Clearing senescent cells should be synergistic with stem cell therapies and partial reprogramming, both combinations expected to provoke regeneration. Senolytics should also be synergistic with cancer therapies, providing better patient outcomes with fewer long-term side-effects. These combinations should receive more attention! Further, some research suggests that combinations of senolytics may synergize to improve on the results of any single drug.

New clinical trials continue to be launched for established senolytics, including one for Alzheimer's disease, and senolytics as a class are approaching clinical use. Novel approaches to reducing the burden of senescent cells continue to emerge as the wheels of drug development begin to turn in earnest. Those mentioned in the last year include the following: use of 25-hydroxycholesterol; improving the efficiency of natural killer cells via several approaches; mitochondrial transfer; applying partial reprogramming to senescent cells, something that continues to seem a bad idea; MCL-1 inhibition; control of viral infection; YAP upregulation; mitochondrially targeted tamoxifen; glutaminase inhibition; overexpression of GPNMB; inhibiting the BDNF-TrkB interaction; p53 upregulation; SFRP4 inhibition; overexpression of DDIT4 and HDAC4; PD-L1 checkpoint inhibition; GATA4 inhibition; USP16 inhibition; reducing mitochondrial dysfunction to prevent the onset of some cellular senescence; targeting antoxidants to telomeres; nintedanib, a similar drug to dasatinib; derivatives of FOXO4-DRI.

Mitochondrial Dysfunction

Mitochondrial dysfunction is a prominent feature of aging, and is accompanied by a decline in mitophagy, meaning the cell maintenance processes of autophagy targeted to mitochondria. Attempting to upregulate mitophagy is a popular topic, with approaches mentioned this year including urolithin A (and a clinical trial), BNIP3 upregulation, and iterations on spermadine. Unfortunately none of the easier, supplement based approaches appear to be any better than exercise or calorie restriction when it comes to improve the operation of autophagy in older individuals. There are other stress responses that can be triggered to improve mitochondrial function, such as the unfolded protein response, influenced via protein import mechanisms.

A range of other potential paths to reversing mitochondrial dysfunction are under development. Reprogramming is one of the more prominent, followed by the various groups developing the basis for mitochondrial transfer therapies. Researchers recently demonstrated editing of mitochondrial DNA in vivo, though it seems challenging to use this technology to deal with stochastic mutational damage. The role of mitochondrial DNA mutation remains much debated, both for and against. Other approaches mentioned this year include: enhancing mitochondrial fission to restore the imbalance in mitochondrial dynamics; magnetic fields used to improve mitochondrial function; use of antifibrosis drugs to improve mitochondrial metabolism; use of mitochondrially derived peptides; sirtuin upregulation; upregulating NAD levels via NMN supplementation and CD38 inhibition; partially inhibiting complex I of the electron transport chain; and mitocondrial uncoupling via newer, safer means than in past decades. Too few of these approaches seem likely to have large effect sizes, unfortunately.

Clocks for Aging

The number of clocks that assess biological age, derived from omics data and other measures, is proliferating rapidly. Even only considering epigenetic clocks the number is steadily increasing. Fortunately, at least some effort is being put into comparing clocks in order to winnow out the less helpful ones. New clocks noted this year incuded: a retinal image clock; a metabolomics clock; a clock for naked mole-rats; and a lipid clock.

This broadening of work on clocks is taking place because a consensus measure of aging would revolutionize the field, enabling rapid, directed progress towards the best approaches to treat aging as as medical condition. This point is widely recognized. We are not there yet, however, as the clocks developed to date are not yet well enough understood. Despite a few inroads, the connections between epigenetic aging and the rest of aging are not yet well mapped.

There appear to be some odd blind spots in many clocks, such as inflammatory status and biases in centenarian epigenetic age. Reduced epigenetic age does not prove slowed or reversed aging, we should probably be suspicious of clocks that use few data points, and all studies measuing clock data must also measure other metrics of health and disease. This state of affairs is not preventing speculation as to whether the existence of cross-species clocks should mean that therapies that actually address root causes of aging should perform equally well between species, or that epigenetic clocks will point the way to a true identification of the causes of aging.

Partial Reprogramming

There is so much money flowing into the exploration of partial reprogramming with Yamanaka factors and potential alternatives, in order to restore more youthful epigenetic patterns and thus more youthful cell behavior, that we're going to see a great deal of coverage, even in the popular press, in the years ahead. Hopefully the obstacles are overcome, such as the inclination of natural killer cells to attack reprogrammed cells, and the techniques improved, and this turns out to be a viable path to rejuvenation at the end of the day. It can't fix everything, but we can hope that it will positively influence many aspects of aging.

The fundamental research in animal models is getting funded as well, and continues apace. Progress in understanding and capabilities is quite rapid. If interested in the present state of play and the road to the clinic, there were a number of popular science overviews published following the large-scale funding of Altos Labs and other companies. Alternative approaches to reprogramming beyond Yamanaka factors are being considered. Is it possible to reprogram effectively with small molecules? Time will tell. Researchers are starting to think about the specific conditions they might treat with reprogramming approaches. Some of those metioned in the last year include: disc degeneration; T cell exhaustion resulting from cancer; and liver injury.

Neurodegeneration

Neurodegeneration is connected to near all of the mechanisms and environmental factors studied in the context of aging. Novel approaches to the treatment of neurodegenerative conditions are constantly suggested, and existing approaches mentioned while under development. A selection from the past year includes the following items: the use of disaggregases to clear amyloid, while noting that amyloid is still the primary focus in Alzheimer's treatment, despite continued failures in clinical trials; forcing microglia into the anti-inflammatory M2 polarization, or clearing them entirely; TREM2 antibodies to prevent the incapacity of microglia in the aging brain; transfer of cerebrospinal fluid from younger donors; a combination of rapamycin, acarbose, and phenylbutyrate; adjusting the aging gut microbiome; greater control of viral infection, particular those involving herpesviruses capable of persistent infection; whole blood exchange to encourage amyloid-β to leave the brain into the vasculature; reprogramming astrocytes into neurons in vivo; drugs to decrease microglial inflammation slow neurodegeneration in early stages; influenza vaccination correlates with a 40% reduced Alzheimer's risk; transcranial direct current stimulation; provoking greater activity in neural progenitor cell populations; Atoh1 gene therapy to regenerate hair cells in the inner ear; activating or somehow expanding the limited supply of precursor neurons; immunization against amyloid-β; use of plasmalogens; GM-CSF treatment improves memory in mice; enhancing neurogenesis to treat Alzheimer's, such as via upregulation of oxytocin.

The good news is that manifestations of neurodegenerative processes, such as cognitive impairment, are in decline, and those on the path to dementia can now be screened early, years in advance of symptoms. This lowered risk is likely the result of improved cardiovascular health, while individually reduced risk is offset by the aging and growth of the population, leading to higher absolute incidence of disease. Being fitter correlates with better late life cognitive function, and exercise with improved synaptic function, as well as improved brain function more generally. Physical fitness also clearly reduces dementia risk and improves brain function, perhaps largely via lowered blood pressure, with as much as 40% of dementia cases being the result of lifestyle choices.

Aging of the Immune System

Chronic unresolved inflammation is a key feature of aging. Immune system aging is these days described as a mix of immunosenescence and inflammaging; every year a few review articles discuss the definitions and relationship between them. Important areas of declining function include the thymus and hematopoietic populations in the bone marrow, though every aspect of the immune system shows loss of function. The thymus atrophies with age, a sizable contribution to the decline of the adaptive immune system. Modest calorie restriction in humans has been shown to produce a surprisingly large regrowth of active thymus tissue, a surprising result that suggests the thymus is more dynamic in adults than suspected. KGF overexpression and introduction of subpopulations of thymic cells produces an enlarged thymus in animal studies, but would need a clever delivery mechanism to get the therapy into the thymus in humans.

Various approaches are under consideration to reverse immune aging, either generally or focused only on narrow issues within the broader set of problems. Lowering the lifetime burden of infection will likely slow hematopoietic aging. Upregulation of autophagy might help slow immune aging. A gene therapy delivering a BPIFB4 variant improved immune function in old mice. PGD2 inhibition can help with the slowdown in some narrow aspects of immune cell communication, improving the immune response. Trained immunity is an interesting phenomonen in which some challenges can improve innate immune function in late life. For example, vaccination with mycobacterium vaccae suppresses chronic inflammation. Calorie restriction has similar effects on innate immune system activation. Lowering inflammation may be a useful treatment for frailty. Targeting the inflammasome may be an improvement on current very blunt methods of suppressing inflammatory signaling, and clearing senescent cells to remove their inflammatory signaling should also help greatly. Other approaches to lowering inflammation mentioned recently include resistance training in older adults and reduced SPARC levels in fat tissue.

The Gut Microbiome in Aging

The balance of populations in the gut microbiome changes with age in detrimental ways, such as via increasing inflammatory signaling, producing harmful metabolites, or a diminished production of beneficial metabolites. This impacts health, and numerous correlations can be drawn between the activity of the microbiome and various manifestations of aging. Adjusting the gut microbiome in lasting ways to restore youthful populations may or may not achieve that much more than choosing a good program of exercise and diet, but it can be accurately measured. One can determine exactly what happened following any given intervention via the sequencing of microbes from a stool sample. Various approaches move the needle, and those in the spotlight this past year include: calorie restriction and methionine restriction; fecal microbiota transplantation was shown to improve function in mice, and this approach was a particularly popular topic in the lead in to FDA approval of one implementation and a few results in aged humans; oral administration of Akkermansia muciniphila; and heterochronic parabiosis, the latter obviously more interesting than useful.

Cardiovascular Disease

Atherosclerosis and consequent cardiovascular disease is the largest single cause of human mortality, and should be a high priority in research and development. A great deal of evidence points to the inflammation of aging as a major driver of atherosclerosis. At the core of the condition, there is macrophage dysfunction where cholesterol overwhelms cells in artery walls. Calcification of vascular and heart tissue occurs in parallel with atherosclerosis, and is known to raise the risk of stroke as well as other cardiovascular events.

Numerous approaches have been suggested in the past year as treatments for cardiovascular diseases and their consequences: upregulation of autophagy; TRPM2 inhibition; targeting matrix vesicles to reduce pro-calcification signaling; CCL17 inhibition reduces inflammation in cardiac hypertrophy; an oligodendrocyte cell therapy, the cells responsible for generating myelin, improves stroke recovery, as does PTPσ inhibition; influenza vaccination can reduce inflammation to reduce stroke risk. Cholesterol continues to be the primary focus of therapeutic development in cardiovascular disease, such as via upregulation of reverse cholesterol transport. Atherosclerosis is in principle highly preventable, and early detection of atherosclerotic lesions might encourage greater success on this front.

Vascular stiffening is a major feature of aging. It is driven in part by degeneration of elastin, but has a broad range of contributing mechanisms. It contributes to many pathologies, even only considering the downstream effects of resulting hypertension, such as vascular restructuring and pressure damage to delicate tissues. Controlling hypertension greatly reduces risk of stroke. Targeting the inflammasome in vascular tissues or the use of SGLT2 inhibitors may reduce the aforementioned vascular dysfunction. Inhibition of piezo1 signaling may block the connection between hypertension and vascular hypertrophy.

Cancer

Cancer is the second largest cause of mortality in our species. It is a numbers game: damage and cell replication versus the odds of the wrong combination of mutations occurring in a cell, leading to unfettered replication. We might imagine that any narrow rejuvenation therapy that improves regeneration and increases cell activity in later life, such as improving mitochondrial function, for example, is going to increase cancer risk. Still, it is clear that a better lifestyle more than halves cancer risk, even just considering exercise.

We might argue that targeting theraputics to cancer cells is the true key to success in treating cancer. Prodrugs are one way to achieve that goal, ensuring that the drug is only active in cells with certain chemical characteristics. One of the reasons why immunotherapies are an improvement over the older approaches of chemotherapy and radiotherapy is that immune cells inherently provide the basis for a targeted approach. Early CAR-T therapies are looking good; long-term remission has occurred in a significant number of patients. Since then, many potential approaches to improve immunotherapies have emerged, such as via engineering T cells to reduce exhaustion in the face of exposure to cancer cells, replacement of checkpoint inhibition with new varieties of T cell therapies, or mRNA cancer vaccines.

Regenerative Medicine

Cell therapies and extracellular vesicle therapies of various sorts are under development for many conditions, including those in which cells are made universal to allow transplantation between individuals, though arguably we don't well understand the more widely used forms of stem cell therapy that presently exist. Some of the stem cell and vesicle therapies mentioned in the past year follow: cell therapies for degenerative disc disease and spinal cord injury; stem cell derived vesicles can reduce epigenetic age; cells sourced from the peripheral nervous system can be used to treat neurodegenerative conditions; brain regeneration might be achieved through suitable cell therapies; first generation stem cell and exosome therapies can upregulate neurogenesis; improving muscle regrowth with vesicles, and using exosomes to treat ventricular arrhythmia­.

Beyond cell therapies, growing and then implanting organoids may have utility, augumenting aged organs with new and functional tissue. Additionally, the use of scaffold material implants continues to be developed, such as for regrowth of dental pulp. Further, organ replacement may benefit from the advent of engineered pig organs; the first such heart transplant was performed this year, but the challenges encountered suggest that a longer road than hoped lies ahead before widespread use.

Is it possible to manipulate native cells to induce regeneration? Targeting fibroblasts to alter their behavior may enable scarless healing in mammals, for example, or reprogramming fibroblasts to cardiomyocytes in the heart. Engineering regrowth of organs in adults is potentially possible, given that highly regenerative species are capable of it, and non-regenerative species can perform much the same feats of regeneration during embryonic development. Enhancer sequences from zebrafish can be used to spur heart regeneration in mice. Further, researchers managed to imperfectly regrow frog limbs using a cocktail of growth factors; the result was not a fully formed limb, but that it worked at all suggests that this line of research may have potential.

Regulation of Medical Development

Early in the year, I noted a charitable view of the problems at the FDA regarding the development of drugs to treat aging. Meanwhile the wrangling continues over the question of whether largely unaccountable international bodies will decide to classify aging as a disease, something that is of importance to the regulation and funding of medicine and medical research, but irrelevant to the science itself. Longevity industry companies involved in developing therapies to treat aging are ignoring this circus in favor of picking specific diseases of aging and proceeding through the regulatory gauntlet as-is, in expectation that widespread off-label use will result. Still, comparatively few trials of genuinely age-targeted therapies have yet taken place. These are still early days.

Cryonics and Cryopreservation

That there should be more support for cryonics research and development is a popular viewpoint in that side of the longevity community. Until recently, cryonics was largely a non-profit industry. It has been proposed that a path to for-profit cryonics might involve first starting a hospital (or a veterinary clinic), and then adding cryonics services to that business, rather than starting with dedicated cryonics providers. Some new capabilities may pay off more than others when it comes to generating greater funding and growth for the cryonics industry, such as reversible vitrification of organs for use in transplantation. At some point in the future, a tipping point will be reached, and cryonics will have its time in the sun, just as the once-fringe field of rejuvenation research is enjoying that time in the sun today.

Rewarming tissue for use without damaging cells, structures, and function is arguably the real challenge in cryopreservation; in the last year use of magnetic nanoparticles has shown potential as a solution that might at least be applied to organs intended for transplantation.

Thoughts and Short Essays

I occasionally set down a few thoughts on topics relevant to longevity. Here are the few times that happened in the past year:

• Be Extraordinary or Be Dead
• Request for Startups in the Rejuvenation Biotechnology Space, 2022 Edition
• A Hypothetical Project: the Fast Track to Partial Reprogramming in Human Volunteers
• Should I Actually Be Working on Cryonics Rather than Rejuvenation?
• Understanding Anencephaly as the Start on the Road to Building Replacement, Youthful Bodies
• Is Reversing Paracrine Senescence a Useful Approach to Alleviating the Age-Related Burden of Senescent Cells?
• Distributed Full Disclosure Medical Development
• A Short Commentary on Why We Advocate for Aging
• Reporting on a Study of One with Khavinson Peptides and Melatonin for Thymic Regrowth
• Two Year Update on a Study of One with Flagellin Immunization to Adjust the Gut Microbiome
• Notes from the Rejuvenation Startup Summit, Held in Berlin in October 2022
• Year End Charitable Donations to Help Advance Rejuvenation Research

Onwards!

Things move slowly when you look at the world a year at at time. They run quite fast when comparing today with ten years ago, or ten years from now. There was no such thing as a longevity industry ten years ago, for example. Ten years from now, doctors will be widely prescribing the first rejuvenation therapies, and it will be the common wisdom that one can and should be treated to slow and reverse processes of aging. We live in interesting times, a great transition over decades from a world in which aging was thought of as immutable to a world in which aging is just another medical condition to be addressed.

Researchers here report on evidence for senescent cells in the stem cell niches supporting muscle tissue to reduce stem cell function and the capacity for muscle regeneration. Senescent cells accumulate with age throughout the body, and their inflammatory secretions are disruptive to tissue function. The development of many varied approaches to selectively destroy these errant cells is well underway in the biotech community, with the hope that late life health will be greatly improved as a result.

Tissue regeneration requires coordination between resident stem cells and local niche cells. Here we identify that senescent cells are integral components of the skeletal muscle regenerative niche that repress regeneration at all stages of life. The technical limitation of senescent-cell scarcity was overcome by combining single-cell transcriptomics and a senescent-cell enrichment sorting protocol. We identified and isolated different senescent cell types from damaged muscles of young and old mice. Deeper transcriptome, chromatin, and pathway analyses revealed conservation of cell identity traits as well as two universal senescence hallmarks (inflammation and fibrosis) across cell type, regeneration time, and ageing.

Senescent cells create an aged-like inflamed niche that mirrors inflammation associated with ageing (inflammageing) and arrests stem cell proliferation and regeneration. Reducing the burden of senescent cells, or reducing their inflammatory secretome through CD36 neutralization, accelerates regeneration in young and old mice. By contrast, transplantation of senescent cells delays regeneration. Our results provide a technique for isolating in vivo senescent cells, define a senescence blueprint for muscle, and uncover unproductive functional interactions between senescent cells and stem cells in regenerative niches that can be overcome. As senescent cells also accumulate in human muscles, our findings open potential paths for improving muscle repair throughout life.

Link: https://doi.org/10.1038/s41586-022-05535-x

Researchers here note that SYP expression declines with age and is involved in mammalian memory function. They find a circular RNA that uprgulates SYP expression, and use it to improve memory in a mouse model. Unfortunately the study didn't use normally aged mice, but rather an artificial model of chemically induced damage as accelerated aging. Nonetheless, there is sufficient existing evidence for the role of SYP to think that the results of this study support running a test in normally aged mice to see if a similar positive outcome can be achieved there.

Age is an established risk factor for neurodegenerative disorders. Aging-related cognitive decline is a common cause of memory impairment in aging individuals, in which hippocampal synaptic plasticity and hippocampus-dependent memory formation are damaged. Circular RNAs (circRNAs) have been reported in many cognitive disorders, but their role in aging-related memory impairment is unclear. In this study, we aimed to investigate the effects of circ-Vps41 on aging-related hippocampus-dependent memory impairment and explore the potential mechanisms. Here, D-galactose was used to produce a conventional aging model resulting in memory dysfunction.

Circ-Vps41 was significantly downregulated in D-galactose-induced aging in vitro and in vivo. The overexpression of circ-Vps41 could upregulate synaptophysin (Syp), thereby promoting the synaptic plasticity and alleviating cognitive impairment in aging mice. Mechanistically, we found that circ-Vps41 upregulated Syp expression by physically binding to miR-24-3p. Moreover, the miR-24-3p mimics reversed the circ-Vps41 overexpression-induced increase in Syp expression.

In conclusion, overexpression of circ-Vps41 alleviated the synaptic plasticity and memory dysfunction via the miR-24-3p/Syp axis. These findings revealed circ-Vps41 regulatory network and provided new insights into its potential mechanisms for improving aging-related learning and memory impairment.

Link: https://doi.org/10.3389/fnmol.2022.1037912

It is becoming increasingly clear that issues in the drainage of cerebrospinal fluid from the brain play an important role in the onset of neurodegenerative conditions in late life. Neurodegenerative conditions are associated with a build up of various forms of molecular waste, such as toxic misfolded and otherwise altered proteins, in and around brain cells. It is likely that other stress signaling that provokes chronic inflammation in brain tissue is effectively amplified in effect as the drainage channels that normally carry metabolic products from the brain are reduced in capacity with age.

Leucadia Therapeutics has focused on the drainage path for the olfactory bulb, through the cribriform plate, in the development of Alzheimer's disease, which begins in this area of the brain specifically. The rest of the research community, meanwhile, is largely interested in the glymphatic system (including meningeal lymphatic vessels) in the context of cerebrospinal fluid drainage. Like the broader lymphatic system, the glymphatic system that drains the brain suffers a range of issues with age that reduce its capacity. Unlike the cribriform plate, there really isn't an obvious starting point for the development of ways to restore this drainage capacity. It seems likely that this is needed, however, and if achieved would significantly slow the degenerative aging of the brain.

Overview of the meningeal lymphatic vessels in aging and central nervous system disorders

The central nervous system (CNS) has been considered a relatively immune-privileged site. While the neuroimmune interactions play an important role in diverse neurological disorders, immune surveillance of the CNS remains unclear. The CNS contains microglia, but these cells are confined to the brain parenchyma and cannot interact with peripheral immune system under healthy conditions. Unlike the brain parenchyma, the meningeal lymphatic network enables immune surveillance of the brain efficiently. The discovery of meningeal lymphatic vessels (MLVs) in the CNS has shattered the traditional notion that the CNS is immune-privileged. Aging is accompanied by a functional decline of MLVs, which contribute to several age-related neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), brain tumors, traumatic brain injury (TBI), multiple sclerosis (MS), and stroke.

Over the past few years, evidence for MLVs in the CNS has been accumulating. Recent studies revealed that some features of the meningeal lymphatic system are also present in humans. Defects in MLVs, which excrete metabolic wastes from the CNS to peripheral surroundings, are implicated in various neurological disorders. Although the contribution of MLVs in these diseases is not completely understood, the accumulation of metabolites, cellular debris, and misfolded proteins in the brain due to impaired drainage, which cannot be transported to deep cervical lymph nodes (dCLNs), may play key roles. It has been gradually recognized that the CNS relies on the function of MLVs to maintain homeostasis, and the draining function of MLVs also decreases with age.

However, for many CNS diseases, the causal relationship between MLVs and neuropathological changes is not fully clear. Here, after a brief historical retrospection, we review recent discoveries about the hallmarks of MLVs and their roles in the aging and CNS diseases, as well as potential therapeutic targets for the treatment of neurologic diseases.

As noted last year, the NIH is setting up the SenNet program to fill in some of the larger gaps in the present detail-level knowledge of the role of senescent cells in aging. The goal is to better steer the numerous efforts presently underway to develop improved senolytic therapies that clear senescent cells from old tissues, thereby producing rapid rejuvenation. Senolytic therapies have produced promising results in animal studies, and the potential for this class of treatment to significantly improve late life health in humans is an attractive prospect.

Multiple lines of evidence suggest that senescent cells (SnCs) drive aging and diverse age-related diseases in preclinical models. Interventions targeting SnCs impact multiple morbidities of old age. In 2011, it was established that genetic clearance of SnCs delays the onset of multiple age-related pathologies in transgenic mice. In 2016, it was established that genetic clearance of SnCs in mice delays all-cause mortality, extending median not maximum lifespan, implicating SnCs in many diseases that kill mice, including cancer, chronic kidney disease, and cardiomyopathy. These genetic studies incentivized the development of senotherapeutics - drugs that selectively target SnCs, either killing them (senolytics) or suppressing the SASP (senomorphics). The first senolytics were described in 2015. Since then, dozens of senotherapeutics have been described, including natural products, repurposed drugs, proteolysis-targeted chimeras, and chimeric antigen receptor T cells.

Despite this promise of SnCs as a therapeutic target, there is sparse information about the identity and features of SnCs in human tissues. Little is known about where and when SnCs arise in humans or the extent of SnC and SASP heterogeneity in vivo. Such knowledge could guide therapeutic and organ-specific targeting of SnCs. Clearly, there is a compelling need to develop tools to map and identify human SnCs with spatial and temporal resolution. To address this need, the SenNet Consortium was created in 2021. The goal of SenNet is to functionally characterize the heterogeneity of SnCs in 18 tissues from healthy humans across lifespan at the single-cell resolution, using mice and other models and perturbations for validation.

Link: https://doi.org/10.1038/s43587-022-00326-5

Over the last decade, an increasing diversity of research groups and companies are working towards the clinical use of senolytic therapies to reverse aspects of aging in older patients by clearing harmful senescent cells. Of the early senolytic therapies, the dasatinib and quercetin combination is the only one with published data in human clinical trials showing clearance of senescent cells. This treatment is in fact easily accessible to self-experimenters, and even being prescribed off-label by more adventurous physicians. The biotech industry is working to produce a next generation of (probably) better approaches, and obtain regulatory approval for their use. A decade from now, clearance of senescent cells in older people will be widespread, and the incidence of serious age-related disease will decrease by some noticeable amount as a result.

There is a growing research movement to halt chronic disease by protecting brains and bodies from the biological fallout of aging. If these researchers are successful, they'll have no shortage of customers: People are living longer, and the number of Americans age 65 and older is expected to double, to 80 million, by 2040. One of their targets is decrepit cells that build up in tissues as people age. These "senescent" cells have reached a point - due to damage, stress or just time - when they stop dividing, but don't die. While senescent cells typically make up only a small fraction of the overall cell population, they don't just sit there quietly. Senescent cells can release a slew of compounds that create a toxic, inflamed environment that primes tissues for chronic illness. Senescent cells have been linked to diabetes, stroke, osteoporosis, and several other conditions of aging.

These noxious cells, along with the idea that getting rid of them could mitigate chronic illnesses and the discomforts of aging, are getting serious attention. The National Institutes of Health is investing $125 million in a new research effort, called SenNet, that aims to identify and map senescent cells in the human body as well as in mice over the natural lifespan. And the National Institute on Aging has put up more than $3 million over four years for the Translational Geroscience Network that is running preliminary clinical trials of potential antiaging treatments. Drugs that kill senescent cells - called senolytics - are among the top candidates. Small-scale trials of these are already underway in people with conditions including Alzheimer's, osteoarthritis, and kidney disease.

Numerous medical companies have jumped on the anti-senescence bandwagon. But results have been mixed. One front-runner, Unity Biotechnology dropped a top program in 2020 after its senolytic medication failed to reduce pain in patients with knee osteoarthritis. More recently, however, the company reported progress in slowing diabetic macular edema, a form of swelling in the back of the eye due to high blood sugar. Despite the excitement, senolytic research remains in preliminary stages. A lot of basic and clinical research must happen first, but if everything goes right, senolytics might someday be part of a personalized medicine plan: The right drugs, at the right time, could help keep aging bodies healthy and nimble.

Link: https://knowablemagazine.org/article/health-disease/2022/could-getting-rid-old-cells-turn-back-clock-aging

The lymphatic system allows rapid transit of large numbers of immune cells throughout the body. Scattered through this system of lymphatic vessels are the lymph nodes. Lymph nodes are vital to the function of the immune system, acting as meeting places where immune cells can communicate to effectively coordinate the response to pathogens. With age, lymph node structure begins to break down, however, becoming fibrotic, or the active tissue replaced by fat. Researchers have shown that this is an obstacle to rejuvenation of the adaptive immune system; one can regrow the atrophied thymus to provide a supply of new T cells, but without a fully functioning lymphatic system, the immune response is not properly coordinated.

Replacement of lymph nodes is a possibility, and it has been demonstrated that suitable organoids or other structures will produce new lymph nodes when implanted into the body. It is an open question as to whether this would work well in older individuals, in an aged tissue environment, however. Forms of regenerative therapy based on adjusting the signals controlling growth in lymphatic tissue, analogous to the approaches that can be used to regrow an atrophied thymus in animal studies, may be the better way forward. Little work has taken place in this part of the field, however. It is only comparatively recently that a broader recognition of the importance of lymph node aging has emerged.

How fat takes over the lymph nodes as we age

As we age, the normal tissue in the lymph nodes (the stroma) is gradually replaced by adipose tissue (fat). The phenomenon is known as lymph node lipomatosis. Although lipomatosis is very common and increases with age, researchers have previously devoted very little discussion and research to it. By careful analysis of more than 200 lymph nodes, researchers have demonstrated that lipomatosis begins in the central part of the lymph node, known as the medulla, and presents evidence linking lipomatosis to the transformation of the supporting cells of lymph nodes (fibroblasts) into adipocytes (fat cells). They also show that specific types of fibroblasts located in the medulla are more prone to become adipocytes.

The study shows that even at early stages of lipomatosis, negative changes arise that impair the ability of the lymph node to provide effective immunity. Among other observations, they note that the specialised blood and lymphatic vessels that normally provide channels for immune cells to enter and leave the lymph node are destroyed in the parts of the node where fat has formed. Lipomatosis of lymph nodes, even at early stages, may therefore be one important factor behind the poorer response to vaccinations observed in elderly people. Ultimately, the fat completely takes over the lymph node and it loses its ability to function.

Stromal transdifferentiation drives lipomatosis and induces extensive vascular remodeling in the aging human lymph node

Lymph node (LN) lipomatosis is a common but rarely discussed phenomenon associated with aging that involves a gradual exchange of the LN parenchyma into adipose tissue. The mechanisms behind these changes and the effects on the LN are unknown. We show that LN lipomatosis starts in the medullary regions of the human LN and link the initiation of lipomatosis to transdifferentiation of LN fibroblasts into adipocytes. The latter is associated with a downregulation of lymphotoxin beta expression. We also show that isolated medullary and CD34+ fibroblasts, in contrast to the reticular cells of the T-cell zone, display an inherently higher sensitivity for adipogenesis.

Progression of lipomatosis leads to a gradual loss of the medullary lymphatic network, but at later stages, collecting-like lymphatic vessels are found inside the adipose tissue. The stromal dysregulation includes a dramatic remodeling and dilation of the high endothelial venules associated with reduced density of naïve T-cells. Abnormal clustering of plasma cells is also observed. Thus, LN lipomatosis causes widespread stromal dysfunction with consequences for the immune contexture of the human LN. Our data warrant an increased awareness of LN lipomatosis as a factor contributing to decreased immune functions in the elderly and in disease.

Researchers here suggest that angiotensin II expression is maladaptive in the context of aging, provoking greater oxidative stress and harmful downstream consequences for cell and tissue function. If looking to produce therapies based on interfering in angiotensin II receptor signaling, an approach already well established in the treatment of hypertension, the question is always the tradeoff between loss of function and avoidance of damage. Few if any molecular interactions in the body are entirely dispensable, and angiotensin II signaling is involved in a range of normal cellular processes. That said, this topic is well explored via the existing uses of angiotensin II receptor blockers.

For the last few decades, the involvement of the renin-angiotensin system (RAS) in mediating vasoconstriction, ion entry and excretion, fibrosis, inflammatory and oxidative stress has been well documented. In addition to the circulating system, elements of the RAS are also found in diverse tissues of the brain, heart, and kidney, and contribute to the aging of these organs. Within the brain, different components of the RAS have been extensively studied in the context of neuroprotection and cognition. Alterations in the brain RAS during aging may establish a link between impairment of autonomic reflex function and metabolic changes in aging. Further evidence for the relevance of the RAS in aging is derived from numerous experiments in vivo and in vitro, indicating that aging is accompanied by the increased activity of angiotensin II (Ang II), which is the major bioactive peptide of this system.

A prospective observational study effectively proved that the lifespan of mice with disrupted Ang II type 1 receptor (AT1R) was remarkably longer than that in the control group and showed that the mice lacking AT1R exhibited less oxidative damage, consequently indicating that Ang II-induced reactive oxygen species (ROS) by AT1R seemed to play a crucial part in the aging process. Considering that mitochondria are a key source of endogenous ROS and telomeres are particularly vulnerable to oxidative stress, in this article, we first describe the diverse components of the RAS as well as their physiological functions coupling with each other. Then, we provide an overview of the primary ROS sources and the mechanistic association of ROS with mitochondria and telomeres. This is followed by the discussion of the seemingly universal roles of mitochondrial dysfunction and telomere attrition in aging and how Ang II influences them, conducing to present new preventive strategies in fighting aging and age-associated diseases.

Link: https://doi.org/10.3389/fnagi.2022.1002138

The Buck Institute recently hosted the 2022 Longevity Summit, and here find some notes on the event from a participant. The number of conferences dedicated to the field of longevity science is increasing steadily, year after year. The best are those in which one finds a mix of entrepreneurs, scientists, and investors, all networking to advance the state of the art in the treatment of aging as a medical condition.

The Longevity Summit at the Buck Institute, a relatively short two-day geroscience and longevity biotech conference held on December 6-7, was nevertheless densely packed with new research - to the point where we can only cover some of the talks here. The conference was organized by Longevity SF, a nonprofit organization founded by the CEO of NeuroAge Therapeutics.

The event opened with a lecture by Buck director Dr. Eric Verdin, who presented some fascinating new research fresh out of the institute's labs. Dr. Verdin's talk touched on one of the most important topics in today's geroscience: finding reliable biomarkers of aging. The next speaker was Morgan Levine, who is one of the best experts on epigenetic clocks and currently with Altos Labs. Levine described her team's work on bringing existing epigenetic clocks closer to her definition of the perfect biomarker of aging.

Dr. Priyanka Joshi, co-founder of NeuroAge, started her presentation by asking the audience whether they believed the amyloid theory of aging. Just like in the longevity community in general, there seemed to be no consensus in the crowd. Whether or not the theory is correct, it is clear that aggregated proteins fail to perform their functions. Neuroage is working on a large postmortem cohort of about 2000 brains, analyzing them using various biological age clocks. The main takeaway is that people whose biological age was younger than their chronological age at death, were less likely to have developed Alzheimer's. Based on this and other insights, NeuroAge has developed a proprietary platform to identify protein products that are specific to slowing brain aging and eventually develop therapeutics against Alzheimer's and other protein misfolding diseases.

Sergio Ruiz, CEO of Turn.bio, presented the company's latest work on CAR T cell rejuvenation. While Turn's solution based on cellular reprogramming can potentially be used in a wide variety of treatments, the company is currently focusing on the two low-hanging fruits that allow immediate commercialization: immunology and dermatology. CAR T cells are genetically modified cells usually procured from the patient themselves, which means there is already some cellular exhaustion due to age. Turn's technology can rejuvenate those cells to make them more aggressive in fighting cancer.

Link: https://www.lifespan.io/news/the-science-packed-longevity-summit-at-the-buck-institute/

A present, the conservative scientific viewpoint on aging is that significant progress has been made in understanding how to produce therapies that might target mechanisms of aging, but these are still very early days in both (a) understanding in detail how those mechanisms give rise to the observed outcomes in aging, and (b) the development of age-slowing and rejuvenating therapies. It is most likely the case that more could be accomplished than is presently being accomplished, given greater will and funding. But the creation of a new field of medicine is a slow process, proceeding incrementally, taking years to convince each new larger and more conservative audience of the merits of the work.

A small number of people were convinced by the SENS proposals for rejuvenation biotechnology twenty years ago, which included a synthesis of the evidence for senescent cells to contribute to degenerative aging. A larger group of people were convinced a decade ago by concrete demonstrations in which clearing senescent cells produced rejuvenation in mice. Since then, bootstrapping of a longevity industry and a greater focus on aging in the research community has proceeded, but the largest and most conservative groups still remain to be convinced. The majority of decision makers in the pharmaceutical industry won't act on the potential for the treatment of aging until a fair number of therapies are approved by regulators, find a large market, and are proven useful in humans, for example.

Aging and aging-related diseases: from molecular mechanisms to interventions and treatments

Research on the mechanisms of aging is a very active area in academia and a difficult area of research in the biomedical field. The study of aging mechanisms will be extremely important for delaying aging, reducing the occurrence of aging-related diseases, and maintaining a long and healthy life in human body. Especially, in recent years, research on epigenetic regulation, proteostasis, autophagy, cellular senescence, stem cell, has provided us with new directions for aging mechanism study. However, the causes of human aging are multifaceted, and the mechanisms of aging are extremely complex.

So far, although a variety of theories on the mechanism of aging have been proposed by academics, all of which have their own experimental basis, but they all have their limitations to explain the complex mechanisms of aging. Therefore, we should adopt a comprehensive and multi-perspective approach when we explain the aging mechanisms. At present, there has been great progress in the research on the molecular mechanisms of aging, and there has been a breakthrough in the understanding of the biological and genetic mechanisms of the aging process, as well as a profound understanding of the pathogenesis of aging-related diseases. However, these findings are still far from being able to delay human aging and reduce the occurrence of aging-related diseases. Therefore, there is still a long way to go in the study of aging mechanisms.

Antiaging interventions and treatments for aging-related diseases face great challenges. An important way to achieve healthy aging is through early intervention and prevention. Early lifestyle intervention can promote healthy longevity and reduce aging-related diseases. Through a variety of lifestyle interventions, it is hoped that the aging process can be slowed and the incidence of aging-related diseases may be reduced. In terms of pharmacological interventions and treatments for aging-related diseases, most of the drugs now applied clinically may focus more on symptom relief after the onset of disease and lack therapeutic approaches to address the causes of aging and aging-related diseases. Research on the latest therapeutic approaches, such as stem cell transplantation, elimination of senescent cells, promotion of antiaging factor expression and inhibition of pro-aging factor expression, and tissue or organ regeneration, provides new directions for treatments of aging-related diseases. In addition, there have been significant technological developments, mainly through gene therapy, nanomaterial drug carriers, therapeutic antibodies, or small molecule drugs, which have also contributed to advances in the treatment of aging-related diseases. Some of these methods and technologies have been applied in the clinic, and some are undergoing model animal studies and small-scale clinical studies. The application of these state-of-the-art technological approaches and new targeted drugs will facilitate the treatment and clinical application of aging-related diseases.

The goal of aging medicine is gradually changing from disease treatment to prevention of the occurrence and development of aging-related diseases. In other words, geriatric medicine is moving away from focusing on postdisease treatment to targeting aging-related chronic disease risk factors for preintervention. Research on the mechanisms of aging and on intervention measures and methods has an important role in improving human health and prolonging lifespan. Due to the aging of the global population, antiaging and healthy aging pursuits are undoubtedly important tasks for public health organizations, scientific research departments and drug research and development departments. Although there are many challenges to the research of aging and aging-related diseases and many questions still need to be addressed, promoting healthy aging has important and far-reaching socioeconomic and public health implications. With the emergence of new technologies and methods of modern biology, and the development and utilization of new drug discovery methods, research on aging mechanisms will further facilitate the prevention, diagnosis, and treatment of aging-related diseases, thus promoting healthy longevity for humans.

Researchers here identify eIF2α as a target for interventions that prevent T cells from shutting down after prolonged activity in a tumor environment. The stress response to extended activity is normally protective, but in this case it prevents T cells from being as effective as they might be, which contributes to an established tumor's compromise of the immune system. This sort of approach offers the promise of improving cancer immunotherapies, increasing the damage that each T cell can do to tumor tissue.

The stress response in T cells can lead to their inability to curtail tumor growth. Researchers found that T cells exposed to the environment of solid cancers undergo a natural response to stress that shuts off their function, limiting T cell ability to kill tumors. By manipulating multiple proteins in the stress response pathway inside T cells, the team showed that it was possible to overcome the intrinsic T cell stress response to allow the immune system to thwart cancer growth.

At the center of this research is a protein called PKR ER-like kinase (PERK), which is a major stress sensor for all cell types, including T cells, but has not been deeply studied in the context of immunity. That is, when a T cell is under duress - like when faced with the hostile environment created by cancer cells - it is PERK that responds to the stress in a way that causes cells to stop secreting proteins in an effort to help the cell survive.

Researchers found that when PERK is activated, modification of one molecule called phosphorylated eIF2-alpha is responsible for the T cell momentarily stopping protein synthesis during the stress response. When researchers forced phosphorylated eIF2-alpha to cease its natural function, the T cells continued protein synthesis, and T cells were able to continue to control tumor growth in mice. This research shows that it is very possible to tweak T cells genetically or pharmacologically to enhance their ability to battle cancer tumor cells.

Link: https://news.unchealthcare.org/2022/12/why-dont-t-cells-destroy-solid-tumors-during-immunotherapy/

Bone density results from the balance of constant activity on the part of osteoblasts and osteoclasts, the former building bone, the latter breaking it down. With advancing age, the balance of activity shifts to favor osteoclasts, producing a gradual loss of bone density that leads to osteoporosis. Therapies have to date typically attempted to reduce osteoclast activity, but researchers here note an approach based on increased osteoblast activity.

Bones appear to be durable and solid. But appearances are deceptive: in fact, bone tissue is in a constant state of remodeling. Bone-degrading osteoclasts and bone-building osteoblasts ensure a fine balance in the healthy organism. But this balance is occasionally disturbed: in osteoporosis, bone resorption takes over, so that fractures and deformities can occur. Bone metastases, which occur in the course of many cancers, are also often caused by bone resorption processes. This is also true for multiple myeloma, which originates and spreads in the bone marrow.

So far, drugs are available that inhibit bone resorption by osteoclasts. However, researchers believe that agents that promote bone formation by osteoblasts are also medically necessary. To identify such substances, the researchers first had to find out which signaling pathways control osteoblast activity. The team identified in mouse osteoblasts the two enzymes MERTK and TYRO3, so-called receptor tyrosine kinases, which regulate bone production. The function of the two enzymes was studied in mice in whose osteoblasts either one or the other receptor tyrosine kinase was genetically switched off. The result: If MERTK was inactivated, the bone mass of the animals increased. Without TYRO3, on the other hand, it decreased.

The small-molecule agent R992 inhibits MERTK activity. When healthy mice were treated with R992, their osteoblast numbers increased and the animals' bone mass increased. Treatment with R992 also reduced bone loss and the number of bone metastases in mouse models with myeloma, lung cancer, and breast cancer cell lines. The agent R992 is not approved as a drug. To potentially study the effects of MERTK blockade in patients, the team is currently developing an antibody that specifically blocks the function of MERTK.

Link: https://www.dkfz.de/en/presse/pressemitteilungen/2022/dkfz-pm-22-74-Enzyme-inhibition-promotes-bone-formation-and-curbs-the-development-of-bone-metastases.php

The balance of microbial populations making up the gut microbiome is now known to change with age in ways that promote chronic inflammation. There are more inflammatory microbes passing the intestinal barrier to enter tissue, and more microbes capable of generating harmful metabolites that aggravate cells. The aging of the microbiome is only loosely connected to the aging of the body, however. Animal studies make it clear that the gut microbiome of an old individual can be restored to a youthful balance of populations via fecal microbiota transplant from a young individual, benefits to health and longevity result, and that one intervention lasts for a long time.

It is in principle possible to achieve the same result as a fecal microbiota transplant using probiotics, given a large enough sustained dose. In practice, that cannot yet be accomplished, however. The right balance of species would have to be manufactured, and present probiotic manufacture is limited to a very small number of microbial species in comparison to what one finds in the gut microbiome.

Even given the point that one or two of the species known to lose abundance with age might be capable of delivering enough of a benefit to be worth it, even if only a fraction of that produced by fecal microbiota transplant, the actual result of present probiotic treatment, the products one can purchase in a store, appears to be at best a comparatively small, short-lived benefit. Still, given what is presently known of the impact of the gut microbiome on health, and how to rejuvenation an aged gut microbiome, it seems likely that probiotics will become a good deal better in the years ahead.

Can probiotics mitigate age-related neuroinflammation leading to improved cognitive outcomes?

Systemic inflammation, which leads to neuroinflammation, is likely a risk factor for the progression of neurodegenerative diseases. Although systemic inflammation can be the result of numerous processes and diseases, one key trigger during aging is changes in the gut, such as the increase in gut permeability and alterations in microbiota composition. During aging, the gut naturally becomes more permeable. The gastrointestinal tract is the second largest interface between the host and the outside world. Therefore, this reduction in its barrier function associated with aging has follow-on consequences, such as allowing unwanted components (antigens and opportunistic pathogenic bacteria) to enter the body, leading to the production of proinflammatory cytokines in the blood. These cytokines can then cross the blood brain barrier to cause neuroinflammation, which impacts brain function.

Whether age-associated increases in gut permeability are a cause or a consequence of other gut related changes is currently unknown. However, a recent study showed that the development of gut barrier dysfunction during aging is not consistent across all people. People with irritable bowel syndrome (IBS) are more susceptible to gut hyperpermeability in later life than healthy individuals. Interestingly, those with IBS are also more at risk at developing Alzheimer's disease (AD), supporting the idea that gut hyperpermeability is a risk factor for AD.

Recent studies have sought to define a microbiota profile associated with healthy aging, but this varies between the study populations. However, gut microbiota composition of people with AD has been shown to differ from that of healthy older adults in a number of studies. Recent studies have also shown there is a difference in the composition of the gut microbiota between people with mild cognitive impairment (MCI) and those without, and that these differences are similar to those seen in people with AD. This implies that microbiota dysbiosis proceeds AD development and, therefore, may be a driver in the disease progression.

It therefore follows that treatments that can maintain healthy gut function may reduce inflammation and protect against, or improve, symptoms of age-associated neurodegeneration. The aim of this mini-review was to evaluate whether probiotics could be used for this purpose. A search resulted in 187 papers describing primary research on probiotic intervention with older adults. A review of this research concluded that there is preliminary evidence to suggest that specific probiotics may improve cognitive function, particularly in those with MCI; however, this is not yet convincing and larger, multilocation, studies focus on the effects of probiotics alone are required. In addition, studies that combine assessment of cognition alongside analysis of inflammatory biomarkers and gut function are needed. Immense gains could be made to the quality of life of the aging population should the hypothesis be proven to be correct.

Monocytes of the innate immune system react to changes in the aging tissue environment by becoming more inflammatory. Those changes include the signaling of growing numbers of senescent cells, the presence of DNA debris from stressed cells, and the like. The innate immune system makes the issue worse by ensuring a state of chronic inflammation that disrupts normal tissue maintenance and function. Finding ways to suppress the inflammation of aging, such as the targeted removal of senescent cells, is an important goal in the treatment of aging as a medical condition.

It has been widely accepted that monocytes are one of the central mediators contributing to inflammaging. However, it remains unclear whether aged monocytes, similar to aged T cells, have characteristics of hyperactivation and increased expression of co-inhibitory molecules. Here, peripheral blood mononuclear cells (PBMCs) were isolated from young (21-40 years old), middle-aged (41-60 years old), and older human subjects (older than 60 years old). Flow cytometry was used to monitor changes in the expression of surface molecules of monocyte subsets and cytokine-producing capacity.

We observed increased TNF-α and decreased IL-6 production in monocytes from older adults compared with young and middle-aged adults. Older adults had a greater percentage of intermediate and non-classical monocyte subsets, along with increased levels of the immune activation markers HLA-DR, and adhesion molecules CD11b and CD62L. Furthermore, we observed increased CCR2 expression on classical monocytes and decreased CX3CR1 expression on non-classical monocytes in older adult subjects. The expression of co-inhibitory receptors was reduced on monocyte subsets in older adults.

In conclusion, circulating monocytes in older adults exhibit increased expression of activation, adhesion, and migration markers, but decreased expression of co-inhibitory molecules.

Link: https://doi.org/10.1186/s12979-022-00321-9

Reprogramming cells using the Yamanaka factors produces both a reset of epigenetic patterns to a more youthful configuration and a change in cell identify. One of the primary challenges inherent in reprogramming to achieve rejuvenation is avoidance of this altered cell identity. Reprogramming isn't an immediate switch, it is a slow process over hours to days, but a fraction of reprogrammed cells do change into induced pluripotent stem cells after some period of exposure to reprogramming factors. This is an undesirable outcome when delivering a reprogramming therapy; if new approaches can be found that do not alter cell identity, that would make reprogramming a much more viable basis for rejuvenation treatments.

Partial somatic cell reprogramming has been touted as a promising rejuvenation strategy. However, its association with mechanisms of aging and longevity at the molecular level remains unclear. We identified a robust transcriptomic signature of reprogramming in mouse and human cells that revealed co-regulation of genes associated with reprogramming and response to lifespan-extending interventions, including those related to DNA repair and inflammation. We found that age-related gene expression changes were reversed during reprogramming, as confirmed by transcriptomic aging clocks.

The longevity and rejuvenation effects induced by reprogramming in the transcriptome were mainly independent of pluripotency gain. Decoupling of these processes allowed predicting interventions mimicking reprogramming-induced rejuvenation (RIR) without affecting somatic cell identity, including an anti-inflammatory compound osthol, ATG5 overexpression, and C6ORF223 knockout. Overall, we revealed specific molecular mechanisms associated with RIR at the gene expression level and developed tools for discovering interventions that support the rejuvenation effect of reprogramming without posing the risk of neoplasia.

Link: https://doi.org/10.1101/2022.12.12.520058

In the process of producing proteins from genetic blueprints, the first step is transcription, the generation of RNA molecules, generally called transcripts. In today's open access paper, researchers present data to support an interesting observation: that age-related changes in the abundance of specific RNA transcripts correlate with transcript length. They offer some suggestions as to mechanisms that might contribute to this effect, such as stochastic DNA damage or dysregulated RNA splicing. RNA splicing is the part of transcription in which RNA to match specific intron and exon sections of a gene are joined together to form the transcript. In recent years researchers have noted that dysfunction arises in the splicing process with age, and that this might cause further downstream issues.

Finding a way to link stochastic DNA damage to the common manifestations of aging has been a challenge. In and of itself, near all stochastic DNA damage doesn't do much obvious harm to any given cell: most of the altered genes are not used in that cell, and, with the exception of the risk of cancer, most of the mutational alterations to DNA are not that important. Further, this sort of damage is completely different in every cell it happens in. So how does it give rise the fairly uniform set of changes noted in aging? Possibilities include (a) somatic mosaicism, in which only the few problematic changes occurring in stem cells matter, as they spread throughout tissues, and (b) the recently discovered way in which double strand break repair might cause epigenetic alterations characteristic of aging, by exhausting resources needed for the correct maintenance of chromatin.

In the context of today's data, it is interesting to consider ways in which stochastic DNA damage might cause uniform disarray in RNA splicing. This might perhaps occur through a similar mechanism to the above mentioned double strand break repair mechanism, some form of resulting alteration in epigenetic patterns as a response to damage that leads to changed expression of critical splicing factors, for example.

Aging is associated with a systemic length-associated transcriptome imbalance

Aging is among the most important risk factors for morbidity and mortality. To contribute toward a molecular understanding of aging, we analyzed age-resolved transcriptomic data from multiple studies. Here, we show that transcript length alone explains most transcriptional changes observed with aging in mice and humans. We present three lines of evidence supporting the biological importance of the uncovered transcriptome imbalance. First, in vertebrates the length association primarily displays a lower relative abundance of long transcripts in aging. Second, eight antiaging interventions of the Interventions Testing Program of the National Institute on Aging can counter this length association. Third, we find that in humans and mice the genes with the longest transcripts enrich for genes reported to extend lifespan, whereas those with the shortest transcripts enrich for genes reported to shorten lifespan.

Perhaps the most pressing question relates to the origin of the length-associated transcriptome imbalance during aging. Our findings about the genes with the shortest and longest transcripts enriching for genes with different roles toward longevity could be viewed as support for longevity-related roles of genes driving the evolution of their transcript length. However, this explanation would presently only appear to account for a fraction of the genes that show a transcript length-associated change during aging.

Turning to earlier literature, a length-associated transcriptome imbalance does not appear specific to aging itself. Moreover, there seem to be multiple potential molecular origins for a length-associated transcriptome imbalance. Most prominent among the specific molecular mechanisms, DNA damage has been explicitly demonstrated to yield a length-associated transcriptome imbalance with a relative fold decrease of the longest transcripts in a progeroid model of aging. Heat shock, which challenges proteostasis, a hallmark of aging, leads to a length-associated transcriptome imbalance by causing premature transcriptional termination through cryptic intronic polyadenylation. Similarly, loss of splicing factor proline/glutamine (Sfpq), encoded by the gene that displays the strongest differential splicing during human aging, has been shown to yield a length-associated transcriptome imbalance by interfering with transcriptional elongation of long genes. Methyl CpG binding protein 2 (MeCP2) opposes a length-associated transcriptome imbalance by dysregulating transcriptional initiation according to the length of the gene body. Further, patients with Alzheimer's disease show a length-associated transcriptome imbalance whose onset has been suspected to stem from somatic mutations that affected transcript stability.

Jointly, these observations invite the unsupported hypotheses that during aging there may not be a single origin for the length-associated transcriptome imbalance and that the length-associated transcriptome imbalance in aging instead represents an intermediate step through which multiple environmental and internal conditions simultaneously affect multiple downstream outputs. The length-associated transcriptome imbalance thus may offer itself as an explanation for the recent observation of inter-tissue convergence of gene expression during aging. Further arguing in favor of an integrative role of the length-associated transcriptome imbalance, we find evidence that several distinct antiaging interventions counter the length-associated transcriptome imbalance against long transcripts despite these different antiaging interventions partially affecting different aspects of cellular and organismal physiology.

The longevity-associated gene klotho is known to act in kidney tissue, in ways that are protective of cell function in the aging environment of damage and inflammation. One of the conclusions that might be drawn from the extended life span produced by increased klotho expression in animal studies is that declining kidney function is an important aspect of aging. If the kidneys are not efficiently clearing waste from the bloodstream, and otherwise providing their contribution to bodily function, then all organs suffer as a result. Faster loss of kidney function means a faster decline into disease and mortality.

The renal condition is one of the crucial predictors of longevity; therefore, early diagnosis of any dysfunction plays an important role. The key role of the kidneys is to remove waste products from the blood and also regulate the levels of many essential compounds. Chronic kidney disease is one of the major causes of death worldwide, as well as a leading cause of years of life lost. Kidneys are highly susceptible to the aging process. Unfavorable conditions may lead to a significant disturbance of the body's homeostasis.

Despite the characteristic changes in the functioning and appearance of the kidneys being wholly assumed, the exact mechanisms of kidney senescence are still uncertain. It is challenging to distinguish between changes in the physiological aging of the kidneys and those in age-related kidney diseases and comorbidities. Apart from physiological changes, there are some conditions such as hypertension, diabetes, or obesity which contribute to the acceleration of the aging process. A determination of macroscopic and microscopic changes is essential for assessing the progression of aging. With age, we observe a decrease in the volume of renal parenchyma and an increase in adipose tissue in the renal sinuses. Senescence may also be manifested by the roughness of the kidney surface or simple renal cysts. The main microscopic changes are a thickening of the glomerular basement membrane, nephrosclerosis, an accumulation of extracellular matrix, and mesangial widening.

A vital factor that also should be taken into consideration in renal aging is oxidative stress mediated by SIRT1, PGC-1α, PPARα, and Klotho. Studies have shown that resveratrol or renin-angiotensin-aldosterone system blockers can be helpful to mitigate renal aging. Yet something that seems to be the most beneficial for renal function is simple habits such as appropriate diet and exercise.

Link: https://doi.org/10.3390/ijms232315435

Researchers here provide evidence for raised levels of ceramide in muscle tissue to be an important part of the metabolic dysfunction of aging. It reduces muscle stem cell activity, contributing to the age-related loss of muscle mass and strength that leads to sarcopenia and frailty. Whether working on this point of intervention, to produce improved ceramide blockers with fewer side-effects, is better or worse than other avenues is an open question. Altered metabolism is thought to be a fair way downstream from the root causes of aging, and tackling root causes should always be a better option. It is is very challenging to track backwards along the chain of cause and effect from an observation such as raised ceremide levels, however. Thus most research and development groups prefer to stop at this point and build a more limited intervention based on what is known now.

Researchers have discovered that when mice age, their muscles become packed with ceramides. Ceramides are sphingolipids, a class of fat molecules that are not used to produce energy but rather perform different tasks in the cell. The researchers found that, in aging, there is an overload of the protein SPT and others, all of which are needed to convert fatty acids and amino acids to ceramides.

Next, the scientists wanted to see whether reducing ceramide overload could prevent age-related decline in muscle function. They treated old mice with ceramide blockers, such as myriocin and the synthetic blocker Takeda-2, and used adeno-associated viruses to block ceramide synthesis specifically in muscle. The ceramide blockers prevented loss of muscle mass during aging, made the mice stronger, and allowed them to run longer distances while improving their coordination.

To study this effect more deeply, the scientists measured every known gene product in the muscle using a technique called RNA sequencing. They found that blockade of ceramide production activates muscle stem cells, making muscles build up more protein and shifting fiber type towards fast-twitch glycolytic to produce larger and stronger muscles in aged mice.

Finally, the scientists looked at whether reducing ceramides in muscle could also be beneficial in humans. They examined thousands of 70-80-year-old men and women, and discovered that 25% of them have a particular form of a gene that reduces the gene products of sphingolipid production pathways in muscle. The people who had this ceramide-reducing gene form were able to walk longer, be stronger, and were better able to stand up from a chair, indicating healthier aging, similar to mice treated with ceramide blockers.

Link: https://www.eurekalert.org/news-releases/974693

This article on senolytic therapies to selectively remove senescent cells in old tissues is in part a matter of Unity Biotechnology talking up their position. The company suffered from first mover disadvantage in bringing senolytic drugs into clinical development. The field has made progress very rapidly over the last decade, and startups founded even just a couple of years after Unity's launch benefited from greater knowledge and a selection of better technologies to work with. Still, one can be talking up one's position and also be right. The accumulation of senescent cells is profoundly harmful, a significant contribution to degenerative aging, and senolytics are indeed a promising approach to the treatment of aging. Widespread use will greatly transform the field of medicine.

The interesting thing about small molecule senolytic therapies is that the first of these tested in animals and humans, the dasatinib and quercetin combination, is actually relative good, even though it clears at most half of the senescent cells in a given tissue, and much less than that in many tissue types. Alternative approaches that followed have struggled to improve on its effectiveness, at least going by published data. While the industry moves slowly, and approvals of new drugs are years away yet, there is little to stop an older individual deciding that the clinical trial safety profile for dasatinib and quercetin looks decent, and setting forth to try it for themselves.

Senolytic Therapies Pose Revolutionary Potential to Roll Back Diseases of Aging

Senolytic therapies are, at this point, as revolutionary as checkpoint inhibitors but with broader effectiveness. This approach delays the onset of diseases of aging by removing senescent cells from the body, thus enabling people to remain healthier longer or to regain some degree of function lost to disease. Senolytics is a new field and most of the research is still in academic centers - most notably, the Mayo Clinic. Approval of any therapeutics is years - perhaps even a decade - away. Currently, there are many unknowns. "We're at the stage where we don't know - in humans - which cells senesce and when, so there would be concern if, for example, post-mitotic cells that can't be replaced were suddenly eliminated by senolytics. We also don't know which senescent cells are the most disadvantageous."

"We're all carrying some burden of senescent cells ... usually at a benign level, and it's very likely contributing to the aging process. But, in certain stressed environments, the risk burden increases." A normal aging eye, for example, shows some accumulation of senescent cells but, when a disease - macular degeneration or diabetes, for example - is also involved, senescent cells are even more abundant. Senescent cells express the protein p16. Unity's approach identifies these cells based on their state - specifically their expression of p16 and their secretion of inflammatory factors. The company's lead asset, UBX1325, targets BCL-xl, which senescent cells - but not healthy cells - require for survival. "If you starve them of that, they are eliminated."

UBX1325 is being developed to treat diabetic macular edema (DME) and age-related macular degeneration. Upwards of 100 patients have been treated in early trials. UBX1325 is injected into the eye. As a result, the pathology of the disease is reduced, the anatomy looks good and the patients see better. The average gain was 7.5 letters or two lines on a vision chart. That gain was also seen in patients who had plateaued on anti-VEGF therapy and were treated with senolytics. A single injection appears to confer durable benefit.

"Nephrologists have begun to realize that acute accumulation of senescent cells drives progression of disease and the pathologies associated with it and that this accumulation of inflammatory cells leads to more fibrosis and more inflammation. Senolytics is exciting because it's the first of a class of therapy that has the potential to go after aging more broadly. Senescence seems to affect everyone and all the major organ systems in the body. One of the first things shown in transgenic animals was that if you remove (these cells) there was meaningful improvement in lifespan and healthspan. If we don't recognize aging as a legitimate target for medical intervention, it will be difficult to move the needle."

Oisín's Biotechnologies furthest-advanced senolytics program addresses kidney disease. One application focuses on blocking the progression of acute kidney injury toward chronic kidney disease. The other application is for people with advanced kidney disease who may be approaching renal failure. Eliminating the senescent cells probably won't return those kidneys to full function, but it may retard or halt disease progression. The goal is to eliminate the p16 cells. The company does that by targeting p16+cells with a caspase-9 suicide gene. The senescent cells then die by apoptosis. Although the p16 pathway is critical in identifying senescent cells, it may not be the only possible pathway. Recognizing that, the company's new frailty study targets both the p16 and p53 pathways, creating a synergistic, two-pronged method of killing senescent cells. That approach may be applied to its kidney program in the future.

Senolytics is a completely new type of therapy that, at this admittedly early stage, appears to have great promise. If it delivers on that promise, it will change what it means to age irrevocably.

It is interesting to see a study in which exercise failed to improve memory function in older adults, given the sizable number of studies showing that it does help. One possibility is that intensity of exercise matters. In general, however, the literature leans in the direction of exercise slowing cognitive decline. Yet no outcome in research is so guaranteed that there will be a complete absence of studies in which it fails to show up in the data; this is one of the challenges inherent in following the output of the scientific community.

A large study that focused on whether exercise and mindfulness training could boost cognitive function in older adults found no such improvement following either intervention. The researchers studied 585 adults ages 65 through 84. None had been diagnosed with dementia, but all had concerns about minor memory problems and other age-related cognitive declines.

All study participants were considered cognitively normal for their ages. The researchers tested them when they enrolled in the study, measuring memory and other aspects of thinking. They also conducted brain-imaging scans. The participants were randomly assigned to one of four groups: a group in which subjects worked with trained exercise instructors; a group supervised by trained experts in the practice of mindfulness; a group that participated in regular exercise and mindfulness training; and a group that did neither, but met for occasional sessions focused on general health education topics. The researchers conducted memory tests and follow-up brain scans after six months and again after 18 months.

At six months and again at 18 months, all of the groups looked similar. All four groups performed slightly better in testing, but the researchers believe that was due to practice effects as study subjects retook tests similar to what they had taken previously. Likewise, the brain scans revealed no differences between the groups that would suggest a brain benefit of the training.

Link: https://source.wustl.edu/2022/12/exercise-mindfulness-dont-appear-to-boost-cognitive-function-in-older-adults/

A great deal of research is focused on cataloguing and correlating specific differences in the gut microbiome with aspects of aging. In years ahead, techniques will be developed to more precisely control the composition of the gut microbiome, removing issues such as too great a number of inflammatory microbes, or those producing harmful metabolites. At the moment, only more crude approaches such as fecal microbiota transplantation from a young donor are well developed. In principle it should be possible to take a probiotic approach and use oral administration to achieve a similar outcome, a rejuvenated gut microbiome, but the knowledge and logistics are still lacking when it comes to producing the desired combination of microbes at scale.

As a complex and dynamic ecosystem, the gut microbiota is associated with major conditions like obesity, type 2 diabetes, cardiovascular disease, and cancer. Associations between aging and gut microbiota have been well-studied. Several studies have suggested that aging is associated with the composition of the gut microbiome and its metabolites, primarily through nutrient signaling pathways, immune regulation mechanisms, and epigenetic mechanisms. Aging-related gut dysbiosis may lead to the occurrence or progression of other metabolic diseases, resulting in a loss of healthy longevity. In addition, aging-related diet patterns can influence gut microbiota health, and dietary interventions can improve intestinal health and immune status in older adults, thereby increasing their healthy longevity. However, the biological mechanism of gut microbiota affecting longevity-related traits, such as healthspan and longevity, remains elusive.

Our study explored the effect of gut microbiota on longevity based on the data from multiple independent large-scale genome wide association studies (GWAS) of gut microbiota and longevity. Findings from linkage disequilibrium score (LDSC) regression analysis indicate a suggestive genetic correlation between gut microbiota and longevity. Utilizing the independent GWAS data, we further tested the causal association between identified candidate gut microbiota and longevity-related traits using Mendelian Randomization (MR) analysis. Our results provided potential clues for the effect of gut microbiota on longevity.

LDSC analysis detected four candidate genetic correlations, including Veillonella (genetic correlation = 0.5578) and Roseburia (genetic correlation = 0.4491 for longevity, Collinsella (genetic correlation = 0.3144 for parental lifespan and Sporobacter (genetic correlation = 0.2092) for healthspan. Further MR analysis observed suggestive causation between Collinsella and parental longevity (father's age at death). Reverse MR analysis also detected several causal effects of longevity-related traits on gut microbiota, such as longevity and Sporobacter.

Link: https://doi.org/10.1186/s12866-022-02703-x

LATE is a comparatively recently discovered form of dementia, connected to aggregation of misfolded TDP-43, one of the few proteins in the body capable of taking on an altered form that encourages other molecules of the same protein to also adopt that form and join together to form clumps. Aggregates are disruptive of cell function, but it is a slow process to understand exactly why this is the case. Researchers have been working on understanding amyloid-β aggregates for decades now, and continue to find that the present state of knowledge is incomplete regarding how the toxic halo of biochemistry that surrounds aggregates causes dysfunction and cell death.

With the growing interest in TDP-43 pathology, researchers have in recent years found it present in many older people to a measurable degree, as is the case for other protein aggregates. It is important to work towards therapies that can clear all of these aggregates, such as potentially those based on the use of catabodies. Even in the absence of very obvious pathology, it is likely the case that protein aggregates contribute to brain aging in more subtle, indirect ways. Medin aggregates, for example, have only recently been found to likely cause pathology, and they have been known for decades.

Looking for an Early Sign of LATE

Limbic predominate age-related TDP-43 encephalopathy or LATE is a recently recognized form of dementia that affects memory, thinking, and social skills. It mimics Alzheimer's disease or AD (and sometimes co-exists with it), but LATE is a different condition, with its own risks and causes. A new study analyzed levels of TDP-43 extracted from the exosomes secreted into the blood stream by various cell types, including neurons and glial cells. Exosomes are extracellular vesicles or sacs that transport DNA, RNA, and proteins inside the cell until their release. Researchers analyzed the brains of 64 patients post-mortem, 22 with autopsy-confirmed LATE and 42 patients who died without an indication of LATE.

The researchers reported significantly elevated plasma levels of TDP-43 in confirmed LATE patients. The effect was detected only in astrocyte-derived exosomes, not neuronal or microglial exosomes. Astrocytes are a sub-type of glial cell that perform many essential functions in the central nervous system, from regulating blood flow to providing the building blocks of neurotransmitters. They outnumber neurons more than fivefold. Effective treatment of all neurological diseases depends greatly upon early diagnosis. At the moment, however, LATE can only be diagnosed after death, and it is often confounded by the fact that living patients may have both LATE and AD. The findings that increased plasma concentrations of TDP-43 could be a tell-tale indicator of LATE are encouraging.

Evaluation of blood-based, extracellular vesicles as biomarkers for aging-related TDP-43 pathology

Limbic predominant age related TDP-43 encephalopathy neuropathological change (LATE-NC) is a recently characterized brain disease that mimics Alzheimer's disease (AD) clinically. TDP-43 was evaluated in neuronal (NDEVs), astrocyte (ADEVs), and microglial derived extracellular vesicles (MDEVs). EV preparations were isolated from the plasma of research subjects with autopsy-confirmed diagnoses of disease.

TDP-43 was significantly elevated in plasma ADEVs derived from autopsy confirmed LATE-NC subjects, with or without comorbid AD pathology. Measurable levels of TDP-43 were also detected in EV-depleted plasma; however, TDP-43 levels were not significantly different between persons with and without eventual autopsy confirmed LATE-NC. Blood-based EVs, specifically measuring TDP-43 accumulation in ADEVs, may serve as a potential diagnostic tool to rapidly identify subjects who are currently living with LATE-NC.

Inflammation in brain tissue is a feature of neurodegenerative conditions, and chronic inflammation is a feature of aging in general. This unresolved inflammatory signaling is disruptive to normal tissue structure and function. Researchers here note a consequence of inflammation in the innate immune cells of the brain, microglia. They produce a signal that draws in active, inflammatory T cells from the body in large numbers, which no doubt makes the situation worse. Normally there is little traffic between the separate immune systems of the brain and body, but the blood-brain barrier enforcing that separation becomes leaky with age, allowing inappropriate cells and molecules into brain tissue, where they can cause damage.

As people age, their cerebrospinal fluid (CSF) immune system becomes dysregulated. In people with cognitive impairment, such as those with Alzheimer's disease, the CSF immune system is drastically different from healthy individuals, a new study discovered. To analyze the CSF, researchers used single-cell RNA sequencing. They profiled 59 CSF immune systems from a spectrum of ages by taking CSF from participants' spines and isolating their immune cells. The first part of the study looked at CSF in 45 healthy individuals aged 54 to 83 years. The second part of the study compared those findings in the healthy group to CSF in 14 adults with cognitive impairment, as determined by their poor scores on memory tests.

Scientists observed genetic changes in the CSF immune cells in older healthy individuals that made the cells appear more activated and inflamed with advanced age. In the cognitively impaired group, inflamed T-cells cloned themselves and flowed into the CSF and brain. Scientists found the cells had an overabundance of a cell receptor - CXCR6 - that acts as an antenna. This receptor receives a signal - CXCL16 - from the degenerating brain's microglia cells to enter the brain. "It could be the degenerating brain activates these cells and causes them to clone themselves and flow to the brain. They do not belong there, and we are trying to understand whether they contribute to damage in the brain."

Link: https://www.eurekalert.org/news-releases/974237

This very interesting work involves identifying enhancer DNA sequences that regulate regeneration in an exceptionally regenerative species, such as zebrafish, and introducing these sequences into mammals via gene therapy. The researchers find a sequence that can be used to regulate expression of genes that drive heart regeneration following injury, a desirable goal given that mammalian hearts regenerate poorly. Zebrafish are capable of scarless healing of heart injuries, and connecting the zebrafish enhancer to mammalian growth genes can improve regeneration, by expressing these genes at the appropriate time in the context of repair of injury.

Researchers borrowed a segment of zebrafish DNA that they call a TREE, tissue regeneration enhancer element. TREEs are a family of gene enhancers included in the genome that are responsible for sensing an injury and orchestrating the activity of repair-related genes for reconstruction in a specific place. These enhancers also can shut off gene activity as healing is completed. These regulatory elements have been found in fruit flies, worms, and mice as well as the zebrafish. "We probably have them too, but it's just easier for us to find them in zebrafish and ask if they work in mammals."

About 1,000 nucleotides long, these enhancer sequences are bristling with recognition sites for different factors and stimuli to attach and change gene activity. "We don't fully understand how they do this and what they're truly responding to. Different cell types within an animal also have different types of these enhancers. Some of them are responsive in multiple tissues - those are the ones we use here. But when we profile regenerating spinal cord or fins in fish, we get different sequences. There may be tens of thousands of these types of enhancers in the human genome."

Rsearchers wanted to know if they could selectively incorporate the enhancer elements into an adult mouse using adeno-associated virus, a familiar gene therapy tool for introducing gene sequences into cells. The virus introduced DNA containing an enhancer to all tissues, but the hope was that the TREEs would only become active in response to an injury. A series of experiments in heart attack models of mice showed that viruses containing a TREE could be infused a week before injury and then the enhancer would jump into action when it detected injury. But they found it also worked when introduced to the animal a day or two after the heart attack.

Then, to see if this system could actually repair damage, rather than just sensing damage and turning on a gene that lights up tissue, they delivered a hyperactivated form of YAP, a powerful tissue growth gene that is implicated in cancer. The key question was whether this "really potent hammer" that can make cell division run amok could be lassoed into working only in the right time and place. They used a mutated YAP controlled by a TREE to see whether they could have safe growth of muscle after a heart attack in mice. The TREE turned on a mutated YAP for a few weeks, just in the injury site, and then it naturally shut down expression. The treatment caused muscle cells to begin to divide and the mouse's heart returned to near normal function after several weeks, though not without some scarring.

Link: https://today.duke.edu/2022/12/gene-therapy-heart-attacks-mice-just-got-more-precise

Familial Alzheimer's disease has an earlier onset in comparison to the sporadic Alzheimer's present in much of the population, and is connected to specific variants in genes associated with amyloid-β metabolism. In some cases that means one has to be careful of drawing conclusions based on studies of familial Alzheimer's. Today's research materials note the discovery of viral infection and signs of inflammatory dysfunction in the brains of familial Alzheimer's patients. These patients are likely more vulnerable to the consequences of viral infection, such as increased generation of amyloid-β in its antimicrobial peptide role, but there is little reason to believe that they are more vulnerable to suffering persistent infections than the rest of the population.

There is an ongoing debate in the research community regarding whether or not Alzheimer's is driven in large part by persistent viral infection, such as by herpesviruses. The mechanisms look plausible, and a major role for infection status might go some way towards explaining why only some people go onto develop Alzheimer's disease. The epidemiological data for the role of viral infection is conflicted, but recent studies suggest that combinations of viruses might be required to cause issues, rather than just one infectious agent. Antiviral treatment has been shown in some studies to reduce Alzheimer's risk.

Olfactory Viral Inflammation Associated with Accelerated Onset of Alzheimer's disease

Researchers focused on the olfactory tract, olfactory bulb, and the hippocampus, the area of the brain which manages memory and learning. They examined messenger RNA in the brain tissue of six individuals who had Familial Alzheimer's disease (FAD) and tissue from a control group without AD. They found signatures of viral infection in the olfactory bulbs of the FAD group and inflammation in the olfactory tract which carries information to the hippocampus. They also discovered altered myelination in the olfactory tract. Myelin is a protective fatty layer around nerves that allows electrical impulses to move quickly and smoothly. If it's damaged, signaling stalls.

"These findings raise the possibility that viral infection and associated inflammation and dysregulation of myelination of the olfactory system may disrupt hippocampal function, contributing to the acceleration of FAD progression. The whole olfactory pathway goes to the hippocampus. If you decrease the signaling along that pathway then you get less signaling to the hippocampus. If you don't use it, you lose it. Our hypothesis is that some viruses accelerate Alzheimer's disease."

Signatures for Viral Infection and Inflammation in the Proximal Olfactory System in Familial Alzheimer's Disease

Alzheimer's disease (AD) is characterized by deficits in olfaction and olfactory pathology preceding diagnosis of dementia. Here we analyzed differential gene and protein expression in the olfactory bulb (OB) and tract (OT) of familial AD (FAD) individuals carrying the autosomal dominant presenilin 1 E280A mutation.

Compared to control, FAD OT had increased immunostaining for β-amyloid (Aβ) and CD68 in high and low myelinated regions, as well as increased immunostaining for Iba1 in the high myelinated region. In FAD samples, RNA sequencing showed: (1) viral infection in the OB; (2) inflammation in the OT that carries information via entorhinal cortex from the OB to hippocampus, a brain region essential for learning and memory; and (3) decreased oligodendrocyte deconvolved transcripts. Interestingly, spatial proteomic analysis confirmed altered myelination in the OT of FAD individuals, implying dysfunction of communication between the OB and hippocampus. These findings raise the possibility that viral infection and associated inflammation and dysregulation of myelination of the olfactory system may disrupt hippocampal function, contributing to acceleration of FAD progression.

Type 2 diabetes is a lifestyle disease for near all patients. It results from excess visceral fat tissue, with some evidence suggesting that the specific issue is excess fat in the pancreas. Low calorie diets produce a reversal of symptoms, perhaps in large part due to loss of visceral fat. Here researchers show that intermittent fasting, another approach to reducing calorie intake, also helps to reduce the symptoms suffered by patients and the dependency on medication.

One might conclude that most type 2 diabetics are choosing to remain type 2 diabetics by refraining from lowered calorie intake and consequent weight loss. It isn't exactly easy to control one's diet, but then suffering type 2 diabetes seems quite challenging as well. Given the choice between those two options, it is strange that so few people choose to control their diet. Rationality is not a human specialty!

Intermittent fasting diets have become popular in recent years as an effective weight loss method. With intermittent fasting, you only eat during a specific window of time. Fasting for a certain number of hours each day or eating just one meal a couple of days a week can help your body burn fat. Research shows intermittent fasting can lower your risk of diabetes and heart disease.

Researchers conducted a 3-month intermittent fasting diet intervention among 36 people with diabetes and found almost 90% of participants, including those who took blood sugar-lowering agents and insulin, reduced their diabetes medication intake after intermittent fasting. 55% of these people experienced diabetes remission, discontinued their diabetes medication and maintained it for at least one year.

The study challenges the conventional view that diabetes remission can only be achieved in those with a shorter diabetes duration (0-6 years). Sixty-five percent of the study participants who achieved diabetes remission had a diabetes duration of more than 6 years (6-11 years). "Diabetes medications are costly and a barrier for many patients who are trying to effectively manage their diabetes. Our study saw medication costs decrease by 77% in people with diabetes after intermittent fasting."

Link: https://www.eurekalert.org/news-releases/974023

Somatic mosaicism is the result of the random mutational damage that occurs to stem cells and progenitor cells, leading to a spread of different mutation patterns throughout the descendant cells making up a tissue. It is thought to be involved in aging, a way for random mutation, different in every cell, to lead to specific dysfunctions occurring throughout a tissue, and potentially prime a tissue for a later combination of mutations that gives rise to cancer. This commentary on recent research discusses somatic mosaicism in the brain, intending to see whether there were differences in neurological disease states, but the findings are more relevant to cancer risk.

Mutagenesis occurs in human cells starting from the fertilized egg and continuing throughout life, resulting in somatic mutations. Most somatic mutations are functionally benign and have neither harmful nor beneficial effects on health. In rare cases, they change cell functions and may lead to diseases. Cancer is the most common example of a genetic disorder caused by somatic mutations.

In our recent study, we analyzed 131 post-mortem human brains from 44 healthy individuals, 19 with Tourette syndrome, nine with schizophrenia and 59 with autism spectrum disorder. The study reported several interesting findings by whole-genome sequencing of the brains to a depth of over 200X. First, most brains had 20-60 detectable single-nucleotide mutations that likely arose in early development. There were no differences in the somatic mutation burden between diseased and normal brains. Unexpectedly, seven brains, about 6% of the total, carried an abnormally large number - at least 100 but as many as 2000 - of somatic mutations. This phenomenon was termed hypermutability. Hypermutability increased with age, reaching ∼16% among old brains (older than 60 years of age), while it was only ∼2% among younger brains (less than 40 years of age). Interestingly, 10 damaging mutations in cancer-driving genes were found in four of the other six hypermutable brains, therefore implying clonal expansion. Consistently, hypermutability is typically localized to one brain region, although that estimate could be biased as no more than two regions per brain were analyzed.

Age is known to be the major factor associated with cancer occurrence. As such, the observed hypermutability carries two major hallmarks of cancers: clonal expansion and age association. This suggests that hypermutability generally represents pre-cancer or undiagnosed cancer cases, implying a theoretical possibility of cancer monitoring and early detection based on genomics. Association with aging also implies that hypermutability could be relevant in other aging-associated diseases such as Parkinson's and Alzheimer's. If proven, they theoretically could be diagnosed early before symptoms develop, using hypermutability as a genomic biomarker. However, it is currently unclear how this could be achieved, given that brain tissue is hardly accessible.

The question of which cell type expanded remains open. It could be interneurons. However, since the cell fractionation experiment may not isolate pure interneurons, clonally expanded cells could theoretically be some other cell type. Unlike post-mitotic neurons, glial cells continue to divide in adult brains. Given previous studies reporting increased glial cell fraction with age, the hypothesis of clonal gliogenesis is consistent with the observation that hypermutable brains are older. Clonal hematopoiesis with infiltration of blood into the brain could be yet another possibility. This hypothesis emerges from the observation that mutated cancer-driving genes in hypermutable brains are frequently associated with clonal hematopoiesis. In aging adults, clonal hematopoiesis increases, and the blood-brain barrier also becomes leakier. So, expanded cell lineages in the blood could be detected in the brain. Further studies are required to determine which hypothesis is correct, but it is possible that all could be correct, and there could be different causes of hypermutability in different individuals.

Link: https://doi.org/10.1002/ctm2.1138

The recently launched Longevity Escape Velocity (LEV) Foundation will, initially at least, focus on testing combinations of interventions. This work is informed by the SENS view of aging, in that degenerative aging is produced by a limited number of forms of cell and tissue damage that result from the normal operation of metabolism. These include the accumulation of senescent cells, cross-linking of the extracellular matrix, mitochondrial DNA damage, and so forth. Each form of damage produces its own contribution to a complex web of interacting downstream consequences, so while repairing any one form of damage should be beneficial, repairing more than one should be better.

Unfortunately the research and development communities operate under incentives that strongly discourage earnest work on combinations of therapies, these incentives largely resulting from the way in which intellectual property and regulation of medical development interact. Research into combined therapies is necessary to achieve the end goal of a comprehensive toolkit of rejuvenation therapies, but it is near entirely ignored as an aspect of this area of medical research. Thus philanthropic efforts are required to fill in the gap and light the way. Combined interventions are on the roadmap of the rejuvenome project, for example. And now they are a focus at the LEV Foundation.

Robust Mouse Rejuvenation - Study 1

LEV Foundation's flagship research program is a sequence of large mouse lifespan studies, each involving the administration of (various subsets of) at least four interventions that have, individually, shown promise in others' hands in extending mean and maximum mouse lifespan and healthspan. We focus on interventions that have shown efficacy when begun only after the mice have reached half their typical life expectancy, and mostly on those that specifically repair some category of accumulating, eventually pathogenic, molecular or cellular damage. The first study in this program is starting in January 2023.

Our ultimate goal in this program is to achieve "Robust Mouse Rejuvenation". We define this as an intervention, almost certainly multi-component, that: (a) is applied to mice of a strain with a historic mean lifespan of at least 30 months; (b) is initiated at an age of at least 18 months; (c) increases both mean and maximum lifespan by at least 12 months.

In each study in this program, we will examine the synergy of (typically at least four) interventions already known individually to extend mouse lifespan when started in mid-life. We will determine not only the ultimate readout of lifespan, but also the interactions between the various interventions, as revealed by the differences between the treatment groups (receiving different subsets of the interventions) in respect of the trajectories with age of cause of death, decline in different functions, etc. In this way we will add greatly to the understanding of which benefits these interventions confer and how they synergize, or possibly antagonize.

There are two key motivations for this program. One is purely biomedical: as with all mouse work with a biomedical end goal, we hope to generate data that will inform the development of therapies to let humans live longer in good health. The other could be called rhetorical, societal, political - it is to demonstrate a definitive proof of concept that aging is much more malleable than society currently insists on thinking it is, and thus must be viewed as a tractable medical problem, rather than a fact of life.

Interventions are chosen on the basis that they 1) act systemically and 2) have individually shown some lifespan-extending effect in naturally aged mice. In this way, we are specifically selecting rejuvenation therapeutics, as opposed to those which are purely preventative and/or require early life intervention. Therapies are also selected to have minimal mechanistic overlap, based on our current understanding of their mechanisms of action. The first four interventions selected for the initial study are rapamycin, hematopoietic stem cell transplant, telomerase upregulation via TERT gene therapy, and senolytic treatment.

Frailty is an end stage of aging, characterized by physical weakness, chronic inflammation, and lack of robustness in response to challenges. Frail individuals tend to spiral downward into organ failure and death in response to adverse circumstances, such as infection or injury, that less frail, younger individuals can survive. The question of how to reverse frailty is an important one; in principle, a good enough way of addressing the underlying causative mechanisms of aging would lead to improvement in patient outcomes. A number of the groups involved in development of first generation age-slowing and rejuvenating therapies are looking to frailty as a target for initial clinical trials.

Frailty is a multi-dimensional and dynamic condition, theoretically defined as "a state of increased vulnerability, resulting from age-associated declines in reserve and function across multiple physiologic systems, such that the ability to cope with every day or acute stressors is compromised". Although declines in physiological reserve are associated with senescence in the normal ageing process, frailty is an extreme consequence of this process, where this decline is accelerated and homeostatic responses begin to fail.

Frailty is a common and clinically significant condition among older adults. This is predominantly due to its association with adverse health outcomes, such as hospitalisation, falls, disability, and mortality. All older adults are susceptible to the risk of developing frailty, and even their younger counterparts. However, this risk is significantly increased with increases in chronological age, in the presence of comorbidities, low physical activity, poor dietary intake, and low-socioeconomic status, among a number of other factors.

While frailty is a dynamic condition, with the possibility of bi-directional transition between frailty states, this transition is more commonly progressive. This is largely due to the association of frailty with a plethora of adverse health outcomes, which can often lead to a spiral of decline. As frailty progresses, interventions to mitigate, manage, or reverse this decline become increasingly difficult to implement, both from practical and physiological perspectives.

The relative prevalence of frailty in older adults may be reduced with future improvements in treatment, particularly those identified as effective at mitigating the onset of frailty. However, irrespective of this, the absolute prevalence, and overall burden of frailty is projected to increase dramatically in the coming decades as the population ages. Perhaps of most concern in this regard, is that several longitudinal birth cohort studies have reported increases in the relative prevalence of frailty among more contemporary generations of older adults, when compared to their generational predecessors.

Link: https://doi.org/10.1159/000528561

Catalase is an important antioxidant enzyme, defending cells against oxidative stress. Aging brings with it mitochondrial dysfunction and other sources of excess oxidative molecules, and some animal studies have shown improved health to result from upregulation of catalase expression. Regardless of whether or not more of a given molecule in cells is beneficial, it is often the case that removing it is harmful, and thus it is usually hard to draw conclusions based on gene knockout studies as to whether a given molecule is a potential target for upregulation.

Lysosomes are a central hub for cellular metabolism and are involved in the regulation of cell homeostasis through the degradation or recycling of unwanted or dysfunctional organelles through the autophagy pathway. Catalase, a peroxisomal enzyme, plays an important role in cellular antioxidant defense by decomposing hydrogen peroxide into water and oxygen.Both impaired lysosomes and catalase have been linked to many age-related pathologies with a decline in lifespan.

Aging is characterized by progressive accumulation of macromolecular damage and the production of high levels of reactive oxygen species. Although lysosomes degrade the most long-lived proteins and organelles via the autophagic pathway, the role of lysosomes and their effect on catalase during aging is not known. The present study investigated the role of catalase and lysosomal function in catalase-knockout (KO) mice.

We performed experiments on wild-type (WT) and catalase KO younger (9 weeks) and mature adult (53 weeks) male mice and mouse embryonic fibroblasts isolated from WT and KO mice from E13.5 embryos as in vivo and in ex vivo respectively. We found that at the age of 53 weeks (mature adult), catalase-KO mice exhibited an aging phenotype faster than WT mice. We also found that mature adult catalase-KO mice induced leaky lysosome by progressive accumulation of lysosomal content, such as cathespin D, into the cytosol. Leaky lysosomes inhibited autophagosome formation and triggered impaired autophagy. The dysregulation of autophagy triggered mTORC1 activation. However, the antioxidant N-acetyl-L-cysteine and mTORC1 inhibitor rapamycin rescued leaky lysosomes and aging phenotypes in catalase-deficient mature adult mice.

Link: https://doi.org/10.1186/s12964-022-00969-2

Hematopoietic stem cells and progenitor cells in the bone marrow produce the red blood cells and immune cells needed for the body to function. Changes in this hematopoietic system make up one the major factors in the age-related decline of the immune system into the incapacity of immunosenescence and chronic inflammatory state known as inflammaging. There is a decline in the diversity of cell populations tasked with producing immune cells, and the types of immune cell produced shifts to favor myeloid lineages of the innate immune system over lymphoid lineages of the adaptive immune system.

The age-related decline of the immune system is in part a feedback loop; dysfunction in immune cells produced in the bone marrow leads to inflammation and altered signaling in the bone marrow, leading to changes in production of immune cells, and consequent greater dysfunction in the immune system. Inflammatory signaling is the obvious suspect when considering how immune cells can disrupt stem cell function, but there are likely other mechanisms at work.

In this context, today's open access paper is interesting for the demonstration that the myeloid-derived neutrophil population plays a role in hematopoietic dysfunction with age. Unfortunately these cells are necessary to a robust immune defense, so one can't just take the approach used here, removing the entire neutrophil population. The next step must be to identify the specific mechanisms involved, and find ways to intervene at that level.

Myeloid cells promote interferon signaling-associated deterioration of the hematopoietic system

Hematopoietic stem cell (HSC) pools are positioned at the hematopoietic hierarchical apex and sustain multi-lineage hematopoiesis throughout the mammalian lifetime. They can do so by maintaining relative quiescence, self-renewal, and infrequent divisions during steady-state hematopoiesis. These critical processes are governed by ancillary cells in so-called stem cell niches, which include endothelial and mesenchymal cells in the mammalian hematopoietic system. Recent findings implicate resident innate and adaptive immune cells in the homeostatic regulation of stem cells. In particular, macrophages and regulatory T cells are established regulators of hematopoietic stem cells under homeostatic conditions.

The contribution of neutrophils, the most abundant innate immune cell in the human bone marrow, to homeostatic stem cell regulation, however, has remained largely elusive. This is mainly due to the lack of models fulfilling the experimental paradigm for defining HSC-regulating cells, which is (long-term) specific depletion of a candidate regulatory cell, followed by rigorous examination of HSC function. Existing models of neutropenia either induce transient, short-term reduction of neutrophil levels and/or employ genetic strategies that target HSCs themselves, precluding conclusions on the effect of neutropenia on long-term HSC biology.

Here, utilizing a mouse model of profound, sustained, and specific depletion of mature myeloid cells (neutrophils and eosinophils), we demonstrate that HSC integrity and function are conserved, implicating divergent responses of stem and progenitor cells to compensate for myeloid lineage shortages. Unexpectedly, the depletion of myeloid cells attenuated inflammatory signaling in stem cells and their niches via the reduction of natural killer (NK) cell numbers and activation status and abrogated the loss of HSC function in serial transplantation, identifying a neutrophil-NK cell axis as a critical determinant of the functional decline of the hematopoietic system.

Chromatin is the packaged structure of DNA in the cell nucleus, and its arrangement determines which genes can be expressed. Researchers here show that chromatin is more accessible to expression in aged muscle stem cells, a part of the change in cell behavior. Whether this can be reversed by partial reprogramming is an interesting question. It seems plausible given that reprogramming changes gene expression patterns in cells, reverting them to a more youthful state, and certainly something that can be tested.

Adult stem cells are essential for tissue regeneration and homeostasis maintenance. Skeletal muscle possesses a remarkable regeneration capacity after acute injury because of its resident stem cells, muscle stem cells, or satellite cells (SCs). pon stimuli such as acute injury, quiescent SCs exit from quiescence to activate and re-enter the cell cycle for proliferation. They will further differentiate to repair the damaged tissue. Some activated SCs will return to quiescence through the self-renewal process to replenish the stem cell pool.

Eukaryotic DNA is highly organized into a nuclear structure called chromatin. The accessibility to the regulatory DNA elements restrains the gene expression, therefore defining the cell identity. In this study, we examined the chromatin accessibility changes of SCs, from quiescence exit, early activation, and regeneration, showing the trajectory of chromatin environment changes for SC activation in young and aged conditions. We showed that the chromatin environment of SCs is very compact during quiescence, becomes highly accessible on early activation, and gradually re-establish the compact state after long-term regeneration. We found that the old SCs exhibit a much more open chromatin environment, suggesting that the old SCs exhibit a chronically activated chromatin state.

Link: https://doi.org/10.1016/j.isci.2022.104954

The struggles and sufferings of the old are largely conducted behind the curtain, not talked about all that much in the public sphere. How does one manage the last phase of life for a failing, complex machine that cannot be repaired, only coaxed into a slightly slower decline? As it turns out, a fair amount of not thinking about it is involved: on the part of younger people, and particularly on the part of research and development institutions that do not wish to be burdened with the very complex, interacting nature of late life age-related diseases. New treatments and adjustments to the standard of care are rarely formally tested in the older, more frail part of the patient population.

30-40% of people hospitalized with ACS are age 75 or older. ACS includes heart attack and unstable angina (heart-related chest pain). Cardiovascular changes that occur with normal aging make ACS more likely and may make diagnosing and treating it more complex: large arteries become stiffer; the heart muscle often works harder but pumps less effectively; blood vessels are less flexible and less able to respond to changes in the heart's oxygen needs; and there is an increased tendency to form blood clots. Sensory decline due to aging may also alter hearing, vision and pain sensations. Kidney function also declines with age, with more than one-third of people ages 65 and older having chronic kidney disease. These changes should be considered when diagnosing and treating ACS in older adults.

Clinical practice guidelines are based on clinical trial research. However, older adults are often excluded from clinical trials because their health care needs are more complex when compared to younger patients. ACS is more likely to occur without chest pain in older adults, presenting with symptoms such as shortness of breath, fainting or sudden confusion. Measuring levels of the enzyme troponin in the blood is a standard test to diagnose a heart attack in younger people. However, troponin levels may already be higher in older people. Age-related changes in metabolism, weight and muscle mass may necessitate different choices in anti-clotting medications to lower bleeding risk. As kidney function declines, the risk of kidney injury increases, particularly when contrast agents are used in imaging tests and procedures guided by imaging. Although many clinicians avoid cardiac rehabilitation for patients who are frail, they often benefit the most.

As people age, they are often diagnosed with health conditions that may be worsened by ACS or may complicate existing ACS. As these chronic conditions are treated, the number of medications prescribed may result in unwanted interactions or medications that treat one condition may worsen another. Older adults differ widely in their independence, physical or cognitive limitations, life expectancy, and goals for the future. The goals of care for older people with ACS should extend beyond clinical outcomes (such as bleeding, stroke, another heart attack or the need for repeat procedures to reopen arteries).

Link: https://newsroom.heart.org/news/hearts-and-bodies-change-with-age-heart-disease-treatments-may-need-to-change-too

Axonal spheroids are a feature of neurodegenerative conditions, bubbles that form on axons and can contain entire cell organelles, in addition to molecular debris and other cell components. These spheroids are comparatively poorly understood, but are thought to be connected to the processes of autophagy and other modes of clearance of waste. Spheroids disrupt axonal function, and may rupture to spill their contents outside the cell, causing further issues. Today's open access paper provides more evidence for the connection to portions of autophagy, specifically the formation of endolysosomes, when an endosome carrying materials ingested by the cell merges with a lysosome in order for those materials to be broken down by enzymes. Connections are also made to the presence of amyloid-β in the aging brain, in that axons close to plaque are those that form axonal spheroids.

Whether the mechanisms underlying these correlations are direct or indirect is a matter for speculation. It has the look of a garbage catastrophe: cellular recycling systems, such as autophagy, that can manage the load in a youthful brain become overloaded in an aged brain. That may be due to the presence of amyloid-β plaques and other problematic materials outside cells that are taken up into endosomes, rising levels of damaged molecular machinery inside cells that requires recycling, or loss of efficiency in autophagy due to that damage, but the end result is a series of maladaptive, possibly compensatory phenomena such as the creation of axonal spheroids. These structures are potentially useful to eject material from the cell, but also harmful to neural function and the surrounding environment.

PLD3 affects axonal spheroids and network defects in Alzheimer's disease

Here we show that hundreds of axons around each amyloid plaque develop spheroids and, rather than being retraction bulbs from degenerating axons, these structures are stable for extended periods of time and could therefore have an ongoing detrimental effect on neuronal connectivity. Given the similarity in the morphology, organelle and biochemical content of plaque-associated axonal spheroids (PAASs) in mice and humans, it is probable that, in humans, these are also stable structures that could disrupt neural circuits for extended intervals.

To better understand the effect of PAASs on axonal function, we implemented in vivo Ca2+ and voltage imaging in individual cortical axons and cell bodies. Both Ca2+ and voltage imaging revealed that a substantial proportion of axons in a mouse model of Alzheimer's disease (AD) had disrupted AP conduction and an overall increase in the threshold for action potential propagation manifested by conduction blockades. This was due to the presence of axonal spheroids and was shown to be correlated with their size. The finding that larger PAASs caused more severe conduction blocks was consistent with computational modelling showing that PAASs resemble electrical capacitors that function as current sinks, and that PAAS size is a major determinant of the degree of conduction defects. Together, our data suggest that the large number of amyloid deposits present in the AD brain have the potential to substantially affect neural networks by widespread disruption of axonal connectivity.

Mechanistically, we found that enlarged LAMP1-positive vesicles (ELPVs) - which probably include multivesicular bodies (MVBs), endolysosomes, and autolysosomes - accumulate within axonal spheroids and that their presence is correlated with spheroid size. Moreover, we found an increased presence of ELPVs within spheroids in older Alzheimer's model mice and in more severely impaired human patients with AD, indicating that ELPV accumulation may be a key feature of disease progression. MVBs are crucial intermediate organelles that evolve through the maturation of endosomes and fuse with autophagosomes and lysosomes. Thus, dysregulation in MVB biogenesis has the potential to affect the normal generation of fusion vesicles.

Spheroid growth was also mechanistically linked with Pld3 - a potential Alzheimer's-disease-associated risk gene that encodes a lysosomal protein that is highly enriched in axonal spheroids. Neuronal overexpression of Pld3 led to endolysosomal vesicle accumulation and spheroid enlargement, which worsened axonal conduction blockades. By contrast, Pld3 deletion reduced endolysosomal vesicle and spheroid size, leading to improved electrical conduction and neural network function. Thus, targeted modulation of endolysosomal biogenesis in neurons could potentially reverse axonal spheroid-induced neural circuit abnormalities in Alzheimer's disease, independent of amyloid removal.

Chronic, unresolved inflammatory signaling is a feature of aging, the result of lingering senescent cells, debris from stressed cells, and other processes. When persistent over time, inflammatory signaling is highly disruptive to cell and tissue function, altering behavior in ways that contribute to a wide variety of pathologies. In the vasculature, this includes atherosclerosis, calcification, loss of compliance in the vascular smooth muscle responsible for contraction and dilation of blood vessels, and a range of more subtle problems, lumped under the heading of endothelial dysfunction, at the inner surface of blood vessels.

Endothelial dysfunction, a leading cause of abnormal vasodilation, is the basis of many cardiovascular diseases. Improving endothelial function has been shown to be beneficial in the prevention and treatment of hypertension and coronary heart disease (CHD). However, to date, little is known about the effects of existing methods on the prevention of endothelial dysfunction. Therefore, exploring the mechanism of endothelial dysfunction may be beneficial in the development of more effective therapeutic targets. Endothelial nitric oxide synthase (eNOS) is a vital enzyme required for NO synthesis in endothelial cells and is the primary regulator of homeostasis and vascular tone. A decline in eNOS expression often leads to increased vascular tension and decreased local blood perfusion, which are responsible for the development of many cardiovascular diseases.

Sterile inflammation has been shown to occur with aging. This type of inflammatory response is due to immune dysfunction and is closely associated with aging-related organ dysfunction. Evidence suggests that the increase in pro-inflammatory factors caused by sterile inflammation reduces vascular eNOS expression and NO production, leading to vasodilation dysfunction and ultimately aging-related cardiovascular diseases. However, the mechanisms involved in the regulation of age-related aseptic inflammation need further exploration.

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a newly discovered component of the innate immune system. The cGAS acts as a cytoplasmic DNA sensor, and its activation leads to activation of the downstream target STING, and subsequent phosphorylation of interferon regulatory factor 3 (IRF3). The main targets of IRF3 are inflammatory genes such as interferon-β (IFNβ), Ifit1, Ifit2, Ifit3, and MCP-1. Increased transcription of pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β) and IL-6 eventually lead to sterile inflammation. Sterile inflammation is similar to inflammation that appears during infection and may be responsible for tissue injury.

A decline in endothelial function, up-regulation of p53, p21, and p16 expression, and activation of the cGAS-STING pathway were observed in aging mice. Inhibition of cGAS was found to improve endothelial function and reverse the increased expression of aging markers. Our in vitro data demonstrated that D-galactose induced a decrease in eNOS expression and cell senescence, which could be partly reversed by cGAS inhibitor, STING inhibitor, siRNA-cGAS and siRNA-STING treatment. Higher expression levels of cGAS, STING, and p-IRF3 were observed in aged human aortic intima tissue compared to young aortic intima tissue. Our study demonstrated that activation of the cGAS-STING pathway played a vital role in aging-related endothelial dysfunction. Thus, the cGAS-STING pathway may be a potential target for the prevention of cardiovascular diseases in the elderly.

Link: https://doi.org/10.14336/AD.2022.0316

Researchers here describe a role for oxytocin in promoting neural plasticity in adults, the integration of new neurons into existing neural circuits. It is possible that upregulation of oxytocin could promote this activity. It is considered that increased neurogenesis, the creation of new neurons and their incorporation into brain activity, is beneficial. Neurogenesis declines with age, and restoration of more youthful levels may go some way towards slowing the decline of cognitive functions in later life.

Learning a new task, mastering a musical instrument or being able to adapt to the constantly changing environment are all possible thanks to the brain's plasticity, or its ability to modify itself by rearranging existing neural networks and forming new ones to acquire new functional properties. This also helps neural circuits to remain healthy, robust and stable. To better understand brain plasticity, researchers used mouse models to investigate how brain cells build connections with new neurons born in adult brains.

The researchers discovered that levels of oxytocin increase in the olfactory bulb, peaking at the time the new neurons incorporate themselves into neural networks. Using viral labeling, confocal microscopy, and cell-type specific RNA sequencing, the team discovered that oxytocin triggers a signaling pathway - a series of molecular events inside cells - that promotes the maturation of synapses, that is, the connections of newly integrated adult-born neurons. When the researchers eliminated the oxytocin receptor, the cells had underdeveloped synapses and impaired function.

"Our findings suggest that oxytocin drives development and synaptic integration of new neurons within the adult brain, directly contributing to adaptability and circuit plasticity. Oxytocin is normally present in our brain, so if we understand how to turn it on or off or mobilize it, we can help keep our circuit connections healthy by promoting the growth of underdeveloped connections or strengthening new ones. Our findings also suggest that oxytocin could promote the growth of new neurons to repair damaged tissue. Further studies are needed to explore these possibilities."

Link: https://www.eurekalert.org/news-releases/973857

Ultimately, we live and die as the brain lives and dies. The rest of the body is a support system, a complex one to be sure, but probably not as complex as the brain. Repairing the cell and tissue damage of aging in the body seems a more tractable challenge, in that replacement is always an option. Replace cells, replace the gut microbiome, add new tissues grown in a lab to organs like the liver and thymus, or grow a new body and transplant the brain. A path of ever increasing control over cells, cell signaling, and regeneration implies a future in which all damaged tissue can be replaced in one way or another ... except for the brain, because the fine structure of brain tissue encodes the data of the mind. Here, a different solution is needed.

Today, of course, researchers understand all too little of the details. Medical biotechnologies are simple, barely at the stage of manipulating one gene or protein interaction at a time, unable to deliver therapeutics to only and exactly the cells that we want to affect, a search for points of intervention in which a change cascades in ways that are more rather than less favorable, discarding the many points of intervention that the present state of the art cannot influence. This will change, the future is golden, but it is worth looking at continued efforts to understand the fine details of aging in the brain with this in mind. The goal at the end of the day is a way to repair all of the biochemistry of the brain in situ, without loss of the data of the mind. How exactly that will be accomplished remains to be determined.

The Ageing Brain: Molecular and Cellular Basis of Neurodegeneration

Currently, various treatment strategies are being investigated to slow or reverse ageing-associated diseases; unfortunately, no preventive or effective treatments have yet been identified. The major challenge associated with this process, thus far, remains the lack of highly efficient disease models of neurodegeneration. In this review, various ageing hallmarks were discussed, most of which have been associated with neurodegenerative diseases.

We propose that future studies of neurodegenerative diseases should focus on these hallmarks of ageing and that ageing models should be developed that show neurodegenerative disease phenotypes. Although this paper primarily focused on DNA damage, cellular senescence, and mitochondrial dysfunction, studies examining the relationships between the nucleus and mitochondria would reveal the mechanistic links between ageing and neurodegeneration. Other hallmarks, such as proteostasis, epigenetic deregulation, and telomerase inactivation, are also important. The loss of proteostasis results in proteasomal and autophagy defects in both Alzheimer's disease and Parkinson's disease, resulting in inflammation and senescence. Metabolic dysfunction has been shown to be associated with mitochondrial dysfunction, oxidative stress, and NAD+ levels.

Although cross-talk between inflammatory pathways and neurodegeneration has been recognized for the past two decades, very few therapeutic strategies have emerged from this line of research due to the lack of a high-throughput screening platform. To harness the therapeutic potential of inflammatory pathways, a better understanding of the neuroprotective role played by TNF-α and NF-κB remains necessary, and new models must be developed that are able to recapitulate microglia-induced neurodegenerative phenomena in vivo. However, neurodegenerative diseases are complex to decipher, and their central mechanisms are further complicated by the interactions that occur between genetic and environmental factors, which drive disease progression. A single-pathway-oriented therapeutic intervention might not be sufficient for the treatment of these complex disease, although combination therapies may be successful.

Identifying functional links between neurodegenerative diseases and ageing hallmarks could reveal new therapeutic avenues. A multi-target, evidence-based approach associated with non-pharmacological approaches, such as lifestyle modifications, may slow neurological disease progression in older individuals.

Researchers here report on the results of a phase III trial of tumor infiltrating leukocyte (TIL) therapy for melanoma. A patient's T cells are multiplied outside the body and then injected, along with chemotherapy beforehand to clear existing T cell populations, and IL-2 delivery afterwards to promote replication of the delivered T cells. It has meaningful side-effects, as do other cancer immunotherapies, but the outcome is an improvement over the present standard approach of checkpoint inhibition for melanoma. Even as better approaches to cancer therapy are in development, such as those based on interference in telomere lengthening, we should expect to see continued iteration and improvement in immunotherapies.

Melanoma is an aggressive type of skin cancer. Ten years ago, metastatic melanoma was almost certainly a death sentence within a year after diagnosis. "Ten years ago, melanoma had such a bad prognosis that I would be seeing an entirely new patient population every year - but now I've been seeing some patients for ten years. This is largely due to the discovery of immunotherapy, which has revolutionized treatment for melanoma. But we still see that about half of the people diagnosed with metastatic melanoma succumb within five years, so we're still not where we want to be - not at all."

TIL stands for tumor-infiltrating lymphocytes: immune cells, T cells in this case, that have entered the tumor. The body trains these T cells to recognize and then kill foreign invaders, such as tumor cells. The presence of T cells in a tumor is a good sign, because it means that the immune system has recognized the tumor as a foreign entity and wants to attack and destroy it. Many tumors, however, do not contain enough potent T cells. TIL therapy aims to multiply the patient's T cells, which are isolated from one of the tumor sites, into a huge army consisting of billions of T cells.

Researchers started an international trial in 2014: the TIL trial, which compared TIL therapy to standard immunotherapy with the checkpoint inhibitor ipilimumab. The results of the TIL trial have now been presented. In almost half (49%) of the patients with metastatic melanoma who received TIL therapy, the metastases had decreased in size. In 20% of patients, the metastases had even disappeared completely. This also proved to be the case in patients who had already received prior treatment at the time of their participation in the trial. These percentages were significantly higher compared to those seen in the patient group receiving standard immunotherapy (ipilimumab). In the ipilimumab group, metastases had decreased in size in 21% of patients, and in 7%, the metastases had disappeared completely.

The progression-free survival, the percentage of patients who do not experience disease progression after a specified time period, was 53% after six months for patients receiving TIL therapy, and 21% in the control group (ipilimumab). At a median follow-up time of 33 months for all patients, the median progression-free survival of patients who had received TIL therapy was significantly better (7 months) than that of patients treated with ipilimumab (3 months).

Link: https://www.nki.nl/news-events/news/patient-s-own-immune-cells-effective-as-living-drug-for-melanoma/

Senescent cells accumulate with age and negatively affect surrounding tissue with their pro-inflammatory secretions. Greater understanding of this contribution to degenerative aging has led to the development of senolytic therapies to selectively destroy these errant cells and thus improve tissue function. Cellular senescence may also occur in tissues undergoing transplantation, a result of the stresses involved, and cause loss of function and related issues following transplantation. Thus senolytics may find a use in the organ transplant industry as a way to improve success rates and patient outcomes following successful transplants.

Liver transplantation is the only curative option for patients with end-stage liver disease. Despite improvements in surgical techniques, nonanastomotic strictures (characterized by the progressive loss of biliary tract architecture) continue to occur after liver transplantation, negatively affecting liver function and frequently leading to graft loss and retransplantation. To study the biological effects of organ preservation before liver transplantation, we generated murine models that recapitulate liver procurement and static cold storage. In these models, we explored the response of cholangiocytes and hepatocytes to cold storage, focusing on responses that affect liver regeneration, including DNA damage, apoptosis, and cellular senescence.

We show that biliary senescence was induced during organ retrieval and exacerbated during static cold storage, resulting in impaired biliary regeneration. We identified decoy receptor 2 (DCR2)-dependent responses in cholangiocytes and hepatocytes, which differentially affected the outcome of those populations during cold storage. Moreover, CRISPR-mediated DCR2 knockdown in vitro increased cholangiocyte proliferation and decreased cellular senescence but had the opposite effect in hepatocytes. Using the p21 knockout model to inhibit senescence onset, we showed that biliary tract architecture was better preserved during cold storage. Similar results were achieved by administering senolytic ABT737 to mice before procurement.

Last, we perfused senolytics into discarded human donor livers and showed that biliary architecture and regenerative capacities were better preserved. Our results indicate that cholangiocytes are susceptible to senescence and identify the use of senolytics and the combination of senotherapies and machine-perfusion preservation to prevent this phenotype and reduce the incidence of biliary injury after transplantation.

Link: https://doi.org/10.1126/scitranslmed.abj4375

The balance of microbial populations making up the gut microbiome changes with age in ways that produce harm, such as loss of beneficial metabolites, and generation of chronic inflammation. This form of aging is only loosely connected to age-related damage in our tissues, in that animal studies appear to show that a readjustment of the balance of populations in the gut microbiome of an aged animal, making it more youthful, will persist even as aging progresses in the body. In killifish, the result is improved health and extended life span; in mice, similar studies have demonstrated improved health, with lifespan studies yet to take place.

One of the approaches capable of rejuvenating the gut microbiome is fecal microbiota transplantation, a procedure that is exactly as it sounds. As a matter of interest to the longevity community, one implementation of fecal microbiota transplant is now FDA approved for treatment of C. difficile infection. This approval will make it a great deal easier for groups with the motivation and funding to run low-cost clinical trials to demonstrate that fecal microbiota transplantation from young to old individuals will improve function and health in the older recipient. I believe that this sort of activity, aimed at convincing physicians and the public that rejuvenation is possible, is important and necessary to accelerate progress towards greater human longevity. Once a treatment is approved for one use, it can in principle be prescribed off-label by any physician. This specific packaging of the fecal microbiota transplant procedure as a medical product is not assembled with young to old transplants in mind, but as is the case for albumin harvested from donated blood, donors tend to be on the younger side.

This FDA approval probably doesn't make a great deal of difference to self-experimenters interested in fecal microbiota transplantation as a way to potentially beneficially adjust an aging gut microbiome. It was already possible to use services, such as Human Microbes, to purchase screened stool samples in order to conduct the treatment oneself. There is a thriving market in this sort of service, forums to connect people, and a plethora of quiet, individual efforts to improve various common forms of gut dysbiosis outside the medical system. Aging is its own form of gut dysbiosis, so why not that as well?

FDA Approves First Fecal Microbiota Product

Today, the U.S. Food and Drug Administration approved Rebyota, the first fecal microbiota product approved by the agency. Rebyota is approved for the prevention of recurrence of Clostridioides difficile infection (CDI) in individuals 18 years of age and older. It is for use after an individual has completed antibiotic treatment for recurrent CDI. Clostridioides difficile (C. difficile) is a bacterium that can cause CDI, a potentially life-threatening disease resulting in diarrhea and significant inflammation of the colon. In the United States, CDI is associated with 15,000-30,000 deaths annually.

The intestinal tract contains millions of microorganisms, often referred to as the "gut flora," or "gut microbiome." Certain situations, such as taking antibiotics to treat an infection, may change the balance of microorganisms in the gut, allowing C. difficile to multiply and release toxins causing diarrhea, abdominal pain and fever, and in some cases, organ failure and death. Other factors that can increase the risk for CDI include age older than 65 years, hospitalization, a weakened immune system and a previous history of CDI. After recovering from CDI, individuals may get the infection again - often multiple times-a condition known as recurrent CDI. The risk of additional recurrences increases with each infection and treatment options for recurrent CDI are limited. The administration of fecal microbiota is thought to facilitate restoration of the gut flora to prevent further episodes of CDI.

Rebyota is administered rectally as a single dose. Rebyota is prepared from stool donated by qualified individuals. The donors and the donated stool are tested for a panel of transmissible pathogens, however, as Rebyota is manufactured from human fecal matter, it may carry a risk of transmitting infectious agents. In addition, Rebyota may contain food allergens; the potential for the product to cause adverse reactions due to food allergens is unknown. The safety of Rebyota was assessed from two randomized, double-blind, placebo-controlled clinical studies and from open-label clinical studies conducted in the United States and in Canada.

The effectiveness of Rebyota was evaluated in an analysis of data from a randomized, double-blind, placebo-controlled, multicenter study. The analysis included 177 adults who received one dose of Rebyota and 85 who received one dose of placebo in this study. It also incorporated success rates from a different placebo-controlled study in which 39 adults received one dose of Rebyota and one dose of placebo and 43 adults received two doses of placebo. Success in preventing recurrent CDI was defined as the absence of CDI diarrhea within 8 weeks of administration of Rebyota or placebo. In a statistical analysis that took into account both studies, the overall estimated rate of success in preventing recurrent CDI through 8 weeks was significantly higher in the Rebyota group (70.6%) than in the placebo group (57.5%).

This open access paper discusses the possible role of CSPα expression and function in neurodegeneration. CSPα is connected to mechanisms involved in clearance of the protein aggregates that build up in the brain with age. Toxicity associated with these aggregates is implicated in the onset and progression of neurodegenerative conditions. Since the connection seems connected to cellular quality control mechanisms, it is plausible that manipulation of CSPα expression will be more effective in short-lived species such as mice than in long-lived species such as our own. Short-lived species appear to respond to more readily to upregulation of autophagy and other stress responses that act to maintain the molecular machinery of the cell.

Adult-onset neuronal ceroid lipofuscinosis (ANCL) is an inherited neurodegenerative disease with progressive neuronal dysfunction characterized by neuronal death and lipofuscin deposition in the neuronal or non-neuronal lysosomes. Although mutations in CSPα, encoded in the human DNAJC5 gene, are known to be associated with ANCL, the pathogenic mechanisms involved remain unknown. The most well-studied function of CSPα is its cytoplasmic chaperone function. CSPα is abundant in presynaptic vesicles, interacting with HSC70 to ensure correct protein folding. Mutant CSPα causes loss of palmitoylation, mislocalization, and aggregation of CSPα, which then triggers a series of reactions and destabilizes key proteins related to its function, such as synaptic SNAP-25 proteins and PPT1 proteins. Although the exact mechanism is unknown, certain changes in these proteins contribute to NCL.

In numerous animal and human studies, defects in CSPα have been shown to cause neurodegeneration. In addition to ANCL, Alzheimer's disease, Parkinson's disease, FTD, and Huntington's disease have been shown to be associated with CSPα. Although the mechanisms of these neurodegenerative diseases have not been fully explained, neurodegenerative diseases are often associated with protein misfolding. Further studies have revealed that CSPα is essential for transporting misfolded proteins. CSPα has been shown to be associated with lysosomal degradation. Inadequate lysosomal degradation can lead to abnormal membrane flow and misfolded protein entry into endolysosomes, thus leading to error-prone protein accumulation. Additionally, CSPα has been shown to be involved in misfolding-associated protein secretion, endosomal microautophagy, and unfolded protein response processes, which are known to play important roles in maintaining the stability of misfolded proteins. However, all the relevant mechanisms researches are not detailed enough, and more evidence is required to reveal the deeper molecular mechanisms.

Link: https://doi.org/10.3389/fnagi.2022.1043384

Researchers here report on a study of LDL-cholesterol and mortality risk in older people. As they note, data on this topic is conflicted once one moves beyond the matter of cardiovascular disease. Over a lifetime, higher LDL-cholesterol makes it easier to reach the tipping point at which cholesterol deposited in blood vessel walls produces enough cellular dysfunction to form a fatty streak and then an atherosclerotic plaque. For other forms of mortality, I would suspect that the unhealthy lifestyle or ongoing chronic disease required to have either an abnormally low or abnormally high LDL-cholesterol level in blood samples is the cause of increased mortality, rather than anything to do with cholesterol metabolism per se.

Low density lipoprotein cholesterol (LDL-C) is a well established causal risk factor for the development of atherosclerosis and cardiovascular disease. High levels of LDL-C consistently predict a risk of future atherosclerotic cardiovascular events in a variety of populations throughout the world. Also, many randomised controlled trials of treatment with lipid lowering agents have clearly shown that lowering LDL-C levels reduces the risk of atherosclerotic cardiovascular events in the future.

Because lowering levels of LDL-C reduces cardiovascular disease outcomes, the general perception is that high levels of LDL-C are associated with an increased risk of mortality but low levels are not. Studies on the association between LDL-C levels and the risk of all cause mortality, however, have provided conflicting results, with some studies showing a counterintuitive inverse association (lower mortality with increasing levels of LDL-C) and some showing no association. Most of these studies were conducted in individuals aged 65 and older, and in historical population based cohorts.

In this study, we determined the association between levels of LDL-C and the risk of all cause and cause specific mortality. Among 108,243 individuals aged 20-100, 11,376 (10.5%) died during the study, at a median age of 81. The association between levels of LDL-C and the risk of all cause mortality was U shaped, with low and high levels associated with an increased risk of all cause mortality. Compared with individuals with concentrations of LDL-C of 3.4-3.9 mmol/L (132-154 mg/dL), the multivariable adjusted hazard ratio for all cause mortality was 1.25 for individuals with LDL-C concentrations of less than 1.8 mmol/L (under 70 mg/dL) and 1.15 for LDL-C concentrations of more than 4.8 mmol/L (over 189 mg/dL).

The concentration of LDL-C associated with the lowest risk of all cause mortality was 3.6 mmol/L (140 mg/dL) in the overall population and in individuals not receiving lipid lowering treatment, compared with 2.3 mmol/L (89 mg/dL) in individuals receiving lipid lowering treatment. Similar results were seen in men and women, across age groups, and for cancer and other mortality, but not for cardiovascular mortality. Any increase in LDL-C levels was associated with an increased risk of myocardial infarction.

Link: https://doi.org/10.1136/bmj.m4266

While much the history of work on sirtuins is one of disappointing results, the majority of that work involved SIRT1. Both SIRT3 and SIRT6 may be more interesting, based on animal studies conducted since the SIRT1 era. SIRT3 localizes to the mitochondria, and mitochondrial function is important in the context of aging. Researchers have shown that SIRT3 upregulation in mice improves hematopoietic stem cell function. SIRT6 upregulation, however, has been shown to modestly extend life in mice, there is a larger body of work surrounding its effects on metabolism than is the case for SIRT3, and at least one group is attempting to produce therapies based on targeting SIRT6.

A good review paper on SIRT6 in aging, inflammation, and cancer was published earlier this year. As a companion piece to that review, today's paper has the theme of aging and inflammation in common, but also touches on cardiovascular disease. The role of the more promising sirtuins in aging is interesting, but it is worth bearing in mind that these may turn out to be approaches that move the needle on life span to a greater degree in short-lived species than in long-lived species. This is true of many of the demonstrated ways to adjust metabolism to modestly slow aging, as they tend converge on a few specific mechanisms of action, such as increasing efficiency of autophagy. Of all the sirtuins, SIRT6 seems the least likely to fall into this category, given that it is known to influence cellular senescence, transposon activation, and DNA repair, rather than the more usual package of stress response mechanisms.

SIRT6 in Aging, Metabolism, Inflammation and Cardiovascular Diseases

Sirtuins, comprising a group of evolutionarily conserved nicotinamide adenine dinucleotide (NAD+)-dependent proteins, beneficially regulate lifespan and cellular senescence. In mammalian cells, seven different sirtuin proteins have been identified (SIRT1-7). SIRT1 and SIRT2 are present in both the nucleus and cytoplasm; SIRT3, SIRT4 and SIRT5 are exclusively found in mitochondria, and SIRT6 and SIRT7 are thought to be located in the nucleus. Notably, in response to stress, SIRT6 localizes to cytoplasmic stress granules, suggesting that SIRT6 is not exclusively a nuclear protein. Sirtuins are involved in a broad range of physiological processes, including genome stability, energy metabolism, aging, tumorigenesis, and cardiovascular biology, via their regulation of key protein activities.

Among sirtuin family members, sirtuin 6 (SIRT6) is of particular interest and has gained more attention due to its distinctive enzymatic activities; for example, SIRT6 catalyzes deacetylation and mono-ADP-ribosylation and exhibits long-chain fatty acid (FA) deacylase activity. These enzymatic activities indicate that SIRT6 is closely related to cellular biological processes, such as DNA repair, genome stability, inflammation, and metabolic homeostasis. Studies have revealed that dysregulation of SIRT6 activity leads to the onset and development of many diseases, including but not limited to metabolic diseases, cardiovascular diseases (CVDs), cancers, and neurodegenerative diseases.

The essential roles of SIRT6 in regulating chromatin and nuclear-cytoplasmic signaling pathways important for cellular homeostasis have been well characterized. In terms of genome stability, SIRT6 enhances DNA repair and maintains telomere integrity by regulating DNA repair and chromatin-associated factors, such as PARP1, DDB2, SNF2H and WRN. With respect to cellular metabolism, SIRT6 regulates multiple metabolic processes, including glycolysis, gluconeogenesis, insulin secretion, lipid synthesis, lipolysis, and thermogenesis, mainly by regulating the multiple transcriptional activities of HIF1α, FOXO proteins, and the PPAR family of transcription factors.

In addition, SIRT6 maintains an appropriate inflammatory response by regulating the TNF-α and NF-κB signaling pathways. These functions can influence cellular senescence and aging-related diseases, including CVDs, cancer, and neurodegenerative diseases. Therefore, studying the biological functions of SIRT6 in different diseases is valuable and helpful for the identification of highly specific SIRT6 cellular targets. With a deeper understanding of SIRT6, certain SIRT6 regulatory compounds have been identified, offering novel and promising therapeutic options for aging-related diseases.

Excess visceral fat tissue accelerates the burden of cellular senescence, which is one of several mechanisms by which being overweight generates chronic inflammation to accelerate degenerative aging. Interestingly, the high fat diet (also known as the Western diet) used to generate obesity in mouse models is shown here to also specifically increase the burden of cellular senescence in skin, thus accelerating skin aging. Expression of p16 is involved in cellular senescence and the inflammatory signaling associated with senescence, and disabling it slows the onset of this process. p16 is a tumor suppressor gene, however, and therapies based on disabling it sound like a bad idea. A better approach is to use senolytics to clear the senescent cells that contribute to an environment of chronic inflammation.

Long term high fat diets (HFD) promote skin aging pathogenesis, but detailed mechanisms remain unclear especially for inflammaging, which has recently emerged as a pathway correlating aging and age-related disease with inflammation. p16INK4a (hereafter termed p16) inhibits the cell cycle, with p16 deletion significantly inhibiting inflammaging. We observed that HFD-induced p16 overexpression in the skin. Therefore, we investigated if p16 exacerbated inflammaging in HFD-induced skin and also if p16 deletion exerted protective effects against this process.

Eight-week-old double knockout (KO) ApoE-/-p16-/- mice and ApoE-/- littermates were fed HFD for 12 weeks and their skin phenotypes were analyzed. We measured skin fibrosis, senescence-associated secretory phenotype (SASP) levels, and integrin-inflammasome pathway activation using histopathological, RNA-sequencing (RNA-seq), bioinformatics analysis, and molecular techniques.

We found that HFD contributed to inflammaging in the skin by activating the NLRP3 inflammasome pathway, increasing inflammatory infiltration, and promoting apoptosis by balancing expression between proapoptotic and antiapoptotic molecules. p16 knockout, when compared with the ApoE-/- phenotype, inhibited skin fibrosis by ameliorating inflammatory infiltration and proinflammatory factor expression via Interleukin-1β (IL-1β), Interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), and also alleviated inflammaging skin progress induced by HFD in the ApoE-/- mouse model. RNA-seq showed that p16 KO mice inhibited both integrin-inflammasome and NF-κB proinflammatory pathway activation.

In conclusion, p16 deletion or p16 positive cell clearance could be a novel strategy preventing long term HFD-induced skin aging.

Link: https://doi.org/10.1155/2022/3415528

Mitochondria have their own genome, and damage to this mitochondrial DNA is thought to be involved in aging. Some forms of mitochondrial DNA damage can result in mitochondria that are both dysfunctional and have a selection advantage over their unmutated peers, allowing them to overtake a cell, turning it into an exporter of harmful oxidative molecules. Cancer is an age-related condition, in the sense that the risk of suffering cancer grows with age, but this interesting paper provides evidence to suggest that there is little to no mechanistic link between mitochondrial DNA damage and cancer.

Mitochondria are small organelles that play an essential role in the energy production of eukaryotic cells. Here, we analyzed the mitochondrial genomes of 532 whole-genome sequencing samples from cancers and normal clonally expanded single cells. We have shown that the speed with which mitochondria in normal tissues accumulate somatic mutations with age was similar between different tissues. By comparing normal cells with cancer from the same tissue, we have also shown that most mitochondrial mutations in cancer are the result of normal mutagenesis and that treatment perturbations do not strongly impact the mitochondrial mutation load.

In general, cancers and treatment did not have a large effect on the mitochondrial genomes. Chemotherapy, for example, did not result in large observable increases in mitochondrial mutation loads both in vivo and in vitro, even though it can lead to large increases in nuclear mutation loads. This suggests that the relation between cancer and mitochondria is not dependent on mitochondrial mutations. One possible explanation for the limited effect of cancer and its treatments is that the mitochondrial DNA damage they cause might be resolved by cells clearing their damaged mitochondria.

Link: https://doi.org/10.1016/j.isci.2022.105610

Senescent cells are constantly created and destroyed throughout life, largely as a result of the replicative senescence that marks the end of life for a somatic cell, the Hayflick limit on cell division. With age, the pace of creation and destruction is disrupted, perhaps largely because the immune system ages to the point at which it falters in all of its tasks, clearance of senescent cells included. Senescent cells accumulate, and while never making up more than a small fraction of all somatic cells in any given tissue, the pro-growth, pro-inflammatory signaling generated by senescent cells is highly disruptive to organ structure and function.

Fibrosis is one of the more noteworthy manifestations of the presence of too many lingering senescent cells. Fibrosis is a malfunction of the normal processes of tissue maintenance, in which excessive collagen is deposited to form scar-like fibrils, disruptive of tissue function. It occurs in the aged kidney, heart, liver, and lungs, and is presently largely irreversible.

A greater degree of fibrosis and consequence loss of function in a given organ passes the threshold to be named as a medical condition, such as the idiopathic pulmonary fibrosis in the lung that is the topic of today's open access paper. It is a long and detailed discussion of what is known of the role of senescent cells in producing lung fibrosis; following a promising clinical trial testing a first generation senolytic therapy in patients with idiopathic pulmonary fibrosis, there is some hope that clearing senescent cells will prove to be a way to reverse fibrosis both in the lung and more generally.

Senescent AECII and the implication for idiopathic pulmonary fibrosis treatment

Idiopathic pulmonary fibrosis (IPF) is an irreversible fibrotic disease in the lungs and is the most common form of idiopathic interstitial pneumonia and idiopathic fibrotic lung disorder. Its biological process is defined as an abnormal repair response to repeated alveolar epithelial cells (AEC) damage and fibroblast-to-myofibroblast differentiation and characterized by the excessive disordered deposition of collagen in the extra- and intra-cellular matrix. Several potential risk factors, such as aging, genetic predisposition, chemical, environmental exposure, and bioenvironmental factor (bacteria and virus), can act on various types of lung cells and enhance the risk of developing IPF.

Of these risk factors, aging is considered an independent risk factor. Even in patients with a genetic predisposition, the onset of IPF seldom occurs before the sixth decade, and the incidence increases exponentially with advancing age. A longitudinal cohort study identifying independent risk factors for the progression of interstitial lung disease has shown that the risk of IPF in people aged 70 or over is 6.9 times that in people aged over 40, confirming that IPF is an age-related disease.

Cell senescence and stem cell exhaustion are the hallmarks of all age-related diseases, as in IPF. Alveolar type II epithelial cells (AECIIs) are the stem cells for the lungs and play a role in maintaining intrapulmonary homeostasis, immunity, and regeneration in the alveoli. Senescent AECIIs secrete high levels of interleukin, interferon, tumor necrosis factor, colony-stimulating factors, growth factors, and chemotactic cytokines, which promote fibroblast-to-myofibroblast differentiation and persistent tissue remodeling.

A recent study has uncovered that pulmonary fibrosis after coronavirus disease 2019 (COVID-19) may be caused by virus-induced AECII senescence. Preventing AECII senescence or targeting senescent cells in patients with COVID-19 can reduce the risk of pulmonary fibrosis. Researchers detected that AECII exhibited high levels of the senescence markers p21 and p16 from patients with IPF. Other numerous studies have shown that AECII senescence promotes the occurrence of IPF. However, pathological mechanisms underlying AECII senescence and specific effects of targeting senescent AECIIs on IPF remain unclear. This review will discuss the mechanism of AECII senescence, which drives the onset and progression of IPF, and highlights the advantages and disadvantages of targeting senescent AECIIs for IPF.

The gut microbiome changes with age in ways that provoke greater chronic inflammation throughout the body. Unresolved inflammation is a feature of aging with numerous contributing causes, such as the growing burden of senescent cells and molecular debris from stressed and damaged cells. Inflammation in brain tissue is a feature of all of the common neurodegenerative conditions, and ever more researchers are beginning to consider that it may occupy a central position in the pathology of Alzheimer's disease.

Several studies investigating the pathogenesis of Alzheimer's disease have identified various interdependent constituents contributing to the exacerbation of the disease, including amyloid-β plaque formation, tau protein hyperphosphorylation, neurofibrillary tangle accumulation, glial inflammation, and the eventual loss of proper neural plasticity. Recently, using various models and human patients, another key factor has been established as an influential determinant in brain homeostasis: the gut-brain axis.

The implications of a rapidly aging population and the absence of a definitive cure for Alzheimer's disease have prompted a search for non-pharmaceutical tools, of which gut-modulatory therapies targeting the gut-brain axis have shown promise. Yet multiple recent studies examining changes in human gut flora in response to various probiotics and environmental factors are limited and difficult to generalize; whether the state of the gut microbiota in Alzheimer's disease is a cause of the disease, a result of the disease, or both through numerous feedback loops in the gut-brain axis, remains unclear.

However, preliminary findings of longitudinal studies conducted over the past decades have highlighted dietary interventions, especially Mediterranean diets, as preventative measures for Alzheimer's disease by reversing neuroinflammation, modifying the intestinal barrier and blood-brain barrier (BBB), and addressing gut dysbiosis. Conversely, the consumption of Western diets intensifies the progression of Alzheimer's disease through genetic alterations, impaired barrier function, and chronic inflammation. This review aims to support the growing body of experimental and clinical data highlighting specific probiotic strains and particular dietary components in preventing Alzheimer's disease via the gut-brain axis.

Link: https://doi.org/10.3389/fnins.2022.1042865

Researchers here note the clear correlation between a measure of arterial stiffness and various assessments of damage and dysfunction to the brain. Arterial stiffness leads to hypertension via its disruption of the feedback systems needed to control blood pressure. That in turn leads to pressure damage to delicate tissues, such as those of the brain. It is associated with dysfunction of the blood-brain barrier, allowing leakage of normally restricted cells and molecules that provoke inflammation in brain tissues, as well as other vascular issues that cause harm to the brain.

We examined the associations of carotid artery stiffness with cerebral small-vessel disease markers, cognition, and dementia subtypes in a memory clinic cohort. A total of 272 participants underwent carotid ultrasonography, brain magnetic resonance imaging, and neuropsychological assessment. Carotid ultrasonography was used to assess β-index, pressure-strain elastic modulus, and pulse-wave velocity-β.

Brain magnetic resonance images were graded for cerebral small-vessel disease markers, including white matter hyperintensities, lacunes, and cerebral microbleeds. Participants were classified as having no cognitive impairment, cognitive impairment and no dementia, or dementia subtyped as Alzheimer disease and vascular dementia. Cognition was assessed using National Institute of Neurological Disorders and Stroke / Canadian Stroke Network harmonization battery.

After adjusting for age, sex, cardiovascular risk factors, and diseases, multivariable models showed that β-index, elastic modulus, and pulse-wave velocity-β were associated with white matter hyperintensities, and elastic modulus (odds ratio [OR] 1.39) and pulse-wave velocity-β (OR 1.47) were independently associated with lacunes. Similarly, β-index (OR 2.04), elastic modulus (OR 2.22), and pulse-wave velocity-β (OR 2.50) were independently associated with vascular dementia. Carotid stiffness measures were independently associated with worse performance in global cognition, visuomotor speed, visuospatial function, and executive function. These associations became largely nonsignificant after further adjusting for cerebral small-vessel disease markers.

Thus in memory clinic patients, carotid artery stiffness was associated with white matter hyperintensities and lacunes, impairment in global and domain-specific cognition, and causative subtypes of dementia, particularly vascular. The effects of carotid stiffness on cognition were not independent of, and were partially mediated by, cerebral small-vessel disease.

Link: https://doi.org/10.1161/JAHA.122.027295

Researchers here report on in vitro experiments to show that introducing functional mitochondria into a cell culture containing senescent cells reduces markers of senescence. It is an interesting question as to how this would work in living tissue, where the numbers of senescent cells are low, and mitochondria will be introduced into all cells. Since several companies are developing mitochondrial transfer as a therapy to treat the loss of mitochondrial function that is characteristic of age-related disease, we'll find out in the years ahead. Those groups are not specifically targeting cellular senescence, but can hardly avoid having senescent cells taking up their therapeutic mitochondria.

For all strategies that might leave senescent cells intact but modulate their harmful signaling, the question is whether or not this is a good idea. This particularly the case for strategies that might allow senescent cells to re-enter the cell cycle and replicate again. Some fraction of senescent cells become senescent for good reasons, such as potentially cancerous mutations or other forms of damage that produce dysfunction. Senolytics that destroy senescent cells seem a safer proposal, and efficient senolytics may turn out to be required in advance of some of the other rejuvenation therapies on the horizon, such as partial reprogramming and mitochondrial transfer.

Inhibition of cellular senescence hallmarks by mitochondrial transplantation in senescence-induced ARPE-19 cells

Retinal pigment epithelium (RPE) damage is a major factor in age-related macular degeneration (AMD). The RPE in AMD shows mitochondrial dysfunction suggesting an association of AMD with mitochondrial function. Mitochondrial transplantation into damaged cells or injured tissues is considered a novel cell-based therapeutic strategy. Delivery of mitochondria isolated from mesenchymal stem cells (MSCs) has the advantage of supplying the required number of mitochondria through rapid replication and multilineage differentiation compared with other cells; further, stem cells have low immunogenicity because of lower levels of surface antigens. A previous study has reported that MSC-derived mitochondrial transplantation protects the cornea against oxidative stress-induced mitochondrial damage.

Here, we investigated the effects of extrinsic mitochondrial transplantation on senescence-induced ARPE-19 cells, an RPE cell line. We demonstrated mitochondrial dysfunction in replicative senescence-induced ARPE-19 cells after repeated passage. Imbalanced mitophagy and mitochondrial dynamics resulted in increased mitochondrial numbers and elevated levels of mitochondrial and intracellular reactive oxygen species.

Exogenous mitochondrial transplantation improved mitochondrial dysfunction and alleviated cellular senescence hallmarks, such as increased cell size, increased senescence-associated β-galactosidase activity, augmented NF-κB activity, increased inflammatory cytokines, and upregulated the cyclin-dependent kinase inhibitors p21 and p16. Further, cellular senescence properties were improved by exogenous mitochondrial transplantation in oxidative stress-induced senescent ARPE-19 cells. These results indicate that exogenous mitochondrial transplantation modulates cellular senescence and may be considered a novel therapeutic strategy for AMD.

The thymus atrophies with age, limiting the supply of new T cells to support the adaptive immune system. This is an important aspect of immune aging. Digging deeper into the mechanisms of thymus aging is of interest to the extent that it might reveal practical approaches to intervention. The challenge of the thymus is near entirely its inaccessible location, making it hard to deliver the known factors that can induce thymic regrowth without side-effects in the rest of the body. Here, researchers find that one population of macrophages characteristic of thymic tissue diminishes with age, while another population expands. The researchers theorize that it might be possible to adjust these cell proportions to provoke thymic regrowth, but at this stage that proposal is quite theoretical. More research would be needed to validate the underlying hypothesis regarding how these macrophages are involved in either supporting thymic tissue or encouraging atrophy.

Tissue-resident macrophages are essential to protect from pathogen invasion and maintain organ homeostasis. The ability of thymic macrophages to engulf apoptotic thymocytes is well appreciated, but little is known about their ontogeny, maintenance, and diversity. Here, we characterized the surface phenotype and transcriptional profile of these cells and defined their expression signature. Thymic macrophages were most closely related to spleen red pulp macrophages and Kupffer cells and shared the expression of the transcription factor SpiC with these cells.

Single-cell RNA sequencing showed that the macrophages in the adult thymus are composed of two populations distinguished by the expression of Timd4 and Cx3cr1. Remarkably, Timd4+ cells were located in the cortex, while Cx3cr1+ macrophages were restricted to the medulla and the cortico-medullary junction. Using chimeras, transplantation of embryonic thymuses, and genetic fate mapping, we found that the two populations have distinct origins. Timd4+ thymic macrophages are of embryonic origin, while Cx3cr1+ macrophages are derived from adult hematopoietic stem cells. Aging has a profound effect on the macrophages in the thymus. Timd4+ cells underwent gradual attrition, while Cx3cr1+ cells slowly accumulated with age and, in older mice, were the dominant macrophage population in the thymus.

The clear correlation between the accumulation of Cx3cr1+ thymic macrophages and thymic involution suggests that some factors produced exclusively by these cells are relevant. For example, Cx3cr1+ thymic macrophages are the predominant producer of the growth factor PDGFα that is required for the maintenance of adipocyte stem cells and can stimulate tissue fibrosis. The gradual accumulation of Cx3cr1+ macrophages could increase the availability of PDGFα in the aging thymus stimulating extracellular matrix production and differentiation of precursors into adipocytes. This model predicts that limiting the influx of Cx3cr1+ macrophage precursors could delay thymus involution.

Link: https://doi.org/10.7554/elife.75148

Cellular senescence is generally thought of as a characteristic of replicating cells; it is an end state reached when telomeres, reduced in length with each cell division, become too short. This is followed by programmed cell death or destruction by immune cells. When senescent cells linger, as is increasingly the case with age, they contribute to degenerative aging via their pro-growth, pro-inflammatory signaling, disruptive of tissue structure and function. Researchers have suggested that non-dividing, post-mitotic cells such as neurons can also exhibit a form of senescence, and here evidence is provided for this to be the case. Senescence in supporting cells in the brain, such as microglia and astrocytes, is known to contribute to neurodegeneration. If some neurons are also senescent, producing similar harmful signaling, then these cells will also contribute to the aging of the brain.

As cells age, they can undergo cellular senescence, which contributes to tissue dysfunction and age-related disorders. Senescence is also thought to play a role in cellular stress, molecular damage, and cancer initiation. However, scientists previously believed that senescence primarily occurred in dividing cells, not in neurons. Little was known about the senescence-like state of aging human neurons.

In this study, researchers took skin samples from people with Alzheimer's disease and converted those cells directly into neurons in the lab. They tested these neurons to see if they undergo senescence and examined the mechanisms involved in the process. They also explored senescence markers and gene expression of post-mortem brains from 20 people with Alzheimer's disease and matched healthy controls. This allowed the team to confirm that their results from the lab held true in actual human brain tissue.

The team found that senescent neurons are a source of the late-life brain inflammation observed in Alzheimer's disease. As the neurons deteriorate, they release inflammatory factors that trigger a cascade of brain inflammation and cause other brain cells to run haywire. Additionally, the gene KRAS, which is commonly involved in cancer, could activate the senescent response. The consequences of even a small number of senescent neurons in the aging brain could have a significant impact on brain function. This is because a single neuron can make more than 1,000 connections with other neurons, affecting the brain's communication system.

In addition to these findings, the authors also administered a therapeutic (a cocktail of Dasatinib + Quercetin) to the patient neurons in a dish. Both drugs are used to remove senescent cells in the body in conditions such as osteoarthritis, so the authors wanted to see if they were effective in senescent cells in the central nervous system as well. They found that the drug cocktail reduced the number of senescent neurons to normal levels. Targeting senescent cells could thus be a useful approach for slowing neuroinflammation and neurodegeneration in Alzheimer's disease.

Link: https://www.salk.edu/news-release/deteriorating-neurons-are-source-of-human-brain-inflammation-in-alzheimers-disease/

Autophagy is the name given to a collection of maintenance processes responsible for tagging and recycling damaged, excess, or harmful proteins and structures in the cell. Better maintenance of molecular machinery means a better operation of cells and tissues. Upregulation of autophagy is a feature of many of the approaches shown to modestly slow aging in animal studies, those that mimic some of the biochemistry of calorie restriction. Calorie restriction itself is thought to improve health and longevity primarily through autophagy.

Here, researchers look at autophagy in the context of neurodegenerative conditions. Autophagy targeted at mitochondria, mitophagy, is particularly important to cell function given the importance of mitochondrial production of chemical energy store molecules, ATP, in energy-hungry tissues such as the brain. Further, given that toxic protein aggregates feature prominently in neurodegenerative conditions, and autophagy assists in clearing aggregates, this is another reason to study autophagy in this context.

That said, near all of the presently available approaches to upregulate autophagy, such as pharmacological means of increasing NAD levels via derivatives of vitamin B3, are not as good as either exercise or calorie restriction. Animal studies show that mTOR inhibition via rapamycin is in fact better than exercise (but not calorie restriction) when it comes to beneficial outcomes on health and life span, but rapamycin has downsides - it is an immunosuppressant. Efforts to produce drugs that inhibit mTOR without these undesirable side-effects are still underway.

The emerging role of autophagy and mitophagy in tauopathies: From pathogenesis to translational implications in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, affecting more than 55 million individuals worldwide in 2021. In addition to the "amyloid hypothesis," an increasing number of studies have demonstrated that phosphorylated tau plays an important role in AD pathogenesis. Both soluble tau oligomers and insoluble tau aggregates in the brain can induce structural and functional neuronal damage through multiple pathways, eventually leading to memory deficits and neurodegeneration.

Autophagy is an important cellular response to various stress stimuli and can generally be categorized into non-selective and selective autophagy. Recent studies have indicated that both types of autophagy are involved in AD pathology. Among the several subtypes of selective autophagy, mitophagy, which mediates the selective removal of mitochondria, has attracted increasing attention because dysfunctional mitochondria have been suggested to contribute to tauopathies.

In this review, we summarize the latest findings on the bidirectional association between abnormal tau proteins and defective autophagy, as well as mitophagy, which might constitute a vicious cycle in the induction of neurodegeneration. Neuroinflammation, another important feature in the pathogenesis and progression of AD, has been shown to crosstalk with autophagy and mitophagy. Additionally, we comprehensively discuss the relationship between neuroinflammation, autophagy, and mitophagy. By elucidating the underlying molecular mechanisms governing these pathologies, we highlight novel therapeutic strategies targeting autophagy, mitophagy and neuroinflammation, such as those using rapamycin, urolithin A, spermidine, curcumin, nicotinamide, and actinonin, for the prevention and treatment of AD.

Glutaminase inhibitors can potentially eliminate senescent cells from aged tissues, another in the growing list of categories of senolytic compound. Researchers here test the proposition in various skin models, some involving immunodeficient mice hosting human skin grafts. At this point there are so many different senolytics that studies should start to focus on comparing efficacy. Where there is data to compare directly, development efforts conducted over the last decade have so far failed to greatly improve on the dasatinib and quercetin approach, the first senolytic treatment tested in mice and humans. It is likely that some of the companies developing novel senolytics can do considerably better, but that data is not yet available for review.

Skin aging caused by various endogenous and exogenous factors results in structural and functional changes to skin components. However, the role of senescent cells in skin aging has not been clarified. To elucidate the function of senescent cells in skin aging, we evaluated the effects of the glutaminase inhibitor BPTES (bis-2-(5-phenylacetamido-1, 3, 4-thiadiazol-2-yl)ethyl sulfide) on human senescent dermal fibroblasts and aged human skin. Here, primary human dermal fibroblasts (HDFs) were induced to senescence by long-term passaging, ionizing radiation, and treatment with doxorubicin, an anticancer drug. Cell viability of HDFs was assessed after BPTES treatment.

A mouse/human chimeric model was created by subcutaneously transplanting whole skin grafts from aged humans into nude mice. The model was treated intraperitoneally with BPTES or vehicle for 30 days. Skin samples were collected and subjected to reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting, and histological analysis. BPTES selectively eliminated senescent dermal fibroblasts regardless of the method used to induce senescence; aged human skin grafts treated with BPTES exhibited increased collagen density, increased cell proliferation in the dermis, and decreased aging-related secretory phenotypes, such as matrix metalloprotease and interleukin. These effects were maintained in the grafts 1 month after termination of the treatment.

In conclusion, selective removal of senescent dermal fibroblasts can improve the skin aging phenotype, indicating that BPTES may be an effective novel therapeutic agent for skin aging.

Link: https://doi.org/10.18632/aging.204391

There is a growing awareness that removal of metabolic waste from the brain is impaired with age, and that this contributes to the onset of neurodegenerative conditions characterized by rising levels of protein aggregates of various sorts in the brain. All of that waste might be better removed from the brain were paths through the cribriform plate and glymphatic system maintained at youthful efficiency. Leucadia Therapeutics is working on a safe way to open a new passage through the cribriform plate, but the glymphatic system is a more challenging prospect. It isn't fully understood how best to intervene in what is most likely a multifaceted degeneration connected to most or all of the fundamental mechanisms of aging.

The glymphatic system is responsible for clearing the brain parenchyma. To date, the terms glymphatic system failure or glymphatic system dysfunction have been used to define its malfunction. In a new paper, the concept of glymphatic insufficiency is defined as the inability of the glymphatic system to properly perform the brain's cleaning function. This makes it possible to describe that the failure can be acute or chronic, depending on the duration of the process, and to specify that the failure can be caused by a failure of the glymphatic system itself or by an overproduction of waste substances that exceeds the clearing capacity of this system.

The wasteosomes or amylase bodies of the human brain were first described in 1837. Researchers have shown that amylase bodies act as containers for waste substances from the brain and can be expelled by astrocytes into the cerebrospinal fluid. A new paper now provides evidence that increased wasteosomes or starch bodies in the human brain are a manifestation of chronic glymphatic system insufficiency. The first indication of this relationship is that most factors that are associated with large amounts of wasteosomes, such as ageing, certain cardiovascular disorders, and poor sleep quality, are also associated with disruptions of the glymphatic system.

The study also mentions several elements and evidence that suggest that chronic lymphatic insufficiency is a risk factor for neurodegenerative diseases, especially neurodegenerative diseases that involve the aggregation of certain fibrillar proteins, such as β-amyloid protein in Alzheimer's disease, phosphorylated tau in frontotemporal dementia and Alzheimer's disease, or α-synuclein in Parkinson's disease. "In case of lymphatic insufficiency, the elimination of these proteins is restricted, and all indications are that this contributes to the development of these diseases."

Link: https://www.eurekalert.org/news-releases/972882

Some species, such as salamanders and zebrafish, exhibit proficient regeneration, in that individuals are capable of regrowing lost tissue in organs and limbs and central nervous system without scarring. In adult mammals, the result of injury is scarring rather than regrowth, even though embryos are capable of both initial growth and later complete regeneration. Following the hypothesis that mechanisms of proficient regeneration do in fact exist in adult mammals, but are in some way silenced, the research community is engaged in trying to identify the specific differences between mammals and highly regenerative species that determine whether regrowth or scarring takes place following injury.

One of the more interesting discoveries of recent years is that differences in the behavior of the innate immune cells known as macrophages appear important. In the central nervous system, microglia are the analogous, very similar cell type. Macrophages and microglia involve themselves in the interactions between various types of somatic cells, stem cells, and progenitor cells that take place during regeneration.

In today's research materials, researchers investigate some of the proteins that appear to change the behavior of microglia to allow for regeneration in the brains of zebrafish. Interestingly, one of them is TDP-43, which is implicated in neurodegeneration in humans due to its ability to misfold and form aggregates. The other, granulin, mediates clearance of TDP-43 aggregates. The work may prove to have relevance not just to inducing regeneration in the central nervous system, but also to addressing forms of neurodegeneration in which TDP-43 plays a prominent role.

Key factors identified for regeneration of brain tissue

In contrast to mammals, the central nervous system (CNS) of zebrafish has exceptional regenerative powers. In the case of injury, neural stem cells generate long-lived neurons, among other responses. Furthermore, CNS injuries prompt merely transitory reactivity of glial cells in zebrafish, which facilitates the integration of nerve cells into injured regions of the tissue.

The scientists deliberately inflicted CNS lesions in zebrafish, prompting the activation of microglia. At the same time, the researchers found an accumulation of lipid droplets and TDP-43 condensates in the lesions. To date, the protein TDP-43 has been primarily associated with neurodegenerative diseases. Granulin also played an important role in the zebrafish model. This protein contributed to the removal of the lipid droplets and TDP-43 condensates, whereupon the microglia transitioned from their activated to their resting form. The unscarred regeneration of the injury was the outcome. Zebrafish with experimentally induced granulin deficiency, by contrast, exhibited poor regeneration of the injury similar to what we see in mammals.

TDP-43 condensates and lipid droplets regulate the reactivity of microglia and regeneration after traumatic brain injury

Decreasing the activation of pathology-activated microglia is crucial to prevent chronic inflammation and tissue scarring. In this study, we used a stab wound injury model in zebrafish and identified an injury-induced microglial state characterized by the accumulation of lipid droplets and TDP-43+ condensates. Granulin-mediated clearance of both lipid droplets and TDP-43+ condensates was necessary and sufficient to promote the return of microglia back to the basal state and achieve scarless regeneration.

Moreover, in postmortem cortical brain tissues from patients with traumatic brain injury, the extent of microglial activation correlated with the accumulation of lipid droplets and TDP-43+ condensates. Together, our results reveal a mechanism required for restoring microglia to a nonactivated state after injury, which has potential for new therapeutic applications in humans.

Lysosomes are the destination for excess and damaged proteins and structures in the cell. A lysosome is a membrane-wrapped collection of enzymes capable of breaking down near everything it encounters into the raw materials a cell uses to manufacture new molecular machinery. Lysosomal function is known to decline with age, and improved lysosomal function might be expected to improve long-term health prospects. Here, researchers look at one specific lysosomal enzyme that is known to exhibit higher levels in human centenarians, and find that it improves health in flies. There is extension of life, but the effect size is so small, a few percentage points, that it shouldn't be taken seriously.

To identify new factors that promote longevity and healthy aging, we studied Drosophila CG13397, an ortholog of the human NAGLU gene, a lysosomal enzyme overexpressed in centenarians. We found that the overexpression of CG13397 (dNAGLU) ubiquitously, or tissue specifically, in the nervous system or fat body could extend fly life span. It also extended the life span of flies overexpressing human Aβ42, in a Drosophila Alzheimer's disease (AD) model.

To investigate whether dNAGLU could influence health span, we analyzed the effect of its overexpression on AD flies and found that it improved the climbing ability and stress resistance, including desiccation and hunger, suggesting that dNAGLU improved fly healthspan. We found that the deposition of Aβ42 in the mushroom body, which is the fly central nervous system, was reduced, and the lysosomal activity in the intestine was increased in dNAGLU over-expressing flies.

When NAGLU was overexpressed in human U251-APP cells, which expresses a mutant form of the Aβ-precursor protein (APP), these cells exhibited stronger lysosomal activity and and enhanced expression of lysosomal pathway genes. The concentration of Aβ42 was reduced, and the growth arrest caused by APP expression was reversed, suggesting that NAGLU could play a wider role beyond its catalytic activity to enhance lysosomal activity.

These results also suggest that NAGLU overexpression could be explored to promote healthy aging and to prevent the onset of neurodegenerative diseases, including AD.

Link: https://doi.org/10.3390/ijms232214433

Researchers here show that, in mice, intermittent fasting can protect against the damage done by cardiovascular aging that leads to a reduced blood supply to the brain. Forms of calorie restriction, such as intermittent fasting, are generally beneficial for long term health. This is well demonstrated in both mice and humans, though only short-lived species exhibit significant gains in life span as a result. It is interesting to note the opinion that intermittent fasting may be better than straight calorie restriction when it comes to mitigation of pathological mechanisms in neurodegenerative conditions.

Vascular cognitive impairment (VCI) embodies a spectrum of cognitive deficits that range from mild cognitive impairment to vascular dementia (VaD). VCI is associated with cerebrovascular diseases that arise from vascular pathological processes such as atherosclerosis, microvascular protein deposits, haemorrhages and microbleeds. These vascular pathologies lead to a state of reduced blood flow to the brain that is referred to as chronic cerebral hypoperfusion (CCH). Decreased cerebral perfusion has been reported to correlate with dementia severity, and has shown to be a predictive marker to identify individuals with mild cognitive impairment who develop dementia. CCH induces a cascade of cellular and molecular mechanisms that contributes to the pathogenesis of VCI - including oxidative stress and inflammation.

Intermittent fasting (IF) is defined as an eating pattern that cycles between periods of eating and fasting. IF has been extensively reported to extend both health and lifespan, and decrease the development of age-related disorders including cardiovascular, metabolic, and neurodegenerative diseases. Recently, IF has gained much interest as being more effective than caloric restriction for inducing neuroprotective effects in the brain.

In this study, we demonstrate for the first time that IF promotes neuroprotective effects in a model of VaD by maintaining the integrity of the neurovascular structures in the brain. We specifically show that IF attenuated vascular pathology by reducing microvascular leakage and blood-brain barrier dysfunction, while maintaining the expression of tight junction (TJ) proteins. IF was also effective in decreasing white matter lesion formation, hippocampal neuronal cell death and cell death markers, while maintaining myelin basic protein levels. Our data suggest that the effects of IF on the structural integrity of the neurovasculature may be mediated through mechanisms that decrease oxidative stress and matrix metalloproteinase expression. Overall, our findings indicate that prophylactic IF may be a potential therapy in reducing and preventing neurovascular pathology associated with VaD.

Link: https://doi.org/10.7150/ijbs.75188

Few genes have been shown to robustly alter mammalian longevity as a result of altered expression, with data obtained primarily in mice. Klotho is perhaps the most well known and well studied of that small but steadily growing portfolio. The topic of today's open access paper is another of these longevity genes, CISD2. Loss of CISD2 shortens lifespan, while increased expression extends life span in mice. CISD2 is upregulated after exercise, and may act through autophagy, a common factor in many approaches shown to modestly slow aging in laboratory species. Like other approaches to upregulation of autophagy, increased CISD2 expression improves liver function in mice. Recently researchers have extended mouse life span by a small degree via pharmacological approaches to upregulation of CISD2.

The authors of the this paper overstate, I think, the level of interest we should have in CISD2 upregulation as a basis for therapy. Any form of upregulation of autophagy might be described as a calorie restriction mimetic strategy, given that increased autophagy appears to be the primary means by which calorie restriction produces benefits to health and longevity. While calorie restriction improves health in humans, it certainly does not move the needle on life span in long-lived mammals the same way it does in short-lived mammals. The underlying reasons for this difference have yet to be established in any detail, but this is why we should be skeptical of most of the methods of slowing aging demonstrated in mice to date. They largely function through stress response pathways that converge on increased autophagy.

Rejuvenation: Turning Back Time by Enhancing CISD2

Currently, only eight genes (BUB1B, CISD2, KLOTHO, PAWR, PPARG, PTEN, SIRT1, and SIRT6) are listed as pro-longevity genes by the Human Aging Genomic Resources, which means that they have been experimentally demonstrated to mediate lifespan in mammals. The aging human population with age-associated diseases has become a problem worldwide. By 2050, the global population of those who are aged 65 years and older will have tripled. In this context, delaying age-associated diseases and increasing the healthy lifespan of the aged population has become an important issue for geriatric medicine.

CDGSH iron-sulfur domain 2 (CISD2), the causative gene for Wolfram syndrome 2 (WFS2), plays a pivotal role in mediating lifespan and healthspan by maintaining mitochondrial function, endoplasmic reticulum integrity, intracellular Ca2+ homeostasis, and redox status. Here, we summarize the most up-to-date publications on CISD2 and discuss the crucial role that this gene plays in aging and age-associated diseases. This review highlights the urgent need for CISD2-based pharmaceutical development to be used as a potential therapeutic strategy for aging and age-associated diseases.

This review mainly focuses on the following topics: (1) CISD2 is one of the few pro-longevity genes identified in mammals. Genetic evidence from loss-of-function (knockout mice) and gain-of-function (transgenic mice) studies have demonstrated that CISD2 is essential to lifespan control. (2) CISD2 alleviates age-associated disorders. A higher level of CISD2 during natural aging, when achieved by transgenic overexpression, improves Alzheimer's disease, ameliorates non-alcoholic fatty liver disease and steatohepatitis, and maintains corneal epithelial homeostasis.

(3) CISD2, the expression of which otherwise decreases during natural aging, can be pharmaceutically activated at a late-life stage of aged mice. As a proof-of-concept, we have provided evidence that hesperetin is a promising CISD2 activator that is able to enhance CISD2 expression, thus slowing down aging and promoting longevity. (4) The anti-aging effect of hesperetin is mainly dependent on CISD2 because transcriptomic analysis of the skeletal muscle reveals that most of the differentially expressed genes linked to hesperetin are regulated by hesperetin in a CISD2-dependent manner. Furthermore, three major metabolic pathways that are affected by hesperetin have been identified in skeletal muscle, namely lipid metabolism, protein homeostasis, and nitrogen and amino acid metabolism.

Medin is one of a number of different amyloids that form in aging tissue, each a protein that can misfold in ways that encourage other molecules of the same protein to do the same, aggregating together to form solid deposits. Some amyloids are evidently toxic and disease-associated, while others, like medin, originally appeared more innocuous. It isn't harmless, however, just more subtle. Recent research suggested a pathological role for medin amyloid in Alzheimer's disease, in that it accelerates the aggregation of amyloid-β. Further, there is evidence for medin aggregation to contribute to cerebrovascular dysfunction. On that topic, researchers here note that cellular senescence in the vascular smooth muscle of blood vessel walls can provoke greater medin aggregation in that tissue, providing a link between those two distinct mechanisms of aging.

Vascular amyloidosis, caused when peptide monomers aggregate into insoluble amyloid, is a prevalent age-associated pathology. Aortic medial amyloid (AMA) is the most common human amyloid and is composed of medin, a 50-amino acid peptide. Emerging evidence has implicated extracellular vesicles (EVs) as mediators of pathological amyloid accumulation in the extracellular matrix (ECM). To determine the mechanisms of AMA formation with age, we explored the impact of vascular smooth muscle cell (VSMC) senescence, EV secretion, and ECM remodeling on medin accumulation.

Medin was detected in EVs secreted from primary VSMCs. Small, round medin aggregates colocalized with EV markers in decellularized ECM in vitro and medin was shown on the surface of EVs deposited in the ECM. Decreasing EV secretion with an inhibitor attenuated aggregation and deposition of medin in the ECM. Medin accumulation in the aortic wall of human subjects was strongly correlated with age and VSMC senescence increased EV secretion, increased EV medin loading, and triggered deposition of fibril-like medin.

Proteomic analysis showed VSMC senescence induced changes in EV cargo and ECM composition, which led to enhanced EV-ECM binding and accelerated medin aggregation. Abundance of the proteoglycan, HSPG2, was increased in the senescent ECM and colocalized with EVs and medin. Isolated EVs selectively bound to HSPG2 in the ECM and its knock-down decreased formation of fibril-like medin structures. These data identify VSMC-derived EVs and HSPG2 in the ECM as key mediators of medin accumulation, contributing to age-associated AMA development.

Link: https://doi.org/10.1111/acel.13746

Some cells are small, others large. Cell size is connected to cell function, and different varieties of cell maintain tight control over their various different sizes. Senescent cells are known to become much larger than their origin cell type, and one effort to detect senescent cells in blood samples made use of this feature. Do non-senescent cells lose control of size in old tissues, however? To what degree is this a feature of aging that produces further downstream issues, versus being a consequence of other problematic changes in cell behavior that occur with age? These are not well-studied questions.

A large body of literature highlights two important findings: 1) Different cell types display different average sizes and 2) cells maintain a uniform size by using several regulatory pathways. This raises the question of why cells invest in maintaining their size. Therefore, understanding what happens when cells fail to regulate their size is important. While the first findings around this topic led to controversial conclusions, budding yeast has been a key model organism to provide the first evidence that cellular enlargement could be directly linked to cellular dysfunction during aging. It is known that budding yeast cells enlarge during aging. Preventing this enlargement with drugs preserves their replicative age. Similarly, preventing cellular enlargement in vitro in primary human cells has been shown to maintain their capacity to enter the cell cycle thereby avoiding cellular senescence.

Our recent publication dissected whether the role of cell size on cell function is based on correlation or causation. An intrinsic challenge was to manipulate cell size without targeting other pathways, and to delineate that the observed changes are causal and not correlative. This hurdle was tackled using hematopoietic stem cells (HSCs) in vivo. Six orthogonal approaches were examined under which HSCs became larger. In each of these conditions, HSC function was also compromised. HSC function was determined as their ability to form a blood system after transplantation into recipient mice. While it could be argued that each single manipulation affected HSC function unrelated to cell size, together these experiments suggest that the dysfunction was not driven by an unaccounted variable. Furthermore, alternate causes were excluded by analyzing other parameters of the hematopoietic system: homing, stem cell identity, differentiation potential and cell cycle state. Therefore, the simplest explanation is that enlargement of HSCs reduces their functionality.

Interestingly, numerous other cell types have also been observed to enlarge during aging. This raises the possibility that cellular enlargement contributes to aging in other cell types. Moving forward, the research community will benefit from further experiments providing critical evidence of whether cellular enlargement is cause or consequence of aging in other stem cell types and differentiating cells.

Link: https://doi.org/10.3389/fcell.2022.1036602

The altered signaling environment in aged tissue produces changes in cell behavior, some of which is adaptive and helpful, and some of which is maladaptive and harmful. In some cases the same process can be one or the other depending on context. Cellular senescence, for example, is helpful in the contexts of cancer suppression and regeneration from injury, but only up until the point at which senescent cells are no longer removed as rapidly as they are created, at which point their continued, unrelenting pro-growth, pro-inflammatory signaling contributes to many of the forms of tissue dysfunction observed in aging.

Vascular smooth muscle is vital to the operation of the vasculature, determining blood pressure via appropriate contraction and dilation of blood vessels in response to environmental cues. Today's open access paper is focused on the ways in which vascular smooth muscle cells change behavior in old tissues. This can change the properties of the smooth muscle, impairing the normal control of blood pressure, but there are also numerous other issues that arise. For example, smooth muscle cells can begin to take on the characteristics of bone cells, and deposit calcium into the vascular wall. This calcification contributes to stiffening of vessels, leading to hypertension and accumulating pressure damage to tissues throughout the body.

How vascular smooth muscle cell phenotype switching contributes to vascular disease

Vascular smooth muscle cells (VSMCs) are the most abundant cell in vessels. Earlier experiments have found that VSMCs possess high plasticity. Vascular injury stimulates VSMCs to switch into a dedifferentiated type, also known as synthetic VSMCs, with a high migration and proliferation capacity for repairing vascular injury. In recent years, largely owing to rapid technological advances in single-cell sequencing and cell-lineage tracing techniques, multiple VSMCs phenotypes have been uncovered in vascular aging, atherosclerosis, aortic aneurysm, etc. These VSMCs all down-regulate contractile proteins such as α-SMA and calponin1, and obtain specific markers and similar cellular functions of osteoblast, fibroblast, macrophage, and mesenchymal cells.

The synthetic VSMCs are considered as the de-differentiated state of contractile VSMCs, accompanied by morphologic changes from spindle shape to irregular shape. With the decrease of contractile protein expression, the proliferation and migration ability of synthetic VSMCs was enhanced, which played a role in repairing vascular injury. And true to its name, synthetic VSMCs secrete large amounts of collagen, elastin, and matrix metalloproteinase (MMP) causing vascular extracellular matrix (ECM) remodeling. Therefore, synthetic VSMCs almost exist in all types of vascular diseases such as atherosclerosis, aneurysm, neointima. Synthetic VSMCs are prone to further differentiate into alternative phenotypes such as macrophage-like and osteogenic VSMCs.

Vascular calcification (VC) is a common sign in the aged population and chronic kidney disease (CKD) population, which could consequent in increased artery hardness, impaired elasticity, and deficient compliance in advanced stage. VC can be regarded as a process of osteogenesis since the activation of osteogenic genes in the vascular cells play a pivotal role. Recent studies have gradually pointed out the fact that VSMCs switching to the osteogenic phenotype is the principal reason for vascular calcification. Osteogenic VSMCs are also called osteoblast-like VSMCs because of their similarity to osteoblast.

Macrophage-like VSMCs are termed for their similar surface markers and function with macrophages. Macrophage-like VSMCs demonstrate low expression of contractile markers and possess functions similar to macrophages such as innate immune signaling, phagocytosis, and efferocytosis. The phagocytosis of VSMCs in atherosclerosis relies on its macrophage-like phenotype, so high oxidized LDL and cholesterol are the primary metabolic factors driving macrophage-like VSMCs. However, the proportion of macrophage-like VSMCs in the pathogenesis of atherosclerosis is lower than that of macrophage itself, and the level of the inflammatory factors in macrophage-like VSMCs is also inferior to that of monocyte-derived macrophages. The degree of contribution to pathogenesis is unclear.

The VSMCs that express partial mesenchymal markers are referred to mesenchymal-like VSMCs, but there is no uniform official definition of mesenchymal-like VSMCs. The role of mesenchymal-like VSMCs in arterial disease is uncertain. Earlier studies believed that tunica adventitia derived mesenchymal-like VSMCs contribute to atherosclerotic plaque growth and CKD-induced vascular calcification. Whereas, a recent study found that adventitial VSCs did not differentiate into the pathogenic VSMCs in atherosclerosis. Other work has indicated that mesenchymal-like VSMCs can be induced into macrophage-like VSMCs, or into contractile VSMCs, depending on external stimulus conditions.

Single-cell transcriptome revealed that fibroblast-like VSMCs are present in atherosclerotis plaque. Nevertheless, the markers used to mark fibroblast-like VSMCs and mesenchymal-like VSMCs in single cell sequencing overlapped, creating confusion over their definition. In respect of the gene expression profile displayed by single-cell transcriptome, fibroblast-like VSMCs perform three main functions: synthesizing ECM, enforcing cell-matrix adhesion, and promoting cell proliferation. Fibroblast-like VSMCs switching is associated with arterial fibrosis resulting in increased arterial stiffness.

Great progress has been made in the study of the role of VSMCs phenotype transformation in vascular diseases in the past 20 years. VSMCs phenotype switching provides a new perspective for understanding the pathogenesis of vascular diseases. Importantly, the studies of VSMCs phenotypes provide new ideas and targets for pharmacological treatment. As the master switch that controls VSMCs switch from contractile to all pathogenic phenotypes, KLF4 may be the best therapeutic target. Since a large population of miRNAs has similar roles in regulating the VSMCs phenotype, vesicles with several miRNAs can be attempted to reverse the VSMCs phenotype at the lesion site.

Another future challenge is to accurately manipulate VSMCs phenotype switching to not only prevent vascular disease, but also preserve its function in repairing vascular damage. This depends on a rigorous understanding of the biology of each VSMCs phenotypes and their relationship with vascular diseases. The same phenotypic VSMCs plays distinct roles in different stages of disease, and so it may be a better strategy to firstly induce synthetic VSMCs to proliferate to an appropriate number and then convert it into contractile VSMCs, so that the aorta can obtain both strong contractile ability and thick tunica media.

After the central nervous system, heart muscle is one of the least capable tissues in the body when it comes to regeneration following injury. This is one of the contributing factors to the downward spiral of heart health in later life, particularly the cell death and scarring that occurs following the ischemia of a heart attack. Researchers here suggest that this lack of regenerative capacity is the rest of an adaptation in the nuclear membrane that protects heart cells from other damaging circumstances by reducing the number of pathways that allow signal molecules to pass into the cell nucleus. That is protective against harmful signals, but also interferes in the signaling necessary for regeneration.

While skin and many other tissues of the human body retain the ability to repair themselves after injury, the same isn't true of the heart. During human embryonic and fetal development, heart cells undergo cell division to form the heart muscle. But as heart cells mature in adulthood, they enter a terminal state in which they can no longer divide. To understand more about how and why heart cells change with age, researchers looked at nuclear pores. These perforations in the lipid membrane that surround a cell's DNA regulate the passage of molecules to and from the nucleus.

Using super-resolution microscopy, researchers visualized and counted the number of nuclear pores in mouse heart cells, or cardiomyocytes. The number of pores decreased by 63% across development, from an average of 1,856 in fetal cells to 1,040 in infant cells to just 678 in adult cells. These findings were validated via electron microscopy to show that nuclear pore density decreased across heart cell development.

Previously, researchers showed that a gene called Lamin b2, which is highly expressed in newborn mice but declines with age, is important for cardiomyocyte regeneration. In the new study, researchers found that blocking expression of Lamin b2 in mice led to a decrease in nuclear pore numbers. Mice with fewer nuclear pores had diminished transport of signaling proteins to the nucleus and decreased gene expression, suggesting that reduced communication with age may drive a decrease in cardiomyocyte regenerative capacity.

In response to stress such as high blood pressure, a cardiomyocyte's nucleus receives signals that modify gene pathways, leading to structural remodeling of the heart. This remodeling is a major cause of heart failure. The researchers used a mouse model of high blood pressure to understand how nuclear pores contribute to this remodeling process. Mice that were engineered to express fewer nuclear pores showed less modulation of gene pathways involved in harmful cardiac remodeling. These mice also had better heart function and survival than their peers with more nuclear pores.

These findings demonstrate that the number of nuclear pores controls information flux into the nucleus. As heart cells mature and the nuclear pores decrease, less information is getting to the nucleus. A reduced number of communication pathways protects the organ from damaging signals, such as those resulting from high blood pressure, but may also prevent adult heart cells from regenerating.

Link: https://www.upmc.com/media/news/102422-heart-cells-regenerate

Calorie restriction is known to suppress inflammation to some degree, alongside many other benefits to health that result from the reaction of cells and biological systems to a reduced calorie intake. Since chronic inflammation in brain tissue is implicated in the onset and development of neurodegenerative conditions, this makes calorie restriction a topic of interest in this part of the field. With a few exceptions, that interest largely manifests as research aimed at reproducing some of the metabolic alterations of calorie restriction with small molecule drugs, however, rather than more more rigorously testing calorie restriction as a therapy.

Parkinson's disease (PD) is the second most common neurodegenerative disease. To date, PD is still incurable and its pathogenesis remains elusive. Evidence from experimental studies reveals that mechanisms including protein misfolding and aggregation, neuroinflammation, mitochondrial dysfunction, and altered gut bacteria composition contribute to PD development. As of now, a number of medication strategies have been widely applied to control the motor and non-motor symptoms of PD and improve the quality of life. However, with long-term application of these drugs and as the disease progresses, adverse effects emerge. Moreover, these medications could neither effectively prevent the disease onset nor stop the disease progression. Recently, lifestyle interventions in the promotion of healthy brain aging and the prevention and treatment of central nervous system (CNS) diseases have risen into the spotlight, which could be promisingly complementary to the conventional PD pharmacotherapy.

Dietary restriction (DR), which involves a moderate reduction in food intake while avoiding malnutrition, has been proven to be effective in holding back aging and relieving age-related chronic diseases, including cancer, cardiovascular disease, diabetes, and neurodegenerative disorders. The beneficial actions of DR involve metabolic, hormonal, and immunomodulatory mechanisms. DR could reduce obesity and visceral fat, thus preventing metabolic risk factors. It increases insulin sensitivity, glucose tolerance, and ghrelin level. It can also induce adipose tissue transcriptional reprogramming, involving ways to regulate mitochondrial bioenergy, anti-inflammatory response, and longevity. Moreover, a potential role of DR in regulating the gut-brain axis has been well described in diseases of CNS and intestinal microbiota transplantation has been shown to be effective in Alzheimer's disease (AD) and multiple sclerosis (MS). Here, we summarize the strategies of DR from clinical and laboratory studies, and review the current findings of DR in preventing and ameliorating PD, with an emphasis on the possible mechanisms.

Link: https://doi.org/10.3390/nu14194108

In recent years, increasing attention has been given to the role of unresolved, chronic inflammation in the development of neurodegenerative disease. Normal tissue maintenance requires the involvement of immune cells, and inflammatory signaling is disruptive to that process. In the brain, immune cells take on a greater range of tasks than is the case elsewhere, becoming involved in maintenance of synaptic connections between neurons, for example. That too is disrupted by inflammatory signaling that changes the behavior of these cells.

Chronic inflammation in the absence of the usual causes, pathogens and injury, is a feature of aging. Researchers are investigating the causes of inflammation and mechanisms of regulation of inflammation in search of ways to damp down the inappropriate excessive inflammatory signaling of aging without also suppressing the necessary inflammation required for a robust immune defense. Some of the causes are reasonably well known. Senescent cells accumulate in tissues throughout the body, including the brain, and secrete pro-inflammatory signaling. DNA debris from cells damaged or destroyed by other processes of aging are misidentified by innate immune cells, that become inflammatory as a result of recognizing these damage-associated molecular patterns.

When it comes to inflammation in the brain, more research is focused on regulation than on causes, alas, but that is ever the case. Today's open access paper is an example of the type. Here, researchers review what is known of the role of galectins in the regulation of neuroinflammation. This is the sort of work that typically leads to screening programs that attempt to find small molecules that can adjust the behavior of one of the galectin interactions with minimal side-effects. Success depends as much on a correct understanding of the behavior and relevance of the target as it does on the quality of the small molecule interaction.

Galectins-Potential Therapeutic Targets for Neurodegenerative Disorders

Advancements in medicine have increased the longevity of humans, resulting in a higher incidence of chronic diseases. Due to the rise in the elderly population, age-dependent neurodegenerative disorders are becoming increasingly prevalent. The available treatment options only provide symptomatic relief and do not cure the underlying cause of the disease. Therefore, it has become imperative to discover new markers and therapies to modulate the course of disease progression and develop better treatment options for the affected individuals. Growing evidence indicates that neuroinflammation is a common factor and one of the main inducers of neuronal damage and degeneration.

This review focuses on summarizing the immune-regulatory activities of three predominant members of the galectin (Gal) family - Gal-1, Gal-3, and Gal-9 - which are known to play a significant role in neurodegenerative ailments. Neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD) display similar characteristics, including native protein accumulation, neuronal degeneration, and cognitive and behavioral impairment.

Gal-1 mRNA and protein levels have been shown to be higher in the spinal cords of SOD1 mice displaying phenotypes similar to ALS in humans. In addition, higher mRNA and protein expression of Gal-3 and Gal-9 has been observed in the spinal cords of SOD1 mice and sporadic ALS patients. Gal-3 specifically has been identified as a biomarker in serum, plasma, and/or cerebrospinal fluid (CSF) in Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). It has also shown detrimental regulation of inflammatory responses in AD. Further, moderate cognitive impairment in AD has been associated with Gal-9.

This information suggests that targeting Gals has a promising therapeutic potential to treat inflammatory and neurodegenerative disorders. In this review, we discuss the role of Gals in the causation and progression of neurodegenerative disorders. We describe the role of Gals in microglia and astrocyte modulation, along with their pro- and anti-inflammatory functions. In addition, we discuss the potential use of Gals as a novel therapeutic target for neuroinflammation and restoring tissue damage in neurodegenerative diseases.

Some of the metabolites produced by the gut microbiome aid function in the brain. For example, there is good evidence for butyrate produced by the microbiome to improve neurogenesis in the brain via modulating expression of BDNF. Unfortunately, the amounts of a number of beneficial metabolites produced by the gut microbiome declines with age, while harmful metabolites and inflammatory signaling increases. Researchers here gather data to support a role in the hippocampus specifically for a number of metabolites that originate in the gut microbiome, the area of the brain most involved in memory function. This and many other lines of research suggest that more attention should be given to the development of therapies capable of lasting restoration of a more youthful gut microbiome, such as fecal microbiota transplantation.

Aging is an intricate biological event that occurs in both vertebrates and invertebrates. During the aging process, the brain, a vulnerable organ, undergoes structural and functional alterations, resulting in behavioral changes. The hippocampus has long been known to be critically associated with cognitive impairment, dementia, and Alzheimer's disease during aging; however, the underlying mechanisms remain largely unknown. In this study, we hypothesized that altered metabolic and gene expression profiles promote the aging process in the hippocampus. Behavioral tests showed that exploration, locomotion, learning, and memory activities were reduced in aged mice.

Metabolomics analysis identified 69 differentially abundant metabolites and showed that the abundance of amino acids, lipids, and microbiota-derived metabolites (MDMs) was significantly altered in hippocampal tissue of aged animals. Our metabolomic analysis identified many known MDMs, including short-chain fatty acids, indoles, phenols, nucleotides, and amino acids. Intriguingly, the abundance of several MDMs, such as TMAO and spermidine, was significantly changed in the hippocampus of aging mice. Furthermore, transcriptomic analysis identified 376 differentially expressed genes in the aged hippocampus. The multi-omics analysis showed that pathways related to inflammation, microglial activation, synapse, cell death, cellular/tissue homeostasis, and metabolism were dysregulated in the aging hippocampus.

In conclusion, our data revealed that metabolic perturbations and gene expression alterations in the aged hippocampus were possibly linked to their behavioral changes in aged mice; we also provide evidence that altered MDMs might mediate the interaction between gut and brain during the aging process.

Link: https://doi.org/10.3389/fnagi.2022.964429

Researcher Judith Campisi, known for her work on cellular senescence and its relevance to degenerative aging, here discusses the present state of knowledge regarding senescent cells. Senescent cells are constantly created throughout life, but with age these cells are no longer efficiently destroyed by the immune system, allowing their numbers to increase. Senescent cells disrupt normal tissue structure and function via their inflammatory secretions. Attempts to treat aging by clearing the age-related buildup of senescent cells are well on their way to the clinic, under development in many different biotech companies.

So, a senescent cell is a cell that has entered a state - a new state. And that state has three compartments. The first compartment is the cell doesn't divide anymore. So it starts out where it can divide if it wants to. But now, it's blocked. And it will never divide again so far as we know. The second is: the cells resist dying. They stick around both in vivo and also in culture when we study these things in human and mouse cultures. And the third thing, which we think is even most important, is they start secreting a lot of molecules that affect their neighbors. Cells with those characteristics increase with age. They're present at sites of age-related pathology in both humans and mice. We think that they're driving aging, and in the mouse, we've proven that. We have not proven it in humans yet.

That senescent cells appear in the brain is driving some neurodegenerative diseases. For example, if we take senescent astrocytes - so they're a support cell within the brain - and incubate them with neurons, healthy human neurons, those two cell types will exist - coexist just fine until we give a little bit of a signal that is common between neurons called glutamate. Senescent astrocytes but not non-senescent astrocytes down-regulate the transporters that get rid of excess glutamate. Excess glutamate kills neurons. We have shown that at senescence, the down-regulation of these proteins that get rid of excess glutamate will cause a neighboring neuron to die in the process of experiencing that glutamate. And that does not happen in a young brain because there are so few senescent astrocytes.

Low-level infiltration of certain immune cells into tissues is called inflammaging. So there are multiple causes of inflammaging, it is a general feature of aging and a general feature of aged tissues. Senescence is one of them. So the type of inflammation that's caused by senescent cells has been called sterile inflammation. There's no evidence for a pathogen. But the immune cells are there. And these immune cells are destructive. So many of them are part of the more primitive part of our immune system called the innate immune system. These guys evolved to get rid of pathogens. And they do it by initially secreting toxic molecules until the more sophisticated part of your immune system called the adaptive immune system can now make the antibodies the other types of proteins that we associate with sophisticated, immune function. So senescent cells attract mostly innate immune cells. But of course, these two immune systems talk to each other. So eventually, you get a full-blown inflammatory response.

There is a mouse where we had eliminated senescent cells. We can manipulate the genome of a mouse pretty well. And we've done that by causing one of these senescent marker genes to drive a foreign gene that is a killer basically but only in the presence of an otherwise benign drug. And so using that mouse, we've shared that mouse with many laboratories, all of them working on a different age-related disease. And they test the hypothesis. Do senescent cells make a difference? And if so, if we eliminate them, is the disease either postponed, which it often is, or ameliorated, meaning it's not so severe. And that often happens - that's why the list of diseases that we know can be driven by senescent cells is so long. And once in a while for a few diseases, it actually can reverse.

Link: https://www.buckinstitute.org/podcasts/understanding-senescence/