Fight Aging!

Epigenetic clocks that measure chronological or biological age are at present largely based on patterns of DNA methylation that change in characteristic ways over a lifetime. There are other options, such as looking at histones, but they are not as well explored. DNA methylation is the process or adding and removing methyl groups from nuclear DNA, changing its structure in ways that expose or hide gene sequences from the machinery of gene expression. These epigenetic decorations this control the production of proteins, and are continually changing in response to environmental factors and cell processes.

Since epigenetic clocks were produced via machine learning, a process of identifying patterns from raw data, it remains largely unknown as to why specific DNA methylation sites on the genome tend to become methylated or unmethylated with age. Explaining these clocks is a work in its infancy, despite their increasing use in research. One of the quirks of the early epigenetic clocks is that they proved to be insensitive to exercise and physical fitness. For example, see the results from a study of sedentary versus physically fit twin pairs. In general, we might take this as a warning that a specific epigenetic clock may well have hidden biases that make it unsuitable to assess a specific intervention to slow or reverse aging. The only way to find out in certainty would be to test the clock and therapy in long, expensive studies.

When it comes to physical fitness, which we know has a measurable, beneficial effect on health and late life mortality, and which should be reflected in a good epigenetic clock, it is reassuring to see that later DNA methylation clocks do appear to react in the right way. Unfortunately, these results have no bearing on whether or not more recent clocks will correctly assess, say, the results of clearing senescent cells, or transplanting mitochondria, or any of the other avenues to eventual human rejuvenation. Finding out will likely require years and a great deal of funding.

Associations between cardiorespiratory fitness and lifestyle-related factors with DNA methylation-based ageing clocks in older men: WASEDA'S Health Study

DNA methylation-based age estimators (DNAm ageing clocks) are currently one of the most promising biomarkers for predicting biological age. However, the relationships between cardiorespiratory fitness (CRF), measured directly by expiratory gas analysis, and DNAm ageing clocks are largely unknown. We investigated the relationships between CRF and the age-adjusted value from the residuals of the regression of DNAm ageing clock to chronological age (DNAmAgeAcceleration: DNAmAgeAccel) and attempted to determine the relative contribution of CRF to DNAmAgeAccel in the presence of other lifestyle factors.

DNA samples from 144 Japanese men aged 65-72 years were used to appraise first-generation (i.e., DNAmHorvath and DNAmHannum) and second-generation (i.e., DNAmPhenoAge, DNAmGrimAge, and DNAmFitAge) DNAm ageing clocks. Various surveys and measurements were conducted, including physical fitness, body composition, blood biochemical parameters, nutrient intake, smoking, alcohol consumption, disease status, sleep status, and chronotype.

Both oxygen uptake at ventilatory threshold (VO2/kg at VT) and peak oxygen uptake (VO2/kg at Peak) showed a significant negative correlation with GrimAgeAccel, even after adjustments for chronological age and smoking and drinking status. Notably, VO2/kg at VT and VO2/kg at Peak above the reference value were also associated with delayed GrimAgeAccel. Multiple regression analysis showed that calf circumference, serum triglyceride, carbohydrate intake, and smoking status, rather than CRF, contributed more to GrimAgeAccel and FitAgeAccel. In conclusion, although the contribution of CRF to GrimAgeAccel and FitAgeAccel is relatively low compared to lifestyle-related factors such as smoking, the results suggest that the maintenance of CRF is associated with delayed biological ageing in older men.

Naked mole rats live far longer than similarly sized mammals, and are near immune to cancer. One of the mechanisms of cancer resistance involves the production of a different form of high molecular weight hyaluronan, and much more of it, improving the anti-cancer mechanism of contact inhibition. In addition, other mechanisms derived from changes in hyaluronan may affect life span through improved cellular function, but this is less well explored. Researchers here take the naked mole-rat version of the gene for high molecular weight hyoluronan, hyaluronan synthase 2, and put it into mice. The result is less cancer, improved metabolism, and longer lives.

Naked mole rats are mouse-sized rodents that have exceptional longevity for rodents of their size; they can live up to 41 years, nearly ten times as long as similar-size rodents. Unlike many other species, naked mole rats do not often contract diseases - including neurodegeneration, cardiovascular disease, arthritis, and cancer - as they age. Researchers previously discovered that high molecular weight hyaluronic acid (HMW-HA) is one mechanism responsible for naked mole rats' unusual resistance to cancer. Compared to mice and humans, naked mole rats have about ten times more HMW-HA in their bodies. When the researchers removed HMW-HA from naked mole rat cells, the cells were more likely to form tumors.

The team genetically modified a mouse model to produce the naked mole rat version of the hyaluronan synthase 2 gene, which is the gene responsible for making a protein that produces HMW-HA. While all mammals have the hyaluronan synthase 2 gene, the naked mole rat version seems to be enhanced to drive stronger gene expression. The researchers found that the mice that had the naked mole rat version of the gene had better protection against both spontaneous tumors and chemically induced skin cancer. The mice also had improved overall health and lived longer compared to regular mice. As the mice with the naked mole rat version of the gene aged, they had less inflammation in different parts of their bodies - inflammation being a hallmark of aging - and maintained a healthier gut. While more research is needed on exactly why HMW-HA has such beneficial effects, the researchers believe it is due to HMW-HA's ability to directly regulate the immune system.

Link: https://www.rochester.edu/newscenter/gene-transfer-hmw-ha-naked-mole-rats-extends-mice-lifespan-565032/

Why are two-thirds of Alzheimer's patients women? Women live longer than men, making up an ever larger share of the surviving cohort at any given age, and Alzheimer's is an age-related disease. This doesn't explain the whole of the difference, however. A dominant hypothesis is that the immune system is sufficiently different between the sexes to produce marginally greater dysfunction and neuroinflammation in women, in the same way that still incompletely understood biochemical differences lead to a greater incidence of autoimmunity in women. Researchers here produce supporting evidence for this hypothesis, showing that female Alzheimer's model mice exhibit a greater burden of cellular senescence in microglia, producing a greater level of neuroinflammation.

Microglia, the brain's principal immune cells, have been implicated in the pathogenesis of Alzheimer's disease (AD), a condition shown to affect more females than males. Although sex differences in microglial function and transcriptomic programming have been described across development and in disease models of AD, no studies have comprehensively identified the sex divergences that emerge in the aging mouse hippocampus. Further, existing models of AD generally develop pathology (amyloid plaques and tau tangles) early in life and fail to recapitulate the aged brain environment associated with late-onset AD. Here, we examined and compared transcriptomic and translatomic sex effects in young and old murine hippocampal microglia.

Hippocampal tissue from C57BL6/N and microglial NuTRAP mice of both sexes were collected at young (5-6 month-old) and old (22-25 monoth-old) ages. There were marginal sex differences identified in the young hippocampal microglia, with most differentially expressed genes (DEGs) restricted to the sex chromosomes. Both sex chromosomally and autosomally encoded sex differences emerged with aging. These sex DEGs identified at old age were primarily female-biased and enriched in senescent and disease-associated microglial signatures. Pathway analyses identified upstream regulators induced to a greater extent in females than in males, including inflammatory mediators IFNG, TNF, and IL1B, as well as AD-risk genes TREM2 and APP.

This data suggests that female microglia adopt disease-associated and senescent phenotypes in the aging mouse hippocampus, even in the absence of disease pathology, to a greater extent than males. This sexually divergent microglial phenotype may explain the difference in susceptibility and disease progression in the case of AD pathology. Future studies will need to explore sex differences in microglial heterogeneity in response to AD pathology and determine how sex-specific regulators (i.e., sex chromosomal or hormonal) elicit these sex effects.

Link: https://doi.org/10.1186/s12974-023-02870-2

The sizable body of work produced on calorie restriction and fasting over the last twenty years is supportive of the hypothesis that time spent hungry is an important factor determining the scale of benefits to health and longevity. The cellular response to a transient lack of nutrients involves improved cell maintenance, such as upregulation of autophagy to clear out damaged and worn molecular machinery. Looking at a level of organization above the cell, a transient state of hunger likely produces many other benefits to the way in which complex tissues and relationships between tissues function in the body. It dampens inflammatory signaling in the aging immune system, for example.

With this in mind, we expect to see many age-related conditions improved by calorie restriction, intermittent fasting, and similar interventions, such as fasting mimicking diets. In today's open access paper, researchers report that intermittent fasting without reduced calories can reduce pathology in a mouse model of Alzheimer's disease. As the researchers note, trying this out in humans is quite straightforward; it only requires funding. Unfortunately, funding for clinical trials of interventions such as intermittent fasting, in which there no profit to be made at the end of the day, is hard to come by. There is a role for philanthropy here that has yet to be fully realized.

Intermittent Fasting Improves Alzheimer's Pathology

One of the hallmarks of Alzheimer's disease is disruption to the body's circadian rhythm, the internal biological clock that regulates many of our physiological processes. Nearly 80% of people with Alzheimer's experience these issues, including difficulty sleeping and worsening cognitive function at night. However, there are no existing treatments for Alzheimer's that target this aspect of the disease.

Boosting the circadian clock is an emerging approach to improving health outcomes, and one way to accomplish this is by controlling the daily cycle of feeding and fasting. The researchers tested this strategy in a mouse model of Alzheimer's disease, feeding the mice on a time-restricted schedule where they were only allowed to eat within a six-hour window each day. For humans, this would translate to about 14 hours of fasting each day.

Compared to control mice who were provided food at all hours, mice fed on the time-restricted schedule had better memory, were less hyperactive at night, followed a more regular sleep schedule and experienced fewer disruptions during sleep. The test mice also performed better on cognitive assessments than control mice, demonstrating that the time-restricted feeding schedule was able to help mitigate the behavioral symptoms of Alzheimer's disease.

The researchers also observed improvements in the mice on a molecular level. In mice fed on a restricted schedule, the researchers found that multiple genes associated with Alzheimer's and neuroinflammation were expressed differently. They also found that the feeding schedule helped reduce the amount of amyloid protein that accumulated in the brain. Amyloid deposits are one of the most well-known features of Alzheimer's disease.

Circadian modulation by time-restricted feeding rescues brain pathology and improves memory in mouse models of Alzheimer's disease

Circadian disruptions impact nearly all people with Alzheimer's disease (AD), emphasizing both their potential role in pathology and the critical need to investigate the therapeutic potential of circadian-modulating interventions. Here, we show that time-restricted feeding (TRF) without caloric restriction improved key disease components including behavioral timing, disease pathology, hippocampal transcription, and memory in two transgenic mouse models of AD.

We found that TRF had the remarkable capability of simultaneously reducing amyloid deposition, increasing Aβ42 clearance, improving sleep and memory, and normalizing daily transcription patterns of multiple genes, including those associated with AD and neuroinflammation. Thus, our study unveils for the first time the pleiotropic nature of timed feeding on AD, which has far-reaching effects beyond metabolism, ameliorating neurodegeneration and the misalignment of circadian rhythmicity. Since TRF can substantially modify disease trajectory, this intervention has immediate translational potential, addressing the urgent demand for accessible approaches to reduce or halt AD progression.

Researchers here demonstrate that aged muscle metabolism can be improved via gene therapy to deliver a short isoform of PGC-1α. Upregulating PGC-1α in muscle tissue is suggested to be a good approach to therapy based on its declining expression with age. It is interesting that the researchers focus on an isoform of the protein shown to be upregulated in exercise, in effect aiming to produce an exercise mimetic gene therapy that switches on one of the reactions to exercise and leaves it switched on indefinitely.

Sarcopenia is characterized of muscle mass loss and functional decline in elder individuals which severely affects human physical activity, metabolic homeostasis, and life quality. Physical exercise is considered effective in combating muscle atrophy and sarcopenia, yet it is not feasible to elders with limited mobility. PGC-1α4, a short isoform of PGC-1α, is strongly induced in muscle under resistance training, and promotes muscle hypertrophy. In the present study, we showed that the transcriptional levels and nuclear localization of PGC1α4 was reduced during aging, accompanied with muscle dystrophic morphology, and gene programs. We thus designed NLS-PGC1α4, a nuclear localization sequence attached to PGC1α4, and ectopically express it in myotubes to enhance PGC1α4 levels and maintain its location in nucleus.

Indeed, NLS-PGC1α4 overexpression increased muscle sizes in myotubes. In addition, by utilizing AAV-mediated NLS-PGC1α4 delivery into gastrocnemius muscle, we found that it could improve sarcopenia with grip strength, muscle weights, fiber size, and molecular phenotypes, and alleviate age-associated adiposity, insulin resistance, and hepatic steatosis, accompanied with altered gene signatures. Mechanistically, we demonstrated that NLS-PGC-1α4 improved insulin signaling and enhanced glucose uptake in skeletal muscle. Besides, via RNA-seq analysis, we identified myokines IGF1 and METRNL as potential targets of NLS-PGC-1α4 that possibly mediate the improvement of muscle and adipose tissue functionality and systemic energy metabolism in aged mice. Moreover, we found a negative correlation between PGC1α4 and age in human skeletal muscle.

Together, our results revealed that NLS-PGC1α4 overexpression improves muscle physiology and systematic energy homeostasis during aging and suggested it as a potent therapeutic strategy against sarcopenia and aging-associated metabolic diseases.

Link: https://doi.org/10.1111/acel.13961

The overall population size of broad immune cell categories, such as T cells, remains remarkably consistent across a lifespan, even given a reduced supply of replacement T cells as the thymus atrophies and hematopoietic stem cell populations become dysfunctional. In an environment of limited supply, numbers are kept up in the face of continued attrition by increased replication, which leads to increased cellular senescence in immune cell populations as ever more cells hit the Hayflick limit. Another aspect of immune aging is a progressively larger shift in the relative count of different types of immune cell, such as diminished numbers of naive T cells capable of responding to novel pathogens.

Ageing is often accompanied with a decline in immune system function, resulting in immune ageing. Numerous studies have focussed on the changes in different lymphocyte subsets in diseases and immunosenescence. The change in immune phenotype is a key indication of the diseased or healthy status. However, the changes in lymphocyte number and phenotype brought about by ageing have not been comprehensively analysed. Here, we analysed T cell and natural killer (NK) cell subsets, the phenotype and cell differentiation states in 43,096 healthy Chinese individuals, aged 20-88 years, without known diseases. Thirty-six immune parameters were analysed and the reference ranges of these subsets were established in different age groups divided into 5-year intervals.

The data were subjected to random forest machine learning for immune-ageing modelling and confirmed using the neural network analysis. Our initial analysis and machine modelling prediction showed that naïve T cells decreased with ageing, whereas central memory T cells (Tcm) and effector memory T cells (Tem) increased CD28-associated T cells.

This is the largest study to investigate the correlation between age and immune cell function in a Chinese population, and provides insightful differences, suggesting that healthy adults might be considerably influenced by age and sex. The age of a person's immune system might be different from their chronological age. Our immune-ageing modelling study is one of the largest studies to provide insights into 'immune-age' rather than 'biological-age'. Through machine learning, we identified immune factors influencing the most through ageing and built a model for immune-ageing prediction.

Link: https://doi.org/10.1007/s43657-023-00106-0

At some point, regulatory bodies that oversee the development of new medicine will accept that therapies can target causative mechanisms of aging in order to slow or reverse the progression of aging, and that there are viable ways to assess new treatments that treat aging. There is growing pressure from the academic community and longevity-focused biotech industry for the ability to run clinical trials to treat aging, rather than to treat one specific age-related disease.

While inevitable, this change will take some years to come to pass, and likely require greater consensus in the research community on reasonable approaches to measure biological age. The scientific community is making good progress towards the adoption of improved epigenetic clocks as as a consensus means of measuring biological age in a natural environment, but it becomes challenging to stand by any of these clocks when any one causative mechanism of aging is slowed or reversed via therapy. The clock may over-represent or under-represent the contributions of that mechanism to degenerative aging, and there is no real way to find out without calibrating the clock against that specific therapy in lengthy animal studies.

In the meanwhile, companies developing therapies that target the mechanisms of aging choose one specific age-related condition for clinical trials and regulatory approval. They move ahead assuming that widespread off-label use will likely follow approval for any one age-related disease, providing further pressure for the regulatory edifice will shift to allow a more defined path towards treatment of aging as a medical condition in all older individuals.

Challenges in developing Geroscience trials

Multiple clinical conditions and pathophysiological processes have long been considered as inescapable and unmodifiable consequences of the aging process. However, these perceptions are changing. Over the past few decades, research focusing on the interplay between the fundamental processes of aging and the biology of co-morbidities has given rise to the concept of Geroscience, the goal of which is to develop new biologically-based therapeutic and preventive approaches that target fundamental aging processes; thus, to decrease age-related multi-morbidities as a group and improve healthspan.

The beneficial effect of using Gerotherapeutic drugs to modulate the fundamental molecular, cellular, and/or genetic mechanisms of aging has been demonstrated in animal models, and offers exciting preventive and even curative therapeutic translational opportunities in humans. However, Geroscience trials face numerous methodological challenges in their study design regarding demonstrating clinical effectiveness successfully in humans. One critical challenge is that the usual design of therapeutic clinical trials is centered on disease-specific diagnosis and physiopathology, whereas Geroscience trials aim to target mechanisms of aging in order to delay or prevent the onset or reduce the progression of multiple age-related diseases, geriatric syndromes, and potentially alleviate or treat such conditions.

The European Medicine Agency (EMA) and the Food and Drug Agency (FDA) have high concordance (91-98%) in decisions on marketing approvals, but the arrival of gerotherapeutic drugs will challenge both agencies to define the terms of marketing approval in the context of Geroscience. Being an emergent discipline, Geroscience will challenge some of the established protocols for fast approval of new drugs and biomarkers needed to meet the challenges of an aging society. In general, FDA or EMA approve drugs for treating diseases; however, aging by itself is not currently considered as a "disease", but as the major risk factor for multiple morbidities.

Basic scientists, clinicians, and drug agency officials already interact so that the concept behind Geroscience is understood and shared. A scale for evaluating FDA-approved drugs for their Gerotherapeutic potential has been proposed. In this context, it is important to highlight that the design of the TAME (Targeting Aging with MEtformin) trial has been approved by the FDA; TAME aims to delay mortality and the onset of several age-related diseases (e.g., myocardial infarction, stroke, cancer, dementia) and conditions (e.g., major decline in mobility or cognitive function) rather than targeting a single disease. The TAME trial may serve as a proof of concept that proves to the medical agencies that aging can be a therapeutic indication in itself. This result would favor conditions for defining new marketing approval, type of approval, and approved indication for new or already approved drugs and will be incentive for pharmaceutical companies to invest in research on Geroscience.

Designing a disease-centric trial remains the only way to date to gain approval from the FDA or EMA, each of which still adheres to the "one disease, one drug" model. The regulatory constraints required for a new drug to be brought to patients and the extent to which the patients benefit from it must also be taken into consideration when designing a trial. However, targeting a single pathology in a clinical trial is not without risk either. Diagnostic criteria change over time, in particular with the emergence of biomarkers, not-withstanding that most diseases of ageing are of complex etiology, resulting from (still poorly understood) interactions between non-modifiable factors (including age, sex, and genetic predisposition) and modifiable factors, related to environmental and other exposures, lifestyle factors, etc. Moreover, it should be emphasized that some Gerotherapeutic drugs could have a very modest and difficult to demonstrate effect in organs evaluated separately, but have a clinically significant overall effect due to their action on the whole organism, and the alternative also exists that a study using a composite score might fail to capture substantial changes within just one domain if not statistically powered for that endpoint alone. A trial centered on only one function or disease is the current conventional approach but is probably not appropriate for certain molecules such as metformin, for which effects are pleiotropic, acting on multiple organs and through multiple biological mechanisms.

Given the advent of various clocks that measure biological age, one might expect that the research community will repeat and update past efforts to quantify the effects of diet, exercise, and other lifestyle factors on the long-term risk of age-related disease and mortality. The open access paper here is an example of this sort of work, focused on the impact of diet. The researchers made use of their own aging clock based on simple biomarkers, similar to Phenotypic Age, in order to determine a relationship between dietary quality and pace of aging.

In this prospective cohort study of 12,784 participants, based on a recently developed biological aging measure acquired at four-time points within an 8-year period, we identified three aging trajectories where participants in medium-degree or high-degree accelerated aging trajectory groups had higher risks of death than those in the slow aging trajectory. We then found that adopting an overall plant-based dietary pattern was associated with lower odds of being in medium-degree or high-degree accelerated aging trajectories. Plant-based dietary patterns were assessed by overall plant-based diet index (PDI), healthful PDI (hPDI), and unhealthful PDI (uPDI) Our study demonstrated a differential impact of plant-based foods on accelerated aging trajectory, i.e., a healthful plant-based diet was more beneficial to aging than an unhealthful plant-based diet. Fresh fruits, fresh vegetables, and legumes were major contributors found in our healthful plant-based diet analysis, whereas refined grain, salt-preserved vegetable, dairy products, and pluck were major contributors from unhealthful plant-based diet analysis.

We identified three latent classes of accelerated aging trajectories: slow aging, medium-degree, and high-degree accelerated aging trajectories. Participants who had higher PDI or hPDI had lower odds of being in medium-degree (odds ratio = 0.75 for PDI; odds ratio = 0.73 for hPDI) or high-degree (odds ratio = 0.63 for PDI; odds ratio = 0.62 for hPDI) accelerated aging trajectories. Participants in the highest quintile of uPDI were more likely to be in medium-degree (odds ratio = 1.72) or high-degree (odds ratio = 1.70) accelerated aging trajectories. With a mean follow-up time of 8.40 years and 803 (6.28%) participants died by the end of follow-up, we found that participants in medium-degree (hazard ratio = 1.56) or high-degree (hazard ratio = 3.72) accelerated aging trajectory groups had higher risks of death than those in the slow aging trajectory.

Link: https://doi.org/10.1186/s12916-023-02974-9

As one might expect, people who better maintain physical fitness into later life exhibit lesser degrees of age-related disease. In this case, the correlation is specifically for forms of cardiovascular disease, but researchers have reported that numerous other improvements in health can be linked to greater fitness. Animal studies can and do show causation in this relationship between fitness and age-related disease. It is reasonable to believe that the human correlations also largely reflect a causal relationship. There are a great many good reasons to make the effort to better maintain physical fitness throughout life.

A new study assessed 15,450 individuals without atrial fibrillation who were referred for a treadmill test between 2003 and 2012. The average age was 55 years and 59% were men. Fitness was assessed using the Bruce protocol, where participants are asked to walk faster and at a steeper grade in successive three-minute stages. Fitness was calculated according to the rate of energy expenditure the participants achieved, which was expressed in metabolic equivalents (METs).

Participants were followed for new-onset atrial fibrillation, stroke, myocardial infarction, and death. The researchers analysed the associations between fitness and atrial fibrillation, stroke, and major adverse cardiovascular events (MACE; a composite of stroke, myocardial infarction and death) after adjusting for factors that could influence the relationships including age, sex, cholesterol level, kidney function, prior stroke, hypertension, and medications.

During a median of 137 months, 515 participants (3.3%) developed atrial fibrillation. Each one MET increase on the treadmill test was associated with an 8% lower risk of atrial fibrillation, 12% lower risk of stroke and 14% lower risk of MACE. Participants were divided into three fitness levels according to METs achieved during the treadmill test: low (less than 8.57 METs), medium (8.57 to 10.72) and high (more than 10.72). The probability of remaining free from atrial fibrillation over a five-year period was 97.1%, 98.4%, and 98.4% in the low, medium and high fitness groups, respectively.

Link: https://www.escardio.org/The-ESC/Press-Office/Press-releases/Keep-fit-to-avoid-heart-rhythm-disorder-and-stroke

While the immune system of the brain is distinct from that of the rest of the body, the central nervous system walled off by the blood-brain barrier, the inflammatory status of the brain is very much influenced by the inflammatory status of the rest of the body. Signals pass back and forth, and at the edges of the brain there are a variety of tissues in which one can find peripheral immune cells such as macrophages of the innate immune system or T cells of the adaptive immune system.

One such tissue is the meninges, the membranes that wrap the brain and spinal cord. In recent years, since the discovery of the glymphatic system that drains waste from the brain, more attention has been given to cell populations in the lymphatic vessels and vasculature of the meninges, as well as other tissues bordering the brain, such as the choroid plexus. As an example of this work, today's open access review discusses what is known of the way in which peripheral immune system involvement in the meninges may influence the inner regions of the brain.

Current views on meningeal lymphatics and immunity in aging and Alzheimer's disease

Alzheimer's disease (AD) is an aging-related form of dementia associated with the accumulation of pathological aggregates of amyloid beta and neurofibrillary tangles in the brain. These phenomena are accompanied by exacerbated inflammation and marked neuronal loss, which altogether contribute to accelerated cognitive decline. The multifactorial nature of AD, allied to our still limited knowledge of its etiology and pathophysiology, have lessened our capacity to develop effective treatments for AD patients.

Over the last few decades, genome wide association studies and biomarker development, alongside mechanistic experiments involving animal models, have identified different immune components that play key roles in the modulation of brain pathology in AD, affecting its progression and severity. As we will relay in this review, much of the recent efforts have been directed to better understanding the role of brain innate immunity, and particularly of microglia. However, and despite the lack of diversity within brain resident immune cells, the brain border tissues, especially the meninges, harbour a considerable number of different types and subtypes of adaptive and innate immune cells. Alongside microglia, which have taken the centre stage as important players in AD research, there is new and exciting evidence pointing to adaptive immune cells, namely T cells and B cells found in the brain and its meninges, as important modulators of neuroinflammation and neuronal (dys)function in AD.

Importantly, a genuine and functional lymphatic vascular network is present around the brain in the outermost meningeal layer, the dura. The meningeal lymphatics are directly connected to the peripheral lymphatic system in different mammalian species, including humans, and play a crucial role in preserving a "healthy" immune surveillance of the central nervous system, by shaping immune responses, not only locally at the meninges, but also at the level of the brain tissue. In this review, we will provide a comprehensive view on our current knowledge about the meningeal lymphatic vasculature, emphasizing its described roles in modulating central nervous system fluid and macromolecule drainage, meningeal and brain immunity, as well as glial and neuronal function in aging and in AD.

There is good evidence for the various forms of later life vaccination, such as for herpes zoster or influenza, to reduce the risk of later suffering Alzheimer's disease. One possibility is that people who take the time to obtain a vaccine tend to take better care of their health across the board. Another possibility is that vaccination produces a trained immunity effect that dampens age-related inflammation for a sustained period of time. It may also be the case that suffering from influenza, pneumonia, or similar infectious diseases causes sufficient additional inflammation to move the odds on suffering later neurodegenerative disease, and this is a large enough effect to show up in sizable study populations with an increased infection risk and severity for the unvaccinated. Regardless, this is an interesting area of research that is clearly connected to the growing interest in the role of chronic inflammation in the development of age-related neurodegenerative conditions.

Accumulating evidence suggests that adult vaccinations can reduce the risk of developing Alzheimer's disease (AD) and Alzheimer's disease related dementias. To compare the risk for developing AD between adults with and without prior vaccination against tetanus and diphtheria, with or without pertussis (Tdap/Td); herpes zoster (HZ); or pneumococcus, a retrospective cohort study was performed. Included patients were free of dementia during a 2-year look-back period and were ≥65 years old by the start of the 8-year follow-up period. We compared two similar cohorts identified using propensity score matching (PSM), one vaccinated and another unvaccinated, with Tdap/Td, HZ, or pneumococcal vaccines. We calculated the relative risk and absolute risk reduction for developing AD.

For the Tdap/Td vaccine, 7.2% (n = 8,370) vaccinated patients and 10.2% (n = 11,857) unvaccinated patients developed AD during follow-up; the relative risk was 0.70 and absolute risk reduction was 0.03. For the HZ vaccine, 8.1% (n = 16,106) vaccinated patients and 10.7% (n = 21,273) unvaccinated patients developed AD during follow-up; the relative risk was 0.75 and absolute risk reduction was 0.02. For the pneumococcal vaccine, 7.92% (n = 20,583) vaccinated patients and 10.9% (n = 28,558) unvaccinated patients developed AD during follow-up; the relative risk was 0.73 and absolute risk reduction was 0.02. Thus several vaccinations, including Tdap/Td, HZ, and pneumococcal, are associated with a reduced risk for developing AD.

Link: https://doi.org/10.3233/JAD-221231

Chimeric antigen receptor (CAR) T cell therapies involve engineering a patient's T cells to add receptors complementary to a specific surface feature of a target cell population that one wants destroyed. This approach to therapy was pioneered in the cancer research community, and has performed well to date. Here, researchers demonstrate that it is possible to use a CAR-T approach to target senescent cells. Clearance of senescent cells in older individuals produces rejuvenation and reversal of many different age-related conditions in animal studies, and we might hope that the same will occur in humans.

Cellular senescence, characterized by stable cell cycle arrest, plays an important role in aging and age-associated pathologies. Eliminating senescent cells rejuvenates aged tissues and ameliorates age-associated diseases. Here, we identified that natural killer group 2 member D ligands (NKG2DLs) are up-regulated in senescent cells in vitro, regardless of stimuli that induced cellular senescence, and in various tissues of aged mice and nonhuman primates in vivo. Accordingly, we developed and demonstrated that chimeric antigen receptor (CAR) T cells targeting human NKG2DLs selectively and effectively diminish human cells undergoing senescence induced by oncogenic stress, replicative stress, DNA damage, or P16INK4a overexpression in vitro.

Targeting senescent cells with mouse NKG2D-CAR T cells alleviated multiple aging-associated pathologies and improved physical performance in both irradiated and aged mice. Autologous T cells armed with the human NKG2D CAR effectively delete naturally occurring senescent cells in aged nonhuman primates without any observed adverse effects. Our findings establish that NKG2D-CAR T cells could serve as potent and selective senolytic agents for aging and age-associated diseases driven by senescence.

Link: https://doi.org/10.1126/scitranslmed.add1951

Few human longevity-associated gene variants are replicated in multiple patient populations. One of those is a variant of BPIFB4, that appears to improve immune function and lower inflammation by adjusting the behavior of macrophage cells of the innate immune system. Delivering the variant to mice using a gene therapy has similar effects. It may well operate via other mechanisms as well, however. Few proteins in a living cell turn out to have only one purpose.

In today's open access paper, researchers report that the BPIFB4 variant reduces the severity of coronary artery disease in humans and mice. Delivering the variant to heart tissue as a gene therapy improves outcomes in a mouse model of heart attack. While reduced inflammation should certainly help in the aftermath of a heart attack, and more broadly in the slow progression of heart disease, this outcome may result from a different mechanism to that involved in the modulation of immune function noted above. The gene therapy approach appears to affect heart cells directly, improving function and protecting against the stresses and damage resulting loss and restoration of blood supply following a heart attack.

BPIFB4 and its longevity-associated haplotype protect from cardiac ischemia in humans and mice

Unhealthy lifestyles and accrual of risk factors contribute to vascular dysfunction highlighted by cellular senescence and impaired synthesis and secretion of endothelium-derived vasoactive molecules. Genetic factors also participate in determining the dichotomy between cardiovascular health and disease. Nonetheless, very few gene polymorphisms proved to capture the divergence of cardiovascular clocks seen in high-risk individuals (HRIs) and long-living individuals (LLIs). Among them, the longevity variant (LAV) of the BPI Fold Containing Family B Member 4 (BPIFB4) gene, showed a preponderant impact on the cardiovascular system and prolonged life span, passing the validation of three geographically unrelated cohorts.

Carriers of the LAV-BPIFB4 gene express high levels of the encoded protein in the blood, circulating mononuclear cells, and vascular cells. Moreover, high levels of circulating BPIFB4 protein protected against carotid stenosis in human cohorts. Contrariwise, BPIFB4 is reportedly downregulated in the heart of patients with end-stage ischemic heart failure.

Importantly, we have provided substantial evidence for the possibility of transferring the healthy phenotype conferred by LAV-BPIFB4 to cardiovascular animal models, suggesting that temporary expression of an evolutionary successful human gene can halt and even reverse age-related damage. LAV-BPIFB4 gene therapy in mice demonstrated anti-atherosclerotic, anti-hypertensive, pro-angiogenic, and neuroprotective activities. Moreover, it improved frailty indices and diabetic and age-related cardiomyopathies, and rejuvenated the elderly vasculature. In addition, replicating the preserved immune function of centenarians, the LAV-BPIFB4 protein encouraged immunomodulatory responses by human myeloid cells.

Researchers here report on a measure of brain aging constructed from expression levels of a variety of genes, noting that it appears to show the greatest changes in white matter rather than grey matter. They use this measure to assess the results of interventions shown to slow aging in old mice, calorie restriction and plasma transfer from young mice, finding that these two treatments have quite different mechanistic outcomes in the brain, slowing brain aging in quite different ways. This suggests that (a) there are multiple ways to intervene, and (b) there are ways to improve on present capabilities.

Researchers sampled 15 regions in both hemispheres of the brains of 59 female and male mice aged 3 to 27 months. They identified and ranked the top genes expressed by cells found in each region of the brain. They identified 82 genes that are frequently found and vary in concentration in 10 or more regions. The team used these genes to develop a common aging score, assessing how gene activity in different regions of the brain change with age. The researchers found that the white matter, which is found deep in the brain and contains nerve fibers protected by white-colored myelin, showed the earliest and most pronounced changes in gene expression for mice 12 and 18 months old. These mice are about as old, in mouse years, as a person in their 50s.

Past work has shown that aging disrupts an otherwise stable gene expression pattern in the brain, turning on genes that regulate inflammation and the immune response, and turning off genes responsible for protein and collagen synthesis. The inflammation and immune response affect the integrity of the myelin sheath, the insulation layer around nerves responsible for transmitting signals across the brain. "White matter has been a rather neglected area in aging research, which usually focuses on the neuron-dense regions like the cortex or hippocampus. The fact that white matter is emerging in our data as an area of particular vulnerability to aging opens up new and intriguing hypotheses."

Interventions to slow the genetic shift that leads to the decline in specific regions of the brain could be beneficial in addressing neurodegenerative disease as well as the general decline associated with aging. During the study, the team explored two interventions - caloric restriction and injections of plasma from young mice - to evaluate whether they protected against the region-specific shifts in gene expression. Each intervention began when the mice were 19 months old and lasted four weeks. The researchers found that the dietary intervention caused genes associated with circadian rhythms to turn on, while the plasma intervention turned on genes involved in stem cell differentiation and neuronal maturation that led to selective reversal of age-related gene expression. "The interventions appeared to act on very different regions in the brain with strikingly different effects. This suggests that there are multiple regions and pathways in the brain that have the potential to improve cognitive performance at old age."

Link: https://med.stanford.edu/news/all-news/2023/08/brain-aging-genes.html

Chronic inflammation and dysfunction of immune cells is a characteristic of neurodegenerative conditions. Attention is usually given to the innate immune cells of the central nervous system in this context, but it is also the case that the adaptive immune system outside the brain tends towards dysfunction in older individuals suffering from age-related disease. Researchers here review what is known of T cell exhaustion, senescence, and other issues in older individuals. It is hoped that clearing these problematic cells from the immune population, such as via the use of senolytic drugs to destroy senescent cells, will have reduce the risk and slow the progression of neurodegenerative conditions.

CD8+ T lymphocytes are adaptive immune cells that, upon antigen recognition, undergo a complex differentiation process. In acute inflammatory responses, when antigen is effectively cleared, short-lived effector T cells undergo controlled apoptosis, while long-lived effector T lymphocytes differentiate into memory T cells, thus efficiently resolving the inflammatory reaction. However, during chronic inflammatory conditions, this natural resolution is impaired, and CD8+ T lymphocytes become exhausted or senescent, retaining a neurotoxic potential and contributing to several neurodegenerative diseases.

CD8+ T cells, reacting against self and non-self antigens are clonally expanded in all brain disorders discussed in this review, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. It is worth noting that although these disorders may have distinct causes, occurrence rates, and clinical presentations, they share common immunopathological characteristics. These include the circulating origin of central nervous system-invading CD8+ T lymphocytes, the clonal expansion of CD8+ T cells, and phenotypical traits that resemble senescence.

In the light of growing evidence suggesting that senescent and exhausted CD8+ T cells contribute to aging and various brain disorders, a promising therapeutic approach for these conditions may be represented by targeting deleterious functions of CD8+ T cells. Indeed, targeting senescent and exhausted CD8+ T cells may create a personalized neuroimmunotherapy, with the ultimate goal to rejuvenate T cells through tailored diagnostic and therapeutic protocols. Strategies such as epigenetic modulation and using senolytic compounds to induce apoptosis in senescent and exhausted CD8+ T cells may also be explored. Several studies are ongoing to prove the effectiveness of interventions targeting tissue-damaging senescent cells, which may slow, prevent, and alleviate disorders in preclinical models. The development of senolytic small molecules that can specifically eliminate senescent cells, may represent a promising strategy for treating multiple CD8+ T cell senescent-mediated disorders and age-related conditions in humans.

Link: https://doi.org/10.3389/fimmu.2023.1233870

Chronic inflammation of brain tissue is characteristic of aging and neurodegenerative conditions. The worse the inflammation, the worse the outcome. Lasting, unresolved inflammation in the absence of the usual causes of inflammation such as injury or infection occurs in aged tissues for a variety of reasons, including the pro-inflammatory signaling of senescent cells and triggering of innate immune responses by the mislocalization of mitochondrial DNA that occurs as a result of mitochondrial dysfunction. Current methods of suppressing inflammation are crude, a matter of blocking specific inflammatory signals passing between cells. This affects both excessive chronic inflammatory signaling and necessary inflammatory signaling involved in defense against pathogens, regeneration from injuries, and so forth. It is hoped that more sophisticated means can be found.

One approach to finding better ways to downregulate inflammation is to decipher the signaling produced during interventions that are known to reduce age-related inflammation without greatly affecting the normal inflammatory response. That is the thrust of today's research materials, in which scientists identify a common signal molecule and regulatory path to dampen inflammation that is triggered during heterochronic parabiosis, in which the circulatory systems of an old mouse and a young mouse are joined, during exercise, and as a result of increased levels of the longevity-associated protein klotho. This is interesting work, as is usually the case whenever commonalities are found in divergent types of treatment.

A Secret in the Blood: How PF4 Restores Youth to Old Brains

For years, scientists have known that the anti-aging hormone klotho, infusions of young blood, and exercise each improve brain function in older mice. But they didn't know why. Now, researchers have identified platelet factor 4 (PF4) - a small protein released by blood platelets - as a common denominator behind all three. Platelets are blood cells that normally release PF4 to alert the immune system and clot blood at wounds. The researchers found that PF4 also rejuvenates the old brain and boosts the young brain, potentially opening the door to new therapies that aim to restore brain function, if not tap into a fountain of youth.

In 2014, researchers found that blood plasma from young mice restored brain function in old animals. His team then found that young plasma contained much more PF4 than old plasma. Moreover, just injecting PF4 into old animals was about as restorative as young plasma. It calmed down the aged immune system in the body and the brain. Old animals treated with PF4 performed better on a variety of memory and learning tasks. "PF4 actually causes the immune system to look younger, it's decreasing all of these active pro-aging immune factors, leading to a brain with less inflammation, more plasticity and eventually more cognition. We're taking 22-month-old mice, equivalent to a human in their 70s, and PF4 is bringing them back to function close to their late 30s, early 40s."

A decade ago, researchers showed that the hormone klotho enhances brain function in young and old animals and also makes the brain more resistant to age-related degeneration. But klotho, injected into the body, never reached the brain. So, how? Researchers found that one connection was PF4, released by platelets after an injection of klotho. PF4 had a dramatic effect on the hippocampus, where memories are formed in the brain. In particular, PF4 enhanced the formation of new neural connections at the molecular level. It also gave both old and young animals a brain boost in behavioral tests.

Exercise can keep the mind sharp for decades. In 2019, researchers found that platelets released PF4 into the bloodstream following exercise. When they tested PF4 on its own, it improved cognition in old animals. "We can now target platelets to promote neurogenesis, enhance cognition, and counteract age-related cognitive decline."

Platelet factors attenuate inflammation and rescue cognition in ageing

Identifying therapeutics to delay, and potentially reverse, age-related cognitive decline is critical in light of the increased incidence of dementia-related disorders forecasted in the growing older population. Here we show that platelet factors transfer the benefits of young blood to the ageing brain. Systemic exposure of aged male mice to a fraction of blood plasma from young mice containing platelets decreased neuroinflammation in the hippocampus at the transcriptional and cellular level and ameliorated hippocampal-dependent cognitive impairments.

Circulating levels of the platelet-derived chemokine platelet factor 4 (PF4) (also known as CXCL4) were elevated in blood plasma preparations of young mice and humans relative to older individuals. Systemic administration of exogenous PF4 attenuated age-related hippocampal neuroinflammation, elicited synaptic-plasticity-related molecular changes and improved cognition in aged mice. We implicate decreased levels of circulating pro-ageing immune factors and restoration of the ageing peripheral immune system in the beneficial effects of systemic PF4 on the aged brain. Mechanistically, we identified CXCR3 as a chemokine receptor that, in part, mediates the cellular, molecular and cognitive benefits of systemic PF4 on the aged brain. Together, our data identify platelet-derived factors as potential therapeutic targets to abate inflammation and rescue cognition in old age.

Red blood cells lack a nucleus, but still undertake a range of interesting activities. For example, they release extracellular vesicles. Researchers here note that these vesicles are protective for macrophages that ingest them, protecting the macrophages from being overwhelmed by excess cholesterol in the environment of an atherosclerotic plaque. Macrophages are responsible for cleaning up excess deposition of cholesterol in blood vessel walls, and when they falter at this task in later life, a tipping point is reached at which atherosclerotic plaque begins to form. Evidently red blood cell extracellular vesicles are not enough to prevent this issue from occurring, but scientists are in search of mechanisms that might be enhanced to protect macrophages and allow them to prevent and repair plaque before it grows to the point of causing narrowing of blood vessels, heart attack, and stroke.

Extracellular vesicles (EVs) can be produced from red blood cells (RBCs). The EVs that originate from red blood cells (RBCEVs) have favourable characteristics for serving as an effective drug delivery platform. They are devoid of DNA and inherit their allogenic transfusion compatibility traits from RBCs, hence potentially providing safe, 'off-the-shelf' medication. In addition, RBCs can be readily collected from volunteers and stimulated with calcium ionophore to release large amounts of RBCEVs.

Since EVs are complex entities which act as carriers of biological agents that can modulate their target cells, applying them for therapeutic purposes requires an in-depth understanding of their interactions with these cells and the potential effects of their various components. In the case of RBCEVs, haemoglobin is the most abundant protein present. In human adults, haemoglobin is mainly present in the form of haemoglobin A. Haemoglobin is safe when carried by RBCs but it is toxic when released from RBCs into the bloodstream and interstitial space due to hemolysis. However, this toxicity of free haemoglobin can be neutralized by haptoglobin, a protein secreted from liver cells. This is because haemoglobin and haptoglobin form a complex that is rapidly processed by macrophages through the CD163 receptor. Upon internalization, the haemoglobin component of the complex is broken down, and the heme groups are processed by an enzyme called heme oxygenase 1 (HO-1).

HO-1 plays a protective role against atherosclerosis. This protective effect is speculated to stem from the catalytically enzymatic degradation of heme by HO-1. During the process, heme is broken down into ferrous ions, CO (which inhibits inflammation), and biliverdin (which has antioxidant properties). Thus we hypothesize that in RBCEVs, haemoglobin is protected in enclosed vesicles, preventing cytotoxicity. In addition, we speculate that the haemoglobin carried by RBCEVs exerts both anti-inflammatory and anti-atherosclerosis effects mediated via the HO-1 pathway when the EVs are taken up by macrophages.

In this study, we investigated the uptake of RBCEVs by macrophages. We also monitored the intracellular trafficking of RBCEVs and the fate of haemoglobin, their most abundant protein cargo. We found that RBCEVs were preferentially taken up by macrophages in the liver and spleen. The EVs then released heme into the cytoplasm via the heme transporter HRG1, which promoted the differentiation of the macrophages to a phenotype characterized by upregulated HO-1 expression, and prevented the accumulation of oxidized low-density lipoproteins (oxLDL) in these cells. This natural therapeutic characteristic of RBCEVs suggests their potential benefits in atherosclerosis treatment, especially when combined with other drug cargoes that can be loaded into and carried by these EVs. In addition, the anti-inflammatory properties of RBCEVs might be effective for the treatment of other inflammatory conditions.

Link: https://doi.org/10.1002/jev2.12354

Researchers have genetically engineered pigs to overcome the known barriers to transplantation of pig organs into humans, and have reached the stage of conducting transplants into terminally ill volunteers and brain dead individuals who donated their bodies to science. To learn by doing is really the only practical way by which the presently unknown problems are discovered. This trial of kidney transplantation ran for longer than prior efforts, and is a step on the path to producing a ready supply of non-human organs for transplantation, a technology that will compete with efforts to grow new organs on demands.

Surgeons have transplanted a genetically engineered pig kidney that continues to function well after 32 days in a man declared dead by neurologic criteria and maintained with a beating heart on ventilator support. This represents the longest period that a gene-edited pig kidney has functioned in a human. The first hurdle to overcome in xenotransplants is preventing so-called hyperacute rejection, which typically occurs just minutes after an animal organ is connected to the human circulatory system. By "knocking out" the gene that encodes the biomolecule known as alpha-gal - which has been identified as responsible for a rapid antibody-mediated rejection of pig organs by humans - immediate rejection has been avoided. Additionally, the pig's thymus gland, which is responsible for educating the immune system, was embedded underneath the outer layer of the kidney to stave off novel, delayed immune responses. The combination of modifications has been shown to prevent rejection of the organ while preserving kidney function.

To ensure the body's kidney function was sustained solely by the pig kidney, both of the transplant recipient's native kidneys were surgically removed. One pig kidney was then transplanted and started producing urine immediately without any signs of hyperacute rejection. During the observation phase, intensive care clinical staff maintained the decedent on support while the pig kidney's performance was monitored and sampled with weekly biopsies. Levels of creatinine, a bodily waste product found in the blood and an indicator of kidney function, were in the optimal range during the length of the study, and there was no evidence on biopsy of rejection.

The kidney and thymus gland used in this procedure were procured from a GalSafe pig, an animal engineered by Revivicor Inc., a subsidiary of United Therapeutics Corporation. In December 2020, the U.S. Food and Drug Administration (FDA) approved the GalSafe pig as a potential source for human therapeutics, as well as a food source for people with alpha-gal syndrome, a meat allergy caused by a tick bite. While previous genetically engineered pig organ transplants have incorporated up to 10 genetic modifications, this latest study shows that a single-gene knockout pig kidney can still perform optimally for at least 32 days without rejection.

Link: https://nyulangone.org/news/pig-kidney-xenotransplantation-performing-optimally-after-32-days-human-body

Age-related deafness arises from some combination of (a) the loss of sensory hair cells in the inner ear, and (b) the loss of connections between those cells and the brain. There is some disagreement in the literature as to which of these mechanisms is the most relevant, but most recent efforts in the field are focused on trying to coerce the body into producing new hair cells. If that production of new hair cells in the inner ear follows the normal developmental processes, then it might solve both of the above mentioned issues, providing both cells and connections to the brain.

Today's research materials illustrate the state of this field of research. The scientists involved have explored the developmental programs active in the inner ear tissue of the embryo in search of regulatory genes that might be used to reactivate the normally dormant production of new hair cells in an adult. Interestingly, they also find that loss of hair cells in an adult can trigger these developmental programs to a modest degree, producing some amount of new hair cell creation - though evidently not enough. Yet if a process operates at all in adult tissues, one might think that it will be an easier target for upregulation via the usual therapeutic strategies than would otherwise be the case.

Mouse studies tune into hearing regeneration

A deafened adult cannot recover the ability to hear, because the sensory hearing cells of the inner ear don't regenerate after damage. In the non-sensory supporting cells of the inner ear, key genes required for conversion to sensory cells are shut off through a process known as epigenetic silencing. By studying how the genes are shut off, researchers can begin to understand how we might turn them back on to regenerate hearing.

Researchers explored when and how the progenitor cells of the inner ear gain the ability to form sensory hearing cells. The scientists pinpointed when progenitor cells acquire this ability: between days 12 and 13.5 of embryonic development in mice. During this window, the progenitor cells acquire the capacity to respond to signals from the master regulator gene Atoh1 that triggers the formation of sensory hearing cells later during development. What primes the progenitor cells to respond to Atoh1 are two additional genes, Sox4 and Sox11, that change the state of these cells.

In adult mice with damaged sensory cells in the inner ear, high levels of Sox4 and Sox11 activity increased the percentage of vestibular supporting cells that converted into sensory receptor cells - from 6 percent to 40 percent. "We're excited to continue exploring the mechanisms by which cells in the inner ear gain the ability to differentiate as sensory cells during development and how these can be used to promote the recovery of sensory hearing cells in the mature inner ear."

One important way that genes are shut off or "silenced" involves chemical compounds called methyl groups that bind to DNA and make it inaccessible. When the DNA that instructs a cell to become a sensory hearing cell is methylated, the cell cannot access these instructions. DNA methylation silences genes that promote conversion into sensory hearing cells, including the gene Atoh1 that is known to be a master regulator of inner ear development.

Researchers tested the extent of gene silencing in supporting cells from a chronically deafened mouse. They found that gene silencing was partially reversed, meaning that the supporting cells had the capacity to respond to signals to transform into sensory hearing cells. This finding has important implications: the loss of sensory hearing cells itself might partially reverse gene silencing in supporting cells in chronically deaf individuals. If so, the supporting cells of chronically deaf individuals might already be naturally primed to convert into sensory hearing cells.

SoxC transcription factors shape the epigenetic landscape to establish competence for sensory differentiation in the mammalian organ of Corti

Understanding the molecular basis of competence acquisition by the lineage-specific progenitor cells provides insights into tissue development and regeneration. The sensory epithelium of the inner ear represents a convenient model to study this process, as only two cell types - the mechanosensory hair cells and their associated supporting cells - are specified from a single pool of progenitors in this lineage. In the present manuscript, we uncover some of the mechanisms by which competence for mechanosensory receptor differentiation is acquired in the early organ of Corti progenitor cells. Specifically, we show that the two SoxC family members, Sox 4 and Sox11, establish a permissive chromatin landscape that allows the hair cell gene regulatory network to be activated upon differentiation cues.

DNA methylation in the mouse cochlea promotes maturation of supporting cells and contributes to the failure of hair cell regeneration

Age-related hearing loss can significantly impact quality of life. One potential approach to restore hearing is to regenerate mechanosensory hair cells responsible for detecting sound by the conversion of neighboring supporting cells into new hair cells. However, mammalian supporting cells can only transdifferentiate during embryonic and early postnatal development, and this ability is lost before the onset of hearing. We show that supporting cells accumulate DNA methylation, a form of epigenetic silencing, to permanently shut off the hair cell gene program required for successful transdifferentiation. Blocking ten-eleven translocation (TET) enzyme activity extends the window in which transdifferentiation can occur. Moreover, the loss of hair cells by deafening partially reverses DNA methylation in supporting cells, suggesting one avenue for therapeutic intervention.

Autophagy is the name given to a collection of processes responsible for recycling damaged and worn proteins and cell structures. Increased autophagy is a feature of the cellular response to various forms of stress. Many ways of adjusting metabolism to extend life span in short-lived species result in improved autophagy. Is improved autophagy also important in the much larger differences in life span observed between species, however? This is an interesting question. Therapeutic enhancement of autophagy, such as via mTOR inhibitors like rapamycin, or via various forms of calorie restriction mimetic drug, so far seems like an uninspiring path to only marginal gains in health and life span in longer-lived mammals. Might there be other, better ways to adjust the operation of autophagy that could be discovered by comparing mechanisms between mammalian species with widely divergent life spans?

Lifespan extension has independently evolved several times during mammalian evolution, leading to the emergence of a group of long-lived animals. Though the mammalian/mechanistic target of rapamycin (mTOR) signaling pathway is shown as a central regulator of lifespan and aging, the underlying influence of mTOR pathway on the evolution of lifespan in mammals is not well understood. Here, we performed evolution analyses of 72 genes involved in the mTOR network across 48 mammals to explore the underlying mechanism of lifespan extension.

In our study, autophagy related genes were identified to be under positive selection (PRKCB, WDR24, NPRL3 and LAMTOR2) or convergent (ATP6V1H and SESN2) in long-lived species, or associated with maximum life span (LAMTOR4), suggesting that enhanced autophagy might be a potential mechanism for mammals to extend lifespan. Moreover, eight genes with evolutionary signals identified in long-lived species were cancer related genes, six of them were also associated with aging, suggesting that regulation of cancer and aging may be another important mechanism for extending lifespan. In conclusion, we identified 20 genes with significant evolutionary signals unique to long-lived species, which provided new insight into the lifespan extension of mammals and might bring new strategies to extend human lifespan.

Link: https://doi.org/10.1186/s12864-023-09554-4

In this age of excess calories, in which a large proportion of the population is significantly overweight, research into lipid metabolism in the context of aging tends overlap with research into lipid metabolism in the context of obesity. People of normal weight still undergo complex changes in lipid metabolism and lipid transport throughout the body with age, however. These lead to prominent, important issues such as atherosclerosis, localized excesses of cholesterol and associated lesions in the arterial walls, for example. Looking at these conditions through the lens of lipid metabolism is looking at just one part of a complex situation, of course. Different systems interact to produce the dysfunctions of aging, and lipid metabolism interacts with changes in gene expression, mitochondrial dysfunction, rising levels of chronic inflammation and oxidative stress, and so forth.

Lipid metabolism plays crucial roles in cellular processes such as hormone synthesis, energy production, and fat storage. Older adults are at risk of the dysregulation of lipid metabolism, which is associated with progressive declines in the physiological function of various organs. With advancing age, digestion and absorption commonly change, thereby resulting in decreased nutrient uptake. However, in the elderly population, the accumulation of excess fat becomes more pronounced due to a decline in the body's capacity to utilize lipids effectively. This is characterized by enhanced adipocyte synthesis and reduced breakdown, along with diminished peripheral tissue utilization capacity.

Lipid metabolism disorder is one of the key pathogenic factors for the occurrence and development of a series of lipid-related chronic diseases. In general, lipid-related diseases include cardiovascular disease, type 2 diabetes, non-alcoholic fatty liver disease, and obesity, which seriously threaten public health. Given that changes in lipid metabolism occur in healthy older adults, it is important to note that these changes may contribute to pathological alterations. Therefore, understanding the role of lipid metabolism in the development of these diseases may provide new insights into their underlying mechanisms and facilitate the development of effective treatments and prevention for the elderly

Link: https://doi.org/10.3390/nu15153433

Researchers are increasingly focusing on the role of the central nervous system innate immune cells known as microglia in the development of neurodegenerative disease. Primarily, this is thought to be a matter of immune cells entering a more inflammatory state, whether that is driven by cellular senescence, activation by damage-associated molecular patterns such as mislocalized mitochondrial DNA, or reaction to persistent infection. Clearing at least some of these inflammatory microglia, such as via the use of senolytic drugs that can pass the blood-brain barrier to force senescent microglia into programmed cell death, has been shown to reduce markers of pathology in mouse models of Alzheimer's disease. The same is true of methods that clear all microglia.

In today's open access paper, researchers classify transcriptomic patterns of microglial state to suggest that it isn't just inflammatory cells, but there are also other forms of dysfunction in microglia that are distinct to the Alzheimer's brain. This is intriguing, but note that the data doesn't tell us whether any specific grouping of immune cell behaviors associated with Alzheimer's is relevant to the creation of the disease state, versus being a side-effect of the disease state, or even the degree to which it contributes to pathology, if it does contribute. This is ever the challenge in age-related diseases; there are many identifiable changes in biochemistry, and considerable difficulty in determining which are important.

Human microglia show unique transcriptional changes in Alzheimer's disease

Microglia, the innate immune cells of the brain, influence Alzheimer's disease (AD) progression and are potential therapeutic targets. However, microglia exhibit diverse functions, the regulation of which is not fully understood, complicating therapeutics development. To better define the transcriptomic phenotypes and gene regulatory networks associated with AD, we enriched for microglia nuclei from 12 AD and 10 control human dorsolateral prefrontal cortices (7 males and 15 females, all 60 years or older) before single-nucleus RNA sequencing. Here we describe both established and previously unrecognized microglial molecular phenotypes, the inferred gene networks driving observed transcriptomic change, and apply trajectory analysis to reveal the putative relationships between microglial phenotypes.

This study identified 10 distinct microglia clusters from aged human brain. These included previously described homeostatic, senescent, and inflammatory microglia transcriptional phenotypes as well as additional clusters of transcriptional specification, which may give insight into AD pathogenesis, providing a platform for hypothesis generation. We describe the diversity of microglia clusters with endolysosomal gene signatures, one of which is enriched with nucleic acid recognition and interferon regulation genes. Inferred gene networks predict that individual clusters are driven by distinct transcription factors, lending further support for the functional diversity of clusters. Using trajectory inference analysis, we observed transitions in microglia phenotypes and predicted relationships that can be tested experimentally. AD cases were distinguished by the emergence of a subcluster expressing homeostatic genes that was characterized by altered transcription of genes involved in calcium activation, response to injury, and motility pathways.

Among the nuclei meeting criteria for a microglia transcriptomic signature, an 'aging signature' was observed in all clusters in this study, consistent with our older age cohort. Inflammaging may not only confound interpretations of gene expression profiles attributable to AD but may also contribute to the disease mechanisms hypothesized to drive AD. Additional studies exploring differences between younger controls and early-onset AD may also help to explore the aging, inflammaging, and AD-specific signatures.

The smaller organs of the body tend to receive less attention from scientists in the field of aging research. There is a lot of ground to cover and only so many research groups. Attention is first given to better studied tissues with proven, direct connections to better studied diseases and causes of mortality. This includes the larger organs such as heart, lungs, liver, and so forth. Chemical factories and cell factories such as the adrenal gland and thymus are clearly important in aging, but indirect effects spread across many different age-related conditions are, it seems, more difficult to study and more difficult to obtain funding to study. Still, while much remains to be filled in at the detail level, much is known of the aging of smaller organs like the adrenal gland. The open access paper here is an interesting read.

The adrenal gland is an essential endocrine organ that is situated above the kidneys and functions to produce essential steroid hormones including mineralocorticoids, glucocorticoids, and androgens. The adrenal is composed of two compartments of distinct embryological origin: the cortex and the medulla, which are surrounded by an outer mesenchymal capsule layer. In this review, we will focus on age-related changes specifically within the adrenal cortex, which is subdivided into three functionally and histologically distinct zones.

The outermost zone, the zona glomerulosa (zG), is responsible for the production of mineralocorticoids that regulate salt and water balance. The intermediate zone, the zona fasciculata (zF), produces glucocorticoids in response to adrenocorticotropin (ACTH) under the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Finally, the innermost zone, the zona reticularis (zR), produces adrenal androgens, including dehydroepiandrosterone (DHEA) and its sulfated form, DHEA-S. As we age, the adrenal gland undergoes changes that disrupt its ability to maintain homeostatic hormone levels, which can significantly affect overall health and well-being. Thus, researching adrenal aging and interventions to delay the onset of age-associated adrenal pathologies has the potential to help increase endocrine function and improve health span.

Studying the effects of aging on the normal adrenal gland is a challenging task. First, information on "healthy" aged human adrenal glands in the literature is scarce. While rodents are the most commonly used model organism to investigate these phenomena, standard laboratory strains lack a functional zR due to silencing of Cyp17a1 after birth, which limits our use of these models to study adrenal androgens. Moreover, the mouse adrenal cortex contains an additional X-zone. The functional significance of the X-zone is incompletely understood.

With increasing age, features such as reduced adrenal cortex size, altered zonation, and increased myeloid immune cell infiltration substantially alter the structure and function of the adrenal cortex. Many of these hallmark features of adrenal cortex aging occur both in males and females, yet are more enhanced in males. Hormonally, a substantial reduction in adrenal androgens is a key feature of aging, which is accompanied by modest changes in aldosterone and cortisol. These hormonal changes are associated with various pathological consequences including impaired immune responses, decreased bone health, and accelerated age-related diseases.

One of the most notable changes with adrenal aging is the increased incidence of adrenal tumors, which is sex dimorphic with a higher prevalence in females. Increased adrenal tumorigenesis with age is likely driven by both an increase in genetic mutations as well as remodeling of the tissue microenvironment. Novel antiaging strategies offer a promising avenue to mitigate adrenal aging and alleviate age-associated pathologies, including adrenal tumors.

Link: https://doi.org/10.1210/jendso/bvad097

This open access review paper discusses what is known of the role of the mitochondrial permeability transition pore in the age-related decrease of mitochondrial membrane potential. This measure is a lens through which one can view the growing dysfunction of mitochondria with advancing age. Every cell contains hundreds of mitochondria, producing chemical energy store molecules, ATP, to power cellular processes. Reduced rates of ATP production lead to cell and tissue dysfunction. This is thought to be an important contribution to degenerative aging, though exactly how it arises from causative mechanisms, such as mitochondrial DNA damage and whatever leads to reduced expression of nuclear proteins necessary to mitochondrial function, remains to be fully determined.

It is widely reported that the mitochondrial membrane potential, ∆Ψm, is reduced in aging animals. It was recently suggested that the lower ∆Ψm in aged animals modulates mitochondrial bioenergetics and that this effect is a major cause of aging since artificially increased ∆Ψm in C. elegans increased lifespan. Here, I critically review studies that reported reduction in ∆Ψm in aged animals, including worms, and conclude that many of these observations are best interpreted as evidence that the fraction of depolarized mitochondria is increased in aged cells because of the enhanced activation of the mitochondrial permeability transition pore, mPTP.

Activation of the voltage-gated mPTP depolarizes the mitochondria, inhibits oxidative phosphorylation, releases large amounts of calcium and reactive oxygen species (ROS), and depletes cellular NAD+, thus accelerating degenerative diseases and aging. Since the inhibition of mPTP was shown to restore ∆Ψm and to retard aging, the reported lifespan extension by artificially generated ∆Ψm in C. elegans is best explained by inhibition of the voltage-gated mPTP. Similarly, the reported activation of the mitochondrial unfolded protein response by reduction in ∆Ψm and the reported preservation of ∆Ψm in dietary restriction treatment in C. elegans are best explained as resulting from activation or inhibition of the voltage-gated mPTP, respectively.

Link: https://doi.org/10.3390/ijms241512295

Why would vision impairment correlate with risk of dementia? The retina is an extension of the central nervous system, so one might think that similar processes of aging and neurodegeneration contribute to both loss of visual capacity and loss of cognitive capacity. But it might also be the case that in the brain, as for muscles, there is a degree of "use it or lose it" taking place over the course of later life. Without stimuli, in other words, the aging brain declines more rapidly. Most of the evidence for an association between visual impairment and cognitive impairment in older individuals doesn't allow us to determine which of these options is the dominant mechanism, however.

Recently, researchers found that one can look at people who did or did not have cataract surgery in order to infer the effects of visual impairment on cognitive function. Mechanisms driving cataract formation should have little in common with mechanisms driving cognitive impairment. Researchers found that cataract induced visual impairment does correlate with cognitive impairment, and removal of cataracts prevents this later loss of cognitive function. This provides strong support for the role of visual stimuli in slowing the pace of brain aging.

Study shows dementia more common in older adults with vision issues

In a sample of nearly 3,000 older adults who took vision tests and cognitive tests during home visits, the risk of dementia was much higher among those with eyesight problems - including those who weren't able to see well even when they were wearing their usual eyeglasses or contact lenses. All of the older adults in the study were over the age of 71, with an average age of 77. They had their up-close and distance vision, and their ability to see letters that didn't contrast strongly with their background, tested by a visiting team member using a digital tablet. They also took tests of memory and thinking ability, and provided health information including any existing diagnosis of Alzheimer's disease or another form of dementia.

Just over 12% of the whole group had dementia. But that percentage was higher - nearly 22% - among those who had impaired vision for seeing up close. In addition, one-third (33%) of those with moderate or severe distance vision impairment, including those who were blind, had signs of dementia. So did 26% of those who had trouble seeing letters that didn't contrast strongly against a background. Even among those with a mild distance vision issue, 19% had dementia. After the researchers adjusted for other differences in health status and personal characteristics, people with moderate to severe distance vision issues were 72% more likely than those with no vision issues to have dementia.

Objectively Measured Visual Impairment and Dementia Prevalence in Older Adults in the US

Estimates of the association between visual impairment (VI) and dementia in the US population are based on self-reported survey data or measures of visual function that are at least 15 years old. Older adults are at high risk of VI and dementia so there is a need for up-to-date national estimates based on objective assessments. This secondary analysis of the 2021 National Health and Aging Trends Study (NHATS), a population-based, nationally representative panel study, included 3,817 respondents 71 years and older.

The weighted prevalence of dementia was 12.3% and increased with near VI (21.5%), distance VI (mild: 19.1%; moderate, severe, or blind: 32.9%), and contrast sensitivity (CS) impairment (25.9%). Dementia prevalence was higher among participants with near VI and CS impairment than those without (near VI prevalence ratio: 1.40; CS impairment prevalence ratio: 1.31) and among participants with moderate to severe distance VI or blindness (prevalence ratio: 1.72) after adjustment for covariates.

Thus in this survey study, all types of objectively measured VI were associated with a higher dementia prevalence. As most VI is preventable, prioritizing vision health may be important for optimizing cognitive function.

One interesting question in the development of new epigenetic clocks to measure biological age, particularly now that a large consortium of researchers has published a universal mammalian clock, is how one demonstrates that a new clock is in some way useful enough or interesting enough to spend time on. There are, after all, many published clocks at this point, and we might expect that the research community will attempt to standardize on the new universal clock. Why use another novel clock? One answer might be that the clock is optimized to give a large signal under a particular set of circumstances. Hence we arrive at studies like the one noted here, in which researchers demonstrate that their novel clock performs in a potentially useful way when assessing the results of plasma transfer from young individuals to old individuals between mammalian species.

Young blood plasma is known to confer beneficial effects on various organs in mice and rats. However, it was not known whether plasma from young pigs rejuvenates old rat tissues at the epigenetic level; whether it alters the epigenetic clock, which is a highly accurate molecular biomarker of aging. To address this question, we developed and validated six different epigenetic clocks for rat tissues that are based on DNA methylation values derived from n=613 tissue samples. As indicated by their respective names, the rat pan-tissue clock can be applied to DNA methylation profiles from all rat tissues, while the rat brain-, liver-, and blood clocks apply to the corresponding tissue types. We also developed two epigenetic clocks that apply to both human and rat tissues by adding n=1366 human tissue samples to the training data.

We employed these six rat clocks to investigate the rejuvenation effects of a porcine plasma fraction treatment in different rat tissues. The treatment more than halved the epigenetic ages of blood, heart, and liver tissue. A less pronounced, but statistically significant, rejuvenation effect could be observed in the hypothalamus. The treatment was accompanied by progressive improvement in the function of these organs as ascertained through numerous biochemical/physiological biomarkers and behavioral responses to assess cognitive functions. An immunoglobulin G (IgG) N-glycosylation pattern shift from pro-to anti-inflammatory also indicated reversal of glycan aging. Overall, this study demonstrates that a young porcine plasma-derived treatment markedly reverses aging in rats according to epigenetic clocks, IgG glycans, and other biomarkers of aging.

Link: https://doi.org/10.1101/2023.08.06.552148

Many of the processes taking place during tissue growth and maintenance, such as the growth of blood vessels, require correct timing in changes of behavior in the participating cells. If that timing is off, the quality of the process suffers. Disruption of complex systems is a characteristic effect of degenerative aging, and researchers here measure that outcome in the context of muscle regeneration. The shifts in gene expression that occur in different cell populations during that process become misaligned, and thus regenerative capacity suffers. Similar issues are likely taking place at a smaller scale, but more widely distributed in incidence, during the ongoing maintenance of muscle tissue, and in the response to exercise.

Skeletal muscle function and regenerative capacity decline during aging, yet factors driving these changes are incompletely understood. Muscle regeneration requires temporally coordinated transcriptional programs to drive myogenic stem cells to activate, proliferate, fuse to form myofibers, and to mature as myonuclei, restoring muscle function after injury. We assessed global changes in myogenic transcription programs distinguishing muscle regeneration in aged mice from young mice by comparing pseudotime trajectories from single-nucleus RNA sequencing of myogenic nuclei.

Aging-specific differences in coordinating myogenic transcription programs necessary for restoring muscle function occur following muscle injury, likely contributing to compromised regeneration in aged mice. Differences in pseudotime alignment of myogenic nuclei when comparing aged with young mice via dynamic time warping revealed pseudotemporal differences becoming progressively more severe as regeneration proceeds. Disruptions in timing of myogenic gene expression programs may contribute to incomplete skeletal muscle regeneration and declines in muscle function as organisms age.

Link: https://doi.org/10.1016/j.stemcr.2023.05.005

The body contains hundreds of different types of lipid molecules, participating in cellular metabolism in ways that are just as complex and relevant to health as the activities of other biomolecules. In the context of aging, this broad range of lipids are perhaps understudied in comparison to levels and roles of proteins and patterns of gene expression. The situation is much the same, however: researchers can readily and cost-effectively amass a vast amount of data, but the analysis of this data lags far behind the accumulation of ever more and ever larger omics databases. It is ever unclear as to whether any particular association is useful or relevant. Is it only a consequence of meaningful processes, a side-effect, something that causes no further significant issues, or does it actually cause pathology, directly or indirection, to a level that makes it worth trying to intervene?

When one has to ask that question of hundreds or thousands of different biomolecules, it begins to look more sensible to focus on known root causes of aging and intervene there. First intervene and evaluate the outcome, rather than first working to increase understanding of the fine details of aging. Doing both is of course the right choice given unlimited time and funding, but that is a luxury that none of us has, least of all scientific organizations. Further, when researchers intervene by, say, clearing senescent cells or improving mitochondrial function, and thereby improve health and extend life, then the resulting changes in specific lipid levels will tell us just as much about the relevance of that data as would a much longer exercise in studying people of varied ages undergoing aging without intervention.

The lipidomic correlates of epigenetic aging across the adult lifespan: A population-based study

Despite the intriguing connection between lipid metabolism and aging, it is still unknown whether and how inter-individual differences in lipid profiles contribute to different rates of biological aging in the general population. The heterogeneous chemical structure of lipids poses challenges for their accurate quantification, and until now only a few lipid species have been investigated in the context of human aging and age-related health outcomes. We investigated 14 complex lipid classes, covering 964 molecular species and 267 fatty acid composites, with biological aging. We found complex lipid species to be differently associated with different rates of biological aging. Higher levels of molecular species belonging to the neutral lipids (MAG, DAG, TAG), phospholipids (PE, PE(O), PE(P)), and sphingolipids (CER, DCER) classes were associated with accelerated biological aging, whereas higher levels of distinct other molecular species (i.e., LPC, HCER, and LCER) were associated with slower biological aging. CE, PC, and LPE molecular species with odd-numbered (i.e., 15 and 17) fatty acid tail lengths were associated with slower biological aging, yet even-numbered fatty acid tail lengths were associated with faster biological aging. Importantly, in silico pathway analysis revealed that lipids that were associated with biological aging estimators were mainly involved in known longevity and aging-related pathways, revealing their role as potential determinants of biological aging across the lifespan in the general population.

Very little work has explicitly assessed the value of LPC species as potential human blood-derived biomarkers of human aging. Circulating LPCs are generated by phospholipases A2 from the PC. The most abundant LPC in human plasma is 16:0, followed by 18:2, 18:0, 18:1, 20:4, and other minor species. Here we found that higher levels of 13 out of 19 LPC species exhibit a robust association with slower biological aging, suggesting that LPC species may contribute to healthy aging. Our findings expand on those from recent epidemiological studies, which assessed a limited number of LPC species, and reported low concentrations of certain circulating LPCs (i.e., 18:2 and/or 17:0) to be associated with several aging-related phenotypes and disorders, including memory impairment, gait speed decline, and incident myocardial infarction. Moreover, elevated LPC (18:1) levels have been reported in centenarians. Potential biological mechanisms through which LPCs could contribute to slower biological aging and less age-associated functional decline are anti-oxidative stress and anti-inflammatory responses.

The major phospholipids in eukaryotic biomembranes are phosphatidylcholine (PC), and phosphatidylethanolamine (PE), which were also quantified in our study. PC can be synthesized by a three-step methylation of PE. We found that higher levels of various PE species were related to accelerated biological aging across the lifespan, whereas higher levels of polyunsaturated PCs were associated with slower biological aging. Higher levels of species with fewer double bonds tended to be associated with accelerated biological aging. These findings are in line with previous studies that found associations between higher levels of saturated and monounsaturated PCs and increased risk of cardiovascular diseases and type 2 diabetes. Conversely, polyunsaturated PC species have been linked to longevity, which might be due to their antioxidative and cardioprotective properties. PE species, the second most abundant membrane phospholipids, have been identified as modulators of inflammation and apoptosis, yet little is known about the properties of specific PE species.

Higher TAG levels are linked to an increased risk of cardiovascular diseases and Alzheimer's disease. Small-scale lipidomic profiling in longevity studies also found lower levels of TAG species (including TAG 46:5, 47:5, 52:1, 54:7, 54:6, 56:6, 56:7, 57:2) to be associated with healthy aging. Our findings extend these previous reports by showing that 361 out of 519 TAG species across different chain lengths and double bonds were associated with accelerated biological aging. Few studies have investigated the association between other neutral lipids (including CE, MAG, and DAG) and longevity or healthy aging. We found that higher levels of DAG species or lower levels of CE species were related to an accelerated rate of biological aging, indicating that almost all neutral lipids could potentially influence longevity.

Researchers here report on their investigation of a problem T cell subpopulation in the context of atherosclerosis and the inflammation that is characteristic of that condition. These T cells appear to be maladapted forms of regulatory T cell, gone rogue and producing harmful inflammatory signaling in response to the environment of an atherosclerotic plaque. There is considerable interest in finding approaches to modulate immune activity to dampen the pace at which atherosclerotic plaques come into being and grow, though much of this centers on the role of the innate immune cells known as macrophages. Once inflammation gets underway, however, any and all immune cells might be drawn in to become involved in ways that contribute to pathology, as this research illustrates.

T regulatory cells (Tregs) have the important job of stopping the other T cells from releasing too many inflammatory, or cytotoxic, molecules as they fight infection. Some T cells contribute to atherosclerosis by attacking a molecule called apolipoprotein B (APOB), the main component in the "bad" cholesterol that builds up into dangerous plaques in the arteries. These T cells ramp up their attacks as atherosclerosis worsens, likely adding to inflammation in the arteries. The weird thing is that these T cells look a lot like the normally helpful Tregs. A new study reveals the true identities of these cells: they are exTregs. ExTregs are like zombie Tregs. They've gone through a genetic "deprogramming" and lost their ability to help regulate inflammation. Scientists don't know exactly why exTregs develop, but the phenomenon may happen when the body misses the mark in an attempt to adapt to chronic disease.

Researchers tagged both Tregs and harmful exTregs in a mouse model prone to atherosclerosis. These fluorescent red and green tags glowed when Tregs were functioning normally. A switch from green and red to only red revealed exTreg development in real time. The team then took organ samples from the mice and used a technique called flow cytometry to detect the green and red tags to sort the Tregs from the exTregs. The researchers used techniques called bulk RNA sequencing to learn more about these cells. The sequencing highlighted vast differences in gene expression and showed that exTregs make a distinct set of genes that sets them apart from Tregs.

Next, the researchers used the exTreg markers found in mice to transpose them to a single cell RNA sequencing performed on human blood samples. Through this process, they successfully identified biomarkers for human exTregs. The researchers found that the exTreg biomarkers they'd seen in mouse samples were also relevant for human exTregs. They discovered that exTregs from humans with atherosclerosis are potentially more potent. Going forward, the researchers hope to use exTreg biomarkers to detect and study the roles of these cells in other chronic health conditions, such as in patients with autoimmune diseases. Resesearchers also interested in studying samples from the same individual patients taken over time. How might exTreg biomarkers change as atherosclerosis changes? Would they see decreased signs of exTregs if a patient was put on an effective medication?

Link: https://www.lji.org/news-events/news/post/when-regulatory-t-cells-go-bad/

Transthyretin is one of the few proteins in the body that can misfold in a way that encourages other copies of the protein to also misfold, forming solid aggregates called amyloid that disrupt tissue structure and function. The resulting condition, transthyretin amyloidosis, clogs up cardiac tissue and thereby contributes to a fraction of all heart failure cases. It is thought to be a major cause of mortality in supercentenarians. Approved therapies targeting a more aggressive form of the condition resulting from a mutated transthyretin gene will not be useful against the much more common version of the condition, as they target the mutated form of the protein. New therapies in development might prove to be useful, however. Everyone accumulates at least some degree of this amyloid in old age, so it is a part of the field worth keeping an eye on.

While medical science has prodigiously slashed death from atherosclerosis, very little progress has been made against other kinds of "heart disease." Deaths from pulmonary heart disease, heart valve disease, and notably disordered heartbeat (arrhythmia) have remained at the same stubborn levels for decades. Worse yet: after years of making at least incremental progress against heart failure and hypertensive heart disease, the number of people suffering from these degenerative heart conditions is now rising again. In the face of this rising threat, the really good news at the center of this post is that the biotech company Neurimmune and their pharma partner AstraZeneca have just run an early-stage trial of a new AmyloSENS therapy that directly removes a malformed protein from patients' hearts. The study was small, but it found no signal for danger, and the data suggest that the antibody successfully pried its target loose from the patients' heart tissue - and that their hearts beat more freely as a result.

Cardiac amyloids are chains of malformed proteins that have twisted out of shape, bound together in chains, and worming its way into the gaps between the heart muscle cells. These deposits then physically impede the heart muscle as it attempts to expand and contract to keep the precious blood of life flowing to our tissues. The most common kind of amyloid afflicting the aging heart is composed of malformed transthyretin (TTR). Mutations in the TTR gene cause a tiny fraction of all the cases of life-threatening cardiac amyloid heart disease. But even the standard-issue TTR protein is inherently unstable and occasionally contorts out of its proper conformation, with the result that TTR cardiac amyloid accumulates in all of us progressively with age. The vast majority of cardiac amyloid disease is caused by the accumulation of this molecular aging damage, which impairs the function of our hearts, even in people who are technically below the threshold at which it is diagnosed as a "disease."

Scientists recently reported the results of a phase 1 clinical trial of NI006, an antibody designed to latch on to TTR amyloid and pry it loose from the heart. This is a critical difference between NI006 and other TTR amyloid treatments that are either in use or currently in development. Previous therapies have been designed to merely slow down the rate at which new cardiac amyloid accumulates, either by partially stabilizing the rattletrap TTR protein or by throttling down the body's ability to produce the protein in the first place. By contrast, NI006 is a true "damage-repair" therapy: if it works, it could prevent and even reverse cardiac amyloid by directly removing existing deposits of mangled TTR from the heart. We can't fully hang our hats on the results of a study with so few patients - but all the results they did see were encouraging. In just the initial four months of treatment, imaging scans of volunteers who got real NI006 showed that much of the amyloid that had invaded their heart muscles had been cleared out - and the amyloid continued to disappear as they continued to receive NI006 during the eight months of all-comers treatment.

By definition, Phase I trials are preliminary - but the Phase I trial for NNC6019 was even more tentative than that for NI006. This author guesses that the reason for this was budgetary constraints. NNC6019 was developed by immunizing mice with a short stretch of TTR protein that is normally shielded from the immune system through its appropriate folding, but which can be exposed when TTR has twisted out of its normal conformation. They then harvested the antibodies the mice produced in response to the normally-shielded fragment and screened them for properties that would make an antibody useful as an AmyloSENS therapy for TTR amyloidosis. With only seven subjects to fully evaluate and no placebo control group, we have to be careful not to cling too tightly to the results of this trial - but those results were quite positive. The seven subjects who had received all doses of NNC6019 suffered barely any worsening on the score of their neuropathy: an increase of 1.29 points, versus a typical 9.2-point exacerbation over a comparable time. And neuropathy didn't progress at all in the two subjects who were receiving only NNC6019 and no other anti-amyloid therapy.

Link: https://www.sens.org/set-heart-free-ttr-cardiac-amyloid/

Epigenetic modifications to the nuclear genome, such as the addition of methyl groups to CpG sites, known as DNA methylation, adjust the structure of double-stranded DNA. That structure determines which gene sequences are accessible to transcription machinery, the first step in producing proteins. Thus epigenetics drives gene expression, and gene expression drives the behavior of cells. It is a feedback loop between environment, cell behavior, and epigenetics. The pattern of epigenetic modifications changes constantly in response to circumstances, but some changes are characteristic of aging. When discovered, this led to the construction of the first epigenetic clocks to measure chronological age and then biological age.

More than a decade later, epigenetic clocks are still very much a work in progress, in the sense that it is not well understood as to how the fundamental mechanisms of aging connect to the methylation of specific CpG sites on the genome. It is presently impossible to say whether any given clock (epigenetic or otherwise) will accurately reflect the effects of a given intervention on future life span and risk of age-related disease. Clocks have also been tissue and species specific, at least until now. Researchers have now mined data from many different species in order to produce a cross-species clock that can be applied to all mammals.

Looking past that advance, it is perhaps more interesting to note that the researchers examining DNA methylation across hundreds of mammalian species found that methylation sites whose status changes with age are largely distinct from methylation sites where status correlates with species life span. This distinction between epigenetic mechanisms of individual longevity and epigenetic mechanisms of species longevity is reinforced by the work of other research groups examining omics data in multiple mammalian species. One hypothesis that we might take away from this is that there is a sizable untapped set of mechanisms that might be targeted to extend healthy life span. Given omics signatures from long-lived mammals that are associated with species life span rather than individual aging, one might perform screening to find novel classes of interventions that slow aging in shorter-lived mammals.

Global consortium creates large-scale, cross-species database and universal 'clock' to estimate age in all mammalian tissues

DNA methylation is a mechanism by which cells can control gene expression - turning genes on or off. In these studies, the researchers focused on DNA methylation differences across species at locations where the DNA sequence is generally the same. To study the effects of DNA methylation, the nearly 200 researchers - collectively known as the Mammalian Methylation Consortium - collected and analyzed methylation data from more than 15,000 animal tissue samples covering 348 mammalian species. They found that changes in methylation profiles closely parallel changes in genetics through evolution, demonstrating that there is an intertwined evolution of the genome and the epigenome that influences the biological characteristics and traits of different mammalian species.

Methylation, as evidenced by the epigenetic "marks" it leaves, bears a substantial correlation with maximum life span across mammalian species. Maximum life span of a species is associated with specific developmental processes, as suggested by the involvement of certain genes and genetic transcription factors. Cytosines whose methylation levels correlate with maximum life span differ from those that change with chronological age, suggesting that molecular pathways pertaining to average life span within a species are distinct from those determining the species' maximum life span.

Researchers used a subset of the database to study the methylation profiles of 185 species of mammals. Identifying changes in methylation levels that occur with age across all mammals, they developed a "universal pan-mammalian clock," a mathematical formula that can accurately estimate age in all mammalian species.

DNA methylation networks underlying mammalian traits

Comparative epigenomics is an emerging field that combines epigenetic signatures with phylogenetic relationships to elucidate species characteristics such as maximum life span. For this study, we generated cytosine DNA methylation (DNAm) profiles (n = 15,456) from 348 mammalian species using a methylation array platform that targets highly conserved cytosines. We first tested whether DNAm levels in highly conserved cytosines captured phylogenetic relationships among species. We constructed phyloepigenetic trees that paralleled the traditional phylogeny. To avoid potential confounding by different tissue types, we generated tissue-specific phyloepigenetic trees. The high phyloepigenetic-phylogenetic congruence is due to differences in methylation levels and is not confounded by sequence conservation.

We then interrogated the extent to which DNA methylation associates with specific biological traits. Both the epigenome-wide association analysis (EWAS) and eigengene-based analysis identified methylation signatures of maximum life span, and most of these were independent of aging, presumably set at birth, and could be stable predictors of life span at any point in life. Several CpGs that are more highly methylated in long-lived species are located near HOXL subclass homeoboxes and other genes that play a role in morphogenesis and development. Some of these life span-related CpGs are located next to genes that are also implicated in our analysis of upstream regulators (e.g., ASCL1 and SMAD6). CpGs with methylation levels that are inversely related to life span are enriched in transcriptional start site and promoter flanking associated chromatin states. Genes located in chromatin state TSS1 are constitutively active and enriched for nucleic acid metabolic processes. This suggests that long-living species evolved mechanisms that maintain low methylation levels in these chromatin states that would favor higher expression levels of genes essential for an organism's survival.

The immune system is very complex, made up of many different populations of specialized cells. Behaviors, surface features, and activities can be highly tissue specific. One can label a broad category of innate immune cells as macrophages, sharing common features, but even within a single tissue that class of macrophages can then be further subdivided by location and distinguishing features and actions. The ongoing discovery of important subpopulations of immune cells is a feature of research into inflammatory diseases. Here, researchers discuss the behavior of macrophages in Parkinson's disease, a condition in which chronic inflammation is thought to play an important role. The researchers provide evidence to suggest that it is macrophages bordering the brain, rather than the analogous microglia in the brain, that are producing disruptive, constant inflammatory signaling in response to the presence of the characteristic α-synuclein aggregation that is a biomarker of the condition.

Parkinson disease (PD) is the most common neurodegenerative movement disorder, characterized pathologically by the abnormal accumulation of alpha-synuclein (α-syn) in Lewy bodies and neurites and resulting in the loss of dopamine-producing neurons in the substantia nigra pars compacta (SNpc). Due to activation of tissue-resident macrophages and the infiltration of both innate and adaptive immune cells, neuroinflammatory mechanisms have been strongly implicated in the neurodegeneration associated with α-syn accumulation.

Central nervous system (CNS) resident macrophages (CRMs) may be key antigen-presenting cells that orchestrate neuroinflammatory and neurodegenerative responses. CRMs include microglia in the parenchyma and border-associated macrophages (BAMs) that reside in the choroid plexus, dural and subdural meninges, and are adjacent to the vasculature within the perivascular space. It is important to note that BAMs have also been referred to as CNS-associated macrophages (CAMs) to highlight their anatomical location.

We found that border-associated macrophages (BAMs) play an essential role in mediating α-synuclein related neuroinflammation due to their unique role as the antigen-presenting cells necessary to initiate a CD4 T cell response whereas the loss of MHCII antigen presentation on microglia had no effect on neuroinflammation. Furthermore, α-synuclein expression led to an expansion in border-associated macrophage numbers and a unique damage-associated activation state. Through a combinatorial approach of single-cell RNA sequencing and depletion experiments, we found that border-associated macrophages played an essential role in immune cell recruitment, infiltration, and antigen presentation.

Furthermore, border-associated macrophages were identified in post-mortem PD brain in close proximity to T cells. These results point to a role for border-associated macrophages in mediating the pathogenesis of Parkinson disease through their role in the orchestration of the α-synuclein-mediated neuroinflammatory response.

Link: https://doi.org/10.1038/s41467-023-39060-w

Overly reactive, senescent, and otherwise inflammatory microglia in the brain are implicated in the development of neurodegenerative conditions. Chronic inflammation in brain tissue disrupts neural function in numerous ways. Thus why not clear or replace microglia? There are established ways to remove these cells, allowing them to regenerative over a few weeks, but these have not yet made their way to human trials for neurodegenerative conditions, despite interesting results in animal models. The replacement of microglia via transplantation of hematopoietic cells is at a similar stage, wherein there are interesting results in animal models of various neurodegenerative conditions.

For a long time, reactive microglia have been considered a consequence of Alzheimer's disease (AD) pathology; however, they are now regarded as potentially playing a role in disease progression and maybe initiation. Sustained microglia inflammation has been identified as a contributor to AD pathogenesis, as the release of inflammatory cytokines, chemokines, and complement proteins increases amyloid-β (Aβ) production. In addition, microglia have been shown to be involved in the clearance of Aβ plaque, which is impaired in AD due to mutations in microglia-related genes, including P2ry12, Apoe, and Trem2. Furthermore, with impaired microglia clearance, debris and other byproducts are diverted for clearance to other brain cells, such as endothelial cells, which do not proliferate efficiently and exhibit similar dysfunction, resulting in cell death and impaired blood flow.

Thus, targeting microglia offers a potential therapeutic opportunity for AD. We have previously demonstrated that a single systemic transplant of wild-type hematopoietic stem and progenitor cells (HSPCs) led to long-term rescue in both mouse models for cystinosis, a lysosomal storage disease, and Friedreich's ataxia, a neurodegenerative disease. In Friedreich's ataxia mouse model, transplanted HSPCs engrafted and differentiated into microglia in the brain and spinal cord, and into macrophages in the dorsal root ganglions (DRGs), resulting in the preservation of the neurons and locomotor function. Efficient replacement of microglia in the central nervous system (CNS) by bone marrow stem cell transplantation has previously been described. Therefore, because microglia may play an important role in AD, we hypothesized that wild-type (WT) HSPC transplantation could result in the generation of healthy microglia that may have a beneficial impact on AD.

Our study showed that single systemic wild-type (WT) hematopoietic stem and progenitor cell (HSPC) transplantation rescued the AD phenotype in 5xFAD mice and that transplantation may prevent microglia activation. Indeed, complete prevention of memory loss and neurocognitive impairment and decrease of β-amyloid plaques in the hippocampus and cortex were observed in the WT HSPC-transplanted 5xFAD mice compared with untreated 5xFAD mice and with mice transplanted with 5xFAD HSPCs. Neuroinflammation was also significantly reduced. Transcriptomic analysis revealed a significant decrease in gene expression related to "disease-associated microglia" in the cortex and "neurodegeneration-associated endothelial cells" in the hippocampus of the WT HSPC-transplanted 5xFAD mice compared with diseased controls. This work shows that HSPC transplant has the potential to prevent AD-associated complications and represents a promising therapeutic avenue for this disease.

Link: https://doi.org/10.1016/j.celrep.2023.112956

Remnant cholesterol refers to circulating cholesterol in the bloodstream that is not attached to LDL transport particles coming from the liver or HDL transport particles going to the liver. The remnant is attached to some mix of VLDL and IDL particles that serve much the same purpose as LDL particles, or incorporated into much larger chylomicron transporters that carry dietary lipids from the intestines throughout the body.

Researchers have noted that remnant cholesterol appears to contribute to cardiovascular risk, speeding the progression of atherosclerosis and increasing the risk of stroke and heart attack. It is perhaps the case that remnant cholesterol increases risk to a greater degree than LDL-cholesterol levels. Certainly, remnant cholesterol is higher in people who are overweight or obese, as one might expect given that chylomicron-encapsulated dietary cholesterol contents make up a sizable fraction of remnant cholesterol.

One doesn't have to propose any great new understanding of how atherosclerotic lesions form to expect remnant cholesterol to contribute to risk. A lesion forms after a tipping point is reached at which localized excess cholesterol overwhelms the macrophage cells responsible for cleaning it up and handing it off to HDL particles. More cholesterol in circulation shifts that tipping point by stressing the cleanup capacity of these macrophages. Greater chronic inflammation shifts the tipping point by making macrophages less able to clean up cholesterol. Both of those points tend to be the case for those who are overweight or obese in addition to being old. We can also talk about the role of toxic oxidized cholesterol and oxidized transport particles such as LDL in disrupting macrophage function, but the generation of these oxidized molecules scales with the overall amount of cholesterol as well, all other factors being equal.

Today's open access paper notes an interesting correlation between remnant cholesterol and frailty. Here is becomes more speculative as to what the mechanism might be to link raised cholesterol and frailty syndrome. The contribution of inflammation arising from oxidized cholesterol and transport particles is one possibility. The researchers here focus on a high fat diet as a driving factor in increasing both frailty and remnant cholesterol (via chylomicrons), but the question still remains as to what exactly is going on as a consequence of increased dietary cholesterol that might lead to the signs of frailty, including loss of muscle mass and strength, impaired immunity, and so forth.

Association of remnant cholesterol with frailty: findings from observational and Mendelian randomization analyses

Recent insights suggest that remnant cholesterol (RC) plays a role in cellular senescence, yet its specific contribution to frailty remains indeterminate. Through the integration of observational and Mendelian randomization (MR) studies, this research explores the impact of elevated serum RC levels on frailty susceptibility. The observational study included 11,838 participants from the National Health and Nutrition Examination Survey. To circumvent observational study limitations, a two-sample MR analysis was conducted using the inverse-variance weighted method, leveraging genome-wide association studies (GWAS) data.

After adjusting for potential confounding variables, the observational study identified a significant association between high serum RC levels and frailty in middle-aged and older adults (odds ratio [OR] = 1.67), exhibiting a non-linear dose-response correlation. This association persisted after propensity score matching (OR = 1.53). The MR study echoed these results, demonstrating a causal association of RC with the frailty index (β = 0.059), consistent with the observational findings (β = 0.017).

Despite a lack of direct epidemiological evidence linking serum circulating RC levels to frailty, recent MR studies have spotlighted the influential role of elevated LDL-C levels in inducing frailty. Substantial increases in RC levels have been documented in adults consuming high-fat diets. The same diets administered to mice resulted in a heightened frailty level, while simultaneously diminishing the anti-frailty benefits of intermittent fasting. Consequently, this indirect evidence suggests a connection between higher RC levels and a heightened frailty risk, which this study substantiates.

Although increased serum RC levels are regarded as a potent independent risk factor for CVD, this analysis reveals that the association between serum RC levels and frailty persists, even after adjusting for CVD and T2DM. This suggests that the contribution of RC to frailty risk is not exclusively attributed to a higher susceptibility to CVD. Furthermore, the results from our epidemiological studies and multivariable MR confirm that this association remains significant, regardless of total cholesterol or LDL-cholesterol levels.

It is clear that new ways of analyzing large amounts of data via machine learning will be used extensively in the near future in the field of aging research, employed to speed up the process of finding new drug targets and small molecules that might alter metabolism to slightly slow aging. This will no doubt be a sizable component of the longevity industry, if we judge the near future by the present distribution of companies and efforts. I can't say that I think that is likely to produce sizable benefits in aging humans, however, when compared to the rational design of therapies to specifically repair underlying causes of aging.

Recently, there has been a growing interest in the development of pharmacological interventions targeting ageing, as well as in the use of machine learning for analysing ageing-related data. In this work, we use machine learning methods to analyse data from DrugAge, a database of chemical compounds (including drugs) modulating lifespan in model organisms. To this end, we created four types of datasets for predicting whether or not a compound extends the lifespan of C. elegans (the most frequent model organism in DrugAge), using four different types of predictive biological features, based on: compound-protein interactions, interactions between compounds and proteins encoded by ageing-related genes, and two types of terms annotated for proteins targeted by the compounds, namely Gene Ontology (GO) terms and physiology terms from the WormBase's Phenotype Ontology.

To analyse these datasets, we used a combination of feature selection methods in a data pre-processing phase and the well-established random forest algorithm for learning predictive models from the selected features. In addition, we interpreted the most important features in the two best models in light of the biology of ageing. One noteworthy feature was the GO term "Glutathione metabolic process", which plays an important role in cellular redox homeostasis and detoxification. We also predicted the most promising novel compounds for extending lifespan from a list of previously unlabelled compounds. These include nitroprusside, which is used as an antihypertensive medication. Overall, our work opens avenues for future work in employing machine learning to predict novel life-extending compounds.

Link: https://doi.org/10.18632/aging.204866

Calorie restriction is the practice of adopting up to a 40% reduction in calorie intake versus an ad libitum diet, while still obtaining optimal micronutrient levels. It is perhaps the most studied of all interventions known to slow aging and extend healthy life span in short-lived species, but equally there is still much that we do not know about how it actually works. The challenge is that calorie restriction changes near everything in the operation of metabolism, so it is hard to determine which of those changes are contributing to an extended life span, and to what degree. The best evidence to date suggests that upregulation of the cell maintenance processes of autophagy is the dominant mechanism, but equally there are any number of other changes for which compelling arguments can be mounted. Loss of visceral fat tissue, for example, or as noted here, improved immune function.

Dietary restriction (DR) is the most reproducible and effective nutritional intervention tested to date for delaying the aging process and prolonging the health span in animal models. Preventive effects of DR on age-related diseases have also been reported in human. In addition, highly conserved signaling pathways from small animal models to humans mediate the effects of DR. Recent studies have reported that DR-induced longevity is regulated by innate immune signaling components.

In C. elegans, the transcription factor ZIP-2 is an innate immune signaling component molecule that is upregulated in response to infection by Pseudomonas aeruginosa (PA14), and is necessary for survival against PA14 infection. It has been reported that ZIP-2 is a key mediator of the effects of DR on healthy aging in C. elegans. ZIP-2 activity increased in response to DR, and zip-2 was necessary for DR-induced longevity and physical activity improvement in worms subjected to DR. ZIP-2 activity was increased by inhibition of the TOR signaling pathway and rapamycin treatment. It was concluded that zip-2 extends longevity through TOR/S6K inhibition by DR.

Consistent with the results in C. elegans, acute DR boosts innate immunity in Drosophila. DR via yeast restriction enhanced Drosophila survival against PA14 infection, and reduced TOR signaling protected flies from pathogenic bacterial infection. In addition, researchers confirmed the beneficial effects of yeast restriction on Drosophila immunity following rapamycin treatment.

The p38-MAPK signaling pathway is an important innate immune pathway that is highly conserved from C. elegans to human. It was reported that the p38-MAPK signaling pathway is related to longevity extension by DR in C. elegans. They found that DR maintained the level of the p38-ATF-7 (ATF-7 is a transcription factor downstream of p38) innate immune response at the basal activation level, and that maintaining p38-ATF-7 activity at the basal level is an important factor for longevity in C. elegans. Thus, these results imply that the regulation of immune signals by DR is an important mechanism for extending longevity.

Link: http://doi.org/10.5483/BMBRep.2023-0095

Today's open access paper provides an interesting example of a pharmacological strategy that is beneficial to specific aspects of memory function in old mice, but detrimental to that same function in young mice. This is certainly possible, as the biochemistry of cells and tissues is nothing if not exceedingly complex, but this outcome tends to be unusual. More commonly, a therapy targeting causative mechanisms of aging, one that improves function in aged individuals, will do little to nothing for younger individuals, but will not be actively harmful.

Here, clearly, the biochemistry of memory formation changes in meaningful ways with age. At present far too little is understood of the fine details of how neural function gives rise to the mind, for all that chemical and structural features relating to memory formation are quite well mapped at the high level. That less well understood details change with age in ways that give rise a treatment that only works in old individuals is a painful reminder that mammalian neural biochemistry is far more complex than we'd like it to be, at least when it comes to the task of developing biotechnologies to maintain its function over time.

Glycogen phosphorylase inhibition improves cognitive function of aged mice

Glycogen phosphorylase (Pyg) catalyzes the first and rate-limiting step in the process of glycogen degradation (glycogenolysis). Inhibition of Pyg was shown to block memory formation in young chickens and induction of the Long Term Potentiation (LTP, a cellular/molecular mechanism of memory formation) in hippocampi and hippocampal slices isolated from young rodents. It was also shown that impairment of synaptic plasticity after Pyg inhibition was associated with decreased transport of glycogen-derived lactate from astrocytes to neurons in a process called the astrocyte-neuronal lactate shuttle (ANLS). The impact of the astrocytic glycogen-derived lactate on neuronal metabolism is the subject of ongoing debate and the mechanism by which this pool of lactate stimulates the LTP is not fully understood. However, it is commonly accepted that disruption of the ANLS affects memory formation.

In contrast to the young animals, inhibition of glycogen breakdown in hippocampal sections isolated from adult and aged rodents was shown to improve the LTP formation, elevating significantly its magnitude. Moreover, in hippocampal slices isolated from old animals, significant alterations in morphology of dendritic spines were observed after inhibition of Pyg, indicating changes in dendritic spines maturation. Mechanisms underlying this different response to Pyg inhibition remain to be discovered but they might be associated with a different organization of hippocampal formation in young and aged animals and global changes in the expression of hippocampal proteins, and in the NAD+/NADH metabolism during aging.

Here, we report that a 2-week treatment with glycogen phosphorylase inhibitor BAY U6751 alleviated memory deficits and stimulated neuroplasticity in old mice. Using the 2-Novel Object Recognition and Novel Object Location tests, we discovered that the prolonged intraperitoneal administration of BAY U6751 improved memory formation in old mice. This was accompanied by changes in morphology of dendritic spines in hippocampal neurons, and by "rejuvenation" of hippocampal proteome. In contrast, in young animals, inhibition of glycogen degradation impaired memory formation; however, as in old mice, it did not alter significantly the morphology and density of cortical dendritic spines. Our findings provide evidence that prolonged inhibition of glycogen phosphorolysis improves memory formation of old animals. This could lead to the development of new strategies for treatment of age-related memory deficits.

CAP2 is involved in maintenance of the actin cytoskeleton of cells, and as such is one of those proteins whose function might indirectly affect near every process of interest in the cell. It is known to be necessary to heart contractility and the actin remodeling observed in neurons, for example. That makes it a little hard to speculate usefully as to why decreased expression might be correlated with frailty in humans, particularly given that expression doesn't otherwise appear to fall with age, and the authors of this epidemiological study don't make much of an attempt at a hypothesis. Current knowledge of CAP2 is the starting point for a thread of investigation that may last a good many years.

Frailty is a geriatric syndrome that results from multisystem impairment caused by age-associated accumulation of deficits. The frailty index is used to define the level of frailty. Several studies have searched for molecular biomarkers associated with frailty, to meet the needs for personalized care. Cyclase-associated protein 2 (CAP2) is a multifunctional actin-binding protein involved in various physiological and pathological processes, that might reflect frailty's intrinsic complexity.

This study aimed to investigate the association between frailty index and circulating CAP2 concentration in 467 community-dwelling older adults (median age: 79; range: 65-92 years). The selected robust regression model showed that circulating CAP2 concentration was not associated with chronological age, as well as sex and education. However, circulating CAP2 concentration was significantly and inversely associated with the frailty index: a 0.1-unit increase in frailty index leads to ~0.5-point mean decrease in CAP2 concentration. Furthermore, mean CAP2 concentration was significantly lower in frail participants (i.e., frailty index ≥0.25) than in non-frail participants.

This study shows the association between serum CAP2 concentration and frailty status for the first time, highlighting the potential of CAP2 as a biomarker for age-associated accumulation of deficits.

Link: https://doi.org/10.1111/acel.13918

Researchers here find that, in mice, microbial DNA from the aging gut readily leaks into circulation. The aging innate immune system falters in its ability to clear this DNA due to a declining population of macrophages capable of this task. As a consequence the microbial DNA provokes inflammatory dysfunction in the heart. This is an interesting advance in understanding the specifics of the broad relationship between the gut microbiome and degenerative aging, and offers pointers to ways in which the aging immune function might be improved.

Emerging evidence indicates the critical roles of microbiota in mediating host cardiac functions in ageing, however, the mechanisms underlying the communications between microbiota and cardiac cells during the ageing process have not been fully elucidated. Bacterial DNA was enriched in the cardiomyocytes of both ageing humans and mice. Antibiotic treatment remarkably reduced bacterial DNA abundance in ageing mice. Gut microbial DNA containing extracellular vesicles (mEVs) were readily leaked into the bloodstream and infiltrated into cardiomyocytes in ageing mice, causing cardiac microbial DNA enrichment.

Vsig4+ macrophages efficiently block the spread of gut mEVs whereas Vsig4+ cell population was greatly decreased in ageing mice. Gut mEV treatment resulted in cardiac inflammation and a reduction in cardiac contractility in young Vsig4-/- mice. Microbial DNA depletion attenuated the pathogenic effects of gut mEVs. cGAS/STING signaling is critical for the effects of microbial DNA. Restoring Vsig4+ macrophage population in ageing WT mice reduced cardiac microbial DNA abundance and inflammation and improved heart contractility.

Link: https://doi.org/10.3389/fimmu.2023.1216344

It probably strains the meaning of the term to call the aftermath of the use of nuclear weapons at the end of the Second World War a natural experiment, but nonetheless there has been considerable study of survivors from those events and their health relative to control populations in other parts of Japan. Irradiation is known to produce what is effectively accelerated aging in the context of cancer treatment, producing an increased burden of senescent cells that then ensure the later course of health for survivors is worse than would otherwise be the case, absent both cancer and treatment. In the case of exposure to radiation deriving from the use of smaller nuclear weapons, analogous lasting effects have emerged.

It is unclear as to how indirect the observed effects on immune function might be most of a lifetime after the event. The researchers here focus on oxidative stress, known to go hand in hand with chronic inflammation. That in turn can arise from an increased burden of senescent cells, but it is far from clear that this is the only (or even primary) mechanism when considering health 50 to 60 years after exposure, rather than the more usual case in medical science of the 10 to 20 years following a later life cancer treatment. Still, the evidence to date suggests that an increased senescent cell burden can last for quite some time, despite the body's demonstrated ability to clear these cells at some pace, even in late life.

In today's open access paper, researchers propose a more T-cell-centric proximate mechanism for immune dysfunction, wherein irradiation leaves behind a lasting tendency for T cells to become more inflammatory, generating more oxidative stress. This may be mediated, carried forward across decades, by alterations in very long-lived memory T cells. How this might relate to underlying mechanisms such as increased cellular senescence following irradiation remains to be resolved.

Early-life atomic-bomb irradiation accelerates immunological aging and elevates immune-related intracellular reactive oxygen species

The immune system matures by deploying a number of responsive lymphocytes in the body and leaving behind memory cells after infection. However, the function of the immune system declines gradually with age, while chronic inflammation and autoimmune responses are enhanced, resulting in metabolic diseases, cardiovascular diseases, cancer, diabetes, and other attributable age-related diseases.

The radiation from the atomic bombs (A-bombs) dropped on Hiroshima and Nagasaki in 1945 has increased the risk of developing certain cancers and non-cancer diseases, including heart disease. Long-term epidemiological and clinical studies of A-bomb survivors have shown that there are significantly increased risks of age- and immune system/inflammation-related diseases among the A-bomb survivors. Although there is no direct evidence that radiation exposure-accelerated immunological aging increases the risk of certain cancers or cardiovascular diseases, it has been presumed that accelerated immunological aging due to radiation exposure is associated with increased risk of age-related diseases.

Reactive oxygen species (ROS) play an important role in immune responses; however, their excessive production and accumulation increases the risk of inflammation-related diseases. Although irradiation is known to accelerate immunological aging, the underlying mechanism is still unclear. To determine the possible involvement of ROS in this mechanism, we examined 10,023 samples obtained from 3,752 atomic-bomb survivors in Hiroshima and Nagasaki, who participated in repeated biennial examinations from 2008 to 2016, for the effects of aging and radiation exposure on intracellular ROS (H2O2 and O2-) levels, percentages of T-cell subsets, and the effects of radiation exposure on the relationship between cell percentages and intracellular ROS levels in T-cell subsets.

The percentages of naïve CD4+ and CD8+ T cells decreased with increasing age and radiation dose, while the intracellular O2- levels in central and effector memory CD8+ T cells increased. Additionally, when divided into three groups based on the percentages of naïve CD4+ T cells, intracellular O2- levels of central, and effector memory CD8+ T cells were significantly elevated with the lowest radiation dose group in the naïve CD4+ T cells. Thus, the radiation exposure-induced decrease in the naïve CD4+ T cell pool size may reflect decreased immune function, resulting in increased intracellular ROS levels in central and effector memory CD8+ T cells, and increased intracellular oxidative stress.

Based on the results of this study, we hypothesize that past radiation exposure, particularly high-dose exposure, affects T-cell function and enhances the persistent inflammatory state, thereby increasing T-cell ROS levels in the blood. To test this hypothesis, we continue to investigate changes in the immune and clinical status with radiation exposure and aging, as well as, an increased risk of disease onset due to radiation exposure in A-bomb survivors, based on interactions between intracellular ROS levels and immune and inflammatory biomarkers. We expect that these studies will provide concrete evidence for the hypothesis of "accelerated immune aging due to radiation exposure".

Researchers here present data on the age-related slowdown in visuospatial processing speed, where visuospatial processing refers to building and updating a mental model of the surrounding environment based on sight alone. Slowing and reduced capacity of cognitive functions is characteristic of aging. This measure is interesting for some of the correlations found with other aspects of degenerative aging, particularly mobility issues. Visuospatial processing is a necessary part of navigating the environment, but it is interesting to speculate on whether the connection with loss of mobility is the obvious one, or whether this is a coincidence in the effects of an increased burden of cell and tissue damage on disparate parts of the body and brain.

Visuospatial processing speed underlies several cognitive functions critical for successful completion of everyday tasks, including driving and walking. While it is widely accepted that visuospatial processing speed peaks in early adulthood, performance across the lifespan remains incompletely characterized. We developed a novel visuospatial processing speed (VIPS) task adapted from two tests sensitive to visuospatial processing speed declines in older adults, the Useful Field of View paradigm and the PERformance CEntered Portable Test. The VIPS task requires participants to make a central orientation discrimination and complete a simultaneous peripheral visual search task.

Data were collected from 86 in-lab volunteers (18-30 years) to compare performance to traditional neuropsychological measures. Consistent with previous literature, performance on the novel VIPS task significantly correlated with measures of selective attention, executive functioning, visual speed, and working memory. An additional 4,395 volunteers (12-62 years) were recruited on TestMyBrain.org to establish lifespan trajectories of visuospatial processing speed and associations with functional disability. VIPS task performance peaked in the early 20's, and steadily decreased such that thresholds doubled in 60-year-olds relative to 20-year-olds (817 ms vs. 412 ms).

VIPS task performance significantly correlated with self-reported cognitive functioning deficits broadly across the lifespan but was specifically related to mobility issues in middle-age. These findings have important implications for early detection of cognitive decline and provide insights into potential early intervention targets for younger and middle-aged adults.

Link: https://doi.org/10.1186/s41235-023-00504-y

At present the research community cannot robustly connect underlying causative processes of aging, such as those described in the SENS view of damage and rejuvenation, or some of the hallmarks of aging, to higher level manifestations of aging, such as declining function or changing biomarkers associated with age-related disease. This gives great freedom to theorize on how exactly the present voluminous but disconnected body of data on aging, cellular biochemistry, and age-related disease all fits together. There is no shortage of theories of aging, and no sign that the research community will cease to create new ones at any point in the near future. Some are quite interesting, as in the case here, regardless of what might think of the likelihood of such mechanisms playing an important role in degenerative aging.

We recently published selective destruction theory (SDT), which suggests a mechanism of ageing which is both independent of accumulating damage and consistent with epigenetic rejuvenation. We argue that in multicellular organisms, neighbouring cells are in constant competition. When mutations arise that increase a cell's growth rate, they bestow a selective advantage (an extreme example would be cancer, but most will not be). If these cells are uncontrolled, their growth advantage will allow them to spread, and their overactive metabolism could result in a host of detrimental or even lethal overactivity disorders. For example, in β-cells where growth is tied to insulin production, fast mutants spreading could produce a lethal drop in blood glucose. Another less tissue-specific example is the increased propensity of fast growing/metabolising fibroblasts to reach the critical threshold required for fibrosis.

Fast mutants are also likely to be more tumorigenic, while slow mutants will be less active, less fibrotic, and less tumorigenic even compared to wildtype cells. We therefore proposed that a maintenance mechanism which selectively destroyed fast cells might undergo positive selection even if it caused the spread of slow mutants as it would reduce the risks of overactivity disorders. The mechanism of selective destruction is currently theoretical. In our most developed model, we demonstrated that if slow cells induced epigenetic changes in faster cells causing their metabolism to slow (rather than killing them) it not only reduced unnecessary cell death, but also further reduced the likelihood of overactivity disorders by preventing the spread of fast cells. The resulting epigenetic growth suppression could therefore reflect a kind of ageing program designed to prevent overactivity disorders, and may explain why the methylation of specific CpG islands provides such accurate ageing clocks. It would also explain epigenetic rejuvenation by Yamanaka factors and parabiosis, so we predict that methylation of CpG islands will affect cell growth.

Link: https://doi.org/10.18632/aging.204956

The burden of cellular senescence increases with age, perhaps largely because the immune system becomes less able to remove senescent cells in a timely fashion. Lingering senescent cells are significantly harmful even when making up one percent or less of all cells in a tissues. This is because cells in a senescent state vigorously generate a mix of pro-growth, pro-inflammatory signals, the senescence-associated secretory phenotype (SASP). The SASP changes cell behavior for the worse, encourages chronic inflammation, and induces nearby cells to also become senescent. This is actively disruptive to tissue function, and contributes directly to the pathology of many age-related conditions.

Much of the medical research and development relating to senescent cells is focused on finding ways to selectively destroy them, the production of senolytic drugs. However, a sizable faction within the research community are interested in instead minimizing or blocking some or all of the SASP, the production of senomorphic drugs. This seems less beneficial as a strategy, since the SASP is not fully mapped, and treatments would have to be continual rather than intermittent, but some researchers are concerned that removal of senescent cells in some tissues may cause harm. To me, that seems to have been already demonstrated a lesser concern, given the evident, lasting benefits produced in mice following clearance of senescent cells.

Today's open access review paper makes the point that the development of senomorphic drugs remains at a very rudimentary stage in comparison to senolytic development. Too little is known of the SASP and its regulation, and too little is known of what exactly the initially identified senomorphic compounds actually do to the SASP. Researchers typically measure levels of a few of the better known pro-inflammatory SASP proteins in order to gain some idea of the effects of a candidate senomorphic drug, but the SASP likely consists of hundreds of different molecules. A great deal of work lies ahead.

Exploring the Communication of the SASP: Dynamic, Interactive, and Adaptive Effects on the Microenvironment

Given the importance of senescence in physiological processes, it is reasonable to think that there is a threshold beyond which the accumulation of senescent cells induces a microenvironment conducive to the development of pathologies via SASP. The accumulation of senescent cells can also occur when the immune system ages, altering the ability of immune cells to clear senescent cells. Elimination of senescent cells by senolytics demonstrated a contributive role of senescent cells in ageing and age-related diseases and paved the way for the development of senotherapeutic approaches. Therefore, over the past 5 years, senotherapeutic research has emerged to slow down the ageing phenotypes. Current senotherapeutic strategies targeting senescent cells are mainly based on drugs that specifically kill senescent cells (senolytics) and components that suppress the detrimental effects of SASP without inducing senescent cell death (senomorphics, also known as senostatics).

We will not cover all senotherapeutic strategies, especially as excellent reviews have recently been published on senolytic developments, but rather focus on those with senomorphic activities, based on their ability to block SASP components.

A first strategy would consist in using neutralizing antibodies, recognizing and blocking specific surface proteins upregulated at senescence. Secretion of IL-6 has been decreased in senescent HUVECs and fibroblasts treated with anti-TNFα or anti-ephrin B2 antibodies, respectively. Several other surface proteins are known to play a role in the regulation of SASP profiles, including SCAMP4, Notch, and CD36. However, it has not yet been reported that the use of neutralizing antibodies targeting SCAMP4, Notch, or CD36 can impact the composition of SASP and, therefore, arrive at a conclusion regarding their senomorphic properties. In a model of bleomycin-induced senescence, the secretion of certain SASP factors (including IL-6 and IL-8) can be directly inhibited with neutralizing antibodies such as those against the membrane-bound IL-1α. It would be interesting to investigate the impact of other neutralizing antibodies directed against other major SASP factors such as circulating IL-1β-, IL-6, or their receptors, on their abilities to alter the chemical composition of SASP, impair SASP-mediated effects, and attenuate other features of senescence in different cell types.

A second strategy would be to use pharmacological and natural compounds. Many senomorphics are polyphenols (including flavonoids, phenolic acids and lignans) that possess antioxidant activities, but their modes of action have not been thoroughly studied. Other senomorphics are plant extracts consisting of a mixture of terpenes, alkaloids, and polyphenols. The biological effects of these compounds are multiple, ranging from the activation of antioxidant enzymes to the reduction in interleukin or MMP expression, and the inhibition of MAPKs. Most senomorphics modulate the senescent phenotypes to disrupt the proinflammatory nature of senescent cells.

Most studies, however, have only assessed a few SASP major factors (such as IL-6, IL-1β, and MMPs) following senomorphic treatments, which is not representative of SASP as a whole. Moreover, the impact of senomorphics on the secretion of extracellular matrix components, microvesicles, and complex lipids remains largely unexplored. Senomorphics can act on multiple targets depending on the context, the nature, and the model of senescence. In some cases, we cannot rule out that they might even increase the secretion of some detrimental factors. This raises the concern that SASP resulting from senomorphic treatment should probably be less deleterious and should be considered as modified rather than non-senescent-like. In addition, few studies are using conditioned media from senescent cells treated with senomorphics to examine the biological effects of the modified SASP (such as the pro-tumoral impact or differentiation) on other cell types. In the absence of more extensive data, it is difficult to assess the real effectiveness of senomorphics on SASP.

It remains unclear as to the degree to which familial longevity is a matter of culture versus genetics. Studies of ever-larger genetic databases are finding that human life expectancy has a smaller genetic component than previously thought, while smaller studies have found very few gene variants broadly correlated with longevity, none of which have large effect sizes. Separately, it continues to be the case that large epidemiological studies show lifestyle choices to produce a sizable effect on life expectancy. It is reasonable to argue that familial longevity is near all a matter of cultural transmission of lifestyle choice, but far from proven or settled, and certainly not the focus of the major research programs in this space, all of which study the genetics of longevity.

Globally, the lifespan of populations increases but the healthspan is lagging behind. Previous research showed that survival into extreme ages (longevity) clusters in families as illustrated by the increasing lifespan of study participants with each additional long-lived family member. Here we investigate whether the healthspan in such families follows a similar quantitative pattern using three-generational data from two databases, the Leiden Longevity Study (LLS, Netherlands) and the Swedish register data available in the Scanian Economic-Demographic Database (SEDD, Sweden). We study healthspan in 2,143 families containing index persons with 26 follow-up years and two ancestral generations, comprising 17,539 persons.

Studying these long-lived families is important to improve our understanding of the molecular and environmental mechanisms that protect from multimorbidity and promote a healthy survival up to high ages. In this study we showed that members of long-lived families have a delayed onset of disease, multimorbidity, and medication use as compared to their partners, thereby extending their healthspan with up to a decade. These members also postponed multimorbidity since those who were already diagnosed with an age-related disease had a 54% lower risk of having a second age-related disease compared to their partners.

An increasing number of long-lived ancestors, as measured with the Longevity Relatives Count (LRC) score, not only associates with a lower mortality at any moment in life it also associates, in a similar way, with a lower disease incidence during mid and later life (60-75 years): With every 10% increase in LRC score the yearly risk to develop an age-related disease decreased with 5% in the LLS, and 6% in the SEDD, maximizing to 50% and 60% respectively when all ancestors were long-lived.

Link: https://doi.org/10.1038/s41467-023-40245-6

The biotech industry experiences a high failure rate, if we wish to define failure as failing to achieve the original goals of the research program that gave rise to a company. The article noted here opens with many examples to give a sense of the prevalence of companies in the early aging-focused space that altered their course to give a return to their investors by other means, after it proved too challenging to achieve the original vision. This is par for the course: the development of novel medical biotechnology is both very difficult and highly regulated. The grail of producing new medicine that is accepted by the regulatory community is a rare success, but it is also true that there are other paths to generating some progress from programs that fail to achieve that goal.

The different strategies that past companies followed are common answers to the same constraint: there is no regulatory pathway to bring geroprotectors the market. So they either: (a) Develop pre-clinical assets and platform that may have value for other pharmaceutical and biotech companies. (b) Commit to the traditional biotech playbook and treat an age-related disease through a drug that targets a specific pathway or mechanism of aging, collect data to support claims for other indications and expand the label of the medicine over time. (c) Commercialise unproven products (supplements) or experimental treatments (gene therapies) in jurisdictions where the regulatory environments may allow such procedures.

The intrinsic scientific difficulties in translating early stage research into an approved treatment often stood in the way of commercialisation, despite the best efforts of companies and researchers. Some assets got acquired and abandoned and others are still on their path to the clinic. In a perfect world, nobody would forget on the shelf an asset that has the potential to slow down aging. But many factors beyond just the science can influence whether an asset continues along the development pipeline. Even the most promising early research can sometimes fail to translate into an approved product, due to the inherent challenges in drug development.

The company pivots to a different therapeutic area and the asset is no longer core to their strategy. Leadership changes at the company and new decision makers have different priorities, so they discontinue programs started under previous leaders. Patent life expires before the asset has progressed far enough to merit continued investment. Another company develops a similar or superior asset that displaces interest in theirs. The company runs out of funding to progress all assets and must make tough choices about which programs to shelve. Leadership simply loses conviction in the asset's potential for unclear reasons and turns attention elsewhere.

It may be possible to treat an age-related disease by targeting a mechanism of aging and I'm confident some companies will achieve that relatively soon. From an investment and commercial perspective, given the scientific and historical risks, a drug that targets a specific pathway or mechanism of aging to treat a disease has no superior value than any other drug. Unless that drug can slow down aging. But in more than 30 years, despite apparently promising science and significant funding raised, no single longevity biotech startup has succeeded to bring a product to market. Product as in: drug that has been approved by a regulatory agency following thorough clinical trials. So maybe it's time to consider a different strategy: assume the regulatory risk, target aging itself and be preventive instead of curative. Preventive drugs approved for several indications already exist. So bringing to market drugs that slow down the aging process and prevent all age-related diseases is just one step away.

Link: https://www.stanete.com/history-longevity-biotech/

Today's open access paper discusses a way to slow neuromuscular junction aging, and thereby age-related loss of muscle function. Loss of muscle strength, dynapenia, and loss of muscle mass, sarcopenia, are characteristic of aging. These declines contribute to age-related frailty directly and evidently, but it is also worth noting that muscle tissue is metabolically active, and appears to contribute beneficial signal molecules to the circulation, collectively called myokines. Loss of muscle tissue likely has a harmful effect on overall metabolism via this mechanism.

What is the chain of cause and consequence that leads to the loss of muscle mass and strength? As is always the case, connections to fundamental mechanisms of aging are up for debate, but when it comes to more proximate contributing causes, the two most interesting lines of inquiry, to my eyes, are (a) loss of muscle stem cell activity, directly causing a decline in tissue maintenance via a smaller supply of new somatic cells, and (b) dysfunction in the neuromuscular junction that connects the nervous system to muscle tissue. Muscle tissue depends on innervation for growth and regeneration cues, and thus this can also cause a decline in tissue maintenance.

Partial inhibition of class III PI3K VPS-34 ameliorates motor aging and prolongs health span

In this study, we designed a fast and efficient genome-wide screening assay in C. elegans to systematically identify potential regulators of motor aging. Among the top hits, we functionally validated the role of VPS-34 in regulating motor aging and revealed its cell type-specific mechanisms. VPS-34 is the class III phosphatidylinositol 3-kinase that phosphorylates phosphatidylinositol (PI) to phosphatidylinositol 3-phosphate (PI(3)P), regulating motor function in aged but not young worms.

Contrary to popular belief that life span and health span are strongly correlated, the global increase of life expectancy over the past decades is rarely accompanied by increased health span. Since aging is characterized by functional decline of multiple organs and tissues, the key to healthy aging is to delay or rescue the decline of essential physiological functions. Motor independence is strongly associated with the quality of life of elderly people, yet motor aging is a common, conserved biological process from worms to humans, leading to frailty, loss of motor independence, falling, and even death. To date, it is still challenging to identify evolutionarily conserved mechanisms that can be exploited to delay or ameliorate motor aging.

Combining genetics, pharmacology, and in situ electrophysiology, we demonstrated that partial inhibition of VPS-34 significantly improved neuromuscular synaptic transmission and the muscle integrity, which ameliorate motor aging in both worms and mice. Previous studies have identified motor aging-associated regulators through candidate approaches, which act in either motor neurons/neuromuscular junctions or skeletal muscles. To our knowledge, VPS34 is the first reported gene that simultaneously regulates neurotransmission of motor neurons and muscle integrity during aging, likely through cell type-specific mechanisms. Thus, it is a promising target that can be exploited to improve both aged neurons and muscle.

Researchers here speculate on the ability of insoluble amyloid-β aggregates to be broadly disruptive of the solubility of many other proteins, and thus disruptive to cell and tissue function. Is this important in aging? The evidence here shows the existence of the mechanism in a lower species, but that doesn't necessarily show that it has a sizable effect in mammals. Still, it is an interesting concept, potentially linking everything we know about why amyloid-β increases with age to the observed general dysfunction of brain cells.

Loss of proteostasis is a highly conserved feature of aging across model organisms and typically results in the accumulation of insoluble protein aggregates. Protein insolubility is a central feature of major age-related neurodegenerative diseases including Alzheimer's Disease (AD), where hundreds of insoluble proteins associate with aggregated amyloid beta (Aβ) in senile plaques. Despite the established connection between aging and AD risk, therapeutic approaches to date have overlooked aging and proteome-wide protein insolubility as causal factors, instead focusing on Aβ and Tau. Here, using an unbiased proteomics approach, we questioned the relationship between Aβ and age-related protein insolubility.

We demonstrate that, in C. elegans, Aβ expression is sufficient to drive proteome-wide protein insolubility. The Aβ-driven insoluble proteome bears a highly significant overlap with the aging-driven insoluble proteome, suggesting there exists a core, sub-proteome which is vulnerable to insolubility. Using human genome-wide association studies (GWAS) we show that this insoluble sub proteome is replete with biological processes implicated across not only neurodegenerative diseases but also across a broad array of chronic, age-related diseases, providing suggestive evidence that age-related loss of proteostasis could play a role in general age-related disease risk.

Link: https://doi.org/10.1101/2023.07.13.548937

The thymus is a small organ in the chest. Thymocytes created in the bone marrow migrate to the thymus where they mature into T cells of the adaptive immune system through a complex process of selection. The thymus atrophies with advancing age, and this reduces the pace at which new T cells are generated to reinforce the immune system. Absent reinforcements the adaptive immune system declines into malfunctioning, senescent, exhausted cell populations over time. This immune dysfunction is an important component of degenerative aging. The same harms are demonstrated in adult individuals who had to have their thymus removed, as noted here.

Surgical removal of the thymus is recommended in patients with the autoimmune disease myasthenia gravis as a way to halt T-cell-induced immune destruction of nerve endings. For the study, researchers mined data from 1,146 adult patients who had undergone thymus removal, alongside demographically matched control patients who had undergone similar surgeries but kept their thymus. Thymectomy patients had a nearly threefold higher risk of death from a variety of causes, including a twofold higher risk of cancer and a more modest increase in autoimmune diseases.

In an analysis involving all patients with more than five years of follow-up, the rate of death was higher in the thymectomy group than in the general U.S. population ­- 9 percent vs. 5.2 percent, as was death due to cancer, or 2.3 percent vs. 1.5 percent. In a subgroup of patients in whom T-cell production was measured, those who had had their thymus removed had less new production of T-cells, including both helper T-cells and cytotoxic T-cells. Those patients also had higher levels of pro-inflammatory cytokines, which are small signaling proteins associated with autoimmunity and cancer, in their blood.

The analysis was facilitated by recent advances in rapid genetic sequencing of T-cell receptors (TCRs). The technology, called TCR sequencing, has enough resolution to allow scientists to not only identify different types of T cells, but also measure their diversity as a population overall. "This study demonstrates just how vital the thymus is to maintaining adult health."

Link: https://news.harvard.edu/gazette/story/2023/08/turns-out-lowly-thymus-may-be-saving-your-life/

It is at present somewhat out of style to point out that, yes, obviously, it will be possible in the future to ensure that humans live for a very, very long time. That will be true for even baseline humans lacking all of the various genetic modifications one might propose a future scientific community to be capable of, modifications to introduce the numerous distinct forms of resilience to the mechanisms of mammalian aging exhibited by naked mole-rats, whales, elephants, bats and so forth. Control over aging is a subset of control over molecules and their positions. To be as reductionist as possible, degenerative aging is a matter of the wrong molecules in the wrong places. In the bigger picture, our technological capabilities are inexorably heading in the direction of far greater control over all matters relating to the arrangement of molecules.

However, we now have a longevity industry that is very focused on the short-term, the next step on what will likely be a very long road towards biotechnologies that will completely control aging. For reasons that remain unclear to me, the cultural complex of media, academia, regulators, and industry is allergic to considering both the short-term and the long-term in the same few breaths. Near all talk of imposing visions vanishes in favor of incrementalist rhetoric as the venture funding ramps up and regulators become involved. Thus it is pleasant to see that at least some few individuals are still willing to stand up and say the obvious: that people will absolutely live for thousands of years at some point in the future, and that what we do now in research and development for the treatment of aging is a part, a small part, but a part nonetheless, of the continuum of technological progress that will lead to that outcome.

How Old Can Humans Get?

How long can human beings live? Although life expectancy has increased significantly over the past century, thanks largely to improved sanitation and medicine, research into hunter-gatherer populations suggests that individuals who escaped disease and violent deaths could live to about their seventh or eighth decade. This means our typical human life span may be static: around 70 years, with an extra decade or so for advanced medical care and cautious behavior. Some geneticists believe a hard limit of of around 115 years is essentially programmed into our genome by evolution.

Other scientists in the fast-moving field of aging research, or geroscience, think we can live much longer. A handful of compounds have been shown to lengthen the life spans of laboratory animals slightly, yet some scientists are more ambitious - a lot more ambitious. João Pedro de Magalhães, a professor of molecular biogerontology at the Institute of Inflammation and Ageing at the University of Birmingham in England, thinks humans could live for 1,000 years. He has scrutinized the genomes of very long-lived animals such as the bowhead whale (which can reach 200 years) and the naked mole rat. His surprising conclusion: if we eliminated aging at the cellular level, humans could live for a millennium - and potentially as long as 20,000 years.

"I actually did some calculations years ago and found that if we could "cure" human aging, average human life span would be more than 1,000 years. Maximum life span, barring accidents and violent death, could be as long as 20,000 years. This may sound like a lot, but some species can already live hundreds of years-and in some cases thousands of years [such as the hexactinellid sponge and the Great Basin bristlecone pine]. If we could redesign our biology to eliminate cancer and evade the detrimental actions of our genetic software program, the health benefits would be mind-boggling. I think it's possible. Is it going to happen soon? I think it's quite unlikely. Even if you can figure out how aging works, it is not easy to develop interventions."

The future of cancer therapy will involve the targeting of mechanisms found broadly in many or all different types of cancer, that cancer cells cannot dispense with as they evolve rapidly within a tumor, and which have little to no effect on non-cancerous cells. Targeting telomerase to prevent the lengthening of telomeres can check the first two of those boxes, leaving the question of how best to effectively restrict the treatment to tumor cells. Targeting alternative lengthening of telomeres can check the second and third boxes, but the mechanism only operates in a minority of cancers. The research community is engaged in finding other approaches that might satisfy some of these goals; a few candidates exist. The research noted here is one example of a potentially broadly applicable strategy that disrupts cancer cell replication.

Proliferating cell nuclear antigen (PCNA) is an evolutionarily conserved multifaceted protein found in all eukaryotic cells, and it plays a critical role in DNA synthesis and in DNA repair. PCNA forms a ring structure encircling DNA and it acts as a central "hub" to provide an anchorage for the many proteins involved in the replication and repair pathways. The cellular functions of PCNA can be modulated through post-translational modifications on the surface of the protein, altering partner interactions. Historically, PCNA has been widely used as a tumor progression marker.

DNA replication stress is a hallmark of cancer cells. It is used as a major anti-cancer therapeutic strategy by exploiting this cancer-associated feature, through introduction of further DNA damage resulting in catastrophic damage to the cancer cell. Due to its central role in DNA replication and repair, PCNA is a potential target for this anti-cancer strategy. Moreover, the identification of a distinct isoform of PCNA associated with cancer cells has potentially opened a novel avenue for the development of new chemotherapeutics. Early effects in targeting PCNA have identified several molecules of interest, both small molecule and peptide-based, which have indicated that directly targeting PCNA for cancer therapy may be a viable approach.

We previously described a compound, AOH1160, functioning as a potential inhibitor hit compound of the cancer-associated PCNA isoform (caPCNA), but this compound lacked suitable metabolic properties to proceed further into preclinical/clinical studies. Here, we describe both the identification and detailed molecular characterization of AOH1996, an analog of AOH1160 that exhibits remarkable therapeutic properties: it is orally administrable in a formulation compatible with its clinical use, and in animal studies it almost completely inhibits the growth of xenograft tumors. AOH1996 causes no discernible toxicity at 6 or more times the effective dose in mice and dogs.

Link: https://doi.org/10.1016/j.chembiol.2023.07.001

The reaction of the innate immune system to damage characteristic of aging biology drives a great deal of age-related chronic inflammation. For example, mislocalized mitochondrial DNA arises as a consequence of age-related mitochondrial dysfunction, and can trigger innate immune sensors that evolved to detect bacterial DNA. Here, researchers look more closely at one of the important signaling pathways involved in the maladaptive innate immune response to damage and dysfunction in aging cells.

Low-grade inflammation is a hallmark of old age and a central driver of ageing-associated impairment and disease. Multiple factors can contribute to ageing-associated inflammation; however, the molecular pathways that transduce aberrant inflammatory signalling and their impact in natural ageing remain unclear. Here we show that the cGAS-STING signalling pathway, which mediates immune sensing of DNA, is a critical driver of chronic inflammation and functional decline during ageing.

Blockade of STING suppresses the inflammatory phenotypes of senescent human cells and tissues, attenuates ageing-related inflammation in multiple peripheral organs and the brain in mice, and leads to an improvement in tissue function. Focusing on the ageing brain, we reveal that activation of STING triggers reactive microglial transcriptional states, neurodegeneration, and cognitive decline. Cytosolic DNA released from perturbed mitochondria elicits cGAS activity in old microglia, defining a mechanism by which cGAS-STING signalling is engaged in the ageing brain. Single-nucleus RNA-sequencing analysis of microglia and hippocampi of a cGAS gain-of-function mouse model demonstrates that engagement of cGAS in microglia is sufficient to direct ageing-associated transcriptional microglial states leading to bystander cell inflammation, neurotoxicity, and impaired memory capacity.

Our findings establish the cGAS-STING pathway as a driver of ageing-related inflammation in peripheral organs and the brain, and reveal blockade of cGAS-STING signalling as a potential strategy to halt neurodegenerative processes during old age.

Link: https://doi.org/10.1038/s41586-023-06373-1

Researchers have found that senescent cells express a senescence-associated glycoprotein (SAGP) localized to the lysosome, likely an attempted compensatory response to lysosomal stress characteristic of the senescent state. Distinctive features of senescent cells can be used to target them for destruction, thereby reducing the burden they place on aged tissues and achieving some degree of rejuvenation. In today's research materials, researchers report on a demonstration to show that using SAGP as a target to clear senescent cells can reduce pathology in a mouse model of Alzheimer's disease.

These mouse models are highly artificial and embody assumptions about the importance of specific forms of pathology in Alzheimer's disease, as mice do not normally suffer anything resembling this condition, and must thus be altered in ways that produce one or more specific forms of pathology. Nonetheless, the models do share with humans an increased inflammatory activation and senescence of microglia and other supporting cells in the brain. Clearing out the worst of these senescent brain cells via other forms of senolytic treatment has been shown to reduce inflammation and improve symptoms in mouse models of Alzheimer's disease, so it is not too surprising to see the same achieved here.

Novel vaccine may hold key to prevent or reduce the impact of Alzheimer's disease

Previously, researchers developed a vaccine to eliminate senescent cells expressing senescence-associated glycoprotein (SAGP) - a senolytic vaccine that improved various age-related diseases including atherosclerosis and type 2 diabetes in mice. Another study also found that SAGPs are highly expressed in glial cells in people with Alzheimer's disease. Based on the findings from these studies, the researchers tested this vaccine in mice to target SAGP-overexpressed cells to treat Alzheimer's disease.

In this study, the research team created an Alzheimer's disease mouse model that mimics a human brain and simulates amyloid-beta-induced Alzheimer's disease pathology. To test the efficacy of the SAGP vaccine, the mice were treated with a control vaccine or the SAGP vaccine at two and four months old. Usually, people in the late stage of Alzheimer's lack anxiety, which means they are not aware of the things around them. The mice who received the vaccine had anxiety, which means that they were more cautious and more aware of things around them - a sign researcher say could indicate a lessening of the disease. In addition, several inflammatory biomarkers of Alzheimer's disease were also reduced.

The SAGP vaccine significantly reduced amyloid deposits in brain tissue located in the cerebral cortex region, which is responsible for language processing, attention and problem solving. The astrocyte cell (the most abundant type of glial cell in the brain and a specific inflammatory molecule) was shown to be decreased in size in mice receiving the vaccine. A reduction in other inflammatory biomarkers was also seen, implying that inflammation in the brain improved in response to the SAGP vaccine. A behavior test on the mice at six months old revealed that those that received the SAGP vaccine responded significantly better to their environment than those who received the placebo vaccine. The SAGP-vaccinated mice tended to behave like normal healthy mice and exhibited more awareness of their surroundings.

The SAGP protein was shown to be located very near to specialized brain cells called microglia, which play a role in the immune defense of the central nervous system. Microglia help clear damaging plaque formed by proteins; however, they also trigger brain inflammation that can damage neurons and worsen cognitive decline in a person, which could be one of the causes of Alzheimer's disease development.

The search for ways to determine whether someone is in the very early stages of developing dementia overlaps with the development of means to determine biological age. The first step in both cases is to gather a sizable database of omics data, usually from blood samples. Once that data is in hand, why not try to achieve both goals? Alzheimer's disease and other neurodegenerative conditions may exhibit years to decades of slow development prior to evident symptoms, and those underlying processes will show up given the right measurements. The research noted here is one example of the exploration of biomarkers that is presently taking place, in search of ways to predict the onset of neurodegeneration.

A study that followed thousands of people over 25 years has identified proteins linked to the development of dementia if their levels are unbalanced during middle age. Most of the proteins have functions unrelated to the brain. "We're seeing so much involvement of the peripheral biology decades before the typical onset of dementia." Equipped with blood samples from more than 10,000 participants, researchers questioned whether they could find predictors of dementia years before its onset by looking at a person's proteome - the collection of all the proteins expressed throughout the body. They searched for any signs of dysregulation - when proteins are at levels much higher or lower than normal. The samples were collected as part of an ongoing study that began in 1987. Participants returned for examination six times over three decades, and during this time, around 1 in 5 of them developed dementia.

The researchers found 32 proteins that, if dysregulated in people aged 45 to 60, were strongly associated with an elevated chance of developing dementia in later life. It is unclear how exactly these proteins might be involved in the disease. For example, one of the proteins found with the strongest association with dementia risk - called GDF15 - was not detected in the brain. The study found altered levels of many of the proteins both in the brain tissues of those who had died with Alzheimer's disease, and in the blood of those still living with it. These were associated with the presence of amyloid and tau proteins, which suggests they are somehow involved in processes specific to the disease. Other proteins identified in the study were linked to the immune system, adding to growing evidence for the role of innate and adaptive immune function in dementia.

Link: https://doi.org/10.1038/d41586-023-02374-2

As the publicity materials here note, it is all too easy to damage your prospects for a longer, healthy life. The potential loss of life expectancy that attends becoming sedentary, obese, or a smoker is arguably somewhat greater than any gains that might be achieved via presently available medical technologies, when used by someone who takes better care of themselves into later life. That said, it is also true that while the losses resulting from lifestyle choices are well established in many large studies, we have no idea as to the extension of human life expectancy that attends, say, the late life use of existing senolytic drugs, or mTOR inhibitors, or other approaches, alone or combined.

A new study involving over 700,000 U.S. veterans reports that people who adopt eight healthy lifestyle habits by middle age can expect to live substantially longer than those with few or none of these habits. Scientists used data from medical records and questionnaires collected between 2011-2019 from 719,147 people enrolled in the Veterans Affairs Million Veteran Program. The eight habits are: being physically active, being free from opioid addiction, not smoking, managing stress, having a good diet, not regularly binge drinking, having good sleep hygiene, and having positive social relationships.

According to the results, men who have all eight habits at age 40 would be predicted to live an average of 24 years longer than men with none of these habits. For women, having all eight healthy lifestyle factors in middle age was associated with a predicted 21 additional years of life compared to women with none of these habits. Overall, the results showed that low physical activity, opioid use, and smoking had the biggest impact on lifespan; these factors were associated with around a 30-45% higher risk of death during the study period. Stress, binge drinking, poor diet, and poor sleep hygiene were each associated with around a 20% increase in the risk of death, and a lack of positive social relationships was associated with a 5% increased risk of death.

Link: https://www.eurekalert.org/news-releases/995553

Mitochondria, hundreds to a cell, are evolved descendants of the ancient bacteria that became symbiotic with the first, primitive cells. Mitochondria still behave a great deal like bacteria, in that they fuse together, replicate, carry a small circular genome, the mitochondrial DNA and promiscuously swap component parts. While the primary role of mitochondria is the generation of adenosine triphosphate (ATP), a chemical energy store used to power cell processes, they are also well integrated cellular components in a broader sense, influential in a range of fundamental cellular activities.

Mitochondrial DNA is a lot smaller than it once was. Evolution has gradually shifted mitochondrial genes into the nuclear DNA resident in the cell nucleus, all except a handful of remaining genes. Arguably the thirteen genes that remain are those for which there is no easy path for evolutionary mechanisms to produce a move into the nucleus. Yet we would like to move those genes into the nucleus, as damage to mitochondrial DNA is likely a major contribution to degenerative aging. Mitochondrial DNA is less well protected and repaired than nuclear DNA, and mutations can lead to mitochondria that are both dysfunctional and able to outcompete their undamaged siblings. The cell suffers as a result. Having a backup copy of a mutated gene that can supply proteins from the nucleus would evade the consequences of damaged mitochondrial DNA.

Finding ways to move the remaining mitochondrial genes into the nucleus, a process known as allotopic expression, is a long-running initiative at the SENS Research Foundation. After years of work, the research team there achieved success with only one of the genes so far, ATP8, and we can add another equally hard-won success by Gensight Biologics for ND4. That leaves another eleven genes that so far have proven resistant. The challenge is not inserting copies into the nucleus, as that is easy to accomplish in a research setting. The challenge lies in finding the alterations that will allow functional, correctly folded proteins to make their way back to the mitochondria where they are needed. As noted, this is something that evolution has failed to achieve, for reasons that we might guess at, but remain unclear.

The latest crowdfunded project to be proposed by the SENS Research Foundation is to use screening of hundreds of thousands of genetic variants of the COX2 mitochondrial gene to seek insight into approaches that will work for the allotopic expression of this and other mitochondrial genes. I think that this is a worthy endeavor, and I donated a modest amount to the project. Screening of very large numbers of options is a good way forward where years of more rational step by step design have failed to cover enough of the possible paths to find success, especially when it can be accomplished for a reasonable cost. The laboratory tools of genetics and gene therapy cost little these days.

Finding a Cure for Mitochondrial DNA Diseases through COX2 Variations to Restore Cell Function

Mitochondrial DNA is highly prone to mutation due to a variety of factors and these mutations result in several pathologies. Our endeavor is in identifying gene therapy approaches to address these mutations. The COX2 gene is a core component of Complex IV in the oxidative phosphorylation relay. Mutations in this gene are associated with Complex IV deficiency affecting a critical step in the oxidation of cytochrome C using molecular oxygen.

Our lab has successfully produced proteins for all 13 genes found in mitochondria by allotopic expression, but only one (ATP8) has successfully restored function in a disease-model cell line. Natural evolution has already transferred more than 1000 genes from mitochondrial DNA to the nucleus. Our goal is to find variants of the COX2 gene that can help cells function properly by mimicking the natural evolutionary process. Results from such an experiment would not only be a significant step towards efficacious COX2 gene therapy but would also provide key insights into the genetic changes necessary for successful allotopic expression of all mitochondrial genes.

We propose to generate more than 1 million variants for the COX2 gene using error-prone PCR similar to a study performed in yeasts and test these variants in rescuing oxidative phosphorylation, a function that is crucial for ATP production in cells. The nutrients that we consume are metabolized to CO2 and high-energy electron donors that further combine with oxygen to convert ADP to ATP. We will test this in a human model cell line that is lacking the COX2 protein. This cell line is unable to grow in nutrient medium restrictive for oxidative phosphorylation. Upon placing the variants in such a medium, only cells that are capable of performing oxidative phosphorylation can survive. Such a screen would allow us to identify functional variants of the COX2 gene for further analysis.

The aged vasculature is diminished in its ability to deliver blood to tissues via a range of different mechanisms and their consequences. Capillary density is lost, and the heart weakens, for example. This affects the ability to supply nutrients and oxygen to energy hungry tissues such as the brain, and this in turn affects function. The balance of supply and demand in the brain is not a steady state situation, however. It is complex, just like everything else in the body. Researchers here find a way to measure the degree to which this dynamic, complex balance becomes disrupted with age, thereby contributing to dysfunction.

A healthy brain requires sufficient supplies of glucose and oxygen to function properly, and any impairment of the vasculature will affect their delivery to the target cells. The brain and cardiovascular system work closely together in a common endeavour to match energy supply to demand. Their intimate relationship is reflected in the concept of the neurovascular unit (NVU), corresponding to consideration of the neurons, astrocytes, microglia, pericytes, endothelial cells, and basement membrane as a single functioning entity.

The risk of neurodegenerative disorders increases with age, due to reduced vascular nutrition and impaired neural function. However, the interactions between cardiovascular dynamics and neural activity, and how these interactions evolve in healthy aging, are not well understood. Here, the interactions are studied by assessment of the phase coherence between spontaneous oscillations in cerebral oxygenation measured by functional near-infrared spectroscopy (fNIRS), the electrical activity of the brain measured by EEG, and cardiovascular functions extracted from ECG and respiration effort, all simultaneously recorded.

Signals measured at rest in 21 younger participants (31.1 ± 6.9 years) and 24 older participants (64.9 ± 6.9 years) were analysed by wavelet transform, wavelet phase coherence, and ridge extraction for frequencies between 0.007 and 4 Hz. Coherence between the neural and oxygenation oscillations at ∼ 0.1 Hz is significantly reduced in the older adults. This reduction in coherence indicates that neurovascular interactions change with age. The approach presented promises a noninvasive means of evaluating the efficiency of the neurovascular unit in aging and disease.

Link: https://doi.org/10.1016/j.brainresbull.2023.110704

The research noted here adds to evidence for the lack of use of the senses to contribute to age-related declines in cognitive function: a sort of "use it or lose it" proposition for the brain that becomes especially pronounced in later life. This effect is better studied in the context of age-related deafness, given the sizable amount of data on hearing aid use. Here, however, researchers focus on the sense of smell, and find that cognitive function can be improved by stimulation via scents.

When a fragrance wafted through the bedrooms of older adults for two hours every night for six months, memories skyrocketed. Participants in this study reaped a 226% increase in cognitive capacity compared to the control group. The project involved men and women aged 60 to 85 without memory impairment. All were given a diffuser and seven cartridges, each containing a single and different natural oil. People in the enriched group received full-strength cartridges. Control group participants were given the oils in tiny amounts. Participants put a different cartridge into their diffuser each evening prior to going to bed, and it activated for two hours as they slept.

People in the enriched group showed a 226% increase in cognitive performance compared to the control group, as measured by a word list test commonly used to evaluate memory. Imaging revealed better integrity in the brain pathway called the left uncinate fasciculus. This pathway, which connects the medial temporal lobe to the decision-making prefrontal cortex, becomes less robust with age. Participants also reported sleeping more soundly.

Scientists have long known that the loss of olfactory capacity, or ability to smell, can predict development of nearly 70 neurological and psychiatric diseases. These include Alzheimer's and other dementias, Parkinson's, schizophrenia, and alcoholism. Evidence is emerging about a link between smell loss due to COVID-19 and ensuing cognitive decrease. Researchers have previously found that exposing people with moderate dementia to up to 40 different odors twice a day over a period of time boosted their memories and language skills, eased depression and improved their olfactory capacities. The team decided to try turning this knowledge into an easy and non-invasive dementia-fighting tool.

Link: https://news.uci.edu/2023/08/01/sweet-smell-of-success-simple-fragrance-method-produces-major-memory-boost/

The signaling environment in the body is generated by cells, communication mediated by the molecules that cells release and take up, many of which are packaged into extracellular vesicles. This signaling changes profoundly between development and adult life, and then again in important ways with advancing age. In principle, providing aged tissues with the signals passed back and forth during embryonic development will spur greater maintenance and regeneration. In practice, tissues are systems of great and only partially understood complexity, and attempts to beneficially manipulate signaling in this way are still very much a work in progress, even after decades of effort.

The transplantation of forms of stem cell is perhaps the most successful approach to date when it comes to manipulation of cell signaling for benefit. Stem cells die off following transplantation, but while they survive, their signals influence surrounding tissues. Yet these therapies are as yet nowhere near as reliable or successful as desired, again a matter of complexity: which cells; how to culture them; how to deliver them; how to replicate winning strategies. Deriving extracellular vesicles from stem cell populations will likely run into many of the same issues, but this approach is at least less logistically complex, and thus less costly. Just as researchers produce evidence for benefits in animal models derived from transplantation of embryonic stem cells, they also demonstrate that extracellular vesicles can produce interesting results. This remains some way from clinical application in the mainstream, though increasingly available via medical tourism.

Today's open access paper is an example of the transition from cell therapy to extracellular vesicle therapy. The authors use a population of progenitor cells derived from the embryonic heart to produce vesicles, and demonstrate positive results in old rats following injection of these vesicles into the heart. This delivery of embryonic signaling may or may not be reducing harmful cellular senescence via reprogramming; it is a little early to say whether or not the reduction in senescence results from that mechanism. It is, however, quite interesting to see benefits throughout the body resulting from an injection of vesicles into the heart.

Rejuvenating effects of young extracellular vesicles in aged rats and in cellular models of human senescence

Cardiosphere-derived cells (CDCs) are cardiac progenitor cells with broad-ranging bioactivity in preclinical and clinical studies. Recently, we found that transplantation of young CDCs exerts anti-aging effects in old rodents, improving heart function. Although we specifically targeted the heart in that study, multiple systemic benefits were evident, hinting that soluble factors might play a prominent role. In vitro experiments revealed that extracellular vesicles (EVs) from CDCs (CDC-EVs) mimicked the anti-senescent effects of CDCs, at least partially through activation of the telomerase-telomere axis. Together with the anti-tumorigenic effects of CDC-EVs in old rats with spontaneous leukemia, it seems reasonable to hypothesize that anti-senescent properties of CDC-EVs may underlie the benefits. If so, EVs might be logical therapeutic candidates for a variety of aging-related diseases.

Treatment with young CDC-EVs induce structural and functional improvements in the heart, lungs, skeletal muscle, and kidneys of old rats, while favorably modulating glucose metabolism and anti-senescence pathways. Repeated systemic administration of young CDC-EVs in aged rodents triggered broad-ranging functional improvements, with concordant structural changes in different organs and associated evidence of tissue rejuvenation. The beneficial effects of CDC-EVs were maintained over mid-term follow-up, with prolongation of survival of treated animals. But, beyond longevity, the changes we observed in heart and kidney function, glucose metabolism, and exercise tolerance have the potential to improve quality of life, which is an important goal of anti-aging therapies.

Using a single cell-free therapeutic agent, young CDC-EVs, we demonstrated that multiple pathologies can be favorably modulated. Moreover, tissue fibrosis contributing to organ dysfunction was broadly ameliorated (heart, lungs, skeletal muscle, and kidneys exhibited less interstitial fibrosis) in CDC-EV treated rats. Based on these findings, CDC-EVs emerge as a strategy capable of targeting pathophysiologic mechanisms underlying many age-related chronic conditions. Both MiR-146 and miR-92a highly enriched in CDC-EVs known to be implicated in aging-related pathways may have played a role in rejuvenating effects observed in our study.

Cellular senescence is thought to contribute to progressive age-related organ dysfunction. Previously, we described an anti-senescent effect of young CDC-EVs in vitro. Here, we confirm that cellular rejuvenation, conceived as partial or total reversal of senescence, can be also achieved in vivo in old animals injected with young CDC-EVs. Benefits include telomere elongation in heart cells, less-active DNA damage response (represented by phosphorylated γH2AX), lower IL-6 levels, and changes in protein levels suggestive of enhanced mitochondrial biogenesis in skeletal muscle. Extensive transcriptomic differences in treated versus control groups were consistent with the observed upregulation of the transcription factor NANOG and extracellular signal-regulated kinase ERK 1/2. Both are recognized regulators and stabilizers of the pluripotency gene regulatory network. Accordingly, we speculate that the mechanism of action of young CDC-EVs is related in part to the control of the dynamic state of pluripotency and reprogramming, a strategy that has been touted in pursuit of rejuvenation.

It has only comparatively recently become widely understood that the microbial populations making up the gut microbiome change in abundance in characteristic ways with age. Similarly, that the gut microbiome tends to be different in characteristic ways in older people who go on to develop Alzheimer's disease. It remains to be seen as to whether an altered gut microbiome is a meaningful contributing cause to Alzheimer's disease, such as via increased chronic inflammation, or a side effect of some other meaningful contribution, such as the aging of the immune system. At the least, it presents a novel way to assess risk in older people. We might hope that it will be more than that, and that means of rejuvenating the gut microbiome, such as fecal microbiota transplantation using young donors, will significantly reduce the incidence of Alzheimer's disease.

Studies have shown that the gut microbiomes of people with symptomatic Alzheimer's differ from those of healthy people with normal cognition. Now, new work shows that these differences arise early on in people who will develop Alzheimer's, even before any obvious symptoms appear. The science still has a way to go before we'll know if specific dietary changes can alter the gut microbiome and modify its influence on the brain in the right ways. But what's exciting about this finding is it raises the possibility that doctors one day could test a patient's stool sample to determine if what's present from their gut microbiome correlates with greater early risk for Alzheimer's dementia. Such a test would help doctors detect Alzheimer's earlier and intervene sooner to slow or ideally even halt its advance.

Researchers enrolled 164 healthy volunteers, age 68 to 94, who performed normally on standard tests of cognition. They also collected stool samples from each volunteer and thoroughly analyzed all the microbes from their gut microbiome. Study participants also kept food diaries and underwent extensive testing, including two types of brain scans, to look for signs of beta-amyloid plaques and tau protein accumulation that precede the onset of Alzheimer's symptoms.

Among the volunteers, about a third (49 individuals) unfortunately had signs of early Alzheimer's. And, as it turned out, their microbiomes showed differences, too. The researchers found that those with preclinical Alzheimer's had markedly different assemblages of gut bacteria. Their microbiomes differed in many of the bacterial species present. Those species-level differences also point to differences in the way their microbiomes would be expected to function at a metabolic level. These microbiome changes were observed even though the individuals didn't seem to have any apparent differences in their diets.

The team is now conducting a five-year study that will follow volunteers to get a better handle on whether the differences observed in the gut microbiome are a cause or a consequence of the brain changes seen in Alzheimer's. If it's a cause, this discovery would raise the tantalizing possibility that specially formulated probiotics or fecal transplants that promote the growth of "good" bacteria over "bad" bacteria in the gut might slow the development of Alzheimer's and its most devastating symptoms.

Link: https://www.nia.nih.gov/news/changes-human-microbiome-precede-alzheimers-cognitive-declines

At some point, the various measures of biological age currently under development and assessment will coalesce into some form of consensus measurement, largely agreed upon, the objections to its use minimal and circumstantial. At that point, a great deal of effort will go into assessing established and new interventions that might decrease or slow the progression of that consensus measure of biological age. It will likely take some decades for the back and forth of real time validation of interventions to treat aging to progress thereafter, but things will certainly become a great deal more heated once the research community agrees on how to best measure biological age. Meanwhile, anyone can propose a measure and demonstrate that some interventions affect it, but as of now it remains unlikely that any great number of other people will agree that this is the right, useful, or in any way proven measure of aging.

Clinical healthy aging recommendations are disease-centric and reactive rather than focusing on holistic, organismal aging. In contrast, biological age (BA) estimation informs risk stratification by predicting all-cause mortality, however current BA clocks are not connected to underlying aging mechanisms, making it difficult to intervene clinically.

To generate actionable BA clocks, we developed and validated a principal component (PC)-based clinical aging clock (PCAge) that identifies signatures (PCs) associated with healthy and unhealthy aging trajectories. We observed that by intervening in PC-specific space, angiotensin-converting-enzyme inhibitors (ACE-Is) or angiotensin receptor blockers (ARBs) normalize several modifiable clinical parameters, involved in renal and cardiac function as well as inflammation. Proactive treatment with ACE-I/ARBs appeared to significantly reduce future mortality risk and prevented BA acceleration.

Finally, we developed a reduced BA clock (PC_mAge), based directly on PCAge, which has equivalent predictive power, but is optimized for immediate application in clinical practice. Our geroscience approach points to mechanisms associated with BA providing targets for preventative medicine to modulate biological processes that drive the shift from healthy functioning toward aging and the eventual manifestations of age-related diseases.

Link: https://doi.org/10.1101/2023.07.14.23292604

It is interesting see an increased focus on assessing the ability of mitochondrial transplantation to be useful in a variety of circumstances, not just as a treatment to reduce the mitochondrial dysfunction that occurs with aging. The limiting factor in bringing mitochondrial transplantation to the clinic is chiefly the speed at which the research and development communities can achieve the logistical advances needed to reliably produce enough mitochondria to deliver to an entire organ (at first), and the whole body (later). It is likely the case that mitochondria will have to be patient-matched by haplotype of mitochondrial DNA, which further multiplies the size of the necessary infrastructure. Several biotech startups are working on this challenge, and the research community anticipates that present small tests will point the way to later clinical trials, once it is possible to manufacture sufficient mitochondria in a cost-effective way.

Today's research materials provide an example of one such small test of mitochondrial transplantation, focused on the treatment of kidney damage in the context of disease and transplantation. It is possible that mitochondrial transplantation can be used to greatly improve the quality of donor organs, reducing the cell death and damage resulting from the stresses of the transplantation process. Though not the focus of the research here, good results in this context also suggest that mitochondrial transplantation would be useful as a treatment for acute kidney injury.

Study Shows Mitochondrial Transplantation Effective in Reversing Damage to Kidneys and Kidney Cells

Mitochondrial transplantation is a regenerative medicine technology where healthy mitochondria are taken from cultured cells or tissue from organ donors and then injected into a diseased or damaged tissue or organ. Mitochondria produce the energy needed for a cell to function. "Here, we provide evidence that mitochondrial transfer lessens the damage that renal cells or the kidneys may suffer from disease or injury." For the study, the research team conducted preliminary tests in cultures of human proximal tubular cells, which are found in the kidneys and play an important in removing toxins. When the damaged cells were exposed to healthy mitochondria, cellular energy increased, and toxicity decreased.

Additional research found that kidneys injected with healthy mitochondria showed signs of recovery. These results are significant because in the U.S., 20% of the kidneys procured for transplantation are eventually discarded because they are too damaged, and this potential new treatment may help. This is especially true in a new type of organ donation called "uncontrolled donation after cardiac death," an area of active research. In this setting, the kidneys do not receive adequate blood supply, and mitochondria and the kidneys are damaged.

Mitochondria Transplantation Mitigates Damage in an In Vitro Model of Renal Tubular Injury and in an Ex Vivo Model of DCD Renal Transplantation

Mitochondrial transplantation (MITO) is a process where exogenous isolated mitochondria are taken up by cells. As virtually any morbid clinical condition is characterized by mitochondrial distress, MITO may find a role as a treatment modality in numerous clinical scenarios including acute kidney injury (AKI).

In vitro, cells treated with MITO showed higher proliferative capacity and ATP production, preservation of physiological polarization of the organelles and lower toxicity and reactive oxygen species production. Ex vivo, kidneys treated with MITO shed fewer molecular species, indicating stability. In these kidneys, pathology showed less damage while RNAseq analysis showed modulation of genes and pathways most consistent with mitochondrial biogenesis and energy metabolism and downregulation of genes involved in neutrophil recruitment

Atherosclerosis is, fundamentally, a condition centered around the function, capabilities, and age-related dysfunction of macrophage cells. These innate immune cells are responsible for clearing excess cholesterol, transported via LDL particles, from blood vessel walls. As macrophages become more dysfunctional with age, or otherwise shift in their activities due to rising inflammatory signaling, deposits of cholesterol can reach a tipping point at which they can no longer be cleared and turn into atherosclerotic lesions. Macrophages in the lesions are overwhelmed by the excess of cholesterol, become inflammatory, and die, adding their mass to the growing lesion while also calling in more macrophages to suffer the same fate.

Researchers have identified a specific subtype of complement-producing macrophages that are present in both mouse as well as human atherosclerotic plaques. The complement system is a family of blood-borne proteins with crucial importance in host defense from pathogens. In addition, complement exerts critical housekeeping functions by aiding the removal of damaged and dying cells by macrophages. Part of the complement is continuously active by the generation of cleavage products of the central component C3 - a process that is highly regulated by CFH. Complement activation has long been implicated in human atherosclerosis - however, the pathologic importance of cellular versus systemic complement activation in lesion progression has not been appreciated.

"In contrast to the conventional understanding that the role of complement in atherosclerosis is primarily driven by liver-derived complement via the circulation, there has been increasing evidence that immune cells can also produce a defined set of complement components. However, if and how complement is controlled within these cells has been unknown. We were able to demonstrate that inflammatory monocyte-derived macrophages accumulate complement C3, the central complement component during inflammation with a concomitant increase in the production of its master regulator, CFH."

"First, we made the surprising observation that global lack of CFH displays an overall beneficial impact on plaque progression, which is dependent on its interaction with C3. Building on these data, we were able pinpoint, that the protective effect is exerted on the cellular level, as selective deletion of CFH in monocytes and macrophages led to a robust decrease in both atherosclerotic lesion size and necrotic area due to an improved capacity to ingest and clear dying cells. Importantly, we identified a distinct inflammatory macrophage subset in human coronary artery plaques that is specifically enriched for C3 and CFH. Based on their gene expression profile, these cells are wired to respond to inflammation and appear to be critical for the engulfment of dying cells in human plaques."

Link: https://www.meduniwien.ac.at/web/en/about-us/news/2023/news-in-july-2023/cardiovascular-disease-key-molecular-pathway-affecting-atherosclerosis-progression-discovered/

Heterochronic parabiosis is the surgical joining of the circulatory systems of an old and young mouse, both of the same genetic background. The younger mouse shows signs of accelerated aging, while the old mouse shows signs of rejuvenation. This has led to a broad range of research and development focused on age-related changes in levels of various signal molecules in the bloodstream. Some groups continue to look at declining levels of specific molecules such as GDF11 and oxytocin that might be boosted in old mice, but at present the consensus appears to be that old blood contains damaging signals, changing cell behavior for the worse. Thus any dilution of those signals is beneficial, whether achieved with young blood or with saline. Here, researchers demonstrate that a few weeks to a few months of parabiosis is enough to modestly extend life span in old mice.

A process of surgically joining the circulatory systems of a young and old mouse slows the aging process at the cellular level and lengthens the lifespan of the older animal by up to 10%. Researchers found that the longer the animals shared circulation, the longer the anti-aging benefits lasted once the two were no longer connected. The findings suggest that the young benefit from a cocktail of components and chemicals in their blood that contributes to vitality, and these factors could potentially be isolated as therapies to speed healing, rejuvenate the body, and add years to an older individual's life.

Earlier studies documented anti-aging benefits in tissues and cells of the older mice after three weeks of parabiosis. These studies found that the older mice became more active and animated, and their tissue showed evidence of rejuvenation. "Our thought was, if we see these anti-aging effects in three weeks of parabiosis, what happens if you bring that out to 12 weeks. That's about 10% of a mouse's lifespan of three years." The ages of the mice were also important, with the young mouse aged four months, and the older mouse aged two years. With follow-up during a two-month detachment period, the older animals exhibited improved physiological abilities and lived 10% longer than animals that had not undergone the procedure.

At the cellular level, parabiosis drastically reduced the epigenetic age of blood and liver tissue, and showed gene expression changes opposite to aging, but akin to several lifespan-extending interventions such as calorie restriction. The rejuvenation effect persisted even after two months of detachment. "The elements that are driving this are what's important, and they are not yet known. Are they proteins or metabolites? Is it new cells that the young mouse is providing, or does the young mouse simply buffer the old, pro-aging blood? This is what we hope to learn next."

Link: https://corporate.dukehealth.org/news/aging-process-slows-when-older-mice-share-circulatory-system-young

It seems clear that many of the varied approaches to adjusting the operation of metabolism in ways that (usually modestly) slow aging in animal models achieve this outcome by acting on a set of common underlying mechanisms. For example, a great deal of effort has gone towards the study of autophagy in this context, a response to mild stress that improves cell function by recycling damaged molecular machinery. Upregulation of autophagy appears to be a feature of most of the better studied approaches to slowing aging, and certainly those derived from investigations of calorie restriction.

What do more sophisticated efforts to find commonalities between age-slowing interventions look like? Today's open access paper offers some insight into that question. The authors report on an approach to the analysis of omics data from biological samples taken from mice following intervention, in search of a greater understanding of the resulting changes in metabolism. This is potentially a vast amount of data, and the exercise is narrowed by considering only liver tissue samples. Even so, the researchers identify changes in the operation of fatty acid metabolism as a common feature of several quite diverse approaches shown to slow aging in short-lived species. The idea is that this sort of analysis will aid in the more deliberate design of different, better interventions in the future.

Lifespan-extending interventions induce consistent patterns of fatty acid oxidation in mouse livers

Some nutritional and pharmacological interventions consistently extend lifespan and healthspan (i.e., the period free from age-associated diseases and disabilities) in mouse and other animal models. Nutritional interventions include calorie restriction (CR), methionine restriction, and ketogenic diet. While the number of possible geroprotectors (i.e., drugs aiming to prevent, slow, or reverse aging process) has been growing, pharmacological interventions whose effects on lifespan extension have been documented by the National Institute on Aging (NIA) Interventions Testing Program (ITP) include acarbose (ACA), canagliflozin, 17α-estradiol (17aE2), glycine, nordihydroguaiaretic acid, Protandim (a Nrf2 inducer), and rapamycin (Rapa).

Rapa modulates nutrient-sensing pathways by inhibiting the activity of mTOR through complex formation with FK506-binding protein 12, which globally attenuates protein translation via mTOR complex 1 (mTORC1) and ultimately reduces inflammation, increases autophagy, and improves stem cell maintenance. ACA could share some aspects of CR; it is an oral antidiabetic drug which competitively inhibits the activity of α-glucosidase enzymes to digest polysaccharides, resulting in the delay of sugar uptake in the gastrointestinal tract. ACA treatment has been shown to extend lifespan in male mice more than in female mice, possibly related to sex-dependent differences observed in heart, liver, and gut metabolite profiles. 17aE2 is a stereoisomer of the dominant female sex hormone 17β-estradiol, having much weaker binding affinity to the classical estrogen receptors, stronger affinity to the brain estrogen receptor, and neuroprotective properties. 17aE2 treatment extends lifespan in male but not in female mice, potentially related to male-specific reduction of age-associated neuroinflammation and sex-specific metabolomic responses observed in liver and plasma metabolite profiles. Because these lifespan-extending drugs were tested with standardized protocols in the NIA ITP and because they have differences in primary mode of action, comparisons of their effects on molecular regulation are valuable for our understanding of common, fundamental, or core aging and longevity mechanisms.

A module of a biological system can be represented as a molecular network where nodes and edges correspond to biomolecules (e.g., gene transcripts, proteins, and metabolites) and relationships (e.g., physical interactions, chemical reactions), respectively. For each sample, ranks of biomolecules can be obtained from experimental data by ordering the values of interest (e.g., abundances, levels of specific post-translational modification) between the biomolecules within a module. When these ranks are highly conserved among the samples within a population of a specific phenotype, the module is considered tightly regulated in the population, because biological regulatory mechanisms or pressures must act consistently across the samples to produce this high conservation pattern. In contrast, low rank conservation among the samples within a phenotype indicates loose module regulation in the population.

In this study, we report systemic changes in the molecular regulation of biological processes under multiple lifespan-extending interventions, by jointly leveraging systems-level analyses on two mouse liver proteomic datasets, which were generated in the NIA Longevity Consortium, and a previously published mouse liver transcriptomic dataset. Differential Rank Conservation (DIRAC) analyses of mouse liver proteomics and transcriptomics data show that mechanistically distinct lifespan-extending interventions (acarbose, 17α-estradiol, rapamycin, and calorie restriction) generally tighten the regulation of biological modules. These tightening patterns are similar across the interventions, particularly in processes such as fatty acid oxidation, immune response, and stress response.

Senescent cells accumulate with age and cause harm via a sustained, energetic production of signal molecules, the senescence-associated secretory phenotype (SASP), that disrupts tissue structure and function. In addition to the search for senolytic drugs that can selectively destroy senescent cells by pushing them into programmed cell death, researchers are also looking for senomorphic drugs that can suppress some or most of the SASP by interfering in its regulatory mechanisms. This seems to me a poor alternative to clearance of senescent cells, as a senomorphic drug must be taken continually, but nonetheless a great many such research programs are underway.

Aging is a major risk factor for most chronic disorders, for which cellular senescence is one of the central hallmarks. Senescent cells develop the pro-inflammatory senescence-associated secretory phenotype (SASP), which significantly contributes to organismal aging and age-related disorders. Development of senotherapeutics, an emerging class of therapeutic agents to target senescent cells, allows to effectively delay aging and alleviate chronic pathologies. Here we report preliminary outputs from screening of a natural medicinal agent library for senotherapeutic candidates and validated several agents with prominent potential as senomorphics.

Rutin, a phytochemical constituent found in a number of plants, showed remarkable capacity in targeting senescent cells by dampening expression of the full spectrum SASP. Further analysis indicated that rutin restrains the acute stress-associated phenotype (ASAP) by specifically interfering with the interactions of ATM with HIF1α, a master regulator of cellular and systemic homeostasis activated during senescence, and of ATM with TRAF6, part of a key signaling axis supporting the ASAP development toward the SASP. Conditioned media produced by senescent stromal cells enhanced the malignant phenotypes of prostate cancer cells, including in vitro proliferation, migration, invasion, and more importantly, chemoresistance, while rutin remarkably downregulated these gain-of-functions. Although classic chemotherapy reduced tumor progression, the treatment outcome was substantially improved upon combination of a chemotherapeutic agent with rutin.

Our study provides a proof of concept for rutin as an emerging natural senomorphic agent, and presents an effective therapeutic avenue for alleviating age-related pathologies including cancer.

Link: https://doi.org/10.1111/acel.13921

Researchers here report on progress in their program of demonstrating that upregulation of VEGF and Runx2 in combination can accelerate bone regrowth. In this animal study the researchers employed a therapy based on delivery of messenger RNA (mRNA) encapsulated in nanomicelle carrier particles formed from polyethylene glycol and polyamino acid. This produces short-term, localized expression of VEGF and Runx2 in the injured bone tissue when injected directly, and is a suitable basis for translation to clinical use, where the carrier might be swapped out for one of the more established lipid nanoparticle carriers.

Bone defects remain a challenge today. In addition to osteogenic activation, the crucial role of angiogenesis has also gained attention. In particular, vascular endothelial growth factor (VEGF) is likely to play a significant role in bone regeneration, not only to restore blood supply but also to be directly involved in the osteogenic differentiation of mesenchymal stem cells. In this study, to produce additive angiogenic-osteogenic effects in the process of bone regeneration, VEGF and Runt-related transcription factor 2 (Runx2), an essential transcription factor for osteogenic differentiation, were coadministered with messenger RNAs (mRNAs) to bone defects in the rat mandible.

The mRNAs were administered to a bone defect prepared in the rat mandible using our original cationic polymer-based carrier, the polyplex nanomicelle. The bone regeneration was evaluated by micro-computerized tomography (μCT) imaging, and histologic analyses.

Osteogenic markers such as osteocalcin (Ocn) and osteopontin (Opn) were significantly upregulated after mRNA transfection. VEGF mRNA was revealed to have a distinct osteoblastic function similar to that of Runx2 mRNA, and the combined use of the two mRNAs resulted in further upregulation of the markers. After in vivo administration into the bone defect, the two mRNAs induced significant enhancement of bone regeneration with increased bone mineralization. Histological analyses using antibodies against CD31, ALP, or OCN revealed that the mRNAs induced the upregulation of osteogenic markers in the defect, together with increased vessel formation, leading to rapid bone formation.

Link: https://doi.org/10.1186/s41232-023-00285-3

Much of the communication between cells passes back and forth in the form of extracellular vesicles, membrane-wrappd packages of molecules that are presently far from completely cataloged or understood. This lack of full understanding hasn't stopped the growth of an industry seeking to replace stem cell therapies with vesicles harvested from those stem cells. It seems clear from the evidence to date that most stem cell therapies produce benefits via signaling, and not because transplanted cells survive to engraft in any meaningful numbers. In principle, use of vesicles allows for less expensive, more logistically practical forms of treatment, as vesicles can be indefinitely stored, and their production involves far fewer of the challenges of quality and consistency found in stem cell manufacture. In practice, this is a still a work in progress in the world of regulated medicine, even given that extracellular vesicle treatments are readily available in the world of medical tourism.

In today's open access paper, researchers discuss the mechanisms by which delivery of extracellular vesicles harvested from embryonic stem cells reduces measures of aging in animal studies and reduces incidence of cellular senescence in cell cultures. It may or may not be a good idea to prevent or reverse cellular senescence, as some cells become senescent for good reason, being damaged in ways that might provoke cancerous behavior if not stopped. Further, some senescent cells exhibit sizable amounts of DNA damage that is induced on the transition into a senescent state. On the other hand, in aged tissues many cells may become senescent only in response to the signaling of other senescent cells, or due to stress that is survivable given a little more resilience or support. Some of the better-studied approaches to slowing aging clearly prevent cellular senescence to some degree, such as mTOR inhibition. One suspects that when it comes to risk, the details of the biochemistry matter greatly for any novel approach to rescuing cells from the senescent state.

Embryonic stem cell-derived extracellular vesicles rejuvenate senescent cells and antagonize aging in mice

A few decades ago, rejuvenation or amelioration of aging seemed impossible. However, in the last decades, the concept of parabiosis and partial reprogramming with pluripotency-related factors has changed our view on the subject, indicating that factors derived from young cells prevent senescence. Researchers found that young circulating extracellular vesicles (EVs) can regenerate aged muscle. Previously, we found that EVs derived from embryonic stem cells (ESCs) could rejuvenate the aged MSCs (mesenchymal stem cells) and rescue their regenerative capacity. Recently, several rejuvenation factors enriched in ESC-EVs or ESC-CM (conditioned medium) have been identified, such as TGF-β, Smad2, PDGF-BB (platelet-derived growth factor-BB), miR-291a-3p, miR-294, and miR-200a. However, the roles and mechanisms of ESC-EVs in vivo are unknown.

Here, we investigate the anti-senescence effects of ESC-EVs in vivo using aged mice. Our data show that ESC-EVs treatment rescues the transcriptome profile of aged mice and ameliorates the senescence status of several aged organs, providing evidence that ESC-EVs may be candidates for the therapy of various age-related diseases. Others have found that EVs from young adipose-derived stem cells improved motor coordination, grip strength, fatigue resistance, and significantly reduced frailty in aged mice. However, the effects of ESC-EVs treatment on cognitive function and motor activity in aged mice remain unclear and require further investigation.

Furthermore, we identify miR-15b-5p and miR-290a-5p, which are enriched in ESC-EVs and exert rejuvenating effects by silencing of the Ccn2-mediated AKT signaling pathway. miR-15b-5p and miR-290a-5p are crucial for ESC-EVs rejuvenation. Their target gene of Ccn2 is upregulated in aged cells and can be rescued by ESC-EVs treatment. Several studies have shown that Ccn2 induces cellular senescence and activates the PI3K/AKT signaling pathway, suggesting that Ccn2 may be a potential target for anti-aging. We found that miR-15b-5p and miR-290a-5p silenced Ccn2, thereby inhibiting the Ccn2-dependent AKT signaling pathway and ameliorating the senescence.

In conclusion, here, we demonstrate a novel mechanism for ESC-EVs to protect cells from senescence. However, whether ESC-EVs rejuvenate aged mice via miR-15b-5p and miR-290a-5p remains unknown. Next, we plan to use miR-15b-5p and miR-290a-5p antagonists while treating aged mice with ESC-EVs to further investigate the mechanism by which ESC-EVs resist aging in vivo.

There are many ways of looking at the pathology of Alzheimer's disease, as it is very complex, layered condition. One of these viewpoints is to note that levels of oxidative stress increase in the Alzheimer's brain, stressing and killing cells. Researchers here report on their investigation of changes in the NRF2-centered regulation of cellular antioxidant systems that take pace in the Alzheimer's brain. A decline in antoxidants accelerates the progression of cell death and dysfunction, but this can be slowed or prevented by suitably targeted intervention aimed at maintaining NRF2 activity. Whether or not this is too far downstream of the causes of Alzheimer's disease to be useful in human patients remains to be seen, but there is enough of a benefit in animal models to ensure continued efforts to build drugs that target this mechanism.

A protein called Nuclear factor erythroid 2-related factor 2 (Nrf2) is regularly activated in response to oxidative stress to protect the brain from oxidative damage. But in the brain of someone with Alzheimer's disease (AD), Nrf2 defense against oxidative stress declines. How that occurs in AD was unknown. A new study found that a protein called Slingshot Homolog-1, or SSH1, stops Nrf2 from carrying out its protective biological activity.

Genetically eliminating SSH1 in mouse models of AD increases Nrf2 activation and slows the development of oxidative damage and buildup of toxic plaques and tangles in the brain - both risk factors for AD. As a result, the regular connections between brain cells are maintained and degeneration of brain nerve cells is avoided.

Link: https://www.eurekalert.org/news-releases/996543

Researchers here report that an overlooked aspect of mitochondrial dysfunction with age, the ability of these organelles to take up calcium ions, provides an important contribution to age-related chronic inflammation when it occurs in the innate immune cells known as macrophages. With advancing age, the immune system falls into a harmful state of overactivation, often referred to as inflammaging. A range of different mechanisms have been shown to contribute to imflammaging, such as the pro-inflammatory secretions of senescent cells, persistent viral infection, mislocated mitochondrial DNA, excess visceral fat tissue, and so forth. Altered mitochondrial calcium metabolism makes an interesting addition to the list; it remains to be seen as to how this issue might be best targeted for therapy.

In this study, we report a surprising discovery that mitochondrial Ca2+ (mCa2+) uptake capacity in macrophages drops significantly with age. This amplifies cytosolic Ca2+ (cCa2+) signaling and promotes NF-κB activation, rendering the macrophages prone to chronic low-grade inflammatory output at baseline and hyper-inflammatory when stimulated. Although mitochondrial dysfunction has long been a suspected driver of aging, our study pinpoints the mitochondrial calcium uniporter (MCU) complex as a keystone molecular apparatus that links age-related changes in mitochondrial physiology to macrophage-mediated inflammation.

Both chronic low-grade inflammation and mitochondrial dysfunction are known hallmarks of aging, but mechanistic links between these two processes have not been defined with clear links to human biology. For example, defective mitophagy in Prkn-/- mice may contribute to inflammaging by shedding mitochondrial DNA as an inflammatory stimulus in senescent cells. Although a progressive age-associated decline in mitophagy is not evident in human myeloid cells, if one supposes that there is a steady age-associated shedding of inflammatory mediators from other senescent cells, our findings predict that the decreased mCa2+-uptake capacity will render the macrophages hyper-responsive to such inflammatory stimuli from senescent cells and thereby drive inflammaging.

A recent study performed a comprehensive analysis of mitochondrial phenotypes in purified human cell types and mixtures but omitted mCa2+ uptake as a marker of mitochondrial fitness. Interestingly, the authors found that their mitochondrial health index was most impaired in monocytes isolated from aged human donors. Although we chose to focus on macrophage-mediated inflammation, the broad outlines of the mechanistic model are likely applicable to other myeloid cells such as neutrophils and mast cells too, and that is an important line for our future investigations.

Link: https://doi.org/10.1038/s43587-023-00436-8