Fight Aging!

It is that time again, an arbitrary midwinter point in the annual pilgrimage around the sun at which we take a look back to summarize some of the high points of the past year. As has been the case for a few years now, progress towards the implementation of rejuvenation therapies is accelerating dramatically, ever faster with each passing year. While far from everyone is convinced that near term progress in addressing human aging is plausible, it is undeniable that we are far further ahead than even a few years ago. Even the public at large is beginning to catch on. While more foresightful individuals of past generations could do little more than predict a future of rejuvenation and extended healthy lives, we are in a position to make it happen.

The State of Funding

A great deal of venture funding is arriving or preparing to arrive to support biotech startups that are working on means to treat aging. This year saw the launch of the Longevity Vision Fund, among others. I can think of three groups presently working to launch new mid-sized longevity-focused venture funds in 2020, and this is as seen from my fairly sedate perch of observation, without any great attempt to reach out and ask folk for a census. This activity will have an beneficial influence on public and private funding available for fundamental science in this part of the field. It also influences non-profit advocacy, as new organizations such as the Academy for Health and Lifespan Research are created. New governmental initiatives are also emerging, such as the Healthy Longevity Global Grand Challenge, and not just in the US: the UK government is putting out position statements on health longevity. Regulators are being petitioned by the scientific community to approve treatment of aging as a recognized goal for medicine. We should expect this trajectory to continue, though beyond the clearance of senescent cells, where development of therapies is very much a going concern, few approaches to rejuvenation are very close to making the leap from laboratory to clinical development.

There is no shortage of new companies targeting aging, many of which are (unfortunately, I think) focused on manipulation of stress responses rather than rejuvenation. BHB Therapeutics works on ketosis mechanisms. Turn.bio aims to produce a safe way to partially reprogram cells in vivo, restoring youthful function. Samsara Therapeutics works on autophagy enhancement. Rejuvenate Bio works on gene therapies to slow aging, initially in dogs. My own company, Repair Biotechnologies, still young, raised a seed round to fund our work on thymic regeneration and reversal of atherosclerosis. The Oisin Biotechnologies spinoff OncoSenX also raised a seed round this year to deploy their suicide gene therapy in cancer patients, and LIfT Biosciences raised funds to develop immune cell transplants that have been shown to do very well against cancer in animal models. Underdog Pharmaceuticals is the SENS Research Foundation spinout targeting 7-ketocholesterol (which may be important in more than just atherosclerosis). They raised a seed round this year and are well on their way. Nanotics has launched a senolytics program based on interfering in mechanisms that senescent cells used to evade immune surveillance. For more you might look at the recently created Aging Biotech Info and its curated list of companies in the longevity industry.

Speaking of funding, the SENS Research Foundation year end fundraiser is coming to a close. More than three quarters of a million dollars were donated last year. I hope that you all did your part and contributed this year - helping this form of research is the most effective form of altruism, given the size of the potential benefits. The SENS Research Foundation remains one of the most important organizations in research aimed at treating aging. Just because senolytics to clear senescent cells are a going concern, we cannot ignore the fact that the rest of the rejuvenation research agenda is nowhere near as advanced. It still needs funding, and near all funding for many of these vital projects remains philanthropic. We fund it. We are the people who make that difference, ensuring that important research projects can advance to the point at which they attract the support of more conservative, mainstream sources of large-scale funding.

Conferences and Community

These days, I'm as often as not out and about in the world raising funding or reporting on progress for a startup biotech company, Repair Biotechnologies. I'm found at many more conferences than would otherwise be the case. Side-effects of the growth of the longevity industry over the past few years include a change in the tenor of existing scientific conferences, as well the addition of new conference series on aging that are focused as much on industry as on academia. This past year, I attended and wrote up a few notes on the following events: the SENS Research Foundation / Juvenescence gathering in San Franscisco held alongside the big JPM Healthcare conference; the first Longevity Therapeutics event, also in San Francisco; the Longevity Leaders conference in London; the vitally important Undoing Aging in Berlin; Biotech Investing in Longevity in San Francisco; the Ending Age-Related Diseases conference organized by LEAF in New York; BASEL Life, Founders Forum, LSX USA, and Giant Health in quick succession later in the year; the Alcor New York Science Symposium; and the Longevity Week events in London coordinated by Jim Mellon and his allies.

Many conference presentations and interviews with members of the growing community have been published over the past year, too many to note each and every one. The few that caught my eye:

• Interviewing Kelsey Moody of Ichor Therapeutics at the Longevity Leaders Conference
• An Interview with Sebastian Aguiar of Apollo Ventures
• David Sinclair on the Academy for Health and Lifespan Research
• Video of Investor Jim Mellon Presenting at Abundance 360 Summit 2019
• An Interview with Carolina Oliveira of OneSkin Technologies
• A Few of the Many Interviews Conducted at the Undoing Aging 2019 Conference
• An Interview with Felix Werth of the German Party for Health Research
• An Interview with Aubrey de Grey at Undoing Aging 2019
• Aubrey de Grey on the Dawn of the Era of Human Rejuvenation
• An Interview with Vittorio Sebastiano of Turn.bio
• An Interview with Jim Mellon of Juvenescence at Undoing Aging 2019
• An Interview with María Blasco on Telomeres and Telomerase
• An Interview with Morgan Levine on the Epigenetic Clock
• Jim Mellon Interviewed by Adam Ford at Undoing Aging 2019
• An Interview with Reason at Undoing Aging 2019
• An Interview with Daniel Ives of Shift Bioscience
• An Interview with Tristan Edwards of Life Biosciences
• Matthew O'Connor Presenting on Underdog Pharmaceuticals at Undoing Aging 2019
• An Interview with Aubrey de Grey at Longevity.Technology
• LEAF Interviews David Sinclair
• A Perspective on Longevity Biotech Investment from James Peyer of Kronos BioVentures
• Kelsey Moody Presenting on the LysoClear Program at Ending Age-Related Diseases 2019
• An Interview with Justin Rebo of BioAge
• An Interview with Amutha Boominathan of the SENS Research Foundation
• An Interview with Sergey Young of the Longevity Vision Fund
• A Profile of Tissue Engineering Efforts at LyGenesis
• An Interview with Brian Kennedy of the Center for Healthy Aging in Singapore
• Declan Doogan of Juvenescence Presenting at Investing in the Age of Longevity
• On Making Philanthropy in Support of Rejuvenation Research Attractive to Investors

Clinical Development

Drug development pipelines are moving forward, though not always smoothly. There is a high failure rate in the development of medical biotechnology. Eidos Therapeutics announced Phase II results for their approach to preventing transthyretin amyloid aggregation. Gensight is presently struggling with phase III for allotopic expression of mitochondrial genes - the mechanism works, the earlier trials passed, and now reaching sufficient efficacy is proving to be a challenge. Intervene Immune published interesting results from their small thymic regeneration trial, while Libella Gene Therapeutics is launching a patient paid trial for telomase gene therapy. The resTORbio approach to inhibition of mTORC1 failed a phase III trial for immunosenescence, which may or may not cast a pall over that part of the industry. The TAME clinical trial for metformin, using a new composite endpoint as a surrogate for aging, was funded this year and will start soon. This despite the point that metformin remains terrible choice of intervention, picked because the FDA couldn't object to it on technical grounds, not because anyone thinks that it will produce meaningful results for patients. Opinions are mixed on this topic.

The first human trials of senolytic therapies to clear senescent cells reported results this year, starting with promising results for lower dose dasatinib and quercetin versus idiopathic pulmonary fibrosis. Data from an as yet incomplete trial of dasatinib and quercetin versus chronic kidney disease has confirmed that these senolytics do clear senescent cells in humans in the same way as in mice. Unity Biotechnology announced results from their first trial of senolytics for osteoarthritis of the knee, and is moving on to phase II. There are those who think that there is still a long road ahead to the clinic. A trial of fisetin by the Mayo Clinic has yet to publish results, but for those who'd like to follow along at home in advance of data, the Forever Healthy Foundation published a risk/benefit analysis covering what is known of fisetin as a senolytic.

Cellular Senescence

Senescent cells accumulate with age and contribute to degenerative disease, despite their many beneficial roles earlier in life. Senolytics to selectively destroy lingering senescent cells continue to show great promise in animal models, and as a class of therapy appear about as close to a panacea as it is possible to be. New supporting evidence published over the course of 2019 offers the potential of effective treatment for a range of conditions: Alzheimer's disease, osteoporosis, osteoarthritis, rheumatoid arthritis, atherosclerosis, cardiac fibrosis and hypertrophy, periodontitis, pulmonary fibrosis, cataracts, aortic aneurysm, acute kidney injury, chronic kidney disease, heart failure, type 1 diabetes, type 2 diabetes, thrombosis, degenerative disc disease, immunosenescence due to changes in hematopoiesis, pulmonary disease resulting from smoking, age-related loss of liver function, neurodegeneration through astrocyte senescence, recovery from heart attack, and recovery from chemotherapy. The accumulation of senescent T cells is an important component of immune aging and chronic inflammation, including some of the issues observed in type 2 diabetes. Visceral fat tissue produces many of its harmful effects via the generation of more senescent cells than would otherwise be created.

Any number of compounds are under evaluation as potential senolytics, though we should always be skeptical of effect size until animal data is in hand, particularly when the compounds include those already in widespread use, as drugs, supplements, or components of diet. Compounds recently examined for senolytic effects include circumin analogs, the fibrate class of drugs used to treat raised blood lipid levels, cardiac glycosides used in treatment of aspects of heart disease, and quercetin coated nanoparticles. Other approaches also exist: exosomes from embryonic stem cells clear senescent cells, and it may be possible to interfere in the mechanisms that senescent cells use to evade the immune system. Further, designed compounds that are transformed into toxins by senescence-associated β-galactosidase, which is upregulated in senescent cells, appear a promising line of attack.

A great deal of research is ongoing into the biochemistry of cellular senescence, not least because any particular mechanism might turn out to be the basis for therapies that meaningfully turn back aging - there is a little of the element of a gold rush to the work. Senescent cells are large because they produce too much protein in expectation of cell division that doesn't occur - or possibly also because they consume neighboring cells. The ceremides found in extracellular vesicles increase senescence. Versican may link the hyperglycemic diabetic metabolism to increased vascular calcification via cellular senescence. The harmful secretions of senescent cells, the senescence-associated secretory phenotype (SASP) depend on certain aspects of the heterochromatin. The activity of L1 retrotransposons also appears relevant to the SASP. Naked mole-rat senescent cells do not exhibit the SASP, which goes a long way towards explaining how this species can exhibit robust good health even while accumulating senescent cells just like other mammals. Meanwhile, researchers are producing a comprehensive map of all of the molecules making up the SASP, many of which are conveyed via exosomes. Another group has published a database of senescence-associated genes. Acute myeloid leukemia turns out to produce senescent cells to aid its own growth. The gene ccna2 is a regulator of the senescent state. Rising levels of aneuploidy may be important in increasing numbers of senescent cells. Upregulation CBX4 or DGCR8 reduces senescence in mice. Melanocytes are the only epidermal cell type to exhibit senescence. Age-related AT1 autoimmunity may spur generation of senescent cells in vascular tissue, and consequent vascular dysfunction.

An important part of the senolytics industry, and one that has so far lagged behind, is the ability to quantify the number of senescent cells in different tissues by age, along with their pace of creation. A start on senescence burden by tissue and age was published this year for mice, accompanied by a good review on the far patchier data for humans. Are these errant cells lingering for years on end, or is turnover and clearance still happening in very old people, and just needs a helping hand? Recent work on topical rapamyin for skin aging and the speed of senescent cell clearance by age suggests that the latter model is more the case. Answering these questions robustly will require better means of quantifying senescence in patients without restoring to a biopsy. This might be achieved via fluorescent reporter genes, or, for senescence in the kidney, by suitable urinalysis. It will likely also require better and more consistent signatures of cellular senescence.

Mitochondria in Aging

Mitochondrial function is clearly important in the progression of aging. Why does it falter consistently in cells throughout the body? Proximate causes appear to involve a loss of fission, leading to worn and damaged mitochondria that are too large to be effectively cleared by mitophagy; this appears to be related to changing expression of PUM2 and MFF, but how that relates to the underlying molecular damage of aging remains a question.

A method of enhancing mitophagy has been shown to improve mitochondrial function in old humans. Other approaches to mitochondrial decline are at various stages of development, such as delivering entire mitochondria that are taken up by cells and put to work. The SENS Research Foundation team continues to work on allotopic expression of mitochondrial genes as a way to prevent certain forms of mitochondrial DNA damage from causing cells to become pathological, and crowdfunded one of the next steps in their program this year.

Efforts to increase NAD+ levels in old mitochondria are enjoying considerable support at present, though it remains to be proven rigorously that they are producing benefits in the many people who are chosen to employ the various supplements. Animal studies and human trials continue, as does the more fundamental research into the biochemistry of NAD+ in mitochondria. An NMNT inhibitor improves NAD+ salvage to increase stem cell function. Nicotinamide riboside improves intestinal stem cell function. The levels of eNAMPT may be important in the way nicotinamide mononucleotide supplementation increases NAD+. Increased NAD+ levels also slows age-related hearing loss in mice.

Nuclear DNA Damage

Random mutations can spread through a tissue when they occur in stem cells or progenitor cells. There are also epigenetic mutations to consider, persistent and aberrant changes in epigenetic markers that alter the production of proteins. Is this damage a meaningful cause of aging beyond its contribution to cancer risk, though? Most mutations happen in genes that are turned off in tissues. There was a discussion earlier this year of the evidence for this sort of clonal expansion of mutations to be involved in neurodegeneration.

The most interesting new work to emerge this year suggests that repair of certain types of DNA damage causes the epigenetic changes observed to take place with age. Since this mechanism doesn't depend on the mutation of specific genes, and the effect arises wherever the DNA damage occurs in the genome, this is viable alternative to explain how mutational damage can contribute to aging in a way that is very similar in every cell, despite the random nature of the damage, and the fact that the damage largely occurs to irrelevant portions of the genome. It also has implications for the viability of epigenetic reprogramming as an intervention. That the pathological outcomes of the DNA repair deficiency Werner syndrome were shown this year to be strongly dependent on mitochondrial dysfunction, which itself emerges from changes in gene expression mediated by epigenetics, might be taken as somewhat supportive of this new line of work.

Cross-Links

There has been little further progress towards bringing approaches to cross-link breaking into a new generation of startup companies this year. Revel Pharmaceuticals, spinning out from the Spiegel Lab at Yale, has yet to raise seed funding to progress beyond initial setup - this is taking far too long, for reasons that have little to do with the technical details. An interesting unrelated advance relates to cross-links in the lens of the eye, which are completely different from those in other tissues in the body and thus require a different approach. A cross-link breaker for these forms of cross-link was trialed for age-related presbyopia, and the results were good.

Neurodegeneration

In neurodegenerative research, the concept that failing drainage of cerebrospinal fluid from the brain is an important component of these conditions is gaining support. Cerebrospinal fluid drainage clears metabolic waste from the brain - and this clearance fails with age as the channels are disrupted by tissue dysfunction. Researchers have suggested that hypertension may contribute to the effect, along with age-related declines in lymphatic vessel function, and have provided evidence for reduced flow to correlate with cognitive decline.

Another growing theme in the study of neurodegenerative conditions is the importance of chronic inflammation. This is thought to be the mechanism by which gum disease is linked to Alzheimer's risk, for example. The neuroinflammation model of Alzheimer's disease inverts the first two steps in the amyloid cascade hypothesis: instead of amyloid aggregation causing chronic inflammation, which in turn produces tau aggregation, the chronic inflammation is the whole of the cause of the early stages of the condition, with amyloid as a side-effect. Much the same view is argued for Parkinson's disease and its protein aggregates. The infection hypothesis is a different aspect of this view, in which amyloid aggregation and chronic inflammation both arise from persistent viral infection. A variant of this hypothesis places more emphasis on the way in which infection generates senescent immune cells in the brain, promoting inflammation via that path. In any of these possibilities, dysfunction in glial cells is an important part of the inflammatory process, and depleting these cells reduces inflammation and consequent tau pathology. There is evidence in mice for herpesviruses to accelerate amyloid buildup. Whatever the order of causation, there is good evidence for amyloid and tau aggregates to synergize with one another in degrading neural function.

The evidence for CMV to generate chronic inflammation and otherwise impact immune function suggests that persistent viral infection is harmful in general, not just when it comes to the brain. The immune system and its decline is an important determinant of aging, and chronic inflammation is the proximate cause of a sizable fraction of age-related disease. Complicating matters, chronic inflammation might even contribute to thymic involution, an important cause of immune aging.

The Alzheimer's community is looking for new approaches. There is an increasing focus in the Alzheimer's research community on targeting tau rather than amyloid-β. A variety of methods are under exploration. An existing farnesyltransferase inhibitor drug was found to reverse tau aggregation in a mouse model. Approaches aimed at clearance of amyloid-β have not gone away, of course, and are still very actively developed. The use of affibodies is becoming explored, to pick one example. Clearance of protein aggregates is still a comparatively underutilized approach for other neurodegenerative conditions, however. There is still work taking place, such as small molecule discovery to interfere in α-synuclein aggregation in Parkinson's disease, or catching α-synuclein aggregation in the gut before it spreads to the brain. Researchers are also investigating the heat shock response as a way to direct greater clearance of protein aggregates, as well as the far more promising use of catabodies as pioneered by Covalent Bioscience.

The blood-brain barrier has long been thought important in neurodegeneration. Dysfunction in the barrier is an early leading indicator of larger neurodegeneration, though, confusingly, amyloid aggregation can cause blood-brain barrier leakage. This dysfunction is centered around the tight junction structures of the barrier, and it isn't just neurodegenerative conditions in which this is a factor. Many forms of damage to the brain are characterized by leakage of the blood-brain barrier. Early disruption of the barrier might be due in part to increased levels of acid sphingomyelinase. The primary contribution of blood-brain barrier dysfunction to neurodegeneration may well be that leaking barrier allows the passage of cells and molecules that drive chronic inflammation in brain tissue, such as fibrinogen.

Upregulation of Cell Maintenance

Upregulation of the various cell maintenance processes in order to modestly slow aging, particularly autophagy (a process that shows up everywhere in aging) and the ubiquitin-proteasome system, is an area of active research. Autophagy is known to decline with age for a variety of reasons, such as progressive failure to form autophagosomes. Recent evidence links this decline to aging in skin, and accumulation of senescent cells in the brain.

Strangely, there hasn't been all that much progress towards the clinic over the past decade, despite all of this ongoing activity. Restoration of mitophagy has been proposed as a potential treatment for neurodegenerative conditions. Upregulation of autophagy in general has recent evidence supporting its use in slowing the progression of sarcopenia, memory B cell decline, and atherosclerosis. Researchers have also proposed altering the behavior of the proteasome to target unwanted molecules, such as those altered by misfolding, or achieving a similar effect by binding unwanted proteins to component parts of the autophagosome, ensuring they get dragged along to the lysosome for disassembly. Targeting the GATA transcription factor can upregulate autophagy. The proteasome can be made more active by increasing production of one of its component parts, which is an interesting potential strategy that is gaining some support in the research community. Improving cellular maintenance in intestinal stem cells extends life in flies, a species in which intestinal function is particularly important in aging.

In Vivo Cell Reprogramming

A number of groups are working on in vivo cell reprogramming, applying similar strategies to that used to produce induced pluripotent stem cells, but in a living animal. Turn.bio launched this year to work on a method of partial reprogramming, and another group has demonstrated regeneration from optic nerve injury. The challenge here is cancer risk, and the gains appear at this point to be some combination of restoring more youthful mitochondrial function and epigenetic control of gene expression.

Parabiosis

Work on parabiosis continues apace, linking the circulatory systems of an old and young animal and observing the results on each. It is a way to identify factors in young blood and tissue or old blood and tissue that can slow or accelerate aging, for all that the evidence is somewhat confusing and contradictory at this time. The two companies in the space in recent years, Ambrosia and Alkahest have produced only marginal results in human trials. Researchers have found MANF as a possible factor in young blood, associated with liver function. Factors in young blood appear to influence kidney function via upregulated autophagy. It is argued that most of the effects of parabiosis are mediated by the contents of extracellular vesicles, not individually secreted proteins. Beyond parabiosis, there are other approaches that involve introducing young tissue into old animals. Researchers have shown that transplanting young bone marrow into old mice is beneficial, resulting in extended life span.

The Gut Microbiome in Aging

Research into the role of changes in the gut microbiome in aging seems to be hitting its stride. The effect size of the loss of beneficial bacteria and gain in harmful bacteria is an open question, but studies in short-lived animals suggest it might be in the same ballpark as that of exercise. Certainly, healthier older people tend to have more youthful-appearing microbial populations, and this is true for thinner, fitter individuals as well. Changes in the microbiome are shown to contribute to inflammation and vascular dysfunction, as well as neurodegenerative conditions. Further, a number of quite concrete, actionable discoveries have been made in the past few years. The secretion of proprionate improves exercise capacity, and the microbes responsible are found in athletes. Optimizing gut microbial populations for greater butyrate production is beneficial to cognitive function. The populations responsible for providing tryptophan and indole decline precipitously in the mid 30s in humans, indicating supplementation of these metabolites or restoration of the lost microbes will be beneficial when started comparatively early in adult life, well ahead of most signs of aging.

Calorie restriction slows changes in the gut microbiome, but can these age-related changes be reversed? The answer is yes: transplantation of young microbes into old animals has produced good results in animal studies. Fecal microbiota transplantation is an established procedure in human medicine for conditions in which the gut is overtaken with pathological microbes, so perhaps it would not be a huge leap to extend it to improving the elderly gut microbiome. There are other approaches: limiting energy generation by pathological bacteria can diminish these populations; immunization against flagellin causes the immune system to more aggressively cull harmful gut microbes.

Biomarkers of Aging

The measurement of aging is an important goal. Quick, low-cost, reliable assessments that can be used shortly before and shortly after application of a potential rejuvenation therapy would greatly speed development of the field. Epigenetic clocks based on DNA methylation are the best known of present development programs aimed at producing biomarkers of aging. These clocks are multiplying rapidly, and do a fair job of predicting disease risk and mortality. Epigenetic age correlates with cancer risk, for example. The GrimAge clock was announced this year, as was a ribosomal DNA focused clock. In a related part of the field of epigenetic research, it was recently found that CpG site density in the genome correlates with species life span.

The clocks are not without their challenges. We don't know what they are actually measuring, and there is no guarantee that the results will be useful for any given therapy. Troubling results have been reported, the most recent of which include the inability of the clocks to distinguish between sedendary versus active twins, and lack of correlation between telomere length measures and epigenetic clocks.

Epigenetic measures are far from the only area of focus. Other groups are set on constructing biomarkers of aging from algorithmic combinations of simple measures such as grip strength, or from the gut microbiome. In the past year, other researchers have proposed intron retention via alternative splicing, the fundamentals of systems biology, measurement of protein levels in blood, and immune system metrics as potential foundations for a biomarker.

Cancer

I don't watch cancer research in as much detail as I did in past years. There is a lot of very interesting work taking place, nonetheless, and the outlook is favorable for those of us who are expecting to tackle our own cancers two decades or more in the future - survival rates continue to improve, and the technologies presently in trials or development are considerably better than past therapeutic approaches. Much of the focus these days is on the refinement of ways to unleash the immune system, removing suppression mechanisms that are preventing it from vigorously attacking tumors. For example by interfering in CD47 signaling or the newly discovered similar role for CD24. There are also more speculative early stage approaches such as permanently increasing the number of natural killer cells to reduce cancer risk, or clearing out subsets of tumor associated macrophages that appear to be suppressing anti-tumor immune function.

That said, some more exciting work turns up at early stages, such as a potentially safe way to suppress telomerase activity. All cancers require lengthening of telomeres, via telomerase or ALT. Turning that off could be a universal cancer therapy. On the ALT side of the house, researchers have found that inhibition of FANCM activity is a potential point of intervention.

The Genetics of Longevity

All things genetic continue to attract a great deal of funding. This is an age of low-cost, high-capacity genetic tools - but given a hammer, perhaps too many things start to look like a nail. Studies of recent years have shown over and again that genetic contributions to human variance in aging are near entirely some combination of rare and inconsistent, small in effect size, and overall not all that important. Essentially, we all age in the same way, because of the same causes, and the observed variance is largely down to environment, chance, and choice. Based on this, I predict, and we can come back and look at this prediction in a few years, that the benefits produced by senolytic rejuvenation therapies will be very little affected by human genetic variation, as this form of therapy targets a mechanism in which the size of effect is significantly larger than the variance in that effect.

Regenerative Medicine

Efforts are underway to replace first generation cell therapies of many sorts, some of which were never even deployed to the clinic, with the delivery of extracellular vesicles harvested from those cells. This appears a very promising line of work. Development is underway aimed at skin regeneration, such as via increased collagen production, as well as osteoporosis and thymic regrowth. One can also mix and match: use exosomes to make a cell therapy more effective. Another possible approach to the replacement of cell therapies is reprogramming of cells in situ, such as to make astrocytes or glial cells become neurons in the brain, or turning supporting retinal cells into photoreceptors, heart fibroblasts into cardiomyocytes, or inner ear cells into sensory hair cells to replace losses. There is also considerable interest in rejuvenating stem cell populations in situ via signaling molecules, gene therapies (such as upregulation of GAS1 in muscle stem cells, or Nrf2 for degenerative disc disease), or other strategies.

Cell therapies are of course still very much a going concern, for all that their implementation in the clinic has proven to be challenging. There are some surprising successes in animal models, such as the use of a stem cell therapy to restore lost sense of smell in mice. Researchers are working on ways to replace lost cell populations or influence disease processes in Parkinsons's disease, atherosclerosis, corneal damage, and hearing loss, just to list a small selection of work from the past year. A large part of working towards success in this goal is to ensure that more cells survive and engraft, and that might be achieved by as simple an approach as culling less healthy cells prior to transplant. The march towards more cost-effective means of cell therapy continues, with the creation of cell lines that can be used in every patient being a priority. That reprogramming cells into induced pluripotent stem cells reverses epigenetic signatures of aging seems like a good reason to put more effort into using these cells as a basis for therapy.

In the tissue engineering space, the research and development community continues to move towards the growth of human organs in animals as a source for transplantation. Meanwhile, organoids are being generated for many tissue types; work on the kidney is being carried out by numerous research groups. Further, some organs are simple enough that simpler, artificial versions are useful - artificial lymph nodes, for example, are a popular topic. Or bioprinted corneal tissue. Arguably the biggest advances of the past year have been demonstrations of printed tissue incorporating microvasculature, either directly printing vascular channels, via a form of sacrificial embedded printing, or by providing a mix of cells that generates a vasculature in and of itself, potentially working around the limits to size on engineered tissues. Justifiably, these advances received considerable attention.

Odds and Ends

As is usually the case, a range of scientific work was published this year relating to approaches that could in principle lead to enhancement biotechnologies that would improve health and capabilities for everyone, not just sick people. There is, sadly, near zero chance that most such approaches will be developed to the point of robust function and widespread availability, given the present regulatory environment. To pick a few examples: symbiotic bacteria that increase oxygen availability in tissues; CXCL12 promotes small artery growth, providing alternative paths for the bloodstream that can reduce mortality and harm from heart attacks and similar blood vessel blockages. One of the possible exceptions to the absence of development efforts is delivery of soluable klotho, which has been picked up by Unity Biotechnology to expand their pipeline beyond senolytics.

There are of course any number of other topics I could have discussed at greater length and chose to skip over for the sake of time. Destruction and recreation of the immune system as a way to put autoimmunity into remission continues to be promising, and continues to need a better, safer approach than hematopoietic stem cell transplantation. Age-associated B cells are a good target for more selective destruction, though, as ever, it doesn't fix as many problems as we'd like it to. Being fit is good for you, and in a world without rejuvenation therapies, exercise capacity is a better predictor of mortality than chronological age. Reversal of atherosclerosis is ever an interesting topic, and earlier this year I summarized some of the past work in this part of the field in the context of nattokinase. In this context, it is fascinating that humans seem to need far less cholesterol than we actually have in our bloodstreams, even in a healthy state. Naked mole-rats have a far more effective and resilient metabolism than other mammalian species, and it is possible that improved mitochondrial antioxidants might be a part of that general superiority - though this is a species that thrives under high oxidative stress. There was a sizable debate over whether or not Jeanne Calment was actually aged 122 at death. Late life mortality is in general tough to examine because the data is of a terrible quality, which makes it difficult to debate propositions such as whether or not there is a limit to human longevity in the present environment of slowly increasing life spans. Does obesity actually accelerate aging? Quite likely yes. Declines in the density of microvasculature may be an important mediating process in aging, linking fundamental molecular damage to declining tissue function as a consequence. TDP-43 protein aggregation is a comparatively newly discovered form of proteopathy causing neurodegeneration, and researchers continue to explore the implications. Human cell division rates decrease with age, which might explain why cancer risk actually declines in very late life. Amyloid buildup in the heart correlates with the risk of atrial fibrillation, adding to data from past years showing that amyloid contributes to heart disease and cardiac mortality. Dogs are a possibly underused model for aging research; that underuse might change with the growth of the Dog Aging Project.

Short Articles

As usual, a number of short articles were written over the past year, though it seems I'm doing this less often than used to be the case. Time is ever fleeting.

• Request for Startups in the Rejuvenation Biotechnology Space, 2019 Edition
• Rejuvenation Therapies Will Also Have Cycles of Hope and Disillusionment
• The Cosmological Noocene
• Taking the Founders Pledge to Donate to Charity Following a Liquidity Event
• How to Start a Biotech Company in the Longevity Industry

In Conclusion

A great deal of progress is being made in the matter of treating aging: in advocacy, in funding, in the research and development. It can never be enough, and it can never be fast enough, given the enormous cost in suffering and lost lives. The longevity industry is really only just getting started in the grand scheme of things: it looks vast to those of us who followed the slow, halting progress in aging research that was the state of things a decade or two ago. But it is still tiny compared to the rest of the medical industry, and it remains the case that there is a great deal of work yet to be done at all stages of the development process. Senolytics must reach the clinic and widespread availability, and that will involve the deployment of vast amounts of funding. At the same time, however, numerous other equally important lines of rejuvenation research are still largely stuck in the labs or in preclinial development at best. There is much left to accomplish.