Fight Aging! Newsletter, January 9th 2017

Fight Aging! provides a weekly digest of news and commentary for thousands of subscribers interested in the latest longevity science: progress towards the medical control of aging in order to prevent age-related frailty, suffering, and disease, as well as improvements in the present understanding of what works and what doesn't work when it comes to extending healthy life. Expect to see summaries of recent advances in medical research, news from the scientific community, advocacy and fundraising initiatives to help speed work on the repair and reversal of aging, links to online resources, and much more.

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  • 360,000 Given or Pledged to SENS Rejuvenation Research at the End of 2016
  • A Few Responses to the Edge Annual Question for 2017
  • An Interview with Neil Copes at Osiris Green, Offering DNA Methylation Biomarker of Aging Assessment as a Service to the Public
  • Glucose Metabolism and Acarbose in Aging
  • Calorie Restriction as a Means to Improve Surgical Outcomes
  • Latest Headlines from Fight Aging!
    • Exercise versus Sarcopenia in Mice
    • The Growth of Programmed Aging Theories in the Research Community
    • The Hallmarks of Aging Outlined for Laypeople
    • Investigating Mechanisms of Age-Related Increase in Fibrosis
    • Investigating the Mechanisms of Piperlongumine
    • Evidence for Some of the Burden of Fat Tissue to Result from Increased Levels of Cellular Senescence
    • Different Amyloid Plaque Structures in Different Forms of Alzheimer's Disease
    • Engineering Functional Stomach Tissue Organoids
    • Manipulating the Wound Healing Process to Prevent Scarring
    • Attempting to Build a Biomarker of Aging from Standard Blood Test Metrics

360,000 Given or Pledged to SENS Rejuvenation Research at the End of 2016

The last SENS rejuvenation research fundraiser of 2016 ended a couple of days ago, with the donations from hundreds of supporters going to the SENS Research Foundation in order to support ongoing scientific programs aimed at bringing an end to aging. Aging is a medical condition with root causes, just like any other, and effectively addressing those causes will allow degenerative aging to brought under control, halted, and reversed. That is the difference between the medicine of yesterday, which didn't have any great impact on the causes of aging, and the medicine of tomorrow, which will. Still, it isn't a sure thing for any specific time frame: most of the relevant areas of research, and the researchers involved, need a lot of help to overcome the technical hurdles and lack of funding endemic in early stage scientific endeavors. That is why we need organizations like the SENS Research Foundation, working to remove roadblocks and fund the areas of great scientific promise, but that are largely neglected by the mainstream. It is why we need grassroots, popular support for rejuvenation research, both to sustain these organizations and to light the way - with donations, discussion, and advocacy - for the more conservative wealthy philanthropists and foundations involved in the support of medical research. The more we help ourselves in the matter of aging research, the more additional help will arrive.

I'm pleased to note that, thanks to the many generous donors and those who put up challenge funds to match donations, 300,000 was raised in the main fundraiser over the course of November and December: 150,000 from donors and 150,000 from a matching fund provided by the Forever Healthy Foundation. In addition a little over 60,000 was pledged as monthly donations to be made over the next year by new SENS Patrons: 30,000 from donors and 30,000 from a challenge fund assembled by Josh Triplett, Christophe and Dominique Cornuejols, and Fight Aging! The SENS Research Foundation hasn't yet updated their site for the last minute donations from December 31st, but those numbers won't change too much. This is on top of the 70,000 raised through a crowdfunding project earlier in the year to support the OncoSENS work: scanning for drug candidates capable of suppressing alternative lengthening of telomeres, which is one half of a universal cancer therapy based on blockade of telomere lengthening. Of course, SENS Project|21 also launched in 2016, founded with a 10 million pledge from Michael Greve of the Forever Healthy Foundation. All in all it was a banner year for SENS Research Foundation funding. The enthusiastic support of our community over the years has helped build up to this, one donation, one act of advocacy, one conversation at a time. Every contribution helps, and many hands make light work.

For my part, while we didn't hit the 72,000 goal for SENS Patron pledges, the amount contributed and the number of people willing to sign up for monthly donations ensures that we'll be trying this again. Patronage is of course as old as science, and the SENS Research Foundation is definitely powered by the patronage of wealthier individuals like Aubrey de Grey, Peter Thiel, and Jason Hope. Until last year, however, the SENS Research Foundation fundraisers didn't do much with the newer crowdfunded patronage models for philanthropy by everyday individuals: collaborating to support the sciences with many modest donations. There is precedent. The very successful Methuselah 300 group provided the funds needed for much of the early success of the Methuselah Foundation, but that initiative stayed with the Methuselah Foundation when SENS rejuvenation research spun off into the SENS Research Foundation, even though the 300 donations continue to fund SENS research programs as they did before the split. I'd like to see some of that recaptured in the form of SENS Patrons, hundreds of people making a meaningful difference not just with their donations, but also because they are a very visible sign of material support and enthusiasm. The phenomenon known as social proof is a significant factor in whether wealthier philanthropists commit to an organization. Much as we'd like everyone to be perfectly rational about aging and rejuvenation research, those with the most to give are also the most conservative in the causes they support. They usually follow the crowd, or to be more charitable, rely on the analysis provided by the members of that crowd.

In any case, onward and upward! The trajectory of these fundraisers is heading upward if you look at the history: 60,000 in 2013, 150,000 in 2014, 250,000 in 2015, 360,000 in 2016. In each of these years, I can honestly say I had no idea how to reach that target; it seemed at the time an impossible mountain. Yet you, the readership here at Fight Aging! and the broader community beyond, rose to the challenge. Only this year were there times when it seemed donor exhaustion had set in, and generous individuals stepped in at several points to kickstart things with a timely five-figure donation. There is only so much that any one community can give in support of even the most vital cause without first growing in size; all along, bringing the ideas of rejuvenation biotechnology to new audiences, to gain new supporters, was as much the point as raising funds in these initiatives. This is still the case. So something to add to your resolutions for 2017: talk to someone new about the SENS Research Foundation and the prospects for reversing aging in our lifetime. You never know where it might lead.

A Few Responses to the Edge Annual Question for 2017

Every year Edge runs an annual question, publishing a few hundred short responses from noted scientists and other thinkers. A number of the folk who run companies or otherwise make waves relating to the development of therapies to treat aging are in this list, so it is usually interesting to see what they have to say. These year, awareness of the prospects for aging to be treated as a medical condition appears to be spreading, as it is mentioned in passing in a number of responses beyond the two linked below. The question for this year is "What scientific term or concept should be more widely known?", but that is somewhat beside the point; it is just a prompt to encourage people to riff on whatever their particular areas of interest might happen to be at the moment.

The two people I pulled from the crowd for this post are Gregory Benford, who is now well underway on his third notable career, this time as a biotechnologist focused on the use of drugs to adjust epigenetics in aging, and Aubrey de Grey of the SENS Research Foundation, who should need little introduction to this audience. These are representative figures from the two sides of a very important divide in the research and development of therapies to treat aging. On the one side we have attempts to modestly slow the pace of aging and onset of age-related disease through drugs, largely attempting to mimic existing natural effects that enhance longevity, such as calorie restriction, exercise, or the outcome of selective breeding to postpone reproduction. This is strongly associated with ongoing efforts to map the biochemistry of aging at the detail level, such as epigenetic and other changes in cellular biochemistry and signaling: greater coverage of the map is needed in order to make progress. On the other side we have efforts like the SENS rejuvenation research portfolio, in which the existing long-established identification of the root cause molecular damage of aging is used as the guide to work towards therapies that can repair that damage, thus turning back aging. The more comprehensive the repair, the more that aging should be halted or reversed.

The difference between these two approaches is night and day. Mapping the biochemistry of cells is enormously expensive and slow, and even a perfect replication of the biochemistry of calorie restriction - something that will be very, very hard to achieve at our present level of technology - will do comparatively little for human longevity, even though it would be very beneficial for overall health. We know this because calorie restriction practitioners don't live very much longer than the rest of humanity. If the effect was as large as it is in mice - 40% or so - it would have been discovered in antiquity. On the other hand SENS-style damage repair therapies are comparatively cheap to build, and produce more reliably beneficial outcomes, as illustrated by present development of senescent cell clearance approaches. They don't require anywhere near as much expensive, time-consuming new research in order to guide this development. Collectively, the effects on human life span will be determined by the effectiveness of the repair, with what should be very high upper limits if started early enough in life. The essential opposition of these two approaches is highlighted in the commentaries below, independently and sight unseen on the part of the authors.

Gregory Benford: Antagonistic Pleiotropy

Aging comes from evolution. It isn't a bug or a feature of life; it's an inevitable side effect. Exactly why evolution favors aging is controversial, but plainly it does; all creatures die. It's not a curse from God or imposed by limited natural resources. Aging arises from favoring short-term benefits, mostly early reproduction, over long-term survival, when reproduction has stopped. Thermodynamics doesn't demand senescence, though early thinkers imagined it did. Similarly, generic damage or "wear and tear" theories can't explain why biologically similar organisms show dramatically different lifespans. Most organisms maintain themselves efficiently until adulthood and then, after they can't reproduce anymore, succumb to age-related damage. Some die swiftly, like flies, and others like we humans can live far beyond reproduction.

In 1957 George Williams proposed the theory called antagonistic pleiotropy. If a gene has two or more effects, with one beneficial and another detrimental, the bad one exacts a cost later on. If evolution is a race to have the most offspring the fastest, then enhanced early fertility could be selected even if it came with a price tag that included decline and death later on. Because ageing was a side effect of necessary functions, Williams considered any alteration of the ageing process to be impossible. Antagonistic pleiotropy is a prevailing theory today, but Williams was wrong: we can offset such effects. Wear and tear can be countered. Wounds heal, dead cells get replaced, claws regrow. Some species are better at maintenance and repair. Some pursued this by deliberately aging animals, like UC Irvine's Michael Rose. Rose simply didn't let fruit fly eggs hatch until half each fly generation had died. This eliminated some genes that promoted early reproduction but had bad effects later. Over 700 generations later, his fruit flies live over four times longer than the control flies. These Methuselahs are more robust than ordinary flies and reproduce more, not less, as some biologists predicted. I bought these Methuselah flies in 2006 and formed a company, Genescient, to explore their genetics. We discovered hundreds of longevity genes shared by both flies and humans. Up-regulating the functioning of those repair genes has led to positive effects in human trials. So though aging is inevitable and emerges from antagonistic pleiotropy, it can be attacked. Recent developments point toward possibly major progress.

Aubrey de Grey: Maladaptation

Many years ago, Francis Crick promoted (attributing it to his long-time collaborator Leslie Orgel) an aphorism that dominates the thinking of most biologists: "Evolution is cleverer than you are." This is often viewed as a more succinct version of Theodosius Dobzhansky's famous dictum: "Nothing in biology makes sense except in the context of evolution." But these two observations, at least in the terms in which they are usually interpreted, are not so synonymous as they first appear. Most of the difference between them comes down to the concept of maladaptation. A maladaptive trait is one that persists in a population in spite of inflicting a negative influence on the ability of individuals to pass on their genes. Orgel's rule, extrapolated to its logical conclusion that evolution is pretty much infinitely clever, would seem to imply that this can never occur: evolution will always find a way to maximize the evolutionary fitness of a population. It may take time to respond to changed circumstances, yes, but it will not stabilize in an imperfect state. And yet, there are many examples where that is what seems to have occurred. In human health, arguably the most conspicuous case is that the capacity to regenerate wounded tissues is lost in adulthood (sometimes even earlier), even though more primitive vertebrates (and, to a lesser extent, even some other mammals) retain it throughout life.

Why is this so important to keep in mind? Many reasons, but in particular it's because when we get this wrong, we can end up making very bad evaluations of the most promising way to improve our health with new medicines. Today, the overwhelming majority of ill-health in the industrialized world consists of the diseases of late life, and we spend billions in the attempt to alleviate them - but our hit rate in developing even very modestly effective interventions has remained pitifully low for decades. Why? It's largely because the diseases of old age, being by definition slowly-progressing chronic conditions, are already being fought by the body to the best of its (evolved) ability throughout life, so that any simplistic attempt to augment those pre-existing defenses is awfully likely to do more harm than good. The example I gave above, of declining regenerative capacity, is a fine example: the body needs to trade better regeneration against preventing cancer, so we will gain nothing by an intervention that merely pushes that trade-off away from its evolved optimum.

An Interview with Neil Copes at Osiris Green, Offering DNA Methylation Biomarker of Aging Assessment as a Service to the Public

Osiris Green is a new clinical services business just getting underway, offering assessment of a DNA methylation biomarker of aging as a consumer product. For the customer it works much like the established consumer services for DNA sequencing that look at alleles and single nucleotide polymorphisms, such as 23andme, in that you send off a saliva sample and get back the results. DNA methylation is one of the forms of epigenetic decoration that controls the pace at which proteins are produced from their genetic blueprints, these markers constantly changing in every cell in response to circumstances and environment. For some years now patterns of DNA methylation have looked very promising as the foundation for a biomarker of aging, a way to assess biological age rather than chronological age. We age because we accumulate forms of cell and tissue damage that occur due to the normal operation of metabolism. That damage then spirals out to cause the wide variety of age-related diseases and disability, but at the base of it all we all age in the same fundamental way and for the same reasons, albeit at slightly difference paces due to our different choices and experiences. Therefore we all share the same cellular reactions to damage, and two people with much the same damage load and degree of aging should have quite similar DNA methylation patterns for at least some genes, there to be picked out from the noise of other changes.

A good biomarker of aging is an important component for the near future development of rejuvenation therapies, such as the senescent cell clearance treatments presently under development. Researchers can evaluate the effectiveness of senescent cell clearance in terms of proportion of these unwanted cells removed, and, based on the evidence showing cellular senescence to contribute to aging and age-related disease, expect to find that long-term health is improved. But how to then determine the results in terms of years of life expectancy gained as a result of that treatment? The only existing approach is to wait and see, which is expensive and time-consuming in animal studies, and out of the question for human trials. A biomarker for biological age that can be applied immediately before and immediately after an alleged rejuvenation treatment changes the entire picture of development, however. It enables a far more rapid assessment of therapies and lines of research, speeding up progress towards effective clinical treatments for the causes of aging. This is why I'm most pleased to see progress towards offering DNA methylation biomarker implementations as a paid service. Commercial development is an important part of breaking this technology out of the laboratory, getting more human data, trying different patterns, and settling upon the optimal set of genes to evaluate. I recently had the chance to talk to Neil Cope at Osiris Green and ask a few questions about this initiative and his thoughts on the industry:

Who is Osiris Green? How did you get together and decide that this was the thing to be doing in this new industry?

Currently, Osiris Green Inc. is myself and Dr. Clare-Anne Canfield, who I've known now for over two decades. Osiris Green really began in 2003 when she and I decided that extending human lifespan was the most important thing that we should be working on. We enrolled at the University of South Florida and earned our PhD's in Cell, Molecular, and Microbiology because of that decision. We officially started the company then after we graduated. By the way, the name Osiris Green isn't just a reference to Osiris, the green-faced Egyptian god of resurrection and regeneration. It's also a reference to a chapter titled "The Green Face of Osiris" in Dr. Michael West's 2003 book "The Immortal Cell," which is actually part of what initially inspired us to pursue lifespan extension in the first place.

The company began with the idea of providing customers with ways to measure various biological parameters that might correlate well with chronological age. We wanted ways for people to easily monitor their own aging at the cell and molecular level, with the idea being that these services could help in evaluating different antiaging therapies. Also, we liked the idea of building databases of anonymized user data that could let people match lifestyle parameters (diet, exercise, etc.) to trends in the molecular results. We began putting together protocols for proteomic and metabolomic profiling of blood and saliva (which closely mirrors the molecular contents of blood). We eventually developed a saliva-based proteomic profiling assay, but the cost for a single test - 200 to 500 depending on the depth of the analysis - seemed pretty prohibitive for most customers. Dr. Canfield and I started looking for faster and cheaper alternatives, which is when we began playing around with ideas for measuring gene promoter methylation. In the end I think it was a fortunate switch - DNA methylation states tend to have a tighter correlation to chronological age than other parameters, as detailed by all the excellent work coming from Steve Horvath.

How did you settle on the particular combination of genes you are testing?

We wanted a method that would be cheaper than using a genome-wide analysis or working with microarrays. I remembered a 2011 paper from Eric Vilain's lab linking chronological age with a fairly linear trend in methylation in the promoters of a small set of genes. We did a test run using just the TOM1L1 and NPTX2 promoters, which were among the top genes in the paper and fairly easy to work with from a technical standpoint. The initial results looked good so we developed the service from there.

You are forging ahead with your own implementation of part of the Horvath approach to epigenetic age; how are you validating it?

We're still a fairly small operation. So far validation has consisted of getting as much saliva as we could from friends and family members, and processing the samples. We then used CpG methylation and known chronological ages to calibrate our model. So far the linear model is estimating samples with an error of 7 years standard deviation from chronological age. The idea then is to continue performing estimates on paid samples and refining the model as necessary, even providing new estimates on older samples so that users can continue to get any refinements to their existing data as time goes on.

The Horvath and Hannum DNA methylation results have been out there for a while now. Why do you think it took so long for efforts like Osiris Green to emerge?

Because we're just now at a point as a species where real life extension is becoming a technological possibility. As such, public interest in life extension is slowly coming around. In 2003 when Dr. Canfield and I started working on our goal, the number of researchers in the field seemed disturbingly low. Since then, a decent amount of talent and funding has started flowing into lifespan research, due both to the advancing technology and to the efforts of people like Dr. Aubrey de Grey to bring awareness to the field. If this trend continues, I imagine the number of similar services as ours - and of life extension oriented companies in general - will only increase. Regardless of what happens with Osiris Green, I find it comforting that so many people and companies are now working on the problem in earnest.

Where do you see this broader field of rejuvenation research going over the next decade? Where does Osiris Green fit in to this picture?

I suspect that we'll see more clinical applications of the life extension technologies that are currently emerging. Human aging is a multifaceted problem, so the various ways to attack it are going to be diverse. I'm hoping to see things emerge like clinical trials of thymic regeneration coupled with immune system resets to eradicate anergic T cells; more and more senolytic drugs developed along with effective treatment regimens; and finally some useful age-breaker drugs making their way to market. Honestly, I'm in this for the long-haul, so I'm hoping to mold Osiris Green to help and provide services in any way that I can. In the short term, I'd like to simply expand the range of age-related markers that we can measure for customers, and to provide better and better resources for people interested in human aging.

If this works really well, and Osiris Green is flooded with customers, what is the next mountain to climb?

Oddly enough, Dr. Canfield and I have recently become fairly interested in the study of long-lived animals. Short-lived organisms, like C. elegans and Drosophila are cheap and easy to work with in a lab environment, and they make for quick experiments, but honestly they're bad models for longer-lived organisms like humans. Researchers are using these short-lived animals in an effort to extend human lives, but nature has already found ways for vertebrates to live longer natural lifespans than us. Dr. Canfield actually just finished writing a book that's a survey of the world's long-lived organisms, and the list of creatures that are relatively close to us evolutionarily is longer than most people realize. This list even includes animals like the American alligator and many species of turtle that are easily accessible in central Florida where we are located. We're currently involved with setting up a nonprofit organization for the study and conservation of long-lived species, and we're hoping that we can apply some of what we've learned from Osiris Green to build DNA methylation models for developing nonlethal ways to assess animal lifespans in the wild.

Glucose Metabolism and Acarbose in Aging

A large proportion of present research into the mechanisms of aging seeks the underlying reasons that link good lifestyle choices with greater life expectancy and lower incidence of age-related disease. When considered in the grand scheme of things, looking towards a future of rejuvenation and life spans ultimately extended by centuries and more, this is a fairly parochial concern: natural variations in longevity will cease to be important shortly after the clinical availability of the first generation of rejuvenation therapies based on the SENS research portfolio. Nonetheless, most investigative research is focused on what takes place today, on the way in which the current operation of metabolism determines the current pace of aging. The open access paper linked below is a good example of the type, focused on glucose metabolism, dysregulated in those who become overweight and diabetic, and the anti-diabetic drug acarbose. In the sense that today's large population of obese and diabetic individuals are a natural experiment in the human biochemistry of aging, members of the research community would like to learn what they can from this data.

Most of the readers here will know that type 2 diabetes is a lifestyle condition for the vast majority of patients, arising due to the effects of excess visceral fat tissue. This abnormal metabolic state in effect accelerates the damage of aging, through mechanisms such as increased chronic inflammation, but also others that stem from the malfunctioning glucose metabolism that diabetic patients exhibit. Researchers have used diabetes in animal models as a substitute for the aging process on a routine basis for decades, as the progression is more rapid and thus the studies are less costly in time and money. Diabetic patients have a shorter life expectancy and greater incidence of age-related disease than their healthy peers. This is also true, to a lesser degree, of those with lower levels of metabolic disorder and visceral fat, people who are on the way to full-blown diabetes but not there yet.

There are a range of drugs that interact with the dysfunctional diabetic metabolism to make matters less terrible, but no substitute for just losing the weight - low-calorie diets work pretty well even in later stage type 2 diabetes, and it is quite amazing that so few people actually undertake this course of action given the reliably positive outcomes. Among these drugs, acarbose is interesting because it has been shown to modestly extend life in normal mice. The effect of the drug is to inhibit uptake of carbohydrates from the diet, and thus reduce the delivery of new glucose into the workings of metabolism. That result suggests that we could all benefit to some degree from a lower intake of complex carbohydrates, such as the readily available sugar that is everywhere these days, not just the overweight and the diabetic. The authors of the paper here go into some detail while considering the mechanisms involved, though note that, like many researchers, they are unwilling to step beyond compression of morbidity within the existing human life span as a viable goal to aim for.

Targeting glucose metabolism for healthy aging

Aging is considered the largest risk factor for a variety of chronic and metabolic diseases. Unlike many risk factors (i.e., smoking, diet, weight gain), aging, by strict definition as the act of growing old, has not historically been considered to be modifiable. Aging and risk of disease development are so well intertwined that skepticism surrounding the idea of longevity extension persists, as a longer lifespan is considered by some as simply a prolonged opportunity to develop additional age-related diseases. Despite this concern, contemporary pursuit of methods to increase lifespan and healthspan through the process of slowing the accumulation of age-related damage to cells and tissues continues. Conceivably, an intervention to extend lifespan and/or healthspan would act through slowing the fundamental aging process(es) rather than preventing a single disease. It is possible that interventions to slow the aging process may result in an individual experiencing an extension of healthspan without significant increases to lifespan, as it is currently unknown if maximal lifespan can be extended in humans. Therefore, an individual might experience a compressed window of morbidity by living the great majority or potentially the entirety of lifespan without developing the disorders now commonly associated with aging.

A common co-morbidity observed in aging is metabolic dysfunction. While metabolic (e.g., glucose and mitochondrial) dysfunction is frequently associated with aging, the causal relationship between aging and metabolic dysfunction remains to be fully understood. The risk relationships among age and metabolic associated diseases suggest some factors may be better primary targets for longevity interventions than others. For instance, curing cancer may not necessarily be expected to significantly affect the subsequent risk for type 2 diabetes (T2D) or cardiovascular disease. In contrast, cardiovascular disease and T2D are more widely recognized as possible contributors to neurological disease risk and when remediated, could reduce the risk of dementia and neurodegenerative disease. Considering the coordinate increase in risk for a number of chronic diseases with advancing age and given the unclear interrelationship between these diseases, a stronger case might be made for targeting glucoregulatory control to decrease disease risk and consequently improve longevity. In fact, T2D is a significant risk factor for most other age-related diseases. If glycemic control were successfully maintained with advanced chronological age, this might slow the aging process, potentially delaying or preventing the development of multiple age-related diseases, allowing an individual to live healthier for longer.

Exactly which cellular or molecular mechanism(s) is primarily responsible for the associations of elevated glucose with chronic disease risks is not fully understood. Proposed causative mechanisms leading to accelerated aging include direct methods such as amplified and inappropriate glycosylation events, along with the production of advanced glycation end products that damage cellular functions from DNA repair to structural integrity and indirect contribution to the production of reactive oxygen species. Alternatively, maintenance of glycemic control may function as a biomarker of health maintenance from the cell to the organismal level. As such, one might expect a range of interventions targeting diverse mechanisms could share this glucoregulatory phenotype, resulting from some combination of maintained integrity of the cell, organelles, hormonal signaling or other factors coordinating metabolism and ultimately aging across the organism. Thus by indirect means, changes in glucose levels could significantly impact transcriptional programs or hormonal signaling to coordinately regulate processes currently known (or unknown) to influence the aging process (e.g., mitochondrial function, autophagy).

Glucose dysregulation, measured as either hypoglycemia or hyperglycemia, can result from problems along the entire glucose uptake, production, and metabolism spectrum. Hyperglycemia is commonly associated with advancing age and can occur as a result of decreasing insulin release in response to glucose and/or increased insulin resistance by tissues. Recent surveys of the adult population in the United States suggest that ≥50% of individuals over 45 years of age have T2D or prediabetes. This prevalence is greater with increasing age, with ∼80% of adults 65 or older showing glucose dysregulation. Thus, impaired glycemic control is approaching epidemic proportions both in the U.S. and throughout the world. Although the source of the metabolic imbalance driving glucose dysregulation may have multiple contributors, a surfeit of energy intake with increasing body weight and BMI are proposed to contribute.

One of the most direct methods of maintaining glucose homeostasis is through diet/nutritional interventions. Paramount among these is the dietary restriction (DR) or calorie restriction (CR) paradigm. Despite these reported health benefits, life-long dietary restriction in humans remains challenging given the current state of modern society in developed countries that has shifted from a limited food supply a century ago to nutritional excess today. Therefore, the identification of interventions that promote health and longevity independent of obligatory food intake reductions has been proposed as an alternative means to "mimic" the physiologic benefits of CR and reap health and longevity gains - a hypothetical class of compounds termed calorie restriction mimetics (CRMs).

The similarities between glucose dysregulation in aging and glucose dysregulation with T2D have led to the hypothesis that an effective CRM could be found by targeting glucoregulatory control. If an intervention is able to improve glucose regulation to treat or prevent T2D, it may prevent development of glucose dysregulation commonly observed with aging. The most well-known T2D drug that has been tested as a CRM is metformin. Metformin is reported to act through multiple pathways; however, the best-characterized pathway is through the activation of the cellular energy regulatory sensor AMP-activated protein kinase (AMPK). More recent pre-clinical work has highlighted another class of diabetic control agents that work upstream of insulin (and presumably metformin-related targets) while providing health and longevity benefits in lab models - namely the α-glucosidase inhibitor acarbose (ACA). When consumed with a complex carbohydrate-containing meal, ACA acts as a competitive inhibitor to carbohydrate breakdown along the brush border of the small intestine, resulting in reduced enzymatic degradation and absorption of glucose from complex carbohydrates. This inhibitor effect lowers the post-prandial blood glucose elevation in a dose-dependent manner.

Studies with non-diseased humans and rodents, as well as diabetic individuals, have described beneficial metabolic effects, most notably as reduced post-prandial blood glucose excursions with ACA. Insulin sensitivity is slightly improved with ACA, though post-prandial insulin levels do not show a consistent significant decrease. While the molecular, inhibitory action of ACA is well-detailed, fewer studies have attempted to explore the effect ACA has on specific nutrient retention from the diet and specifically if the weight loss sometimes reported with ACA administration is the result of reduced overall energy retention from the diet. Given the important roles of insulin signaling and IGF1 in body weight homeostasis and longevity, the benefits of ACA are more likely a result of the slowed uptake of sugars from the diet, resulting in lower post-prandial glucose excursions and moderated insulin responses. Considered as a whole, even in the absence of overt disease, these data suggest targeting glucoregulatory maintenance by acarbose or other means may be a viable nutritional target for maintaining health and delaying aging.

Calorie Restriction as a Means to Improve Surgical Outcomes

The long-term response to calorie restriction has long been of interest to the aging research community, and particularly in the past few decades as the tools of biotechnology allowed for a more detailed analysis of the metabolic changes that accompany a reduced calorie intake. A restricted diet extends healthy life spans in near all species tested to date, though to a much greater extent in short-lived species than in long-lived species such as our own. Considerable effort is presently devoted to the development of drugs that can replicate some fraction of calorie restriction - more effort than is merited in my opinion, given that the optimal result for extension of human life span achieved via calorie restriction mimetics will be both hard to achieve safely and very limited in comparison to the gains possible through rejuvenation therapies after the SENS model. Repairing damage within the existing system should be expected to outdo attempts to change the system in order to slow the accumulation of damage, in both efficiency and size of result.

Not everyone is interested in the long term, however. The short term health benefits of calorie restriction appear quickly and are surprisingly similar in mice and humans, given that calorie restriction in mice results in significantly extended life and calorie restriction in humans does not. The beneficial adjustments to metabolism and organ function are for the most part larger and more reliable than similar gains presently achievable through forms of medicine. That is more a case of medical science having a long way to go yet than calorie restriction being wondrous, however. Still, the short term benefits are coming to the attention to wider audience within the research and medical community. For example, calorie restriction and fasting are proving to be useful adjuvant treatments that improve outcomes for cancer patients: you might recall an interview with one of the researchers involved, as well as a paper from a few years back showing that periodic fasting improves recovery of the immune system from the damage caused by chemotherapy. In addition there is good evidence for calorie restriction and fasting to improve the outcomes following surgery, priming the body for the stress of that experience. Researchers have made some inroads in tracing the important mechanisms in this effect, as outlined in the following open access review paper:

Is Overnight Fasting before Surgery Too Much or Not Enough? How Basic Aging Research Can Guide Preoperative Nutritional Recommendations to Improve Surgical Outcomes

Dietary restriction (DR), or reduced food intake without malnutrition, was found in 1935 to extend lifespan of laboratory rats. Since that time, longevity extension by DR has been demonstrated in numerous experimental organisms from yeast to non-human primates. Fortunately, DR confers other important benefits that do not require long periods of food restriction, including increased resistance to multiple forms of acute stress. One of the biggest planned stressors many people will face in their life is that of major elective surgery, which carries inherent risks of complications. A novel concept in surgical risk mitigation emerging from basic research on DR and aging is dietary preconditioning, or short-term DR lasting one week or less prior to surgery. In rodent models of surgical stress ranging from ischemia reperfusion injury (IRI) to vascular restenosis (intimal hyperplasia), short-term DR or fasting before surgery, followed by a return to normal food intake after surgery, leads to improved outcomes.

Because of the plethora of physiological and molecular changes that occur even upon short-term restriction of a single essential amino acid from the diet, identification of critical downstream mechanisms of DR-mediated protection against surgical stress is challenging. Elucidation of upstream nutrient-sensing pathways such as GCN2 and mTORC1, for which genetic full-body or tissue-specific knockout models are available, has proven a critical step forward. Using experimental designs in which dietary interventions are combined with genetic models lacking upstream nutrient sensors that fail to gain protection upon DR, two major downstream mechanisms involving increased prosurvival insulin signaling and endogenous H2S production have recently been elucidated.

How does the DR-mediated improvement in hepatic insulin sensitivity contribute to protection from hepatic IRI? In addition to regulating energy metabolism, insulin can act as a prosurvival factor via negative regulation of apoptosis. Consistent with this mechanism of action, circulating insulin levels and antiapoptotic signaling are both increased in the hours after liver reperfusion in wild-type mice preconditioned on DR, while this effect is absent in mice with constitutive insulin resistance. Taken together, these data suggest that a major mechanism of DR action is via increased insulin sensitivity prior to an injury, which then facilitates increased prosurvival signaling and reduced hepatocyte apoptosis after injury.

Although toxic at high levels, endogenously produced H2S by one of three evolutionarily conserved enzymes is now recognized to have pleiotropic cytoprotective, anti-inflammatory and vasodilatory effects resulting in cardioprotection and resistance to ischemic injury. H2S also has direct antioxidant properties, and can participate in mitochondrial energy production by donating electrons to the mitochondrial electron transport chain protein SQR, with a potential role in protection from ischemia. Since pharmacological delivery of H2S also protects in models of surgical stress, as well as more broadly in preclinical models of cardiovascular disease, it remains to be seen if supplementation with exogenous sources of H2S, or increased endogenous H2S production through dietary or other means, will ultimately turn out to be more beneficial in the context of surgical stress resistance.

The findings that short-term fasting or restriction of food intake - on the order of days to a week - leads to robust functional benefits in rodents has profound implications for the mechanism of DR action in mammals. Rather than previous notions of DR as an intervention whose benefits accumulate over long periods of time due to reduced calorie intake, DR is now viewed as a rapid adaptation to the mild stress of calorie and/or nutrient deprivation with the potential to protect against many other forms of stress. This new understanding has important practical implications for attempts to leverage DR against clinically relevant endpoints, including planned surgery. If future clinical trials identify brief DR regimens or pharmacological DR mimetics that are safe and effective against the stress and potential complications of surgery, how would this change current preoperative nutritional standards? With few exceptions, there is currently no consensus on what should or should not be eaten up to 1 day prior to surgery, so long as the patient is not suffering from malnutrition.

Currently, the duration of preoperative fasting used as an "anesthetic precaution" in humans is likely too short to tap into DR benefits, while the progressive clinical application of existing nutritional guidelines promotes an alternate although not mutually exclusive concept of increased nutrition immediately prior to surgery. Future clinical trials are required to test the safety, feasibility, and potential efficacy of short-term DR, including extended periods of fasting, to reduce risk of surgical complications and improve outcomes. If successful, this approach has the potential to change the paradigm for preoperative nutritional care based on concepts derived from research into the basic biology of aging.

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Exercise versus Sarcopenia in Mice

Exercise helps to slow the age-related loss of muscle mass and strength known as sarcopenia, something we should all bear in mind as we age. This open access paper reporting on a study of exercise and aging in mice is one of a number to provide evidence on this topic. Beyond helping to slow the onset of physical frailty, exercise also improves numerous other aspects of our cellular biochemistry and organ function over the long term. There is no available medical technology, as yet, that can do anywhere near as much for overall health, and thus it is a very good idea to put in the effort to make and maintain good lifestyle choices as best as possible while we await the arrival of future rejuvenation therapies. A few years here or there might make the difference between living to benefit from these technologies or missing out.

In men and women, the annual rate of muscle mass loss is reported as approximately 0.9 and 0.7%, respectively, after the age of 75 years. Sarcopenia can be greatly accelerated by physical inactivity and poor nutrition, and loss of function is more pronounced in the muscles of the lower limbs. Sarcopenia can result in severe muscle weakness and contributes to frailty, reduced mobility, diminished independence, and an increased susceptibility to falls and fractures, with escalating costs to the global healthcare system. Resistance exercise is an effective intervention used to counteract the detrimental effects of sarcopenia. In humans aged 60 years and older, marked gains in strength, muscle mass, functional mobility, muscle protein synthesis, and mitochondrial function have been observed after progressive resistance training programs that range from 8 weeks to 1 year. These studies provide evidence that elderly men and women (including nonagenarians) are physiologically capable of adapting to progressive loading, and in some instances have reported relative gains in muscle strength and mass that are comparable to younger individuals and between sexes.

Voluntary wheel running (endurance or aerobic exercise) is often used to monitor the long-term benefits of exercise, with rodent models being widely used due to their relatively short lifespan; a 24-month-old mouse is considered roughly equivalent to a 70-year-old human. Although an age-related decline in voluntary wheel running is well documented in mice and rats, relatively small amounts of physical activity can have many benefits. Beyond the protection of muscle mass, long-term voluntary wheel running has a variety of physiological benefits including decreased weight gain, restoration of neuromuscular junction (NMJ) architecture, and preserved muscle innervation, increased mitochondrial biogenesis and autophagy, improved oxygen uptake (VO2 max), and the overall metabolic enhancement of the skeletal muscle. Investigations in young men and elderly women (aged 22 to 75 years) show that combined resistance and endurance training can contribute to greater gains in muscle strength and/or mass, compared with endurance exercise alone. Whether resistance exercise (with progressive loading of voluntary wheel running) can increase the hypertrophic potential of aging muscles has not been thoroughly tested in rodents.

The present study investigates the effect of 34 weeks of voluntary resistance wheel exercise (RWE) initiated from mid-life (15 months of age) on skeletal muscle mass and function in male and female C57BL/6J mice (aged 23 months). Overall, our data show that the introduction of resistance wheel running from middle age was effective in preventing sarcopenia in the hindlimb muscles of both male and female mice. Specifically, weights of the exercised quadriceps, gastrocnemius, and EDL muscles at 23 months were maintained at values similar to 15 months, while mass of the soleus muscles increased. The maintenance of muscle mass into old age was accompanied by striking changes to morphological and molecular parameters of the muscles, including myofiber size and type, with some increased markers of mitochondrial and autophagic activity. Since exercising muscles produce many factors with systemic effects, it is possible that other tissues may subsequently feedback and contributes (indirectly) to the prevention of sarcopenia, by exercise. This study shows that aging mice of both sexes have a good capacity for such resistance exercise and that this exercise helps to maintain healthy old muscles.

The Growth of Programmed Aging Theories in the Research Community

There are two important battles in the matter of aging research. The first is to convince people that aging should be treated as a medical condition at all. This has, finally, largely been won within the scientific community, or at least those parts of it that matter, but is still very much an ongoing concern when it comes to the public and potential sources of large-scale funding. The second battle is between the classes of theory of aging that determine what types of therapy should be developed. On the one hand there is the prevailing majority view of aging as the result of accumulated molecular damage to cells and tissues, that in turn produces all sorts of further harm and reactions in cellular behavior. That means therapies should aim to repair that damage, though, sadly, most researchers who hold to the damage theories of aging are in fact more focused on therapies that only slow down the rate at which damage accumulates. On the other hand, there is the growing minority view of aging as an evolved program in which epigenetic changes cause changes in cellular behavior that in turn lead to the accumulation of damage. There is a lot of debate within the programmed aging community as to the nature of this program and its relationship with evolutionary theories on aging, but regardless of that, the basic concept implies that repair of damage is marginal and therapies should try to revert epigenetic changes that occur with age, such as via the use of drugs or gene therapies to alter cell behavior.

So we have two views of aging that stand in opposition to one another because the strategy for development of therapies that emerges from each is opposed. The yet-to-be-developed therapies thought to be effective in one paradigm are expected to be marginal in the other - and that matters greatly for those of us likely to age to death if the wrong lines of development come to dominate the field for too long. If you think that damage is the first cause of aging, then tinkering with epigenetics is evidently going to do little good. If you think that epigenetic changes are the first cause of aging, then repairing the damage without changing cellular operations is not the way to go. Interestingly, I think that the past decade of growth in publications and discussion of programmed aging has its roots in changes outside the scientific community; that it has a lot to do with the widespread adoption of automated translation technologies, as these have enabled closer ties between the Russian and English language aging research communities and their supporting network of advocates and funding sources. The Russian aging research community is much more in favor of programmed aging, and provides the necessary critical mass of thought and work to bring programmed aging to a larger audience in the English-language community.

For my part, I think that the best argument against programmed aging is that there are forms of metabolic waste that the body cannot effectively break down. Components of lipofuscin and glucosepane cross-links for example. You can change all the epigenetics you want, assuming a way can be found to force cells into a replica of their youthful state, but that won't enable them to clear out that harmful waste. Further, there is plentiful evidence for higher levels of these metabolic waste compounds to contribute directly to age-related pathologies, and it would be hard to postulate a way for that to happen with it also producing epigenetic changes in cells. These two points interact to strongly suggest that programmed aging is incorrect. I'm also of the mind that this debate will be settled fairly conclusively within the next decade, as the first therapies resulting from both sides are deployed. My expectation is that efforts to repair damage will produce robust rejuvenation and that efforts to restore youthful epigenetic patterns and signaling in cell environments will, where successful, produce results that look a lot like those achieved via stem cell therapies to date - putting damaged cells back to work, but not repairing underlying causes of aging. Regeneration, to some degree, but not rejuvenation. These are quite different outcomes, and should be clearly distinct from one another once biomarkers of aging are used in their assessment. At the moment, however, I suspect there is a quite of lot of confusing regeneration for rejuvenation taking place.

Twenty years ago, I first started writing that aging is something the body does to itself, a body function, rather than deterioration or loss of function. Journals would not even send my submission out for peer review. The conflict with prevailling evolutionary theory was just too deep. But in the interim, the evidence has continued to pile up, and many medical researchers have taken the message to heart in a practical way, setting aside the evolutionary question and just pursuing approaches that seem to work. The most promising developments in anti-aging medicine involve changing the signaling environment rather than trying to "fix what goes wrong" with the body.

My popular book exploring the evolutionary origins of aging (and implications for medical science) came out in June, and an academic version of the same content came out in October. Gandhi taught me, "First they ignore you, then they laugh at you, then they fight you, then you win." The paradigm of programmed aging passed this year from stage 2 to stage 3, with prominent articles arguing against the possibility of programmed aging. Current Aging Sciences devoted a full issue to the question. I welcome the discussion. This is a debate that colleagues and I have sought to initiate for many years. There are powerful theoretical arguments on one side, and diverse empirical observations on the other. The scientific community will eventually opt for empiricism, but not until theory digs in its heels and fights to the death. A basic principle of evolution is at stake, and many theorists will rise to defend the basis of their life work; but a re-evaluation of basic evolutionary theory is long overdue. The idea that fitness consists in reproducing as fast as possible is no longer tenable. For plants, this may be approximately true. But animal populations cannot afford to reproduce at a pace faster than the base of their food chain can support. Animals that exploit their food supply unsustainably will starve their own children, and there is no evolutionary future in that. This is a principle that links together entire ecologies, and the foundation of evolutionary theory will have to be rewritten to take it into account.

For many years, I put forward the argument that programmed aging means there are genes that serve no other purpose than to hasten our death, and that medical research should be targeting the products of those genes. But in recent years, epigenetics has eclipsed genetics as the major theme in molecular biology. Everything that happens in the body is determined by which genes are expressed where and when. The vast majority of our DNA is devoted not to coding of proteins but to promoter and repressor regions that control gene expression with exquisite subtlety. There has been a growing recognition of aging as an epigenetic program. As we get older, genes that protect us are dialed down, and genes for inflammation and apoptosis are dialed up so high that healthy tissue is being destroyed. Many epigenetic scientists have discovered this, and they find it natural to see aging as a programmed phenomenon.

A few years ago, I wrote about transcription factors as the key to aging. At first blush, it seems that an epigenetic program is just as amenable to pharmaceutical intervention as a genetic program. Transcription factors bind to DNA and turn whole suites of genes on and off in a coordinated way. This summer, I had a chance to work in a worm genetics lab and consult closely with people who know the experimental details. I learned that there is no clear line between functional proteins and transcription factors, that many proteins have multiple functions, and that metabolites feed back to control gene expression. I still believe that there are one or more aging clocks that inform the body of an age-appropriate metabolic state, and synchronize the aging of different systems. Telomere length is one such clock. If we can reset an aging clock, the body will repair and clean itself up. If we can reset several clocks, the body may be able to restore itself to a younger state. But I recognize the possibility that the clock is diffused through the detailed epigenetic status of a trillion cells, and may be beyond the reach of foreseeable technology. Short of resetting the aging clock, there are several technologies just over the horizon that should offer substantial life extension benefit. I believe the best prospects are senolytics (ridding the body of senescent cells), telomerase activators (rejuvenating old stem cells), and adjusting blood levels of key hormones and cytokines that increase or decrease with age.

The Hallmarks of Aging Outlined for Laypeople

More than a decade after the SENS view of the causes of aging was first assembled, the noted Hallmarks of Aging paper attempted another catalog of the important processes of aging. There is some overlap between the two, though I'd categorize portions of the Hallmarks of Aging list as secondary or later processes in aging, not primary causes, and thus poor targets for intervention. In both cases the aim of putting together such a list is to treat aging as a medical condition, though the Hallmarks of Aging authors were much more oblique when it came to stating the end goal of extended healthy human life spans, something that continues to be an issue in many parts of the research community. The goal of medical control over aging and radical extension of healthy life spans is important and desirable, and the failure of much of the scientific community to clearly say as much is why we need advocacy organizations like the SENS Research Foundation and Life Extension Advocacy Foundation, the latter of which is revamping their web presence at the moment. Among the new content going up at the Life Extension Advocacy Foundation site is this tour of the Hallmarks of Aging outline, explained for laypeople:

According to modern science, aging is the accumulation of damage that the body cannot completely eliminate, due to the imperfections of its protection and repair system. As a result, bodily functions start to deteriorate, leading ultimately to the development of age-related diseases. Aging comprises of a number of distinct and interconnected processes which we will explore briefly. Once you begin to understand the processes of aging it becomes possible to understand the ways we might intervene against them in order to treat and prevent age-related diseases, hence enabling people to live healthier lives for longer.

Genomic instability is considered one of the main causes of aging. Somatic cells are constantly exposed to a range of sources of DNA damage. When DNA is damaged, some proteins can stop being produced or can have the wrong shape, which, in turn, compromises the function of the cell. When there are many cells with this kind of damage in the organ, some important body functions can start to deteriorate. DNA damage during aging appears to be a stochastic process. However, chromosomal regions such as the telomeres have a somewhat more predictable pattern of deterioration. Telomere loss is technically a subset of genomic instability but warrants its own category as a form of aging damage due to this more predictable nature. Telomeres are a protective cap at the end of a chromosome. Each time a cell divides, telomeres get increasingly shorter and once they become critically short the cell ceases to divide and enters replicative senescence, better known as the Hayflick limit. Importantly, as telomeres shorten they influence the gene expression profile (the production of proteins) of a cell changing it from a functionally young one to an old one.

Changes to gene expression patterns (deactivation of useful genes and activation of potentially harmful ones) are a key influence in aging. Generally speaking, these changes (known as epimutations) lead to detrimental changes in gene expression patterns. Epigenetic alterations are a complex and not fully understood process. They can be considered almost like a program in a computer, but in this case it is the cell, not the computer, being given instructions. Ultimately these changes contribute to the cell moving from an efficient "program" of youth to a dysfunctional one of the old age. However the process appears to be plastic and is not the one-way process people once assumed. Indeed recent research shows that epigenetic alterations can be made to reverse this process of aging to restore youthful function and increase lifespan.

Proteostasis is the process by which cells control the abundance and folding of the proteins - building blocks of each cell. Proteostasis consists of a complex network of systems that integrates the regulation of gene expression, signaling pathways, molecular chaperones and protein degradation systems. Aging is linked to the impairment of proteostasis and the various quality control systems it incorporates. Even during regular operation misfolding of proteins can occur and they are immediately broken down and recycled. However with aging and the decline of proteostasis misfolded proteins increase and lead to aggregation.

The scientific evidence to date suggests that anabolic signaling (internal alarm about the abundance of nutrients) appears to accelerate aging, and that decreased nutrient signaling is shown to extend lifespan. We see from experiments that adjusting signalling using substances like rapamycin to mimic limited nutrient availability can increase lifespan in mice. Consistent with deregulated nutrient sensing, we see that dietary restriction increases lifespan in various species. There is also increasing evidence for the healthspan benefits of dietary restriction in humans.

Mitochondria are the "power plants" of the cells: they convert the energy-rich nutrients into energy store molecules that directly power the biochemical reactions in the cell. Unlike any other part of the cell, mitochondria have their own DNA (mtDNA), especially vulnerable to damage from free radicals. A free radical strike to the mtDNA can cause deletions in its genetic code, destroying the mitochondria's ability to make proteins that are critical components of their energy-generating system. Without the ability to produce cellular energy the normal way, these damaged mutant mitochondria enter into an abnormal metabolic state to survive. This state produces little energy, and generates large amounts of waste that the cell cannot metabolize. Strangely, the cell favours keeping these defective, mutant mitochondria, while recycling normal ones. Whilst this only happens to a few cells in our body, these cells do a large amount of damage to the body as a whole.

As the body ages, increasing amounts of cells enter a state of senescence. Senescent cells do not divide or support the tissue they are a part of, but instead emit a range of potentially harmful signals known collectively as the senescent associated secretory phenotype (SASP). Senescent cells normally destroy themselves via a programmed process called apoptosis and they are removed by the immune system. However, the immune system weakens with age, increasing numbers of these senescent cells escape this process and build up. By the time people reach old age significant numbers of these senescent cells have accumulated in the body and cause havoc, driving the aging process further and increasing the risk of diseases.

Every day, our cells are damaged. Some of these damaged cells are successfully repaired and keep serving the body. Others are either completely destroyed via apoptosis, or become dysfunctional and enter a 'senescent' state where they can no longer divide. Some of these lost cells are replaced from reserves of tissue-specific stem cells, but the aging process makes these stem cell pools less effective at repairs over time, and eventually those reserves run out. Over the passage of time, long-lived tissues, such as those in the brain, heart, and skeletal muscles, begin to progressively lose cells, and their function becomes increasingly compromised. Muscles weaken, and don't respond to exercise. The brain loses neurons, leading to cognitive decline and dementia. Ultimately the loss of reserves of replacement cells leads to the failure of tissue repair and is a significant driver of aging.

Aging causes changes to communication outside of the cell, which ultimately affects the function of all cells and tissues. Cellular communication has endocrine, neuroendocrine or neuronal origins. One of the best known age-related changes in intercellular communication is chronic inflammation (often called 'inflammaging'), which implies an increasingly rising background level of inflammation as we age. In addition to inflammatory signals, the so called bystander effect, in which senescent cells induce senescence in neighboring cells through the toxic signals they give off, is also a part of altered intercellular communication.

A suspected cause of degenerative aging is the accumulation of sugary metabolic wastes known as advanced glycation end-products (AGEs). These are wastes that are in some cases hard for our metabolism to break down fast enough or even at all. Some types, such as glucosepane, can form cross-links, gumming together important proteins like those making up the supporting extracellular matrix scaffold. The properties of elastic tissues (skin and blood vessel walls) derive from the particular structure of the extracellular matrix, and cross-links degrade that structure, preventing it from functioning correctly. AGE presence contributes to blood vessel stiffening with age, and is implicated in hypertension and diabetes.

Investigating Mechanisms of Age-Related Increase in Fibrosis

Fibrosis is a form of scarring, important in many medical conditions, notably those of the liver, and a process that increases in many internal organ tissues with advancing age. Inappropriate levels of cellular construction of fibrotic structures disrupts the proper function of tissues, leading to dysfunction and disease. Researchers here look into the underlying mechanisms driving that age-related increase in fibrosis, and suggest that the problem lies in a reduced ability to clear out fibrosis rather than an increased tendency to generate these structures in response to damage. The researchers point to the presence of cross-links as one possible contributing cause for that change, which is yet another reason to push for greater support of efforts to produce therapies to clear cross-links.

Liver fibrosis results from a sustained wound healing response due to chronic liver injury and occurs when extracellular matrix (ECM) production exceeds ECM degradation. Activated hepatic stellate cells (aHSCs) are the main cells involved in fibrogenesis as the key source of ECM compounds and a major modulator of hepatic inflammation. Next to aHSCs, the hepatic macrophages also promote fibrosis progression by driving HSCs activation, by releasing pro-inflammatory and pro-fibrogenic factors and by supporting the infiltration of pro-fibrogenic immune cells. Liver fibrosis reversibility has been documented for several years. In animal models, liver damages reverse and fibrotic scar degradation occurs when the hepatotoxic agent is removed or when a normal biliary outflow is restored after common bile duct ligation. Evidences of fibrosis regression come also from clinical practice, especially after the arrival of new anti-viral therapies enabling high rate of hepatitis C virus (HCV) eradication. During fibrosis resolution, aHSCs disappear by senescence, inactivation or apoptosis while inflammatory and pro-fibrogenic macrophages differentiate into pro-resolution cells able to secrete large quantities of fibrolytic matrix metalloproteinases (MMP) and anti-inflammatory cytokines.

The human liver is affected by aging. It manifests by a reduced volume and blood flow as well as by cellular changes such as increased oxidative stress, decreased number and dysfunction of mitochondria, accelerated cellular senescence and decreased regenerative ability. Aging is also a risk factor for several specific hepatic diseases. In non-alcoholic fatty liver disease (NAFLD), evolution from simple steatosis to steatohepatitis and fibrosis occurs more frequently in old patients. In HCV chronic infection, age at time of infection is a strong determinant of fibrosis progression. Although those data emphasize the susceptibility due to aging to develop more severe disease and significant fibrosis, the mechanisms underlying this propensity are not fully understood. In viral hepatitis, an impaired immune response against foreign antigens may explain a different immunopathogenesis in the elderly and more sustained hepatic fibrotic process. In rodents, a more severe fibrosis is also observed in older animals but mechanisms remain debated. Aging-dependent hepatic susceptibility to toxic agents, reduced ECM proteins degradation and variation in inflammatory cells infiltrating the injured liver are discussed as differences in rodent genetic strains may explain at least partially divergent results. Interestingly, evidence points to a quantitatively different ECM turnover according to the age of rat models. Indeed, type I and II collagen turnover was significantly reduced in old compared to young animals, while type IV and V collagen and biglycan degradation biomarkers were significantly upregulated in old rats.

In this work, we reproduced a higher susceptibility to fibrosis in old mice compared to young mice after repetitive administrations of carbon tetrachloride (CCl4). A single dose of CCl4 disrupts hepatocytes integrity that wound healing processes tend to restore. In case of repeated exposures, recurrent profibrotic stimulation occurs prior to the resolution of the previous healing round. In our study, Collagen I and alphaSma mRNA were significantly upregulated in treated groups compared to controls but no difference was observed between age-groups, mitigating the role of variable fibrogenic processes in the severity of ECM deposition. Rather, this is in favor of an equal propensity to initiate profibrotic events in response to a toxic injury.

MMPs are involved both in fibrosis progression and resolution through their ability to degrade virtually all compounds of the ECM. The capacity of the liver to resorb scar or in the contrary to "preserve" the pathologic matrix accumulated after injury will depend on the balance between MMPs and their respective inhibitors. Among all MMPs, MMP-13 is the main interstitial collagenase in rodents and largely involved in fibrosis resolution. We observed a strong induction of Mmp13 gene expression in young mice at peak of fibrosis while old mice expressed significantly less Mmp13 mRNA. No difference was noticed concerning tissue inhibitor metalloproteinases (TIMPs) expression suggesting that the balance MMP/TIMP was overtly tilted in favor of matrix degradation in young mice but less so in old ones. This was confirmed by the nearly complete clearance of scar matrix in young animals 4 days after the last toxic injection while virtually no remodeling occurred in old mice, and by the reduced collagenolytic activity in this last group.

We demonstrated a higher proportion of thick and dense collagen fibers in old mice as well as an enhanced expression of the enzymes involved in collagen maturation changes. There are features that limit fibrosis remodeling: old, pauci-cellular, thick and heavily cross-linked septae resist proteases degradation. More than biochemical impact on matrix fibrils, cross-linking enzymes support also HSCs activation by maintaining a stiff environment and may have immunomodulatory functions in liver fibrosis influencing the changes in balance between fibrogenesis and fibrolysis.

To date, no antifibrotic therapy exists besides the suppression of the causative agent. Our work, demonstrating that liver fibrosis is less prone to reverse in old animals, has several clinical implications. First, impact of aging on reduced ability for fibrosis degradation may partially explain some disappointing results of antifibrotic agents in clinical trials while promising when preclinically tested. Indeed, pre-clinical studies usually use young animals (6-8 weeks old) while patients concerned by treatment classically suffer from fibrosis that has developed over decades rather than weeks in animals. Secondly, our study highlights the importance to target the correct underlying processes in the perspective of an effective therapy. Based on our results, this target may be different according to the age of the patients, and therapies supporting the fibrolysis or opposing the cross-linking of the matrix might be of particular interest in an old population.

Investigating the Mechanisms of Piperlongumine

The present candidate senolytic drugs that produce selective destruction of senescent cells, done as a means to prevent their contribution to the aging process, all arrive from the cancer research community, where they have been tested for their ability to destroy cancerous cells. Piperlongumine is no exception. Here researchers explore more its likely mechanisms, with a focus on the outcome of increased oxidative stress in the cell due to reduced levels of the antioxidant glutathione, among other possibilities. Recent research suggests, however, that increased oxidative stress isn't the mechanism by which cells are pushed into self-destruction by piperlongumine. While adding new information, the research noted below - there is an open access paper in addition to the publicity materials - doesn't greatly clarify the uncertainty over the way in which piperlongumine works, nor does it clarify whether the method is the same for cancerous and senescent cells. Like many drugs, piperlongumine influences a large number of distinct processes in the cell, and there is no comprehensive map of outcomes. The reason why it is interesting as a potential senolytic therapy, versus other cancer drugs where the mechanisms of action are better mapped, is that it has far fewer side-effects in comparison.

Scientists have uncovered the chemical process behind anti-cancer properties of a spicy Indian pepper plant called the long pepper, whose suspected medicinal properties date back thousands of years. The secret lies in a chemical called piperlongumine (PL), which has shown activity against many cancers. Using x-ray crystallography, researchers were able to create molecular structures that show how the chemical is transformed after being ingested. X-ray crystallography allows scientists to determine molecular structures that reveal how molecules interact with targets - in this case how PL interacts with a gene called GSTP1. Viewing the structures helps in developing drugs for those targets. PL converts to hPL, an active drug that silences GSTP1. The GSTP1 gene produces a detoxification enzyme that is often overly abundant in tumors. "We are hopeful that our structure will enable additional drug development efforts to improve the potency of PL for use in a wide range of cancer therapies."

Glutathione S-transferase pi 1 (GSTP1), is frequently overexpressed in cancerous tumors and is a putative target of the plant compound piperlongumine (PL), which contains two reactive olefins and inhibits proliferation in cancer cells but not normal cells. PL exposure of cancer cells results in increased reactive oxygen species and decreased glutathione (GSH). This data in tandem with other information led to the conclusion that PL inhibits GSTP1, which forms covalent bonds between GSH and various electrophilic compounds, through covalent adduct formation at PLs C7-C8 olefin, while PLs C2-C3 olefin was postulated to react with GSH. However, direct evidence for this mechanism has been lacking.

To investigate, we solved the x-ray crystal structure of GSTP1 bound to PL and GSH to rationalize previously reported structure activity relationship studies. Surprisingly, the structure showed a hydrolysis product of PL (hPL) was conjugated to glutathione at the C7-C8 olefin, and this complex was bound to the active site of GSTP1; No covalent bond formation between hPL and GSTP1 was observed. Mass spectrometric (MS) analysis of reactions between PL and GSTP1 confirmed that PL does not label GSTP1. Moreover, MS data also indicated that nucleophilic attack on PL at the C2-C3 olefin led to PL hydrolysis. Although hPL inhibits GSTP1 enzymatic activity in vitro, treatment of cells susceptible to PL with hPL did not have significant anti-proliferative effects, suggesting hPL is not membrane permeable. Altogether, our data suggest a model wherein PL is a prodrug whose intracellular hydrolysis initiates the formation of the hPL:GSH conjugate, which blocks the active site of and inhibits GSTP1 and thereby cancer cell proliferation.

Evidence for Some of the Burden of Fat Tissue to Result from Increased Levels of Cellular Senescence

Excess visceral fat tissue is very bad for long-term health. Being obese is by some measures as harmful as a smoking habit when it comes to remaining life expectancy. Even modest amounts of excess weight have a measurable negative impact on the future trajectory of health and longevity. There is an enormous mountain of data to support these points, ranging from large human studies to simple but compelling experiments in which the surgical removal of fat from mice leads to extended life spans. Unfortunately we evolved in an environment of scarcity and so find it a challenge to stay slim in an environment of plenty; this is a high class problem to have in exchange for an end to unavoidable famine and malnutrition, but a problem nonetheless.

One of the contributing causes of degenerative aging is the growing presence of senescent cells in tissues. While investigating the effects of changes in the amount of fat tissue in mice, researchers here find evidence to suggest that some portion of the damage done by fat tissue occurs because it hosts many more senescent cells than would otherwise be present in the body. These cells produce a mix of inflammatory signals, and may well be a sizable cause of the well-known link between visceral fat and increased inflammation. Chronic inflammation alone drives a faster progression of most of the common fatal age-related conditions, and that is without considering all of the other damage done due to the signaling produced by senescent cells.

With obesity rates on the rise, more individuals are attempting to lose weight for improved health. Unfortunately, the vast majority of weight loss attempts are short-lived and are followed by weight gain. That is, for individuals that successfully achieve weight loss of at least 10%, approximately 80% will regain the weight in the first year alone. Repeated attempts at weight loss results in a phenomenon referred to as weight cycling. As global rates of obesity increase, weight cycling is becoming increasingly common. Unfortunately, clinical studies have produced conflicting results with some studies suggesting that weight cycling may decrease lifespan while others suggest that weight cycling has no negative effect. Review of these clinical studies suggests that inclusion of confounding factors, such as unintentional weight loss, likely accounts for the discrepancies and that further research is needed.

In attempts to perform a controlled animal study, our laboratory set out to evaluate the impact of lifelong weight cycling on longevity in mice. Results of this study showed that weight-cycled mice lived significantly longer than obese mice (801 vs 544 days), suggesting that periodic, repeated, weight loss attempts were preferable to no weight loss attempts in obese mice. To better understand the molecular changes that occur during weight cycling, we analyzed cellular senescence via senescence-associated β-galactosidase staining in white adipose tissue (WAT) and circulating levels of activin A, a recently identified marker of cellular senescence.

In this study and in agreement with other studies, we show that obesity induced by a high fat (HF) diet results in a significant increase in senescent cells in WAT compared to low fat (LF) controls. Circulating activin A levels were also increased in the HF group compared to the LF controls. Importantly, our data indicate that 28 days of weight loss are sufficient to significantly reduce the number of senescent cells as shown by significantly reduced activin A levels and a significant reduction in senescent beta-galactosidase stained cells in inguinal and retroperitoneal WAT depots. Of note, since inguinal and retroperitoneal WAT were the most responsive to the weight loss, there appears to be a depot specific difference in cellular senescence in response to this dietary manipulation.

Recently a comprehensive study identified activin A as a marker for cellular senescence in humans and mice. In this study, it was determined that i) human senescent fat cell progenitors release activin A, ii) activin A impedes the normal function of stem cells and fat tissue, iii) older mice have higher levels of activin A in both their blood and fat tissue than young mice, and iv) eliminating senescent cells from mice leads to lower levels of activin A. Since most procedures used to determine senescent cell accumulation require tissue collection, the discovery of a circulating marker of cellular senescence represents an important step for detection of senescent-related disease. This is particularly important in a clinical setting since blood is relatively easy to collect. Research has shown there is a correlation between obesity and increased cellular senescence, which may account for increased mortality and progression of age-related diseases. Thus, the possibility of senolytic treatment (agents that clear senescent cells), particularly in WAT, has been suggested as a potential therapeutic target. For those reasons, clearance of senescent cells in WAT with senolytic agents or, as we show here, with dietary manipulation, may be a promising approach for treatment of metabolic syndrome, type 2 diabetes, and other age-related complications.

Different Amyloid Plaque Structures in Different Forms of Alzheimer's Disease

Alzheimer's is a single defined medical condition that may soon be split into numerous forms, separate named diseases with distinctive differences that happen to look very similar in their later stages. The characteristic changes of Alzheimer's include the accumulation of amyloid-β and altered tau protein in solid depositions in brain tissues, but just as there are different types of tau aggregates involved in the various tauopathies, there may well be subtly different classes of amyloid-β aggregates involved in various forms of Alzheimer's disease.

At the core of Alzheimer's disease are amyloid-beta (Aβ) peptides, which self-assemble into protein fibrils that form telltale plaques in the brain. Now, the results of a study suggest that certain fibril formations are more likely to appear in cases of rapidly progressive Alzheimer's disease, as opposed to less-severe subtypes. The findings increase scientists' understanding of the structure of these fibrils, and may eventually contribute to new tests and treatments for Alzheimer's disease. "It is generally believed that some form of the aggregated Aβ peptide leads to Alzheimer's disease, and it's conceivable that different fibril structures could lead to neurodegeneration with different degrees of aggressiveness. But the mechanism by which this happens is uncertain. Some structures may be more inert and benign. Others may be more inherently toxic or prone to spread throughout the brain tissue."

Prior research has demonstrated that Aβ fibrils with various molecular structures exhibit different levels of toxicity in neuronal cell cultures, a finding confirmed in subsequent mouse trials. One study even demonstrated that Aβ fibrils cultured from patients with rapidly progressive Alzheimer's disease are different in size and resistance to chemical denaturation than those isolated from patients with more slowly progressing disease. Building on these observations, researchers set out to better characterize the structures of these fibrils and get a better handle on the potential correlations between structure and disease subtype. They examined 37 brain tissue samples from 18 deceased individuals - some with rapidly progressive Alzheimer's disease and others who had experienced more common subtypes - with solid-state NMR spectroscopy. The process can be incredibly labor intensive, because solid-state NMR requires milligram-scale quantities of isotopically labeled fibrils. In order to prepare the samples, the team had to amplify and label structures in brain tissue and generate "seeds" - short bits of fibrils - and grow them with synthetic peptides. "You have to make individual samples for individual patients, one by one. It takes about half a year to one year of work. It's not a high-throughput technique. The main barrier is that it's not an easy thing to do and it takes a long time. We were able to look at some 30 tissue samples, and that was really a tour de force."

After examining the solid-state NMR spectra, the researchers found that one specific fibril structure appeared to be statistically correlated with both typical Alzheimer's disease and posterior cortical atrophy Alzheimer's - a condition that involves disruption of visual processing. The researchers also found that range of different fibril structures are statistically correlated with the rapidly progressive disease subtype. "The work shows that distinct clinical presentations of the disease are associated with particular packings of the amyloid beta molecules in the fibrils. Our goal is not really to develop a diagnostic procedure for the clinic. It's to try to understand something fundamental about how the disease develops."

Engineering Functional Stomach Tissue Organoids

Researchers continue to expand the types of tissue that can be produced in small amounts to form organoids, lacking the integrated blood vessel network needed to support larger sections, but otherwise at least partially functional. This stage of development in the tissue engineering field offers considerable benefits, both as a way to speed up research with a cheaper alternative to animal studies, but also the potential for transplantation. Even small tissue patches can be an effective therapy for some conditions: the tissue will integrate with the body, and blood vessels will grow in to support it. For organs that are essentially chemical factories or filters, such as the kidney and liver, transplant of numerous functional organoids grown from a patient's own cells may well prove to be good enough to address a number of presently incurable degenerative conditions. Here, researchers demonstrate construction of stomach tissue organoids:

Scientists report using pluripotent stem cells to generate human stomach tissues in a petri dish that produce acid and digestive enzymes. Researchers grew tissues from the stomach's corpus/fundus region. The study comes two years after the same team generated the stomach's hormone-producing region (the antrum). The discovery means investigators now can grow both parts of the human stomach to study disease, model new treatments and understand human development and health in ways never before possible. "Now that we can grow both antral- and corpus/fundic-type human gastric mini-organs, it's possible to study how these human gastric tissues interact physiologically, respond differently to infection, injury and react to pharmacologic treatments." The current study caps a series of discoveries since 2010 in which research teams used human pluripotent stem cells (hPSC) - which can become any cell type in the body - to engineer regions of the human stomach and intestines. They are using the tissues to identify causes and treatments for diseases of the human gastrointestinal tract. This includes a study in which scientists generated human intestine with an enteric nervous system. These highly functional tissues are able to absorb nutrients and demonstrate peristalsis, the intestinal muscular contractions that move food from one end of the GI tract to the other.

A major challenge investigators encountered in the current study is a lack of basic knowledge on how the stomach normally forms during embryonic development. "We couldn't engineer human stomach tissue in a petri dish until we first identified how the stomach normally forms in the embryo." To fill that gap, the researchers used mice to study the genetics behind embryonic development of the stomach. In doing so, they discovered that a fundamental genetic pathway (WNT/β-catenin) plays an essential role in directing development of the corpus/fundus region of the stomach in mouse embryos. After this, researchers manipulated the WNT/β-catenin in a petri dish to trigger the formation of human fundus organoids from pluripotent stem cells. The team then further refined the process, identifying additional molecular signaling pathways that drive formation of critical stomach cell types of the fundus. These include chief cells, which produce a key digestive enzyme called pepsin, and parietal cells. Parietal cells secrete hydrochloric acid for digestion and intrinsic factor to help the intestines absorb vitamin B-12, which is critical for making blood cells and maintaining a healthy nervous system. It takes about six weeks for stem cells to form gastric-fundus tissues in a petri dish. Researchers now plan to study the ability of tissue-engineered human stomach organoids to model human gastric diseases by transplanting them into mouse models.

Manipulating the Wound Healing Process to Prevent Scarring

While there are some engineered mammalian lineages that can heal small wounds without scarring, further investigations of the biochemistry involved have yet to lead to a robust clinical treatment. Other lines of research are starting to look more promising, however. Here researchers demonstrate early implementations of a methodology that may prove to be the basis for a practical therapy to reduce scar tissue formation in wound healing:

Fat cells called adipocytes are normally found in the skin, but they're lost when wounds heal as scars. The most common cells found in healing wounds are myofibroblasts, which were thought to only form a scar. Scar tissue also does not have any hair follicles associated with it, which is another factor that gives it an abnormal appearance from the rest of the skin. Researchers used these characteristics as the basis for their work - changing the already present myofibroblasts into fat cells that do not cause scarring. "Essentially, we can manipulate wound healing so that it leads to skin regeneration rather than scarring. The secret is to regenerate hair follicles first. After that, the fat will regenerate in response to the signals from those follicles."

The study showed hair and fat develop separately but not independently. Hair follicles form first, and the researchers previously discovered factors necessary for their formation. Now they've discovered additional factors actually produced by the regenerating hair follicle to convert the surrounding myofibroblasts to regenerate as fat instead of forming a scar. That fat will not form without the new hairs, but once it does, the new cells are indistinguishable from the pre-existing fat cells, giving the healed wound a natural look instead of leaving a scar.

As they examined the question of what was sending the signal from the hair to the fat cells, researchers identified a factor called Bone Morphogenetic Protein (BMP). It instructs the myofibroblasts to become fat. This signaling was groundbreaking on its own, as it changed what was previously known about myofibroblasts. "Typically, myofibroblasts were thought to be incapable of becoming a different type of cell, but our work shows we have the ability to influence these cells, and that they can be efficiently and stably converted into adipocytes." This was shown in both the mouse and in human keloid cells grown in culture. These discoveries have the potential to be revolutionary in the field of dermatology. The first and most obvious use would be to develop a therapy that signals myofibroblasts to convert into adipocytes - helping wounds heal without scarring.

Attempting to Build a Biomarker of Aging from Standard Blood Test Metrics

Is it possible to assemble a useful biomarker of biological aging from a combination of existing metrics easily obtained via blood tests? This is an open question, but a number of research groups have made the attempt. To be useful, it would have to work at least as well as the DNA methylation biomarkers currently under development. The combination of metrics outlined in this open access paper is a start in that direction, but much more work and validation is needed. A robust, discriminating biomarker that reflects biological age, the level of molecular damage to cells and tissues and consequences thereof, would allow faster development, verification, and improvement of rejuvenation therapies. Without such a tool, it is very slow and expensive to determine the degree to which any particular candidate therapy has beneficial long-term effects on healthy life span. That in turn makes it hard to discard less effective approaches in favor of more effective approaches, and the greater cost means that less progress is made for a given investment in research and development.

The steady increase in human average life expectancy in the 20th century is considered one of the greatest accomplishments of public health. Improved life expectancy has also led to a steady growth in the population of older people, age-related illnesses and disabilities, and consequently the need for prevention strategies and interventions that promote healthy aging. A challenge in assessing the effect of such interventions is 'what to measure'. Chronological age is not a sufficient marker of an individual's functional status and susceptibility to aging-related diseases and disabilities. As has been said many times, people can age very differently from one another. Individual biomarkers show promise in capturing specificity of biological aging, and the scientific literature is rich in examples of biomarkers that correlate with physical function, anabolic response, and immune aging. However, single biomarker correlations with complex phenotypes that have numerous and complex underlying mechanisms is limited by poor specificity.

Moving from a simple approach based on one biomarker at a time to a systems analysis approach that simultaneously integrates multiple biological markers provides an opportunity to identify comprehensive biomarker signatures of aging. Analogous to this approach, molecular signatures of gene expression have been correlated with age and survival, and a regression model based on gene expression predicts chronological age with substantial accuracy, although differences between predicted and attained age could be attributed to some aging-related diseases. The well-known DNA methylation clock developed by Horvath has been argued to predict chronological age. Alternative approaches that aggregate the individual effects of multiple biological and physiological markers into an 'aging score' have also been proposed. These various aging scores do not attempt to capture the heterogeneity of aging. In addition, many of these aging scores use combinations of molecular and phenotypic markers and do not distinguish between the effects and the causes of aging.

Here we propose a system-type analysis of 19 circulating biomarkers to discover different biological signatures of aging. The biomarkers were selected based upon their noted quantitative change with age and specificity for inflammatory, hematological, metabolic, hormonal, or kidney functions. The intuition of the approach is that in a sample of individuals of different ages, there will be an 'average distribution' of these circulating biomarkers that represents a prototypical signature of average aging. Additional signatures of biomarkers that may correlate to varying aging patterns, for example, disease-free aging, or aging with increased risk for diabetes or cardiovascular disease (CVD), will be characterized by a departure of subsets of the circulating biomarkers from the average distribution. We implemented this approach using data from the Long Life Family Study (LLFS), a longitudinal family-based study of healthy aging and longevity that enrolled individuals with ages ranging between 30 and 110 years.

We used an agglomerative algorithm to group LLFS participants into clusters thus yielding 26 different biomarker signatures. To test whether these signatures were associated with differences in biological aging, we correlated them with longitudinal changes in physiological functions and incident risk of cancer, cardiovascular disease, type 2 diabetes, and mortality using longitudinal data collected in the LLFS. Signature 2 was associated with significantly lower mortality, morbidity, and better physical function relative to the most common biomarker signature in LLFS, while nine other signatures were associated with less successful aging, characterized by higher risks for frailty, morbidity, and mortality. The predictive values of seven signatures were replicated in an independent data set from the Framingham Heart Study with comparable significant effects, and an additional three signatures showed consistent effects. This analysis shows that various biomarker signatures exist, and their significant associations with physical function, morbidity, and mortality suggest that these patterns represent differences in biological aging.


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