The New York Academy of Sciences
Aging and Nutrition: Novel Approaches and Techniques
Posted February 02, 2017
More than 46 million people living in the United States today are 65 years of age or older, and that number is expected to more than double by 2060. This demographic trend is echoed in the global population, as the number of people older than 65 will soon outnumber those under age five for the first time in human history. As average life expectancy has increased, so too has interest in preserving and extending healthspan by improving understanding of both the aging process itself and the factors that contribute to age-related illness and decline.
On December 2, the Orentreich Foundation for the Advancement of Science and the Sackler Institute for Nutrition Science at the New York Academy of Sciences convened the conference Aging and Nutrition: Novel Approaches and Techniques. Leading researchers in the field gathered to discuss the use of established and emerging interventions in nutrition and metabolism to extend lifespan and impact healthy aging.
Use the tabs above to find a meeting report and multimedia from this event.
Presentations available from:
Matt Kaeberlein, PhD (University of Washington)
Arlan Richardson, PhD (University of Oklahoma Health Sciences Center)
How to cite this eBriefing
The New York Academy of Sciences. Aging and Nutrition: Novel Approaches and Techniques. Academy eBriefings. 2016. Available at: www.nyas.org/AgingNutrition-eB
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Gene Ables, PhD
Gene Ables received his doctorate of veterinary medicine from the University of the Philippines. He then obtained his PhD from Hokkaido University (Japan). His post-doctoral research in preventive medicine and nutrition at Columbia University focused on liver lipid metabolism. In 2006, he was appointed associate research scientist at the Columbia University Medical Center. Ables joined the Orentreich Foundation in April 2011 as a senior scientist. Recently appointed associate science director, he leads staff in investigations of the methionine-restricted diet's effects on metabolism, cancer, and epigenetics.
Gilles Bergeron, PhD
Executive Director, The Sackler Institute for Nutrition Science
Gilles Bergeron has worked in international nutrition for more than 25 years. He has extensive experience in nutrition in the life cycle, food security, agriculture/nutrition linkages and monitoring and evaluation. A founding member and deputy director of the Food and Nutrition Technical Assistance (FANTA) project, he spent 18 years overseeing FANTA's work in policies and programs; nutrition and infectious diseases; maternal and child nutrition; agriculture/nutrition linkages and emergency nutrition response. Prior to joining FANTA, he spent six years as Research Fellow with the International Food Policy Research Institute (IFPRI) and three years with the Institute of Nutrition for Central America and Panama (INCAP) in Guatemala. He has operated in Africa, Latin America and Asia, and his work has been published in leading scientific journals such as The Lancet, Advances in Nutrition, World Development, The Journal of Development Studies, and Food and Nutrition Bulletin. He received his PhD in development sociology from Cornell University in 1994.
Jay Johnson, PhD
Jay Johnson received his doctorate in Molecular Biology from Case Western Reserve University in Cleveland, OH. His post-doctoral work at Fox Chase Cancer Center (Philadelphia, PA) used a liposarcoma model system to investigate the maintenance of telomeres, important nucleoprotein structures with roles in aging and cancer. Johnson then joined the University of Pennsylvania, where his early work explored cellular defects in patients with Werner and Bloom's syndromes, genetic diseases characterized by accelerated aging and cancer predisposition. Johnson's recent work has focused on exploring the mechanistic basis of the benefits of methionine restriction in S. cerevisiae and cultured mouse and human cells.
Mireille Mclean, MA, MPH
Director, The Sackler Institute for Nutrition Science
Mireille Seneclauze Mclean joined the Sackler Institute for Nutrition Science at the New York Academy of Sciences in 2011 as a program manager and was later promoted to director. Her activities include managing the growing pool of research grants issued through the Sackler Institute's Research Funds, organizing multidisciplinary workshops and symposia in the field of nutrition, and supporting the dissemination of research. Prior to this, she spent over 10 years doing fieldwork for several international NGOs intervening in crisis situations. She holds an MA in development economics and international development from the University of Sussex and a Master of public health from the Liverpool Faculty of Medicine.
George Church, PhD
George Church is a professor of genetics at Harvard Medical School and professor of health sciences and technology at Harvard and the Massachusetts Institute of Technology (MIT). He is director of the U.S. Department of Energy Center on Bioenergy at Harvard and MIT and director of the National Institutes of Health Center of Excellence in Genomic Science at Harvard.
Church is widely recognized for his innovative contributions to genomic science and his many pioneering contributions to chemistry and biomedicine. In 1984, he developed the first direct genomic sequencing method, which resulted in the first commercial genome sequence (the human pathogen, H. pylori). He helped initiate the Human Genome Project in 1984 and the Personal Genome Project in 2005. Church invented the broadly applied concepts of molecular multiplexing and tags, homologous recombination methods, and array DNA synthesizers.
Lenore Launer, PhD
Lenore Launer is a senior scientist and chief of the Neuroepidemiology Section in the Intramural Research Program at NIA. She directs a suite of prospective, community-based cohorts, which provide a virtual life-course study of risk factors and early biomarkers for, and consequences of brain aging. Specific research interests include the role of microvascular disease, cerebral changes in physiologic functioning, and cardio-vascular risk factors as they are studied in observational cohorts and incorporated into prevention trials.
Jan van Deursen, PhD
Jan van Deursen received his PhD in cell biology at the University of Nijmegen and is currently a professor of biochemistry, molecular biology and pediatrics at the Mayo Clinic. He is the Vita Valley Professor of Cellular Senescence and director of the Senescence Program in the Robert and Arlene Kogod Center on Aging.
The aging-related work of the van Deursen lab focuses on the progeroid gene BubR1, which encodes a core component of the mitotic checkpoint whose level of expression markedly declines with aging. In addition, using the BubR1 progeroid model, the van Deursen lab was the first to show an in vivo link between p16-induced cellular senescence and the development of age-related pathologies. Then, in collaboration with several laboratories in the Kogod Center on Aging, including the Kirkland and the LeBrasseur labs, his lab went on to show that clearance of p16-positive senescent cells from BubR1 progeroid mice delays the onset of age-related disease.
Vadim Gladyshev, PhD
Vadim N. Gladyshev is a professor of medicine at Brigham and Women's Hospital, Harvard Medical School, director of the Center for Redox Medicine, and associate member of the Broad Institute. He received his PhD from Moscow State University, Russia, followed by postdoctoral training at NIH. In 1998, he joined the University of Nebraska faculty, where he became a Charles Bessey Professor of Biochemistry in 2005 and the director of the Redox Biology Center in 2007. Since 2009, he has been at the Brigham and Women's Hospital, Harvard Medical School. Gladyshev works in the areas of micronutrients and redox biology as applied to aging and cancer. He has a longterm interest in the mechanisms of aging and regulation of lifespan. Gladyshev has published approximately 300 articles and elected as an AAAS fellow. He is a recipient of the NIH Eureka, Merit, and most recently the NIH Director's Pioneer Award to study mechanisms of lifespan control.
Vera Gorbunova, PhD
Vera Gorbunova is a professor of biology at the University of Rochester and a co-director of the Rochester Aging Research Institute. Her research is focused on understanding the mechanisms of longevity and genome stability and on the studies of exceptionally long-lived mammals. Gorbunova earned her BSc degrees at Saint Petersburg State University, Russia and her PhD at the Weizmann Institute of Science, Israel. Recently the focus of her research has been on the longestlived rodent species the naked mole rats and the blind mole rat. Gorbunova has over 60 research papers including publications in Nature and Science. Her work on cancer resistance in the naked mole rat was awarded the Cozzarelli Prize from PNAS for outstanding scientific excellence and originality. Most recently she was awarded a prize for research on aging from ADPS/Alianz, France, Prince Hitachi Prize in Comparative Oncology, Japan, and Davey prize from Wilmot Cancer Center.
Matt Kaeberlein, PhD
Matt Kaeberlein is a professor of pathology, adjunct professor of genome sciences, and adjunct professor of oral health sciences at the University of Washington. Kaeberlein currently serves on the editorial boards for Science, npj Aging and Mechanisms of Disease, Aging Cell, Cell Cycle, Oncotarget, BioEssays, PloS One, Frontiers in Genetics of Aging, F1000 Research, and Ageing Research Reviews.
His research has been featured in national and international media outlets, including the New York Times, UK Telegraph, Boston Globe, Chicago Tribune, Popular Science, Time Magazine, Scientific American, NPR, MIT Technology Review, Wired Magazine, Bloomberg News, USA Today, National Geographic, and many others.
He is currently co-director of the University of Washington Nathan Shock Center of Excellence in the Basic Biology of Aging, founding director of the Healthy Aging and Longevity Research Institute at the University of Washington, and founder and co-director of the Dog Aging Project.
Arlan Richardson, PhD
Arlan Richardson's laboratory was the first group to show that dietary restriction altered the expression of genes through changes in specific transcription factors, and he is currently studying the effect of various levels of dietary restriction on the longevity of 8 genotypes of mice. Richardson's laboratory tested the oxidative stress theory of aging by measuring the effect of alterations in the antioxidant defense system on the lifespan and pathology of transgenic and knockout mice. These data have led to the field re-evaluating the role oxidative damage plays in aging. Richardson has received several awards for his research in aging, such as the Nathan W. Shock Award, the Robert W. Kleemeier Award; the Denham Harman Research Award; the Irving Wright Award of Distinction in Aging; and the Lord Cohen Medal for Services to Gerontology.
Nicholas Stroustrup, PhD
Nicholas Stroustrup is an independent research fellow in the Department of Systems Biology at Harvard Medical School. In 2017, he will start as a group leader at the Center for Genomic Regulation in Barcelona, Spain. He designed and built a high-throughput imaging platform dubbed "the lifespan machine" that is now used by many research groups. His research focuses on the influence of genetic and environmental factors on stochastic processes in aging, using C. elegans as a model for how individuals vary in their response to interventions that alter health and lifespan.
Hallie Kapner is a science writer based in Chappaqua, NY. She works with research universities and scientific organizations in the New York area, and has been writing about science for lay audiences and the media for more than 15 years. She has also written for the New York Academy of Sciences Magazine.
University of Oklahoma Health Sciences Center
University of Washington
University of Rochester
Dietary restriction is the most well-studied aging intervention. Some forms of restriction are definitively shown to extend lifespan, although the mechanisms of this effect are not fully understood.
Dietary restriction can induce changes in gene expression and DNA methylation, and many of these changes persist when a normal diet is resumed.
mTOR inhibitors such as rapamycin extend lifespan in a wide range of species including yeast, worms, flies, and mice. Efforts to translate such results to higher-order animals are underway.
Short-term treatment with rapamycin improves multiple measures of cardiac function in middle-aged companion dogs.
Some especially long-lived animals, such as the naked mole rat, have evolved biological processes that naturally inhibit the mTOR pathway, mimicking the effects of rapamycin and contributing to longevity.
Effects of dietary restriction on DNA methylation
Eighty years of research data show definitively that caloric restriction in the 30–40 percent range extends lifespan in species both simple and complex, from yeast and worms to flies, rodents, dogs, and non-human primates, explained Arlan Richardson of University of Oklahoma Health Sciences Center. This phenomenon is evidenced when such restriction begins early in life, i.e. shortly after weaning, as well as when initiated in adulthood.
Dietary restriction (DR) is the most well-studied aging intervention, yet the complete mechanisms of its impact on longevity are unknown. Increased stress resistance, reduced inflammation and oxidative damage, as well as a reduction in mTOR signaling, have been shown to contribute to the longevity effects of DR, but recently, researchers have begun probing the possibility that DR may also induce epigenetic changes that promote longevity.
Richardson noted that environmental and physical stresses on the body are known to induce changes in DNA methylation, and that these modifications can persist long after the stress abates. If DNA methylation plays a role in the anti-aging effects of dietary restriction, these changes should be evidenced soon after DR is implemented, and persist upon resumption of a normal diet. "This would be an example of a memory effect, which is a hallmark characteristic of epigenetics," Richardson said.
Mouse studies published dating from the 1980s to 2009 confirm that dietary restriction for as few as 20 days and up to four months, implemented as early as the first days of life and as late as six months of age, universally extended lifespan, offering evidence of both early impact and a memory effect. Additional studies show that DR has an early and long-lasting impact on physiological parameters such as insulin resistance: after just ten days of DR, mice show a significant improvement in glucose utilization, and these benefits persist long after DR is discontinued.
Such phenomena neither confirm nor illuminate the precise impact of dietary restriction on the transcriptome—the dynamic set of RNA transcripts produced by the genome. Richardson and his collaborators have investigated more than 30,000 genes in tissues from the liver, colon, fat, hypothalamus, and hippocampus in search of changes in DNA methylation following a period of dietary restriction—a key step in determining whether such changes exist, what the precise changes are, and if they persist after DR is removed. Mice exposed to one month of DR showed significant changes in gene expression (both up-and downregulation), and 20–30 percent of those changes persisted once the animals were fed ad libitum (AL).
Richardson analyzed a select group of genes that showed significant expression changes following DR to determine if and how such restriction affects methylation. While the results varied considerably between the genes discussed—some genes remained consistently up- or downregulated following resumption of an AL diet with no changes in methylation—one gene, NTSR1, displayed changes in methylation indicative of a memory effect following a period of dietary restriction. Specifically, NTSR1 is significantly upregulated during dietary restriction, and decreases only slightly upon discontinuation. Methylation is decreased overall, and each of the three CpG sites of the NTSR1 promoter region shows decreased methylation at the onset of DR, with even greater decreases after DR is discontinued. This is the first evidence that dietary restriction can alter DNA methylation in the promoter region of a gene, and that such changes can be long-lasting.
Translational geroscience: from mice to dogs to humans
Currently, the most promising research on mitigating the impacts of aging and extending longevity is limited to rodents living in laboratories, not humans living in the real world. "We are on the verge of actually having interventions that we may be able to apply to improve the quality of life of people ... but how do we move out of the laboratory?" asked University of Washington researcher Matt Kaeberlein. "How do we get from mice to people?" Kaeberlein's work in translational geroscience seeks to close the gap between promising lab findings and possible applications for humans by using a familiar stepping stone: man's best friend.
Dogs age similarly to humans and suffer from many of the same age-related diseases, but their lives are shorter, and thus they age much faster. Unlike a clinical trial using human subjects, where results take decades and are prone to ambiguities of correlation and causality, dog studies on aging can yield answers in as little as 3–5 years. Companion dogs, which are the subject of Kaeberlein's work, are especially relevant models for learning about human aging and healthy longevity, as they share the human environment.
The Dog Aging Project is the first national, large-scale longitudinal study of the genetic and environmental factors that influence healthy aging in dogs. Kaeberlein will enroll up to 10,000 dogs living different lifestyles in various environments—urban, rural, active, sedentary, and stray—using veterinary records, owner surveys, and biological samples to build a rich database of factors that influence canine aging and health. "We can actually do this for dogs in a decade, where it would take 50 years to do it with humans," Kaeberlein said.
Among the enrollees are several experimental cohorts, the first of which is a group of 40 middle-aged companion dogs treated with a 10-week course of the drug rapamycin. Most often used to prevent organ transplant rejection, rapamycin—an mTOR inhibitor—has the remarkable and well-documented side effects of delaying age-related diseases and increasing healthy longevity in every species in which it has been tested, including worms, mice, flies, and yeast. The drug is typically well-tolerated, and experiments in mice show that even a transient course of rapamycin in middle age produces functional improvements in cardiac and immune function. "This is exactly the kind of intervention we're interested in from a translational perspective—something you can start in middle-age and still see benefits," said Kaeberlein, adding that among the 24 dogs that completed his first rapamycin trial, those who received the drug showed improvements in multiple measurements of cardiac function. The dogs showed improved systolic function, as measured by ejection fraction and fractional shortening—both indicators of cardiac output and the heart's pumping capabilities—and improved relaxation, or diastolic function, as measured by E/A ratio. Further, dogs with weaker cardiac output at the beginning of the trial showed the greatest improvement after 10 weeks of treatment.
While Kaeberlein cautioned that broad conclusions about the benefits of a short course of rapamycin cannot be drawn from a single trial in a small cohort of dogs, he believes the initial results are promising enough to expand the protocol to include 300 dogs, with long-term follow up of cardiac and cognitive functioning.
Mechanisms of longevity in long-lived mammals
The naked mole rat is a hairless, nearly blind, underground-dwelling rodent that more than compensates in intrigue for what it lacks in beauty, according to Vera Gorbunova of University of Rochester in her introduction to the longest living member of the rodent family. With a lifespan that can top 30 years and an innate resistance to cancer and age-related degeneration, the naked mole rat is considered perhaps the ultimate animal model for longevity and oncology research.
When grown in culture, naked mole rat cells do not grow to confluence. Unlike mouse cells, which easily proliferate to fill a dish, naked mole rat cells are highly sensitive to contact inhibition—a critical trait in preventing tumor formation, as malignant cells lose the ability to interpret cellular cues to cease division. Gorbunova's team discovered that naked mole rat cells secrete hyaluronic acid (HA), a viscous substance present in connective tissues throughout the body, as a signal to halt cell division. This finding led to several additional implications for the role of hyaluronic acid in both longevity and cancer resistance.
The biological properties of HA depend on the molecule's length—long molecules are anti-proliferative and anti-inflammatory, and short chains, which are found at wound sites and in metastases, have the opposite properties. The naked mole rat genome has an unusual sequence of hyaluronan synthase 2 (HAS2) which produces extremely high molecular weight HA—up to five times the length of human or mouse HA. Further, while other mammals regularly degrade and replace HA in cells, naked mole rats recycle very little HA, allowing it to accumulate in tissues throughout the body, including in the bone marrow.
Gorbunova reported the results of experiments to determine whether this unusually long-chain, well-preserved HA plays a role in the naked mole rat's cancer resistance. Typically, the perturbations in signaling pathways that trigger malignancy in mouse fibroblasts fail to produce cancer in naked mole rat cells. However, inhibiting HAS2 or overexpressing an HA-degrading enzyme makes naked mole rat cells susceptible to malignancy. "If you remove the ability to make hyaluronan from a naked mole rat, it becomes as susceptible [to cancer] as a mouse," she said. "But what happens if you add the ability to produce high-molecular weight hyaluronan to a mouse? Can we make them, or maybe even humans, more resistant to cancer?"
Gorbunova and her collaborators have yet to answer the latter question, but by creating a transgenic mouse that overexpresses the naked mole rat variant of HAS2, they discovered that long chain hyaluronan confers several benefits likely associated with longevity.
Hyaluronan is a key part of the stem cell niche, and naked mole rats have higher quantities of HA in the niche than mice and other mammals, as well as more hematopoietic stem cells. These cells are quiescent compared to mouse stem cells, multiplying less frequently and displaying increased stress resistance. The bone marrow of transgenic mice that overexpress HAS2 shows a threefold increase in fully functional, long-term hematopoietic stem cells versus control mice, with stress resistance similar to that of naked mole rat stem cells. The evidence indicates that long-chain HA serves both to protect quiescent stem cells and bolster stress resistance, allowing for long-term maintenance of the hematopoietic system and likely staving off age-related decline.
Naked mole rats also show a natural downregulation of mTOR, a factor associated with longevity when induced by drugs like rapamycin. Gorbunova explained that this suppression of the cell's main nutrient sensing pathway in the naked mole rat is directly related to the synthesis of high molecular weight hyaluronan. Producing such long-chain polymers is energy intensive, forcing cells to deplete their glucose stores and activating AMPK, which mediates inhibition of mTOR. In experiments with transgenic HAS2 mice, inhibiting the AMPK pathway diminishes mTOR suppression.
Jan van Deursen
The Mayo Clinic
Brigham and Women's Hospital, Harvard Medical School
Wide variations in lifespan exist between individual of the same species and even individuals with identical genes; the factors that influence this distribution of lifespan are not well understood.
Lifespan varies greatly among mammals, as do the genetic, epigenetic, and metabolic factors that confer longevity benefits on the longest-lived animals.
Technological advances in collecting lifespan data have allowed researchers to conduct large-scale studies of factors that influence longevity in model animals, including C. elegans.
Studies of senescent cells have shown that the unique, pro-inflammatory secretome of such cells is a key driver of atherosclerosis in mice.
Removing senescent cells significantly extend life and healthspan in mice, and can both reduce arterial plaque formations in early-stage atherosclerosis and stabilize mature plaques.
Linking molecular interventions to systemic outcomes in aging
Nicholas Stroustrup delivered the first of three presentations on new approaches to studying aging and lifespan. Referencing a graph depicting the range of human lifespan from birth to age 100, he explained that while individuals of the same species show wide variation in lifespan, little is known about the factors that influence this variation. Genetics, environmental factors, and chance all play some role in determining longevity, but even when genetic and environmental diversity is eliminated, as is the case in cloned laboratory animals raised in isolation, variations in lifespan between seemingly identical individuals persist.
Stroustrup seeks to understand lifespan diversity by placing aging in the context of a multiscale systems biology problem. Thus, variations in the makeup and performance of individual organs, tissues, cells, and molecules interact in parallel to determine a person's healthspan and longevity, and these differ from person to person. To quantify the impact of these variations on the lifespan of a model animal, he devised novel experiments and measurement techniques in C. elegans populations.
Lifespan experiments have long been hampered in scale by the arduous process of data collection— in the case of C. elegans, a researcher must manually assess the vitality of each individual worm daily for several weeks. The tedium of this task dictates the trend toward relatively small population studies. Stroustrup developed an automated scanning and image analysis system consisting of fleets of consumer flatbed scanners retrofitted to house dishes of C. elegans and capable of producing daily vitality information as well as high-resolution images and video for thousands of individual worms.
Thus equipped with robust imaging and assessment tools for collecting lifespan data at unprecedented scale and resolution, the researchers began testing the impact of various interventions on C. elegans populations. These included environmental and dietary interventions as well as genetic mutations.
Some interventions, such as raising environmental temperature, are known to shorten lifespan in C. elegans. Others, such as inducing a mutation in the IGF receptor gene DAF-2, are known to extend it. Stroustrup and his collaborators were surprised to observe that all interventions altered the lifespan distribution curve in C. elegans populations through an apparent stretching or shrinking of time, where individuals experienced the same set of expected outcomes, only at a proportionally earlier or later time. Stroustrup explained that in the high temperature experiments, "the proportion of animals that would have lived a shorter time at a normal temperature [based on controls] had their lives shortened by the same fold factor as the animals who would have been living longer. Regardless of the intervention, it's as if all the physical processes in the worm that are dependent on time are being sped up or slowed down by a constant amount."
While an intervention like temperature could feasibly affect many molecular mechanisms that impact lifespan, it is unlikely that the single genetic mutations tested has an equally global impact on these factors. Perplexed by the universality of temporal scaling in all tested lifespan interventions, Stroustrup and his collaborators hypothesized that the phenomenon may be a result of a relationship between the factors that influence lifespan. "Maybe if you influence a subset of these mechanisms, you can have a global effect on all such mechanisms," he said.
The mechanisms that influence lifespan may more closely resemble a signaling network, where interdependent nodes rely on the strength of their neighboring nodes, and failure of a single node propagates additional failed dependencies throughout the network. Conversely, if a subset of molecular mechanisms or nodes are strengthened, it may increase the resilience of the entire network. As Stroustrup commented in closing, "Perhaps there's an aspect of aging that is inherently systemic, where different intervention targets are interacting in complex ways that systematize the consequences of these interventions."
Comparative genomics of lifespan control
Vadim Gladyshev of Brigham and Women's Hospital at Harvard Medical School steered the conversation to the wide range of maximum lifespan among mammals, which can top four years in a mouse and more than 200 for a bowhead whale. As mammalian species diverged from a common ancestor, their lifespan, as well as morphology, has been shaped through evolution, indicating that there are many routes for a species to achieve longevity. Gladyshev questions whether there are common mechanisms and patterns among the longest-lived animals, and if so, whether they may form the basis for interventions capable of shifting an organism from a short-lived state to a longer one.
The genetic determinants of longevity exist on multiple levels and in a range of mammalian systems. Even within a single organism, variations in lifespan arise at the cellular level: neurons can function for a century, whereas monocytes die within days. Identifying the mechanisms that drive longer-living cells, as well as commonalities in gene expression and metabolite profiles in long-lived species, is key to understanding the possibilities for boosting longevity.
"There are various ways to extend lifespan from an evolutionary standpoint," said Gladyshev, explaining that genomic data from long-lived animals indicates that there are both private mechanisms of longevity as well as common ones. For example, the naked mole rat and Brandt's bat—two different species with exceptional longevity—show distinct gene alterations that confer an advantage in longevity. However, many long-lived animals also display common gene expression patterns associated with longevity, such as upregulation in genes involved in DNA repair and glucose metabolism, and downregulation in genes involved with proteolysis.
Mouse studies show that different types of interventions enhance longevity, including pharmacological treatments like rapamycin and acarbose, nutritional approaches such as dietary and methionine restriction, and genetic alterations. "The question is whether these things extend lifespan using similar mechanisms or not, and if there is any overlap," said Gladyshev.
Gene expression studies reveal that while global gene expression in mice following life-extending interventions varies considerably, certain interventions do produce similar changes. A map of these changes illustrates that genetic alterations tend to trigger correlated changes in gene expression, and pharmacological interventions including rapamycin and metformin induce completely different, unrelated changes.
Organ-specific gene regulation also governs some degree of longevity in mammals, as a study of brain, kidney, and liver tissue from 41 mammals reveals. A common cohort of genes in each organ is differentially up-or down-regulated in each organ over time. Notably, genes that regulate metabolic processes are significantly downregulated in the liver and kidney as mammals age, yet expression of these same genes remains largely unchanged in the brain. "What this means is that living a long time is gene-specific, mechanism-specific, and organ-specific," Gladyshev said. "We don't know the best way to extend lifespan, because it's clear there are multiple ways."
Identifying gene expression patterns associated with longer life, which Gladyshev terms "longevity signatures," has allowed him and his collaborators to test small molecules in cell culture to identify those that produce similar effects. Rapamycin, as well as several of its analogs, have emerged as top compounds.
Slowing aging and disease through senescent cell elimination
In the meeting's final presentation, Jan van Deursen of the Mayo Clinic discussed the role of senescent cells as potent drivers of age-related disease and degeneration, particularly in the case of atherosclerosis. Cellular senescence occurs when the cumulative impact of stressors and DNA damage causes replicating cells to cease dividing—a normal, irreversible arrest process that is important for tumor prevention. However, senescent cells possess a unique secretory phenotype associated with aging, and senescent cells accumulate in the body over time.
The secretome of senescent cells is rich in pro-inflammatory cytokines, growth factors, and proteases, which can disrupt neighboring cell function and tissue architecture, and, paradoxically, may even contribute to tumor progression. Senescent cells are abundant in atherosclerotic and Alzheimer's-associated plaques, as well as at sites of osteoarthritis.
Van Deursen reports that several different transgenes have been used in concert with small molecules to induce apoptosis in senescent mouse cells, effectively clearing them from the animal. Mice treated weekly with this protocol experienced a 25–30 percent extension in lifespan and attenuation of age-related deterioration in several organ systems with few or no side effects. Video footage of an experimental mouse next to a mouse given only the transgene (without the small molecule to trigger apoptosis) showed dramatic differences in ease of mobility and external measures of wellness and vitality between the two animals.
Additional mouse studies show that senescent cells are not merely present in atherosclerotic plaques, but are in fact key drivers of atherogenesis. Van Deursen tracked the process in both wild-type and LDL-receptor knockout mice, revealing the role of senescent cells from the earliest stages of atheroma formation through eventual plaque rupture resulting in myocardial infarction or stroke.
Arterial plaques, even in the earliest stages, are highly SABG-positive, a primary biomarker for senescent cells. SABG staining and transmission electron microscopy analysis of arterial deposits show that foamy macrophages possess these senescence markers well before a mature plaque forms. Further, the pro-inflammatory secretome of senescent cells advances atherosclerosis through production of VCAM1 and MCP1, recruitment factors that further draw monocytes from the circulation into the subendothelial space. In late-stage plaques, senescent cells produce enzymes that erode the fibrous cap that serves to stabilize plaques, rendering them vulnerable to rupture.
Van Deursen explained that frequent removal of senescent cells in LDL-receptor knockout mice, either through a transgene/small molecule approach or by using senolytic drugs, shows positive results during all stages of plaque development. Thus, removal of senescent cells can inhibit plaque initiation and growth in the early stages of atherosclerosis, and can stabilize mature plaques in late-stage disease.