2019 Symposium on Healthy Aging
October 16-18, 2019, Mohonk Mountain House
- Tracy G Anthony, Rutgers University
Dietary sulfur amino acid restriction and the integrated stress response
Dietary sulfur amino acid restriction (SAAR) increases food intake and energy expenditure and improves body composition in rodents, resulting in improved metabolic health and longer lifespan. While SAAR promote leanness and longevity in rodent models, the underlying mechanisms are only partly understood. Among the known nutrient-responsive signaling pathways, the evolutionary conserved integrated stress response (ISR) is a lesser-understood candidate in mediating the hormetic effects of dietary SAAR. A key feature of the ISR is the concept that a family of protein kinases phosphorylates the translation factor eIF2, dampening general protein synthesis to conserve cellular resources. This slowed translation simultaneously allows for preferential translation of genes with special sequence features in the 5′ leader. Among this class of mRNAs is activating transcription factor 4 (ATF4), an orchestrator of transcriptional control during nutrient stress. Several ATF4 gene targets help execute key processes affected by SAAR, such as lipid metabolism, the transsulfuration pathway, and antioxidant defenses. This presentation will summarize current understanding of how the evolutionary conserved ISR is involved in the physiological response to SAAR and then detail my lab’s efforts to reveal the role of ATF4 in this regard.
- Sebastian Brandhorst, University of Southern California
Fasting-mimicking diet reduces risk factors for ageing, diabetes, cancer, and cardiovascular disease in preclinical and clinical studies
The “fasting-mimicking diet” (FMD), a periodic, short-term, low-calorie, and low-protein dietary intervention, is a nutrition-based program focused on health and longevity. The FMD promotes cellular protection, regeneration, and rejuvenation of multiple organs and systems in old mice, thereby reducing chronic disease incidence and extending healthspan. In a randomized crossover-style clinical trial that included 100 generally healthy participants, the FMD reduced body weight and trunk and total body fat, lowered blood pressure, and decreased IGF-1 in all subjects that completed the trial. A post hoc analysis demonstrated that biomarkers associated with CVD risk such as body mass index, blood pressure, fasting glucose, triglycerides, total cholesterol and LDL, and C-reactive protein were more beneficially affected in participants at risk for disease than in subjects who were not at risk.
- Veronica Galvan, The University of Texas Health Science Center at San Antonio
Mechanisms linking aging to Alzheimer’s disease
Brain vascular dysfunction was recently identified as the earliest and most abnormal biomarker in the progression of Alzheimer’s disease (AD). We showed that the mammalian target of rapamycin (mTOR), a key driver of organismal aging, promotes brain microvascular dysfunction and disintegration in surrogate models of AD through the inhibition of brain vascular reactivity and neurovascular coupling, both dependent on nitric oxide (NO) bioavailability. This reduces clearance of Aβ from brain and thus drives disease progression. We recently discovered that pathogenic tau, which is also causally implicated in AD, accumulates in brain microvascular endothelial cells during normative aging and in AD. Our studies show that, similar to neuron-to-neuron prion-like pathogenic tau transmission, pathogenic tau aggregates propagate to human brain endothelial cells in vitro and in vivo in mouse models of AD tauopathy, where they destabilize the microtubule cytoskeleton, reduce NO production, and trigger endothelial cell senescence, profoundly impairing microvascular function. Our findings add to growing evidence for a role of age-associated microvascular dysfunction in AD pathogenesis, suggest that propagation of pathogenic tau to brain microvascular endothelial cells may represent a novel mechanism in AD and other tauopathies, and support mTOR attenuation and tau removal as potential therapies for microvascular dysfunction in aging and AD.
- Vera Gorbunova, University of Rochester
Mechanisms of longevity: lessons from long-lived mammals
Animals evolved a dramatic diversity of aging rates with lifespans ranging from 2 years to 200 years. This natural diversity can be exploited to understand the mechanisms of longevity. Our goal is to identify mechanisms that allow exceptionally long-lived animals to live long and healthy lives and then use these mechanisms to benefit human health. One example is the naked mole rat, the longest-lived rodent with the maximum lifespan of 32 years. We discovered that longevity and cancer resistance in the naked mole rat are mediated by high-molecular-weight hyaluronan. Recently we generated a mouse model that the naked mole rat hyaluronan synthase and shows increased healthspan and lifespan. I will discuss the strategies we developed to implement this mechanism in humans. I will also discuss our studies of the role of Sirtuin 6 in genome and epigenome stability and in promoting longevity across mammalian species and in human centenarians.
- Andrei Greșiță, University of Medicine and Pharmacy Craiova
Genetic conversion of proliferative astroglia into neurons after cerebral ischemia. A new therapeutic tool for the aged brain
Post stroke, neurons are lost in the infarct core while cells such as astrocytes become reactive and proliferative, disrupting the neuronal vs non-neuronal cell balance in the lesioned area, especially in the aged brain. Therefore, restoring the cell balance within the post-stroke perilesional area is crucial for recovery. Proliferating glia form gliotic scars that are initially protective by confining the damaged area. In the long-term, the gliotic scar acts as a barrier to neural regeneration. However, “melting” glial scars has been attempted with little success. Alternative strategies include transforming inhibitory gliotic tissue into an environment conducive to neuronal regeneration and axonal growth. The latter idea has gained momentum following the discovery that in vivo direct lineage reprogramming in the adult mammalian brain is a feasible strategy for reprogramming non-neuronal cells into neurons; this technology emerged as a new approach to circumvent cell transplantation. The potential of this methodology has not been tested to improve restoration of structure and function in the hostile environment caused by the fulminant inflammatory reaction in the brains of aged animals following stroke. To this end, we used a retroviral delivery system, encoding the transcription factor NeuroD1 alone or in combination with the antiapoptotic factor Bcl-2 to target proliferating astrocytes in the neocortex of young and aged mice after cerebral ischemia. Successful direct in vivo reprogramming of reactive glia into neuroblasts and mature neurons was assessed by cellular phenotyping. We found that the conversion efficacy of proliferating astrocytes into neurons after stroke in aged mice is disappointingly low, most likely because the therapeutic vectors carrying the conversion gene are engulfed by phagocyting macrophages shortly after intracortical administration. We speculate that other viral vectors such as adeno-associated viruses might be more efficient in promoting the conversion of reactive astrocytes to neurons after stroke in the aged brain.
- Derek M Huffman, Albert Einstein College of Medicine
Role of one-carbon metabolism and related metabolites in aging
A hallmark of aging is a decline in metabolic homeostasis, which is attenuated by dietary restriction (DR). We have recently reported on the interaction of aging and DR at the level of the metabolome and found that DR is a stronger modulator of the rat metabolome than age in plasma and tissues. Moreover, a comparative metabolomic screen in rodents and humans identified circulating sarcosine as being similarly reduced with aging and increased by DR, while sarcosine is also elevated in long-lived Ames dwarf mice. Sarcosine is produced by a methyl-donor reaction involving the conversion of S-adenosyl-methionine (SAM) to S-adenosyl-homocysteine (SAH) via methylation of glycine to sarcosine by the cytosolic enzyme glycine-N-methyl transferase (GNMT), and we found that DR significantly boosted GNMT activity in liver. Pathway analysis in aged sarcosine-replete rats further placed this biogenic amine as an integral node in the metabolome network. Finally, while no previously defined role has been clearly attributed to sarcosine in vivo, we have found that sarcosine can activate autophagy in cultured cells and enhances autophagic flux in vivo, suggesting a potential role in autophagy induction by DR. This novel link between sarcosine and aging is of particular interest given several other established and emerging lines of evidence implicating one-carbon metabolism in aging via GNMT. Indeed, it is previously established that a reduction in dietary methionine extends lifespan in rats and mice, while more recent evidence implicates glycine supplementation as a potential geroprotective-strategy, as it has been reported to extend lifespan in C. elegans and in both male and female mice by the Intervention Testing Program. Collectively, these data along with growing evidence implicating methionine, glycine, and GNMT in lifespan, suggest that this pathway may play an important fundamental role in the aging process.
- Thomas Jeitner, Weill Cornell Medicine
Role of liver cystathionine γ-lyase in persulfide formation and its upregulation in mice fed a methionine-restricted diet
The methionine-restricted diet increases both the lifespan and healthspan of experimental animals. One effect of this diet is to increase the levels of cystathionine γ-lyase. Thus, the first objective of the present study was to confirm the increases in tissue cystathionine γ-lyase activities. The beneficial effects of dietary methionine restriction may be due, in part, to the generation of persulfide/sulfane sulfur (S0). One possible source of S0 is cystathionine γ-lyase acting on various biological disulfides. Thus, the second objective of the study is to determine the ability of various disulfides and thiols to act as substrates for cystathionine γ-lyase. The first objective was satisfied by measuring cystathionine γ-lyase activities in the liver, kidney, bone marrow, and various fat depots of adult mice fed a methionine-restricted diet. The cystathionine γ-lyase specific activity, protein concentration, and mRNA level are substantially increased in the livers of methionine-restricted mice relative to those of controls. In addition, the specific activity of kidney cystathionine γ-lyase is increased in the methionine restricted mice. By contrast, the cystathionine γ-lyase specific activity in marrow and fat depots is barely detectable. The second objective was assessed using partially purified rat liver cystathionine γ-lyase. The catalytic efficiency (i.e., Vmax/Km) exhibited by this enzyme toward L,L-cystine (a β-lyase substrate) is high and comparable to that exhibited toward the in vivo substrate L,L-cystathionine (γ-lyase substrate). On the other hand, the L-cysteine-L-homocysteine mixed disulfide is a moderately good substrate. L-Homocystine and L-cysteine are extremely poor substrates. Moreover, L-cysteine is a noncompetitive substrate inhibitor of CGL. These observations suggest the following notions. First, the increases in cystathionine γ-lyase specific activity observed in methionine restricted mice may serve to spare sulfur for L-cysteine synthesis. Second, that cystathionine γ-lyase is a source or S0 which can then be used directly to persulfidate proteins and thereby control function.
- Jay E Johnson, Orentreich Foundation for the Advancement of Science
Novel methionine-related interventions that confer healthspan benefits to yeast and rodents
Methionine restriction (MR) is one of only a few dietary manipulations known to robustly extend healthspan in mammals. Methionine-restricted rodents are up to 45% longer-lived than control-fed littermates, and multiple studies suggest that humans may enjoy similar benefits from this intervention. Despite the fact that a methionine-restricted human diet is technically feasible, widespread compliance to such a regimen might not be practical or desirable. Therefore, an important goal is to identify and/or develop more facile dietary interventions, or preferably, pharmacological agents that mimic MR. Toward this end, we have made use of the yeast chronological lifespan and replicative lifespan assays, which serve as models of aging in quiescent and mitotic cells, respectively. Importantly, our lab and others have demonstrated that MR dramatically extends yeast lifespan, and thus we reasoned that novel methionine-related interventions that improve healthspan might be identified using yeast. Here we show work aimed at developing novel MR-like interventions that extend yeast lifespan, as well as preliminary data demonstrating that such interventions significantly improve the healthspan of mice.
- Brian Kennedy, National University of Singapore
Targeting human aging – can we extend healthspan
There is a growing sense that a holistic understanding of aging biology may be achievable. This would represent a tremendous advance in our collective biological understanding and afford opportunities for novel interventions to enhance human healthspan. Aging is the biggest risk factor for the major chronic diseases growing in prominence. These include cardiovascular and neurodegenerative diseases, diabetes, and cancer. If ageing can be slowed, the effect would be simultaneous protection from many of the chronic diseases. One strategy is to use animal model organisms to find common pathways that modulate aging and then to seek methods for their manipulation in humans. The TOR pathway is one point of convergence, and a clinically approved drug targeting the TOR kinase, rapamycin, extends murine lifespan and healthspan. Many more small molecules are being added to the list of anti-aging compounds. Here, I will discuss known and novel small molecule interventions, including natural products, focusing on healthspan. It is critical to understand the mechanisms by which these interventions delay ageing. We are now entering a stage in aging research in which it is imperative to test aging interventions in humans. The potential to directly impact human healthspan is emerging from aging research and this approach, if successful, will have global impact.
- Caroline Kumsta, Sanford Burnham Presbys Medical Discovery Institute
The autophagy receptor SQSTM1/p62 promotes longevity in C. elegans
Mammalian SQSTM1/p62 acts as a selective autophagy receptor for substrates such as ubiquitinated protein aggregates. SQSTM1/p62 is involved in different cellular processes, including proteostasis, and its loss has been linked to accelerated aging in mice and to age-related diseases in human tissues. However, it remains unclear how age affects the regulation of SQSTM1/p62, and by what molecular mechanisms SQSTM1/p62 can modulate aging. To address these questions we used the short-lived nematode C. elegans, a significant model organism to study the role of autophagy in aging and longevity. The C. elegans homolog of SQSTM-1/p62, SQST-1, is involved in autophagy during embryogenesis, but its role during aging is unclear. Here we show that overexpression of SQST-1 in C. elegans extends lifespan in an autophagy-dependent manner and improves the lifespan of temperature-sensitive folding mutants, indicating that SQST-1 mediates lifespan and proteostasis in C. elegans. We also find that sqst-1 is required for autophagosome formation in specific tissues under basal conditions, yet is more broadly required upon an autophagy-inducing hormetic heat shock. These findings demonstrate that the autophagy receptor SQST-1 has tissue- and context-specific roles in mediating autophagy, proteostasis, and lifespan in C. elegans. Thus, improving p62-mediated autophagy could be important for the development of strategies to enhance healthspan in humans.
- Lucy Liaw, Maine Medical Center Research Institute
Dietary effects on perivascular adipose tissue and implications for cardiovascular disease
Changes in diet affect aging, and attention has turned to improving healthspan, the duration of healthy life. Two dietary modifications, calorie restriction (CR) and methionine restriction (MR), have garnered significant interest as anti-aging regimens. CR extends lifespan and improves measures of cardiovascular health. Likewise, MR in rodents decreases body mass, extends lifespan, and increases health, even in the presence of an obesogenic diet. Cardiovascular disease is the leading cause of mortality in the USA, and significantly decreases healthspan. The NIH clinical trial, CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy), found that CR reduced risk factors for cardiovascular disease. Conversely, a high-fat diet leads to obesity and hyperglycemia and promotes cardiovascular disease progression. Our laboratory is focused on a specialized adipose depot, perivascular adipose tissue (PVAT), which resides within the vascular microenvironment and is a paracrine regulator of vascular function. In the mouse, healthy PVAT surrounding the aorta has a thermogenic phenotype, similar to brown adipose tissue, and functions to burn calories to generate heat. On an obesogenic diet, PVAT converts to a pathological phenotype, characterized by increased lipid storage similar to white adipose tissue, increased inflammation, changes in molecular markers, and changes in protein secretion. Despite continuation on a high-fat diet, reduction in dietary methionine is sufficient to revert the PVAT phenotype, concomitant with reduced body weight and reversion to a lean phenotype. We are interested in the mechanisms by which these dietary changes affect adipocyte differentiation in PVAT, as well as changes its secretion profile. Our prediction is that modulation of PVAT to promote the thermogenic phenotype will have consequences to protect against cardiovascular disease.
- Richard A Miller, University of Michigan
Drugs that slow aging: Report from the ITP
Identification of small molecules that extend mouse lifespan provides new insights into mechanisms of longevity determination in mammals, and may lay the groundwork for eventual anti-aging therapies in humans. The NIA Interventions Testing Program (ITP) evaluates agents proposed to extend mouse lifespan by retardation of aging or postponement of late life diseases. Interventions proposed by multiple collaborating scientists from the research community are tested, in parallel, at three sites, using standardized protocols, and using sufficient numbers of genetically heterogeneous mice to provide 80% power for detecting changes in lifespan of 10%, for either sex. Seventy-two such lifespan experiments, involving various doses of 44 distinct agents, have been initiated in the first fifteen years of the ITP. Thirty-seven experiments have involved comparative tests of multiple doses of effective agents, variable starting ages, or alternative dosing schedules. Significant effects on longevity, in one or both sexes, have been documented and then confirmed for NDGA, rapamycin, acarbose, and 17-α-estradiol (17aE2), with significant (but currently unconfirmed) effects also noted for Protandim, glycine and, in an interim analysis, canagliflozin. Lifespan trials are now underway for 18 new agents. ITP survival results have also documented longevity benefits from three agents started in middle-age: rapamycin, acarbose, and 17aE2. Today’s presentation will include updates from the latest survival studies, data on health outcomes when drugs are initiated in middle-age, and tests of molecular hypotheses about cellular and neuroendocrine pathways shared by multiple drugs, and genetic mutations, that slow aging and extend healthy lifespan in mice.
Support: NIA. Key colleagues: David Harrison, Randy Strong, Francesca Macchiarini.
- John Newman, Buck Institute for Research on Aging
Ketone body signaling in health and aging
Ketone bodies are a normal part of human metabolism, small molecules made by the body during fasting, exercise, or other times when carbohydrates become scarce. They are made in the liver from fats mobilized from adipose tissue, and then act as a convenient source of energy for the brain, muscles, heart, and other organs. But alongside this classic role as a fasting fuel, we are learning that ketone bodies act as signals, too. By binding to proteins, inhibiting enzymes, and activating receptors, they can have effects on gene expression, inflammation, metabolism, and other processes. We helped identify ketone bodies as endogenous histone deacetylase inhibitors. These signaling activities are only beginning to be understood, but suggest discrete mechanisms by which ketone bodies can affect health and disease. We recently showed that exposing mice to ketone bodies long-term using a non-obese ketogenic diet can extend healthy lifespan, and identified a new mechanism by which ketone bodies affect Alzheimer’s disease. We also developed a set of compounds that permit feeding ketone bodies in a normal diet and allow the mechanistic study of the effects of ketone bodies on aging phenotypes. Understanding the signaling activities of ketone bodies will help to guide the creation of new therapies derived from ketone bodies, target these therapies to certain diseases, and inform their clinical use.
- Adam Salmon, The University of Texas Health Science Center at San Antonio
Intervention with rapamycin to improve healthy aging and longevity in a non-human primate
Interventions to extend lifespan and improve health with increasing age will have significant impact on a growing aged population. Among pharmaceutical interventions reported to extend lifespan in laboratory rodent models, the FDA-approved drug rapamycin, an inhibitor of mechanistic target of rapamycin (mTOR), has been the most effective and most well studied. The question remains, though, whether interventions in rodent models will reap the same longevity benefits among humans. Bridging towards translation, we have an ongoing long-term study testing whether rapamycin treatment can extend lifespan and delay the progression of age-related disease in a short-lived non-human primate species, the common marmoset (Callithrix jacchus). As an aging model, the marmoset offers many advantages over other non-human primates including relatively short life (~10 yr avg) and small size. Marmosets exhibit many of the same age-related pathologies and diseases that occur naturally with age in humans. We show that daily oral dosing of slow-releasing, encapsulated rapamycin will result in clinically effective concentrations of rapamycin in the blood and inhibit mTOR signaling. This treatment is well tolerated and does not dramatically promote known side effects of this drug, including altering clinical hematology, immune cell subsets, or promoting metabolic dysfunction including glucose intolerance in comparison to control aging marmosets. Unlike previous reports in rodents, rapamycin does not have clear effects on aging cardiovascular function in marmosets. However, in our oldest cohorts daily rapamycin treatment tends to prevent age-associated changes in body mass and composition and prevent decline in kidney function. Now more than three years after beginning treatment, we are now starting to assess the effects of rapamycin on marmoset longevity. When complete, this study will describe for the first time the potential for pharmaceutical intervention to extend longevity of a primate species, with the ultimate goal of significant translational impact to human aging.
- Jeffrey S Smith, University of Virginia School of Medicine
Caloric restriction extends yeast chronological lifespan through a cell-extrinsic mechanism
Caloric restriction (CR) promotes longevity in a wide variety of eukaryotes ranging from yeast to mammals, prompting extensive investigation into the underlying molecular mechanisms. We utilize chronological lifespan (CLS) of the budding yeast Saccharomyces cerevisiae as a cellular model for CR, whereby glucose in the growth medium is reduced from 2% (non-restricted; NR) to 0.5% (CR). CLS is then measured as the number of days that cells remain viable once cultures reach stationary phase. The glucose sensing Snf1 (AMPK) signaling pathway is activated by CR and mediates the beneficial effects on CLS by optimizing the transcriptional and metabolic transition from glycolysis to respiration (the diauxic shift), a cell-intrinsic process required for long term survival. Interestingly, CLS extension by CR also has a cell-extrinsic component, such that conditioned media from stationary phase CR cultures extends CLS when supplemented into NR cultures, suggesting the existence of extracellular longevity factors. Partial purification of the longevity activity from concentrated CR media using size exclusion chromatography indicated the presence of one or more water soluble small molecules. Metabolomics then revealed an unexpected accumulation of specific amino acids in the CR media compared to NR media, which we further confirmed by amino acid profiling. Serine showed the strongest relative CR enrichment, which was intriguing because the serine biosynthesis gene, SER1, was independently identified as a strong QTL for CLS under high glucose concentrations. Indeed, serine supplementation extended CLS of NR cultures in a dose-dependent manner. Serine is therefore strongly limiting for CLS in high glucose conditions. RNA-seq analysis comparing CR and 10mM serine supplementation revealed significantly overlapping changes in gene expression, including elevated oxidative stress resistance, suggesting that at least part of the CR effect on CLS is due to the sustained presence of extracellular serine. Downstream mechanisms are currently under investigation.
- Jessica Tyler, Weill Cornell Medicine
Identifying drivers of replicative aging in budding yeast
Aging is a complex, multi-factorial biological process shared by all living organisms. It is manifested by a gradual accumulation of molecular alterations that lead to the decline of normal physiological functions in a time-dependent fashion. The ultimate goal of the aging research field is to develop therapeutic means to extend human lifespan while reducing susceptibility to many age-related diseases, including cancer, metabolic disorders, and cardiovascular and neurodegenerative disorders. However, this first requires elucidation of the causes of aging, which has been greatly facilitated by the use of model organisms. In particular, the budding yeast Saccharomyces cerevisiae has been invaluable in the identification of conserved molecular and cellular determinants of aging and for the development of approaches to manipulate these aging determinants to extend lifespan. Strikingly, where examined, virtually all means to experimentally extend lifespan result in the induction of cellular stress responses. Our laboratory uses the unique advantages of yeast as an experimental organism to elucidate conserved mechanisms that decay during aging, in order to identify novel ways to achieve lifespan extension that are likely to drive therapeutic approaches to extend human lifespan and healthspan in the future.