Kirkland, James L.

Abstract Background Extensive work in basic and clinical science suggests that biological mechanisms of aging are causally related to the development of disease and disability in late life. Modulation of the biological mechanisms of aging can extend both life span and health span in animal models, but translation to humans has been slow. Methods Summary of workshop proceedings from the 2018–2019 Epidemiology of Aging Workshop hosted by the Intramural Research Program at the National Institute on Aging. Results Epidemiologic studies play a vital role to progress in this field, particularly in evaluating new risk factors and measures of biologic aging that may influence health span, as well as developing relevant outcome measures that are robust and relevant for older individuals. Conclusions Appropriately designed epidemiological studies are needed to identify targets for intervention and to inform study design and sample size estimates for future clinical trials designed to promote health span.

Abstract The geroscience hypothesis holds that targeting fundamental mechanisms of aging has the potential to prevent or reduce severity of multiple age-related diseases. Cellular senescence is a key mechanism that may be driving disease in human aging, including Idiopathic pulmonary fibrosis (IPF), a progressive, ultimately fatal, senescence-associated disease. Importantly, cellular senescence may be targeted therapeutically. Senolytic agents are drugs that selectively induce senescent cell apoptosis by transiently disabling anti-apoptotic pathways. Selective ablation of senescent cells using the senolytic drug combination dasatinib plus quercetin (DQ) alleviates IPF-related dysfunction in bleomycin-administered IPF mouse model. We conducted the first-in-human trial of senolytics in IPF patients, and our data indicate that short-term, intermittent administration of DQ may alleviate physical dysfunction that accompanies IPF in human aging, including clinically-meaningfully improvements in mobility (p<0.05). This geroscience-guided clinical feasibility study supports evaluation of senolytics in larger randomized, controlled trials of cellular senescence-associated age-related diseases.

Advances in understanding fundamental processes of aging have led to a variety of investigational therapies to delay or prevent age‐related diseases and conditions. These geroscience therapeutics hold the promise of revolutionizing medical care of older adults by treating the complex syndromes of aging and preserving health and independence. A crucial bottleneck is the study of geroscience therapeutics in early‐stage, first‐in‐human, or proof‐of‐concept clinical trials. There is a limited pool of clinical investigators with the combination of knowledge and skills at the interface of clinical research, care of older adults, and aging biology needed to successfully design, fund, and implement geroscience trials. Current training pipelines are insufficient to meet the need. The sixth retreat of the National Institute on Aging R24 Geroscience Network brought together basic scientists, gerontologists, clinicians, and clinical researchers from the United States and Europe to discuss how to identify, recruit, and train investigators who can perform early‐stage clinical trials in geroscience. We present herein the group's consensus on necessary subject domains and competencies, identification of candidate learners, credentialing learners, and the efficient and rapid implementation of training programs. Foundations and funding agencies have crucial roles to play in catalyzing the development of these programs. Geriatrician investigators are indispensable but cannot meet the need alone. Translational geroscience training programs can create a cadre of groundbreaking investigators from a variety of backgrounds and foster institutional cultures supportive of multidisciplinary translational aging research to turn innovative ideas into transformative therapeutics that can improve the health and independence of older adults. J Am Geriatr Soc 67:1934–1939, 2019

Abstract17α-Estradiol (17α-E2) is a “non-feminizing” estrogen that extends life span in male, but not female, mice. We recently reported that 17α-E2 had robust beneficial effects on metabolic and inflammatory parameters in aged male mice. However, it remains unclear if 17α-E2 also delays other “hallmarks” of aging, particularly maintaining proteostasis. Here, we used isotope labeling methods in older mice to examine proteostatic mechanisms. We compared weight-matched mild calorie restricted (CR) and 17α-E2 treated male mice with the hypothesis that 17α-E2 would increase protein synthesis for somatic maintenance. 17α-E2 had no effect on protein synthesis or DNA synthesis in multiple tissues, including white adipose tissue. Conversely, mild short-term CR decreased DNA synthesis and increased the protein to DNA synthesis ratio in multiple tissues. Examination of individual protein synthesis and content did not differentiate treatments, although it provided insight into the regulation of protein content between tissues. Contrary to our hypothesis, we did not see the predicted differences in protein to DNA synthesis following 17α-E2 treatment. However, mild short-term CR elicited differences consistent with both lifelong CR and other treatments that curtail aging processes. These data indicated that despite similar maintenance of body mass, 17α-E2 and CR treatments elicit distinctly different proteostatic outcomes.

ABSTRACT Estrogen deficiency is a seminal mechanism in the pathogenesis of osteoporosis. Mounting evidence, however, establishes that cellular senescence, a fundamental mechanism that drives multiple age-related diseases, also causes osteoporosis. Recently, we systematically identified an accumulation of senescent cells, characterized by increased p16Ink4a and p21Cip1 levels and development of a senescence-associated secretory phenotype (SASP), in mouse bone/marrow and human bone with aging. We then demonstrated that elimination of senescent cells prevented age-related bone loss using multiple approaches, eg, treating old mice expressing a “suicide” transgene, INK-ATTAC, with AP20187 to induce apoptosis of p16Ink4a-senescent cells or periodically treating old wild-type mice with “senolytics,” ie, drugs that eliminate senescent cells. Here, we investigate a possible role for estrogen in the regulation of cellular senescence using multiple approaches. First, sex steroid deficiency 2 months after ovariectomy (OVX, n = 15) or orchidectomy (ORCH, n = 15) versus sham surgery (SHAM, n = 15/sex) in young adult (4-month-old) wild-type mice did not alter senescence biomarkers or induce a SASP in bone. Next, in elderly postmenopausal women, 3 weeks of estrogen therapy (n = 10; 74 ± 5 years) compared with no treatment (n = 10; 78 ± 5 years) did not alter senescence biomarkers or the SASP in human bone biopsies. Finally, young adult (4-month-old) female INK-ATTAC mice were randomized (n = 17/group) to SHAM+Vehicle, OVX+Vehicle, or OVX+AP20187 for 2 months. As anticipated, OVX+Vehicle caused significant trabecular/cortical bone loss compared with SHAM+Vehicle. However, treatment with AP20187, which eliminates senescent cells in INK-ATTAC mice, did not rescue the OVX-induced bone loss or alter senescence biomarkers. Collectively, our data establish independent roles of estrogen deficiency and cellular senescence in the pathogenesis of osteoporosis, which has important implications for testing novel senolytics for skeletal efficacy, as these drugs will need to be evaluated in preclinical models of aging as opposed to the current FDA model of prevention of OVX-induced bone loss. © 2019 American Society for Bone and Mineral Research.

Abstract Adipose tissue inflammation and dysfunction are associated with obesity‐related insulin resistance and diabetes, but mechanisms underlying this relationship are unclear. Although senescent cells accumulate in adipose tissue of obese humans and rodents, a direct pathogenic role for these cells in the development of diabetes remains to be demonstrated. Here, we show that reducing senescent cell burden in obese mice, either by activating drug‐inducible “suicide” genes driven by the p16 Ink4a promoter or by treatment with senolytic agents, alleviates metabolic and adipose tissue dysfunction. These senolytic interventions improved glucose tolerance, enhanced insulin sensitivity, lowered circulating inflammatory mediators, and promoted adipogenesis in obese mice. Elimination of senescent cells also prevented the migration of transplanted monocytes into intra‐abdominal adipose tissue and reduced the number of macrophages in this tissue. In addition, microalbuminuria, renal podocyte function, and cardiac diastolic function improved with senolytic therapy. Our results implicate cellular senescence as a causal factor in obesity‐related inflammation and metabolic derangements and show that emerging senolytic agents hold promise for treating obesity‐related metabolic dysfunction and its complications.

Abstract Aging leads to increased cellular senescence and is associated with decreased potency of tissue‐specific stem/progenitor cells. Here, we have done an extensive analysis of cardiac progenitor cells (CPCs) isolated from human subjects with cardiovascular disease, aged 32–86 years. In aged subjects (>70 years old), over half of CPCs are senescent (p16 INK4A , SA‐β‐gal, DNA damage γH2AX, telomere length, senescence‐associated secretory phenotype [SASP]), unable to replicate, differentiate, regenerate or restore cardiac function following transplantation into the infarcted heart. SASP factors secreted by senescent CPCs renders otherwise healthy CPCs to senescence. Elimination of senescent CPCs using senolytics abrogates the SASP and its debilitative effect in vitro. Global elimination of senescent cells in aged mice (INK‐ATTAC or wild‐type mice treated with D + Q senolytics) in vivo activates resident CPCs and increased the number of small Ki67‐, EdU‐positive cardiomyocytes. Therapeutic approaches that eliminate senescent cells may alleviate cardiac deterioration with aging and restore the regenerative capacity of the heart.