Citations

AbstractSenescent cells compromise tissue structure and function in older organisms. We recently identified senescent fibroadipogenic progenitors (FAPs) with activated chemokine signaling pathways in the skeletal muscle of old mice, and hypothesized these cells may contribute to the age‐associated accumulation of immune cells in skeletal muscle. In this study, through cell–cell communication analysis of skeletal muscle single‐cell RNA‐sequencing data, we identified unique interactions between senescent FAPs and macrophages, including those mediated by Ccl2 and Spp1. Using mouse primary FAPs in vitro, we verified increased expression of Ccl2 and Spp1 and secretion of their respective proteins in the context of both irradiation‐ and etoposide‐induced senescence. Compared to non‐senescent FAPs, the medium of senescent FAPs markedly increased the recruitment of macrophages in an in vitro migration assay, an effect that was mitigated by preincubation with antibodies to either CCL2 or osteopontin (encoded by Spp1). Further studies demonstrated that the secretome of senescent FAPs promotes polarization of macrophages toward an M2 subtype. These data suggest the unique secretome of senescent FAPs may compromise skeletal muscle homeostasis by recruiting and directing the behavior of macrophages.

Cachexia is a debilitating skeletal muscle wasting condition for which we currently lack effective treatments. In the context of cancer, certain chemotherapeutics cause DNA damage and cellular senescence. Senescent cells exhibit chronic activation of the transcription factor NF-κB, a known mediator of the proinflammatory senescence-associated secretory phenotype (SASP) and skeletal muscle atrophy. Thus, targeting NF-κB represents a logical therapeutic strategy to alleviate unintended consequences of genotoxic drugs. Herein, we show that treatment with the IKK/NF-κB inhibitor SR12343 during a course of chemotherapy reduces markers of cellular senescence and the SASP in liver, skeletal muscle, and circulation and, correspondingly, attenuates features of skeletal muscle pathology. Lastly, we demonstrate that SR12343 mitigates chemotherapy-induced reductions in body weight, lean mass, fat mass, and muscle strength. These findings support senescent cells as a promising druggable target to counteract the SASP and skeletal muscle wasting in the context of chemotherapy.

Abstract Calorie restriction (CR) with adequate nutrient intake is a potential geroprotective intervention. To advance this concept in humans, we tested the hypothesis that moderate CR in healthy young‐to‐middle‐aged individuals would reduce circulating biomarkers of cellular senescence, a fundamental mechanism of aging and aging‐related conditions. Using plasma specimens from the Comprehensive Assessment of Long‐term Effects of Reducing Intake of Energy (CALERIE™) phase 2 study, we found that CR significantly reduced the concentrations of several senescence biomarkers at 12 and 24 months compared to an ad libitum diet. Using machine learning, changes in biomarker concentrations emerged as important predictors of the change in HOMA‐IR and insulin sensitivity index at 12 and 24 months, and the change in resting metabolic rate residual at 12 months. Finally, using adipose tissue RNA‐sequencing data from a subset of participants, we observed a significant reduction in a senescence‐focused gene set in response to CR at both 12 and 24 months compared to baseline. Our results advance the understanding of the effects of CR in humans and further support a link between cellular senescence and metabolic health.

Abstract Studies in mice and cross-sectional studies in humans support the premise that cellular senescence is a contributing mechanism to age-associated deficits in physical function. We tested the hypotheses that circulating proteins secreted by senescent cells are (i) associated with the incidence of major mobility disability (MMD), the development of persistent mobility disability (PMMD), and decrements in physical functioning in older adults, and (ii) influenced by physical activity (PA). Using samples and data obtained longitudinally from the Lifestyle Interventions in Elders Study clinical trial, we measured a panel of 27 proteins secreted by senescent cells. Among 1 377 women and men randomized to either a structured PA intervention or a healthy aging (HA) intervention, we observed significant associations between several senescence biomarkers, most distinctly vascular endothelial growth factor A (VEGFA), tumor necrosis factor receptor 1 (TNFR1), and matrix metallopeptidase 7 (MMP7), and the onset of both MMD and PMMD. Moreover, VEGFA, GDF15, osteopontin, and other senescence biomarkers were associated with reductions in short physical performance battery scores. The change in senescence biomarkers did not differ between PA and HA participants. In the whole cohort, higher levels of PA were associated with significantly greater reductions in 10 senescence-related proteins at 12 and/or 24 months. These data reinforce cellular senescence as a contributing mechanism of age-associated functional decline and the potential for PA to attenuate this hallmark of aging. Clinical Trials Registration Number: NCT01072500

AbstractA robust and heterogenous secretory phenotype is a core feature of most senescent cells. In addition to mediators of age‐related pathology, components of the senescence associated secretory phenotype (SASP) have been studied as biomarkers of senescent cell burden and, in turn, biological age. Therefore, we hypothesized that circulating concentrations of candidate senescence biomarkers, including chemokines, cytokines, matrix remodeling proteins, and growth factors, could predict mortality in older adults. We assessed associations between plasma levels of 28 SASP proteins and risk of mortality over a median follow‐up of 6.3 years in 1923 patients 65 years of age or older with zero or one chronic condition at baseline. Overall, the five senescence biomarkers most strongly associated with an increased risk of death were GDF15, RAGE, VEGFA, PARC, and MMP2, after adjusting for age, sex, race, and the presence of one chronic condition. The combination of biomarkers and clinical and demographic covariates exhibited a significantly higher c‐statistic for risk of death (0.79, 95% confidence interval (CI): 0.76–0.82) than the covariates alone (0.70, CI: 0.67–0.74) (p < 0.001). Collectively, these findings lend further support to biomarkers of cellular senescence as informative predictors of clinically important health outcomes in older adults, including death.

Abstract Dynamic measures of resilience—the ability to resist and recover from a challenge—may be informative of the rate of aging before overt manifestations such as chronic disease, disability, and frailty. From this perspective mid-life resilience may predict longevity and late-life health. To test this hypothesis, we developed simple, reproducible, clinically relevant challenges, and outcome measures of physical resilience that revealed differences between and within age groups of genetically heterogeneous mice, and then examined associations between mid-life resilience and both lifespan and late-life measures of physiological function. We demonstrate that time to recovery from isoflurane anesthesia and weight change following a regimen of chemotherapy significantly differed among young, middle-aged, and older mice, and were more variable in older mice. Females that recovered faster than the median time from anesthesia (more resilient) at 12 months of age lived 8% longer than their counterparts, while more resilient males in mid-life exhibited better cardiac (fractional shortening and left ventricular volumes) and metabolic (glucose tolerance) function at 24 months of age. Moreover, female mice with less than the median weight loss at Day 3 of the cisplatin challenge lived 8% longer than those that lost more weight. In contrast, females who had more weight loss between Days 15 and 20 were relatively protected against early death. These data suggest that measures of physical resilience in mid-life may provide information about individual differences in aging, lifespan, and key parameters of late-life health.

Abstract Obesity-related type II diabetes (diabesity) has increased global morbidity and mortality dramatically. Previously, the ancient drug salicylate demonstrated promise for the treatment of type II diabetes, but its clinical use was precluded due to high dose requirements. In this study, we present a nitroalkene derivative of salicylate, 5-(2-nitroethenyl)salicylic acid (SANA), a molecule with unprecedented beneficial effects in diet-induced obesity (DIO). SANA reduces DIO, liver steatosis and insulin resistance at doses up to 40 times lower than salicylate. Mechanistically, SANA stimulated mitochondrial respiration and increased creatine-dependent energy expenditure in adipose tissue. Indeed, depletion of creatine resulted in the loss of SANA action. Moreover, we found that SANA binds to creatine kinases CKMT1/2, and downregulation CKMT1 interferes with the effect of SANA in vivo. Together, these data demonstrate that SANA is a first-in-class activator of creatine-dependent energy expenditure and thermogenesis in adipose tissue and emerges as a candidate for the treatment of diabesity.

We propose the beneficial effects of exercise are in part mediated through the prevention and elimination of senescent cells. Exercise counters multiple forms of age-related molecular damage that initiate the senescence program and activates immune cells responsible for senescent cell clearance. Preclinical and clinical evidence for exercise as a senescence-targeting therapy and areas needing further investigation are discussed.

Physical resilience, defined as the ability to resist and respond to challenges and return to homeostasis, has been postulated to be a determinant of healthspan and lifespan. To test this premise, we have begun to optimize a standardized, clinically relevant battery of resilience challenges, including anesthesia and cisplatin chemotherapy, and recovery outcome measures in younger (2–3 month) and older (26–29 month) mice. We have also started to test whether interventions shown to increase murine lifespan‐acarbose, rapamycin, and 17a‐estradiol‐impact the resilience of older mice. Our preliminary data demonstrate that younger mice (n = 10) have faster dorsal to sternal recumbence recovery time compared to older mice (n = 8) (39 ± 1 sec vs. 67 ± 6 sec, p < 0.001) following a 5‐minute 4% isoflurane anesthesia challenge. In response to a 5‐day cisplatin (2 mg/kg/day) challenge, both younger (n=5) and older (n=4) mice lost a significant percent of their baseline body weight (younger mice −10.6 ± 0.8% and older mice −13.2 ± 2.1%, p = 0.26), however, older mice failed to regain body weight 11 days after the challenge (younger mice −0.9 ± 0.8% and older mice −9.8 ± 0.8%, p < 0.01). Changes in body weight in younger and older mice were largely attributable to the loss/regain of fat mass. Interestingly, 8 weeks of either acarbose (1,000 ppm) or 17α‐estradiol (14.4 ppm) administration to older female mice improved body weight recovery after the cisplatin challenge, while rapamycin (14 ppm) had no appreciable effect. Our preliminary results demonstrate that younger mice, as expected, have greater resilience than older mice to clinically relevant physical challenges. The age at which physical resilience starts to decline requires further investigation. Our early observations suggest interventions that extend health‐ and lifespan may impact resilience in older mice. Ultimately, a standardized battery of resilience challenges may provide a new framework for testing and translating interventions that target the fundamental biology of aging. Support or Funding Information This work was supported by grant AG52958 from the National Institutes of Health. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .