Citations

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 .

Adipocytes accumulate within and around skeletal muscle with advancing age. Adipose progenitor cells, preadipocytes, are prone to cellular senescence, a state of stable growth arrest associated with the secretion of cytokines, chemokines and matrix remodeling proteins, collectively referred to as the senescence‐associated secretory phenotype (SASP). Considerable evidence implicates the SASP in age‐related tissue inflammation and degeneration; however, its impact on skeletal muscle is poorly understood. Herein, we examined the effects of conditioned media (CM) collected from healthy human (control CM) and senescent by irradiation (senescent CM) preadipocytes on human skeletal muscle cells (SkMCs). Compared to control CM, senescent CM had more than 10‐fold higher concentrations of IL‐6, IL‐1β, IL‐8, PAI‐1, MCP‐1 and TNFα as quantified by a multiplexed antibody‐based assay. Senescent CM increased expression of IL‐6 (5‐fold), IL‐1α (1.6‐fold), IL‐1β (3.5‐fold), MCP‐1 (2.5‐fold), PAI‐1 (1.7‐fold) and MMP‐3 (3‐fold) in differentiated SkMCs relative to control CM as measured by qPCR (all p < 0.05). Senescent CM increased proliferation of undifferentiated SKMCs by 20%; however, inhibited differentiation relative to control CM per the fusion index. Preliminary data further suggest senescent CM compromises insulin‐ and IGF‐1‐mediated activation of Akt. Collectively, our data suggest that the SASP of senescent preadipocytes may drive inflammation in SkMCs and compromise their differentiation and, potentially, response to metabolic an anabolic stimuli. These effects may contribute to age‐related changes in skeletal muscle health and regeneration. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

We recently demonstrated that high dietary fat (HFD) consumption results in a dramatic loss of myelinating cells and their progenitors in the adult CNS (Yoon et al., 2016). However, the mechanism(s) by which HFD drives dysmyelination are unknown. Since epidemiological studies indicate that metabolic syndrome is a key risk factor for multiple sclerosis (MS), a better understanding of how HFD contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. In mice fed HFD, we found significant decreases in vertical activity by 4 wk and significant changes in ambulatory and stereotypy movements by 12 wk in the Open Field Test. HFD‐fed mice also spent less time in the center of the field as opposed to the perimeter, indicating an anxious phenotype. Mitochondrial isolated from the spinal cord of mice consuming HFD for 4 wk had significantly higher state 3 and state 4 respiration as determined by high‐resolution respirometry. However, by 12 wk, state 4 mitochondrial respiration was significantly less in the HFD group. Targeted LC‐LC‐mass spectroscopy approaches demonstrated that Citric Acid Cycle intermediates are also depleted in the spinal cord of mice consuming HFD for 12 wk compared to controls. Changes in genes related to mitochondrial morphology, quality control processes, and oxidative stress response were also found. In addition, there were significantly fewer Olig2+ cells and increased signs of lipid peroxidation products (4‐Hydroxynonenal‐immunoreactivity) in the corpus callosum of HFD consuming mice compared to those fed a regular diet. Supporting in vivo findings that oligodendrocytes are reduced in the spinal cord of mice consuming HFD, we observed increased mitochondrial fragmentation and a reduced oxygen consumption rate in oligodendrocyte precursors cultured with palmitic acid. Astrocytes however, significantly increased oxygen consumption following exposure to palmitic acid. Together, these findings suggest that changes in the adult spinal cord in response to HFD consumption creates an environment that is less conducive to neural repair by impacting mitochondria function and morphology and impairing oligodendrocyte function. To determine any impact of HFD on myelin regeneration, studies are ongoing to examine myelin regeneration using a murine model of Cuprizone‐mediated demyelination. Neurobehavioral assessments to date reveal significant interactions between HFD and myelin injury and repair. Understanding the cellular environment in response to dietary factors such as HFD consumption can help to guide care for individuals with MS and other conditions in which myelin loss plays a pathological role and has potential to identify new targets for intervention. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Inflammation is a hallmark of aging and a likely contributor to skeletal muscle loss ( sarcopenia ). We investigated whether the inflammatory phenotype of differentiated primary skeletal muscle‐derived cells (SkMDCs) from a 17‐year‐old (young) differed from that of a 68‐year‐old (older) donor. Under basal conditions, expression of genes encoding pro‐inflammatory cytokines was in fact lower in older compared to younger SkMDCs. However, in response to lipopolysaccharide (LPS), these factors were more highly upregulated in older cells. Specifically, in young compared to older SkMDCs, interleukin‐6 (IL‐6) increased 3‐ vs. 9‐fold, tumor necrosis factor‐alpha (TNF‐alpha) increased 11‐ vs. 80‐fold, and IL‐1alpha increased 14‐ vs. 21‐fold (all differences were p < 0.01). Given adipose tissue is a primary source of pro‐inflammatory stimuli and infiltrates skeletal muscle with age, we hypothesized that secreted factors from senescent preadipocytes drive a similar molecular phenotype to LPS. Exposure of SkMDCs to conditioned medium from senescent‐preadipocytes increased expression IL‐6 and TNF‐alpha in young and even more so in older cells (both p < 0.05). Thus, there are inherent differences in the molecular inflammatory phenotype and its response between young and older SkMDCs. These data also suggest that the age‐related accumulation of senescent preadipocytes may contribute to sarcopenia.

Infiltration of fat cells into skeletal muscle is a hallmark of aging that has been associated with insulin resistance and the pathogenesis of type 2 diabetes mellitus (T2DM). The mechanisms by which fat cells affect the health and metabolic state of skeletal muscle are poorly understood. Given the evidence for cross‐talk between these tissues and the secretory phenotype of senescent preadipocytes, we first utilized real time‐PCR to examine the expression of inflammatory cytokines in primary human skeletal muscle‐derived cells (SkMDCs) in response to conditioned medium (CM) from either control human preadipocytes (Normal CM) or from human preadipocytes driven to senescence by irradiation (Senescent CM). Exposure of SkMDCs to either Normal CM or Senescent CM for 24 hours significantly increased their expression of IL‐6 (5.1±1.7‐and 14.1±4.7‐fold, respectively), TNFα (1.3±0.2‐and 2.1±0.67‐fold, respectively) and MCP‐1 (2.9±1.1‐and 6.8±2.3‐fold, respectively). Next, we investigated the effects of CM on insulin signaling in SkMDCs via Western blot analysis. Exposure of SKMDCs to preadipocyte CM significantly blunted insulin‐stimulated phosphorylation of its downstream effectors, including Akt (14–24%, p<0.05). Finally, we examined the effects of CM on the proliferative capacity of undifferentiated SkMDCs. Senescent CM inhibited SkMDC proliferation by more than 30% (p < 0.05). In conclusion, factors secreted by preadipocytes, and in particular, senescent preadipocytes, negatively impact the inflammatory and metabolic phenotype and the proliferative capacity of skeletal muscle cells. Elucidation of the biologic materials that are secreted from fat cells and mediate these effects may lead to novel therapeutic strategies for the treatment of age‐related conditions, including T2DM. The authors acknowledge the support of Mayo Clinic and a generous gift from Robert and Arlene Kogod.

Omega‐3 polyunsaturated fatty acids (n‐3 PUFAs) protect insulin sensitivity and glucose homeostasis in rodent models of insulin resistance. These effects of n‐3 PUFAs are linked with anti‐inflammatory properties, but emerging data suggests that mechanisms may also converge on mitochondria. We evaluated the influence of dietary n‐3 PUFAs on mitochondrial physiology in the context of high‐fat diet (HFD) in mice. We hypothesized that the insulin‐sensitizing effects of n‐3 PUFAs would be accompanied by enhanced mitochondrial function in skeletal muscle, leading to attenuated levels of lipid metabolites known to interfere with insulin signaling. We fed mice HFD with or without fish oil for 10 weeks. HFD decreased glucose tolerance, but not in the presence of fish oil. Skeletal muscle long chain acyl coenzyme‐As and ceramides were significantly elevated with HFD, but attenuated in the presence of fish oil. Mitochondrial oxidative capacity was similarly increased in mice fed HFD with and without fish oil. These results indicate that n‐3 PUFAs protect insulin sensitivity, in part, by preventing the accumulation of lipid intermediated that interfere with insulin action. Furthermore, the respiratory function of skeletal muscle mitochondria does not appear to be a major factor in ectopic lipid accumulation, diet‐induced insulin resistance, or the protective effects of n‐3 PUFAs on insulin sensitivity.

In angiotensin II‐induced hypertension, activation of NADPH oxidase is a major contributor to reactive oxygen species generation and endothelial dysfunction. As exercise has been associated with the augmentation of antioxidant enzyme expression in endothelial cells, we hypothesized that exercise would improve endothelial function in mice angiotensin II‐induced hypertension. Three‐month old received either saline or a pressor dose of angiotensin II (1000 ng/kg/min) using subcutaneous osmotic minipumps, and were housed in cages with or without a running wheel. Endothelium‐dependent relaxation in response to acetylcholine was studied in carotid arteries using isolated organ chamber baths. Gene expression was examined using qRT‐PCR. In angiotensin II‐infused sedentary mice, endothelium‐dependent relaxation was significantly impaired, and was partially improved when NADPH oxidase was inhibited by apocynin. mRNA levels of SOD1, SOD2, SOD3, and NOX2 were increased in aorta, and mRNA levels of NOX4 and NOS3 were substantially decreased. In contrast to our hypothesis, endothelium‐dependent relaxation was not improved in angiotensin II‐infused exercised mice housed with running wheels, despite marked increases in physical activity over the two week time period. We conclude that angiotensin II‐induced hypertension results in profound endothelial dysfunction that is not attenuated by voluntary wheel running exercise. Ongoing work is examining molecular mechanisms underlying these observations, as well as evaluation of the protective effects of regimented exercise of varying intensities.

Introduction: Senescent cells with essentially irreversible loss of replicative potential accumulate in various tissues with aging. Cellular senescence is associated with a pro‐inflammatory senescence‐associated secretory phenotype which the Janus‐associated kinase (JAK) pathway plays a role in. We hypothesized that senescent preadipocytes contribute to age‐related dysfunction of healthy cells. Methods: Preadipocytes from lean subjects were X‐irradiated to induce senescence. We co‐cultured non‐senescent cells with senescent cells or cultured them in conditioned medium (CM) from senescent preadipocytes to test the inflammation, differentiation and insulin sensitivity. Macrophage migration in response to CM was assayed as well. Moreover, we treated old or obese mice with Ruxolitinib, a JAK1/2 inhibitor, to test the beneficial effect. Results: The adipogenesis of preadipocytes was impaired by exposure to senescent cells. Macrophage migration was greater in response to senescent preadipocytes. Inflammation was increased in both adipose tissue and preadipocytes exposed to CM from senescent cells. All these adverse effect could be partially rescued by JAK inhibitor. In addition, senescent preadipocytes inhibited insulin‐induced phosphor‐AKT in adipose tissue and HepG2 cells. Insulin‐induced glycogen synthesis was also inhibited in HepG2 cells. Two months of Ruxolitinib treatment reduced inflammation, reversed age‐related lipodystrophy and improved physical function in frail, 24 month old mice. It also improved insulin sensitivity in diet‐induced obese mice. Conclusion: Senescent preadipocytes contribute to age‐related impairment in adipogenesis, fat tissue inflammation, and insulin resistance. Grant Funding Source : supported by NIH AG13925 and Robert and Arlene Kogod Center on Aging in Mayo Clinic.

Nutrient excess and physical inactivity are primary drivers of numerous age‐related chronic diseases. A growing body of evidence has implicated cellular senescence, a process in which cells lose the ability to divide and concurrently damage neighboring cells by the factors they secrete, as an underlying mechanism of aging and its associated conditions. However, the impact of lifestyle choices on the age‐associated accumulation of senescent cells remains poorly understood. Thus, we examined the effects of a fast food diet (FFD) and a voluntary exercise intervention on multiple parameters of healthspan and cellular senescence using a transgenic mouse model that expresses green fluorescent protein (GFP) in p16 Ink4a ‐positive senescent cells. As expected, 12‐month old male mice that had received the FFD diet for 5 months demonstrated significantly greater gains in body weight and fat mass compared to mice fed a standard chow diet. Moreover, mice fed the FFD exhibited hyperinsulinemia, impaired glucose tolerance, reduced exercise capacity, and diastolic dysfunction. Impressively, providing an exercise wheel (26.9 ± 6.9 km/wk) in parallel with the FFD nullified the deleterious effects of the FFD on body weight and composition, whole‐body metabolism, physical performance and cardiac function. Strikingly, our data further suggest that exercise markedly lowers the number of cells in visceral fat depots that express GFP and stain positively for senescent‐associated β‐galactosidase; markers of senescence, that are highly abundant in sedentary mice fed the FFD. Correspondingly, FFD‐induced expression of senescence‐associated inflammatory factors was also diminished by the exercise intervention. Collectively, our data suggest that lifestyle choices may affect the abundance of senescence cells with advancing age, and exercise may partly mediate its salutary effects on multiple organ systems by preventing their accumulation and/or mediating their removal.