Effects of Altering Mitochondrial Antioxidant Capacity on Molecular and Phenotypic Drivers of Fibrocalcific Aortic Valve Stenosis.

Background: While a small number of studies suggest that oxidative stress has an influential role in fibrocalcific aortic valve disease (FCAVD), the roles of specific antioxidant enzymes in progression of this disease remain poorly understood. Here, we focused on selectively altering mitochondrial-derived oxidative stress-which has been shown to alter progression of a myriad of age-associated diseases-on the progression of molecular and phenotypic drivers of FCAVD. Methods: We generated low-density lipoprotein receptor-deficient, Apolipoprotein B100-only mice (LA) that were either haploinsufficient for MnSOD (LA-MnSOD +/-) or genetically overexpressing MnSOD (LA-MnSOD Tg/0). After 6 months of Western diet feeding, mice underwent echocardiography to assess valvular and cardiac function and tissues were harvested. Quantitative-RT PCR, immunohistochemistry, and histopathology were used to measure changes in molecular pathways related to oxidative stress, calcification, and fibrosis. Results: While reductions in MnSOD increased oxidative stress, there was not an overt phenotypic effect of MnSOD deficiency on valvular and cardiac function in LA-MnSOD +/- mice. While markers of canonical bone morphogenetic protein signaling tended to increase in valve tissue from LA-MnSOD +/- (e.g., p-SMAD1/5/8 and osterix), we did not observe statistically significant increases in osteogenic signaling. We did, however, observe highly significant reductions in expression of osteopontin, which were associated with significant increases in calcium burden in LA-MnSOD +/- mice. Reciprocally, genetically increasing MnSOD did not preserve valve function in LA-MnSOD Tg/0, but we did observe slight reductions in p-SMAD1/5/8 levels compared to their non-transgenic littermates. Interestingly, overexpression of MnSOD dramatically increased expression of osteopontin in valve tissue from LA-MnSOD Tg/0 mice, but was not sufficient to attenuate calcium burden when compared to their LA-MnSOD 0/0 littermates. Conclusions: Collectively, this study demonstrates that maintenance of mitochondrial antioxidant capacity is important in preventing accelerated disease progression in a mouse model of FCAVD, but that effectively altering mitochondrial antioxidant capacity as a monotherapeutic approach to slow key histopathological and molecular drivers of FCAVD remains biologically and therapeutically challenging.

Late-life time-restricted feeding and exercise differentially alter healthspan in obesity.

Aging and obesity increase multimorbidity and disability risk, and determining interventions for reversing healthspan decline is a critical public health priority. Exercise and time-restricted feeding (TRF) benefit multiple health parameters when initiated in early life, but their efficacy and safety when initiated at older ages are uncertain. Here, we tested the effects of exercise versus TRF in diet-induced obese, aged mice from 20 to 24 months of age. We characterized healthspan across key domains: body composition, physical, metabolic, and cardiovascular function, activity of daily living (ADL) behavior, and pathology. We demonstrate that both exercise and TRF improved aspects of body composition. Exercise uniquely benefited physical function, and TRF uniquely benefited metabolism, ADL behavior, and circulating indicators of liver pathology. No adverse outcomes were observed in exercised mice, but in contrast, lean mass and cardiovascular maladaptations were observed following TRF. Through a composite index of benefits and risks, we conclude the net healthspan benefits afforded by exercise are more favorable than those of TRF. Extrapolating to obese older adults, exercise is a safe and effective option for healthspan improvement, but additional comprehensive studies are warranted before recommending TRF.

Senolytics improve physical function and increase lifespan in old age.

Physical function declines in old age, portending disability, increased health expenditures, and mortality. Cellular senescence, leading to tissue dysfunction, may contribute to these consequences of aging, but whether senescence can directly drive age-related pathology and be therapeutically targeted is still unclear. Here we demonstrate that transplanting relatively small numbers of senescent cells into young mice is sufficient to cause persistent physical dysfunction, as well as to spread cellular senescence to host tissues. Transplanting even fewer senescent cells had the same effect in older recipients and was accompanied by reduced survival, indicating the potency of senescent cells in shortening health- and lifespan. The senolytic cocktail, dasatinib plus quercetin, which causes selective elimination of senescent cells, decreased the number of naturally occurring senescent cells and their secretion of frailty-related proinflammatory cytokines in explants of human adipose tissue. Moreover, intermittent oral administration of senolytics to both senescent cell-transplanted young mice and naturally aged mice alleviated physical dysfunction and increased post-treatment survival by 36% while reducing mortality hazard to 65%. Our study provides proof-of-concept evidence that senescent cells can cause physical dysfunction and decreased survival even in young mice, while senolytics can enhance remaining health- and lifespan in old mice.

Exercise Prevents Diet-Induced Cellular Senescence in Adipose Tissue.

Considerable evidence implicates cellular senescence in the biology of aging and chronic disease. Diet and exercise are determinants of healthy aging; however, the extent to which they affect the behavior and accretion of senescent cells within distinct tissues is not clear. Here we tested the hypothesis that exercise prevents premature senescent cell accumulation and systemic metabolic dysfunction induced by a fast-food diet (FFD). Using transgenic mice that express EGFP in response to activation of the senescence-associated p16(INK4a) promoter, we demonstrate that FFD consumption causes deleterious changes in body weight and composition as well as in measures of physical, cardiac, and metabolic health. The harmful effects of the FFD were associated with dramatic increases in several markers of senescence, including p16, EGFP, senescence-associated ß-galactosidase, and the senescence-associated secretory phenotype (SASP) specifically in visceral adipose tissue. We show that exercise prevents the accumulation of senescent cells and the expression of the SASP while nullifying the damaging effects of the FFD on parameters of health. We also demonstrate that exercise initiated after long-term FFD feeding reduces senescent phenotype markers in visceral adipose tissue while attenuating physical impairments, suggesting that exercise may provide restorative benefit by mitigating accrued senescent burden. These findings highlight a novel mechanism by which exercise mediates its beneficial effects and reinforces the effect of modifiable lifestyle choices on health span.

The Achilles' heel of senescent cells: from transcriptome to senolytic drugs.

The healthspan of mice is enhanced by killing senescent cells using a transgenic suicide gene. Achieving the same using small molecules would have a tremendous impact on quality of life and the burden of age-related chronic diseases. Here, we describe the rationale for identification and validation of a new class of drugs termed senolytics, which selectively kill senescent cells. By transcript analysis, we discovered increased expression of pro-survival networks in senescent cells, consistent with their established resistance to apoptosis. Using siRNA to silence expression of key nodes of this network, including ephrins (EFNB1 or 3), PI3Kδ, p21, BCL-xL, or plasminogen-activated inhibitor-2, killed senescent cells, but not proliferating or quiescent, differentiated cells. Drugs targeting these same factors selectively killed senescent cells. Dasatinib eliminated senescent human fat cell progenitors, while quercetin was more effective against senescent human endothelial cells and mouse BM-MSCs. The combination of dasatinib and quercetin was effective in eliminating senescent MEFs. In vivo, this combination reduced senescent cell burden in chronologically aged, radiation-exposed, and progeroid Ercc1(-/Δ) mice. In old mice, cardiac function and carotid vascular reactivity were improved 5 days after a single dose. Following irradiation of one limb in mice, a single dose led to improved exercise capacity for at least 7 months following drug treatment. Periodic drug administration extended healthspan in Ercc1(-/∆) mice, delaying age-related symptoms and pathology, osteoporosis, and loss of intervertebral disk proteoglycans. These results demonstrate the feasibility of selectively ablating senescent cells and the efficacy of senolytics for alleviating symptoms of frailty and extending healthspan.

Obesity as a risk factor for the progression of paroxysmal to permanent atrial fibrillation: a longitudinal cohort study of 21 years.

AIMS: Obesity has been shown to be a risk factor for first atrial fibrillation (AF), but whether it is associated with progression from paroxysmal to permanent AF is unknown. METHODS AND RESULTS: In this longitudinal cohort study, Olmsted County, MN residents confirmed to have developed paroxysmal AF during 1980-2000 were identified and followed passively to 2006. The interrelationships of body mass index (BMI), left atrial (LA) size, and progression to permanent AF were analysed. Of a total of 3248 patients (mean age 71 +/- 15 years; 54% men) diagnosed with paroxysmal AF, 557 (17%) progressed to permanent AF (unadjusted incidence, 36/1000 person-years) over a median follow-up period of 5.1 years (interquartile range 1.2-9.4). Adjusting for age and sex, BMI independently predicted the progression to permanent AF (hazard ratio, HR 1.04, CI 1.03-1.06; P < 0.0001). Compared with normal BMI (18.5-24.9 kg/m(2)), obesity (30-34.9 kg/m(2)) and severe obesity (>or=35 kg/m(2)) were associated with increased risk for progression [HR 1.54 (CI 1.2-2.0; P = 0.0004) and 1.87 (CI 1.4-2.5; P < 0.0001, respectively)]. BMI remained highly significant even after multiple adjustments. In the subgroup with echocardiographic assessment (n = 744), LA volume was incremental to BMI for independent prediction of progression after multiple adjustments, and did not weaken the association between BMI and progression to permanent AF (HR 1.04; CI 1.02-1.05; P < 0.0001). CONCLUSION: There was a graded risk relationship between BMI and progression from paroxysmal to permanent AF. This relationship was not weakened by LA volume, which was independent of and incremental to BMI for the prediction of progression to permanent AF.

Prognostic significance of echocardiographically defined mitral regurgitation early after acute myocardial infarction.

BACKGROUND: There are limited data regarding the clinical correlates and prognostic significance of echocardiographically defined mitral regurgitation (MR) early after acute myocardial infarction (MI). The current study addressed these issues. METHODS: Seven hundred thirty-seven patients with acute MI who underwent transthoracic echocardiography with assessment of MR during their index admission were identified. Patients were followed up a median of 19 months later. The study end point was all-cause mortality. RESULTS: The prevalence of MR increased with age. It was more common in women, in patients with non-ST-elevation MI, and in those with a history of diabetes, hypertension, prior MI, or previous revascularization. Patients with MR had worse left ventricular (LV) systolic function, more LV dilatation, and more clinical evidence of LV failure. Patients with moderate or severe MR had worse survival than those with no or mild MR (hazard ratio 2.3, 95% CI 1.6-3.2, P < .0001). Even mild MR predicted a higher mortality when compared with no MR (hazard ratio 1.7, 95% CI 1.2-2.4, P = .004). Mild or moderate MR was not independently predictive of outcome, although, in multivariable analyses, a trend toward worse survival was maintained in patients with severe MR. CONCLUSIONS: Mitral regurgitation, identified by echocardiography, early after acute MI predicts poorer survival after acute MI. However, if mild or moderate, it is not an independent prognostic indicator.