Exercise training modulates apoptotic signaling in the aging rat heart

Abstract

Aging is characterized by a progressive decline in cardiac function. A critical contributor to the age-related impairment in heart function is the loss of cardiac myocytes through ??apoptosis??, or programmed cell death. A dramatic increase in the rate of apoptosis has been reported with aging in the rat left ventricle. In contrast, exercise training not only improves cardiac function, but also reduces the risk of heart disease. However, the ability of exercise training to modulate apoptotic signaling and apoptosis in the aging heart remains unknown. Therefore, the purpose of this study was to determine the effects of exercise training on apoptotic signaling and apoptosis in the aging heart. We hypothesized that (1) aging would increase pro-apoptotic signaling and apoptosis in the rat left ventricle, and (2) exercise training would ameliorate upregulation of Bcl-2 family-driven apoptosis in the heart. Four and 25 month old Fischer-344 rats were assigned to four groups: young control (YC), young trained (YT), old control (OC), and old trained (OT). Exercise training groups ran on a treadmill for 60 min/day at 15 m/min (15˚ incline), 5 d/wk for 12 wk. Protein expression of Bax, Bcl-2, caspase-9, and cleaved caspase-3 was measured using Western immunoblot analysis. Apoptosis (DNA fragmentation) was assessed using a cell death detection ELISA. Bax levels in OC were dramatically higher (+176.0%) compared to YC. In contrast, exercise training resulted in a significant decrease (-53.4%) in Bax in OT compared to OC. Bcl-2 levels in OC were lower (-26.3%) compared to YC. Conversely, exercise training significantly increased Bcl-2 levels by 117.8% in OT compared to OC. Caspase-9 levels were higher (+98.7%) in OC than YC, while exercise training significantly reduced caspase-9 levels in YT (-52.6%) and OT (-76.9%), respectively. Aging resulted in a dramatic increase (+122.8%) in cleaved caspase-3 levels and a significant decrease (-32.9%) with exercise training. Finally, apoptosis (DNA fragmentation) significantly increased (+163.8%) with aging and decreased (-43.9%) with exercise training. These novel data indicate that aging increases pro-apoptotic signaling and apoptosis in the left ventricle, while exercise training is effective in diminishing pro-apoptotic signaling and apoptosis in the aging heart.