Age and attenuation of exercise-induced myocardial HSP72 accumulation

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Abstract
Overexpression of heat shock protein (HSP)72 is associated with cardioprotection. Hyperthermia-induced HSP72 overexpression is attenuated with senescence. While exercise also increases myocardial HSP72 in young animals, it is unknown whether this effect is attenuated with aging. Therefore, we investigated the effect of aging on exercise-induced myocardial heat shock factor (HSF)-1 activation and HSP72 expression. Male Fischer-344 rats (6 or 24 mo) were randomized to control, exercise, and hyperthermic groups. Exercise consisted of 2 days of treadmill running (60 min/day, ∼75% maximal oxygen consumption). Hyperthermia, 15 min at ∼41°C (colonic temperature), was achieved using a temperature-controlled heating blanket. Analyses included Western blotting for myocardial HSP72 and HSF-1, electromobility shift assays for HSF-1 activation, and Northern blotting for HSP72 mRNA. Exercise and hyperthermia increased (P < 0.05) myocardial HSP72 in both young (>3.5- and 2.5-fold, respectively) and aged (>3- and 1.5-fold, respectively) animals. Both exercise and hyperthermic induction of HSP72 was attenuated with age. Myocardial HSF-1 protein, HSF-1 activation, and HSP72 mRNA did not differ with age. These data demonstrate that aging is associated with diminished exercise-induced myocardial HSP72 expression. Mechanisms other than HSF-1 activation and transcription of HSP72 mRNA are responsible for this age-related impairment.