Expression of Heat Shock Proteins (HSPs) in Aged Skeletal Muscles Depends on the Frequency and Duration of Exercise Training

The skeletal muscle in aged rats adapts rapidly following a period of exercise. This adaptation includes structural remodeling and biochemical changes such as an up-regulation of antioxidant enzymes, content of stress and heat shock proteins (HSPs). However, the associated molecular mechanisms mediating different types of exercise training-induced adaptations are not yet completely understood. Therefore, the purpose of this study was to investigate the effects of duration and frequency exercise on the expression of HSPs, antioxidant enzymes, and mitogen-activated protein kinase (MAPKs) in the skeletal muscles of aged rats. Young (3-month-old) and aged (20-month-old) male Sprague-Dawley rats were randomly assigned to 6 groups and extensor digitorum longus (EDL; fast twitch muscle fiber) and soleus (SOL; slow twitch muscle fiber) skeletal muscles were collected immediately. The expression pattern of HSPs in skeletal muscles was decreased in old groups compared with young groups. Especially, HSPs showed lower expression in SOL than EDL muscle. Interestingly, HSPs in aged rats was increased significantly after S1 (single long-duration; 1x30 min, 5 days/week for 6 weeks) and M1 types (multiple short-duration; 3x10 min.day(-1), 5 days.week(-1) for 6 weeks) than S2 (single long-duration; 1x30 min, 3 days/week for 6 weeks) and M2 (multiple short-duration; 3x10 min.day(-1), 3 days.week(-1) for 6 weeks) types of exercise training. Also, superoxide dismutase (SODs) showed similar expression as HSP did. On the contrary, the p-ERK and p-JNK were down regulated. In addition, p-p38 level in the SOL muscle was activated markedly in all exercise groups. These results demonstrate that increasing of HSP expression through duration and frequency exercise can lead to protection and training-induced adaptation against aging-induced structural weakness in skeletal muscles.