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; 1×30 min, 5 days/week for 6 weeks) and M1 types (multiple short-duration; 3×10 min·day(-1), 5 days·week(-1) for 6 weeks) than S2 (single long-duration; 1×30 min, 3 days/week for 6 weeks) and M2 (multiple short-duration; 3×10 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. Key pointsThe expression of heat shock proteins (HSPs) in aged rats was increased significantly after single long-duration (S1) and multiple short-duration (M1) types than S2 and M2 types of exercise training in soleus (SOL) skeletal muscles.Superoxide dismutase (SODs) showed similar expression as HSPs 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.Induction of HSPs and SODs by high duration and frequency of exercise training such as S1 and M1 types with concomitant MAPKs pathway depending on the type of muscles.The frequency and duration of exercise training could affect the functional adaptation and protection against aging-induced structural weakness of skeletal muscles through changing expression of related molecules.