The purpose of this study was to investigate the effects of cold and mechanical stresses on mice soleus muscle. Male C57BL/6J mice (10 weeks old) were assigned into cold-stressed and mechanical-stressed groups. Mice hindlimbs of cold-stressed group were exposed to ice-cold water (4℃) for 10 min. Mice hindlimbs of mechanical-stressed group were kept at maximal dorsiflexion for 10 min. In soleus, the mRNA expression of basic fibroblast growth factor (bFGF), which plays a key role in the regeneration of injured tissues, was up-regulated by the exposure to cold stress. Pax7 is a marker for muscle-specific stem cells, so-called muscle satellite cells. Pax7 mRNA in soleus was up-regulated by mechanical stress. A role of stress response in skeletal muscle plasticity was investigated by using heat shock transcription factor 1 (HSF1)-knock out (HSF1-KO) and overexpressed (HSF1-Tg) mice. HSF1 highly regulates the stress response in mammalian skeletal muscles. The regrowth of atrophied soleus muscles was partially depressed in HSF1-KO mice. Fuctional overloading-associated hypertrophy of soleus muscles was enhanced in HSF1-Tg mice. These observations suggested that the stress response plays an important role in the plasticity of skeletal muscles. The effects of training and conditioning could be enhanced by the selective application (s) of cellular stresses on skeletal muscles.

DESCENTE SPORTS SCIENCE Vol.32/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE