Effects of apotesis-related proteins in the size and phenotypes of rat skeletal msucles

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1. To investigate the apoptotic responses, rat soleus muscles were subjected to 14-day of hindlimb unloading (14U)and 14-day reloading. After HU, soleus fiber size and the myonuclear number/fiber were significantly decreased, while the apoptotic myonuclear number increased. During ambulatory recovery day〜14 after HU, fiber size and myonuclear number were gradually increased, concomitant with the decrease in apoptotic nuclei Our results suggested that soleus fiber atrophy was induced by the decrement of myonuclear number via, in part, by apoptotic response.2.We further analyzed the effects of heat stress (HS)on regenerating soleus fibers. The soleus fibers were degenerated by bupivacaine injection. Compared with regenerating fibers without HS, regenerating fibers with HS were greater in cross-sectional area and myonuclear numbers. Also, activation of satellite cells and the expression levels of heat shock protein (Hsp)72 and calcineurin were enhanced in HS-regenerating soleus fibers. Our results suggest that the growth of regenerating fibers is possible to be accelerated by heat stress via enhancement of satellite cell activation.