Hsp70 prevents disuse muscle atrophy in senescent rats.

This study determined the effects of heat shock protein 70 (Hsp70) overexpression on disuse muscle atrophy in senescent rats. Solei of young and senescent rats were co-injected with Hsp70 plus a nuclear factor kappa B (NF-kappaBeta) reporter plasmid. After 4 days, the hind limbs of half the young and senescent rats were immobilized for 6 days with the remainder serving as weight bearing controls. Hsp70 protein levels and cross-sectional area decreased in both groups (~20%) after immobilization. Atrophy was prevented in those fibers overexpressing Hsp70. NF-kappaBeta activity increased in the soleus of both young (three-fold) and senescent (five-fold) animals after immobilization and was prevented by Hsp70 overexpression. Inhibitor of kappaBeta decreased in young (~30%) and senescent (~10%) animals with immobilization and returned to normal with Hsp70. Heat shock protein 70 overexpression prevents disuse atrophy in senescent rats, possibly through suppression of the NF-kappaB pathway.