A possible role of NF-kappaB and HSP72 in skeletal muscle hypertrophy induced by heat stress in rats.

Effects of heat stress on phosphorylated nuclear factor-kappaB (phospho-NF-kappaB) and tumor necrosis factor alpha (TNFalpha) contents in skeletal muscles were studied. Male Wistar rats (7-week-old) were randomly assigned to control and heat-stressed groups. Rats in heat-stressed group were exposed to heat stress (42 degrees C for 60 min) in an incubator without anesthesia. Soleus muscles were dissected and weighted 1, 3, and 7 days after the heat exposure. Significant increases in the wet weight and protein content of soleus were observed 7 days following the exposure (p < 0.05). Heat stress also induced the up-regulation of heat shock protein 72 (HSP72), IkappaBalpha (inhibitor of NF-kappaB) and the increase in the relative population of Pax7-positive satellite cells to total muscle nuclei before the increase in muscle mass. The content levels of phospho-NF-kappaB and TNFalpha were significantly decreased 1 and 3 days after heat stress, respectively (p < 0.05). A negative correlation between HSP72 and phospho-NF-kappaB contents was observed 1 day after the heat exposure. These observations suggest that the decrease in NF-kappaB signaling may play a part of a role in heat stress-associated muscle hypertrophy.