Heat stress-induced phosphorylation of FoxO3a signalling in rat skeletal muscle

AimA recent study demonstrated that FoxO3a was directly induced by the overexpression of Hsp72 in rat soleus muscle. However, whether heat stress treatment induces FoxO3a phosphorylation in rat skeletal muscle remains unclear. This study examined the effects of heat stress on the regulation of the FoxO3a signalling pathway in rat skeletal muscle. MethodsThirty-two male Wistar rats (15weeks old) were randomly assigned into two groups; sedentary control group (Sed, n=8) and experimental group (n=24). After an overnight fast, one leg of each rat (HS leg) in the experimental group was immersed in hot water (43 degrees C) for 30min, and the soleus and plantaris muscles in both legs were removed immediately (0min), 30min, 60min, or 24h after the heat stress (n=6 each group). The contralateral, non-heated leg in the experimental group served as an internal control (CT leg). ResultsHeat stress treatment resulted in a significant increase in FoxO3a phosphorylation (Ser253) in the soleus and plantaris muscles of heat-stressed legs after 24h. Hsp72 expression in heat-stressed legs was significantly higher at 60min and 24h in these muscles. Activation of the PTEN/Akt and MEK/ERK pathways was also observed in these muscles immediately after stress, but not at 24h. There were no differences in FoxO1 and AMPK phosphorylation in either muscle. ConclusionHeat stress in rat skeletal muscle induces phosphorylation of FoxO3a signalling, and it may be related to Hsp72 upregulation, and the activation of the PTEN/Akt and MEK/ERK pathways.