Role of adenosine 5'-monophosphate-activated protein kinase in interleukin-6 release from isolated mouse skeletal muscle.

IL-6 is released from skeletal muscle during exercise and has consequently been implicated to mediate beneficial effects on whole-body metabolism. Using 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), a pharmacological activator of 5'-AMP-activated protein kinase (AMPK), we tested the hypothesis that AMPK modulates IL-6 release from isolated muscle. Skeletal muscle from AMPKalpha2 kinase-dead transgenic, AMPKalpha1 knockout (KO) and AMPKgamma3 KO mice and respective wild-type littermates was incubated in vitro, in the absence or presence of 2 mmol/liter AICAR. Skeletal muscle from wild-type mice was also incubated with the AMPK activator A-769662. Incubation of mouse glycolytic extensor digitorum longus and oxidative soleus muscle for 2 h was associated with profound IL-6 mRNA production and protein release, which was suppressed by AICAR (P < 0.001). Basal IL-6 release from soleus was increased between AMPKalpha2 kinase-dead and AMPKalpha1 KO and their respective wild-type littermates (P < 0.05), suggesting AMPK participates in the regulation of IL-6 release from oxidative muscle. The effect of AICAR on muscle IL-6 release was similar between AMPKalpha2 KD, AMPKalpha1 KO, and AMPKgamma3 KO mice and their respective wild-type littermates (P < 0.001), indicating AICAR-mediated suppression of IL-6 mRNA expression and protein release is independent of AMPK function. However, IL-6 release from soleus, but not extensor digitorum longus, was reduced 45% by A-769662. Our results on basal and A-769662-mediated IL-6 release provide evidence for a role of AMPK in the regulation of IL-6 release from oxidative skeletal muscle. Furthermore, in addition to activating AMPK, AICAR suppresses IL-6 release by an unknown, AMPK-independent mechanism.