Contraction-induced interleukin-6 gene transcription in skeletal muscle is regulated by c-Jun terminal kinase/activator protein-1

Abstract Exercise increases the expression of the prototypical myokine interleukin (IL)-6, but the precise mechanism by which this occurs has yet to be identified. To mimic exercise conditions, C2C12 myotubes were mechanically stimulated via electric-pulse-stimulation (EPS). We compared the responses of EPS with the pharmacological Ca2+ carrier [calcimycin A23187 (CAL)], since contraction induces marked increases in cytosolic Ca2+ levels, or the classical IκB Kinase (IKK)/nuclear factor κB (NFκB) inflammatory response elicited by hydrogen peroxide (H2O2). We demonstrate that, unlike H2O2 stimulated increases in IL-6 mRNA, neither CAL nor EPS induced IL-6 mRNA expression is under the transcriptional control of NFκB. Rather, we show that EPS increased the phosphorylation of c-jun terminal kinase (JNK), the reporter activity of the downstream transcription factor activator protein 1 (AP-1) and the recruitment of AP-1 to the promoter region of the IL-6 gene. Furthermore, JNK inhibition abolished the EPSinduced increase in IL-6 mRNA and protein expression. Finally, we observed an exerciseinduced increase in both the phosphorylation of JNK and IL-6 mRNA expression in the skeletal muscles of mice after 30 min of treadmill running. Importantly, exercise did not increase IL-6 mRNA expression in skeletal muscle-specific JNK deficient mice. These data identify a novel contraction mediated transcriptional regulatory pathway for IL-6 in skeletal muscle.