Both Membrane Depolarization And Il-6 Induce Calcium-Dependent Hsp70 Expression In Skeletal Muscle Cells

Adaptive response of skeletal muscle to challenges imposed by contractile activity is associated to changes in specific genes expression. IL-6 and Hsp70 are proteins involved in the maintenance of skeletal muscle homeostasis during stress episodes and are markedly expressed in skeletal muscle after physiological contraction. Muscle-derived IL-6 has systemic and local effects acting in a hormone-like fashion, nevertheless the molecular bases of its functional role on skeletal muscle is poorly understood. We have demonstrated that depolarization evoked IP3 mediated slow calcium transients, associated to cell nuclei are involved in the up-regulation of IL-6 transcriptional activity in skeletal muscle cells.The aim of this work was to investigate calcium involvement in Hsp70 expression in both depolarized and IL-6 treated skeletal muscle cells.We observed that electrical stimulation of myotubes increases Hsp70 mRNA level and protein expression. Depolarization performed in the presence of the intracellular calcium chelator BAPTA-AM resulted in a complete inhibition of Hsp70 induced expression. Inhibitors of IP3-dependent calcium signals like 2-aminoethoxydiphenyl borate (2-APB) and LY294002, decreased Hsp70 mRNA induction and the protein expression in depolarized cells. In addition we determined that inhibitors of calcium dependent PKC abolished Hsp70 mRNA induction.We established that IL-6 treatment of myotubes induced changes in intracellular calcium and promoted the increase of Hsp70 mRNA levels. Observed calcium transients could be associated to early events of IL-6-mediated Hsp70 expression.Our results provide evidence for the involvement of slow calcium transients and PKC in the activation of Hsp70 expression in skeletal muscle cells and suggest that intracellular calcium signals also participate in IL-6 induced Hsp70 expression.FONDAP 15010006