H2O2 activation of HSP25/27 protects desmin from calpain proteolysis in rat ventricular myocytes

Ischemia-reperfusion-induced Ca2+ overload results in activation of calpain-1 in the heart. Calpain-dependent proteolysis contributes to myocardial dysfunction and cell death. Previously, preischemic treatment with low doses of H2O2 was shown to improve postischemic function and reduce myocardial infarct size. Our aim was to determine the mechanism by which H2O2 protects the heart. We hypothesized that H2O2 causes the activation of p38 MAPK which initiates translocation of heat shock protein 25/27 (HSP25/27) to the myofilament Z disk. We further hypothesized that HSP25/27 shields structural proteins, particularly desmin, from calpain-induced proteolysis. To address this hypothesis, we first determined that an ischemia-reperfusion-induced decrease in desmin content could be blocked by H2O2 pretreatment of hearts from rats. We next determined that ventricular myocytes that underwent Ca2+ overload also demonstrated a calpain-dependent disruption of desmin that could be reduced by H2O2/p38 MAPK activation. Furthermore, myocytes acutely treated with H2O2 exhibited a decrease in cleavage of desmin upon exposure to exogenous calpain-1 compared with myocytes not pretreated with H2O2. The H2O2-induced attenuation of desmin degradation by calpain-1 was blocked by inhibition of p38 MAPK. In a final series of experiments, we demonstrated that cardiac myofilaments exposed to recombinant phosphorylated HSP27, but not nonphosphorylated HSP27, had a significant reduction in the calpain-induced degradation of desmin compared with non-HSP27-treated myofilaments. These findings are consistent with the hypothesis that H2O2-induced activation of p38 MAPK and subsequent HSP25/27 translocation attenuates desmin degradation brought about by calpain-1 activation in ischemia-reperfused hearts.