Mechanisms of erythropoietin‐mediated cardioprotection during ischemia‐reperfusion injury: role of protein kinase C and phosphatidylinositol 3‐kinase signaling

Langendorff-perfused rat hearts treated with EPO exhibited significantly improved postischemic recovery of left ventricular developed pressure (LVDP) and reduced infarct size compared with control hearts. Perfusion with the mitogen/extracellular signal-regulated kinase (MEK) inhibitor U0126 just before and concomitant with EPO treatment abolished EPO-induced phosphorylation of the MEK substrate extracellular signal-regulated kinase (ERK) but had no effect of EPO-mediated cardioprotection. EPO treatment of the perfused hearts induced translocation of protein kinase C (PKC) epsilon isoform to the membrane fraction of the hearts and the protective effect of EPO was significantly inhibited by the PKC catalytic inhibitor chelerythrine added before and concomitant with EPO. These data demonstrate that EPO-mediated activation of the PKC signaling pathway before or during ischemia is required for the cardioprotective effect of EPO during ischemia-reperfusion injury. Perfusion with the phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 or wortmannin just before and concomitant with EPO treatment attenuated EPO-induced phosphorylation of the PI3K substrate Akt but had no effect on EPO-mediated cardioprotection. However, when wortmannin was added during EPO treatment and continued during reperfusion, EPO-mediated cardioprotection was significantly inhibited. We also show that postischemia EPO treatment at the onset of reperfusion significantly improved recovery of LVDP and reduced infarct size. Postischemia cardioprotection by EPO required the PI3K pathway but was not affected by inhibition of PKC at the time of EPO treatment.