Protective effects of erythropoietin on ischemic brain

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Erythropoietin (EPO) is a glycoprotein that acts as a main regulator of erythropoiesis and has been used in clinical medicine over the last decade for the treatment of renal anemia. Recently, several lines of evidence demonstrate the expressions of EPO and its receptor in the brain suggesting that the EPO-EPO receptor (EPOR) system functions in the brain as well.In the present study, we have investigated the effects of erythropoietin (EPO) on ischemia-induced neuronal damage in vivo and in vitro. In vivo experiments showed that EPO rescued neurons in the hippocampal CA 1 field after 3-min transient forebrain ischemia in gerbils and reduced infarct volume after permanent middle cerebral artery (MCA) occlusion in spontaneously hypertensive rats (SHR). EPO also ameliorated ischemia-induced learning disability in gerbils and ischemia-induced place navigation disability in SHR. Furthermore, intracerebroventricular infusion of soluble EPOR that could inhibit EPO signal transmission enhanced ischemic neuronal damage.Western blot and RT-PCR analysis showed that EPO infusion induced significantly more intense expressions of Bcl-x_L mRNA and protein in the hippocampal CA 1 field of ischemic gerbils than did vehicle infusion. In situ hybridization histochemistry also indicated that EPOR mRNA was upregulated in the periphery of cerebrocortical infarct lesion after MCA occlusion in rats. This suggests that an increased number of EPOR in neurons facilitates the EPO signal transmission in favor of neuronal survival.In vitro experiments showed that EPO attenuated neuronal damage caused by chemical hypoxia and upregulated Bcl-x_L mRNA and protein expressions in cultured neurons.In conclusion, EPO protects neurons against hypoxic and ischemic insults possibly through upregulation of the anti-apoptotic gene product Bcl-x_L.The present study proposes the possible therapeutic application of EPO to patients with stroke.