Erythropoietin protects CA1 neurons against global cerebral ischemia in rat: potential signaling mechanisms.

Erythropoietin (EPO) is a hormone that is neuroprotective in models of neurodegenerative diseases. This study examined whether EPO can protect against neuronal death in the CA1 region of the rat hippocampus following global cerebral ischemia. Recombinant human EPO was infused into the intracerebral ventricle either before or after the induction of ischemia produced by using the four-vessel-occlusion model in rat. Hippocampal CA1 neuron damage was ameliorated by infusion of 50 U EPO. Administration of EPO was neuroprotective if given 20 hr before or 20 min after ischemia, but not 1 hr following ischemia. Coinjection of the phosphoinositide 3 kinase inhibitor LY294002 with EPO inhibited the protective effects of EPO. Treatment with EPO induced phosphorylation of both AKT and its substrate, glycogen synthase kinase-3beta, in the CA1 region. EPO also enhanced the CA1 level of brain-derived neurotrophic factor. Finally, we determined that ERK activation played minor roles in EPO-mediated neuroprotection. These studies demonstrate that a single injection of EPO ICV up to 20 min after global ischemia is an effective neuroprotective agent and suggest that EPO is a viable candidate for treating global ischemic brain injury. Copyright 2006 Wiley-Liss, Inc.