Erythropoietin (Epo) exerts neuroprotective, glioprotective, and vascular protective effects in the nervous system. However, the mechanisms of the cytoprotective effect of Epo have not been fully clarified. Here, we investigated whether Epo affects the transcription and activation of nuclear factor erythroid 2-related factor 2 (Nrf2), which is a key transcription factor of the cellular anti-oxidant defense system, and mRNA expression of its target genes including heme oxygenase-1 (HO-1). Epo was added to SH-SY5Y cells at 1 U mL(-1) and cultures were incubated for 24 h and then mRNA expression of Nrf2 target genes were analyzed with real-time PCR. SH-SY5Y cells were incubated with Epo at different time points and the nuclear and cytoplasmic levels of Nrf2 protein expression were examined by Western blotting and immunohistochemistry. Specific inhibitors of mitogen-activated protein kinases (MAPKs) and phosphatidylinositol-3 kinase (PI3K) were used to find out the possible signaling pathways that mediate the activating effect of Epo on Nrf2 activation. In cultured human SH-SY5Y neuroblastoma cells, Western blotting, immunohistochemistry, and real-time PCR analysis demonstrated that Epo-induced nuclear translocation of Nrf2 and upregulates HO-1 expression. Inhibitors of MAPKs and PI3K decreased Epo-induced nuclear translocation of Nrf2 and HO-1 mRNA expression. These results suggest that Epo induces neural HO-1 expression through the activation of PI3K, MAPK, and Nrf2 pathways, and this may unveil a novel mechanism which mediates the cytoprotective responses elicited by Epo.
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