Erythropoietin Inhibits Anoxia/Reoxygenation‐Induced Cardiomyocyte Apoptosis via Heme Oxygenase‐1

Abstract

Recent studies have shown that erythropoietin (EPO), a 165 amino acid cytokine best known for its ability to increase red blood cell production, can decrease apoptosis in the heart. As of yet, the mechanisms by which this occurs are not fully understood. Heme oxygenase 1 (HO-1) has been shown to protect cardiomyocytes from apoptosis during myocardial ischemia and reperfusion. The present study sought to determine if increased HO-1 expression is involved in the anti-apoptotic effects of EPO during anoxia and reoxygenation (A/R), an in vitro counterpart of myocardial ischemia and reperfusion. Neonatal mouse ventricular cardiomyocytes were isolated from the hearts of C57BL6 mice and cultured in M199. Cells were subjected to 1 hour of anoxia, followed by 30 minutes of reoxygenation. Apoptosis was measured using a caspase-3 activity assay. Pre-treatment with EPO (20 U/mL 24 hours prior to anoxia) significantly reduced apoptosis following anoxia and reoxygenation (P<0.05). The reduction in apoptosis was coupled with increases in HO-1 mRNA and protein expression. Furthermore, inhibition of HO-1 activity using tin protoporphyrin-IX resulted in significant attenuation of the anti-apoptotic effects of EPO. Co-treatment of EPO with SB203885, an inhibitor of p38 activity, blocked the EPO-mediated increases in HO-1 expression, however inhibition of Akt-1 activity with LY294002 had no significant effect. Taken together, our data suggest that EPO upregulates HO-1 in cardiomyocytes via p38 activation and that HO-1 upregulation is partially responsible for the anti-apoptotic effects of EPO during anoxia and reoxygenation. Supported by HSFO.