Purpose: We aimed to evaluate whether ischemia is required for erythropoietin (EPO) induced stimulation of endothelial progenitor cells (EPCs) and their related effects on endothelial and cardiac function.
Methods: Bone marrow of rats was replaced by transgenic cells to allow tracking of EPCs. Ischemic heart failure was induced by left coronary artery ligation to induce myocardial infarction (MI) and control rats received a sham procedure. Three weeks after surgery, rats were randomized to receive EPO (darbepoetin alfa 40 microg/kg per 3 weeks) or vehicle and were sacrificed 9 weeks after surgery.
Results: In all treated groups, EPO significantly increased circulating EPCs and their incorporation into the endothelium of the ischemic and non-ischemic hearts as well as in the control organs; kidney and liver. This was associated with significantly improved endothelial function, which was strongly correlated with circulating EPCs (R = 0.7, p < 0.01). However, additional EPCs preferentially homed to the ischemic MI borderzone (p < 0.01) resulting in specific EPO-induced improvement of cardiac microvascularization and performance only in ischemic hearts (all p < 0.05). The differential stimulation of neovascularization by EPO was associated with increased EPO-receptor and VEGF expression in ischemic hearts only.
Conclusions: In general, EPO stimulates normal endothelial progenitor cell-mediated endothelial turnover, but improves cardiac microvascularization and function only in the presence of ischemia.