BACKGROUND: Endothelial progenitor cells (EPCs) participate in vascular repair 
and angiogenesis. Thus, EPC transplantation into ischemic myocardium might 
improve cardiac function; however, the vast majority of cells die within a short 
period. The present study was designed to investigate whether exogenous 
erythropoietin (EPO) delivery could improve the survival of transplanted EPCs 
and enhance the efficiency of EPC-based cell therapy.
METHODS: Myocardial infarction was induced in wild-type mice by ligating the 
left anterior descending coronary artery. Enhanced green fluorescent 
protein-EPCs with or without EPO were transplanted into peri-infarct myocardium. 
Enhanced green fluorescent protein-EPCs were detected 7 and 28 d after surgery. 
The amount of circulating EPCs was analyzed 3 and 28 d after surgery. The 
stromal cell-derived factor-1α and vascular endothelial growth factor 
concentrations, microvessel density, apoptosis, fibrosis in the peri-infarct 
myocardium, and cardiac function were compared among the groups.
RESULTS: More enhanced green fluorescent protein-EPCs were found in the hearts 
treated with EPC + EPO than in those treated with EPC alone. The circulating EPC 
level was markedly elevated after EPC + EPO treatment compared with EPC 
application alone. Stromal cell-derived factor-1α and vascular endothelial 
growth factor were increased accordingly, along with increased microvessel 
density, decreased apoptosis, and reduced fibrosis in the peri-infarct 
myocardium. Left ventricular fractional shortening was greater and the 
interventricular septum was thicker after EPC + EPO treatment compared with EPC 
treatment alone.
CONCLUSIONS: EPO improved the efficiency of EPC therapy in mice with myocardial 
infarction. This effect was associated with enhanced transplanted EPC survival 
and autologous EPC mobilization.