Heme oxygenase-1 (HO-1) is a stress-inducible enzyme with multiple protective functions in cardiovascular systems. Studies have shown that the timely cardiac HO-I overexpression at acute phase of ischemic infarction (MI) provides protection via its anti-apoptotic and anti-inflammatory effects. Here we demonstrate that a delayed HO-1 transduction mediated by a recombinant adeno-associated virus in ischemic hearts of mice with permanent coronary artery ligation significantly attenuated left ventricular fibrosis and cardiac dysfunctions examined at 4 weeks post MI. HO-1-mediated protection was correlated with enhanced vascularization in the ischemic myocardium. HO-1 gene transfer resulted in a notable increase in the number of c-kit(+)-stem cells recruited to the infarcted area at 10 days after ligation. HO-1-mediated stem cell recruitment was also demonstrated in the heart of non-ischemic mice receiving intravenous infusion of green fluorescent protein-bearing bone marrow stem cells. Additional experiments revealed that vascular endothelial growth factor (VEGF) and stromal cell-derived factor-1 (SDF-1) were highly induced in HO-1-transduced myocardium. Mononuclear cell infiltration was evident and colocalized with angiogenic factors in the same region. Flow cytometry analysis of the mononuclear cells isolated from HO-1-transduced left ventricles revealed that over 50% of cells expressed CD34, a marker of hematopoietic stem cells and endothelial progenitor cells. VEGF and SDF-1 blockade by neutralizing antibodies significantly attenuated HO-1-mediated neovascularization and protection in infarcted mice. These data suggest that cardiac HO-1 gene transfer post MI provides protection at least in part by promoting neovascularization through inducing angiogenic factors and the recruitment of circulating progenitor/stem cells.
