Hypoxia-response elements (HREs) regulate the expression of the vascular endothelial growth factor 165 (VEGF₁₆₅) gene and enhance the safety and efficacy of therapeutic angiogenesis. However, the role of hypoxic regulation of VEGF₁₆₅ gene-modified stem cells in promoting angiogenesis in the ischemic myocardium remains unclear. In this study, the effects of the hypoxic regulation of genetically modified endothelial progenitor cells (EPCs) on angiogenesis in the ischemic myocardium and on changes in cardiac function following acute myocardial infarction (AMI) were investigated through the transplantation of hypoxia-regulated VEGF₁₆₅ gene-modified EPCs into the ischemic myocardium. Rat bone marrow-derived EPCs transfected with plasmid p6HRE-CMV‑VEGF₁₆₅ (6HRE-VEGF₁₆₅-E), and plasmid pCMV-VEGF₁₆₅ (VEGF₁₆₅-E) were injected into rats with a successfully established model of AMI. The levels of VEGF₁₆₅ mRNA and protein expression in the EPCs and ischemic myocardium were determined using reverse transcription-polymerase chain reaction and western blot assay, respectively, and the capillary density in the ischemic myocardium and the cardiac function of the rats were detected using immunohistochemistry and echocardiography, respectively. We found that the hypoxia promoter 6HRE-CMV effectively regulated the expression of the VEGF₁₆₅ gene in the EPCs and the ischemic myocardium. In rats of the 6HRE-VEGF₁₆₅-E-transplanted group, the levels of VEGF₁₆₅ gene expression and capillary density in the ischemic myocardium were significantly higher than those in the other experimental groups. Moreover, cardiac function was also improved compared with that in other groups. VEGF₁₆₅ gene-modified EPCs are able to significantly promote angiogenesis in the ischemic myocardium and markedly ameliorate the cardiac function of rats following AMI, especially under 6HRE regulation.
Keywords: angiogenesis; hypoxia; gene therapy; endothelial progenitor cells; myocardial infarction.