Mesenchymal stem cells modified with miR-126 release angiogenic factors and activate Notch ligand Delta-like-4, enhancing ischemic angiogenesis and cell survival

The endothelial cell-specific microRNA (miRNA), miR-126, is considered a master regulator of physiological angiogenesis. Transplanted mesenchymal stem cells (MSCs) release soluble factors contributing to neoangiogenesis and cardiac repair. Therefore, we hypothesized that the overexpression of miR-126 may prolong MSC survival and enhance the cell secretome, thereby improving post-infarction angiogenesis and cardiac function. In this study, MSCs harvested from male C57BL16 mouse bone marrow were infected in vitro with miR-126 (MSCmiR-126) by using recombinant lentiviral vectors; the control cells were either non-transfected or transduced with mock vectors (MSCnull). The results showed an increased secretion of angiogenic factors and a higher resistance against hypoxia in MSCmiR-126 compared with the control cells. The expression of the Notch ligand Delta-like (Dll)-4 in the MSCmiR-126 group was also increased. For in vivo experiments, MSCmiR-126 cultures were intramyocardially injected into the infarct region of the hearts of female C57BL/6 mice (an acute myocardial infarction model) who had undergone ligation of the left anterior descending coronary artery. The survival of MSCmiR-126 cultures, determined by Sry expression, was increased at 7 days after transplantation. MSCmiR-126-treated animals showed significantly improved cardiac function as assessed by echocardiography 2 weeks later. The expression levels of angiogenic factors and Dll-4 in the infarcted myocardium were further increased by MSCmiR-126 compared with MSCs or MSCnull cultures. Furthermore, fluorescent microsphere and histological studies revealed that myocardial blood flow and microvessel density were significantly increased in the MSCmiR-126-transplanted animals. In addition, we found increased immature vessel proliferation following the transplantation of MSCmiR-126 cultures in which the expression of Dll-4 had been knocked down. However, blood vessels with lumen were barely detected, which indicated that Dll-4 plays a key role in tubulogenesis. We conclude that the transplantation of MSCs overexpressing miR-126 can further enhance functional angiogenesis in the ischemic myocardium possibly by the secretion of angiogenic factors and the activation of Dll-4, thus increasing MSC survival. Therefore, MSCs modified with miR-126 may represent a novel and efficient therapeutic approach for ischemic angiogenesis and the improvement of cardiac function.