The objective of this study was to investigate whether vascular endothelial growth factor (VEGF) secreted by mesenchymal stem cells (MSC) improves myocardial survival and the engraftment of implanted MSC in infarcted hearts and promotes recruitment of stem cells through paracrine release of myocardial stromal cell-derived factor-1α (SDF-1α). VEGF-expressing MSC (^VEGFMSC)-conditioned medium enhanced SDF-1α expression in heart slices and H9C2 cardiomyoblast cells via VEGF and the vascular endothelial growth factor receptor (VEGFR). The ^VEGFMSC-conditioned medium markedly promoted cardiac stem cell (CSC) migration at least in part via the SDF-1α/CXCR4 pathway and involved binding to VEGFR-1 and VEGFR-3. In vivo, ^VEGFMSC-stimulated SDF-1α expression in infarcted hearts resulted in massive mobilization and homing of bone marrow stem cells and CSC. Moreover, VEGF-induced SDF-1α guided the exogenously introduced CSC in the atrioventricular groove to migrate to the infarcted area, leading to a reduction in infarct size. Functional studies showed that ^VEGFMSC transplantation stimulated extensive angiomyogenesis in infarcted hearts as indicated by the expression of cardiac troponin T, CD31, and von Willebrand factor and improved the left ventricular performance, whereas blockade of SDF-1α or its receptor by RNAi or antagonist significantly diminished the beneficial effects of ^VEGFMSC. Exogenously expressed VEGF promotes myocardial repair at least in part through SDF-1α/CXCR4-mediated recruitment of CSC.

The effect of transplanted mesenchymal stem cells (MSCs) on the left ventricular (LV) function and morphology in a rat myocardial infarct heart with reperfusion model were analyzed. One week after 60 min of myocardial ischemia and reperfusion by left anterior descending artery (LAD) occlusion, 1.0x10(7) 6-diamidino-2-phenylindole (DAPI)-labeled MSCs were injected into the infarcted myocardium and compared with controls, and sham-operated rats, in which a cell-free serum medium was injected into the infarcted region or the myocardial wall, respectively. Measurement of vascular endothelial growth factor (VEGF) expression 1 week after MSC injection using Western blot analysis (n=5), and immunohistochemical staining using HE staining and fluorescent microscopy of the DAPI-positive regions from MSC implantation, cTnT immunostaining of potential myocardial-like cells, and SM-actin and CD31 immunostaining demonstrating neovascular transformation of implanted MSCs 1 week, 2 weeks and 4 weeks after transplantation (n=5). Hemodynamic measurements were performed after 4 weeks in vivo. Subsequently, hearts were quickly removed and cut for histological analysis using HE staining with measurement of the infarcted LV-area, the LV-wall thickness within the scar segment compared to non-infarcted scar segments, and the capillary density counting capillary vessels with 400x light microscopy (n=10). Measurement of hemodynamics 4 weeks after transplantation in vivo showed LV function to be significantly greater in MSCs than in the control group. Semi-quantitative histomorphometric examinations showed a significantly lower infract size, a greater LV-wall thickness, and a lower Hochman-Choo expansion index in the MSC-treated group compared to the control group. Immunofluorescence demonstrated that transplanted MSCs were positive for cTnT, suggesting that a small number of transplanted MSCs can differentiate into cardiomyocytes. Other MSCs were positive for CD31 and SM-actin. The transplanted MSCs in MI area had significantly higher expression rates of cTnT, CD31 and SM-actin 2 weeks after transplantation. HE staining showed marked augmentation of neovascularization in the MSC group. Semi-quantitative analysis demonstrated that capillary density was significantly higher in the MSC group than in the control group. Implanted MSCs could improve cardiac structure and function through the combined effect of myogenesis and angiogenesis.

In addition to its multipotent capability, the mesenchymal stem cell (MSC) can secrete and supply a large amount of vascular endothelial growth factor (VEGF). The stromal-derived factor-1 alpha (SDF-1alpha) plays an important role in the homing of stem cells to the injured tissues of the heart. Therefore, the MSCs over-expressing SDF-1alpha could augment the angiogenesis pathway. In vitro, the differentiation of the MSCs into endothelial-like cells was induced by cultivation of cells in 10% foetal calf serum and 50 ngml(-1) SDF-1alpha or in specific inhibitors for endothelial nitrous oxide synthase (eNOS). In vivo, the rat model of myocardial infarction was established by occlusion of the left anterior descending coronary artery. Seven days following surgery, 5.0 x 10(9)pfu Ad-SDF-1alpha (adenoviral vector containing human SDF-1alpha gene under the control of the rous sarcoma virus (RSV) promoter), 5.0 x 10(6) Ad-LacZ-MSC or 5.0 x 10(6) Ad-SDF-MSC suspension in a 0.2-ml serum-free medium was injected into four sites in infarcted areas (0.05 ml per site). The rats receiving Ad-SDF-MSC also received the nitrous oxide (NO) synthesis inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) in drinking water (1 mgkg(-1)). The rats in the control group received the same volume of cell-free medium. Four weeks following transplantation, the heart function was assessed, and histological and molecular analyses were conducted. The MSCs could differentiate into endothelial cells in the presence of SDF-1alpha, and the effect could be inhibited by l-NAME in vitro and in vivo. Western Blotting revealed an increased expression of VEGF, Akt and eNOS. Four weeks following transplantation, a reduced infarct size and fibrosis, greater vascular density and thicker left ventricular wall were observed in the Ad-SDF-MSC group. The measurement of haemodynamic parameters showed an improvement in the left ventricular performance in the Ad-SDF-MSC group as compared with other groups. The MSCs over-expressing the SDF-1alpha can produce effective angiogenesis, resulting in the prevention of progressive heart dysfunction after a myocardial infarction.

Mesenchymal stem cells (MSCs) are a promising source for cell-based treatment of myocardial infarction (MI), but existing strategies are restricted by low cell survival and engraftment. We examined whether SDF-1 transfection improve MSC viability and paracrine action in infarcted hearts. We found SDF-1-modified MSCs effectively expressed SDF-1 for at least 21days after exposure to hypoxia. The apoptosis of Ad-SDF-1-MSCs was 42% of that seen in Ad-EGFP-MSCs and 53% of untreated MSCs. In the infarcted hearts, the number of DAPI-labeling cells in the Ad-SDF-1-MSC group was 5-fold that in the Ad-EGFP-MSC group. Importantly, expression of antifibrotic factor, HGF, was detected in cultured MSCs, and HGF expression levels were higher in Ad-SDF-MSC-treated hearts, compared with Ad-EGFP-MSC or control hearts. Compared with the control group, Ad-SDF-MSC transplantation significantly decreased the expression of collagens I and III and matrix metalloproteinase 2 and 9, but heart function was improved in d-SDF-MSC-treated animals. In conclusion, SDF-1-modified MSCs enhanced the tolerance of engrafted MSCs to hypoxic injury in vitro and improved their viability in infarcted hearts, thus helping preserve the contractile function and attenuate left ventricle (LV) remodeling, and this may be at least partly mediated by enhanced paracrine signaling from MSCs via antifibrotic factors such as HGF.