Transplanted mesenchymal stem cells (MSC) release soluble factors that contribute to cardiac repair and vascular regeneration. We hypothesized that overexpression of GATA-4 enhances the MSC secretome, thereby increasing cell survival and promoting postinfarction cardiac angiogenesis. MSCs harvested from male rat bone marrow were transduced with GATA-4 (MSC(GATA-4)) using the murine stem cell virus retroviral expression system; control cells were either nontransduced (MSC(bas)) or transduced with empty vector (MSC(Null)). Compared with these control cells, MSC(GATA-4) were shown by immunofluorescence, real-time PCR, and Western blotting to have higher expression of GATA-4. An increased expression of angiogenic factors in MSC(GATA-4) and higher MSC resistance against hypoxia were observed. Human umbilical vein endothelial cells (HUVEC) treated with MSC(GATA-4) conditioned medium exhibited increased formation of capillary-like structures and promoted migration, compared with HUVECs treated with MSC(Null) conditioned medium. MSC(GATA-4) were injected into the peri-infarct region in an acute myocardial infarction model in Sprague-Dawley rats developed by ligation of the left anterior descending coronary artery. Survival of MSC(GATA-4), determined by Sry expression, was increased at 4 days postengraftment. MSC(GATA-4)-treated animals showed significantly improved cardiac function as assessed by echocardiography. Furthermore, fluorescent microsphere and histological studies revealed increased blood flow and blood vessel density and reduced infarction size in MSC(GATA-4)-treated animals. We conclude that GATA-4 overexpression in MSCs increased both MSC survival and angiogenic potential in ischemic myocardium and may therefore represent a novel and efficient therapeutic approach for postinfarct remodeling.

Transplantation of mesenchymal stem cells (MSCs) has emerged as a potential treatment for ischemic heart repair. Previous studies have suggested that Wnt11 plays a critical role in cardiac specification and morphogenesis. In this study, we examined whether transduction of Wnt11 directly increases MSC differentiation into cardiac phenotypes. MSCs harvested from rat bone marrow were transduced with both Wnt11 and green fluorescent protein (GFP) (MSCWnt11) using the murine stem cell virus (pMSCV) retroviral expression system; control cells were only GFP-transfected (MSCNull). Compared with control cells, MSCWnt11 was shown to have higher expression of Wnt11 by immunofluorescence, real-time polymerase chain reaction, and western blotting. MSCWnt11 shows a higher expression of cardiac-specific genes, including GATA-4, brain natriuretic peptide (BNP), islet-1, and α-actinin, after being cultured with cardiomyocytes (CMs) isolated from ventricles of neonatal (1–3 day) SD rats. Some MSCWnt11 were positive for α-actinin when MSCs were cocultured with native CMs for 7 days. Electron microscopy further confirmed the appearance of sarcomeres in MSCWnt11. Connexin 43 was found between GFP-positive MSCs and neonatal rat CMs labeled with red fluorescent probe PKH26. The transdifferentiation rate was significantly higher in MSCWnt11 than in MSCNull, as assessed by flow cytometery. Functional studies indicated that the differentiation of MSCWnt11 was diminished by knockdown of GATA-4 with GATA-4-siRNA. Transduction of Wnt11 into MSCs increases their differentiation into CMs by upregulating GATA-4.

Our previous studies have suggested that transduction of Wnt11 directly increases bone marrow-derived mesenchymal stem cell (MSC) differentiation into cardiac phenotypes. In this study, we investigated whether Wnt11 enhances MSC-mediated cardioprotection via paracrine fashion following acute ischemia. Methods MSCs were harvested from male rat bone marrow (BM) and transduced with Wnt11 (MSCWnt11). An acute myocardial infarction (MI) model in rats was developed by ligation of the left anterior descending coronary artery (LAD). MSCWnt11 were transplanted into the peri-infarct region following acute MI. To mimic ischemic injury, cultured cardiomyocytes (CM) isolated from neonatal ventricles were exposed to hypoxia. Results ELISA studies indicated that the release of Wnt11 (3.45-fold) as well as transforming growth factor-β2 (TGFβ2) (1.5-fold) was significantly increased from MSCWnt11 compared to transduced control MSC (MSCNull). Hypoxia induced apoptosis and cell death was significantly reduced when CM were co-cultured with MSCWnt11 in a dual chamber system. The cell protection mediated by MSCWnt11 was mimiced by treating CM with conditioned medium (CdM) obtained from MSCWnt11 and abrogated by Wnt11- and TGFβ2-neutralizing antibodies. Furthermore, animals receiving MSCWnt11 showed a significant improvement in cardiac contractile function as assessed by echocardiography. Masson trichrome and TUNEL staining showed a significant reduction on infarct size and apoptosis of CM in MSCWnt11 treated animals. Conclusions Transplantation of MSCWnt11 improved cardiac function. The release of Wnt11 and other factors from transplanted MSCWnt11 is more likely responsible for protection of native CM at risk.