Mesenchymal stem cells (MSCs) have potential application for the treatment of ischemic heart diseases. Besides differentiation properties, MSCs protect ischemic cardiomyocytes by secretion of paracrine factors. In this study, we found exosomes enriched with miR-22 were secreted by MSCs following ischemic preconditioning (ExoIPC) and mobilized to cardiomyocytes where they reduced their apoptosis due to ischemia. Interestingly, by time-lapse imaging, we for the first time captured the dynamic shedding of miR-22 loaded exosomes from cytosol to extracellular space. Furthermore, the anti-apoptotic effect of miR-22 was mediated by direct targeting of methyl CpG binding protein 2 (Mecp2). In vivo data showed that delivery of ExoIPC significantly reduced cardiac fibrosis. Our data identified a significant benefit of ExoIPC for the treatment of cardiac diseases by targeting Mecp2 via miR-22.

MicroRNAs have been appreciated in various cellular functions, including the regulation of angiogenesis. Mesenchymal-stem-cells (MSCs) transplanted to the MI heart improve cardiac function through paracrine-mediated angiogenesis. However, whether microRNAs regulate MSC induced angiogenesis remains to be clarified. Using microRNA microarray analysis, we identified a microRNA expression profile in hypoxia-treated MSCs and observed that among all dysregulated microRNAs, microRNA-377 was decreased the most significantly. We also validated that vascular endothelial growth factor (VEGF) is a target of microRNA-377 using dual-luciferase reporter assay and Western-blotting. Knockdown of endogenous microRNA-377 promoted tube formation in human umbilical vein endothelial cells. We then engineered rat MSCs with lentiviral vectors to either overexpress microRNA-377 (MSCmiR-377) or knockdown microRNA-377 (MSCAnti-377) to investigate whether microRNA-377 regulated MSC-induced myocardial angiogenesis, using MSCs infected with lentiviral empty vector to serve as controls (MSCNull). Four weeks after implantation of the microRNA-engineered MSCs into the infarcted rat hearts, the vessel density was significantly increased in MSCAnti-377-hearts, and this was accompanied by reduced fibrosis and improved myocardial function as compared to controls. Adverse effects were observed in MSCmiR-377-treated hearts, including reduced vessel density, impaired myocardial function, and increased fibrosis in comparison with MSCNull-group. These findings indicate that hypoxia-responsive microRNA-377 directly targets VEGF in MSCs, and knockdown of endogenous microRNA-377 promotes MSC-induced angiogenesis in the infarcted myocardium. Thus, microRNA-377 may serve as a novel therapeutic target for stem cell-based treatment of ischemic heart disease.

Background and ObjectiveImplantation of cell-sheets into damaged regions of the heart after myocardial infarction (MI) has been shown to improve heart function. However, the tissue morphology following application of induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CM) has not been studied in detail at the level afforded by electron microscopy. We hypothesized that increasing the number of CM derived from iPSC would increase the effectiveness of cell-sheets used to treat ischemic cardiomyopathy. We report here on the ultrastructural features after application of a bio-membrane ‘cell patch’.MethodsiPSC-derived progenitor cells were transduced using lentivirus vectors with or without NCX1 promoter. iPSC-CM sheets were transplanted over the transmural MI region in a mouse model of regional ischemic cardiomyopathy. Mice were divided into four groups, 1) Sham; 2) MI; 3) MI + iPSC without NCX1 treated cells (MI + iPSCNull) and 4) MI + iPSC receiving NCX1 promoter treated cells (MI + iPSCNCX1). Echocardiography was performed 4 weeks after cell patch application, followed by histological and transmission electron microscopy (TEM) analysis.ResultsLarge numbers of transplanted CM were observed with significant improvements in left ventricular performance and remodeling in group 4 as compared with group 3. No teratoma formation was detected in any of the treatment groups.ConclusionManipulation of iPSC yields large numbers of iPSC-CM and favorable morphological and ultrastructural tissue changes. These changes have the potential to enhance current methods used for restoration of cardiac function after MI.

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