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 antiapoptotic 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.
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