Exosomes from Human Cardiac Progenitor Cells Preserve Cardiac Function Long Term after Myocardial Infarction

Introduction: Recent evidence suggests cardiac progenitor cells (CPC) may improve cardiac function after injury. The underlying mechanisms are indirect, but their mediators remain unidentified. Exosomes (Exo) act as paracrine signalling mediators. Here we report that Exo secreted by human CPC are crucial cardioprotective agents that improve left ventricular ejection fraction (LVEF %) in long term animal model of infarct. Methods: Medium from CPC or normal human dermal fibroblasts (NHDF) was conditioned for 5-7 days and subjected to differential centrifugation for Exo isolation. Exo from CPC (Exo-CPC) were tested in-vitro for their functional activity such as anti-apoptotic and pro-angiogenic effects and compared with Exo from NHDF (Exo-F). The content of micro-RNA (miRNA) has been analysed by real-time PCR in Exo-CPC vs Exo-F. Exo-CPC derived from six patients were pooled and intramyocardially injected in-vivo in animal model of permanent left anterior descending (LAD) coronary ligation. One and four weeks after injection LVEF was evaluated by echocardiography and hearts were processed for histological analysis. Results: Exo-CPC inhibited apoptosis in cardiomyocytes, while enhancing tube formation in human endothelial cells invitro compared to Exo-F. Exo-CPC were enriched in miR-210, miR-132, miR-146a, and miR-181a compared to Exo-F. In gain-of-function studies, miR-210 and miR-146a inhibited apoptosis in cardiomyocytes by downregulating their targets ephrinA3/PTP1b and Nox4 respectively. miR-132 downregulated its target RasGAP-p120 and enhanced angiogenesis. Moreover, Exo-CPC, but not Exo-F, downregulated anti-apoptotic factors in cardiomyocytes. Infarcted hearts injected with Exo-CPC significantly preserved the LVEF after one week (84.00±1.6%) and the effect was preserved after four weeks (80.57±2.3%) compared with animals injected with Exo-F (60.71±7.4%; 48.00±4.6% one and four weeks respectively). Moreover Exo-CPC injected hearts showed significantly reduced scar size (6.7±2.0% Exo-CPC vs 19.25±3.4% Exo-F). Summary/Conclusion: Exo are the active component of the paracrine secretion of human CPC. They are enriched in miRNA with cardioprotective and proangiogenic activities. Exo-CPC preserve heart function in a long term animal model of permanent LAD ligation. As a cell-free approach, Exo could circumvent many of the limitations of cell transplantation.