Exosomes from human cardiac progenitor cells, but not those from patient-matched bone marrow-derived mesenchymal stem cells,improve cardiac function after myocardial infarction in vivo

Background: Both human cardiac progenitor cells (CPC) and bone marrow-derived mesenchymal stem cells (MSC) have been tested in clinical trials of cell transplantation in patients with myocardial infarction (MI). We have recently shown that Exosomes (secreted nanovesicles; Exo) from CPC account for cardioprotective and proangiogenic activities of these cells both in vitro and in vivo. This study aimed to compare Exo-CPC and Exo-MSC in terms of cardioprotective effects and functional improvement after MI. The role of microRNA (miRNA) and ischemic preconditioning (IPC) were assessed. Methods: CPC and MSC were derived from right atrial appendage and bone aspirate from patients undergoing heart valve surgery. Samples from both tissues were obtained for a patient-matched comparison of Exo from the two cell lines. Exo were isolated by differential ultracentrifugation of conditioned media from CPC or MSC. Anti-apoptotic and proangiogenic effects of Exo-CPC and Exo-MSC were assessed in vitro and compared with Exo from human dermal fibroblast cell line (Exo-F). IPC was performed by subjecting CPC or MSC to two short rounds of hypoxia and glucose deprivation. miRNA profiles of Exo were assessed by real-time PCR. Exo-CPC and Exo-MSC from 8 patients were injected intramyocardially in 8 rats each after permanent ligation of the left anterior descending coronary artery. Left ventricular ejection fraction (LVEF) was measured by echocardiography 1 and 4 weeks after MI. Results: Although both Exo-CPC and Exo-MSC inhibited cardiomyocyte (CM) apoptosis after serum starvation in vitro if compared with Exo-F, Exo-CPC showed higher efficacy (21±4% Exo-CPC; 28±4% Exo-MSC; 40±5% Exo-F). IPC of Exo-producing cells further reduced numbers of apoptotic CM (17±1% Exo-CPC; 23±3% Exo-MSC). Exo-CPC, but not Exo-F, were proangiogenic in HUVEC cells. miR-210, miR132 and miR-146a were among the most highly enriched miRNA in Exo-CPC. CM transfected with miR-210 or miR-132 mimics showed increased tolerance to apoptosis, whereas siRNA specific for these miRNA had opposite effects. In vivo, LVEF was significantly improved in hearts injected with Exo-CPC compared to those injected with patient-matched Exo-MSC both at 1 week (87.0±9.9% vs 61.1±11.9; p<0.05) and 4 weeks after MI (75.4±8.9% vs 58.7±18.4%; p<0.05). Conclusion: These results from patient-matched analyses show, for the first time, that Exo-CPC is superior to Exo-MSC at inhibiting CM apoptosis in vitro, and at improving cardiac function after MI in vivo. As a cell-free approach, Exo could streamline clinical translation of regenerative heart therapy.