Hypoxia-elicited mesenchymal stem cell-derived exosomes facilitates cardiac repair through miR-125b-mediated prevention of cell death in myocardial infarction

Exosomes (Exo) secreted from hypoxia-conditioned bone marrow mesenchymal stem cells (BM-MSCs) were found to be protective for ischemic disease.However, the role of exosomal miRNA in the protective effect of hypoxia-conditioned BM-MSCs-derived Exo (Hypo-Exo) remains largely uncharacterized and the poor specificity of tissue targeting of Exo limits their clinical applications.Therefore, the objective of this study was to examine the effect of miRNA in Hypo-Exo on the repair of ischemic myocardium and its underlying mechanisms.We further developed modified Hypo-Exo with high specificity to the myocardium and evaluate its therapeutic effects.Methods: Murine BM-MSCs were subjected to hypoxia or normoxia culture and Exo were subsequently collected.Hypo-Exo or normoxia-conditioned BM-MSC-derived Exo (Nor-Exo) were administered to mice with permanent condition of myocardial infarction (MI).After 28 days, to evaluate the therapeutic effects of Hypo-Exo, infarction area and cardio output in Hypo-Exo and Nor-Exo treated MI mice were compared through Masson’s trichrome staining and echocardiography respectively.We utilized the miRNA array to identify the significantly differentially expressed miRNAs between Nor-Exo and Hypo-Exo.One of the most enriched miRNA in Hypo-Exo was knockdown by applying antimiR in Hypoxia-conditioned BM-MSCs.Then we performed intramyocardial injection of candidate miRNA-knockdown-Hypo-Exo in a murine MI model, changes in the candidate miRNA’s targets expression of cardiomyocytes and the cardiac function were characterized.We conjugated Hypo-Exo with an ischemic myocardium-targeted (IMT) peptide by bio-orthogonal chemistry, and tested its targeting specificity and therapeutic efficiency via systemic administration in the MI mice.Results: The miRNA array revealed significant enrichment of miR-125b-5p in Hypo-Exo compared with Nor-Exo.Administration of miR-125b knockdown Hypo-Exo significantly increased the infarction area and suppressed cardiomyocyte survival post-MI.Mechanistically, miR-125b knockdown Hypo-Exo lost the capability to suppress the expression of the proapoptotic genes p53 and BAK1 in cardiomyocytes.Intravenous administration of IMT-conjugated Hypo-Exo (IMT-Exo)Ivyspring