Exosomal MicroRNA Transfer Into Macrophages Mediates Cellular Postconditioning.

BACKGROUND: Cardiosphere-derived cells (CDCs) confer cardioprotection in acute myocardial infarction by distinctive macrophage (Mϕ) polarization. Here we demonstrate that CDC-secreted exosomes (CDC(exo)) recapitulate the cardioprotective effects of CDC therapy known as cellular postconditioning. METHODS: Rats and pigs underwent myocardial infarction induced by ischemia/reperfusion before intracoronary infusion of CDC(exo), inert fibroblast exosomes (Fb(exo); control), or vehicle. Two days later, infarct size was quantified. Macrophages were isolated from cardiac tissue or bone marrow for downstream analyses. RNA sequencing was used to determine exosome content and alterations in gene expression profiles in Mϕ. RESULTS: Administration of CDC(exo) but not Fb(exo) after reperfusion reduces infarct size in rat and pig models of myocardial infarction. Furthermore, CDC(exo) reduce the number of CD68+ Mϕ within infarcted tissue and modify the polarization state of Mϕ so as to mimic that induced by CDCs. CDC(exo) are enriched in several miRNAs (including miR-146a, miR-181b, and miR-126) relative to Fb(exo). Reverse pathway analysis of whole-transcriptome data from CDC(exo)-primed Mϕ implicated miR-181b as a significant (P=1.3x10(-21)) candidate mediator of CDC-induced Mϕ polarization, and PKCδ (protein kinase C δ) as a downstream target. Otherwise inert Fb(exo) loaded selectively with miR-181b alter Mϕ phenotype and confer cardioprotective efficacy in a rat model of myocardial infarction. Adoptive transfer of PKCδ-suppressed Mϕ recapitulates cardioprotection. CONCLUSIONS: Our data support the hypothesis that exosomal transfer of miR-181b from CDCs into Mϕ reduces PKCδ transcript levels and underlies the cardioprotective effects of CDCs administered after reperfusion.