Exosomal MicroRNA Transfer Into Macrophages Mediates Cellular Postconditioning

BACKGROUND: Cardiosphere-derived cells (CDCs) confer cardioprotection in acute myocardial infarction by distinctive macrophage (M phi) polarization. Here we demonstrate that CDC-secreted exosomes (CDCexo) 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 CDCexo, 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 M phi. RESULTS: Administration of CDCexo but not Fb(exo) after reperfusion reduces infarct size in rat and pig models of myocardial infarction. Furthermore, CDCexo reduce the number of CD68+ M phi within infarcted tissue and modify the polarization state of M phi so as to mimic that induced by CDCs. CDCexo 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 CDCexo-primed M phi implicated miR-81b as a significant (P= 1.3x10(-21)) candidate mediator of CDC-induced M phi polarization, and PKC delta (protein kinase C delta) as a downstream target. Otherwise inert Fb(exo) loaded selectively with miR-181b alter M phi phenotype and confer cardioprotective efficacy in a rat model of myocardial infarction. Adoptive transfer of PKC delta-suppressed M phi recapitulates cardioprotection. CONCLUSIONS: Our data support the hypothesis that exosomal transfer of miR-181b from CDCs into M phi reduces PKC delta transcript levels and underlies the cardioprotective effects of CDCs administered after reperfusion.