Abstract 16389: Exosomal MicroRNAs Regulate Myofibroblast Activation in Myocardial Infarction

Introduction:Mounting evidence has shown that exosomal non-coding-RNAs play a pivotal role in cell-cell communication. However, their contribution in the phenoconversion of cardiac fibroblasts to active myofibroblasts in myocardial infarction (MI) has not been investigated.Hypothesis:We hypothesize that exosomal microRNAs (miRs) are involved in the activation of myofibroblasts following ischemic injury.Methods:We tested our hypothesis trough means of bioinformatic tools and a murine model of MI, obtained via surgical ligation of the left anterior coronary artery; we measured the expression levels of a set of miRs in fibroblasts and cardiomyocyte-derived exosomes; we used miR inhibitors and mimics to evaluate post-MI myofibroblast phenoconversion.Results:Compared with SHAM conditions, miR-92a was significantly (p<.01) upregulated (absolute values) in cardiomyocyte-derived exosomes as well as in fibroblasts isolated at different time points after MI. This miRs was shown to specifically target SMAD7 (Mothers against decapentaplegic homolog 7), an established inhibitor of ?SMA (?-Smooth muscleactin)expression (a fundamental player in myofibroblast activation); such interaction was predicted using bioinformatic tools and validated via luciferase assays. Furthermore, primary isolated cardiac fibroblasts were activated both when incubated with exosomes derived from ischemic cardiomyocytes and when cultured in conditioned medium of post-MI cardiomyocytes, whereas no significant effects were observed after incubation with exosomes or medium from sham cardiomyocytes. Myofibroblast activation was assessed measuring the expression of ?SMA, periostin, collagen I/III, fibroblast activation protein, and fibronectin ED-A. Additionally, miR-92a regulated the post-MI inflammatory response (also in terms of IL-6 and CXCL1). Inhibiting exosome release (GW4869 10?M 12h) significantly attenuated all these responses. The mechanistic contribution of miR-92a to fibroblast phenoconversion was further confirmed using miR-92a mimics and inhibitors.Conclusions:Taken together, our findings indicate that miR-92a is transferred to fibroblasts in form of exosomal cargo, and is crucial for post-MI activation of myofibroblasts.