Abstract 19186: Role of Exosomes and Their microRNA Constituents in Mediating the Therapeutic Benefits of Human Cardiosphere-Derived Cells in vitro and in Mice With Myocardial Infarction

Abstract

Background: Exosomes are nano-sized bilayer vesicles that are secreted by most cell types. Exosomes are rich in microRNAs (mirs) which may function in a paracrine fashion. Cardiosphere-derived cells (CDCs) have been shown to regenerate heart after myocardial infarction (MI) in animal models and in the CADUCEUS clinical trial. However, most of the regenerated muscle is of innate origin, which suggests that CDCs function mainly through indirect pathways. Methods and Results: In vitro and in vivo, we compared three treatment groups: vehicle only (control), CDC-derived exosomes and normal human dermal fibroblast (NHDF)-derived exosomes. Neonatal rat cardiomyocytes (NRCMs) incubated with CDC exosomes were more frequently positive for Ki67 (n=4, p<0.001), and less frequently tunel-positive, compared to NHDF exosomes or control (n=4, p<0.01). CDC exosomes also stimulated tube formation in HUVEC cells compared to NHDF exosomes or control (p<0.05). SCID mice injected with exosomes from CDCs during acute MI showed higher LVEF at two weeks (n=6, p<0.05) and four weeks (n=6, p<0.05) post MI, as well as increased viable mass. The therapeutic benefits of exosomes were equivalent to those of 105 injected human CDCs (p=ns). Inhibition of exosome secretion by ceramide synthesis inhibition abrogated the beneficial effects by CDCs in vivo and in vitro. Mir microarray analysis identified mirs146a as the most highly-up regulated mirs in CDC-exosomes compared to NHDF (262-fold, n=4). Mir-146a-treated NRCMs were more resistant to H2O2-induced stress compared to a mimic control. Array analysis of these NRCMs treated also showed suppression of IRAK1 and TRAF6 transcripts. SCID mice injected with 80 ng of mir-146a during acute MI showed higher LVEF at two weeks (n=6, p<0.05) and four weeks (n=6, p<0.05) post MI, as well as increased viable mass compared to mimic control. Conclusions: Mir-containing exosomes secreted by CDCs exhibit multiple beneficial effects on injured myocardium, suggesting that exosomes may mediate some of the therapeutic effects of CDCs. Most notably mir-146a provides cardioprotection in an acute model of MI.