Abstract 15483: Regenerative Effects of Exosomes Secreted by Cardiospheres in a Rat Model of Chronic Myocardial Infarction Are Mimicked by Exosome-primed Fibroblasts

Abstract

Background: Multicellular self-assembling cardiospheres (CSps) exert regenerative and anti-fibrotic effects via paracrine mechanisms. CSp-derived cells are known to secrete exosomes which mediate most or all of the beneficial therapeutic effects. Objective: We evaluated the regenerative capacity of CSp-secreted exosomes in a model of chronic myocardial infarction (MI). We also determined whether CSp-exosomes could convert the phenotype of therapeutically-inert cells. Methods: Exosomes were isolated from CSp-conditioned media by adding a precipitation solution followed by centrifugation. One month post-MI, Wistar Kyoto rats (n=46) with permanent LAD ligation were injected intramyocardially with: a) human dermal fibroblasts (DFs), b) CSp exosomes, c) DFs primed with CSp-exosomes, d) CSps only or e) vehicle. Functional and histological analyses were performed 4 weeks after therapy. Mechanisms were also probed in vitro . Results: In vivo, CSp-exosomes and CSps equally increased ejection fraction (EF= 45±1% [CSp-exo], 44±2% [CSps], 33±1% [placebo] and 35±2% [DFs]) and reduced scar mass (48±8mg [CSp-exo], 45±4mg [CSps], 96±12mg [placebo] and 90±6mg [DFS]; both p<0.01 by one way ANOVA). DFs that had been incubated with CSp-exosomes for 24 hours in culture conferred enhanced benefits compared to unprimed DFs (EF= 41±1% [primed-DFs]; p=0.05 vs unprimed DFs; scar mass= 49±5mg [primed-DFs]; p<0.01 vs unprimed DFs). Confocal imaging revealed internalization of fluorescently-labeled CSp-exosomes in exosome-primed DFs. In vitro , exosome-primed DFs increased tube formation by HUVECs and inhibited cardiomyocyte apoptosis. Immunohistochemistry showed increased vessel density in all groups compared to vehicle or unprimed DFs. Conclusions: Administration of CSp-exosomes recapitulates the regenerative potential and functional benefits of CSps themselves. The surprising ability of CSp-exosomes to confer therapeutic efficacy on inert DFs may represent an unanticipated amplification mechanism for exosome-mediated benefits.