How do Extracellular Vesicles Protect the Ischemic Myocardium?

Abstract

Background & Aim Introduction Cell therapy for chronic heart failure has demonstrated that Cardiac Progenitor Cells (CPCs) delivered to the heart exert their beneficial effects through a paracrine mechanism harnessing endogenous repair pathways largely mediated by extracellular vesicles (EVs). We used a bi-transgenic fate-mapping MerCreMer/ZEG mouse model to assess whether the cardioprotection could be partly explained by de novo cardiogenesis. Methods, Results & Conclusion Methods Myocardial infarction (MI) was induced by permanent left anterior descending coronary artery ligation in MerCreMer/ZEG mice. Surviving animals (n=30) with a left ventricular ejection fraction (LVEF) ≤ 45% were treated 3 weeks after MI with either EV (from 1.4 × 106 human iPS-derived CPC; 10 × 109 particles; n=15) or PBS (n=15) delivered by echo-guided intra-myocardial injections targeted to the peri-infarcted area. To track a putative proliferation of endogenous cardiomyocytes, osmotic pumps delivering EdU were implanted for 10-13 days after EV or PBS treatnent. Cardiac function was assessed 4-6 weeks after injections by echocardiography (n=15 p/group) and MRI (n=6-7 p/group), blinded to treatment group. Hearts were harvested and subjected to histological and transcriptomic analyses by qRT-PCR and genome-wide microarrays (Affymetrix). Results In controls, echocardiographically assessed EF slightly decreased over time whereas in the EV-treated group, it increased so that at the end-study time point, the between-group difference in changes from baseline averaged 20.7 % ± 10.5 % (p=0.048). This improvement was confirmed by MRI (11%, p=0.05). EV-treated hearts did not show a different number of new cardiomyocytes (TnT+/EdU+/GFP+) compared to controls (32 analyzed sections/mouse). However, EV-treatment was associated with a reduction in infarct size (-11.9% ± 5.75%), and reduced expression of 4 pro-fibrotic genes (Col1a2, Col3a1, Lox, Col1a2) as assessed by qRT-PCR (n=5-6 p/group). Further, the EV-treatment group showed an over-expression of the anti-fibrotic miRNA 133a-1 (2.13 fold) as compared to controls (n=3 p/group; p=0.0015). Conclusions EV secreted by iPSC-CPC improve cardiac function in chronic heart failure by mechanisms which seem to be largely related to the modulation of fibrosis without participation of a de novo cardiogenesis. Funding Labex Revive, Fondation pour la Recherche Medicale, Fonds Marion Elizabeth BRANCHER