Electrical Stimulation Increases the Secretion of Cardioprotective Extracellular Vesicles from Cardiac Mesenchymal Stem Cells

Clinical trials have shown that electric stimulation (ELSM) using either cardiac resynchronization therapy (CRT) or cardiac contractility modulation (CCM) approaches is an effective treatment for patients with moderate to severe heart failure, but the mechanisms are incompletely understood. Extracellular vesicles (EV) produced by cardiac mesenchymal stem cells (C-MSC) have been reported to be cardioprotective through cell-to-cell communication. In this study, we investigated the effects of ELSM stimulation on EV secretion from C-MSCs (C-MSC(ELSM)). We observed enhanced EV-dependent cardioprotection conferred by conditioned medium (CM) from C-MSC(ELSM) compared to that from non-stimulated control C-MSC (C-MSC(Ctrl)). To investigate the mechanisms of ELSM-stimulated EV secretion, we examined the protein levels of neutral sphingomyelinase 2 (nSMase2), a key enzyme of the endosomal sorting complex required for EV biosynthesis. We detected a time-dependent increase in nSMase2 protein levels in C-MSC(ELSM) compared to C-MSC(Ctrl). Knockdown of nSMase2 in C-MSC by siRNA significantly reduced EV secretion in C-MSC(ELSM) and attenuated the cardioprotective effect of CM from C-MSC(ELSM) in HL-1 cells. Taken together, our results suggest that ELSM-mediated increases in EV secretion from C-MSC enhance the cardioprotective effects of C-MSC through an EV-dependent mechanism involving nSMase2.