Hypoxic Small Extracellular Vesicle Preconditioning of AC16 Cardiomyocytes Increase Caspase-3 and Caspase-8 Activity During Hypoxia.

Small extracellular vesicles (sEVs) are increasingly recognized as crucial mediators of cell-cell communication. This study aims to determine the influence of sEV mediation on cardiomyocytes (CMs) under hypoxic conditions and identify the molecular modifications induced by hypoxia-derived sEVs (H-sEVs). Using a preconditional approach, we administered hypoxic AC16 CM-derived sEVs to recipient AC16 CMs before hypoxic stimulation. Molecular and biochemical analyses were performed to evaluate the biological effects of H-sEVs, e.g., cell viability assay, caspase assays, Western blotting, and quantitative sandwich ELISA. Our results showed a significant decrease in CM viability following hypoxic stimulation, as well as elevated caspase-3 and caspase-8 activity, and increased Bcl-2-associated X protein (BAX) translocation to the mitochondria followed by an increased release of Cytochrome C from mitochondria to cytosol. Preconditioning with H-sEVs further exacerbated caspase-3 and caspase-8 activation, which was explained by aggravated translocation of BAX to the mitochondria with consequences of cytochrome C release and increased apoptotic signaling. Our research indicates that sEVs secreted by hypoxic AC16 CMs negatively impact the biological properties of recipient CMs exposed to hypoxic stress. Thus, these findings widen our current understanding of sEV-mediated cellular communication during hypoxic events and provide insights into potential therapeutic targets for cardiac ischemic injury.