Shear stress-induced influx of extracellular calcium ions: a pivotal trigger amplifying the production of mesenchymal stem cell-derived extracellular vesicles

Extracellular vesicles (EVs) have drawn attention as promising therapeutic agents whose characteristics resemble their parent cells. However, their practical utility is limited by low EV yields. Cell culture under fluidic flow to enhance EV secretion has been proposed to address this challenge. However, the precise mechanism of increased EV production in response to flow conditions has not been studied thoroughly. We investigated the mechanism of higher release of EVs from mesenchymal stem cells under flow conditions, focusing on the correlation between intracellular calcium ions and EV production. Shear stress was applied to cells through shaking cultures, and stimulated cells showed increased EV production. Results suggested that the stimulation of EV secretion was promoted by an increasing intracellular concentration of calcium ions, primarily due to their transport through calcium ion channels in the plasma membrane, which was induced by shear stress. Furthermore, we confirmed that the essential characteristics of the EVs released under shear stress remained intact by analyzing individual EVs and assessing their regeneration efficacy in a model of kidney injury in vitro. Unveiling the reason for the high production of EVs under shear stress is expected to contribute to the development of EV-application research by increasing the reliability of EV utilization.