Mechanically induced integrin ligation mediates intracellular calcium signaling with single pulsating cavitation bubbles

Ultrasound or shockwave-induced cavitation is used therapeutically to stimulate neural and muscle tissue, but the mechanisms underlying this mechanotransduction are unclear. Intracellular Ca2+ signaling is one of the earliest events in mechanotransduction. In this study, we investigate the mechanism of Ca2+ signaling in individual HEK293T cells stimulated by single cavitation bubbles. Ca2+ responses are rare at cell-bubble distance that avoids membrane poration, even with overexpression of the mechanosensitive ion channel Piezo1, but could be increased in frequency to 42% of cells by attaching RGD beads to the apical surface of the cells. By using Piezo1 knockout and Piezo1-expressing cells, integrin-blocking antibodies, and inhibitors of P2X ion channels, key molecular players are identified in the RGD bead-enhanced Ca2+ response: increased integrin ligation by substrate ECM triggers ATP release and activation of P2X--but not Piezo1--ion channels. These molecular players have not been examined previously in cavitation-induced Ca2+ signaling. The resultant Ca2+ influx causes dynamic changes in cell spread area. This approach to eliciting a Ca2+ response with cavitation microbubbles without cell injury, and the uncovered mechanotransduction mechanism by which increased integrin-ligation mediates ATP release and Ca2+ signaling will inform new strategies to stimulate tissues with ultrasound and shockwaves.