Mechanomemory after short episodes of intermittent stresses induces YAP translocation via increasing F-actin

How forces and mechanics influence and regulate living cells remains elusive. Mechanomemory, the response to a mechanical perturbation that persists after the perturbation is removed, is believed to be a key to understanding the impact of forces and mechanics on cell functions. Recently, our lab has demonstrated the presence of mechanomemory that lasts for ∼30 min after applying external stress via integrins. Herein, we test the hypothesis that applications of short intermittent episodes of stress exert long-term effects on mechanomemory via the process of mechanotransduction. An Arginine-Glycine-Aspartic acid (RGD)-peptides-coated 4-μm magnetic bead was bound to the integrin receptors to apply stresses to the surface of a Chinese Hamster Ovary cell. At the same stress magnitude and frequency (15 Pa at 0.3 Hz), multiple cycles of externally applied intermittent 2 or 10 min stresses with 15 min intervals, 10 min stresses with 10 min intervals, or a 30 min stress plus a 30 min load-free interval increased nuclear translocation of YAP (Yes-Associated Protein) and Ctgf gene expression, like that by a 60 min continuous stress, but a 30 min continuous stress did not. Short durations of intermittent stresses increased F-actin in the cytoplasm, which coincided with the elevated YAP translocation. Inhibiting F-actin or actomyosin but not microtubules blocked stress-induced YAP translocation to the nucleus. Cells on soft substrates translocate more YAP than on stiff substrates after external load release. These results highlight the impact of multiple intermittent stresses-induced cytoplasmic mechanomemory on cell biological functions via YAP translocation.