Cyclic Force Applied to FAs Induces Actin Recruitment Depending on the Dynamic Loading Pattern

Mechanical forces acting on focal adhesions (FAs) are believed to be an important determinant for cytoskeletal reorganization. However, the effect of the temporal pattern of forces on cellular responses has not been elucidated. In the present study, we examined the responses of FAs to locally-applied cyclic forces. Magnetic micro beads coated with fibronectin were attached to the apical surface of endothelial cells and continuous or cyclic forces at frequencies of 0.1-10 Hz with duty cycles of 0-100% were applied to the beads using a newly developed electromagnetic tweezer. A significant increase in actin recruitment around the beads was observed when cyclic forces at 1-2 Hz and 25-50% duty cycles were applied. This tendency disappeared upon modification of myosin activity. These results indicate that the sensitivity to temporal patterns of forces is detemined by the viscoelastic properes of FAs and depends on myosin activity.