F-actin Severing Facilitates Distinct Mechanisms of Stress Relaxation in the Actin Cytoskeleton

Rheological behaviors of actin cytoskeleton play an important role in physiological processes including cell migration and division. The actin cytoskeleton shows a wide variety of viscoelastic responses to external mechanical cues, such as strain-stiffening and stress relaxation. It has been hypothesized that the stress relaxation originates mainly from transient nature of cross-linkers that connect pairs of F-actins. By contrast, potential impacts of rich F-actin dynamics to the stress relaxation have been neglected in most previous studies. Here, using a computational model, we demonstrated that severing of F-actins induced by buckling during strain-stiffening can facilitate a very distinct mode of stress relaxation in the actin cytoskeleton from that induced by the transient cross-linkers. We also explored conditions where the severing-induced stress relaxation becomes prominent. This finding provides a more complete understanding of rheological behaviors of the actin cytoskeleton.