Actin crosslinking by α-actinin averts viscous dissipation of myosin force transmission in stress fibers

Contractile force generated in actomyosin stress fibers (SFs) is transmitted along SFs to the extracellular matrix (ECM), which contributes to cell migration and sensing of ECM rigidity. In this study, we show that efficient force transmission along SFs relies on actin crosslinking by alpha-actinin. Upon reduction of alpha-actinin-mediated crosslinks, the myosin II activity induced flows of actin filaments and myosin II along SFs, leading to a decrease in traction force exertion to ECM. The fluidized SFs maintained their cable integrity probably through enhanced actin polymerization throughout SFs. A computational modeling analysis suggested that lowering the density of actin crosslinks caused viscous slippage of actin filaments in SFs and, thereby, dissipated myosin-generated force transmitting along SFs. As a cellular scale outcome, alpha-actinin depletion attenuated the ECM-rigidity-dependent difference in cell migration speed, which suggested that alpha-actinin-modulated SF mechanics is involved in the cellular response to ECM rigidity.

Automated summary

In this study, the researchers discovered that contractile force generated in actomyosin stress fibers is transmitted to the extracellular matrix. They found that efficient force transmission relies on actin crosslinking by alpha-actinin. Decreasing the density of actin crosslinks led to decreased traction force exertion and a decrease in the difference in cell migration speed dependent on ECM rigidity. These findings shed light on the importance of alpha-actinin and actin crosslinking in cell mechanosensing and response to ECM rigidity.