Two Distinct Actin Networks Mediate Traction Oscillations to Confer Focal Adhesion Mechanosensing

Focus adhesive spot (FA) is an integrin-based transmembrane component that connects cells to their extracellular matrix (ECM). They are mechanical sensors that use actin cytoskeletal mediated towing to sense ECM hardness. Interestingly, the FA itself is a dynamic structure and responds to the mechanical force to respond to its growth. It is not clear how cells will manage the plasticity of the FA structure and associated traction and accurately sense the ECM stiffness. Surprisingly, FA traction vibrates in time and space, controlling the mechanical mechanical sensing of ECM stiffness. However, the exact method and cause of vibration of FA traction is unknown. We developed an FA growth model integrating the contribution of branched actin network and stress fiber (SF). We use this model in combination with experimental tests to show that it promotes the proximal growth of retrograde flux FA of the bifurcated actin network and contributes to the traction peak near the distal tip of the FA. The traction gradient occurring in the growing FA promotes the formation of SF near the proximal end of the FA. SF mediated actomyosin contractility further stabilizes FA and produces a second traction peak near the FA center. The negative feedback of Hormin-mediated SF stretch and agonistic contraction resulted in central traction peak oscillation. This is the basis of the observed FA traction vibration and it is important to broaden the ECM stiffness range where FA can accurately adapt to the occurrence of traction force. The growth and maturation of FA via the actin cytoskeleton thus reaches the climax with FA's traction oscillation to promote efficient mechanical sensing of FA

Schematic diagrams of adhesions (fibrous adhesions, focal adhesions and focal complexes) and related actin filaments (parallel bundles, branching nets, dorsal and ventral stressed fibers and lateral arcs). This schematic emphasizes the polarization characteristics of adhesion and filament. In the active cell, the focal complex and the branching actin network are located at the front edge of the cell and the dorsal fiber is located behind the leading edge. There is stickiness. And the transverse arc is arranged parallel to the leading edge. It is noteworthy that excessive transformation into ventral stressed fibers and fibrosis is an inhibitory effect on cell migration and polarization two dimensional migration.

Focus adhesive spot (FA) is an integrin-based transmembrane component that connects cells to their extracellular matrix (ECM). They are mechanical sensors that use actin cytoskeletal mediated towing to sense ECM hardness. Interestingly, the FA itself is a dynamic structure and responds to the mechanical force to respond to its growth. It is not clear how cells will manage the plasticity of the FA structure and associated traction and accurately sense the ECM stiffness. Surprisingly, FA traction vibrates in time and space, controlling the mechanical mechanical sensing of ECM stiffness. However, the exact method and cause of vibration of FA traction is unknown. We developed an FA growth model integrating the contribution of branched actin network and stress fiber (SF). The traction gradient occurring in the growing FA is preferred for the formation of SF near the proximal end of the FA.