Coordination between Intra- and Extracellular Forces Regulates Focal Adhesion Dynamics

Focal adhesions (FAs) are important mediators of cell substrate interactions. One of their key functions is the transmission of forces between the intracellular acto-myosin network and the substrate. However, the relationships between cell traction forces, FA architecture, and molecular forces within FAs are poorly understood. Here, by combining Forster resonance energy transfer (FRET)-based molecular force biosensors with micropillar-based traction force sensors and high-resolution fluorescence microscopy, we simultaneously map molecular tension across vinculin, a key protein in FAs, and traction forces at FAs. Our results reveal strong spatiotemporal correlations between vinculin tension and cell traction forces at FAs throughout a wide range of substrate stiffnesses. Furthermore, we find that molecular tension within individual FAs follows a biphasic distribution from the proximal (toward the cell nucleus) to distal end (toward the cell-edge). Using super-resolution imaging, we show that such a distribution relates to that of FA proteins. On the basis of our experimental data, we propose a model in which FA dynamics results from tension changes along the FAs.