LAUSR

Tensional homeostasis is widely recognized to exist at the length scales of organs and tissues, but the cellular length scale mechanism for tension regulation is not known. In this study, we explored whether tensional homeostasis emerges from the behavior of the individual focal adhesion (FA), which is the subcellular structure that transmits cell stress to the surrounding extracellular matrix. Past studies have suggested that cell contractility builds up until a certain displacement is achieved, and we thus hypothesized that tensional homeostasis may require a threshold level of substrate displacement. Micropattern traction microscopy was used to study a wide range of FA traction forces generated by bovine vascular smooth muscle cells and bovine aortic endothelial cells cultured on substrates of stiffness of 3.6, 6.7, 13.6, and 30 kPa. The most striking feature of FA dynamics observed here is that the substrate displacement resulting from FA traction forces is a unifying feature that determines FA tensional stability. Beyond approximately 1 μm of substrate displacement, FAs, regardless of cell type or substrate stiffness, exhibit a precipitous drop in temporal fluctuations of traction forces. These findings lead us to the conclusion that traction force dynamics collectively determine whether cells or cell ensembles develop tensional homeostasis, and this insight is necessary to fully understand how matrix stiffness impacts cellular behavior in healthy conditions and, more important, in pathological conditions such as cancer or vascular aging, where environmental stiffness is altered.