Effect of Substrate Stiffness and Formin on Fibrillar Force Generation by Fibroblasts

Fibroblasts in connective tissues often interact with a fibrillar extra-cellular matrix (ECM) that restricts their shape along one-dimension (1D, along the fiber). At the same time, the fibroblast responds to and affects the mechanical nature of its microenvironment which consists of the inter-woven fibrillary ECM, other matrix components and cells. The determinants of force generation by fibroblasts, which is necessary to understand normal physiology and disease, is however unclear. In order to construct the 1D geometry of fibroblasts, we plated NIH 3T3 fibroblasts on micropatterned 1.5 μm-wide fibronectin lines on polyacrylamide gels with stiffness of 13 or 45 kPa. We used traction force microscopy to quantify the cellular traction force exerted and the associated strain energy stored in the substrate. We found that strain energy or maximum traction stress is not a function of cell length. Even though cell length depends on substrate stiffness, the strain energy and the maximum traction forces exerted were independent of substrate stiffness. Besides, we found that fibroblasts in a 1D morphology have prominent linear actin structures and inhibition of a family of actin nucleators (formin) significantly reduced linear actin level. Importantly, we found that the fibrillar force exerted by fibroblasts also strongly decreased, implicating formin in fibrillar fibroblast force exertion.https://digitalcommons.odu.edu/engineering_batten/1010/thumbnail.jp