Myofibroblasts exhibit enhanced fibronectin assembly that is intrinsic to their contractile phenotype [Cell Biology]

January 27th, 2015 by Torr, E. E., Ngam, C. R., Bernau, K., Tomasini-Johansson, B., Acton, B., Sandbo, N.

Myofibroblasts have increased expression of contractile proteins and display augmented contractility. It is not known if the augmented contractile gene expression characterizing the myofibroblast phenotype impacts its intrinsic ability to assemble fibronectin (FN) and extracellular matrix (ECM). In this study, we investigated whether myofibroblasts displayed increased rates of FN fibril assembly when compared to their undifferentiated counterparts. Freshly plated myofibroblasts assemble exogenous FN (488-FN) into a fibrillar matrix more rapidly than fibroblasts that have not undergone myofibroblast differentiation. The augmented rate of FN matrix formation by myofibroblasts was dependent on intact Rho/ROCK and myosin signals, inasmuch as treatment with Y27632 or blebbistatin attenuated 488-FN assembly. Inhibiting contractile gene expression by pharmacologic disruption of the transcription factors, Megakaryoblastic Leukemia-1/Serum Response Factor during myofibroblast differentiation resulted in decreased contractile force generation and attenuated 488-FN incorporation, although not FN expression. Furthermore, disruption of the MKL1/SRF target gene, smooth muscle α-actin (α-SMA) via siRNA knockdown resulted in attenuation of 488-FN assembly. In conclusion, this study demonstrates a linkage between increased contractile gene expression, most importantly α-SMA, and the intrinsic capacity of myofibroblasts to assemble exogenous FN into fibrillar extracellular matrix.