Cyclic mechanical stress downregulates endothelin-1 and its responsive genes independently of TGFβ1 in dermal fibroblasts.

Mechanical forces are highly variable ranging from the ubiquitous gravity force to compression, fluid shear, torsion, tension and other forms. Mechanical forces act on cells and modulate their biological responses by regulating gene transcription, enzyme and growth factor activity. In soft connective tissues, formation of myofibroblasts strictly requires a mechanically loaded environment in addition to local transforming growth factor (TGF)-β activity, which itself can be modulated by the mechanical status of the environment. The aim of this study was to monitor the adaptive responses of primary dermal fibroblasts towards cyclic mechanical stress under conditions of high force to better understand the regulation of gene expression in normal skin and mechanisms of gene regulation in mechanically altered fibrotic skin. Primary murine dermal fibroblasts were exposed to equi-biaxial tensile strain. Cyclic mechanical tension was applied at a frequency of 0.1 Hz (6× /min) for 24 h with a maximal increase in surface area of 15%. This treatment resulted in downregulation of alpha smooth muscle actin (αSMA) and connective tissue growth factor (CTGF) but not of TGFβ1 expression. Cyclic strain also strongly reduced endothelin-1 (ET-1) expression and supplementing strained cultures with exogenous ET-1 rescued αSMA and CTGF levels. Of note, no biologically significant levels of TGFβ1 activity were detected in strained cultures. We provide evidence for a novel, TGFβ1-independent mechanism regulating ET-1 expression in dermal fibroblasts by biomechanical forces. Modulation of ET-1-dependent activities regulates downstream fibrotic marker genes; this pathway might therefore provide an approach to attenuate myofibroblast differentiation.