The influence of low levels of fluid flow on fibroblast behaviour.

Fibroblasts are a type of cell which forms the structural framework of the connective tissue and are key players of wound closure, fibrosis and cancer. These cells experience mechanical perturbations due to matrix remodelling and interstitial fluid movement. Chemical signals from the tissue microenvironment such as Transforming growth factor β1 (TGF-β1) promote differentiation of fibroblasts to a myofibroblastic phenotype marked by enhanced expression of α-smooth muscle actin (α-SMA) rich stress fibres. However most of the evidence for this has been derived in static cultures which do not fully recapitulate the mechanically dynamic environment in vivo. The response of primary human fibroblasts to physiological levels of fluid movement and chemical perturbations from TGF-β1 is examined in this study. Findings show that fluid flow induced widespread changes in gene expression compared to static cultures and up-regulated genes such as α-SMA and Collagen 1A1. Surprisingly the combination of flow and exogenous TGF-β1 resulted in reduced myofibroblast differentiation. Myofibroblastic differentiation under flow was partially inhibited by follistatin-288 and blocked by TGF-β1 supplementation. This was associated with caveolin-mediated internalisation of TGF-β receptor type II. These findings suggest that fluid flow modulates fibroblast response to pro-differentiation signals such as TGF-β1. We propose that this may be a novel mechanism by which mechanical forces buffer responses to chemical signals in vivo, maintaining a context-specific fibroblast phenotype.