Interstitial fluid flow induces myofibroblast differentiation and collagen alignment in vitro

TLDR

Fibroblast‑to‑myofibroblast differentiation, marked by α‑SMA expression, is essential for wound healing and fibrosis, and while TGF‑β1 from inflammatory cells drives this process, increased interstitial flow during inflammation may also contribute. Low‑level interstitial flow alone triggers fibroblast differentiation, collagen alignment, and proliferation via TGF‑β1 and α1β1 integrin signaling, and blocking either pathway abolishes these effects, indicating that fluid shear can drive fibrogenesis.

Abstract

The differentiation of fibroblasts to contractile myofibroblasts, which is characterized by de novo expression of α-smooth muscle actin (α-SMA), is crucial for wound healing and a hallmark of tissue scarring and fibrosis. These processes often follow inflammatory events, particularly in soft tissues such as skin, lung and liver. Although inflammatory cells and damaged epithelium can release transforming growth factor β1 (TGF-β1), which largely mediates myofibroblast differentiation, the biophysical environment of inflammation and tissue regeneration, namely increased interstitial flow owing to vessel hyperpermeability and/or angiogenesis, may also play a role. We demonstrate that low levels of interstitial (3D) flow induce fibroblast-to-myofibroblast differentiation as well as collagen alignment and fibroblast proliferation, all in the absence of exogenous mediators. These effects were associated with TGF-β1 induction, and could be eliminated with TGF-β1 blocking antibodies. Furthermore, α1β1 integrin was seen to play an important role in the specific response to flow, as its inhibition prevented fibroblast differentiation and subsequent collagen alignment but did not block their ability to contract the gel in a separate floating gel assay. This study suggests that the biophysical environment that often precedes fibrosis, such as swelling, increased microvascular permeability and increased lymphatic drainage – all which involve interstitial fluid flow – may itself play an important role in fibrogenesis.