Myofibroblast contraction activates latent TGF-β1 from the extracellular matrix

TLDR

Mechanical stress together with active TGF‑β1 is required to transform fibroblasts into contractile myofibroblasts that drive tissue contractures in fibrotic disease. The study proposes that integrin‑mediated myofibroblast contraction activates TGF‑β1, serving as a checkpoint that limits autocrine myofibroblast generation on stiffened ECM during fibrosis. Cultured myofibroblasts under tunable tension show that their contraction directly activates latent TGF‑β1 stored in the extracellular matrix. Contraction releases active TGF‑β1 from the ECM, an effect blocked by integrin antagonists or reduced matrix compliance, independent of proteases, and ECM stretching by stress fibers immediately activates latent TGF‑β1, resulting in higher Smad2/3 signaling in stressed wounds.

Abstract

The conjunctive presence of mechanical stress and active transforming growth factor beta1 (TGF-beta1) is essential to convert fibroblasts into contractile myofibroblasts, which cause tissue contractures in fibrotic diseases. Using cultured myofibroblasts and conditions that permit tension modulation on the extracellular matrix (ECM), we establish that myofibroblast contraction functions as a mechanism to directly activate TGF-beta1 from self-generated stores in the ECM. Contraction of myofibroblasts and myofibroblast cytoskeletons prepared with Triton X-100 releases active TGF-beta1 from the ECM. This process is inhibited either by antagonizing integrins or reducing ECM compliance and is independent from protease activity. Stretching myofibroblast-derived ECM in the presence of mechanically apposing stress fibers immediately activates latent TGF-beta1. In myofibroblast-populated wounds, activation of the downstream targets of TGF-beta1 signaling Smad2/3 is higher in stressed compared to relaxed tissues despite similar levels of total TGF-beta1 and its receptor. We propose activation of TGF-beta1 via integrin-mediated myofibroblast contraction as a potential checkpoint in the progression of fibrosis, restricting autocrine generation of myofibroblasts to a stiffened ECM.