Dysregulated Collagen Homeostasis by Matrix Stiffening and TGF-β1 in Fibroblasts from Idiopathic Pulmonary Fibrosis Patients: Role of FAK/Akt

TLDR

Idiopathic pulmonary fibrosis is an aggressive disease in which normal lung parenchyma is replaced by a stiff scar rich in activated fibroblasts and collagen‑I. The study aimed to determine how matrix stiffening and TGF‑β1 together regulate collagen homeostasis at the transcriptional level in normal and fibrotic fibroblasts. Fibroblasts from IPF patients and healthy donors were cultured on hydrogels of tunable elasticity, including 3D collagen‑I and 2D polyacrylamide gels, to model pre‑fibrotic and fibrotic stiffness. TGF‑β1 increased COL1A1 and decreased MMP1 mRNA in hydrogels of pre‑fibrotic or fibrotic rigidity, a response amplified in IPF fibroblasts and dependent on FAK/Akt activation, and FAK depletion abolished these effects, demonstrating that matrix stiffening and TGF‑β1 synergistically drive excessive collagen‑I deposition via the FAK/Akt pathway.

Abstract

Idiopathic pulmonary fibrosis (IPF) is an aggressive disease in which normal lung parenchyma is replaced by a stiff dysfunctional scar rich in activated fibroblasts and collagen-I. We examined how the mechanochemical pro-fibrotic microenvironment provided by matrix stiffening and TGF-β1 cooperates in the transcriptional control of collagen homeostasis in normal and fibrotic conditions. For this purpose we cultured fibroblasts from IPF patients or control donors on hydrogels with tunable elasticity, including 3D collagen-I gels and 2D polyacrylamide (PAA) gels. We found that TGF-β1 consistently increased COL1A1 while decreasing MMP1 mRNA levels in hydrogels exhibiting pre-fibrotic or fibrotic-like rigidities concomitantly with an enhanced activation of the FAK/Akt pathway, whereas FAK depletion was sufficient to abrogate these effects. We also demonstrate a synergy between matrix stiffening and TGF-β1 that was positive for COL1A1 and negative for MMP1. Remarkably, the COL1A1 expression upregulation elicited by TGF-β1 alone or synergistically with matrix stiffening were higher in IPF-fibroblasts compared to control fibroblasts in association with larger FAK and Akt activities in the former cells. These findings provide new insights on how matrix stiffening and TGF-β1 cooperate to elicit excessive collagen-I deposition in IPF, and support a major role of the FAK/Akt pathway in this cooperation.