Activation of WNT/β-Catenin Signaling in Pulmonary Fibroblasts by TGF-β1 Is Increased in Chronic Obstructive Pulmonary Disease

Background: Chronic obstructive pulmonary disease (COPD) is characterized by abnormal extracellular matrix (ECM) turnover. Recently, activation of the WNT/beta-catenin pathway has been associated with abnormal ECM turnover in various chronic diseases. We determined WNT-pathway gene expression in pulmonary fibroblasts of individuals with and without COPD and disentangled the role of beta-catenin in fibroblast phenotype and function. Methods: We assessed the expression of WNT-pathway genes and the functional role of beta-catenin, using MRC-5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD. Results: Pulmonary fibroblasts expressed mRNA of genes required for WNT signaling. Stimulation of fibroblasts with TGF-beta(1), a growth factor important in COPD pathogenesis, induced WNT-5B, FZD(8), DVL3 and beta-catenin mRNA expression. The induction of WNT-5B, FZD(6), FZD(8) and DVL3 mRNA by TGF-beta(1) was higher in fibroblasts of individuals with COPD than without COPD, whilst basal expression was similar. Accordingly, TGF-beta(1) activated beta-catenin signaling, as shown by an increase in transcriptionally active and total beta-catenin protein expression. Furthermore, TGF-beta(1) induced the expression of collagen1 alpha 1, alpha-sm-actin and fibronectin, which was attenuated by beta-catenin specific siRNA and by pharmacological inhibition of beta-catenin, whereas the TGF-beta(1)-induced expression of PAI-1 was not affected. The induction of transcriptionally active beta-catenin and subsequent fibronectin deposition induced by TGF-beta(1) were enhanced in pulmonary fibroblasts from individuals with COPD. Conclusions: beta-catenin signaling contributes to ECM production by pulmonary fibroblasts and contributes to myofibroblasts differentiation. WNT/beta-catenin pathway expression and activation by TGF-beta(1) is enhanced in pulmonary fibroblasts from individuals with COPD. This suggests an important role of the WNT/beta-catenin pathway in regulating fibroblast phenotype and function in COPD.