Abstract
BackgroundChronic obstructive pulmonary disease (COPD) is characterized by abnormal extracellular matrix (ECM) turnover. Recently, activation of the WNT/β-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 β-catenin in fibroblast phenotype and function.MethodsWe assessed the expression of WNT-pathway genes and the functional role of β-catenin, using MRC-5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD.ResultsPulmonary fibroblasts expressed mRNA of genes required for WNT signaling. Stimulation of fibroblasts with TGF-β1, a growth factor important in COPD pathogenesis, induced WNT-5B, FZD8, DVL3 and β-catenin mRNA expression. The induction of WNT-5B, FZD6, FZD8 and DVL3 mRNA by TGF-β1 was higher in fibroblasts of individuals with COPD than without COPD, whilst basal expression was similar. Accordingly, TGF-β1 activated β-catenin signaling, as shown by an increase in transcriptionally active and total β-catenin protein expression. Furthermore, TGF-β1 induced the expression of collagen1α1, α-sm-actin and fibronectin, which was attenuated by β-catenin specific siRNA and by pharmacological inhibition of β-catenin, whereas the TGF-β1-induced expression of PAI-1 was not affected. The induction of transcriptionally active β-catenin and subsequent fibronectin deposition induced by TGF-β1 were enhanced in pulmonary fibroblasts from individuals with COPD.Conclusionsβ-catenin signaling contributes to ECM production by pulmonary fibroblasts and contributes to myofibroblasts differentiation. WNT/β-catenin pathway expression and activation by TGF-β1 is enhanced in pulmonary fibroblasts from individuals with COPD. This suggests an important role of the WNT/β-catenin pathway in regulating fibroblast phenotype and function in COPD.
Highlights
Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation, which is associated with an abnormal inflammatory response of the lungs to noxious particles or gases
The WNTligands WNT-5A, WNT-5B and WNT-16, the Frizzled (FZD) receptors FZD2, FZD6 and FZD8 as well as the intracellular signaling protein dishevelled (DVL3) and the key-effector of canonical WNT signaling, b-catenin, were abundantly expressed. This subset of specific WNT pathway genes was selected for further studies based on their abundant expression at baseline, on previous findings indicating the regulation of these genes by TGF-b1 in airway smooth muscle, and based on recent literature indicating the involvement of the selected WNT ligands, FZD receptors and intracellular signaling molecules in cellular processes relevant for fibroblasts function [35,36,37]
A role for additional WNT pathway genes in fibroblast function can, not be ruled out. To investigate if these genes were highly expressed in primary human lung fibroblasts, we performed qRT-PCR analysis of these WNT pathway genes in fibroblasts of individuals without COPD and compared them to the expression in MRC-5 fibroblasts, which produced similar results
Summary
Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation, which is associated with an abnormal inflammatory response of the lungs to noxious particles or gases. Aberrant extracellular matrix (ECM) turnover contributes to both airway remodeling and pulmonary emphysema. In the peripheral lung with pulmonary emphysema, there is inadequate tissue repair and associated damage, which is perhaps due to fibroblast dysfunction [10,11] This discrepancy may be explained by insufficient activation of fibroblast in regions affected by emphysema to compensate for the tissue destruction by proteases. Extrinsic and intrinsic dysregulation of fibroblast function in COPD along with phenotypically distinct fibroblast populations in the airways and parenchyma, may contribute to the development of both small airway fibrosis and emphysema [16,17]. Activation of the WNT/b-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 b-catenin in fibroblast phenotype and function
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