Muc1 bioactivation contributes to lung fibrosis

Resumen

Background Idiopathic pulmonary fibrosis (IPF) is a specific form of chronic, progressive fibrosing interstitial pneumonia of unknown cause. Recently, it has been proposed that IPF results from repeated episodes of injury to alveolar epithelial cells, which may be associated with a release of profibrotic mediators (such as transforming growth factor β1 (TGFβ1)) fostering uncontrolled fibroblast activation, cell transformations into mesenchymal like myofibroblasts and an overwhelming matrix accumulation in the lung interstitium, which destroys normal alveolar architecture and disrupts gas exchange. The median survival time from IPF diagnosis is 2–4 years and to date, despite extensive research on IPF, no pharmacologic therapies have definitively been shown to meaningfully improve IPF life expectancy. Mucin 1 (MUC1) is a transmembrane mucin whose overexpression in carcinomas potentiates intracellular signalling by MUC1 cytoplasmic tail (MUC1-CT) phosphorylation, bioactivation and interaction with several proteins implicated in different cellular processes linked to IPF disease. MUC1 extracellular domain contains the KL6 epitope domain, which serves as biomarker in IPF. However, there is no evidence on the role of MUC1 intracellular bioactivation in the development of pulmonary fibrosis. Objective To characterize MUC1 intracellular bioactivation in IPF. Methods and Results The expression of MUC1 cytoplasmic tail (CT) and its phosphorylated forms at Thr41 and Tyr46 were analysed by western blot and immunohistochemistry in healthy and IPF lung tissue. Lung fibroblasts and alveolar type II epithelial cells were stimulated with TGFβ1 or the pro-fibrotic factor galectin 3 to evaluate the role of MUC1 on the epithelial and fibroblast to mesenchymal transition, proliferation and senescence in vitro. A model of bleomycin-induced lung fibrosis was used in MUC1-Knockout (KO) and Wild type mice. The expression of MUC1-CT and its phosphorylated forms at Thr41 and Tyr46 were increased in lung tissue from IPF patients and bleomycin-induced fibrotic mice. TGFβ1 increased MUC1-CT Thr41 and Tyr46 phosphorylations, thus increasing the expression of the active pro-fibrotic factor β-catenin to form a nuclear complex of phospho-Smad3/MUC1-CT and MUC1-CT/β-catenin. The nuclear complex activated alveolar epithelial type II and fibroblast to myofibroblast transitions as well as cell senescence and fibroblast proliferation. The antifibrotic pirfenidone as well as the inhibition of MUC1-CT nuclear translocation reduced cellular transformations, senescence and proliferation in vitro. The pro-fibrotic galectin 3 directly activated MUC1-CT and served as a bridge between TGFβ receptors and MUC1-C domain, indicating a TGFβ1 dependent and independent bioactivation of MUC1-CT. Lung fibrosis development was attenuated in MUC1-KO bleomycin-induced lung fibrosis mice. Conclusions MUC1-CT bioactivation is enhanced in IPF and may lead to future strategies as a druggable target for IPF.