Several mucins are implicated in idiopathic pulmonary fibrosis (IPF); however, there is no evidence regarding the role of MUC4 in the development of IPF. Here we demonstrated that MUC4 was overexpressed in IPF patients (n = 22) compared with healthy subjects (n = 21) and located in pulmonary arteries, bronchial epithelial cells, fibroblasts, and hyperplastic alveolar type II cells. Decreased expression of MUC4 using siRNA–MUC4 inhibited the mesenchymal/myofibroblast transformations of alveolar type II A549 cells and lung fibroblasts, as well as cell senescence and fibroblast proliferation induced by TGF-β1. The induction of the overexpression of MUC4 increased the effects of TGF-β1 on mesenchymal/myofibroblast transformations and cell senescence. MUC4 overexpression and siRNA–MUC4 gene silencing increased or decreased, respectively, the phosphorylation of TGFβRI and SMAD3, contributing to smad-binding element activation. Immunoprecipitation analysis and confocal immunofluorescence showed the formation of a protein complex between MUC4β/p-TGFβRI and p-SMAD3 in the cell membrane after TGF-β1 stimulation and in lung tissue from IPF patients. Bleomycin-induced lung fibrosis was reduced in mice transiently transfected with siRNA–MUC4. This study shows that MUC4 expression is enhanced in IPF and promotes fibrotic processes in collaboration with TGF-β1 canonical pathway that could be an attractive druggable target for human IPF.

几种粘蛋白与特发性肺纤维化 (IPF) 有关；然而，没有证据表明 MUC4 在 IPF 发展中的作用。在这里，我们证明了 MUC4 在 IPF 患者 ( n  = 22) 与健康受试者 ( n = 21)，位于肺动脉、支气管上皮细胞、成纤维细胞和增生性肺泡 II 型细胞中。使用 siRNA–MUC4 降低 MUC4 表达可抑制肺泡 II 型 A549 细胞和肺成纤维细胞的间充质/肌成纤维细胞转化，以及 TGF-β1 诱导的细胞衰老和成纤维细胞增殖。MUC4 过表达的诱导增加了 TGF-β1 对间充质/肌成纤维细胞转化和细胞衰老的影响。MUC4 过表达和 siRNA-MUC4 基因沉默分别增加或减少了 TGFβRI 和 SMAD3 的磷酸化，从而促进了 smad 结合元件的激活。免疫沉淀分析和共聚焦免疫荧光显示，在 TGF-β1 刺激后的细胞膜和 IPF 患者的肺组织中，MUC4β/p-TGFβRI 和 p-SMAD3 之间形成了蛋白质复合物。在用 siRNA–MUC4 瞬时转染的小鼠中，博来霉素诱导的肺纤维化减少。这项研究表明，MUC4 表达在 IPF 中增强，并与 TGF-β1 经典通路协作促进纤维化过程，这可能是人类 IPF 的一个有吸引力的药物靶点。