Involvement of let-7c in alveolar macrophage M2 polarization in coal mine dust-induced epithelial-mesenchymal transition in rat lung tissue

BackgroundCoal workers' pneumoconiosis (CWP) is a serious occupational lung disease and one of the prescript occupational diseases in China. Epithelial-mesenchymal transition (EMT) is involved in the diffuse fibrosis of lung tissue of pneumoconiosis patients, and its mechanism may be related to the polarization of macrophages regulated by let-7c.ObjectiveTo investigate the effect of let-7c on the regulation of macrophage polarization in EMT in rats induced by coal dust exposure with different content of free SiO2.MethodsSD rats were randomly divided into a control group, a 5% SiO2 group, a 30% SiO2 group, and a 99.9% SiO2 group, with 16 rats in each group. The rats in each group were tracheally titrated with 100 μL of 20 mg·mL−1 suspension (5% SiO2, 30% SiO2, and 99.9% SiO2) or normal saline, respectively. Alveolar lavage fluid was collected at the ends of the 1st month and the 3rd month. The relative expression levels of M1 or M2 markers, CD86 or CD206, in alveolar macrophages (AMs) were detected by immunofluorescence. The inflammation and fibrosis of lung tissue were observed by hematoxylin-eosin (HE) staining and Masson staining. The expression levels of transforming growth factor-β1 (TGF-β1), E-cadherin, and vimentin were detected by Western blotting. The expression levels of let-7c and c/EBP-δ genes were detected by real-time fluorescence quantitative PCR.ResultsThe HE and Masson staining results showed that compared with the control group, the degree of pulmonary fibrosis in the 5% SiO2 group, the 30% SiO2 group, and the 99.9% SiO2 group gradually increased with the increase of dust exposure time. Compared with the control group, the expressions of CD86 and CD206 in the 5% SiO2 group, the 30% SiO2 group, and the 99.9% SiO2 group gradually increased at the end of the 1st month (F=330.904, 146.801, P