Functions of key genes involved in TGF-β/Smad signaling pathway in progression of pulmonary fibrosis

Abstract

BackgroundAlthough transforming growth factor-β (TGF-β)/Smad signaling pathway is important in regulating the occurrence and development of pulmonary fibrosis, the pathogenesis of pulmonary fibrosis remains elusive. ObjectiveTo explore the functions of genes associated with TGF-β/Smad signaling pathway in the progression of pulmonary fibrosis. MethodsA NIH-3T3 fibroblast model induced by TGF-β1 was established. The experiment samples were divided into a control group and a TGF-β1 treatment group. The control group was exposed to normal saline, while the TGF-β1 treatment group was exposed to 10 ng·mL−1 TGF-β1 for 12 h. The RNAs of the two groups were extracted, sequenced, and analyzed by bioinformatics methods to identify seven key genes in TGF-β pathway, including Dcn, Smad3, Smad7, Fbn1, Thbs1, TGF-β1, and TGF-β3. The gene expression levels of five markers [Collagen1α1, Collagen1α2, α-smooth muscle actin (α-SMA), TGF-β1, and TGF-β3] and the seven key genes were detected by quantitative real-time PCR (qRT-PCR). The proteins of the two groups were extracted. The important marker protein expression levels of Smad3, the phosphorylation of Smad3 (P-Smad3), and α-SMA were detected by Western blotting. At the same time, 30 healthy SPF-grade C57BL/6 mice were randomly divided into three groups, with 10 mice in each group: a control group, a SiO2 inhalation exposure group for 28 d (10 mice), and a SiO2 inhalation exposure group for 56 d (10 mice). The mice in the two treatment groups were exposed to a natural SiO2 environment for 4 h per day with a 10-min pause for breathing fresh air at 2 h intervals. The lung tissues of the mice were taken after execution. The changes of pulmonary fibrosis were detected by Masson staining, and mRNAs and proteins were extracted to detect the expression of the above key genes and proteins. ResultsThe expression levels of the five marker genes Collagen1α1, Collagen1α2, α-SMA, TGF-β1, and TGF-β3 were significantly increased in the TGF-β1-induced NIH-3T3 fibroblasts than those in the control group (P < 0.01); the expression levels of P-Smad3 and α-SMA proteins increased significantly (P < 0.01); the expression results of the seven key genes screened in the TGF pathway were that Dcn and Smad3 were obviously down-regulated (P < 0.01), and Smad7, Fbn1, Thbs1, TGF-β1, and TGF-β3 were obviously up-regulated (P < 0.01). The changes in gene expression levels of the transcriptome sequencing showed the same trend. The results of Masson staining showed that the content of collagen fibers in the lung tissues also increased in the SiO2 inhalation exposure groups over time. In the mouse experiment, five marker genes were obviously up-regulated compared with the control group (P < 0.01); no obvious change was found in the expression of Smad3 protein, and the expression levels of P-Smad3 and α-SMA were obviously higher in the SiO2 exposure groups than those in the control group (P < 0.01); the expression levels of Dcn and Smad3 showed a down-regulated trend, while the expression levels of Smad7, Fbn1, Thbs1, TGF-β1, and TGF-β3 showed an up-regulated trend with the increase of SiO2 inhalation exposure days (P < 0.01). The expression levels of the above five marker genes, three important marker proteins, and seven key genes were consistent with the expression trends of TGF-β1-induced NIH-3T3 fibroblasts. ConclusionThe expression levels of pulmonary fibrosis-related marker genes and proteins change significantly in TGF-β1-induced fibroblast cells, and the lung tissues of mice under natural SiO2 inhalation exposure has obvious fibrosis characteristics. Seven genes (Dcn, Smad3, Smad7, Fbn1, Thbs1, TGF-β1, and TGF-β3) may be involved in the regulation of pulmonary fibrosis by the TGF-β/Smad signaling pathway.

Keywords

• pulmonary fibrosis
• transforming growth factor-β
• tgf-β/smad signaling pathway
• nih-3t3cells
• transcriptome sequencing.