[Inhibition of the TGF-β/Smad3 signaling pathway by SB431542: A study of the intervention effect of SB431542 on silicotic fibrosis in rats].

Objective: To investigate the intervention effect of SB431542, which inhibits the TGF-β/Smad3 signaling pathway, on silicotic fibrosis in rats. Methods: A total of 40 specific pathogen-free Sprague-Dawley rats were divided into normal saline control group, model group, SB431542 inhibitor group, and SB431542 inhibitor control group using a random number table, with 10 rats in each group. All rats except those in the normal saline control group were given non-exposed single intratracheal instillation of free silicon dioxide dust suspension 1 mL (50 mg/mL) ; the rats in the SB431542 inhibitor group were given intraperitoneal injection of SB431542 (5 mg/kg) on days 7 and 30 after dust exposure, those in the SB431542 inhibitor control group were given intraperitoneal injection of SB431542 cosolvent (5 mg/kg) on days 7 and 30 after dust exposure, and those in the normal saline control group were given intratracheal instillation of an equal volume of normal saline (5 mg/kg). On day 60 after dust exposure, the paraffin-embedded section of the right upper lobe of lung was collected for HE staining; the left upper lobe of lung was collected to measure the mRNA levels of fibronectin (FN) , collagen type I (COL-I) , and collagen type III (COL-III) by quantitative real-time PCR; the right inferior lobe of lung was collected to measure the protein levels of FN, COL-I, COL-III, phosphorylated Smad3 (p-Smad3) , and Smad3. Results: Compared with the normal saline control group, the model group had nodules with various sizes in lung tissue, with rupture of some alveolar septa, emphysema changes, and pulmonary interstitial fibrosis, as well as significant increases in the mRNA expression of FN, COL-I, and COL-III and the protein expression of FN, COL-I, COL-III, p-Smad3, and Smad3 in lung tissue ( P <0.05) . Compared with the SB431542 inhibitor control group, the SB431542 inhibitor group had a relatively complete structure of lung tissue without marked nodules and with a small amount of exudate in alveolar space and the lumen of bronchioles, as well as significant reductions in the mRNA expression of FN, COL-I, and COL-III and the protein expression of FN, COL-I, COL-III, p-Smad3, and Smad3 in lung tissue ( P <0.05) . There were no significant differences in the mRNA expression of FN, COL-I, and COL-III and the protein expression of FN, COL-I, COL-III, p-Smad3, and Smad3 between the model group and the SB431542 inhibitor control group ( P >0.05) . Conclusion: SB431542 exerts an intervention effect on silicotic fibrosis by blocking the TGF-β/Smad3 signaling pathway and reducing the expression of the downstream fibrosis factors FN, COL-I, and COL-III.