Effect of TGF-β receptor blocker SB431542 on expression of related transcription factors in rats with silicosis induced by SiO₂ dust

Background  The pathogenesis of silicosis is not clear, and the relevant treatment is limited. A recognized mechanism is epithelial-mesenchymal transition (EMT) induced by transforming growth factor-β (TGF-β). SB431542, as a specific receptor blocker of TGF-β, can block TGF-β/Smad3 signaling pathway and downstream EMT pathway in many diseases. However, its role in silicosis induced by SiO₂ dust has not been elucidated.

Objective  This experiment investigates the effect of SB431542, a specific receptor blocker of TGF-β, on the expression of transcription factors in rats with silicotic fibrosis induced by SiO₂ dust.

Methods  Forty male SD rats were randomly divided into four groups:a normal saline control group, a silicosis model group, a SB431542 inhibitor group, and an inhibitor control group. Non-exposed intratracheal instillation was used to inject 1 mL (50 g·L^-1) of free SiO₂ dust suspension into the trachea of rats in all groups except the first group, and the same amount of normal saline (5 mg·kg^-1) was injected into the normal saline control group. On the 7th and 30th days after the dust exposure, the SB431542 inhibitor group was injected intraperitoneally with SB431542 (5 mg·kg^-1), and the inhibitor control group was injected intraperitoneally with cosolvent of SB431542 (5 mg·kg^-1). After 60 d of the dust exposure, the lung tissue samples were isolated, and the upper lobe of the right lung was stained with HE and Masson to observe the pathological changes under microscope. The mRNA expression levels of neuronal cadherin (N-cadherin), zinc finger transcription factor 1 (Snail1), E-box binding zinc finger protein 1 (ZEB1), and twisted gene (Twist) in the upper lobe of the left lung samples were detected by quantitative real-time PCR, and the protein expression levels of N-cadherin, Snail1, ZEB1, and Twist in the lower lobe of the right lung samples were detected by Western blotting.

Results  The pathological results showed that compared with the normal saline control group, there were obvious gray-white silicotic nodules, emphysema-like changes, partial rupture of the pulmonary septum, and fibrosis in the pulmonary interstitium in the lung tissues of the silicosis model group; compared with the inhibitor control group, no obvious silicotic nodules were found in the lung tissues of the SB431542 inhibitor group, and the alveolar structure was basically intact. Compared with the normal saline control group, the gene and protein expression levels of N-cadherin and transcription factors (Snail1, ZEB1, and Twist) in the silicosis model group were increased:the relative mRNA expression levels were 6.88, 4.71, 3.41, and 3.80 times higher respectively, and the relative protein expression levels were 1.48, 1.94, 1.49, and 1.45 times higher respectively (P < 0.05). Compared with the inhibitor control group, the gene and protein expression levels of N-cadherin and transcription factors (Snail1, ZEB1, and Twist) were decreased in the SB431542 inhibitor group (P < 0.05). Compared with the inhibitor control group, there were no significant difference in the expression levels of genes or proteins in the silicosis model group (P>0.05).

Conclusion  SB431542 can down-regulate the transcription factors and inhibit the EMT induced by the transcription factors by blocking the binding of TGF-β to the receptor, which can potentially inhibit the progression of silicosis.