[Lung fibrosis and changes in autophagy-related proteins in rats exposed to silica dust].

Objective: To explore the changes in the autophagy marker microtubule-associated protein 1 light chain 3 (LC3) and yeast autophagy-related gene 6 (Beclin1) in rat lungs exposed to free silica (SiO(2)) dust for different periods. Methods: A total of 72 male specific pathogen-free Wistar rats were randomly divided into solvent control group and SiO(2) model group. The SiO(2) model group received one-time non-exposed intratracheal instillation of suspension of SiO(2) particles to establish a model of silicosis. The solvent control group received an equal amount of saline. Six rats each were sacrificed at 1, 7, 14, 21, 28, and 60 days after model establishment. The pathological changes and fibrosis of rat lungs at different time points were evaluated by H&E staining and Masson staining, respectively. Enzyme-linked immunosorbent assay (ELISA) was used to determine the levels of transforming growth factor-ß (TGF-ß) , interleukin-1 (IL-1) , and tumor necrosis factor-α (TNF-α) in lung tissue homogenate. Western blot was used to determine the relative expression levels of LC3 and Beclin1 in the lung tissue. Results: The results of H&E staining showed that the model group had continuous inflammation in the lung tissue from day 1 to day 60, and the inflammatory scores were significantly higher in the model group than in the control group (P<0.05) . The results of Masson staining showed that rats in the model group had a small amount of collagen fibers in the lung tissue on day 14 and a large amount of collagen fibers on day 60. The fibrosis score was significantly higher in the model group than in the control group (P<0.05) . No collagen fibrosis was observed in the lung tissue in the control group. The results of ELISA showed that the model group had significantly higher levels of IL-1, TNF-α, and TGF-ß in lung tissue homogenate than the control group at each time point after exposure (P<0.05) . The results of Western blot showed that the model group had decreased expression of Beclin1 protein in the lung tissue on days 7, 14, 21, 28, and 60, which was significantly higher than that of the control group (P<0.05) . The model group also had a decreased ratio of LC3II/LC3I on days 1, 7, 14, 21, 28, and 60, which were significantly higher than that of the control group (P<0.05) . Conclusion: In the rat model of silicosis induced by free SiO(2) dust, the expression levels of autophagy-related proteins, LC3 and Beclin1, are correlated with different stages of silicosis. In the early stage of silicosis, the lung tissue has inflammation, substantially increased ratio of LC3II/LC3I and expression of Beclin1, and active autophagy. With the progression of silicosis, the ratio of LC3II/LC3I and expression level of Beclin1 gradually decrease and autophagy becomes weak.