Background Long-term exposure to free silica particles will lead to fibrosis of lung tissue, and abnormal expression of microRNA (miRNA) may affect the occurrence and process of fibrosis.

Objective To observed possible intervention effect of miR-204-3p overexpression adenovirus on silicosis fibrosis induced by silica dust using a silicosis rat model via non-exposed intratracheal instillation.

Methods Forty SD rats were randomly divided into four groups: control group, silicosis model group, miRNA-NC group, and miR-204-3p intervention group. Under ether anesthesia, rats in the silicosis model group, miRNA-NC group, and miR-204-3p intervention group were injected with 1 mL (50 mg·mL⁻¹) of free silica dust suspension into the trachea, while the control group was injected with the same volume of normal saline. After 30 d of dust exposure, the miR-204-3p intervention group was injected with rno-mir-204 adenovirus vector to overexpress miR-204-3p, and the miRNA-NC group was given empty virus vector. After 30 d of normal feeding, the animals were sacrificed by chloral hydrate anesthesia, and the lung tissue was taken for subsequent experiments. The relative expression level of miR-204-3p in lung tissue of rats in each group was detected by real-time fluorescence quantitative PCR (RT-qPCR). HE staining, Masson staining, and Sirius red staining were used for pathological observation. Immunohistochemistry was used to detect the expression of Fibronectin and Collagen I in lung tissue of rats in each group. RT-qPCR was used to detect the relative gene expression levels of fibrosis markers Fibronectin, Vimentin, Collagen I, and Collagen III in lung tissue of rats in each group. Western blot was used to detect the protein expression levels of fibrosis markers Fibronectin, Vimentin, Collagen I, and Collagen III in lung tissue of rats in each group.

Results The anatomical features of lung tissue in the control group were pink lung tissue with soft texture and smooth surface, while those in the silicosis model were grayish white tissue with hard texture and scars and grayish white silicon nodules on the surface. Compared with the silicosis model group, the color of lung tissue in the miR-204-3p intervention group became ruddy, the surface was smooth, and the texture became soft. The staining results showed that the alveolar wall of the control group was thin, there were a small number of capillaries in the alveoli, and the alveolar structure was clear and complete. In the silicosis model group, the alveolar wall became thicker, the pulmonary septum was partially broken, the alveolar structure was defective, and a large amount of collagen fibers were deposited. The alveolar structure of the miR-204-3p intervention group was relatively clear and there was a small amount of collagen fiber deposition. RT-qPCR results showed that compared with the control group, the relative expression levels of miR-204-3p in lung tissue of the silicosis model group and the miRNA-NC group were decreased (P<0.05), and the relative expression level of miR-204-3p in lung tissue of the miR-204-3p intervention group was increased (P＜0.05). The results of immunohistochemistry showed that compared with the control group, the expression levels of Fibronectin and Collagen I in lung tissue of the silicosis model group were increased (P＜0.05). Compared with the silicosis model group, the relative expression levels of Fibronectin and Collagen I in lung tissue of the rats in the miR-204-3p intervention group were significantly decreased (P<0.05). The results of RT-qPCR and Western blot showed that compared with the control group, the relative protein and gene expression levels of fibrosis factors Fibronectin, Vimentin, Collagen I, and Collagen III in lung tissue of the silicosis model group increased (P＜0.05). Compared with the silicosis model group, the relative gene and protein expression levels of fibrosis factors Fibronectin, Vimentin, Collagen I, and Collagen III in lung tissue of rats in the miR-204-3p intervention group were decreased (P＜0.05).

Conclusion Silica dust can cause lung fibrosis in rats, and overexpression of miR-204-3P in vivo can reduce silicosis fibrosis in rats caused by silica dust.