Mechanism of osteoclast stimulatory transmembrane protein promoting silicosis fibrosis by inducing ferroptosis

Abstract

BackgroundOsteoclast stimulatory transmembrane protein (OC-STAMP) is involved in silicosis fibrosis induced by silicon oxide (SiO2) exposure. Its role in silicosis fibrosis by inducing ferroptosis of alveolar type II epithelial cells and its related mechanism remain unclear. ObjectiveTo explore the effect and possible mechanism of OC-STAMP on ferroptosis of alveolar type II epithelial cells and silicosis fibrosis in rats under SiO2 exposure. MethodsTwenty male Wistar rats of SPF grade were randomly divided into two groups: control (Sham) group and SiO2 group, 15 rats in each group. Rats in the SiO2 group were given 1 mL of 50 mg·L−1 SiO2 suspension at one time through the non-exposed intratracheal instillation method to establish an animal model of silicosis, and rats in the Sham group were give 1 mL of 0.9% sodium chloride solution in the same way. Rats were sacrificed after 8 weeks. Samples of lung tissue were fixed in glutaraldehyde or paraformaldehyde for observing ultrastructure of mitochondria by transmission electron microscopy; HE, Masson, VG, and Prussian blue were used to observe changes in lung tissue structure and iron deposition. The expression level of OC-STAMP and the degree of lung fibrosis were evaluated by immunohistochemistry and immunofluorescence. The expression level of OC-STAMP in rat lung tissue was detected and the transfection effect of OC-STAMP was verified by real-time fluorescence quantitative polymerase chain reaction (RT-PCR). Overexpression (OCS group) and inhibition expression (SI-OC group) models were constructed by OC-STAMP plasmid and OC-STAMP small interfering RNA (siRNA) transfection to cultured MLE-12 cells, respectively. The relative expression levels of glutathione peroxidase 4 (GPX4), solute carrier family 7 member 11 (SLC7A11), and other proteins in lung tissue and MLE-12 were detected by Western blotting. ResultsThe results of HE, Masson, and VG staining showed that the silicosis modeling was successful after 8 weeks of SiO2 exposure. The immunofluorescence results showed that OC-STAMP and ATP binding cassette subfamily A member 3 (ABCA3) co-localized in alveolar type II epithelium. The immunohistochemical results showed that the levels of OC-STAMP and collagen I in the SiO2 group were significantly higher than those in the Sham group (P<0.01). The RT-PCR results showed that the OC-STAMP mRNA in the lung tissue of the SiO2 group was significantly higher than that of the Sham group (P<0.01). The Prussian blue staining in the lung tissue of the SiO2 group showed positive brownish-yellow particles. Compared with the Sham group which showed normal mitochondrial structure, the mitochondrial structure was generally swollen and the mitochondrial cristae dissolved and disappeared in the SiO2 group by transmission electron microscope observation. The Western blotting results showed that the expression levels of SLC7A11 and GPX4 both decreased in the lung tissue of the SiO2 group (P<0.05, P<0.01), and the expression level of Vimentin increased (P<0.01). In the transfected MLE-12 cells, compared with the Sham group, the expression levels of SLC7A11 and GPX4 in the OCS group were significantly reduced (P<0.05, P<0.01). ConclusionOC-STAMP may affect the expression of proteins related to ferroptosis, and promote lung fibrosis induced by SiO2 exposure.

Keywords

• silicosis
• osteoclast stimulatory transmembrane protein
• ferroptosis
• fibrosis