Mechanism of MDA5 in macrophages in SiO2-induced epithelial-mesenchymal transition

Objective To explore the mechanism of MDA5 derived from macrophages in SiO2-induced epithelial-mesenchymal transition (EMT).Methods First, a silicosis mouse model was established by intratracheal instillation of 50 μl of 50 mg/mL silica suspension. Subsequently, clustering analysis was performed to investigate the expression and enriched pathways of MDA5 in macrophages. Following this, THP-1 cells were treated with silica suspensions at concentrations of 0, 50, 100, 150, 200, and 250 μg/mL to detect the protein and mRNA levels of MDA5. Using siRNA to knock down the expression of MDA5 in THP-1 cells, and the the subsequent effects on the expression of inflammation-related factors, including TNF-α, IL-1β, IL-6, CCL2, and CCL3, were evaluated through western blot and qRT-PCR analyses. Ultimately, A549 cells were treated with conditioned media derived from THP-1 cells to investigate the impact of MDA5 knockdown on EMT in A549 cells.Results Single-cell RNA sequencing of mouse lung tissue revealed an elevated expression of MDA5 in macrophages exposed to silica, accompanied by an increased enrichment of MDA5-related pathway in these macrophages (P < 0.05). As the concentration of silica treatment increased, the expression of MDA5 in THP-1 cells also showed a corresponding increase (P < 0.05). Further research revealed that MDA5 expression was upregulated in the lung tissue of mice exposed to silica. Knocking down MDA5 expression in macrophages reduced the protein and mRNA levels of inflammation-related molecules (P < 0.01). Conditioned media derived from THP-1 cells treated with silica promoted EMT in A549 cells while knocking down MDA5 in THP-1 cells inhibited the above effects.Conclusion Exposure to silica upregulates the expression of MDA5 in macrophages both in vitro and in vivo, and this upregulation can mediate EMT in epithelial cells, thereby promoting the occurrence of pulmonary fibrosis.