Silica induces pulmonary fibrosis by upregulating ROS-driven Mitophagy via the PINK1/LC3B/MFN2 Signaling pathway in rats

Abstract

Previous studies from our group have demonstrated that silica-induced reactive oxygen species (ROS) cause mitochondrial damage, potentially triggering mitophagy. However, the precise mechanisms linking silica-induced ROS to mitophagy and its downstream effects remain unclear. Here, a rat silicosis model was established by a single intratracheal instillation of a SiO₂ suspension, followed by daily intravenous administration of N-acetylcysteine (NAC; 20, 40, or 80 mg/kg) or phosphate-buffered saline for 40 days. Oxidative stress was evaluated by measuring serum MDA levels and SOD activity. Lung samples were collected for histopathological analysis, and mitochondrial damage and mitophagy were observed by transmission electron microscopy. Furthermore, the levels of NF-κB p65, PINK1, LC3B, MFN2, IL-1β, TGF-β1, CTGF, cytochrome c (Cyt c), and COX IV were also evaluated. The results indicated that, compared with controls, rats in the silicosis model group exhibited heightened oxidative stress (elevated MDA and reduced SOD) accompanied by severe pulmonary inflammation and fibrosis. The expression of NF-κB p65, PINK1, LC3B, and MFN2 was significantly upregulated at both the transcriptional and protein levels, with prominent mitophagy evident in lung tissues. Moreover, marked mitochondrial dysfunction occurred, manifested as a remarkable decrease in Cyt c and COX IV levels. Additionally, the levels of IL-1β, TGF-β1, and CTGF were markedly elevated in silica-exposed lung tissues. NAC administration reversed all these alterations in a dose-dependent manner. Collectively, these findings demonstrate that silica-induced ROS activate the NF-κB p65-mediated PINK1/LC3B/MFN2 signaling pathway, thereby inducing excessive mitophagy and impairing cellular function, which promotes silicosis progression by upregulating IL-1β, TGF-β1, and CTGF.