SiO₂ exposure triggers NOX1/ROS-dependent epithelial necroptosis and drives Th17 cell activation to initiate pneumonia in mice.

SiO₂ (silicon dioxide) particles have been classified as one of the most hazardous environmental pollutants for the respiratory system, yet their hazards are often overlooked. The abnormal activation of Th17 helper T cells that produce interleukin-17 (IL-17) is associated with the development of multiple inflammatory diseases. However, it is unclear whether SiO₂ exposure-induced pneumonia is attributed to the recruitment and differentiation of pathogenic Th17 cells, and its specific mechanism. Thus, in this study, we exposed C57BL/6 J mice to 50 nm, 300 nm, and 1 μm SiO₂ particles, and employed Transwell methods to establish co-culture models of lung epithelial cells with Th17 cells. Based on RNA-seq analysis, we demonstrated that the activation of pro-inflammatory Th17 cells relied on NOX1 (NADPH oxidase 1)-mediated reactive oxygen species (ROS) burst in damaged epithelial cells, in a size-dependent manner. NOX1/ROS stress evoked the sustained elevation of calcium ions (Ca2+) in epithelial cells, activated phosphorylated Ca2+/calmodulin-dependent protein kinase II (p-CaMKII)/phosphorylated AMP-activated protein kinase (p-AMPK) pathways, leading to necroptosis, as well as increased expression of damage-associated molecular patterns (DAMPs), chemokines and pro-inflammatory cytokines. The enrichment of these signaling factors promoted the activation of Th17 cells, which exacerbated epithelial cell death, contributing to a vicious cycle of inflammation. Treating MLE12 cells with siNOX1 (small interfering RNA targeting NOX1), NAC (N-acetylcysteine) or KN-93 (a CaMKII inhibitor) to alleviate NOX1/ROS stress suppressed the elevation of transcription factors retinoic acid receptor-related orphan receptor gamma t (RORγt) and signal transducer and activator of transcription 3 (STAT3) in Th17 cells, and their activation. Additionally, notably, SiO₂ exposure-triggered NOX1/ROS stress was equally closely associated with Th17 cell activation. Collectively, this research reveals that under conditions of SiO₂ exposure, NOX1-mediated oxidative stress acts as a hub inducing necroptosis of lung epithelial cells to enhance Th17 cell recruitment and differentiation, thereby initiating pneumonia. This research establishes a scientific basis for evaluating pneumonia caused by environmental pollutant SiO₂ and provides reference for comparative medicine.