IL-23 amplifies the epithelial-mesenchymal transition of mechanically conditioned alveolar epithelial cells in RA-ILD through mTOR/S6 signaling.

Epithelial-mesenchymal transition (EMT) creates an environment facilitating fibrosis following alveolar epithelial cell injury. IL-23 has important roles in chronic autoimmune conditions like rheumatoid arthritis (RA), but its role in the interstitial lung disease that affects RA patients is unclear. This study aimed to determine the pro-fibrogenic role of IL-23 on somatic alveolar type I (ATI) epithelial cells. Primary ATI cells were isolated from rats and cultured on plastic dishes for 1-3 weeks. After prolonged culture (≥14 days) on rigid culture dishes, primary ATI cells gradually acquired a mesenchymal phenotype, identified by decreased expression of caveolin-1, and reorganization of F-actin cytoskeleton, indicating the initiation of EMT by matrix stiffness. To determine how IL-23 promotes EMT in vitro, transitioning ATI cells, cultured on a stiff substrate for ≥14 days were stimulated with IL-23. The EMT phenotype was significantly enhanced by IL-23 which upregulated α-SMA, collagen I/III protein, and decreased caveolin-1. Furthermore, IL-23 significantly promoted cell invasion as well as apoptotic resistance on transitioning ATI cells. Mechanistically, IL-23 induced EMT was mTOR/S6 signaling dependent and reversible by rapamycin. Transcriptional sequencing analysis of human lung fibrosis biopsy tissue revealed key roles for IL-23 in RA-ILD. This result was further validated by significantly upregulated IL-23 expression at the mRNA level in RA-ILD lung sections. Notably, transitioning ATI epithelial cells were abundantly detected in RA-ILD tissue. Taken together, these data support a role for IL-23 in the pathogenesis of RA lung fibrosis by promoting EMT in alveolar epithelial cells through mTOR/S6 signaling.