Exosome miR‐6990‐5p from MMP14 ^high Macrophage Promotes Fibrosis Through Th17 Cell Differentiation in Hypersensitivity Pneumonia

Th17 cells contribute to pulmonary fibrosis, but the mechanisms driving their differentiation remain unclear. Using single-cell RNA sequencing (scRNA-seq) and a decision tree model, we identify IL17A as a key marker in mice exposed to Saccharopolyspora rectivirgula antigen (SR-Ag). Trajectory and T cell receptor (TCR) analyses reveal IL17A⁺ CD4 T cells as terminally differentiated and clonally expanded. Blocking IL17A reduces SR-Ag-induced lung inflammation and fibrosis. Exosomal miR-6990-5p from MMP14-overexpressing macrophages promotes Th17 differentiation and fibroblast-to-myofibroblast transition (FMT) in vitro. It directly targets STAT1, as confirmed by luciferase assays. Co-immunoprecipitation (Co-IP) and docking analyses show STAT1 interacts with ROR-γt and RUNX1. STAT1 knockdown upregulates ROR-γt, IL17A, and RUNX1 in co-cultures with naïve CD4 T cells. In vivo, miR-6990-5p exacerbates fibrotic hypersensitivity pneumonitis (FHP) in SR-Ag-exposed mice. These findings indicate that miR-6990-5p induces Th17 cell differentiation through the STAT1/RUNX1/ROR-γt/IL17A pathway, contributing to FMT and fibrosis progression. This highlights miR-6990-5p as a potential therapeutic target for FHP.