Inhibition of macrophage migration inhibitory factor attenuates bleomycin-induced murine pulmonary fibrosis via the MAPK pathway

BACKGROUND: Idiopathic Pulmonary Fibrosis (IPF) is a chronic progressive disease marked by excessive extracellular matrix deposition and deteriorating lung function. Although macrophage migration inhibitory factor (MIF) has been implicated in pulmonary fibrosis, the downstream mechanisms-particularly whether MIF drives fibrosis through its receptor CD74-remain insufficiently understood. This study investigated whether MIF/CD74 signaling promotes fibroblast activation through specific downstream pathways that regulate proliferation and matrix production. METHODS: Single-cell RNA sequencing and ELISA were used to characterize MIF-CD74 interactions and circulating MIF levels in IPF patients. Bleomycin-induced fibrosis models were established using C57BL/6J mice, Mif⁻/⁻ mice, and the MIF inhibitor 4-IPP. Macrophage-fibroblast co-culture systems were treated with bleomycin, 4-IPP, or CD74 shRNA. Lung injury, fibrosis, and signaling activation were assessed by histology, qRT-PCR, Western blotting, and functional assays. RESULTS: scRNA-seq identified MIF-CD74 as a dominant macrophage-fibroblast signaling axis in fibrotic lungs, and serum MIF levels were elevated in IPF patients. In mice, bleomycin markedly increased MIF and CD74 expression and activated MAPK signaling. Genetic deletion or pharmacologic inhibition of MIF attenuated collagen deposition, improved lung architecture, and reduced profibrotic and inflammatory signaling. In vitro, MIF promoted fibroblast proliferation, migration, and matrix synthesis, whereas CD74 knockdown or MIF inhibition significantly attenuated fibroblast profibrotic responses. CONCLUSIONS: MIF promotes pulmonary fibrosis by activating CD74-dependent MAPK signaling in fibroblasts, enhancing their proliferation and extracellular matrix production. Targeting the MIF/CD74 axis reduces tissue remodeling and represents a promising therapeutic strategy for IPF.