Suppression of Macrophage Migration Inhibitory Factor Attenuates Pulmonary Fibrosis by Regulating Macrophage-Fibroblast Interactions via AKT, AMPK, and ERK Pathways

<bold>Background and aim:</bold> The microenvironment that intricately regulates the interactions among lung cells, particularly in relation to the macrophage migration inhibitory factor (MIF)/CD74 pathway in idiopathic pulmonary fibrosis (IPF) , an irreversible and life-threatening lung disease, is not yet fully understood. This study aimed to elucidate the macrophage-fibroblast interactions in IPF by modulating the MIF/CD74 signaling pathway. <bold>Methods and results:</bold> Single-cell sequencing revealed abnormal activation of the MIF/CD74 signaling pathway in the lung tissues of the IPF patients, underscoring its role as a key mediator in the interactions between macrophages and fibroblasts. Both the protein and mRNA expression of MIF and CD74 were elevated in vivo and in vitro. Treatment with 4-iodo-6-phenylpyrimidine (4-IPP), an inhibitor of MIF, during the late phase (10 to 21 days after BLM) or throughout the entire phase (1 to 21 days after BLM) or in MIF^−/− mice demonstrated attenuation of BLM-induced lung fibrosis. Exogenous 4-IPP, MIF^−/− down-regulation, or CD74-shRNA Lentivirus-mediated inhibition of CD74 expression resulted in the enhanced fibroblasts apoptosis and autophagy, and the reduced fibroblasts migration and proliferation in a macrophage-fibroblast co-culture system through the AKT, AMPK, or ERK1/2 pathways respectively. <bold>Conclusions:</bold> The MIF/CD74 signaling pathway was activated in IPF patients, and BLM-induced mice model and macrophages in vitro as well. Inhibiting MIF can mitigate lung fibrosis by mediating macrophage-fibroblast interactions through the AKT, AMPK, and ERK pathways.