Role of IRGM in acute lung injury: Inducing mitophagy and inactivating cGAS-STING signaling to improve lipopolysaccharide-induced alveolar epithelial barrier dysfunction

Acute lung injury (ALI) is a common disorder of the respiratory system with high mortality. Inducing mitophagy is generally considered to be an effective target for alleviating ALI. We aimed to elucidate the role of immunity related GTPase M (IRGM) in ALI by using a lipopolysaccharide (LPS)-induced alveolar epithelial cell model. Firstly, IRGM expression in A549 cells under LPS conditions was evaluated. Then, IRGM was upregulated and oxidative stress was evaluated by measuring intracellular reactive oxygen species (ROS) using 2′, 7′-Dichlorofluorescin diacetate (DCFH-DA) staining. The permeability of A549 cells was determined by detecting transepithelial electrical resistance (TEER) value and fluorescein isothiocyanate-dextran 4 (FITC-FD4) fluorescence. Proteins related to epithelial barrier, mitophagy and mitochondrial function were assessed. Further Mdivi-1 (an inhibitor of mitophagy) addition or cyclic GMP-AMP synthase (cGAS)- stimulator of interferon genes (STING) signaling overexpression was conducted to investigate the potential mechanism. Results suggested that IRGM was downregulated in LPS-treated A549 cells and IRGM upregulation alleviated LPS-induced oxidative stress, inflammation and barrier dysfunction in A549 cells. IRGM upregulation induced mitophagy and maintains mitochondrial function in LPS-treated A549 cells. Particularly, Mdivi-1 treatment or cGAS overexpression abrogated the impacts of IRGM upregulation on oxidative stress, inflammation and barrier dysfunction in LPS-treated A549 cells. Collectively, IRGM attenuates LPS-triggered alveolar epithelial cell damage by enhancing mitophagy to inactivate cGAS/STING signaling.