USP18 improves mitochondrial homeostasis by stabilizing PKM2 and promoting M2 polarization in macrophages to relieve acute lung injury.

Abstract

BACKGROUND: Acute lung injury (ALI) has high incidence and mortality rates among patients. Studies have shown that USP18 is widely involved in the immunomodulatory process and that macrophage polarization plays a key role in the progression of ALI. This study aimed to explore the potential molecular mechanism through which USP18 promotes M2 macrophage polarization and alleviates ALI. METHODS: RAW264.7 cell injury and ALI mouse animal models were established by LPS induction. Lung tissue injury was evaluated by HE staining. Protein expression was evaluated by Western blotting, immunofluorescence and ELISA. Mitochondrial function was evaluated using JC-1 staining and ROS and ATP assays. RESULTS: USP18 is highly expressed in the lung tissues of ALI model mice. Overexpression of USP18 significantly alleviated pathological injury to lung tissue in mice with LPS-induced ALI; reduced MPO activity, the number of inflammatory cells and the protein content in BALF; and decreased the levels of the M1 markers iNOS, CD80, and CD86 and the proinflammatory factors IL-1β, IL-6, and TNF-α. Moreover, the expression of the M2 markers Arg1, CD206, and CD163 and the anti-inflammatory factor IL-10 increased, thereby inhibiting the M1 polarization of macrophages induced by LPS. Furthermore, USP18 markedly increased mitochondrial ATP levels and transmembrane potential, reduced ROS levels, and alleviated mitochondrial dysfunction in macrophages. Further studies have shown that USP18 stabilizes the expression of PKM2 through deubiquitination, while knockdown of PKM2 weakens the ability of USP18 to improve mitochondrial function and inhibit LPS-induced M1 polarization in macrophages. CONCLUSION: USP18 stabilizes the expression of PKM2 via deubiquitination, thereby enhancing mitochondrial homeostasis and promoting M2 macrophage polarization to alleviate ALI.