ObjectiveTo investigate the role of mammalian STE20-like kinase 1 (MST1) in sepsis-induced acute lung injury (ALI) and its molecular mechanisms in regulating the nuclear factor-erythroid 2 related factor 2 (Nrf2)/heme oxygenase 1(HO-1) antioxidant signaling pathway. MethodsA murine sepsis-induced ALI model was established by intraperitoneal injection of lipopolysaccharide (LPS, 5 mg/kg). Lung injury was assessed by hematoxylin-eosin (HE) staining, lung injury scoring, and bronchoalveolar lavage fluid (BALF) analysis. Mst1 knockout mice and RAW264.7 macrophages were used. Related proteins and inflammatory factors were detected by Western blot, qRT-PCR, immunofluorescence, and ELISA. The regulatory relationship of the Mst1-Nrf2/HO-1 signaling axis was verified using siRNA knockdown and overexpression techniques combined with Nrf2 inhibitor and activator treatments. ResultsAfter LPS treatment, mouse lung tissues showed typical ALI pathological changes, and Mst1 protein expression was upregulated in a time-dependent manner. Mst1 deficiency significantly alleviated lung injury and reduced protein concentration and inflammatory cell counts in BALF. In vitro experiments showed that Mst1 knockdown in RAW264.7 macrophages inhibited LPS-induced secretion of tumor necrosis factor-α, interleukin-6, and interleukin-1β. Mechanistic studies revealed that Mst1 promoted oxidative stress and inflammatory responses by inhibiting Nrf2 nuclear translocation and HO-1 expression. Nrf2 inhibitor partially reversed the protective effects of Mst1 knockdown, while the Nrf2 activator tBHQ significantly improved lung injury. ConclusionsMst1 promotes the development of sepsis-induced ALI through negative regulation of the Nrf2/HO-1 antioxidant signaling pathway. Mst1 may serve as a potential therapeutic target for sepsis-induced ALI.