TRIM56 inhibits M1 macrophage polarization and mitigates sepsis-induced acute lung injury via promoting STING ubiquitination-degradation.

Sepsis-induced acute lung injury (ALI) is a life-threatening clinical disorder with high mortality, and its pathogenesis is closely linked to excessive M1 macrophage polarization and overactivation of the STING signaling pathway. TRIM56, an E3 ubiquitin ligase, is known to participate in immune and inflammatory regulation; however, its specific role and underlying molecular mechanism in sepsis-induced ALI remain largely unclear. Here, we aimed to determine whether TRIM56 alleviates sepsis-induced ALI by inhibiting M1 macrophage polarization via promoting STING ubiquitination and proteasomal degradation. We conducted in vivo and in vitro experiments: LPS-induced ALI mouse models were established, and MH-S alveolar macrophage experiments were performed, including TRIM56 silencing, TRIM56 overexpression, and treatment with the proteasome inhibitor MG132. Lung injury was assessed using hematoxylin-eosin (HE) staining and measurement of the lung wet/dry weight ratio. The expression levels of TRIM56, STING, M1 macrophage polarization markers (F4/80+ iNOS+ cells and CD86), and pro-inflammatory cytokines (TNF-α and IL-6) were measured by western blot, RT-qPCR, immunofluorescence, and ELISA. The interaction and ubiquitination between TRIM56 and STING were verified via immunofluorescence co-localization, co-immunoprecipitation (Co-IP), and ubiquitination assays. In sepsis-induced ALI mouse models, the proportion of M1 macrophages was significantly increased, accompanied by marked downregulation of TRIM56 and upregulation of STING in alveolar macrophages. In vitro, TRIM56 silencing significantly elevated STING protein expression (without affecting its mRNA level) and promoted M1 macrophage polarization, whereas TRIM56 overexpression reduced STING protein expression and suppressed M1 polarization. Mechanistically, TRIM56 colocalized with and directly interacted with STING in the cytoplasm, thereby promoting STING ubiquitination and proteasomal degradation-an effect abrogated by MG132 treatment. In vivo, TRIM56 overexpression significantly alleviated lung injury, reduced M1 macrophage infiltration, and inhibited pro-inflammatory cytokine secretion by downregulating STING protein. In conclusion, TRIM56 inhibits M1 macrophage polarization by promoting STING ubiquitination and proteasomal degradation, thereby mitigating sepsis-induced ALI. The TRIM56-STING axis may serve as a novel and promising therapeutic target for sepsis- induced ALI.