USP7-mediated stabilization of CXCL3 aggravates inflammation in models of acute lung injury.

BACKGROUND: CXCL3 is involved in the pathogenesis of asthmatic lungs; however, its specific function in sepsis-induced acute lung injury (ALI) remains unclear. This study aimed to elucidate the modulatory function of CXCL3 and its relationship to the deubiquitinating enzyme USP7 in lung inflammation. As model systems, we used lipopolysaccharide (LPS) stimulation of human lung microvascular endothelial cells (HLMVECs) and macrophages in vitro and a mouse model of sepsis-induced ALI. METHODS: Cell behavior was assessed using Cell Counting Kit-8, 5-Ethynyl-2'-deoxyuridine assays, flow cytometry, biochemical, and Western blotting assays. STAT3-binding sites on CXCL3 were predicted via the JASPAR database. Interactions between CXCL3, STAT3, and USP7 were confirmed through chromatin immunoprecipitation, dual-luciferase, and co-immunoprecipitation assays. RESULTS: CXCL3 expression was substantially increased in ALI. CXCL3 knockdown could improve LPS-induced apoptosis, inflammatory responses, and oxidative stress, and inhibited the M1 polarization of THP-1 cells. STAT3 activated CXCL3 transcription, while USP7 modulated CXCL3 through deubiquitination. USP7 silencing alleviated LPS-induced HLMVEC injury and inhibited M1 macrophage polarization through the regulation of CXCL3. USP7 depletion inactivated the NF-κB pathway by regulating CXCL3. Furthermore, CXCL3 knockdown ameliorated cecal ligation and puncture (CLP)-induced lung injury in vivo. CONCLUSIONS: CXCL3 knockdown ameliorated sepsis-induced ALI. In in-vitro models, USP7 modulated CXCL3 through deubiquitination, and USP7 silencing alleviated LPS-induced HLMVEC injury and inhibited M1 macrophage polarization via the regulation of CXCL3. Although the direct role of USP7 in the in-vivo CLP model was not experimentally demonstrated, our in-vitro findings suggest a potential mechanism by which CXCL3, in relation to USP7, contributes to the pathogenesis of sepsis-induced ALI.