[LCN2 knockout protects endothelial barrier function in mice with sepsis-induced acute lung injury by regulating the NF-κB signaling pathway].

OBJECTIVES

To investigate the protective effect of lipocalin-2 (LCN2) gene knockout against sepsis-induced acute lung injury (ALI) and vascular endothelial dysfunction in mice and the mediating role of the nuclear factor-κB (NF-κB) signaling pathway.

METHODS

Wild-type (WT) C57BL/6 mice receiving sham operation or cecal ligation and puncture (CLP) to induce sepsis were randomized into 3 subgroups for intraperitoneal injections of saline, PDTC, or Bay 11-7082 (n=10). Twenty LCN2 knockout (LCN2KO) mice were randomized for sham operation or CLP modeling. Pulmonary histopathological changes, lung wet-to-dry (W/D) ratio, lung index, Evans blue extravasation, and serum TNF-α and IL-6 levels in the mice were assessed. The colocalization of NF-κB, ICAM-1, and VCAM-1 with CD31 were analyzed using immunofluorescence staining, and endothelial cell apoptosis was examined with TUNEL/CD31 double staining. Western blotting and co-immunoprecipitation assay were performed to analyze the protein expressions of LCN2, p-P65/P65, ICAM-1, VCAM-1 and VE-cadherin and the interaction between LCN2 and P65.

RESULTS

The WT mice receiving CLP showed severe lung structural damage with obvious edema and inflammation. In contrast, both the LCN2KO mouse and PDTC-treated WT mouse models of CLP showed milder lung injury with lower W/D ratio, lung index, Evans blue leakage, serum TNF‑α and IL-6 levels and markedly reduced colocalization signals of NF-κB, ICAM-1, and VCAM-1 with CD31. CLP resulted in significantly increased expression levels of LCN2, p-P65/P65, ICAM-1, and VCAM-1, lowered VE-cadherin levels, and enhanced endothelial cell apoptosis, and all these changes were significantly ameliorated in LCN2KO mice and WT mice with NF‑κB inhibitor treatment. Co-immunoprecipitation results suggested the interaction between lung LCN2 and P65. Bay 11-7082 significantly reduced inflammatory cytokine production, downregulated p-P65 expression and its downstream adhesion molecules, and restored VE-cadherin expression.

CONCLUSIONS

LCN2 knockout alleviates sepsis-induced ALI and vascular endothelial dysfunction in mice by inhibiting NF-κB signaling.