13 Lipocalin 2 exerts protective activity by alleviating inflammatory responses

Abstract

Abstract Lipocalin 2 (Lcn2) is an essential component of the innate immune system and exerts significant immunomodulatory effects in vitro. The aim of current study was to investigate the expression profile of Lcn2 during inflammatory process and explore the role of Lcn2 in the anti-inflammatory responses. Western blot, real-time quantitative PCR, immunofluorescence (IF) and enzyme-linked immunosorbent assay (ELISA) were employed. Firstly, we evaluated the temporospatial expression of Lcn2 of mice after inflammatory stimuli by lipopolysaccharides (LPS). In vivo, LPS induced both mRNA and protein levels of Lcn2 significantly (P < 0.01) in liver, jejunum and ileum. Lcn2 exhibited a continuous increase by 8 h and peaked by 24 h post challenges. Secondly, we challenged Lcn2-deficient (Lcn2-/-) mice and wild-type (WT) mice with peripheral LPS and determined effects on inflammation. In contrast to WT mice, Lcn2-/- mice showed distinct inflammatory injury in liver, jejunum, ileum and spleen with significantly elevated pro-inflammatory cytokines interleukin-6 (IL-6) and interleukin-1b (IL-1b) and decreased anti-inflammatory cytokine interleukin-10 (IL-10). Thirdly, we isolated bone marrow-derived macrophages (BMDM) from Lcn2-/- mice and WT mice to evaluate their functions. After LPS challenge, Lcn2-/- BMDM showed aggravated inflammatory reaction as pro-inflammatory factors tumour necrosis factor-α (TNF-α), IL-6, IL-1b and inducible nitric oxide synthase (iNOS) increased (P < 0.05) while anti-inflammatory cytokines IL-10, transforming growth factor β1 (TGF-β1) and arginase-1(Arg-1) decreased significantly (P < 0.05) compared with WT BMDM. This phenomenon could be relieved when adding recombinant Lcn2 (P < 0.05). The exogenous addition of Lcn2 on mice RAW264.7 macrophages stimulated by LPS also conformed this point. These findings demonstrated that Lcn2 served as a potent protective factor in response to systemic inflammation, and elevated Lcn2 expression during inflammatory conditions was presumed to play an effective role in alleviating inflammatory responses.