Macrophage Inflammatory Protein-2 in High Mobility Group Box 1 Secretion of Macrophage Cells Exposed to Lipopolysaccharide

Background/aims: Macrophage inflammatory protein-2 (MIP-2), a type of leukocyte chemokine, is primarily produced by macrophages, and levels increase significantly in early inflammation. However, the precise biological functions and mechanisms of MIP-2 in the development of inflammation remain unclear. The purposes of the present study were to investigate the role of MIP-2 in inflammation induced by lipopolysaccharide (LPS) in vitro and to determine the possibility of blocking the high mobility group box 1 (HMGB1) signalling pathway via MIP-2 inhibition.

Methods: Macrophage cells (RAW264.7, U937 and THP-1 cells) were divided into control and treatments groups. Expression levels of interleukin-6 (IL-6), interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α), HMGB1, chemokine (C-C motif) ligand-2 (Ccl-2), Toll-like receptor-4 (TLR-4), inducible nitric oxide synthase (iNOS), phosphorylated MAPKs (p38, ERKs, JNKs), PI3K/Akts, JAKs/STAT3, IκB, and cytoplasmic and nuclear NF-κB p65 in RAW264.7 cells were detected by qRT-PCR, enzyme-linked immunosorbent assay (ELISA) or western blot assays.

Results: mip-2 siRNA and an anti-MIP-2 antibody significantly reduced the expression levels of Ccl-2, TLR-4, iNOS, IL-6, IL-1β, HMGB1, and TNF-α in RAW264.7 cells exposed to LPS (P<0.01). Additionally, mRNA expression levels of HMGB1 and TLR-4 in cells treated with LPS+mip-2 siRNA were significantly lower than those in cells treated with LPS alone (P<0.01 or P<0.05). The MIP-2 antibody significantly suppressed activation of p38-MAPK, p-STAT3, and p-Akts and translocation of NF-κB p65 from the cytoplasm to the nucleus in RAW264.7 exposed to LPS (P<0.01 or P<0.05).

Conclusion: mip-2 siRNA and the MIP-2 antibody can reduce the inflammatory effects induced by LPS in macrophage cells. The mechanisms may occur through down-regulation of p38-MAPK, STAT3 and Akts phosphorylation and translocation of NF-κB p65. MIP-2 plays an important role in inflammation induced by LPS.