Lipoxin A4 Inhibits Lipopolysaccharide-induced Production of Inflammatory Cytokines in Keratinocytes by Up-regulating SOCS2 and Down-regulating TRAF6

Liopxin A4(LXA4) is considered to be a crucial modulator in the inflammatory responses. In the present study, we aimed to study the effect of LXA4 on the inflammatory cytokines production induced by lipopolysaccharide(LPS) and the possible mechanism in normal human epidermal keratinocytes(NHEKs). NHEKs were isolated and cultured. The expression of toll-like receptor 4(TLR4), LXA4 receptor(ALXR) and aryl hydrocarbon receptor(Ah R) in NHEKs was detected by reverse transcription polymerase chain reaction(RT-PCR). The m RNA and protein levels of tumor necrosis factor-alpha(TNF-α) and interleukin-1β(IL-1β) were determined in NHEKs stimulated by LPS(10 μg/m L) with or without preincubation with LXA4(100 nmol/L) for 30 min by real-time quantitative PCR(real-time q PCR) and enzyme-linked immunosorbent assay(ELISA), respectively. The expression levels of tumor necrosis factor receptor-associated factor 6(TRAF6) and suppressors of cytokine signaling 2(SOCS2) m RNAs and proteins, and nuclear translocation of NF-k B-p65 were measured by real-time q PCR and Western blotting, respectively. The results showed that NHEKs expressed TLR4, ALXR and Ah R. LXA4 significantly inhibited the m RNA and protein expression levels of TNF-α, IL-1β and TRAF6 induced by LPS in NHEKs, and LXA4 obviously increased the expression of SOCS2 at m RNA and protein levels. The nuclear NF-k B-p65 protein expression induced by LPS was inhibited after preincubation with LXA4 in NHEKs. It was concluded that LXA4 inhibits the LPS-induced production of TNF-α and IL-1β in NHEKs by up-regulating SOCS2 and down-regulating TRAF6.