Liver X Receptor Activation Promotes THP-1 Macrophage Inflammatory Cytokine MRNA Degradation

LXRs have anti-inflammatory properties. Whether LXRs play a role in post-transcriptional regulation of inflammatory cytokine expression is not clear. The regulation of m RNA stability plays an important role in post-transcriptional regulation of gene expression.AREs-mediated m RNA decay regulats the expression of many inflammatory mediators. Tristetraprolin(TTP) is an immediate early response gene that functions to destabilize m RNA of many cytokines. TTP exerts its action by binding to cis-acting elements that are ARE. To investigate whether the inhibition effect of LXRs activation on proinflammatory cytokine expression was related to their m RNA decay,we examined the physiological function of LXRs in posttranscriptional regulation of inflammatory cytokine m RNA expression in vitro.Methods:Human THP-1 monocytes were treated with phorbol 12-myristate 13-acetate(PMA) for 12 h to become THP-1 macrophages. THP-1 macrophages were pretreated with T0901317(10 μmol/L) for 6h, and then stimulated with LPS(10 ng/m L) for 6h. Protein was extracted and subjected to ELISA or Western-blotting analysis for TNF-α, IL-6, IL-1β, TTP. Cells were treated with different conditions followed by treatment of act D(5μg/m L) to stop the transcription. After the indicated time points, cytokines m RNA were isolated and quantified using RT-PCR. Remnant cytokine m RNA in percentage of the amount at the time point 0 of act D treatment was depicted. Cells were transfected with or without TTP si RNA for 18 h, and then TTP protein expression was measured by western blot.Protein and RNA were extracted and subjected to ELISA,Western-blotting or RT-PCR analysis for inflammatory cytokines.Result : ELISA and q RT-PCR results showed T0901317 reduce LPS-induced expression of several proinflammatory cytokines, including IL-1β, IL-6 and TNF-α. T0901317 treatment substantially increased the expression of TTP m RNA and protein.The results of q RT-PCR indicated that T0901317 reduced LPS-induced TNF-α, IL-6, IL-1β m RNA level,T0901317 reduces the m RNA levels of TNF-α, IL-6, IL-1β at the different time points after treatment of act D, suggesting T0901317 increased TNF-α, IL-6, IL-1β m RNA degradation.Treatment with si RNA for TTP significantly down-regulated T0901317 induced TTP protein expression in LPS-treated THP-1 macrophages,TTP si RNA abrogated the destabilization of LXRs activation on LPS-induced IL-1β, IL-6 and TNF-α m RNA in THP-1 macrophages. Conclusion:These results imply that LXRs activation suppresses inflammatory cytokine expression, at least partially, through promoting the m RNA destabilization.LXRs activation-mediated inflammatory cytokine m RNA decay in LPS-stimulated THP-1 macrophages is mediated by TTP. Our study deepen the understanding of the new molecular mechanisms of LXRs on inflammatory response, explore new ideas for multi-target,broad-spectrum anti-inflammatory approach to systemic inflammatory response syndrome and other acute and chronic inflammatory diseases therapy, provide new target for the development of anti-inflammatory drugs.