Peroxisome Proliferator-activated Receptor γ Negatively Regulates IFN-β Production in Toll-like Receptor (TLR) 3-and TLR4-stimulated Macrophages by Preventing Interferon Regulatory Factor 3 Binding to the IFN-β Promoter

Toll-like receptors 3 and 4 utilize adaptor TRIF to activate interferon regulatory factor 3 (IRF3), resulting in IFN-beta production to mediate anti-viral and bacterial infection. Peroxisome proliferator-activated receptor (PPAR)-gamma is a ligand-activated transcription factor expressed in various immune cells and acts as a transcriptional repressor to inhibit the transcription of many proinflammatory cytokines. But, the function of PPAR-gamma in TLR3- and -4-mediated IFN-beta production is not well elucidated. Here, we have analyzed the effect of the PPAR-gamma agonists on IFN-beta production in peritoneal primary macrophages in response to LPS and poly(I:C). PPAR-gamma agonists inhibited LPS and poly(I:C)-induced IFN-beta transcription and secretion. siRNA knockdown of PPAR-gamma expression and transfection of PPAR-gamma expression plasmid demonstrated that PPAR-gamma agonist inhibits IFN-beta production in a PPAR-gamma-dependent manner. The ability of the PPAR-gamma agonist to inhibit IFN-beta production was confirmed in vivo as mice treated with troglitazone exhibited decreased levels of IFN-beta upon LPS and poly(I:C) challenge. Chromatin immunoprecipitation (CHIP) assay and electrophoretic mobility shift assay (EMSA) demonstrated that troglitazone treatment impaired IRF3 binding to the IFN-beta promoter. Furthermore, troglitazone could inhibit LPS and poly(I:C)-induced STAT1 phosphorylation and subsequent ISRE activation. These results demonstrate that PPAR-gamma negatively regulates IFN-beta production in TLR3- and 4-stimulated macrophages by preventing IRF3 binding to the IFN-beta promoter.