IFN-? selectively suppresses a subset of TLR4-activated genes and enhancers to potentiate M1-like macrophage polarization [ChIP-seq II]

Complete activation of macrophage proinflammatory and antimicrobial phenotype is promoted by combined action of IFN-g and LPS. Synergistic activation of canonical inflammatory NF-kB target genes by IFN-g and LPS is well appreciated, but less is known about whether IFN-g negatively regulates components of the LPS response, and how this affects polarization. A combined transcriptomic and epigenomic approach revealed that IFN-g selectively abrogates LPS-induced feedback and select metabolic pathways by suppressing TLR4-mediated activation of gene enhancers. In contrast to superinduction of inflammatory genes via enhancers that harbor IRF sequences and bind STAT1, IFN-g-mediated repression targeted enhancers with STAT sequences that bound STAT3. TLR4-activated IFN-g-suppressed enhancers comprised two subsets distinguished by differential regulation of histone acetylation and recruitment of STAT3, CDK8 and cohesin, and were functionally inactivated by IFN-g. These findings reveal that IFN-g suppresses feedback inhibitory and metabolic components of the TLR response to achieve full macrophage activation and provide insights into mechanisms by which IFN-g selectively inhibits TLR4-induced transcription. Overall design: ChIP-seq analysis of epigenomic changes in human macrophages that were cultured with or without IFN-? and then stimulated with LPS