The Transcription Factor STAT6 Mediates Direct Repression of Inflammatory Enhancers and Limits Activation of Alternatively Polarized Macrophages

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The molecular basis of signal-dependent transcriptional activation has been extensively studied in macrophage polarization, but our understanding remains limited regarding the molecular determinants of repression. Here we show that IL-4-activated STAT6 transcription factor is required for the direct transcriptional repression of a large number of genes during in vitro and in vivo alternative macrophage polarization. Repression results in decreased lineage-determining transcription factor, p300, and RNA polymerase II binding followed by reduced enhancer RNA expression, H3K27 acetylation, and chromatin accessibility. The repressor function of STAT6 is HDAC3 dependent on a subset of IL-4-repressed genes. In addition, STAT6-repressed enhancers show extensive overlap with the NF-κB p65 cistrome and exhibit decreased responsiveness to lipopolysaccharide after IL-4 stimulus on a subset of genes. As a consequence, macrophages exhibit diminished inflammasome activation, decreased IL-1β production, and pyroptosis. Thus, the IL-4-STAT6 signaling pathway establishes an alternative polarization-specific epigenenomic signature resulting in dampened macrophage responsiveness to inflammatory stimuli.

The molecular bases of repressive transcriptional mechanisms contributing to macrophage polarization are not well understood. Czimmerer et al. show that in alternatively polarized macrophages, IL-4-activated STAT6 represses a large set of enhancers modulating the transcriptional program. STAT6-repressed enhancers are characterized by reduced chromatin accessibility, eRNA expression, LDTF, and p300 binding. IL-4-STAT6-mediated repression limits the inflammatory responsiveness including inflammasome activation, IL-1β production, and pyroptosis. Thus, the IL4-STAT6 pathway establishes an epigenomic signature to selectively repress the macrophage inflammation program.

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