NFAT5 Amplifies Antipathogen Responses by Enhancing Chromatin Accessibility, H3K27 Demethylation, and Transcription Factor Recruitment.

The ability of innate immune cells to respond to pathogen-associated molecular patterns across a wide range of intensities is fundamental to limit the spreading of infections. Studies on transcription responses to pathogen-activated TLRs have often used relatively high TLR ligand concentrations, and less is known about their regulation under mild stimulatory conditions. We had shown that the transcription factor NFAT5 facilitates expression of antipathogen genes under TLR stimulation conditions corresponding to low pathogen loads. In this study, we analyze how NFAT5 optimizes TLR-activated responses in mouse macrophages. We show that NFAT5 was required for effective recruitment of central effectors p65/NF-κB and c-Fos to specific proinflammatory target genes, such as Nos2, Il6, and Tnf in primary macrophages responding to low doses of the TLR4 ligand LPS. By contrast, NFAT5 was not required for p65/NF-κB recruitment in response to high LPS doses. Using the transposase-accessible chromatin with high-throughput sequencing assay, we show that NFAT5 facilitated chromatin accessibility mainly at promoter regions of multiple TLR4-responsive genes. Analysis of various histone marks that regulate gene expression in response to pathogens identified H3K27me3 demethylation as an early NFAT5-dependent mechanism that facilitates p65 recruitment to promoters of various TLR4-induced genes. Altogether, these results advance our understanding about specific mechanisms that optimize antipathogen responses to limit infections.