A Polycomb Group Protein EED Epigenetically Regulates Responses in Lipopolysaccharide Tolerized Macrophages via Metabolic Flux and TGF-/Runx3 Axis

To avoid exaggerated inflammation and injury, innate immune cells adapt to become hypo-responsive or “tolerance” in response to successive exposure to stimuli, which is a part of innate immune memory. Polycomb repressive complex 2 (PRC2) mediates the transcriptional repression by catalyzing histone H3 lysine 27 trimethylation (H3K27me3) but little is known about its roles in tolerant macrophages. We examined the impact of deletion of the PRC2 component, EED on lipopolysaccharide (LPS)-induced tolerant macrophages. In Eed KO macrophages, significant reduction in global H3K27me3 and increased global active histone mark, H3K27ac was observed. Eed KO macrophages exhibited dampened pro-inflammatory cytokine productions (TNF-α and IL-6) while increased non-tolerizeable genes upon LPS tolerance. In addition, LPS tolerized Eed KO macrophages exhibited lower glycolytic activity than its wild-type control. RNA-Seq analyses revealed that the hallmarks of hypoxia, TGF-β, and Wnt/β-catenin signaling were enriched in LPS tolerized Eed KO macrophages. Among the upregulated genes, EED was found to be associated with the Runx3 promoter. Silencing Runx3 in Eed KO macrophages partially rescued the dampened pro-inflammatory response during LPS tolerance. Enrichment of H3K27me3 was decreased in genes that are upregulated in Eed KO LPS tolerance macrophages. Taken together, our results provided mechanistic insight into how the PRC2 via EED regulates LPS tolerance in macrophages via TGF-/Runx3 axis by epigenetically silencing genes that play a central role during LPS tolerance.