EED in the Polycomb Repressive Complex 2 Epigenetically Regulates Responses in Lipopolysaccharide Tolerized Macrophages

To avoid exaggerated inflammation and injury, host cells adapt to become hypo-responsive or “tolerance” in response to successive exposure to stimuli. Such tolerized response is a part of innate immune memory which is mainly regulated via epigenetics changes and metabolic reprograming. Polycomb repressive complex 2 (PRC2) mediates the transcriptional repression by catalyzing histone H3 lysine 27 trimethylation (H3K27me3) but little is known about the roles of PRC2 in tolerant macrophages. We examined the impact of PRC2 components, EED and Ezh2, on lipopolysaccharide (LPS)-induced tolerant macrophages. In Eed KO macrophages, not only the significant reduction in H3K27me3, but also the augmentation of an active histone mark, H3K27Ac. Upon EED deletion but not Ezh2, macrophages exhibited attenuated pro-inflammatory cytokines productions (TNF-a and IL-6) in LPS-tolerant cells. In addition, LPS tolerant Eed KO macrophages exhibited low glycolytic activity rather than its littermate wild-type control. RNA-Seq analyses revealed that most of differentially expressed genes are involved in oxidative phosphorylation and TGF-ß signaling. Alteration of H3K27me3 and H3K27ac in the regulatory regions of some of these genes were validated. These results indicated that PRC2 via EED epigenetically suppresses these genes in response to LPS re-exposure and lacking PRC2 activity results in hypo-responsive to LPS re-stimulation. Therefore, we provide strong evidences that PRC2 via EED mediates LPS tolerance in macrophages by epigenetically suppressing proinflammatory responses with the link to dysregulated metabolic pathway. Overall design: LPS-induced tolerance in EED deficient BMDMs