Epigenetic changes in gut macrophages in health and disease
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A major feature of intestinal macrophages in the normal gut is inflammatory anergy, a state of tolerance essential for intestinal homeostasis, changes in which lead to inflammatory bowel disease (IBD). Intestinal macrophages undergo a specific process of differentiation. Under homeostatic conditions, cytokines in the local environment drive functional differentiation of newly recruited monocytes into noninflammatory intestinal macrophage. This process is associated with downregulation of proinflammatory cytokines. Growing evidence supports the idea that epigenetic changes contribute to macrophage reprogramming, and lead to tailored gene expression in response to gut environmental factors. However, current knowledge on how chromatin modification drives genes expression in human intestinal macrophages is still limited. This project aimed to define the relationship between chromatin modification (histone methylation) and the repression of inflammatory genes in intestinal macrophages isolated from mucosa of control subjects and IBD patients. It was of particular interest to understand if the anergic state of macrophages in normal gut is associated with repressive marks. Also in IBD, if there are any differences in epigenetic modifications between resident and infiltrating macrophages. Finally, if by blocking histone methylation, it is possible to prevent/reduce TNFα production by macrophages from IBD mucosa. TNF-α is an inflammatory cytokine that plays a critical role in innate and adaptive immune responses and its dysregulation has been implicated in the pathology of IBD. Considering its central role in IBD pathology, the TNFA gene was selected and different repressive and permissive histone modifications were investigated. Silencing marks H3K27me3, H3K9me3 and H3K9me1, as well as activating marks H3K4me3, H3K4me1 and also RNAPII were selected and analysed using chromatin immunoprecipitation (ChIP) assays. Based on data collected, it was speculated that a break of anergic phenotype in IBD macrophages might be associated with changes in level of silencing marks. Macrophages isolated from mucosa of CD patients showed decreased enrichment of H3K27me3 and H3K9me3, with H3K27me3 having the greatest reduction. Additional analysis of peripheral blood monocytes suggested that in healthy gut, the differentiation of blood monocytes into resident intestinal macrophages is associated with deposition of H3K27me3 and H3K9me3 silencing marks at the TNFA TSS, and that this process fails in IBD environment.
AuthorsKucik, Aneta Katarzyna
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