Aim: To explore the relationship between chromatin modification and the repression of inflammatory genes in intestinal macrophages.
Methods: Lamina propria mononuclear cells (LPMCs) were obtained from gut tissue resections of healthy control (HC) and IBD patients. IMACs were purified using positive selection with anti-CD33 antibodies. Using the same method, blood monocytes were isolated from peripheral blood mononuclear cells (PBMCs) with anti-CD14 antibodies. Cells analysed using chromatin immunoprecipitation (ChIP-qPCR) assay to determine associations between key histone modifications and tnfa gene expression.
Results: Macrophages from normal control subjects displayed significantly (P < 0.05) higher binding of the silencing mark H3K27me3 to the tnfa transcription start site than CD macrophages. Moreover, the repressed state of tnfa promoter in HC macrophages was associated with increased binding of H3K9me3 and H3K9me1. Additional analysis of peripheral blood monocytes suggests that the acquisition of H2K27me3 is tissue type-specific.
Conclusions: We have identified key epigenetic histone modifications at the tnfa gene, which may explain why the repressed state of the tnfa promoter in healthy macrophages is disturbed during gut inflammation, leading to an increased transcription and production of proinflammatory cytokines.