Methyltransferase G9A regulates T cell differentiation during murine intestinal inflammation

Abstract

Inflammatory bowel disease (IBD) pathogenesis is associated with dysregulated CD4 + Th cell responses, with intestinal homeostasis depending on the balance between IL-17-producing Th17 and Foxp3 + Tregs. Differentiation of naive T cells into Th17 and Treg subsets is associated with specific gene expression profiles; however, the contribution of epigenetic mechanisms to controlling Th17 and Treg differentiation remains unclear. Using a murine T cell transfer model of colitis, we found that T cell-intrinsic expression of the histone lysine methyltransferase G9A was required for development of pathogenic T cells and intestinal inflammation. G9A-mediated dimethylation of histone H3 lysine 9 (H3K9me2) restricted Th17 and Treg differentiation in vitro and in vivo. H3K9me2 was found at high levels in naive Th cells and was lost following Th cell activation. Loss of G9A in naive T cells was associated with increased chromatin accessibility and heightened sensitivity to TGF-β1. Pharmacological inhibition of G9A methyltransferase activity in WT T cells promoted Th17 and Treg differentiation. Our data indicate that G9A-dependent H3K9me2 is a homeostatic epigenetic checkpoint that regulates Th17 and Treg responses by limiting chromatin accessibility and TGF-β1 responsiveness, suggesting G9A as a therapeutic target for treating intestinal inflammation. IntroductionThe inflammatory bowel diseases (IBDs) are a group of chronic intestinal inflammatory diseases that include ulcerative colitis (UC) and Crohn disease (CD). IBD is thought to occur as a result of a complex interplay between host genetics and environmental factors leading to a dysregulated intestinal immune response (1). A recent meta-analysis of existing genome-wide association studies identified over 160 loci associated with both UC and CD (2). Gene ontology (GO) analysis of these IBD loci showed that the terms "regulation of cytokine production" and "T cell activation" were significantly enriched (2), suggesting that dysregulated production of cytokines by activated T cells is a critical factor in the development of IBD. Thus, a better understanding of the molecular mechanisms that regulate T cell activation and function may provide novel pathways to target therapeutically.A pathogenic role for CD4 + Th cells in intestinal inflammation has been clearly shown in a murine T cell transfer model of IBD. Adoptive transfer of highly purified naive CD4 + CD25 -CD45RB hi Th cells into immunodeficient Rag1 -/-mice results in the development of chronic intestinal inflammation, leading to weight loss and death (3,4). Disease pathology of Th cell transfer colitis shares many similarities with human IBD, including transmural inflammation,

Harnessing the plasticity of CD4+ T cells to treat immune-mediated disease

“…This probably contributes to the diversity of consequences observed with the disruption of different H3K9 HMTs, as each enzyme may interact with different binding partners or target unique genomic loci. For example, deletion of H3K9 HMT SUV39H1 allows T H 2-polarized cells to express IFNγ when restimulated in T H 1 cell-polarizing conditions, whereas deficiency for HMT G9A (also known as EHMT2) drives T Reg cell and T H 17 cell polarization by opening the Foxp3 and Rorc loci 157,158 . In human T Reg cells, H3K9 HMT SETDB1 is coupled to FOXP3 by a FOXP3-interacting KRAB domain-containing protein (FIK)-KRAB domain-associated protein (KAP; also known as TIF1β) complex to maintain repressive chromatin states at the IL2 and IFNG loci 159 .…”

Regulation of cell differentiation and function by the euchromatin histone methyltranserfases G9a and GLP

“…In culture, G9a deficient Th cells fail to express the appropriate Th2 cytokines upon stimulation and show inappropriate activation of Il-17 (Lehnertz et al 2010). G9a deposits H3K9me2 at the IL-17 gene in naïve Th cells, and in the absence of G9a, naïve Th cells show an increased tendency towards Th17 differentiation(Antignano et al 2014). Thus, in mice, the optimal cytokine response to infection requires G9a-mediated repression and activation of cell type specific cytokine genes.…”

Methyltransferase inhibitors for modulation of the epigenome and beyond

“…This had an especially pronounced effect at the g-globin promoter in adult CD34(+) erythroid progenitor cells, creating a permissive epigenetic state for production of HbF, and suggesting a potential epigenetic therapy for sickle cell disease and other hemoglobinopathies [42 ,43 ]. G9a inhibitors also revealed therapeutic potential for intestinal inflammation [44], and treatment of neuropathic pain [45 ]. In both cases, inhibition of G9a/GLP led to tissue specific activation of key genes that were epigenetically repressed by G9a-mediated H3K9me2 at gene promoters.…”