The polycomb protein Ezh2 regulates differentiation and plasticity of CD4(+) T helper type 1 and type 2 cells

Recent findings in the genetics and epigenetics of asthma and allergy

In asthma and allergy genetics, a trend towards a few main topics developed over the last 2 years. First, a number of studies have been published recently which focus on overlapping and/or very specific phenotypes: within the allergy spectrum but also reaching beyond, looking for common genetic traits shared between different diseases or disease entities. Secondly, an urgently needed focus has been put on asthma and allergy genetics in populations genetically different from European ancestry. This acknowledges that the majority of new asthma patients today are not white and asthma is a truly worldwide disease. In epigenetics, recent years have seen several large-scale epigenome-wide association studies (EWAS) being published and a further focus was on the interaction between the environment and epigenetic signatures. And finally, the major trends in current asthma and allergy genetics and epigenetics comes from the field of pharmacogenetics, where it is necessary to understand the susceptibility for and mechanisms of current asthma and allergy therapies while at the same time, we need to have scientific answers to the recent availability of novel drugs that hold the promise for a more individualized therapy.

EZH2 deficiency attenuates Treg differentiation in rheumatoid arthritis

The chromatin modifier enhancer of zeste homolog 2 (EZH2) methylates lysine 27 of histone H3 (H3K27) and regulates T cell differentiation. However, the potential role of EZH2 in the pathogenesis of rheumatoid arthritis (RA) remains elusive. We analyzed EZH2 expression in PBMC, CD4⁺ T cells, CD19⁺ B cell, and CD14⁺ monocytes from active treatment-naïve RA patients and healthy controls (HC). We also suppressed EZH2 expression using EZH2 inhibitor GSK126 and measured CD4⁺ T cell differentiation, proliferation and apoptosis. We further examined TGFβ-SMAD and RUNX1 signaling pathways in EZH2-suppressed CD4⁺ T cells. Finally, we explored the regulation mechanism of EZH2 by RA synovial fluid and fibroblast-like synoviocyte (FLS) by neutralizing key proinflammatory cytokines. EZH2 expression is lower in PBMC and CD4⁺ T cells from RA patients than those from HC. EZH2 inhibition suppressed regulatory T cells (Tregs) differentiation and FOXP3 transcription, and downregulated RUNX1 and upregulated SMAD7 expression in CD4⁺ T cells. RA synovial fluid and fibroblast-like synoviocytes suppressed EZH2 expression in CD4⁺ T cells, which was partially neutralized by anti-IL17 antibody. Taken together, EZH2 in CD4⁺ T cells from RA patients was attenuated, which suppressed FOXP3 transcription through downregulating RUNX1 and upregulating SMAD7 in CD4⁺ T cells, and ultimately suppressed Tregs differentiation. IL17 in RA synovial fluid might promote downregulation of EZH2 in CD4⁺ T cells. Defective EZH2 in CD4⁺ T cells might contribute to Treg deficiency in RA.

miRNA-Mediated Immune Regulation in Islet Autoimmunity and Type 1 Diabetes

The important role of microRNAs as major modulators of various physiological processes, including immune regulation and homeostasis, has been increasingly recognized. Consequently, aberrant miRNA expression contributes to the defective regulation of T cell development, differentiation, and function. This can result in immune activation and impaired tolerance mechanisms, which exert a cardinal function for the onset of islet autoimmunity and the progression to T1D. The specific impact of miRNAs for immune regulation and how miRNAs and their downstream targets are involved in the pathogenesis of islet autoimmunity and T1D has been investigated recently. These studies revealed that increased expression of individual miRNAs is involved in several layers of tolerance impairments, such as inefficient Treg induction and Treg instability. The targeted modulation of miRNAs using specific inhibitors, resulting in improved immune homeostasis, as well as improved methods for the targeting of miRNAs, suggest that miRNAs, especially in T cells, are a promising target for the reestablishment of immune tolerance.

MiR-1165-3p Suppresses Th2 Differentiation via Targeting IL-13 and PPM1A in a Mouse Model of Allergic Airway Inflammation

PURPOSE

CD4⁺T cells are essential in the pathogenesis of allergic asthma. We have previously demonstrated that microRNA-1165-3p (miR-1165-3p) was significantly reduced in T-helper type (Th) 2 cells and that miR-1165-3p was a surrogate marker for atopic asthma. Little is known about the mechanisms of miR-1165-3p in the regulation of Th2-dominated allergic inflammation. We aimed to investigate the associations between Th2 differentiation and miR-1165b-3p in asthma as well as the possible mechanisms.

METHODS

CD4⁺ naïve T cells were differentiated into Th1 or Th2 cells in vitro. MiR-1165-3p was up-regulated or down-regulated using lentiviral systems during Th1/Th2 differentiation. In vivo, the lentiviral particles with the miR-1165-3p enhancer were administered by tail vein injection on the first day of a house dust mite -induced allergic airway inflammation model. Allergic inflammation and Th1/Th2 differentiation were routinely monitored. To investigate the potential targets of miR-1165-3p, biotin-microRNA pull-down products were sequenced, and the candidates were further verified with a dual-luciferase reporter assay. The roles of a target protein phosphatase, Mg²⁺/Mn²⁺-dependent 1A (PPM1A), in Th2 cell differentiation and allergic asthma were further explored. Plasma PPM1A was determined by ELISA in 18 subjects with asthma and 20 controls.

RESULTS

The lentivirus encoding miR-1165-3p suppressed Th2-cell differentiation in vitro. In contrast, miR-1165-3p silencing promoted Th2-cell development. In the HDM-induced model of allergic airway inflammation, miR-1165-3p up-regulation was accompanied by reduced airway hyper-responsiveness, serum immunoglobulin E, airway inflammation and Th2-cell polarization. IL-13 and PPM1A were the direct targets of miR-1165-3p. The expression of IL-13 or PPM1A was inversely correlated with that of miR-1165-3p. PPM1A regulated the signal transducer and activator of transcription and AKT signaling pathways during Th2 differentiation. Moreover, plasma PPM1A was significantly increased in asthmatic patients.

CONCLUSIONS

MiR-1165-3p negatively may regulate Th2-cell differentiation by targeting IL-13 and PPM1A in allergic airway inflammation.

Therapeutic potential of enhancer of zeste homolog 2 in autoimmune diseases

Introduction: Autoimmune diseases (ADs) are idiopathic and heterogeneous disorders with contentious pathophysiology. Great strides have been made in epigenetics and its involvement in ADs. Zeste homolog 2 (EZH2) has sparked extensive interest because of its pleiotropic roles in distinct pathologic contexts.Areas covered: This review summarizes the epigenetic functions and the biological significance of EZH2 in the etiology of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), type 1 diabetes (T1D), inflammatory bowel disease (IBD), multiple sclerosis (MS), and systemic sclerosis (SSc). A brief recapitulation of the therapeutic potential of EZH2 targeting is provided.Expert opinion: There are questions marks and controversies surrounding the feasibility and safety of EZH2 targeting; it is recommended in RA and SLE, but queried in T1D, IBD, MS, and SSc. Future work should focus on contrast studies, systematic analyses and preclinical studies with optimizing methodologies. Selective research studies conducted in a stage-dependent manner are necessary because of the relapsing-remitting clinical paradigms.

Epigenetic modifiers as new immunomodulatory therapies in solid tumours

Background

Immune therapies have revolutionized cancer treatment over the last few years by allowing improvements in overall survival. However, the majority of patients is still primary or secondary resistant to such therapies, and enhancing sensitivity to immune therapies is therefore crucial to improve patient outcome. Several recent lines of evidence suggest that epigenetic modifiers have intrinsic immunomodulatory properties, which could be of therapeutic interest.

Material and methods

We reviewed preclinical evidence and clinical studies which describe or exploit immunomodulatory properties of epigenetic agents. Experimental approaches, clinical applicability and corresponding ongoing clinical trials are described.

Results

Several epigenetic modifiers, such as histone deacetylase inhibitors, DNA methyl transferase inhibitors, bromodomain inhibitors, lysine-specific histone demethylase 1 inhibitors and enhancer of zeste homolog 2 inhibitors, display intrinsic immunomodulatory properties. The latter can be achieved through the action of these drugs either on cancer cells (e.g. presentation and generation of neoantigens, induction of immunogenic cell death, modulation of cytokine secretion), on immune cells (e.g. linage, differentiation, activation status and antitumor capability), or on components of the microenvironment (e.g. regulatory T cells and macrophages). Several promising combinations, notably with immune checkpoint blockers or adoptive T-cell therapy, can be envisioned. Dedicated clinically relevant approaches for patient selection and trial design will be required to optimally develop such combinations.

Conclusion

In an era where immune therapies are becoming a treatment backbone in many tumour types, epigenetic modifiers could play a crucial role in modulating tumours' immunogenicity and sensitivity to immune agents. Optimal trial design, including window of opportunity trials, will be key in the success of this approach, and clinical evaluation is ongoing.

EZH2 abnormalities in lymphoid malignancies: underlying mechanisms and therapeutic implications

EZH2 is the catalytic subunit of the polycomb repressive complex 2 (PRC2), which along with other PRC2 components mediates gene expression suppression via the methylation of Histone H3 at lysine 27. Recent studies have revealed a dichotomous role of EZH2 in physiology and in the pathogenesis of cancer. While it plays an essential role in the development of the lymphoid system, its deregulation, whether due to genetic or non-genetic causes, promotes B cell- and T cell-related lymphoma or leukemia. These findings triggered a boom in the development of therapeutic EZH2 inhibitors in recent years. Here, we discuss physiologic and pathogenic function of EZH2 in lymphoid context, various internal causes of EZH2 aberrance and how EZH2 modulates lymphomagenesis through epigenetic silencing, post-translational modifications (PTMs), orchestrating with surrounding tumor micro-environment and associating with RNA or viral partners. We also summarize different strategies to directly inhibit PRC2-EZH2 or to intervene EZH2 upstream signaling.

Age-Related Dopaminergic Innervation Augments T Helper 2-Type Allergic Inflammation in the Postnatal Lung

Young children are more susceptible to developing allergic asthma than adults. As neural innervation of the peripheral tissue continues to develop after birth, neurons may modulate tissue inflammation in an age-related manner. Here we showed that sympathetic nerves underwent a dopaminergic-to-adrenergic transition during post-natal development of the lung in mice and humans. Dopamine signaled through a specific dopamine receptor (DRD4) to promote T helper 2 (Th2) cell differentiation. The dopamine-DRD4 pathway acted synergistically with the cytokine IL-4 by upregulating IL-2-STAT5 signaling and reducing inhibitory histone trimethylation at Th2 gene loci. In murine models of allergen exposure, the dopamine-DRD4 pathway augmented Th2 inflammation in the lungs of young mice. However, this pathway operated marginally after sympathetic nerves became adrenergic in the adult lung. Taken together, the communication between dopaminergic nerves and CD4⁺ T cells provides an age-related mechanism underlying the susceptibility to allergic inflammation in the early lung.

Epigenetic mechanisms regulating T-cell responses

During the last decade, advances in sequencing technologies allowed production of a wealth of information on epigenetic modifications in T cells. Epigenome maps, in combination with mechanistic studies, have demonstrated that T cells undergo extensive epigenome remodeling in response to signals, which has a strong effect on phenotypic stability and function of lymphocytes. In this review we focus on DNA methylation, histone modifications, and chromatin structure as important epigenetic mechanisms involved in controlling T-cell responses. In particular, we discuss epigenetic processes in light of the development, activation, and differentiation of CD4⁺ T helper (T_H), regulatory T, and CD8⁺ T cells. As central aspects of the adaptive immune system, we review mechanisms that ensure molecular memory, stability, plasticity, and exhaustion of T cells. We further discuss the effect of the tissue environment on imprinting T-cell epigenomes with potential implications for immunotherapy.

Continuous Developmental and Early Life Trichloroethylene Exposure Promoted DNA Methylation Alterations in Polycomb Protein Binding Sites in Effector/Memory CD4+ T Cells

Trichloroethylene (TCE) is an industrial solvent and drinking water pollutant associated with CD4⁺ T cell-mediated autoimmunity. In our mouse model, discontinuation of TCE exposure during adulthood after developmental exposure did not prevent immunotoxicity. To determine whether persistent effects were linked to epigenetic changes we conducted whole genome reduced representation bisulfite sequencing (RRBS) to evaluate methylation of CpG sites in autosomal chromosomes in activated effector/memory CD4⁺ T cells. Female MRL+/+ mice were exposed to vehicle control or TCE in the drinking water from gestation until ~37 weeks of age [postnatal day (PND) 259]. In a subset of mice, TCE exposure was discontinued at ~22 weeks of age (PND 154). At PND 259, RRBS assessment revealed more global methylation changes in the continuous exposure group vs. the discontinuous exposure group. A majority of the differentially methylated CpG regions (DMRs) across promoters, islands, and regulatory elements were hypermethylated (~90%). However, continuous developmental TCE exposure altered the methylation of 274 CpG sites in promoters and CpG islands. In contrast, only 4 CpG island regions were differentially methylated (hypermethylated) in the discontinuous group. Interestingly, 2 of these 4 sites were also hypermethylated in the continuous exposure group, and both of these island regions are associated with lysine 27 on histone H3 (H3K27) involved in polycomb complex-dependent transcriptional repression via H3K27 tri-methylation. CpG sites were overlapped with the Open Regulatory Annotation database. Unlike the discontinuous group, continuous TCE treatment resulted in 129 DMRs including 12 unique transcription factors and regulatory elements; 80% of which were enriched for one or more polycomb group (PcG) protein binding regions (i.e., SUZ12, EZH2, JARID2, and MTF2). Pathway analysis of the DMRs indicated that TCE primarily altered the methylation of genes associated with regulation of cellular metabolism and cell signaling. The results demonstrated that continuous developmental exposure to TCE differentially methylated binding sites of PcG proteins in effector/memory CD4⁺ cells. There were minimal yet potentially biologically significant effects that occurred when exposure was discontinued. These results point toward a novel mechanism by which chronic developmental TCE exposure may alter terminally differentiated CD4⁺ T cell function in adulthood.

BCL-6 suppresses miR-142-3p/5p expression in SLE CD4+ T cells by modulating histone methylation and acetylation of the miR-142 promoter

The reduced expression of miR-142-3p/5p in CD4⁺ T cells of SLE patients caused T cell hyperactivity and B cell hyperstimulation. This study aimed to investigate the mechanisms of regulating miR-142-3p/5p expression in SLE CD4⁺ T cells. The BCL-6 expression was significantly increased in SLE CD4⁺ T cells compared with normal controls, and the BCL-6 expression was inversely correlated with miR-142-3p/5p expression. BCL-6 suppresses the expression of miR-142-3p/5p by increasing H3K27me3 level and reducing H3K9/K14ac levels in SLE CD4⁺ T cells. BCL-6 regulates histone modifications in miR-142 promoter by recruiting EZH2 and HDAC5. Furthermore, we observed significantly decreased CD40L, ICOS, and IL-21 expression levels in SLE CD4⁺ T cells with BCL-6 interference, and obviously reduced autoantibody IgG production in autologous B cells co-cultured with BCL-6 inhibited SLE CD4⁺ T cells. Our study found that increased BCL-6 up-regulates H3K27me3 and down-regulates H3K9/14ac at miR-142 promoter in SLE CD4⁺ T cells. These factors induce a declination in miR-142-3p/5p expression, consequently resulting in CD4⁺ T cell hyperactivity.

Increased Expression of Circulating microRNA 101-3p in Type 1 Diabetes Patients: New Insights Into miRNA-Regulated Pathophysiological Pathways for Type 1 Diabetes

MicroRNAs (miRs) are master regulators of post-transcriptional gene expression, and they are often dysregulated in individuals suffering from diabetes. We investigated the roles of miR-101-3p and miR-204-5p, both of which negatively regulate insulin secretion and cell survival and are highly expressed in pancreatic β cells, in the context of type 1 diabetes (T1D) pathogenesis. Using quantitative real time PCR, we evaluated serum levels of miR-101-3p and miR-204-5p in four groups, including recent-onset T1D patients (T1D group; n = 50), individuals with normal glucose levels expressing one islet autoantibody (Ab) (single Ab group; n = 26) or multiple autoantibodies (multiple Ab group; n = 12), and healthy controls (control group; n = 43). An in silico analysis was performed to identify potential target genes of these miRNAs and to delineate enriched pathways. The relative expression of serum miR-101-3p was approximately three times higher in the multiple Ab and T1D groups than that in the single Ab and control groups (p < 0.0001). When considering all groups together, miR-101-3p expression was positively correlated with the level of islet autoantibodies GADA (r = 0.267; p = 0.0027) and IA-2A (r = 0.291; p = 0.001), and the expression of the miRNA was not correlated with levels of ZnT8A (r = 0.125; p = 0.183). miR-101-3p expression did not correlate with HbA1c (r = 0.178; p = 0.052) or glucose levels (r = 0.177; p = 0.051). No significant differences were observed in miR-204-5p expression among the analyzed groups. Computational analysis of the miR-101-3p target gene pathways indicated a potential activation of the HGF/c-Met, Ephrin receptor, and STAT3 signaling pathways. Our study demonstrated that the circulating levels of miR-101-3p are higher in T1D patients and in individuals with normal glucose levels, testing positive for multiple autoantibodies, indicating that miR-101-3p precedes loss of glucose homeostasis. The pathogenic role of miR-101-3p in T1D may involve multiple molecular pathways.

Shaping the diversity of Th2 cell responses in epithelial tissues and its potential for allergy treatment

Th2 cells have evolved to protect from large helminth infections and to exert tissue protective functions in response to nonmicrobial noxious stimuli. The initiation, maintenance, and execution of these functions depend on the integration of diverse polarizing cues by cellular sensors and molecular programs as well as the collaboration with cells that are coopted for signal exchange. The complexity of input signals and cellular collaboration generates tissue specific Th2 cell heterogeneity and specialization. In this review, we aim to discuss the advances and recent breakthroughs in our understanding of Th2 cell responses and highlight developmental and functional differences among T cells within the diversifying field of type 2 immunity. We will focus on factors provided by the tissue microenvironment and highlight factors with potential implications for the pathogenesis of allergic skin and lung diseases. Especially new insights into the role of immunometabolism, the microbiota and ionic signals enhance the complexity of Th2 cell regulation and warrant a critical evaluation. Finally, we will discuss how this ensemble of established knowledge and recent breakthroughs about Th2 immunobiology advance our understanding of the pathogenesis of allergic diseases and how this could be exploited for future immunotherapies.

EZH2 inhibitor DZNep modulates microglial activation and protects against ischaemic brain injury after experimental stroke

Enhancer of zeste homolog-2 (EZH2), a histone methyltransferase, has been recognized to play a pivotal role in regulating the immune response in various diseases. However, its role in the inflammatory response induced by ischaemic stroke remains to be further investigated. The aim of this study was to determine the role of EZH2 in microglia-associated inflammation in ischaemic stroke and to further detect the effects of the EZH2 inhibitor, 3-deazaadenosine A (DZNep), in ischaemic brain injury. Here, we found that both in vivo ischemic/reperfusion (I/R) injury and in vitro oxygen-glucose deprivation (OGD) treatment induced a marked upregulation of EZH2 in microglia. The administration of the EZH2 inhibitor DZNep improved behavioural performance and reduced the infarct volume in mice after experimental stroke. Furthermore, we showed that DZNep blocked pro-inflammatory (CD86⁺) microglial activation and triggered anti-inflammatory (CD206⁺) microglial polarization in experimental stroke. Pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and CXCL10 were also significantly downregulated by DZNep. In addition, it was found that DZNep blocked the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in microglia, which was increased by I/R injury and OGD. Collectively, we demonstrated that EZH2 is implicated in regulating microglial activation and exacerbates neurological deficits after ischaemic stroke, probably via activating STAT3, and that the EZH2 inhibitor DZNep can exert neuroprotective effects after ischaemic stroke.

Targeting EZH2 histone methyltransferase activity alleviates experimental intestinal inflammation

Enhancer of zeste homolog 2 (EZH2)-mediated trimethylation of histone 3 lysine 27 (H3K27Me3) is critical for immune regulation. However, evidence is lacking to address the effect of EZH2 enzyme's activity on intestinal immune responses during inflammatory bowel disease (IBD). Here we report that suppressing EZH2 activity ameliorates experimental intestinal inflammation and delayed the onset of colitis-associated cancer. In addition, we identified an increased number of functional MDSCs in the colons, which are essential for EZH2 inhibitor activity. Moreover, inhibition of EZH2 activity promotes the generation of MDSCs from hematopoietic progenitor cells in vitro, demonstrating a previously unappreciated role for EZH2 in the development of MDSCs. Together, these findings suggest the feasibility of EZH2 inhibitor clinical trials for the control of IBD. In addition, this study identifies MDSC-promoting effects of EZH2 inhibitors that may be undesirable in other therapeutic contexts and should be addressed in a clinical trial setting.

Polycomb repressive complex 2 is a critical mediator of allergic inflammation

Strategies that intervene with the development of immune-mediated diseases are urgently needed, as current treatments mostly focus on alleviating symptoms rather than reversing the disease. Targeting enzymes involved in epigenetic modifications to chromatin represents an alternative strategy that has the potential to perturb the function of the lymphocytes that drive the immune response. Here, we report that 2 major epigenetic silencing pathways are increased after T cell activation. By specific inactivation of these molecules in the T cell compartment in vivo, we demonstrate that the polycomb repressive complex 2 (PRC2) is essential for the generation of allergic responses. Furthermore, we show that small-molecule inhibition of the PRC2 methyltransferase, enhancer of zeste homolog 2 (Ezh2), reduces allergic inflammation in mice. Therefore, by systematically surveying the pathways involved in epigenetic gene silencing we have identified Ezh2 as a target for the suppression of allergic disease.

The role of invariant T cells in inflammation of the skin and airways

Invariant and semi-invariant T cells are emerging as important regulators of host environment interactions at barrier tissues such as the airway and skin. In contrast to conventional T cells, invariant natural killer T (iNKT) cells and mucosal associated invariant T (MAIT) cells express T cell receptors of very limited diversity. iNKT and MAIT cells recognise antigens presented by the MHC class 1-like monomorphic molecules CD1d and MR1, respectively. Both iNKT cells and MAIT cells have been identified in the skin and airways and can rapidly produce cytokines after activation. Numerous studies have implicated iNKT cells in the pathology of both skin and airway disease, but conflicting evidence in human disease means that more studies are necessary to resolve the exact roles of iNKT in inflammation. The functions of MAIT cells in skin and lung inflammation are even less well defined. We herein describe the current literature on iNKT and MAIT cells in allergic and non-allergic skin diseases (dermatitis and psoriasis) and airway diseases (asthma, chronic obstructive pulmonary disease, rhinitis, and chronic rhinosinusitis).

Regulation of T cell differentiation and function by epigenetic modification enzymes

Peripheral naive CD4⁺ and CD8⁺ cells are developed in the thymus and proliferate and differentiate into various specialized T cell subsets upon activation by peptide-major histocompatibility complexes in periphery to execute different functions during immune responses. Cytokines, transcription factors, and a large number of intracellular molecules have been shown to affect T cell development, activation, and function. In addition, epigenetic modifications, such as histone modification and DNA methylation, regulate T cell biology. The epigenetic modifications are regulated by a range of DNA methyltransferases, DNA demethylation enzymes, and histone modification enzymes. Dysregulations of epigenetic modifications are closely associated with autoimmune diseases and tumorigenesis. Here, we review the current literature about the functions of DNA and histone modification enzymes in T cell development, activation, differentiation, and function.

Control of Intra-Thymic αβ T Cell Selection and Maturation by H3K27 Methylation and Demethylation

In addition to transcription factor binding, the dynamics of DNA modifications (methylation) and chromatin structure are essential contributors to the control of transcription in eukaryotes. Research in the past few years has emphasized the importance of histone H3 methylation at lysine 27 for lineage specific gene repression, demonstrated that deposition of this mark at specific genes is subject to differentiation-induced changes during development, and identified enzymatic activities, methyl transferases and demethylases, that control these changes. The present review discusses the importance of these mechanisms during intrathymic αβ T cell selection and late differentiation.

Antigen receptor control of methionine metabolism in T cells

Immune activated T lymphocytes modulate the activity of key metabolic pathways to support the transcriptional reprograming and reshaping of cell proteomes that permits effector T cell differentiation. The present study uses high resolution mass spectrometry and metabolic labelling to explore how murine T cells control the methionine cycle to produce methyl donors for protein and nucleotide methylations. We show that antigen receptor engagement controls flux through the methionine cycle and RNA and histone methylations. We establish that the main rate limiting step for protein synthesis and the methionine cycle is control of methionine transporter expression. Only T cells that respond to antigen to upregulate and sustain methionine transport are supplied with methyl donors that permit the dynamic nucleotide methylations and epigenetic reprogramming that drives T cell differentiation. These data highlight how the regulation of methionine transport licenses use of methionine for multiple fundamental processes that drive T lymphocyte proliferation and differentiation.

Ezh2 controls development of natural killer T cells, which cause spontaneous asthma-like pathology

BACKGROUND

Natural killer T (NKT) cells express a T-cell receptor that recognizes endogenous and environmental glycolipid antigens. Several subsets of NKT cells have been identified, including IFN-γ-producing NKT1 cells, IL-4-producing NKT2 cells, and IL-17-producing NKT17 cells. However, little is known about the factors that regulate their differentiation and respective functions within the immune system.

OBJECTIVE

We sought to determine whether the polycomb repressive complex 2 protein enhancer of zeste homolog 2 (Ezh2) restrains pathogenicity of NKT cells in the context of asthma-like lung disease.

METHODS

Numbers of invariant natural killer T (iNKT) 1, iNKT2, and iNKT17 cells and tissue distribution, cytokine production, lymphoid tissue localization, and transcriptional profiles of iNKT cells from wild-type and Ezh2 knockout (KO) iNKT mice were determined. The contribution of NKT cells to development of spontaneous and house dust mite-induced airways pathology, including airways hyperreactivity (AHR) to methacholine, was also assessed in wild-type, Ezh2 KO, and Ezh2 KO mice lacking NKT cells.

RESULTS

Ezh2 restrains development of pathogenic NKT cells, which induce spontaneous asthma-like disease in mice. Deletion of Ezh2 increased production of IL-4 and IL-13 and induced spontaneous AHR, lung inflammation, mucus production, and IgE. Increased IL-4 and IL-13 levels, AHR, lung inflammation, and IgE levels were all dependent on iNKT cells. In house dust mite-exposed animals Ezh2 KO resulted in enhanced AHR that was also dependent on iNKT cells.

CONCLUSION

Ezh2 is a central regulator of iNKT pathogenicity and suppresses the ability of iNKT cells to induce asthma-like pathology.

Targeting DNA Methylation and EZH2 Activity to Overcome Melanoma Resistance to Immunotherapy

Methylation of DNA at CpG sites is the most common and stable of epigenetic changes in cancer. Hypermethylation acts to limit immune checkpoint blockade immunotherapy by inhibiting endogenous interferon responses needed for recognition of cancer cells. By contrast, global hypomethylation results in the expression of programmed death ligand 1 (PD-L1) and inhibitory cytokines, accompanied by epithelial-mesenchymal changes that can contribute to immunosuppression. The drivers of these contrasting methylation states are not well understood. DNA methylation also plays a key role in cytotoxic T cell 'exhaustion' associated with tumor progression. We present an updated exploratory analysis of how DNA methylation may define patient subgroups and can be targeted to develop tailored treatment combinations to help improve patient outcomes.

The histone methyltransferase EZH2 primes the early differentiation of follicular helper T cells during acute viral infection

Epigenetic modifications to histones dictate the differentiation of naïve CD4⁺ T cells into different subsets of effector T helper (T_H) cells. The histone methyltransferase enhancer of zeste homolog 2 (EZH2) has been implicated in the mechanism regulating the differentiation of T_H1, T_H2 and regulatory T (T_reg) cells. However, whether and how EZH2 regulates follicular helper T (T_FH) cell differentiation remain unknown. Using a mouse model of acute lymphocytic choriomeningitis virus (LCMV) infection, we observed abundant EZH2 expression and associated H3K27me3 modifications preferentially in the early committed virus-specific T_FH cells compared to those in T_H1 cells. Ablation of EZH2 in LCMV-specific CD4⁺ T cells leads to a selective impairment of early T_FH cell fate commitment, but not late T_FH differentiation or memory T_FH maintenance. Mechanistically, EZH2 specifically stabilizes the chromatin accessibility of a cluster of genes that are important for T_FH fate commitment, particularly B cell lymphoma 6 (Bcl6), and thus directs T_FH cell commitment. Therefore, we identified the chromatin-modifying enzyme EZH2 as a novel regulator of early T_FH differentiation during acute viral infection.

Inhibition of EZH2 prevents fibrosis and restores normal angiogenesis in scleroderma

Scleroderma (SSc) is a complex disease that involves activation of the immune system, vascular complications, and tissue fibrosis. The histone methyltransferase enhancer of zeste homolog 2 (EZH2) mediates trimethylation of lysine 27 of histone 3 (H3K27me3), which acts as a repressive epigenetic mark. Both EZH2 and H3K27me3 were elevated in SSc dermal fibroblasts and endothelial cells compared with healthy controls. EZH2 inhibitor DZNep halted fibrosis both in vitro and in vivo. In SSc fibroblasts, DZNep dose-dependently reduced the expression of profibrotic genes and inhibited migratory activity of SSc fibroblasts. We show that epigenetic dysregulation and overexpression of LRRC16A explains EZH2-mediated fibroblast migration in SSc. In endothelial cells, inhibition of EZH2 restored normal angiogenesis in SSc via activating the Notch pathway, specifically by up-regulating the Notch ligand DLL4. Our results demonstrate that overexpression of EZH2 in SSc fibroblasts and endothelial cells is profibrotic and antiangiogenic. Targeting EZH2 or EZH2-regulated genes might be of therapeutic potential in SSc.

EZH2 Inhibitor GSK126 Suppresses Antitumor Immunity by Driving Production of Myeloid-Derived Suppressor Cells

Enhancer of zeste homolog (EZH2) is a key epigenetic regulator of gene expression and is frequently overexpressed in various cancer types, suggesting a role in oncogenesis. The therapeutic potential of EZH2 inhibitors is currently being explored, but their effect on antitumor immunity is largely unknown. Here we report that suppressing EZH2 activity using EZH2 inhibitor GSK126 resulted in increased numbers of myeloid-derived suppressor cells (MDSC) and fewer CD4⁺ and IFNγ⁺CD8⁺ T cells, which are involved in antitumor immunity. Addition of a neutralizing antibody against the myeloid differentiation antigen GR-1 or gemcitabine/5-fluorouracil-depleted MDSCs alleviated MDSC-mediated immunosuppression and increased CD4⁺ and CD8⁺ T-cell tumor infiltration and GSK126 therapeutic efficacy. Mechanistically, we identified a novel pathway of MDSC production in cancer in which EZH2 inhibition directs myeloid differentiation from primitive hematopoietic progenitor cells. These findings suggest that modulating the tumor immune microenvironment may improve the efficacy of EZH2 inhibitors. SIGNIFICANCE: This study uncovers a potential mechanism behind disappointing results of a phase I clinical trial of EZH2 inhibitor GSK126 and identifies a translatable combinational strategy to overcome it.

FoxP3 and Ezh2 regulate Tfr cell suppressive function and transcriptional program

Tfr cells regulate Tfh-mediated antibody responses. Hou et al. demonstrate that FoxP3 and Ezh2 control the Tfr transcriptional program, and loss of this program results in dysfunctional ex-Tfr cells.

Follicular regulatory T (Tfr) cells are a regulatory T cell subset that controls antibody production by inhibiting T follicular helper (Tfh)–mediated help to B cells. Tfh and Tfr cells possess opposing functions suggesting unique programming. Here we elucidated the transcriptional program controlling Tfr suppressive function. We found that Tfr cells have a program for suppressive function fine-tuned by tissue microenvironment. The transcription factor FoxP3 and chromatin-modifying enzyme EZH2 are essential for this transcriptional program but regulate the program in distinct ways. FoxP3 modifies the Tfh program to induce a Tfr-like functional state, demonstrating that Tfr cells coopt the Tfh program for suppression. Importantly, we identified a Tfr cell population that loses the Tfr program to become “ex-Tfr” cells with altered functionality. These dysfunctional ex-Tfr cells may have roles in modulating pathogenic antibody responses. Taken together, our studies reveal mechanisms controlling the Tfr transcriptional program and how failure of these mechanisms leads to dysfunctional Tfr cells.

Tackling molecular targets beyond PD-1/PD-L1: Novel approaches to boost patients' response to cancer immunotherapy

In the new era of immunotherapy, which has changed the clinical oncology practice guidelines, there is a pressing need for finding novel approaches to tune up the clinical outcomes of immunotherapy and extend its benefits to a wider cohort of cancer patients. Several non-classical molecular immune targets beyond PD-1/PD-L1 signaling were shown to be engaged as feedback resistance circuits to shut down the antitumor immune response mediated by the classical immune checkpoint inhibitors. Those include T-cell inducible co-stimulator (ICOS), CD40, CD47, V-domain Ig suppressor of T-cell activation (VISTA), cyclin-dependent kinase (CDK)12, enhancer of Zeste homolog 2 (EZH2), toll-like receptors (TLRs) and OX-40 (CD134). Herein we critically discussed the latest studies concerned with understanding the mechanisms involved in the negative clinical response to classical immunotherapies and strategies to optimize the efficacy of cancer immunotherapy through novel combinatorial approaches.

A chemical biology toolbox to study protein methyltransferases and epigenetic signaling

Protein methyltransferases (PMTs) comprise a major class of epigenetic regulatory enzymes with therapeutic relevance. Here we present a collection of chemical probes and associated reagents and data to elucidate the function of human and murine PMTs in cellular studies. Our collection provides inhibitors and antagonists that together modulate most of the key regulatory methylation marks on histones H3 and H4, providing an important resource for modulating cellular epigenomes. We describe a comprehensive and comparative characterization of the probe collection with respect to their potency, selectivity, and mode of inhibition. We demonstrate the utility of this collection in CD4⁺ T cell differentiation assays revealing the potential of individual probes to alter multiple T cell subpopulations which may have implications for T cell-mediated processes such as inflammation and immuno-oncology. In particular, we demonstrate a role for DOT1L in limiting Th1 cell differentiation and maintaining lineage integrity. This chemical probe collection and associated data form a resource for the study of methylation-mediated signaling in epigenetics, inflammation and beyond.

Protein methyltransferases (PMTs) are epigenetic regulatory enzymes with significant therapeutic relevance. Here the authors describe a collection of chemical inhibitors and antagonists to modulate most of the key methylation marks on histones H3 and H4, and use the collection to study of the role of PMTs in mouse and human T cell differentiation.

Ezh2 programs TFH differentiation by integrating phosphorylation-dependent activation of Bcl6 and polycomb-dependent repression of p19Arf

Ezh2 is an histone methyltransferase (HMT) that catalyzes H3K27me3 and functions in T_H1, T_H2, and Treg cells primarily via HMT activity. Here we show that Ezh2 ablation impairs T follicular helper (T_FH) cell differentiation and activation of the T_FH transcription program. In T_FH cells, most Ezh2-occupied genomic sites, including the Bcl6 promoter, are associated with H3K27ac rather than H3K27me3. Mechanistically, Ezh2 is recruited by Tcf1 to directly activate Bcl6 transcription, with this function requiring Ezh2 phosphorylation at Ser21. Meanwhile, Ezh2 deploys H3K27me3 to repress Cdkn2a expression in T_FH cells, where aberrantly upregulated p19Arf, a Cdkn2a protein product, triggers T_FH cell apoptosis and antagonizes Bcl6 function via protein-protein interaction. Either forced expression of Bcl6 or genetic ablation of p19Arf in Ezh2-deficient cells improves T_FH cell differentiation and helper function. Thus, Ezh2 orchestrates T_FH-lineage specification and function maturation by integrating phosphorylation-dependent transcriptional activation and HMT-dependent gene repression.

Ezh2 is an histone methyltransferase that catalyzes H3K27me3. Here the authors show that Ezh2 promotes T follicular helper (T_FH) differentiation and helper activity, by cooperating with Tcf1 to activate Bcl6 transcription and epigenetically repressing p19Arf, an antagonist of Bcl6 function and T_FH cell survival.

The Role of Histone Methyltransferases and Long Non-coding RNAs in the Regulation of T Cell Fate Decisions

T cell lineage decisions are critical for the development of proper immune responses to pathogens as well as important for the resolution of inflammatory responses. This differentiation process relies on a combination of intrinsic and extrinsic factors converging upon epigenetic regulation of transcriptional networks relevant to specific T cell lineages. As these biochemical modifications represent therapeutic opportunities in cancer biology and autoimmunity, implications of writers and readers of epigenetic marks to immune cell differentiation and function are highly relevant. Given the ready adoption of histone methyltransferase inhibitors in the clinic, we focus this review on the role of three histone modifying complexes: PRC-1, PRC-2, and G9A in modulating T cell fate decisions. Furthermore, we explore the role of long non-coding RNAs in regulating these processes, and discuss recent advances and challenges of implementing epigenetic therapies into clinical practice.

Epigenetic and Transcriptional Regulation in the Induction, Maintenance, Heterogeneity, and Recall-Response of Effector and Memory Th2 Cells

Antigen-primed T cells respond to restimulation much faster than naïve T cells and form the cellular basis of immunological memory. The formation of memory Th2 cells starts when naïve CD4 T cells are transformed into effector Th2 cells and is completed after antigen clearance and a long-term resting phase accompanied by epigenetic changes in the Th2 signature genes. Memory Th2 cells maintain their functions and acquired heterogeneity through epigenetic machinery, on which the recall-response of memory Th2 cells is also dependent. We provide an overview of the epigenetics in the whole Th2 cell cycle, mainly focusing on two different histone lysine methyltransferase complexes: the Polycomb and Trithorax groups. We finally discuss the pathophysiology and potential therapeutic strategies for the treatment of Th2-mediated inflammatory diseases in mice and humans.

Selective targeting of histone modification fails to prevent graft versus host disease after hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation is often complicated by graft versus host disease (GvHD), primarily mediated through allo-reactive donor T cells in the donor stem cell graft. Enhancer of Zeste Homolog 2 (EZH2), a histone-lysine N-methyltransferase and a component of the Polycomb Repressive Complex 2, has been shown to play a role in GvHD pathology. Although not yet clear, one proposed mechanism is through selective tri-methylation of lysine 27 in histone 3 (H3K27me3) that marks the promoter region of multiple pro-apoptotic genes, leading to repression of these genes in allo-reactive T cells. We found that selective pharmacologic inhibition of H3K27me3 with EPZ6438 or GSK126 did not prevent murine GvHD. This suggests the GvHD mitigating properties of DZNep are independent from H3K27me3 inhibition. Furthermore, while pharmacologic inhibition of EZH2 by DZNep has been shown to be effective in abrogating mouse GvHD, we found that DZNep was not effective in preventing GvHD in a human T cell xenograft mouse model. Although EZH2 is an attractive target to harness donor allo-reactive T cells in the post-transplant setting to modulate GvHD and the anti-leukemia effect, our results suggest that more selective and effective ways to inhibit EZH2 in human T cells are required.

Epigenetic mechanisms of tumor resistance to immunotherapy

The recent impact of cancer immunotherapies has firmly established the ability and importance of the immune system to fight malignancies. However, the intimate interaction between the highly dynamic tumor and immune cells leads to a selection process driven by genetic and epigenetic processes. As the molecular pathways of cancer resistance mechanisms to immunotherapy become increasingly known, novel therapeutic targets are being tested in combination with immune-stimulating approaches. We here review recent insights into the molecular mechanisms of tumor resistance with particular emphasis on epigenetic processes and place these in the context of previous models.

Complex Immune Contextures Characterise Malignant Peritoneal Mesothelioma: Loss of Adaptive Immunological Signature in the More Aggressive Histological Types

Malignant peritoneal mesothelioma (MpM), arising in the setting of local inflammation, is a rare aggressive tumour with a poor prognosis and limited therapeutic options. The three major MpM histological variants, epithelioid (E-MpMs), biphasic, and sarcomatoid MpMs (S-MpMs), are characterised by an increased aggressiveness and enhanced levels of EZH2 expression. To investigate the MpM immune contexture along the spectrum of MpM histotypes, an extended in situ analysis was performed on a series of 14 cases. Tumour-infiltrating immune cells and their functionality were assessed by immunohistochemistry, immunofluorescence, qRT-PCR, and flow cytometry analysis. MpMs are featured by a complex immune landscape modulated along the spectrum of MpM variants. Tumour-infiltrating T cells and evidence for pre-existing antitumour immunity are mainly confined to E-MpMs. However, Th1-related immunological features are progressively impaired in the more aggressive forms of E-MpMs and completely lost in S-MpM. Concomitantly, E-MpMs show also signs of active immune suppression, such as the occurrence of Tregs and Bregs and the expression of the immune checkpoint inhibitory molecules PD1 and PDL1. This study enriches the rising rationale for immunotherapy in MpM and points to the E-MpMs as the most immune-sensitive MpM histotypes, but it also suggests that synergistic interventions aimed at modifying the tumour microenvironment (TME) should be considered to make immunotherapy beneficial for these patients.

Modulation of EZH2 expression in T cells improves efficacy of anti-CTLA-4 therapy

Enhancer of zeste homolog 2-mediated (EZH2-mediated) epigenetic regulation of T cell differentiation and Treg function has been described previously; however, the role of EZH2 in T cell-mediated antitumor immunity, especially in the context of immune checkpoint therapy, is not understood. Here, we showed that genetic depletion of EZH2 in Tregs (FoxP3creEZH2fl/fl mice) leads to robust antitumor immunity. In addition, pharmacological inhibition of EZH2 in human T cells using CPI-1205 elicited phenotypic and functional alterations of the Tregs and enhanced cytotoxic activity of Teffs. We observed that ipilimumab (anti-CTLA-4) increased EZH2 expression in peripheral T cells from treated patients. We hypothesized that inhibition of EZH2 expression in T cells would increase the effectiveness of anti-CTLA-4 therapy, which we tested in murine models. Collectively, our data demonstrated that modulating EZH2 expression in T cells can improve antitumor responses elicited by anti-CTLA-4 therapy, which provides a strong rationale for a combination trial of CPI-1205 plus ipilimumab.

Role of EZH2 in liver disease

Overexpression of enhancer of zeste homolog 2 (EZH2) protein has been found in several malignant tumor tissues and is closely related to the degree of tumor differentiation, clinical stage, tumor size, and prognosis. The latest research shows that overexpression of EZH2 is related not only with immunoregulation but also with the replication of hepatitis B virus, the occurrence of non-alcoholic fatty liver disease, and the progress of liver fibrosis, which may become an important subject in the field of liver disease research. This paper reviews the role of EZH2 in some liver diseases and its potential application in treatment of these diseases in recent ten years.

Enhancer of zeste homolog 2-catalysed H3K27 trimethylation plays a key role in acute-on-chronic liver failure via TNF-mediated pathway

Acute-on-chronic liver failure is mainly due to host immunity self-destruction. The histone H3 lysine 27 (H3K27) trimethylating enzyme, enhancer of zeste homolog 2 (EZH2) mediates epigenetic silencing of gene expression and regulates immunity, also involves pathogenesis of several liver diseases. The current study was to determine the role of methyltransferase EZH2 and its catalysed H3K27 trimethylation (H3K27me3) in liver failure, and to further investigate the potential target for liver failure treatment. EZH2 and its catalysed H3K27me3 were determined in peripheral blood mononuclear cells (PBMC) from liver failure patients and Kupffer cells from experimental mice. Furthermore, GSK126 (an inhibitor for EZH2 trimethylation function) was applied in liver failure mice in vivo, and lipopolysaccharide-stimulated mononuclear cells in vitro. EZH2 and H3K27me3 were significantly upregulated in human PBMC from liver failure patients or murine Kupffer cells from the liver failure animals, respectively. GSK126 ameliorated disease severity in liver failure mice, which maybe attribute to down-regulate circulating and hepatic proinflammatory cytokines, especially TNF via reducing H3K27me3. In-depth chromatin immunoprecipitation analysis unravelled that decreased enrichment of H3K27me3 on Tnf promotor, resulting in TNF elevation in Kupffer cells from liver failure mice. Nuclear factor kappa B (NF-κB) and protein kinase B (Akt) signalling pathways were activated upon lipopolysaccharide stimulation, but attenuated by using GSK126, accompanied with decreased TNF in vitro. In conclusion, EZH2 and H3K27me3 contributed to the pathogenesis of liver failure via triggering TNF and other indispensable proinflammatory cytokines. EZH2 was to modify H3K27me3 enrichment, as well as, activation of the downstream NF-κB and Akt signalling pathways.

Let-7e inhibits TNF-α expression by targeting the methyl transferase EZH2 in DENV2-infected THP-1 cells

Tumor necrosis factor α (TNFα), an important inflammatory cytokine, is associated with dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), a severe pathological manifestation of dengue virus (DENV) infection. However, the regulatory mechanism of microRNA on TNFα is currently unknown. Our study showed that the TNFα expression increased immediately and then later decreased, while a marked increase for the miRNA let-7e was detected in dengue virus type 2 (DENV2)-infected peripheral blood mononuclear cells (PBMCs). From this study, we found that let-7e was able to inhibit TNFα expression, but bioinformatics analysis showed that the enhancer of zeste homolog 2 (EZH2) was the potential direct target of let-7e instead of TNFα. EZH2 methyl transferase can produce H3K27me3 and has a negative regulatory role. Using a dual-luciferase reporter assay and Western blotting, we confirmed that EZH2 was a direct target of let-7e and found that siEZH2 could inhibit TNFα expression. In the further study of the regulatory mechanism of EZH2 on TNFα expression, we showed that siEZH2 promoted EZH1 and H3K4me3 expression and inhibited H3K27me3 expression. More importantly, we revealed that siEZH2 down-regulated NF-κB p65 within the nucleus. These findings indicate that the let-7e/EZH2/H3K27me3/NF-κB p65 pathway is a novel regulatory axis of TNFα expression. In addition, we determined the protein differences between siEZH2 and siEZH2-NC by iTRAQ and found a number of proteins that might be associated with TNFα.

Schistosomiasis Induces Persistent DNA Methylation and Tuberculosis-Specific Immune Changes

Epigenetic mechanisms, such as DNA methylation, determine immune cell phenotype. To understand the epigenetic alterations induced by helminth coinfections, we evaluated the longitudinal effect of ascariasis and schistosomiasis infection on CD4⁺ T cell DNA methylation and the downstream tuberculosis (TB)-specific and bacillus Calmette-Guérin-induced immune phenotype. All experiments were performed on human primary immune cells from a longitudinal cohort of recently TB-exposed children. Compared with age-matched uninfected controls, children with active Schistosoma haematobium and Ascaris lumbricoides infection had 751 differentially DNA-methylated genes, with 72% hypermethylated. Gene ontology pathway analysis identified inhibition of IFN-γ signaling, cellular proliferation, and the Th1 pathway. Targeted real-time quantitative PCR after methyl-specific endonuclease digestion confirmed DNA hypermethylation of the transcription factors BATF3, ID2, STAT5A, IRF5, PPARg, RUNX2, IRF4, and NFATC1 and cytokines or cytokine receptors IFNGR1, TNFS11, RELT (TNF receptor), IL12RB2, and IL12B (p < 0.001; Sidak-Bonferroni). Functional blockage of the IFN-γ signaling pathway was confirmed, with helminth-infected individuals having decreased upregulation of IFN-γ-inducible genes (Mann-Whitney p < 0.05). Hypomethylation of the IL-4 pathway and DNA hypermethylation of the Th1 pathway was confirmed by Ag-specific multidimensional flow cytometry demonstrating decreased TB-specific IFN-γ and TNF and increased IL-4 production by CD4+ T cells (Wilcoxon signed-rank p < 0.05). In S. haematobium-infected individuals, these DNA methylation and immune phenotypic changes persisted at least 6 mo after successful deworming. This work demonstrates that helminth infection induces DNA methylation and immune perturbations that inhibit TB-specific immune control and that the duration of these changes are helminth specific.

Macrophage/microglial Ezh2 facilitates autoimmune inflammation through inhibition of Socs3

Histone 3 Lys27 (H3K27) trimethyltransferase Ezh2 is implicated in the pathogenesis of autoimmune inflammation. Nevertheless, the role of Ezh2 in macrophage/microglial activation remains to be defined. In this study, we identified that macrophage/microglial H3K27me3 or Ezh2, rather than functioning as a repressor, mediates toll-like receptor (TLR)-induced proinflammatory gene expression, and therefore Ezh2 depletion diminishes macrophage/microglial activation and attenuates the autoimmune inflammation in dextran sulfate sodium-induced colitis and experimental autoimmune encephalomyelitis. Mechanistic characterizations indicated that Ezh2 deficiency directly stimulates suppressor of cytokine signaling 3 (Socs3) expression and therefore enhances the Lys48-linked ubiquitination and degradation of tumor necrosis factor receptor-associated factor 6. As a consequence, TLR-induced MyD88-dependent nuclear factor κB activation and the expression of proinflammatory genes in macrophages/microglia are compromised in the absence of Ezh2. The functional dependence of Ezh2 for Socs3 is further illustrated by the rescue experiments in which silencing of Socs3 restores macrophage activation and rescues autoimmune inflammation in macrophage/microglial Ezh2-deficient mice. Together, these findings establish Ezh2 as a macrophage lineage-specific mediator of autoimmune inflammation and highlight a previously unknown mechanism of Ezh2 function.

Repressing the repressor: Ezh2 mediates macrophage activation

In this issue of JEM, Zhang et al. (https://doi.org/10.1084/jem.20171417) show that the suppressive epigenetic enzyme Ezh2 is an important regulator of macrophage activation. The absence of Ezh2 leads to reduced cytokine secretion and suppresses macrophage-dependent disease development. They identify the antiinflammatory factor Socs3 as an important target for Ezh2 and thus show that regulation of suppressive histone modifications controls macrophage activation in disease.

Ezh2 Regulates Activation-Induced CD8+ T Cell Cycle Progression via Repressing Cdkn2a and Cdkn1c Expression

Transition from resting to cell cycle in response to antigenic stimulation is an essential step for naïve CD8⁺ T cells to differentiate to effector and memory cells. Leaving the resting state requires dramatic changes of chromatin status in the key cell cycle inhibitors but the details of these concerted events are not fully elucidated. Here, we showed that Ezh2, an enzymatic component of polycomb repressive complex 2 (PRC2) catalyzing the trimethylation of lysine 27 on histone 3 (H3K27me3), regulates activation induced naïve CD8⁺ T cells proliferation and apoptosis. Upon deletion of Ezh2 during thymocyte development (Ezh2^fl/flCd4Cre⁺ mice), naive CD8⁺ T cells displayed impaired proliferation and increased apoptosis in response to antigen stimulation. However, naive CD8⁺ T cells only had impaired proliferation but no increase in apoptosis when Ezh2 was deleted after activation (Ezh2^fl/flGzmBCre⁺ mice), suggesting cell cycle and apoptosis are temporally separable events controlled by Ezh2. We then showed that deletion of Ezh2 resulted in the increase in expression of cyclin-dependent kinase inhibitors Cdkn2a (p16 and Arf) and Cdkn1c (p57) in activated naïve CD8⁺ T cells as the consequence of reduced levels of H3K27me3 at these two gene loci. Finally, with real time imaging, we observed prolonged cell division times of naïve CD8⁺ T cells in the absence of Ezh2 post in vitro stimulation. Together, these findings reveal that repression of Cdkn1c and Cdkn2a by Ezh2 plays a critical role in execution of activation-induced CD8⁺ T cell proliferation.

Epigenetic regulation of T-helper cell differentiation, memory, and plasticity in allergic asthma

An estimated 300 million people currently suffer from asthma, which causes approximately 250 000 deaths a year. Allergen-specific T-helper (Th) cells produce cytokines that induce many of the hallmark features of asthma including airways hyperreactivity, eosinophilic and neutrophilic inflammation, mucus hypersecretion, and airway remodeling. Cytokine-producing Th subsets including Th1 (IFN-γ), Th2 (IL-4, IL-5, IL-13), Th9 (IL-9), Th17 (IL-17), Th22 (IL-22), and T regulatory (IL-10) cells have all been suggested to play a role in the development of asthma. Th differentiation involves genetic regulation of gene expression through the concerted action of cytokines, transcription factors, and epigenetic regulators. We describe how Th differentiation and plasticity is regulated by epigenetic histone and DNA modifications, with a focus on the regulation of histone methylation by members of the polycomb and trithorax complexes. In addition, we outline environmental influences that could influence epigenetic regulation of Th cells and discuss the potential to regulate Th plasticity and function through drugs targeting the epigenetic machinery. It is also becoming apparent that epigenetic regulation of allergen-specific memory Th cells may be important in the development and persistence of chronic allergies. Finally, we describe how epigenetic modifiers regulate cytokine memory in Th cells and describe recently identified hybrid, plastic, and pathogenic memory Th subsets the context of allergic asthma.

Identification of Casz1 as a Regulatory Protein Controlling T Helper Cell Differentiation, Inflammation, and Immunity

While T helper (Th) cells play a crucial role in host defense, an imbalance in Th effector subsets due to dysregulation in their differentiation and expansion contribute to inflammatory disorders. Here, we show that Casz1, whose function is previously unknown in CD4+ T cells, coordinates Th differentiation in vitro and in vivo. Casz1 deficiency in CD4+ T cells lowers susceptibility to experimental autoimmune encephalomyelitis, consistent with the reduced frequency of Th17 cells, despite an increase in Th1 cells in mice. Loss of Casz1 in the context of mucosal Candida infection severely impairs Th17 and Treg responses, and lowers the ability of the mice to clear the secondary infection. Importantly, in both the models, absence of Casz1 causes a significant diminution in IFN-γ+IL-17A+ double-positive inflammatory Th17 cells (Th1* cells) in tissues in vivo. Transcriptome analyses of CD4+ T cells lacking Casz1 show a signature consistent with defective Th17 differentiation. With regards to Th17 differentiation, Casz1 limits repressive histone marks and enables acquisition of permissive histone marks at Rorc, Il17a, Ahr, and Runx1 loci. Taken together, these data identify Casz1 as a new Th plasticity regulator having important clinical implications for autoimmune inflammation and mucosal immunity.

Potential Epigenetic Regulation in the Germinal Center Reaction of Lymphoid Tissues in HIV/SIV Infection

The production of high-affinity and broadly neutralizing antibodies plays a key role in the defense against pathogens. These antibody responses require effective germinal center (GC) reaction within anatomical niches of GCs, where follicular helper T (Tfh) cells provide cognate help to B cells for T cell-dependent antibody responses. Emerging evidences indicate that GC reaction in normal state and perhaps establishment of latent Tfh cell reservoir in HIV/SIV infection are tightly regulated by epigenetic histone modifications, which are responsible for activating or silencing chromatin. A better understanding of the mechanisms behind GC responses at cellular and molecular levels thus provides necessary knowledge for vaccination and immunotherapy. In this review, we discussed the epigenetic regulation of GC responses, especially for GC B and Tfh cell under normal state or HIV/SIV infection.

Connections Between Metabolism and Epigenetics in Programming Cellular Differentiation

Researchers are intensifying efforts to understand the mechanisms by which changes in metabolic states influence differentiation programs. An emerging objective is to define how fluctuations in metabolites influence the epigenetic states that contribute to differentiation programs. This is because metabolites such as S-adenosylmethionine, acetyl-CoA, α-ketoglutarate, 2-hydroxyglutarate, and butyrate are donors, substrates, cofactors, and antagonists for the activities of epigenetic-modifying complexes and for epigenetic modifications. We discuss this topic from the perspective of specialized CD4⁺ T cells as well as effector and memory T cell differentiation programs. We also highlight findings from embryonic stem cells that give mechanistic insight into how nutrients processed through pathways such as glycolysis, glutaminolysis, and one-carbon metabolism regulate metabolite levels to influence epigenetic events and discuss similar mechanistic principles in T cells. Finally, we highlight how dysregulated environments, such as the tumor microenvironment, might alter programming events.