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.

Dynamic regulation of T follicular regulatory cell responses by interleukin 2 during influenza infection.

Interleukin 2 (IL-2) promotes Foxp3+ regulatory T (Treg) cell responses, but inhibits T follicular helper (TFH) cell development. However, it is not clear how IL-2 affects T follicular regulatory (TFR) cells, a cell type with properties of both Treg and TFH cells. Using an influenza infection model, we found that high IL-2 concentrations at the peak of the infection prevented TFR cell development by a Blimp-1-dependent mechanism. However, once the immune response resolved, some Treg cells downregulated CD25, upregulated Bcl-6 and differentiated into TFR cells, which then migrated into the B cell follicles to prevent the expansion of self-reactive B cell clones. Thus, unlike its effects on conventional Treg cells, IL-2 inhibits TFR cell responses.

Defining Barriers that Impede Choices.

Committing to a differentiation pathway means leaving alternative pathways behind. Adoue et al. (2019) report that the H3K9-methyltrasferase Setdb1 plays a role in inhibiting the Th1 program in committed Th2 cells, and mechanistically, its role might relate to the selective targeting of endogenous retroviruses adjacent to Th1 enhancers.

Defining Genetic Variation in Widely Used Congenic and Backcrossed Mouse Models Reveals Varied Regulation of Genes Important for Immune Responses.

Genetic variation influences how the genome is interpreted in individuals and in mouse strains used to model immune responses. We developed approaches to utilize next-generation sequencing datasets to identify sequence variation in genes and enhancer elements in congenic and backcross mouse models. We defined genetic variation in the widely used B6-CD45.2 and B6.SJL-CD45.1 congenic model, identifying substantial differences in SJL genetic content retained in B6.SJL-CD45.1 strains on the basis of the vendor source of the mice. Genes encoding PD-1, CD62L, Bcl-2, cathepsin E, and Cxcr4 were within SJL genetic content in at least one vendor source of B6.SJL-CD45.1 mice. SJL genetic content affected enhancer elements, gene regulation, protein expression, and amino acid content in CD4+ T helper 1 cells, and mice infected with influenza showed reduced expression of Cxcr4 on B6.SJL-CD45.1 T follicular helper cells. These findings provide information on experimental variables and aid in creating approaches that account for genetic variables.

T-bet Transcription Factor Promotes Antibody-Secreting Cell Differentiation by Limiting the Inflammatory Effects of IFN-γ on B Cells.

Although viral infections elicit robust interferon-γ (IFN-γ) and long-lived antibody-secreting cell (ASC) responses, the roles for IFN-γ and IFN-γ-induced transcription factors (TFs) in ASC development are unclear. We showed that B cell intrinsic expression of IFN-γR and the IFN-γ-induced TF T-bet were required for T-helper 1 cell-induced differentiation of B cells into ASCs. IFN-γR signaling induced Blimp1 expression in B cells but also initiated an inflammatory gene program that, if not restrained, prevented ASC formation. T-bet did not affect Blimp1 upregulation in IFN-γ-activated B cells but instead regulated chromatin accessibility within the Ifng and Ifngr2 loci and repressed the IFN-γ-induced inflammatory gene program. Consistent with this, B cell intrinsic T-bet was required for formation of long-lived ASCs and secondary ASCs following viral, but not nematode, infection. Therefore, T-bet facilitates differentiation of IFN-γ-activated inflammatory effector B cells into ASCs in the setting of IFN-γ-, but not IL-4-, induced inflammatory responses.

Bcl-6 directly represses the gene program of the glycolysis pathway.

Despite the increasing knowledge of the molecular events that induce the glycolysis pathway in effector T cells, very little is known about the transcriptional mechanisms that dampen the glycolysis program in quiescent cell populations such as memory T cells. Here we found that the transcription factor Bcl-6 directly repressed genes encoding molecules involved in the glycolysis pathway, including Slc2a1, Slc2a3, Pkm and Hk2, in type 1 helper T cells (TH1 cells) exposed to low concentrations of interleukin 2 (IL-2). Thus, Bcl-6 had a role opposing the IL-2-sensitive glycolytic transcriptional program that the transcription factors c-Myc and HIF-1α promote in effector T cells. Additionally, the TH1 lineage-specifying factor T-bet functionally antagonized the Bcl-6-dependent repression of genes encoding molecules in the glycolysis pathway, which links the molecular balance of these two factors to regulation of the metabolic gene program.

Discovering effector domains in human transcription factors.

Genomic studies are transforming knowledge about the epigenetic, transcription factor, and 3D landscapes of the genome. However, comprehensive information is lacking about the effector domains used by transcription factors to influence gene expression. Addressing this gap, DelRosso et al. developed a high-throughput screen to discover effector domains in human regulatory factors.

CCCTC-Binding Factor Translates Interleukin 2- and α-Ketoglutarate-Sensitive Metabolic Changes in T Cells into Context-Dependent Gene Programs.

Despite considerable research connecting cellular metabolism with differentiation decisions, the underlying mechanisms that translate metabolite-sensitive activities into unique gene programs are still unclear. We found that aspects of the interleukin-2 (IL-2)-sensitive effector gene program in CD4+ and CD8+ T cells in type 1 conditions (Th1) were regulated by glutamine and alpha-ketoglutarate (αKG)-induced events, in part through changes in DNA and histone methylation states. We further identified a mechanism by which IL-2- and αKG-sensitive metabolic changes regulated the association of CCCTC-binding factor (CTCF) with select genomic sites. αKG-sensitive CTCF sites were often associated with loci containing IL-2- and αKG-sensitive genome organization patterns and gene expression in T cells. IL-2- and αKG-sensitive CTCF sites in T cells were also associated with genes from developmental pathways that had αKG-sensitive expression in embryonic stem cells. The data collectively support a mechanism wherein CTCF serves to translate αKG-sensitive metabolic changes into context-dependent differentiation gene programs.

One degree of separation: urgent questions surrounding new USA laws in women's healthcare.

The criminalization of women's healthcare in many USA states has created uncertainty about women's access to evidence-based medical care and will affect the physical, mental, and emotional health and well-being of women. This article is intended to start a discussion on this complex topic in the immunology community.

Molecular mechanisms that control the expression and activity of Bcl-6 in TH1 cells to regulate flexibility with a TFH-like gene profile.

The transcription factors T-bet and Bcl-6 are required for the establishment of a T helper type 1 cell (T(H)1 cell) and follicular helper T cell (T(FH) cell) gene-expression profile, respectively. Here we found that high concentrations of interleukin 2 (IL-2) inhibited Bcl-6 expression in polarized T(H)1 cells. Mechanistically, the low concentrations of Bcl-6 normally found in effector T(H)1 cells did not repress its target genes because a T-bet-Bcl-6 complex masked the Bcl-6 DNA-binding domain. T(H)1 cells increased their Bcl-6/T-bet ratio in response to limiting IL-2 conditions, which allowed excess Bcl-6 to repress its direct target Prdm1 (which encodes the transcriptional repressor Blimp-1). The Bcl-6-dependent repression of Blimp-1 effectively induced a partial T(FH) profile because Blimp-1 directly repressed a subset of T(FH) signature genes, including Cxcr5. Thus, IL-2-signaling regulates the Bcl-6-Blimp-1 axis in T(H)1 cells to maintain flexibility with a T(FH) cell-like gene profile.

Conservation and divergence in gene regulation between mouse and human immune cells deserves equal emphasis.

Model organisms such as mice are important for basic research and serve as valuable tools in preclinical translational studies. A challenge with translating findings from mice to humans is identifying and separating evolutionarily conserved mechanisms in the immune system from those diverging between species. A significant emphasis has been placed on defining conserved gene regulation principles, with divergent mechanisms often overlooked. We put forward the perspective that both conserved and divergent mechanisms that regulate gene expression programs are of equal importance. With recent advances and availability of datasets, immunologists should take a closer look at the role for genetic diversity in altering gene expression programs between mouse and human immune cells.

Transcription factor T-bet represses expression of the inhibitory receptor PD-1 and sustains virus-specific CD8+ T cell responses during chronic infection.

T cell exhaustion has a major role in failure to control chronic infection. High expression of inhibitory receptors, including PD-1, and the inability to sustain functional T cell responses contribute to exhaustion. However, the transcriptional control of these processes remains unclear. Here we demonstrate that the transcription factor T-bet regulated the exhaustion of CD8(+) T cells and the expression of inhibitory receptors. T-bet directly repressed transcription of the gene encoding PD-1 and resulted in lower expression of other inhibitory receptors. Although a greater abundance of T-bet promoted terminal differentiation after acute infection, high T-bet expression sustained exhausted CD8(+) T cells and repressed the expression of inhibitory receptors during chronic viral infection. Persistent antigenic stimulation caused downregulation of T-bet, which resulted in more severe exhaustion of CD8(+) T cells. Our observations suggest therapeutic opportunities involving higher T-bet expression during chronic infection.

Are You There? Genetic Variation Impacts Long-Distance Connections in Diabetes.

A new study by Fasolino et al. defines how genetic variation in a mouse model of type 1 diabetes mellitus (T1DM) affects long-distance genomic interactions. The research has widespread implications for understanding how genetic diversity impacts disease susceptibility, and raises important concepts about mechanisms that can be influenced by genetic diversity between individuals.

Protein Kinase CK2 Controls the Fate between Th17 Cell and Regulatory T Cell Differentiation.

CK2 is a highly conserved and pleiotropic serine/threonine kinase that promotes many prosurvival and proinflammatory signaling pathways, including PI3K/Akt/mTOR and JAK/STAT. These pathways are essential for CD4+ T cell activation and polarization, but little is known about how CK2 functions in T cells. In this article, we demonstrate that CK2 expression and kinase activity are induced upon CD4+ T cell activation. Targeting the catalytic activity of CK2 using the next-generation small molecule inhibitor CX-4945 in vitro significantly and specifically inhibited mouse and human Th17 cell differentiation while promoting the generation of Foxp3+ regulatory T cells (Tregs). These findings were associated with suppression of PI3K/Akt/mTOR activation and STAT3 phosphorylation upon CX-4945 treatment. Furthermore, we demonstrate that CX-4945 treatment inhibits the maturation of Th17 cells into inflammatory IFN-γ-coproducing effector cells. The Th17/Treg axis and maturation of Th17 cells are major contributing factors to the pathogenesis of many autoimmune disorders, including multiple sclerosis. Using a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis, we demonstrate that in vivo administration of CX-4945 targets Akt/mTOR signaling in CD4+ T cells and the Th17/Treg axis throughout disease. Importantly, CX-4945 treatment after disease initiation significantly reduced disease severity, which was associated with a significant decrease in the frequency of pathogenic IFN-γ+ and GM-CSF+ Th17 cells in the CNS. Our data implicate CK2 as a regulator of the Th17/Treg axis and Th17 cell maturation and suggest that CK2 could be targeted for the treatment of Th17 cell-driven autoimmune disorders.

CCCTC-binding factor and the transcription factor T-bet orchestrate T helper 1 cell-specific structure and function at the interferon-gamma locus.

How cell type-specific differences in chromatin conformation are achieved and their contribution to gene expression are incompletely understood. Here we identify a cryptic upstream orchestrator of interferon-gamma (IFNG) transcription, which is embedded within the human IL26 gene, compromised of a single CCCTC-binding factor (CTCF) binding site and retained in all mammals, even surviving near-complete evolutionary deletion of the equivalent gene encoding IL-26 in rodents. CTCF and cohesins occupy this element in vivo in a cell type-nonspecific manner. This element is juxtaposed to two other sites located within the first intron and downstream of Ifng, where CTCF, cohesins, and the transcription factor T-bet bind in a T helper 1 (Th1) cell-specific manner. These interactions, close proximity of other elements within the locus to each other and to the gene encoding interferon-gamma, and robust murine Ifng expression are dependent on CTCF and T-bet. The results demonstrate that cooperation between architectural (CTCF) and transcriptional enhancing (T-bet) factors and the elements to which they bind is required for proper Th1 cell-specific expression of Ifng.

Jmjd3 and UTX play a demethylase-independent role in chromatin remodeling to regulate T-box family member-dependent gene expression.

The stable and heritable H3K27-methyl mark suppresses transcription of lineage-specific genes in progenitor cells. During developmental transitions, histone demethylases are required to dramatically alter epigenetic and gene expression states to create new cell-specific profiles. It is unclear why demethylase proteins that antagonize polycomb-mediated repression continue to be expressed in terminally differentiated cells where further changes in H3K27 methylation could be deleterious. In this study, we show that the H3K27 demethylases, Jmjd3 and UTX, mediate a functional interaction between the lineage-defining T-box transcription factor family and a Brg1-containing SWI/SNF remodeling complex. Importantly, Jmjd3 is required for the coprecipitation of Brg1 with the T-box factor, T-bet, and this interaction is necessary for Ifng remodeling in differentiated Th1 cells. Thus, Jmjd3 has a required role in general chromatin remodeling that is independent from its H3K27 demethylase potential. This function for H3K27 demethylase proteins may explain their presence in differentiated cells where the epigenetic profile is already established.