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

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.

The spectrum of T cell metabolism in health and disease

In healthy individuals, metabolically quiescent T cells survey lymph nodes and peripheral tissues in search of cognate antigens. During infection, T cells that encounter cognate antigens are activated and - in a context-specific manner - proliferate and/or differentiate to become effector T cells. This process is accompanied by important changes in cellular metabolism (known as metabolic reprogramming). The magnitude and spectrum of metabolic reprogramming as it occurs in T cells in the context of acute infection ensure host survival. By contrast, altered T cell metabolism, and hence function, is also observed in various disease states, in which T cells actively contribute to pathology. In this Review, we introduce the idea that the spectrum of immune cell metabolic states can provide a basis for categorizing human diseases. Specifically, we first summarize the metabolic and interlinked signalling requirements of T cells responding to acute infection. We then discuss how metabolic reprogramming of T cells is linked to disease.

Biochemical Underpinnings of Immune Cell Metabolic Phenotypes

The metabolism of immune cells affects their function and influences host immunity. This review explores how immune cell metabolic phenotypes reflect biochemical dependencies and highlights evidence that both the metabolic state of immune cells and nutrient availability can alter immune responses. The central importance of oxygen, energetics, and redox homeostasis in immune cell metabolism, and how these factors are reflected in different metabolic phenotypes, is also discussed. Linking immune cell metabolic phenotype to effector functions is important to understand how altering metabolism can impact the way in which immune cells meet their metabolic demands and affect the immune response in various disease contexts.

Metabolic Regulation of the Immune Humoral Response

Productive humoral responses require that naive B cells and their differentiated progeny move among distinct micro-environments. In this review, we discuss how studies are beginning to address the nature of these niches as well as the interplay between cellular signaling, metabolic programming, and adaptation to the locale. Recent work adds evidence to the expectation that B cells at distinct stages of development or functional subsets are influenced by the altered profiles of nutrients and metabolic by-products that distinguish these sites. Moreover, emerging findings reveal a cross-talk among the external milieu, signal transduction pathways, and transcription factors that direct B cell fate in the periphery.

Integrated STAT3 and Ikaros Zinc Finger Transcription Factor Activities Regulate Bcl-6 Expression in CD4+ Th Cells

B cell lymphoma-6 (Bcl-6) is a transcriptional repressor that is required for the differentiation of T follicular helper (T_FH) cell populations. Currently, the molecular mechanisms underlying the transcriptional regulation of Bcl-6 expression are unclear. In this study, we have identified the Ikaros zinc finger transcription factors Aiolos and Ikaros as novel regulators of Bcl-6. We found that increased expression of Bcl-6 in CD4⁺ Th cell populations correlated with enhanced enrichment of Aiolos and Ikaros at the Bcl6 promoter. Furthermore, overexpression of Aiolos or Ikaros, but not the related family member Eos, was sufficient to induce Bcl6 promoter activity. Intriguingly, STAT3, a known Bcl-6 transcriptional regulator, physically interacted with Aiolos to form a transcription factor complex capable of inducing the expression of Bcl6 and the T_FH-associated cytokine receptor Il6ra Importantly, in vivo studies revealed that the expression of Aiolos was elevated in Ag-specific T_FH cells compared with that observed in non-T_FH effector Th cells generated in response to influenza infection. Collectively, these data describe a novel regulatory mechanism through which STAT3 and the Ikaros zinc finger transcription factors Aiolos and Ikaros cooperate to regulate Bcl-6 expression.

Proteasome activity regulates CD8+ T lymphocyte metabolism and fate specification

During an immune response, CD8+ T lymphocytes can undergo asymmetric division, giving rise to daughter cells that exhibit distinct tendencies to adopt terminal effector and memory cell fates. Here we show that "pre-effector" and "pre-memory" cells resulting from the first CD8+ T cell division in vivo exhibited low and high rates of endogenous proteasome activity, respectively. Pharmacologic reduction of proteasome activity in CD8+ T cells early during differentiation resulted in acquisition of terminal effector cell characteristics, whereas enhancement of proteasome activity conferred attributes of memory lymphocytes. Transcriptomic and proteomic analyses revealed that modulating proteasome activity in CD8+ T cells affected cellular metabolism. These metabolic changes were mediated, in part, through differential expression of Myc, a transcription factor that controls glycolysis and metabolic reprogramming. Taken together, these results demonstrate that proteasome activity is an important regulator of CD8+ T cell fate and raise the possibility that increasing proteasome activity may be a useful therapeutic strategy to enhance the generation of memory lymphocytes.

Lymphocyte Fate and Metabolism: A Clonal Balancing Act

Activated lymphocytes perform a clonal balancing act, yielding a daughter cell that differentiates owing to intense PI3K signaling, alongside a self-renewing sibling cell with blunted anabolic signaling. Divergent cellular anabolism versus catabolism is emerging as a feature of several developmental and regenerative paradigms. Metabolism can dictate cell fate, in part, because lineage-specific regulators are embedded in the circuitry of conserved metabolic switches. Unequal transmission of PI3K signaling during regenerative divisions is reminiscent of compartmentalized PI3K activity during directed motility or polarized information flow in non-dividing cells. The diverse roles of PI3K pathways in membrane traffic, cell polarity, metabolism, and gene expression may have converged to instruct sibling cell feast and famine, thereby enabling clonal differentiation alongside self-renewal.

Signals that drive T follicular helper cell formation

T follicular helper (Tfh) cells are a distinct type of CD4⁺ T cell specialized in providing help to B cells during the germinal centre (GC) reaction. As such, they are critical determinants of the quality of an antibody response following antigen challenge. Excessive production of Tfh cells can result in autoimmunity whereas too few can result in inadequate protection from infection. Hence, their differentiation and maintenance must be tightly regulated to ensure appropriate but limited help to B cells. Unlike the majority of other CD4⁺ T-cell subsets, Tfh cell differentiation occurs in three phases defined by their anatomical location. During each phase of differentiation the emerging Tfh cells express distinct patterns of co-receptors, which work together with the T-cell receptor (TCR) to drive Tfh differentiation. These signals provided by both TCR and co-receptors during Tfh differentiation alter proliferation, survival, metabolism, cytokine production and transcription factor expression. This review will discuss how engagement of TCR and co-receptors work together to shape the formation and function of Tfh cells.

Unsupervised learning techniques reveal heterogeneity in memory CD8+ T cell differentiation following acute, chronic and latent viral infections

CD8⁺ T lymphocytes are critical for the control of gammaherpesvirus latency. To determine how memory CD8⁺ T cells generated during latency differ from those primed during acute or chronic viral infection, we adoptively transferred naive P14 CD8⁺ T cells into uninfected recipients, and examined surface proteins, cytokines and transcription factors following infection with the Armstrong (acute) or Clone 13 (chronic) strains of lymphocytic choriomeningitis virus (LCMV), or murine gammaherpesvirus 68 (MHV68) expressing the LCMV epitope D^bGP33-41. By performing k-means clustering and generating self organizing maps (SOM), we observed increased short-lived effector-like, CD27^lo CD62L^lo and Bcl-6^lo CD8⁺ T cells following latent infection. In addition, we found that memory CD8⁺ T cells from latent primed mice underwent less expansion following adoptive transfer and antigen rechallenge. Data from cluster models were combined and visualized by principal component analysis (PCA) demonstrating memory CD8⁺ T cells from latent infection occupy an intermediate differentiation space.

Human Immunodeficiency Virus Playing Hide-and-Seek: Understanding the TFH Cell Reservoir and Proposing Strategies to Overcome the Follicle Sanctuary

Human immunodeficiency virus (HIV) infects millions of people worldwide, and new cases continue to emerge. Once infected, the virus cannot be cleared by the immune system and causes acquired immunodeficiency syndrome. Combination antiretroviral therapeutic regimen effectively suppresses viral replication and halts disease progression. The treatment, however, does not eliminate the virus-infected cells, and interruption of treatment inevitably leads to viral rebound. The rebound virus originates from a group of virus-infected cells referred to as the cellular reservoir of HIV. Identifying and eliminating the HIV reservoir will prevent viral rebound and cure HIV infection. In this review, we focus on a recently discovered HIV reservoir in a subset of CD4⁺ T cells called the follicular helper T (T_FH) cells. We describe the potential mechanisms for the emergence of reservoir in T_FH cells, and the strategies to target and eliminate this viral reservoir.

Metabolic Instruction of Immunity

Choices have consequences. Immune cells survey and migrate throughout the body and sometimes take residence in niche environments with distinct communities of cells, extracellular matrix, and nutrients that may differ from those in which they matured. Imbedded in immune cell physiology are metabolic pathways and metabolites that not only provide energy and substrates for growth and survival, but also instruct effector functions, differentiation, and gene expression. This review of immunometabolism will reference the most recent literature to cover the choices that environments impose on the metabolism and function of immune cells and highlight their consequences during homeostasis and disease.

Dysfunctional T cell metabolism in the tumor microenvironment

Metabolic and signaling pathways are integrated to determine T cell fate and function. As stimulated T cells gain distinct effector functions, specific metabolic programs and demands are also adopted. These changes are essential for T cell effector function, and alterations or dysregulation of metabolic pathways can modulate T cell function. One physiological setting that impacts T cell metabolism is the tumor microenvironment. The metabolism of cancer cells themselves can limit nutrients and accumulate waste products. In addition to the expression of inhibitory ligands that directly modify T cell physiology, T cell metabolism may be strongly inhibited in the tumor microenvironment. This suppression of T cell metabolism may inhibit effector T cell activity while promoting suppressive regulatory T cells, and act as a barrier to effective immunotherapies. A thorough understanding of the effect of the tumor microenvironment on the immune system will support the continued improvement of immune based therapies for cancer patients.

mTORC1 Promotes T-bet Phosphorylation To Regulate Th1 Differentiation

CD4⁺ T cells lacking the mTORC1 activator Rheb fail to secrete IFN-γ under Th1 polarizing conditions. We hypothesized that this phenotype is due to defects in regulation of the canonical Th1 transcription factor T-bet at the level of protein phosphorylation downstream of mTORC1. To test this hypothesis, we employed targeted mass-spectrometry proteomic analysis-multiple reaction monitoring mass spectrometry. We used this method to detect and quantify predicted phosphopeptides derived from T-bet. By analyzing activated murine wild-type and Rheb-deficient CD4⁺ T cells, as well as murine CD4⁺ T cells activated in the presence of rapamycin, a pharmacologic inhibitor of mTORC1, we were able to identify six T-bet phosphorylation sites. Five of these are novel, and four sites are consistently dephosphorylated in both Rheb-deficient CD4⁺ T cells and T cells treated with rapamycin, suggesting mTORC1 signaling controls their phosphorylation. Alanine mutagenesis of each of the six phosphorylation sites was tested for the ability to impair IFN-γ expression. Single phosphorylation site mutants still support induction of IFN-γ expression; however, simultaneous mutation of three of the mTORC1-dependent sites results in significantly reduced IFN-γ expression. The reduced activity of the triple mutant T-bet is associated with its failure to recruit chromatin remodeling complexes to the Ifng gene promoter. These results establish a novel mechanism by which mTORC1 regulates Th1 differentiation, through control of T-bet phosphorylation.

Transcription Factor T-bet Orchestrates Lineage Development and Function in the Immune System

T-bet was originally described as the key transcription factor defining type 1 T helper (Th) cells. However, it is now clear that it drives the orchestrated generation of effector and memory cells in multiple different lymphocyte lineages. In addition to Th1 cells, CD8 T cells, B cells and some innate lymphocyte populations require T-bet for their development or differentiation in response to antigen. Furthermore, other Th cell populations, including T follicular helper and Th17, as well as regulatory T cells can co-opt T-bet expression to promote functional diversification and colocalization. Thus, T-bet broadly regulates transcriptional programs in response to type 1 inflammatory signals and mediates the coordinated differentiation, function, migration and survival of effector and memory lymphocyte subsets in the affected tissue. Therefore, T-bet expression is essential for effective clearance of pathogens and maintenance of immunity.

IL2 is required for functional maturation of regulatory T cells

Regulatory T cells (Tregs), specified by the expression of transcription factor Foxp3, operate Foxp3-dependent programs to maintain self-tolerance. In addition to Foxp3, other tissue-specific transcription factors are also required by Tregs to control the corresponding immune responses like follicular Tregs which express both Foxp3 and Bcl6 controlling germinal center reactions. Here, we show that Interleukin 2 (IL2) is required for the optimal expression of T helper type 1 (Th1) transcription factor T-box 21 (Tbx21, T-bet) in Tregs. The expression levels of CXCR3 and T-bet were reduced in IL2 deficient Tregs. Furthermore, IL2 deficient Treg cells failed to control the proliferation of CD4⁺ T cells in vitro and could not prevent the progression of colitis characterized by Th1 immune responses. Taken together, our data suggest that IL2 is essential for the functional maturation of Tregs including the optimal suppressive activity and the expression of tissue-specific transcription factors like T-bet.

S-2-hydroxyglutarate regulates CD8+ T-lymphocyte fate

R-2-hydroxyglutarate accumulates to millimolar levels in cancer cells with gain-of-function isocitrate dehydrogenase 1/2 mutations. These levels of R-2-hydroxyglutarate affect 2-oxoglutarate-dependent dioxygenases. Both metabolite enantiomers, R- and S-2-hydroxyglutarate, are detectible in healthy individuals, yet their physiological function remains elusive. Here we show that 2-hydroxyglutarate accumulates in mouse CD8+ T cells in response to T-cell receptor triggering, and accumulates to millimolar levels in physiological oxygen conditions through a hypoxia-inducible factor 1-alpha (HIF-1α)-dependent mechanism. S-2-hydroxyglutarate predominates over R-2-hydroxyglutarate in activated T cells, and we demonstrate alterations in markers of CD8+ T-cell differentiation in response to this metabolite. Modulation of histone and DNA demethylation, as well as HIF-1α stability, mediate these effects. S-2-hydroxyglutarate treatment greatly enhances the in vivo proliferation, persistence and anti-tumour capacity of adoptively transferred CD8+ T cells. Thus, S-2-hydroxyglutarate acts as an immunometabolite that links environmental context, through a metabolic-epigenetic axis, to immune fate and function.

AMP kinase promotes Bcl6 expression in both mouse and human T cells

The transcription factor Bcl6 is a master regulator of follicular helper T (T_FH) cells, and understanding the signaling pathway that induces Bcl6 and T_FH cell differentiation is therefore critical. IL-2 produced during T cell activation inhibits Bcl6 expression but how T_FH cells evade IL-2 inhibition is not completely understood. Here we show that Bcl6 is highly up-regulated in activated CD4 T cells following glucose deprivation (GD), and this pathway is insensitive to inhibition by IL-2. Similar to GD, the glucose analog 2-deoxyglucose (2DG) inhibits glycolysis, and 2DG induced Bcl6 expression in activated CD4 T cells. The metabolic sensor AMP kinase (AMPK) is activated when glycolysis is decreased, and the induction of Bcl6 by GD was inhibited by the AMPK antagonist compound C. Additionally, activation of AMPK by the drug AICAR caused Bcl6 up-regulation in activated CD4 T cells. When mice were immunized with KLH using AICAR as an adjuvant, there was a strong T_FH-dependent enhancement of KLH-specific antibody (Ab) responses, and higher Bcl6 expression in T_FH cells in vivo. Activation of AMPK strongly induced BCL6 and the up-regulation of T_FH cell marker expression by human CD4 T cells. Our data reveal a major new pathway for T_FH cell differentiation, conserved by both mouse and human T cells. Mature T_FH cells are reported to have a lower metabolic state compared to T_H1 cells. Our data indicates that decreased metabolism may be deterministic for T_FH cell differentiation, and not simply a result of T_FH cell differentiation.

Linear ubiquitin chain assembly complex coordinates late thymic T-cell differentiation and regulatory T-cell homeostasis

The linear ubiquitin chain assembly complex (LUBAC) is essential for innate immunity in mice and humans, yet its role in adaptive immunity is unclear. Here we show that the LUBAC components HOIP, HOIL-1 and SHARPIN have essential roles in late thymocyte differentiation, FOXP3⁺ regulatory T (Treg)-cell development and Treg cell homeostasis. LUBAC activity is not required to prevent TNF-induced apoptosis or necroptosis but is necessary for the transcriptional programme of the penultimate stage of thymocyte differentiation. Treg cell-specific ablation of HOIP causes severe Treg cell deficiency and lethal immune pathology, revealing an ongoing requirement of LUBAC activity for Treg cell homeostasis. These data reveal stage-specific requirements for LUBAC in coordinating the signals required for T-cell differentiation.

LUBAC is a ubiquitin ligase complex of HOIL-1, HOIP and SHARPIN important for signal transduction of a range of stimuli. Here the authors define the function of all three LUBAC components in T cell development and homeostasis.

Metabolic response to glatiramer acetate therapy in multiple sclerosis patients

Glatiramer acetate (GA; Copaxone) is a random copolymer of glutamic acid, lysine, alanine, and tyrosine used for the treatment of patients with multiple sclerosis (MS). Its mechanism of action has not been already fully elucidated, but it seems that GA has an immune-modulatory effect and neuro-protective properties. Lymphocyte mitochondrial dysfunction underlines the onset of several autoimmune disorders. In MS first diagnosis patients, CD4⁺, the main T cell subset involved in the pathogenesis of MS, undergo a metabolic reprogramming that consist in the up-regulation of glycolysis and in the down-regulation of oxidative phosphorylation. Currently, no works exist about CD4⁺ T cell metabolism in response to GA treatment. In order to provide novel insight into the potential use of GA in MS treatment, blood samples were collected from 20 healthy controls (HCs) and from 20 RR MS patients prior and every 6 months during the 12 months of GA administration. GA treated patients' CD4⁺ T cells were compared with those from HCs analysing their mitochondrial activity through polarographic and enzymatic methods in association with their antioxidant status, through the analysis of SOD, GPx and CAT activities. Altogether, our findings suggest that GA is able to reduce CD4⁺ T lymphocytes' dysfunctions by increasing mitochondrial activity and their response to oxidative stress.

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GA is able to reduce CD4 + T cell's dysfunctions in MS patients;

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A CD4 + T cell metabolic response in GA treated patients is proposed;

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Metabolic response relies on changes in mitochondrial activity and in antioxidative status.

Short-Lived Antigen Recognition but Not Viral Infection at a Defined Checkpoint Programs Effector CD4 T Cells To Become Protective Memory

Although memory CD4 T cells are critical for effective immunity to pathogens, the mechanisms underlying their generation are still poorly defined. We find that following murine influenza infection, most effector CD4 T cells undergo apoptosis unless they encounter cognate Ag at a defined stage near the peak of effector generation. Ag recognition at this memory checkpoint blocks default apoptosis and programs their transition to long-lived memory. Strikingly, we find that viral infection is not required, because memory formation can be restored by the addition of short-lived, Ag-pulsed APC at this checkpoint. The resulting memory CD4 T cells express an enhanced memory phenotype, have increased cytokine production, and provide protection against lethal influenza infection. Finally, we find that memory CD4 T cell formation following cold-adapted influenza vaccination is boosted when Ag is administered during this checkpoint. These findings imply that persistence of viral Ag presentation into the effector phase is the key factor that determines the efficiency of memory generation. We also suggest that administering Ag at this checkpoint may improve vaccine efficacy.

Foxp3 and Toll-like receptor signaling balance Treg cell anabolic metabolism for suppression

CD4⁺ effector T cells (T_eff cells) and regulatory T cells (T_reg cells) undergo metabolic reprogramming to support proliferation and immunological function. Although signaling via the lipid kinase PI(3)K (phosphatidylinositol-3-OH kinase), the serine-threonine kinase Akt and the metabolic checkpoint kinase complex mTORC1 induces both expression of the glucose transporter Glut1 and aerobic glycolysis for T_eff cell proliferation and inflammatory function, the mechanisms that regulate T_reg cell metabolism and function remain unclear. We found that Toll-like receptor (TLR) signals that promote T_reg cell proliferation increased PI(3)K-Akt-mTORC1 signaling, glycolysis and expression of Glut1. However, TLR-induced mTORC1 signaling also impaired T_reg cell suppressive capacity. Conversely, the transcription factor Foxp3 opposed PI(3)K-Akt-mTORC1 signaling to diminish glycolysis and anabolic metabolism while increasing oxidative and catabolic metabolism. Notably, Glut1 expression was sufficient to increase the number of T_reg cells, but it reduced their suppressive capacity and Foxp3 expression. Thus, inflammatory signals and Foxp3 balance mTORC1 signaling and glucose metabolism to control the proliferation and suppressive function of T_reg cells.

mTORC1 and mTORC2 Kinase Signaling and Glucose Metabolism Drive Follicular Helper T Cell Differentiation

Follicular helper T (Tfh) cells are crucial for germinal center (GC) formation and humoral adaptive immunity. Mechanisms underlying Tfh cell differentiation in peripheral and mucosal lymphoid organs are incompletely understood. We report here that mTOR kinase complexes 1 and 2 (mTORC1 and mTORC2) are essential for Tfh cell differentiation and GC reaction under steady state and after antigen immunization and viral infection. Loss of mTORC1 and mTORC2 in T cells exerted distinct effects on Tfh cell signature gene expression, whereas increased mTOR activity promoted Tfh responses. Deficiency of mTORC2 impaired CD4(+) T cell accumulation and immunoglobulin A production and aberrantly induced the transcription factor Foxo1. Mechanistically, the costimulatory molecule ICOS activated mTORC1 and mTORC2 to drive glycolysis and lipogenesis, and glucose transporter 1-mediated glucose metabolism promoted Tfh cell responses. Altogether, mTOR acts as a central node in Tfh cells by linking immune signals to anabolic metabolism and transcriptional activity.

Complement-Mediated Regulation of Metabolism and Basic Cellular Processes

Complement is well appreciated as a critical arm of innate immunity. It is required for the removal of invading pathogens and works by directly destroying them through the activation of innate and adaptive immune cells. However, complement activation and function is not confined to the extracellular space but also occurs within cells. Recent work indicates that complement activation regulates key metabolic pathways and thus can impact fundamental cellular processes, such as survival, proliferation, and autophagy. Newly identified functions of complement include a key role in shaping metabolic reprogramming, which underlies T cell effector differentiation, and a role as a nexus for interactions with other effector systems, in particular the inflammasome and Notch transcription-factor networks. This review focuses on the contributions of complement to basic processes of the cell, in particular the integration of complement with cellular metabolism and the potential implications in infection and other disease settings.

T follicular helper cell programming by cytokine-mediated events

CD4⁺ T cells, or T helper cells, are critical mediators and coordinators of adaptive immunity. Unique effector T helper cell populations have been identified that perform distinct functions in response to pathogenic infection. The T follicular helper (Tfh) cells are one such subset, which has been identified as the primary T-cell population responsible for interacting with B cells to promote effective antibody-mediated immune responses. Since their initial description at the turn of the century, and subsequent classification as a distinct T helper cell subset, there has been substantial interest in elucidating the regulatory mechanisms that govern Tfh cell formation. The collective insight from this body of work has demonstrated that Tfh cell differentiation is a complex and multistage process regulated by a litany of cell-intrinsic and cell-extrinsic factors. As with the development of the other recognized T helper cell subsets, specific cytokines exercise prominent roles in both the positive and negative regulation of Tfh cell development. However, the exact composition of, and stage-specific requirements for, these environmental factors in the governance of Tfh cell differentiation remain incompletely understood. In this review, we summarize what is known regarding the role of cytokines in both the promotion and inhibition of Tfh cell differentiation and function.

The PI3K pathway in B cell metabolism

B cell growth and proliferation is tightly regulated by signaling through the B cell receptor and by other membrane bound receptors responding to different cytokines. The PI3K signaling pathway has been shown to play a crucial role in B cell activation, differentiation and survival. Activated B cells undergo metabolic reprograming in response to changing energetic and biosynthetic demands. B cells also need to be able to coordinate metabolic activity and proliferation with nutrient availability. The PI3K signaling network has been implicated in regulating nutrient acquisition, utilization and biosynthesis, thus integrating receptor-mediated signaling with cell metabolism. In this review, we discuss the current knowledge about metabolic changes induced in activated B cells, strategies to adapt to metabolic stress and the role of PI3K signaling in these processes.

IL-2, IL-7, and IL-15: Multistage regulators of CD4(+) T helper cell differentiation

Cytokines represent a class of environmental factors that are critical drivers of immune cell development. Cytokines of the common gamma-chain family, including interleukin (IL)-2, IL-7, and IL-15, have been the subject of intense experimental scrutiny and have well-defined roles as regulators of diverse immune cell types including CD4(+) T helper cells. Because of their pleiotropic effects on T-cell development and function, researchers and clinicians have attempted to harness the capabilities of these cytokines for therapeutic benefit. In this review, we summarize the recent progress in our understanding of the molecular mechanisms underlying the effects of these cytokines on CD4(+) T cell development and briefly discuss how these immunomodulatory cytokines are being used in efforts to treat human disease.

Early changes in the metabolic profile of activated CD8(+) T cells

Background

Antigenic stimulation of the T cell receptor (TCR) initiates a change from a resting state into an activated one, which ultimately results in proliferation and the acquisition of effector functions. To accomplish this task, T cells require dramatic changes in metabolism. Therefore, we investigated changes of metabolic intermediates indicating for crucial metabolic pathways reflecting the status of T cells. Moreover we analyzed possible regulatory molecules required for the initiation of the metabolic changes.

Results

We found that proliferation inducing conditions result in an increase in key glycolytic metabolites, whereas the citric acid cycle remains unaffected. The upregulation of glycolysis led to a strong lactate production, which depends upon AKT/PKB, but not mTOR. The observed upregulation of lactate dehydrogenase results in increased lactate production, which we found to be dependent on IL-2 and to be required for proliferation. Additionally we observed upregulation of Glucose-transporter 1 (GLUT1) and glucose uptake upon stimulation, which were surprisingly not influenced by AKT inhibition.

Conclusions

Our findings suggest that AKT plays a central role in upregulating glycolysis via induction of lactate dehydrogenase expression, but has no impact on glucose uptake of T cells. Furthermore, under apoptosis inducing conditions, T cells are not able to upregulate glycolysis and induce lactate production. In addition maintaining high glycolytic rates strongly depends on IL-2 production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-016-0104-x) contains supplementary material, which is available to authorized users.

Cross-talk between signaling and metabolism in the vasculature

The link between signaling and metabolism was first recognized with insulin signal transduction. Efficient glucose uptake by the endothelium requires insulin receptor activation to deliver GLUT receptors to the cell surface. More recently however, additional evidence has emerged for a broader crosstalk as signaling events have been shown to regulate a large number of metabolic enzymes. Changes in the metabolic status of endothelial and smooth muscle cells are observed at times of increased proliferative activity and these coincide with activation of cell surface receptors. Intriguingly, a rise in glycolysis appears to be associated with remodeling of the actin cytoskeleton during migration and angiogenesis. Overall, understanding how do signaling and metabolic pathways intersect and cross-regulate each other has become an important question and an emerging cornerstone in vascular biology.

Candida albicans Induces Metabolic Reprogramming in Human NK Cells and Responds to Perforin with a Zinc Depletion Response

As part of the innate immune system, natural killer (NK) cells are directly involved in the response to fungal infections. Perforin has been identified as the major effector molecule acting against many fungal pathogens. While several studies have shown that perforin mediated fungicidal effects can contribute to fungal clearance, neither the activation of NK cells by fungal pathogens nor the effects of perforin on fungal cells are well-understood. In a dual approach, we have studied the global gene expression pattern of primary and cytokine activated NK cells after co-incubation with Candida albicans and the transcriptomic adaptation of C. albicans to perforin exposure. NK cells responded to the fungal pathogen with an up-regulation of genes involved in immune signaling and release of cytokines. Furthermore, we observed a pronounced increase of genes involved in glycolysis and glycolysis inhibitor 2-deoxy-D-glucose impaired C. albicans induced NK cell activation. This strongly indicates that metabolic adaptation is a major part of the NK cell response to C. albicans infections. In the fungal pathogen, perforin induced a strong up-regulation of several fungal genes involved in the zinc depletion response, such as PRA1 and ZRT1. These data suggest that fungal zinc homeostasis is linked to the reaction to perforin secreted by NK cells. However, deletion mutants in PRA1 and ZRT1 did not show altered susceptibility to perforin.

mTOR Regulation of Lymphoid Cells in Immunity to Pathogens

Immunity to pathogens exists as a fine balance between promoting activation and expansion of effector cells, while simultaneously limiting normal and aberrant responses. These seemingly opposing functions are kept in check by immune regulators. The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that senses nutrient availability and, in turn, regulates cell metabolism, growth, and survival accordingly. mTOR plays a pivotal role in facilitating immune defense against invading pathogens by regulating the differentiation, activation, and effector functions of lymphoid cells. Here, we focus on the emerging and sometimes contradictory roles of mTOR in orchestrating lymphoid cell-mediated host immune responses to pathogens. A thorough understanding of how mTOR impacts lymphoid cells in pathogen defense will provide the necessary base for developing therapeutic interventions for infectious diseases.

Glucose Metabolism in T Cells and Monocytes: New Perspectives in HIV Pathogenesis

Activation of the immune system occurs in response to the recognition of foreign antigens and receipt of optimal stimulatory signals by immune cells, a process that requires energy. Energy is also needed to support cellular growth, differentiation, proliferation, and effector functions of immune cells. In HIV-infected individuals, persistent viral replication, together with inflammatory stimuli contributes to chronic immune activation and oxidative stress. These conditions remain even in subjects with sustained virologic suppression on antiretroviral therapy. Here we highlight recent studies demonstrating the importance of metabolic pathways, particularly those involving glucose metabolism, in differentiation and maintenance of the activation states of T cells and monocytes. We also discuss how changes in the metabolic status of these cells may contribute to ongoing immune activation and inflammation in HIV- infected persons and how this may contribute to disease progression, establishment and persistence of the HIV reservoir, and the development of co-morbidities. We provide evidence that other viruses such as Epstein-Barr and Flu virus also disrupt the metabolic machinery of their host cells. Finally, we discuss how redox signaling mediated by oxidative stress may regulate metabolic responses in T cells and monocytes during HIV infection.

4-1BB signaling activates glucose and fatty acid metabolism to enhance CD8+ T cell proliferation

4-1BB (CD137) is a strong enhancer of the proliferation of CD8⁺ T cells. Since these cells require increased production of energy and biomass to support their proliferation, we hypothesized that 4-1BB signaling activated glucose and fatty acid metabolism. We found that treatment with agonistic anti-4-1BB mAb promoted the proliferation of CD8⁺ T cells in vitro, increasing their size and granularity. Studies with a glycolysis inhibitor and a fatty acid oxidation inhibitor revealed that CD8⁺ T cell proliferation required both glucose and fatty acid metabolism. Anti-4-1BB treatment increased glucose transporter 1 expression and activated the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK)-acetyl-CoA carboxylase (ACC) signaling pathway, which may be responsible for activating the metabolism of glucose and fatty acids. We also examined whether blocking glucose or fatty acid metabolism affected cell cycle progression and the anti-apoptotic effect of 4-1BB signaling. The increase of anti-apoptotic factors and cyclins in response to anti-4-1BB treatment was completely prevented by treating CD8⁺ T cells with the fatty acid oxidation inhibitor, etomoxir, but not with the glycolysis inhibitor, 2-deoxy-D-glucose. We conclude that anti-4-1BB treatment activates glucose and fatty acid metabolism thus supporting the increased demand for energy and biomass, and that fatty acid metabolism plays a crucial role in enhancing the cell cycle progression of anti-CD3-activated CD8⁺ T cells in vitro and the anti-apoptotic effects of 4-1BB signaling on these cells.

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

CD4(+) T cells differentiate and acquire distinct functions to combat specific pathogens but can also adapt their functions in response to changing circumstances. Although this phenotypic plasticity can be potentially deleterious, driving immune pathology, it also provides important benefits that have led to its evolutionary preservation. Here, we review CD4(+) T cell plasticity by examining the molecular mechanisms that regulate it - from the extracellular cues that initiate and drive cells towards varying phenotypes, to the cytosolic signalling cascades that decipher these cues and transmit them into the cell and to the nucleus, where these signals imprint specific gene expression programmes. By understanding how this functional flexibility is achieved, we may open doors to new therapeutic approaches that harness this property of T cells.

IL-7 signalling represses Bcl-6 and the TFH gene program

The transcriptional repressor Bcl-6 is linked to the development of both CD4⁺ T follicular helper (T_FH) and central memory T (T_CM) cells. Here, we demonstrate that in response to decreased IL-2 signalling, T helper 1 (T_H1) cells upregulate Bcl-6 and co-initiate T_FH- and T_CM-like gene programs, including expression of the cytokine receptors IL-6Rα and IL-7R. Exposure of this potentially bi-potent cell population to IL-6 favours the T_FH gene program, whereas IL-7 signalling represses T_FH-associated genes including Bcl6 and Cxcr5, but not the T_CM-related genes Klf2 and Sell. Mechanistically, IL-7-dependent activation of STAT5 contributes to Bcl-6 repression. Importantly, antigen-specific IL-6Rα⁺IL-7R⁺ CD4⁺ T cells emerge from the effector population at late time points post influenza infection. These data support a novel role for IL-7 in the repression of the T_FH gene program and evoke a divergent regulatory mechanism by which post-effector T_H1 cells may contribute to long-term cell-mediated and humoral immunity.

It remains incompletely understood how cytokines shape T_H1 cell differentiation to central memory T (T_CM) and follicular T helper (T_FH) cells. Here the authors show that T_H1 cells can co-initiate the expression of both T_FH and T_CM gene programs and that IL-7 signalling represses T_FH-associated but not T_CM-associated genes.

Regulatory T cell memory

Memory for antigen is a defining feature of adaptive immunity. Antigen-specific lymphocyte populations show an increase in number and function after antigen encounter and more rapidly re-expand upon subsequent antigen exposure. Studies of immune memory have primarily focused on effector B cells and T cells with microbial specificity, using prime-challenge models of infection. However, recent work has also identified persistently expanded populations of antigen-specific regulatory T cells that protect against aberrant immune responses. In this Review, we consider the parallels between memory effector T cells and memory regulatory T cells, along with the functional implications of regulatory memory in autoimmunity, antimicrobial host defence and maternal-fetal tolerance. In addition, we discuss emerging evidence for regulatory T cell memory in humans and key unanswered questions in this rapidly evolving field.

Hypoxia-inducible factors regulate T cell metabolism and function

Resolution of infection requires the coordinated response of heterogeneous cell types to a range of physiological and pathological signals to regulate their proliferation, migration, differentiation, and effector functions. One mechanism by which immune cells integrate these signals is through modulating metabolic activity. A well-studied regulator of cellular metabolism is the hypoxia-inducible factor (HIF) family, the highly conserved central regulators of adaptation to limiting oxygen tension. HIF's regulation of cellular metabolism and a variety of effector, signaling, and trafficking molecules has made these transcription factors a recent topic of interest in T cell biology. Low oxygen availability, or hypoxia, increases expression and stabilization of HIF in immune cells, activating molecular programs both unique and common among cell types, including glycolytic metabolism. Notably, numerous oxygen-independent signals, many of which are active in T cells, also result in enhanced HIF activity. Here, we discuss both oxygen-dependent and -independent regulation of HIF activity in T cells and the resulting impacts on metabolism, differentiation, function, and immunity.

Regulators of Glucose Metabolism in CD4+ and CD8+ T Cells

Much like cancer cells, activated T cells undergo various metabolic changes that allow them to grow and proliferate rapidly. By adopting aerobic glycolysis upon activation, T cells effectively prioritize efficiency in biosynthesis over energy generation. There are distinct differences in the way CD4⁺ and CD8⁺ T cells process activation signals. CD8⁺ effector T cells are less dependent on Glut1 and oxygen levels compared to their CD4⁺ counterparts. Similarly the downstream signaling by TCR also differs in both effector T cell types. Recent studies have explored PI3K/Akt, mTORC, HIF1α, p70S6K and Bcl-6 signaling in depth providing definition of the crucial roles of these regulators in glucose metabolism. These new insights may allow improved therapeutic manipulation against inflammatory conditions that are associated with dysfunctional T-cell metabolism such as autoimmune disorders, metabolic syndrome, HIV, and cancers.

Immunometabolism: Cellular Metabolism Turns Immune Regulator

Immune cells are highly dynamic in terms of their growth, proliferation, and effector functions as they respond to immunological challenges. Different immune cells can adopt distinct metabolic configurations that allow the cell to balance its requirements for energy, molecular biosynthesis, and longevity. However, in addition to facilitating immune cell responses, it is now becoming clear that cellular metabolism has direct roles in regulating immune cell function. This review article describes the distinct metabolic signatures of key immune cells, explains how these metabolic setups facilitate immune function, and discusses the emerging evidence that intracellular metabolism has an integral role in controlling immune responses.

Trans-presentation of IL-15 modulates STAT5 activation and Bcl-6 expression in TH1 cells

During infection, naïve CD4⁺ T helper cells differentiate into specialized effector subsets based upon environmental signals propagated by the cytokine milieu. Recently, this paradigm has been complicated by the demonstration that alterations in the cytokine environment can result in varying degrees of plasticity between effector T helper cell populations. Therefore, elucidation of the mechanisms by which cytokines regulate T helper cell differentiation decisions is increasingly important. The gamma common cytokine IL-15 is currently undergoing clinical trials for the treatment of malignancies, due to its well-established role in the regulation of natural killer and CD8⁺ T cell immune responses. However, the effect of IL-15 signaling on CD4⁺ T cell activity is incompletely understood. One mechanism by which IL-15 activity is conferred is through trans-presentation via the IL-15 receptor alpha subunit. Here, we demonstrate that differentiated T_H1 cells are responsive to trans-presented IL-15. Importantly, while trans-presentation of IL-15 results in STAT5 activation and maintenance of the T_H1 gene program, IL-15 treatment alone allows for increased Bcl-6 expression and the upregulation of a T_FH-like profile. Collectively, these findings describe a novel role for IL-15 in the modulation of CD4⁺ T cell responses and provide valuable insight for the use of IL-15 in immunotherapeutic approaches.

Attenuation of AMPK signaling by ROQUIN promotes T follicular helper cell formation

T follicular helper cells (Tfh) are critical for the longevity and quality of antibody-mediated protection against infection. Yet few signaling pathways have been identified to be unique solely to Tfh development. ROQUIN is a post-transcriptional repressor of T cells, acting through its ROQ domain to destabilize mRNA targets important for Th1, Th17, and Tfh biology. Here, we report that ROQUIN has a paradoxical function on Tfh differentiation mediated by its RING domain: mice with a T cell-specific deletion of the ROQUIN RING domain have unchanged Th1, Th2, Th17, and Tregs during a T-dependent response but show a profoundly defective antigen-specific Tfh compartment. ROQUIN RING signaling directly antagonized the catalytic α1 subunit of adenosine monophosphate-activated protein kinase (AMPK), a central stress-responsive regulator of cellular metabolism and mTOR signaling, which is known to facilitate T-dependent humoral immunity. We therefore unexpectedly uncover a ROQUIN–AMPK metabolic signaling nexus essential for selectively promoting Tfh responses.

DOI:http://dx.doi.org/10.7554/eLife.08698.001

The immune system protects the body from invading microbes like bacteria and viruses. Upon recognizing the presence of these microbes, cells in the immune system are activated to destroy the foreign threat and clear it from the body.

A type of immune cell called T follicular helper cells (or Tfh for short) are formed during an infection and are essential for coordinating other immune cells to produce high-quality antibody proteins that attack the microbes. Without Tfh cells, life-long production of these protective antibodies is severely crippled, which can cause common variable immune deficiency and other serious immunodeficiency diseases. On the other hand, the body must also avoid generating excessive numbers of Tfh cells, which can lead to the production of antibodies that attack healthy cells of the body.

ROQUIN is a protein that inhibits the formation of Tfh cells and other types of active T cells. A region on the protein called the ROQ domain destabilizes particular molecules of ribonucleic acid (RNA) that are required for these specialist T cells to form and work properly. ROQUIN belongs to a large family of enzymes that have a so-called RING domain, which is a feature that enables these enzymes to attach tags onto specific target proteins to modify their activity or stability. However, it was not known whether the RING domain of ROQUIN was active.

Ramiscal et al. now address this question in mice. Unexpectedly, the experiments show that the RING domain is required to promote the formation of Tfh cells, but not other types of active T cells. This domain allows ROQUIN to repress an enzyme called AMPK, which normally blocks cell growth by regulating cell metabolism. The findings suggest that the different roles of the ROQ and RING domains allow ROQUIN to fine-tune the numbers of Tfh cells so that they remain within a safe range. In the future, these findings may aid the development of vaccines that are more efficient at generating protective Tfh cells to prevent infectious diseases.

DOI:http://dx.doi.org/10.7554/eLife.08698.002

Comparative physiogenomic analyses of weight loss in response to 2 modes of bariatric surgery: demonstration with candidate neuropsychiatric and cardiometabolic genes

BACKGROUND

Surgical weight loss response is variable, with suboptimal outcomes in some patients. We hypothesized that genetic biomarkers may be related to weight change.

METHODS

We tested 330 single nucleotide polymorphisms (SNPs) in genes relevant to metabolic regulation in 161 patients whose decrease in body mass index (BMI), 1 year after laparoscopic adjustable gastric banding (LAGB) or Roux-en-Y gastric bypass (RYGB), was small (lowest quartile response) or large (highest quartile response). LAGB patients whose BMI decreased≤4.7 or≥10.2 units comprised groups I (n = 43) and II (n = 40), respectively. RYGB patients whose BMI decreased≤13.6 or≥19.8 units comprised groups III (n = 39) and IV (n = 39), respectively. Within each surgery, SNPs with large differences in reference allele frequency (z score>2, corresponding to values displaced 2 standard deviations [SD] from the mean for all SNPs) in low versus high quartiles, were identified. We compared reference allele frequencies, within surgical procedure, using the χ(2) test (using Bonferroni correction for multiple testing).

RESULTS

The mean percent excess weight losses (±SD) corresponding to groups I, II, III, and IV were: 16 (±12), 64 (±30), 55 (±16), and 75 (±17), respectively. SNPs with z score>2 were identified in genes involved in LAGB response, lipid metabolic regulation (APOE, rs439401; APOC4, rs2288911), neural processes (DRD3, rs167771; HTR3 B, rs3758987), and xeno- or endobiotic metabolism (CYP3 A4, rs12333983); and for RYGB response, in lipid transport (SCARB1, rs10846744), folate metabolism (MTHFR, rs2066470), regulation of glycolysis in immune cells (HIF1 A, rs1951795), vitamin K cycling (VKORC1, rs2359612), and xeno- or endobiotic metabolism (CYP3 A4, rs2242480). For LAGB response, APOE SNP frequencies were significantly different.

CONCLUSIONS

With further validation, information derived from patient DNA may be useful to predict surgical weight loss outcomes and guide selection of surgical approach.

The Interleukin-2-mTORc1 Kinase Axis Defines the Signaling, Differentiation, and Metabolism of T Helper 1 and Follicular B Helper T Cells

The differentiation of CD4(+) helper T cell subsets with diverse effector functions is accompanied by changes in metabolism required to meet their bioenergetic demands. We find that follicular B helper T (Tfh) cells exhibited less proliferation, glycolysis, and mitochondrial respiration, accompanied by reduced mTOR kinase activity compared to T helper 1 (Th1) cells in response to acute viral infection. IL-2-mediated activation of the Akt kinase and mTORc1 signaling was both necessary and sufficient to shift differentiation away from Tfh cells, instead promoting that of Th1 cells. These findings were not the result of generalized signaling attenuation in Tfh cells, because they retained the ability to flux calcium and activate NFAT-transcription-factor-dependent cytokine production. These data identify the interleukin-2 (IL-2)-mTORc1 axis as a critical orchestrator of the reciprocal balance between Tfh and Th1 cell fates and their respective metabolic activities after acute viral infection.

The pharmacology of second-generation chimeric antigen receptors

Second-generation chimeric antigen receptors (CARs) retarget and reprogramme T cells to augment their antitumour efficacy. The combined activating and co-stimulatory domains incorporated in these CARs critically determine the function, differentiation, metabolism and persistence of engineered T cells. CD19-targeted CARs that incorporate CD28 or 4-1BB signalling domains are the best known to date. Both have shown remarkable complete remission rates in patients with refractory B cell malignancies. Recent data indicate that CD28-based CARs direct a brisk proliferative response and boost effector functions, whereas 4-1BB-based CARs induce a more progressive T cell accumulation that may compensate for less immediate potency. These distinct kinetic features can be exploited to further develop CAR-based T cell therapies for a variety of cancers. A new field of immunopharmacology is emerging.

TCF1 Is Required for the T Follicular Helper Cell Response to Viral Infection

T follicular helper (TFH) and T helper 1 (Th1) cells generated after viral infections are critical for the control of infection and the development of immunological memory. However, the mechanisms that govern the differentiation and maintenance of these two distinct lineages during viral infection remain unclear. We found that viral-specific TFH and Th1 cells showed reciprocal expression of the transcriptions factors TCF1 and Blimp1 early after infection, even before the differential expression of the canonical TFH marker CXCR5. Furthermore, TCF1 was intrinsically required for the TFH cell response to viral infection; in the absence of TCF1, the TFH cell response was severely compromised, and the remaining TCF1-deficient TFH cells failed to maintain TFH-associated transcriptional and metabolic signatures, which were distinct from those in Th1 cells. Mechanistically, TCF1 functioned through forming negative feedback loops with IL-2 and Blimp1. Our findings demonstrate an essential role of TCF1 in TFH cell responses to viral infection.

Transcriptional regulation of T cell metabolism

T cells express specific metabolic programs to promote diverse cellular differentiation states. The activation of naïve T cells upregulates the expression of genes encoding components of the glycolysis, glutaminolysis, and lipid biosynthesis pathways to promote robust proliferation and effector T cell activity. In contrast, memory T cells downregulate these pathways and predominantly rely on catabolic pathways for long-term survival. Dynamic changes in the expression of the genes encoding components of metabolic pathways in part define which metabolic programs are utilized in diverse T cell states. The current data suggest that key transcription factors involved in T cell specialization decisions, including T-bet, Bcl-6, HIF1, IRF4 and Myc, link the selective programming of cellular metabolism with fate decisions. In this review, we will highlight the transcriptional regulatory events that define metabolic pathways involved in effector and memory T cell differentiation.

T cell metabolism drives immunity

Buck et al. discuss the role of lymphocyte metabolism on immune cell development and function.

Lymphocytes must adapt to a wide array of environmental stressors as part of their normal development, during which they undergo a dramatic metabolic remodeling process. Research in this area has yielded surprising findings on the roles of diverse metabolic pathways and metabolites, which have been found to regulate lymphocyte signaling and influence differentiation, function and fate. In this review, we integrate the latest findings in the field to provide an up-to-date resource on lymphocyte metabolism.

Glucose, glycolysis and lymphocyte responses

Activated lymphocytes engage in robust growth and rapid proliferation. To achieve this, they tend to adopt a form of glucose metabolism termed aerobic glycolysis. This type of metabolism allows for the use of large amounts of glucose to generate energy, but also to support biosynthetic processes. This review article will discuss how aerobic glycolysis supports the biosynthetic demands of activated T cells, B cells and Natural Killer cells, and the emerging concept that glycolysis is integrally linked to the differentiation and function of these lymphocyte populations.