Polyamine metabolism is a central determinant of helper T cell lineage fidelity

Autophagy-inducing nutritional interventions in experimental and clinical oncology

Numerous pro-autophagic dietary interventions are being investigated for their potential cancer-preventive or therapeutic effects. This applies to different fasting regimens, methionine restriction and ketogenic diets. In addition, the supplementation of specific micronutrients such as nicotinamide (vitamin B3) or spermidine induces autophagy. In humans, leanness, plant-based diets (that may lead to partial methionine restriction) and high dietary uptake of spermidine are associated with a low incidence of cancers. Moreover, clinical trials have demonstrated the capacity of nicotinamide to prevent non-melanoma skin carcinogenesis. Multiple interventional trials are evaluating the capacity of autophagy-inducing regimens to improve the outcome of chemotherapy and immunotherapy. Here, we discuss the mechanistic underpinnings of autophagy induction by nutritional interventions, as well as the mechanisms through which autophagy induction in malignant or immune cells improves anticancer immunosurveillance.

Metabolic regulation and function of T helper cells in neuroinflammation

Neuroinflammatory conditions such as multiple sclerosis (MS) are initiated by pathogenic immune cells invading the central nervous system (CNS). Autoreactive CD4⁺ T helper cells are critical players that orchestrate the immune response both in MS and in other neuroinflammatory autoimmune diseases including animal models that have been developed for MS. T helper cells are classically categorized into different subsets, but heterogeneity exists within these subsets. Untangling the more complex regulation of these subsets will clarify their functional roles in neuroinflammation. Here, we will discuss how differentiation, immune checkpoint pathways, transcriptional regulation and metabolic factors determine the function of CD4⁺ T cell subsets in CNS autoimmunity. T cells rely on metabolic reprogramming for their activation and proliferation to meet bioenergetic demands. This includes changes in glycolysis, glutamine metabolism and polyamine metabolism. Importantly, these pathways were recently also implicated in the fine tuning of T cell fate decisions during neuroinflammation. A particular focus of this review will be on the Th17/Treg balance and intra-subset functional states that can either promote or dampen autoimmune responses in the CNS and thus affect disease outcome. An increased understanding of factors that could tip CD4⁺ T cell subsets and populations towards an anti-inflammatory phenotype will be critical to better understand neuroinflammatory diseases and pave the way for novel treatment paradigms.

How Microbiota-Derived Metabolites Link the Gut to the Brain during Neuroinflammation

Microbiota-derived metabolites are important molecules connecting the gut to the brain. Over the last decade, several studies have highlighted the importance of gut-derived metabolites in the development of multiple sclerosis (MS). Indeed, microbiota-derived metabolites modulate the immune system and affect demyelination. Here, we discuss the current knowledge about microbiota-derived metabolites implications in MS and in different mouse models of neuroinflammation. We focus on the main families of microbial metabolites that play a role during neuroinflammation. A better understanding of the role of those metabolites may lead to new therapeutical avenues to treat neuroinflammatory diseases targeting the gut–brain axis.

Spermidine protects against acute kidney injury by modulating macrophage NLRP3 inflammasome activation and mitochondrial respiration in an eIF5A hypusination-related pathway

Background

Acute kidney injury (AKI) is still a critical problem in clinical practice, with a heavy burden for national health system around the world. It is notable that sepsis is the predominant cause of AKI for patients in the intensive care unit and the mortality remains considerably high. The treatment for AKI relies on supportive therapies and almost no specific treatment is currently available. Spermidine is a naturally occurring polyamine with pleiotropic effects. However, the renoprotective effect of spermidine and the underlying mechanism remain elusive.

Methods

We employed mice sepsis-induced AKI model and explored the potential renoprotective effect of spermidine in vivo with different administration time and routes. Macrophage depleting was utilized to probe the role of macrophage. In vitro experiments were conducted to examine the effect of spermidine on macrophage cytokine secretion, NLRP3 inflammasome activation and mitochondrial respiration.

Results

We confirmed that spermidine improves AKI with different administration time and routes and that macrophages serves as an essential mediator in this protective effect. Meanwhile, spermidine downregulates NOD-like receptor protein 3 (NLRP3) inflammasome activation and IL-1 beta production in macrophages directly. Mechanically, spermidine enhances mitochondrial respiration capacity and maintains mitochondria function which contribute to the NLRP3 inhibition. Importantly, we showed that eukaryotic initiation factor 5A (eIF5A) hypusination plays an important role in regulating macrophage bioactivity.

Conclusions

Spermidine administration practically protects against sepsis-induced AKI in mice and macrophages serve as an essential mediator in this protective effect. Our study identifies spermidine as a promising pharmacologic approach to prevent AKI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00533-1.

The role of polyamine metabolism in remodeling immune responses and blocking therapy within the tumor immune microenvironment

The study of metabolism provides important information for understanding the biological basis of cancer cells and the defects of cancer treatment. Disorders of polyamine metabolism is a common metabolic change in cancer. With the deepening of understanding of polyamine metabolism, including molecular functions and changes in cancer, polyamine metabolism as a new anti-cancer strategy has become the focus of attention. There are many kinds of polyamine biosynthesis inhibitors and transport inhibitors, but not many drugs have been put into clinical application. Recent evidence shows that polyamine metabolism plays essential roles in remodeling the tumor immune microenvironment (TIME), particularly treatment of DFMO, an inhibitor of ODC, alters the immune cell population in the tumor microenvironment. Tumor immunosuppression is a major problem in cancer treatment. More and more studies have shown that the immunosuppressive effect of polyamines can help cancer cells to evade immune surveillance and promote tumor development and progression. Therefore, targeting polyamine metabolic pathways is expected to become a new avenue for immunotherapy for cancer.

Herpesvirus-induced spermidine synthesis and eIF5A hypusination for viral episomal maintenance

Spermidine is essential for cellular growth and acts as a prerequisite of hypusination, a post-translational modification of eukaryotic initiation factor 5A (eIF5A), allowing the translation of polyproline-containing proteins. Here, we show that oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV) increases spermidine synthesis and eIF5A hypusination to enhance expression of polyproline-containing latency-associated nuclear antigen (LANA) for viral episomal maintenance. KSHV upregulates intracellular spermidine levels by dysregulating polyamine metabolic pathways in three-dimensional (3D) culture and 2D de novo infection conditions. Increased intracellular spermidine leads to increased eIF5A hypusination, ultimately enhancing LANA expression. In contrast, inhibition of spermidine synthesis or eIF5A hypusination alleviates LANA expression, decreasing viral episomal maintenance and KSHV-infected cell proliferation in vitro and in vivo, which is reversed by spermidine supplement. This demonstrates that KSHV hijacks spermidine synthesis and eIF5A hypusination pathways to enhance LANA expression for viral episomal maintenance, suggesting polyamine metabolism and eIF5A hypusination as therapeutic targets for KSHV-induced tumorigenesis.

Sulforaphane diminishes moonlighting of pyruvate kinase M2 and interleukin 1β expression in M1 (LPS) macrophages

Murine macrophages activated by the Toll-like receptor 4 agonist lipopolysaccharide (LPS) polarize to the M1 type by inducing proinflammatory marker proteins and changing their energy metabolism to increased aerobic glycolysis and reduced respiration. We here show that the aliphatic isothiocyanate sulforaphane (Sfn) diminishes M1 marker expression (IL-1β, IL-6, TNF-α, iNOS, NO, and ROS) and leads to highly energetic cells characterized by both high glycolytic and high respiratory activity as assessed by extracellular flux analysis. Focusing on a potential connection between high glycolytic activity and low IL-1β expression in M1 (LPS/Sfn) macrophages, we reveal that Sfn impedes the moonlighting function of pyruvate kinase M2 (PKM2) in M1 macrophages. Sfn limits mono/dimerization and nuclear residence of PKM2 accompanied by reduced HIF-1α levels, Stat3 phosphorylation at tyrosine 705, and IL-1β expression while preserving high levels of cytosolic PKM2 tetramer with high glycolytic enzyme activity. Sfn prevents glutathionylation of PKM2 in LPS-stimulated macrophages which may account for the reduced loss of PKM2 tetramer. Overall, we uncover PKM2 as a novel affected hub within the anti-inflammatory activity profile of Sfn.

Polyamines in cancer: integrating organismal metabolism and antitumour immunity

The natural mammalian polyamines putrescine, spermidine and spermine are essential for both normal and neoplastic cell function and replication. Dysregulation of metabolism of polyamines and their requirements is common in many cancers. Both clinical and experimental depletion of polyamines have demonstrated their metabolism to be a rational target for therapy; however, the mechanisms through which polyamines can establish a tumour-permissive microenvironment are only now emerging. Recent data indicate that polyamines can play a major role in regulating the antitumour immune response, thus likely contributing to the existence of immunologically 'cold' tumours that do not respond to immune checkpoint blockade. Additionally, the interplay between the microbiota and associated tissues creates a tumour microenvironment in which polyamine metabolism, content and function can all be dramatically altered on the basis of microbiota composition, dietary polyamine availability and tissue response to its surrounding microenvironment. The goal of this Perspective is to introduce the reader to the many ways in which polyamines, polyamine metabolism, the microbiota and the diet interconnect to establish a tumour microenvironment that facilitates the initiation and progression of cancer. It also details ways in which polyamine metabolism and function can be successfully targeted for therapeutic benefit, including specifically enhancing the antitumour immune response.

Interrogation of T Cell-Enriched Tumors Reveals Prognostic and Immunotherapeutic Implications of Polyamine Metabolism

Metabolic features of the tumor microenvironment (TME) antagonize anti-tumor immunity. We hypothesized that T cell infiltrated tumors with a known antigen should exhibit superior clinical outcomes, though some fare worse given unfavorable metabolic features leveraging T cell-infiltrated (Thi), human papillomavirus-related (HPV+) head and neck squamous cell carcinomas (HNSC) to test this hypothesis. Expression of 2,520 metabolic genes were analyzed among Thi HPV+ HNSCs stratified by high-risk molecular subtype. RNAseq data from The Cancer Genome Atlas (TCGA; 10 cancer types), single cell RNAseq data, and an immunotherapy-treated melanoma cohort were used to test the association between metabolic gene expression and clinical outcomes and contribution of tumor versus stromal cells to metabolic gene expression. Polyamine (PA) metabolism genes were overexpressed in high-risk, Thi HPV+ HNSCs. Genes involved in PA biosynthesis and transport were associated with T cell infiltration, recurrent or persistent cancer, overall survival status, primary site, molecular subtype, and MYC genomic alterations. PA biogenesis gene sets were associated with tumor intrinsic features while myeloid cells in HPV+ HNSCs were enriched in PA catabolism, regulatory, transport, putrescine, and spermidine gene set expression. PA gene set expression also correlated with IFNγ or cytotoxic T cell ssGSEA scores across TCGA tumor types. PA transport ssGSEA scores were associated with poor survival whereas putrescine ssGSEA scores portended better survival for several tumor types. Thi melanomas enriched in PA synthesis or combined gene set expression exhibited worse anti-PD-1 responses. These data address hurdles to anti-tumor immunity warranting further investigation of divergent polyamine metabolism in the TME.

Helping the helpers: polyamines help maintain helper T-cell lineage fidelity

The awareness that polyamines play a critical role in immune system regulation and function is coming into focus as the biological systems and analytical tools necessary to evaluate their roles have become available. Puleston et al have recently demonstrated that polyamine metabolism plays a central role in helper T-cell lineage determination through the production of the translational cofactor hypusinated eIF5A and faithful epigenetic regulation through proper histone acetylation. Their findings add to the rapidly growing body of data implicating properly controlled polyamine metabolism as essential for a normally functioning immune system.

T cell phenotype switching in autoimmune disorders: Clinical significance of targeting metabolism

Increasing efforts points to the understanding of how to maximize the capabilities of the adaptive immune system to fight against the development of immune and inflammatory disorders. Here we focus on the role of T cells as immune cells which subtype imbalance may lead to disease onset. Specifically, we propose that autoimmune disorders may develop as a consequence of a metabolic imbalance that modulates switching between T cell phenotypes. We highlight a Systems Biology strategy that integrates computational metabolic modelling with experimental data to investigate the metabolic requirements of T cell phenotypes, and to predict metabolic genes that may be targeted in autoimmune inflammatory diseases. Thus, we propose a new perspective of targeting T cell metabolism to modulate the immune response and prevent T cell phenotype imbalance, which may help to repurpose already existing drugs targeting metabolism for therapeutic treatment.

Polyamine Depletion Strategies in Cancer: Remodeling the Tumor Immune Microenvironment to Enhance Anti-Tumor Responses

Polyamine biosynthesis is frequently dysregulated in cancers, and enhanced flux increases intracellular polyamines necessary for promoting cell growth, proliferation, and function. Polyamine depletion strategies demonstrate efficacy in reducing tumor growth and increasing survival in animal models of cancer; however, mechanistically, the cell-intrinsic and cell-extrinsic alterations within the tumor microenvironment underlying positive treatment outcomes are not well understood. Recently, investigators have demonstrated that co-targeting polyamine biosynthesis and transport alters the immune landscape. Although the polyamine synthesis-targeting drug 2-difluoromethylornithine (DFMO) is well tolerated in humans and is FDA-approved for African trypanosomiasis, its clinical benefit in treating established cancers has not yet been fully realized; however, combination therapies targeting compensatory mechanisms have shown tolerability and efficacy in animal models and are currently being tested in clinical trials. As demonstrated in pre-clinical models, polyamine blocking therapy (PBT) reduces immunosuppression in the tumor microenvironment and enhances the therapeutic efficacy of immune checkpoint blockade (ICB). Thus, DFMO may sensitize tumors to other therapeutics, including immunotherapies and chemotherapies.

Metabolic reprogramming: a bridge between aging and tumorigenesis

Aging is the most robust risk factor for cancer development, with more than 60% of cancers occurring in those aged 60 and above. However, how aging and tumorigenesis are intertwined is poorly understood and a matter of significant debate. Metabolic changes are hallmarks of both aging and tumorigenesis. The deleterious consequences of aging include dysfunctional cellular processes, the build‐up of metabolic byproducts and waste molecules in circulation and within tissues, and stiffer connective tissues that impede blood flow and oxygenation. Collectively, these age‐driven changes lead to metabolic reprogramming in different cell types of a given tissue that significantly affects their cellular functions. Here, we put forward the idea that metabolic changes that happen during aging help create a favorable environment for tumorigenesis. We review parallels in metabolic changes that happen during aging and how these changes function both as adaptive mechanisms that enable the development of malignant phenotypes in a cell‐autonomous manner and as mechanisms that suppress immune surveillance, collectively creating the perfect environment for cancers to thrive. Hence, antiaging therapeutic strategies that target the metabolic reprogramming that occurs as we age might provide new opportunities to prevent cancer initiation and/or improve responses to standard‐of‐care anticancer therapies.

Microbial Metabolites in Multiple Sclerosis: Implications for Pathogenesis and Treatment

Metabolites produced by the gut microbiota have been shown to play an important role in numerous inflammatory, neuropsychiatric, and neurodegenerative diseases. Specifically, microbial metabolites have been implicated in the modulation of innate and adaptive immunity, especially in the generation of regulatory T cells (Tregs), which are key regulators of multiple sclerosis (MS) pathogenesis. Furthermore, they affect processes relevant to MS pathophysiology, such as inflammation and demyelination, which makes them attractive molecules to be explored as therapeutics in MS. In this review, we discuss the importance of these metabolites as factors contributing to disease pathogenesis and as therapeutic targets in MS. Establishing an improved understanding of these gut-microbiota derived metabolites may provide new avenues for the treatment of MS.

T Cell Responses to the Microbiota

The immune system employs recognition tools to communicate with its microbial evolutionary partner. Among all the methods of microbial perception, T cells enable the widest spectrum of microbial recognition resolution, ranging from the crudest detection of whole groups of microbes to the finest detection of specific antigens. The application of this recognition capability to the crucial task of combatting infections has been the focus of classical immunology. We now appreciate that the coevolution of the immune system and the microbiota has led to development of a lush immunological decision tree downstream of microbial recognition, of which an inflammatory response is but one branch. In this review we discuss known T cell-microbe interactions in the gut and place them in the context of an algorithmic framework of recognition, context-dependent interpretation, and response circuits across multiple levels of microbial recognition resolution. The malleability of T cells in response to the microbiota presents an opportunity to edit immune response cellularity, identity, and functionality by utilizing microbiota-controlled pathways to promote human health.

T Cell Responses to the Microbiota

The immune system employs recognition tools to communicate with its microbial evolutionary partner. Among all the methods of microbial perception, T cells enable the widest spectrum of microbial recognition resolution, ranging from the crudest detection of whole groups of microbes to the finest detection of specific antigens. The application of this recognition capability to the crucial task of combatting infections has been the focus of classical immunology. We now appreciate that the coevolution of the immune system and the microbiota has led to development of a lush immunological decision tree downstream of microbial recognition, of which an inflammatory response is but one branch. In this review we discuss known T cell-microbe interactions in the gut and place them in the context of an algorithmic framework of recognition, context-dependent interpretation, and response circuits across multiple levels of microbial recognition resolution. The malleability of T cells in response to the microbiota presents an opportunity to edit immune response cellularity, identity, and functionality by utilizing microbiota-controlled pathways to promote human health.

Role of Polyamines and Hypusine in β Cells and Diabetes Pathogenesis

The polyamines-putrescine, spermidine, and spermine-are polycationic, low molecular weight amines with cellular functions primarily related to mRNA translation and cell proliferation. Polyamines partly exert their effects via the hypusine pathway, wherein the polyamine spermidine provides the aminobutyl moiety to allow posttranslational modification of the translation factor eIF5A with the rare amino acid hypusine (hydroxy putrescine lysine). The "hypusinated" eIF5A (eIF5Ahyp) is considered to be the active form of the translation factor necessary for the translation of mRNAs associated with stress and inflammation. Recently, it has been demonstrated that activity of the polyamines-hypusine circuit in insulin-producing islet β cells contributes to diabetes pathogenesis under conditions of inflammation. Elevated levels of polyamines are reported in both exocrine and endocrine cells of the pancreas, which may contribute to endoplasmic reticulum stress, oxidative stress, inflammatory response, and autophagy. In this review, we have summarized the existing research on polyamine-hypusine metabolism in the context of β-cell function and diabetes pathogenesis.

The Interplay Between TGF-β Signaling and Cell Metabolism

The transforming growth factor-β (TGF-β) signaling plays a critical role in the development and tissue homeostasis in metazoans, and deregulation of TGF-β signaling leads to many pathological conditions. Mounting evidence suggests that TGF-β signaling can actively alter metabolism in diverse cell types. Furthermore, metabolic pathways, beyond simply regarded as biochemical reactions, are closely intertwined with signal transduction. Here, we discuss the role of TGF-β in glucose, lipid, amino acid, redox and polyamine metabolism with an emphasis on how TGF-β can act as a metabolic modulator and how metabolic changes can influence TGF-β signaling. We also describe how interplay between TGF-β signaling and cell metabolism regulates cellular homeostasis as well as the progression of multiple diseases, including cancer.

Polyamine Immunometabolism: Central Regulators of Inflammation, Cancer and Autoimmunity

Polyamines are ubiquitous, amine-rich molecules with diverse processes in biology. Recent work has highlighted that polyamines exert profound roles on the mammalian immune system, particularly inflammation and cancer. The mechanisms by which they control immunity are still being described. In the context of inflammation and autoimmunity, polyamine levels inversely correlate to autoimmune phenotypes, with lower polyamine levels associated with higher inflammatory responses. Conversely, in the context of cancer, polyamines and polyamine biosynthetic genes positively correlate with the severity of malignancy. Blockade of polyamine metabolism in cancer results in reduced tumor growth, and the effects appear to be mediated by an increase in T-cell infiltration and a pro-inflammatory phenotype of macrophages. These studies suggest that polyamine depletion leads to inflammation and that polyamine enrichment potentiates myeloid cell immune suppression. Indeed, combinatorial treatment with polyamine blockade and immunotherapy has shown efficacy in pre-clinical models of cancer. Considering the efficacy of immunotherapies is linked to autoimmune sequelae in humans, termed immune-adverse related events (iAREs), this suggests that polyamine levels may govern the inflammatory response to immunotherapies. This review proposes that polyamine metabolism acts to balance autoimmune inflammation and anti-tumor immunity and that polyamine levels can be used to monitor immune responses and responsiveness to immunotherapy.

Steroid-Refractory Gut Graft-Versus-Host Disease: What We Have Learned From Basic Immunology and Experimental Mouse Model

Intestinal graft-versus-host disease (Gut-GVHD) is one of the major causes of mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). While systemic glucocorticoids (GCs) comprise the first-line treatment option, the response rate for GCs varies from 30% to 50%. The prognosis for patients with steroid-refractory acute Gut-GVHD (SR-Gut-aGVHD) remains dismal. The mechanisms underlying steroid resistance are unclear, and apart from ruxolitinib, there are no approved treatments for SR-Gut-aGVHD. In this review, we provide an overview of the current biological understanding of experimental SR-Gut-aGVHD pathogenesis, the advanced technology that can be applied to the human SR-Gut-aGVHD studies, and the potential novel therapeutic options for patients with SR-Gut-aGVHD.

A New Trend in Cancer Treatment: The Combination of Epigenetics and Immunotherapy

In recent years, immunotherapy has become a hot spot in the treatment of tumors. As an emerging treatment, it solves many problems in traditional cancer treatment and has now become the main method for cancer treatment. Although immunotherapy is promising, most patients do not respond to treatment or develop resistance. Therefore, in order to achieve a better therapeutic effect, combination therapy has emerged. The combination of immune checkpoint inhibition and epigenetic therapy is one such strategy. In this review, we summarize the current understanding of the key mechanisms of how epigenetic mechanisms affect cancer immune responses and reveal the key role of epigenetic processes in regulating immune cell function and mediating anti-tumor immunity. In addition, we highlight the outlook of combined epigenetic and immune regimens, particularly the combination of immune checkpoint blockade with epigenetic agents, to address the limitations of immunotherapy alone.

Metabolic adaptation of lymphocytes in immunity and disease

Adaptive immune responses mediated by T cells and B cells are crucial for protective immunity against pathogens and tumors. Differentiation and function of immune cells require dynamic reprogramming of cellular metabolism. Metabolic inputs, pathways, and enzymes display remarkable flexibility and heterogeneity, especially in vivo. How metabolic plasticity and adaptation dictate functional specialization of immune cells is fundamental to our understanding and therapeutic modulation of the immune system. Extensive progress has been made in characterizing the effects of metabolic networks on immune cell fate and function in discrete microenvironments or immunological contexts. In this review, we summarize how rewiring of cellular metabolism determines the outcome of adaptive immunity in vivo, with a focus on how metabolites, nutrients, and driver genes in immunometabolism instruct cellular programming and immune responses during infection, inflammation, and cancer in mice and humans. Understanding context-dependent metabolic remodeling will manifest legitimate opportunities for therapeutic intervention of human disease.

Harnessing Antitumor CD4+ T Cells for Cancer Immunotherapy

Simple Summary

Diverse evidence revealed that CD4⁺ T cells play an important role in antitumor immunity by promoting or suppressing cytotoxic T cell responses. This review outlines the role of CD4⁺ T subsets within the tumor microenvironment and summarizes the latest progress regarding their potentials in cancer immunotherapy and methods for improving outcomes in cancer strategies by modulating CD4⁺ T responses.

Abstract

Over the past decades, CD4⁺ T cells have been considered as a supporting actor in the fields of cancer immunotherapy. Until recently, accumulating evidence has demonstrated the critical role of CD4⁺ T cells during antitumor immunity. CD4⁺ T cells can either suppress or promote the antitumor cytotoxic CD8⁺ T cell responses, either in secondary lymphoid organs or in the tumor. In this review, we provide an overview of the multifaceted role of different CD4⁺ T cell subsets in cancer immune response and their contribution during cancer therapies. Specifically, we focus on the latest progress regarding the impact of CD4⁺ T cell modulation on immunotherapies and other cancer therapies and discuss the prospect for harnessing CD4⁺ T cells to control tumor progression and prevent recurrence in patients.

A Compass to Guide Insights into TH17 Cellular Metabolism and Autoimmunity

T cells rapidly convert their cellular metabolic requirements upon activation, switching to a highly glycolytic program to satisfy their increasingly complex energy needs. Fundamental metabolic differences have been established for the development of Foxp3⁺ T regulatory (Treg) cells versus T_H17 cells, alterations of which can drive disease. T_H17 cell dysregulation is a driver of autoimmunity and chronic inflammation, contributing to pathogenesis in diseases such as multiple sclerosis. A recent paper published in Cell by Wagner, et al. combined scRNA-seq and metabolic mapping data to interrogate potential metabolic modulators of T_H17 cell pathogenicity. This Compass to T_H17 cell metabolism highlights the polyamine pathway as a critical regulator of T_H17/Treg cell function, signifying its potential as a therapeutic target.

The eukaryotic initiation factor 5A (eIF5A1), the molecule, mechanisms and recent insights into the pathophysiological roles

Since the demonstration of its involvement in cell proliferation, the eukaryotic initiation factor 5A (eIF5A) has been studied principally in relation to the development and progression of cancers in which the isoform A2 is mainly expressed. However, an increasing number of studies report that the isoform A1, which is ubiquitously expressed in normal cells, exhibits novel molecular features that reveal its new relationships between cellular functions and organ homeostasis. At a first glance, eIF5A can be regarded, among other things, as a factor implicated in the initiation of translation. Nevertheless, at least three specificities: (1) its extreme conservation between species, including plants, throughout evolution, (2) its very special and unique post-translational modification through the activating-hypusination process, and finally (3) its close relationship with the polyamine pathway, suggest that the role of eIF5A in living beings remains to be uncovered. In fact, and beyond its involvement in facilitating the translation of proteins containing polyproline residues, eIF5A is implicated in various physiological processes including ischemic tolerance, metabolic adaptation, aging, development, and immune cell differentiation. These newly discovered physiological properties open up huge opportunities in the clinic for pathologies such as, for example, the ones in which the oxygen supply is disrupted. In this latter case, organ transplantation, myocardial infarction or stroke are concerned, and the current literature defines eIF5A as a new drug target with a high level of potential benefit for patients with these diseases or injuries. Moreover, the recent use of genomic and transcriptomic association along with metadata studies also revealed the implication of eIF5A in genetic diseases. Thus, this review provides an overview of eIF5A from its molecular mechanism of action to its physiological roles and the clinical possibilities that have been recently reported in the literature.

Quantitative genome-scale metabolic modeling of human CD4+ T cell differentiation reveals subset-specific regulation of glycosphingolipid pathways

T cell activation, proliferation, and differentiation involve metabolic reprogramming resulting from the interplay of genes, proteins, and metabolites. Here, we aim to understand the metabolic pathways involved in the activation and functional differentiation of human CD4⁺ T cell subsets (T helper [Th]1, Th2, Th17, and induced regulatory T [iTreg] cells). Here, we combine genome-scale metabolic modeling, gene expression data, and targeted and non-targeted lipidomics experiments, together with in vitro gene knockdown experiments, and show that human CD4⁺ T cells undergo specific metabolic changes during activation and functional differentiation. In addition, we confirm the importance of ceramide and glycosphingolipid biosynthesis pathways in Th17 differentiation and effector functions. Through in vitro gene knockdown experiments, we substantiate the requirement of serine palmitoyltransferase (SPT), a de novo sphingolipid pathway in the expression of proinflammatory cytokines (interleukin [IL]-17A and IL17F) by Th17 cells. Our findings provide a comprehensive resource for selective manipulation of CD4⁺ T cells under disease conditions characterized by an imbalance of Th17/natural Treg (nTreg) cells.

Intestinal immunity: to be, or not to be, induced? That is the question

The intestinal immune system maintains intestinal homeostasis in collaboration with diverse immune cell subsets residing at the epithelial layer, lamina propria and gut-associated lymphoid tissue (GALT). Bacterial components and their metabolites are essential for the establishment of the gut immune system. In addition, nutritional signals contribute to maintaining the mucosal immune response. Specialized epithelial microfold (M) cells in GALT facilitate immune surveillance on the mucosal surface by actively taking up external antigens to transport them into the lymphoid follicles. Because hyperplasia of M cells causes an excessive immune response in GALT, there is a self-regulatory mechanism to control the development of M cells appropriately. In this review, we will discuss the molecular mechanisms of mucosal immune regulation and their biological importance.

Polyamine: A metabolic compass for T helper cell fate direction

Interplay between metabolic and epigenetic remodeling may be key to cell fate control. In this issue of Cell, Puleston et al. and Wagner et al. use metabolomic, computational, and genetic approaches to uncover that polyamine metabolism directs T helper cell lineage choices, epigenetic state, and pathogenic potential in inflammation.