Keap1-Nrf2 System Plays an Important Role in Invariant Natural Killer T Cell Development and Homeostasis

The redox sensor KEAP1 facilitates adaptation of T cells to chronic antigen stimulation by preventing hyperactivation

During persistent antigen stimulation, exhausted CD8+ T cells are continuously replenished by self-renewing stem-like T cells. However, how CD8+ T cells adapt to chronic stimulation remains unclear. Here, we show that persistent antigen stimulation primes chromatin for regulation by the redox-sensing KEAP1-NRF2 pathway. Loss of KEAP1 in T cells impaired control of chronic viral infection. T cell-intrinsic KEAP1 suppressed NRF2 to promote expansion and persistence of virus-specific CD8+ T cells, drive a stem-like T cell response, down-regulate immune checkpoint molecules, and limit T cell receptor (TCR) hyperactivation and apoptosis. NRF2 epigenetically derepressed BACH2 targets and opposed a stem-like program driven by BACH2. In exhausted T cells induced by tonic GD2 chimeric antigen receptor (CAR) signaling, the effects of KEAP1 deficiency were rescued by inhibiting proximal TCR signaling. Enhancing mitochondrial oxidation improved the expansion and survival of KEAP1-deficient CD8+ GD2 CAR T cells and up-regulated markers associated with stem-like cells. Thus, the KEAP1-NRF2 axis regulates stem-like CD8+ T cells and long-term T cell immunity during chronic antigen exposure.

Targeting ROS-sensing Nrf2 potentiates anti-tumor immunity of intratumoral CD8+ T and CAR-T cells

Cytotoxic T lymphocytes (CTLs) play a crucial role in cancer rejection. However, CTLs encounter dysfunction and exhaustion in the immunosuppressive tumor microenvironment (TME). Although the reactive oxygen species (ROS)-rich TME attenuates CTL function, the underlying molecular mechanism remains poorly understood. The nuclear factor erythroid 2-related 2 (Nrf2) is the ROS-responsible factor implicated in increasing susceptibility to cancer progression. Therefore, we examined how Nrf2 is involved in anti-tumor responses of CD8+ T and chimeric antigen receptor (CAR) T cells in the ROS-rich TME. Here, we demonstrated that tumor growth in Nrf2-/- mice was significantly controlled and was reversed by T cell depletion and further confirmed that Nrf2 deficiency in T cells promotes anti-tumor responses using an adoptive transfer model of antigen-specific CD8+ T cells. Nrf2-deficient CTLs are resistant to ROS, and their effector functions are sustained in the TME. Furthermore, Nrf2 knockdown in human CAR-T cells enhanced the survival and function of intratumoral CAR-T cells in a solid tumor xenograft model and effectively controlled tumor growth. ROS-sensing Nrf2 inhibits the anti-tumor T cell responses, indicating that Nrf2 may be a potential target for T cell immunotherapy strategies against solid tumors.

Gpx4 Regulates Invariant NKT Cell Homeostasis and Function by Preventing Lipid Peroxidation and Ferroptosis

Invariant NKT (iNKT) cells are a group of innate-like T cells that plays important roles in immune homeostasis and activation. We found that iNKT cells, compared with CD4+ T cells, have significantly higher levels of lipid peroxidation in both mice and humans. Proteomic analysis also demonstrated that iNKT cells express higher levels of phospholipid hydroperoxidase glutathione peroxidase 4 (Gpx4), a major antioxidant enzyme that reduces lipid peroxidation and prevents ferroptosis. T cell-specific deletion of Gpx4 reduces iNKT cell population, most prominently the IFN-γ-producing NKT1 subset. RNA-sequencing analysis revealed that IFN-γ signaling, cell cycle regulation, and mitochondrial function are perturbed by Gpx4 deletion in iNKT cells. Consistently, we detected impaired cytokine production, elevated cell proliferation and cell death, and accumulation of lipid peroxides and mitochondrial reactive oxygen species in Gpx4 knockout iNKT cells. Ferroptosis inhibitors, iron chelators, vitamin E, and vitamin K2 can prevent ferroptosis induced by Gpx4 deficiency in iNKT cells and ameliorate the impaired function of iNKT cells due to Gpx4 inhibition. Last, vitamin E rescues iNKT cell population in Gpx4 knockout mice. Altogether, our findings reveal the critical role of Gpx4 in regulating iNKT cell homeostasis and function, through controlling lipid peroxidation and ferroptosis.

The role of Nrf2 in immune cells and inflammatory autoimmune diseases: a comprehensive review

INTRODUCTION

Nrf2 regulates mild stress, chronic inflammation, and metabolic changes by regulating different immune cells via downstream signaling. Collection of information about the role of Nrf2 in inflammatory autoimmune diseases will better understand the therapeutic potential of targeting Nrf2 in these diseases.

AREAS COVERED

In this review, we comprehensively discussed biological function of Nrf2 in different immune cells, including Nrf2 preventing oxidative tissue injury, affecting apoptosis of immune cells and inflammatory cytokine production. Moreover, we discussed the role of Nrf2 in the development of inflammatory autoimmune diseases.

EXPERT OPINION

Nrf2 binds to downstream signaling molecules and then provides durable protection against different cellular and organ stress. It has emerged as an important target for inflammatory autoimmune diseases. Development of Nrf2 modulator drugs needs to consider factors such as target specificity, short/long term safety, disease indication identification, and the extent of variation in Nrf2 activity. We carefully discussed the dual role of Nrf2 in some diseases, which helps to better target Nrf2 in the future.

NKT Cells and Other Innate T Cells: The Immune Cells That Do Not Follow the Rules

This Pillars of Immunology article is a commentary on “A subset of CD4+ thymocytes selected by MHC class I molecules,” a pivotal article by A. Bendelac, N. Killeen, D.R. Littman, and R.H. Schwartz published in Science in 1994, marking the discovery of NKT cells and paving the way for the identification and characterization of other innate T cells. https://doi.org/10.1126/science.7907820.

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Maternal exposure to hyperbaric oxygen at the preimplantation stages increases apoptosis and ectopic Cdx2 expression and decreases Oct4 expression in mouse blastocysts via Nrf2-Notch1 upregulation and Nf2 downregulation

BACKGROUND

The environmental oxygen tension has been reported to impact the blastocyst quality and cell numbers in the inner cell mass (ICM) during human and murine embryogenesis. While the molecular mechanisms leading to increased ICM cell numbers and pluripotency gene expression under hypoxia have been deciphered, it remains unknown which regulatory pathways caused the underweight fetal body and overweight placenta after maternal exposure to hyperbaric oxygen (HBO).

RESULTS

The blastocysts from the HBO-exposed pregnant mice revealed significantly increased signals of reactive oxygen species (ROS) and nuclear Nrf2 staining, decreased Nf2 and Oct4 expression, increased nuclear Tp53bp1 and active caspase-3 staining, and ectopic nuclear signals of Cdx2, Yap, and the Notch1 intracellular domain (N1ICD) in the ICM. In the ICM of the HBO-exposed blastocysts, both Nf2 cDNA microinjection and Nrf2 shRNA microinjection significantly decreased the ectopic nuclear expression of Cdx2, Tp53bp1, and Yap whereas increased Oct4 expression, while Nrf2 shRNA microinjection also significantly decreased Notch1 mRNA levels and nuclear expression of N1ICD and active caspase-3.

CONCLUSION

We show for the first time that maternal exposure to HBO at the preimplantation stage induces apoptosis and impairs ICM cell specification via upregulating Nrf2-Notch1-Cdx2 expression and downregulating Nf2-Oct4 expression.

Nrf2 regulates the activation-driven expansion of CD4 + T-cells by differentially modulating glucose and glutamine metabolism

Upon antigenic stimulation, CD4 + T-cells undergo clonal expansion, elevating their bioenergetic demands and utilization of nutrients like glucose and glutamine. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a well-known regulator of oxidative stress, but its involvement in modulating the metabolism of CD4 + T-cells remains unexplored. Here, we elucidate the role of Nrf2 beyond the traditional antioxidation, in modulating activation-driven expansion of CD4 + T-cells by influencing their nutrient metabolism. T-cell-specific activation of Nrf2 enhances early activation and IL-2 secretion, upregulates TCR-signaling, and increases activation-driven proliferation of CD4 + T-cells. Mechanistically, high Nrf2 inhibits glucose metabolism through glycolysis but promotes glutamine metabolism via glutaminolysis to support increased T-cell proliferation. Further, Nrf2 expression is temporally regulated in activated CD4 + T-cells with elevated expression during the early activation, but decreased expression thereafter. Overall, our findings uncover a novel role of Nrf2 as a metabolic modulator of CD4 + T-cells, thus providing a framework for improving Nrf2-targeting therapies and T-cell immunotherapies.

Synergistic effect of PS-MPs and Cd on male reproductive toxicity: Ferroptosis via Keap1-Nrf2 pathway

It has been wildly reported that microplastics (MPs) can adsorb heavy metals and act as carriers for their transport into organisms. However, the combined toxicity of MPs and heavy metals remains poorly studied. In this study, we established single or co-exposure (i.e. complex/combined exposure) mice models to investigate the combined toxicity of MPs and cadmium (Cd) on male reproduction. The complexation of MPs and Cd enhanced the bioavailability of Cd, while the combination of MPs and Cd exerted synergistic effect. Ultimately, the co-exposure was reported to enhance the reproduction toxicity by single exposure, which reflected in testicular structure, spermatogenesis and sex hormone synthesis. More in-depth mechanistic investigation suggested that MPs and Cd synergistically inhibited the Keap1-Nrf2 pathway and its downstream genes, induced lipid peroxidation and ferroptosis, ultimately caused damage to reproductive structures and functions. Our results highlighted the synergistic effect of MPs and Cd on the reproductive toxicity in male mammals for the first time, which also provided valuable insights into the combined toxicity mechanisms of MPs and other pollutants.

The Multifaceted Roles of NRF2 in Cancer: Friend or Foe?

Physiological concentrations of reactive oxygen species (ROS) play vital roles in various normal cellular processes, whereas excessive ROS generation is central to disease pathogenesis. The nuclear factor erythroid 2-related factor 2 (NRF2) is a critical transcription factor that regulates the cellular antioxidant systems in response to oxidative stress by governing the expression of genes encoding antioxidant enzymes that shield cells from diverse oxidative alterations. NRF2 and its negative regulator Kelch-like ECH-associated protein 1 (KEAP1) have been the focus of numerous investigations in elucidating whether NRF2 suppresses tumor promotion or conversely exerts pro-oncogenic effects. NRF2 has been found to participate in various pathological processes, including dysregulated cell proliferation, metabolic remodeling, and resistance to apoptosis. Herein, this review article will examine the intriguing role of phase separation in activating the NRF2 transcriptional activity and explore the NRF2 dual impacts on tumor immunology, cancer stem cells, metastasis, and long non-coding RNAs (LncRNAs). Taken together, this review aims to discuss the NRF2 multifaceted roles in both cancer prevention and promotion while also addressing the advantages, disadvantages, and limitations associated with modulating NRF2 therapeutically in cancer treatment.

Invariant natural killer T cells in lung diseases

Invariant natural killer T (iNKT) cells are a subset of T cells that are characterized by a restricted T-cell receptor (TCR) repertoire and a unique ability to recognize glycolipid antigens. These cells are found in all tissues, and evidence to date suggests that they play many immunological roles in both homeostasis and inflammatory conditions. The latter include lung inflammatory diseases such as asthma and infections: the roles of lung-resident iNKT cells in these diseases have been extensively researched. Here, we provide insights into the biology of iNKT cells in health and disease, with a particular focus on the role of pulmonary iNKT cells in airway inflammation and other lung diseases.

ROS fine-tunes the function and fate of immune cells

The redox state is essential to the process of cell life, which determines cell fate. As an important signaling molecule of the redox state, reactive oxygen species (ROS) are crucial for the homeostasis of immune cells and participate in the pathological processes of different diseases. We discuss the underlying mechanisms and possible signaling pathways of ROS to fine-tune the proliferation, differentiation, polarization and function of immune cells, including T cells, B cells, neutrophils, macrophages, myeloid-derived inhibitory cells (MDSCs) and dendritic cells (DCs). We further emphasize how excessive ROS lead to programmed immune cell death such as apoptosis, ferroptosis, pyroptosis, NETosis and necroptosis, providing valuable insights for future therapeutic strategies in human diseases.

Beyond Antioxidation: Keap1-Nrf2 in the Development and Effector Functions of Adaptive Immune Cells

Ubiquitously expressed in mammalian cells, the Kelch-like ECH-associated protein 1 (Keap1)-NF erythroid 2-related factor 2 (Nrf2) complex forms the evolutionarily conserved antioxidation system to tackle oxidative stress caused by reactive oxygen species. Reactive oxygen species, generated as byproducts of cellular metabolism, were identified as essential second messengers for T cell signaling, activation, and effector responses. Apart from its traditional role as an antioxidant, a growing body of evidence indicates that Nrf2, tightly regulated by Keap1, modulates immune responses and regulates cellular metabolism. Newer functions of Keap1 and Nrf2 in immune cell activation and function, as well as their role in inflammatory diseases such as sepsis, inflammatory bowel disease, and multiple sclerosis, are emerging. In this review, we highlight recent findings about the influence of Keap1 and Nrf2 in the development and effector functions of adaptive immune cells, that is, T cells and B cells, and discuss the knowledge gaps in our understanding. We also summarize the research potential and targetability of Nrf2 for treating immune pathologies.

Cullin 3-Mediated Regulation of Intracellular Iron Homeostasis Promotes Thymic Invariant NKT Cell Maturation

The E3 ubiquitin ligase cullin 3 (Cul3) is critical for invariant NKT (iNKT) cell development, as iNKT cells lacking Cul3 accumulate in the immature developmental stages. However, the mechanisms by which Cul3 mediates iNKT cell development remain unknown. In this study, we investigated the role of Cul3 in both immature and mature thymic iNKT cells using a mouse model with a T cell-specific deletion of Cul3. We found that mature iNKT cells lacking Cul3 proliferated and died more than wild-type cells did. These cells also displayed increased glucose metabolism and autophagy. Interestingly, we found that tight regulation of iron homeostasis is critical for iNKT cell development. Without Cul3, mature iNKT cells harbored higher levels of cytosolic iron, a phenotype associated with increased cell death. Taken together, our data suggest that Cul3 promotes iNKT cell development partially through intracellular iron homeostasis.

Nutraceuticals as Potential Therapeutic Modulators in Immunometabolism

Nutraceuticals act as cellular and functional modulators, contributing to the homeostasis of physiological processes. In an inflammatory microenvironment, these functional foods can interact with the immune system by modulating or balancing the exacerbated proinflammatory response. In this process, immune cells, such as antigen-presenting cells (APCs), identify danger signals and, after interacting with T lymphocytes, induce a specific effector response. Moreover, this conditions their change of state with phenotypical and functional modifications from the resting state to the activated and effector state, supposing an increase in their energy requirements that affect their intracellular metabolism, with each immune cell showing a unique metabolic signature. Thus, nutraceuticals, such as polyphenols, vitamins, fatty acids, and sulforaphane, represent an active option to use therapeutically for health or the prevention of different pathologies, including obesity, metabolic syndrome, and diabetes. To regulate the inflammation associated with these pathologies, intervention in metabolic pathways through the modulation of metabolic energy with nutraceuticals is an attractive strategy that allows inducing important changes in cellular properties. Thus, we provide an overview of the link between metabolism, immune function, and nutraceuticals in chronic inflammatory processes associated with obesity and diabetes, paying particular attention to nutritional effects on APC and T cell immunometabolism, as well as the mechanisms required in the change in energetic pathways involved after their activation.

Battles against aberrant KEAP1-NRF2 signaling in lung cancer: intertwined metabolic and immune networks

The Kelch-like ECH-associated protein 1/nuclear factor erythroid-derived 2-like 2 (KEAP1/NRF2) pathway is well recognized as a key regulator of redox homeostasis, protecting cells from oxidative stress and xenobiotics under physiological circumstances. Cancer cells often hijack this pathway during initiation and progression, with aberrant KEAP1-NRF2 activity predominantly observed in non-small cell lung cancer (NSCLC), suggesting that cell/tissue-of-origin is likely to influence the genetic selection during malignant transformation. Hyperactivation of NRF2 confers a multi-faceted role, and recently, increasing evidence shows that a close interplay between metabolic reprogramming and tumor immunity remodelling contributes to its aggressiveness, treatment resistance (radio-/chemo-/immune-therapy) and susceptibility to metastases. Here, we discuss in detail the special metabolic and immune fitness enabled by KEAP1-NRF2 aberration in NSCLC. Furthermore, we summarize the similarities and differences in the dysregulated KEAP1-NRF2 pathway between two major histo-subtypes of NSCLC, provide mechanistic insights on the poor response to immunotherapy despite their high immunogenicity, and outline evolving strategies to treat this recalcitrant cancer subset. Finally, we integrate bioinformatic analysis of publicly available datasets to illustrate the new partners/effectors in NRF2-addicted cancer cells, which may provide new insights into context-directed treatment.

METTL14-dependent m6A modification controls iNKT cell development and function

N⁶-methyladenosine (m⁶A), the most common form of RNA modification, controls CD4⁺ T cell homeostasis by targeting the IL-7/STAT5/SOCS signaling pathways. The role of m⁶A modification in unconventional T cell development remains unknown. Using mice with T cell-specific deletion of RNA methyltransferase METTL14 (T-Mettl14^−/−), we demonstrate that m⁶A modification is indispensable for iNKT cell homeostasis. Loss of METTL14-dependent m⁶A modification leads to the upregulation of apoptosis in double-positive thymocytes, which in turn decreases Vα14-Jα18 gene rearrangements, resulting in drastic reduction of iNKT numbers in the thymus and periphery. Residual T-Mettl14^−/− iNKT cells exhibit increased apoptosis, impaired maturation, and decreased responsiveness to IL-2/IL-15 and TCR stimulation. Furthermore, METTL14 knockdown in mature iNKT cells diminishes their cytokine production, correlating with increased Cish expression and decreased TCR signaling. Collectively, our study highlights a critical role for METTL14-dependent-m⁶A modification in iNKT cell development and function.

Cao et al. show that T cell-specific deletion of METTL14, a component of RNA m⁶A writer complex, leads to severe defects in iNKT cell development, survival, and function. Mechanistically, METTL14-dependent m⁶A modification controls iNKT cell development in a cell-intrinsic manner by regulating the apoptosis pathway and TCR signaling pathway.

Orchestrated Action of AMPK Activation and Combined VEGF/PD-1 Blockade with Lipid Metabolic Tunning as Multi-Target Therapeutics against Ovarian Cancers

Ovarian cancer is one of the most lethal gynecological malignancies worldwide, and chemoresistance is a critical obstacle in the clinical management of the disease. Recent studies have suggested that exploiting cancer cell metabolism by applying AMP-activated protein kinase (AMPK)-activating agents and distinctive adjuvant targeted therapies can be a plausible alternative approach in cancer treatment. Therefore, the perspectives about the combination of AMPK activators together with VEGF/PD-1 blockade as a dual-targeted therapy against ovarian cancer were discussed herein. Additionally, ferroptosis, a non-apoptotic regulated cell death triggered by the availability of redox-active iron, have been proposed to be governed by multiple layers of metabolic signalings and can be synergized with immunotherapies. To this end, ferroptosis initiating therapies (FITs) and metabolic rewiring and immunotherapeutic approaches may have substantial clinical potential in combating ovarian cancer development and progression. It is hoped that the viewpoints deliberated in this review would accelerate the translation of remedial concepts into clinical trials and improve the effectiveness of ovarian cancer treatment.

Brief homogeneous TCR signals instruct common iNKT progenitors whose effector diversification is characterized by subsequent cytokine signaling

Innate-like T cell populations expressing conserved TCRs play critical roles in immunity through diverse developmentally acquired effector functions. Focusing on the prototypical lineage of invariant natural killer T (iNKT) cells, we sought to dissect the mechanisms and timing of fate decisions and functional effector differentiation. Utilizing induced expression of the semi-invariant NKT cell TCR on double positive thymocytes, an initially highly synchronous wave of iNKT cell development was triggered by brief homogeneous TCR signaling. After reaching a uniform progenitor state characterized by IL-4 production potential and proliferation, effector subsets emerged simultaneously, but then diverged toward different fates. While NKT17 specification was quickly completed, NKT1 cells slowly differentiated and expanded. NKT2 cells resembled maturing progenitors, which gradually diminished in numbers. Thus, iNKT subset diversification occurs in dividing progenitor cells without acute TCR input but utilizes multiple active cytokine signaling pathways. These data imply a two-step model of iNKT effector differentiation.

Wdr1 and cofilin are necessary mediators of immune-cell-specific apoptosis triggered by Tecfidera

Despite the emerging importance of reactive electrophilic drugs, deconvolution of their principal targets remains difficult. The lack of genetic tractability/interventions and reliance on secondary validation using other non-specific compounds frequently complicate the earmarking of individual binders as functionally- or phenotypically-sufficient pathway regulators. Using a redox-targeting approach to interrogate how on-target binding of pleiotropic electrophiles translates to a phenotypic output in vivo, we here systematically track the molecular components attributable to innate immune cell toxicity of the electrophilic-drug dimethyl fumarate (Tecfidera®). In a process largely independent of canonical Keap1/Nrf2-signaling, Keap1-specific modification triggers mitochondrial-targeted neutrophil/macrophage apoptosis. On-target Keap1–ligand-engagement is accompanied by dissociation of Wdr1 from Keap1 and subsequent coordination with cofilin, intercepting Bax. This phagocytic-specific cell-killing program is recapitulated by whole-animal administration of dimethyl fumarate, where individual depletions of the players identified above robustly suppress apoptosis.

The mechanism-of-action of many electrohilic drugs remains poorly understood. Here, the authors use a redox-targeting approach to elucidate the basis for the innate immune cell toxicity of dimethyl fumarate, showing that it modifies Keap1 to trigger mitochondrial-targeted neutrophil/macrophage apoptosis.

Virus Infection Induces Keap1 Binding to Cytokine Genes, Which Recruits NF-κB p50 and G9a-GLP and Represses Cytokine Transcription

Proinflammatory cytokine gene transcription must be moderated to avoid the pathological consequences of excess cytokine production. The relationships between virus infection and the mechanisms that moderate cytokine transcription are incompletely understood. We investigated the influence of Keap1 on cytokine gene induction by Sendai virus infection in mouse embryo fibroblasts. Virus infection induced Keap1 binding to the Ifnb1, Tnf, and Il6 genes. Keap1 moderated viral induction of their transcription by mechanisms that did not require Nrf2. Keap1 was required for NF-κB p50 recruitment, but not for NF-κB p65 or IRF3 recruitment, to these genes. Keap1 formed complexes with NF-κB p50 and NF-κB p65, which were visualized using bimolecular fluorescence complementation analysis. These bimolecular fluorescence complementation complexes bound chromosomes in live cells, suggesting that Keap1 could bind chromatin in association with NF-κB proteins. Keap1 was required for viral induction of G9a-GLP lysine methyltransferase binding and H3K9me2 modification at cytokine genes. G9a-GLP inhibitors counteracted transcription repression by Keap1 and enhanced Keap1 and NF-κB recruitment to cytokine genes. The interrelationships among Keap1, NF-κB, and G9a-GLP recruitment, activities, and transcriptional effects suggest that they form a feedback circuit, which moderates viral induction of cytokine transcription. Nrf2 counteracted Keap1 binding to cytokine genes and the recruitment of NF-κB p50 and G9a-GLP by Keap1. Whereas Keap1 has been reported to influence cytokine expression indirectly through its functions in the cytoplasm, these findings provide evidence that Keap1 regulates cytokine transcription directly in the nucleus. Keap1 binds to cytokines genes upon virus infection and moderates their induction by recruiting NF-κB p50 and G9a-GLP.

Oxidative Stress in SLE T Cells, Is NRF2 Really the Target to Treat?

Oxidative stress is a major component of cellular damage in T cells from patients with systemic lupus erythematosus (SLE) resulting amongst others in the generation of pathogenic Th17 cells. The NRF2/Keap1 pathway is the most important antioxidant system protecting cells from damage due to oxidative stress. Activation of NRF2 therefore seems to represent a putative therapeutic target in SLE, which is nevertheless challenged by several findings suggesting tissue and cell specific differences in the effect of NRF2 expression. This review focusses on the current understanding of oxidative stress in SLE T cells and its pathophysiologic and therapeutic implications.

Mitochondrial metabolism is essential for invariant natural killer T cell development and function

We show CD1d-restricted natural killer (NK)T cells have distinct metabolic profiles compared with CD4⁺ conventional T cells. Mature NKT cells have poor fatty acid oxidation and exhibit reduced mitochondrial respiratory reserve in the steady state. In addition, NKT cell development is more sensitive to alterations in mitochondrial electron transport chain function than conventional T cells. Using T cell-specific mitochondrial complex III ablation in mice, we further demonstrate that mitochondrial metabolism plays a crucial role in NKT cell development and function by modulating T cell receptor/interleukin-15 signaling and NFAT activity. Collectively, our data provide evidence for a critical role of mitochondrial metabolism in NKT cell development and activation, opening a new avenue for NKT cell-based immunotherapy by manipulating NKT cell metabolism.

Conventional T cell fate and function are determined by coordination between cellular signaling and mitochondrial metabolism. Invariant natural killer T (iNKT) cells are an important subset of “innate-like” T cells that exist in a preactivated effector state, and their dependence on mitochondrial metabolism has not been previously defined genetically or in vivo. Here, we show that mature iNKT cells have reduced mitochondrial respiratory reserve and iNKT cell development was highly sensitive to perturbation of mitochondrial function. Mice with T cell-specific ablation of Rieske iron-sulfur protein (RISP; T-Uqcrfs1^−/−), an essential subunit of mitochondrial complex III, had a dramatic reduction of iNKT cells in the thymus and periphery, but no significant perturbation on the development of conventional T cells. The impaired development observed in T-Uqcrfs1^−/− mice stems from a cell-autonomous defect in iNKT cells, resulting in a differentiation block at the early stages of iNKT cell development. Residual iNKT cells in T-Uqcrfs1^−/− mice displayed increased apoptosis but retained the ability to proliferate in vivo, suggesting that their bioenergetic and biosynthetic demands were not compromised. However, they exhibited reduced expression of activation markers, decreased T cell receptor (TCR) signaling and impaired responses to TCR and interleukin-15 stimulation. Furthermore, knocking down RISP in mature iNKT cells diminished their cytokine production, correlating with reduced NFATc2 activity. Collectively, our data provide evidence for a critical role of mitochondrial metabolism in iNKT cell development and activation outside of its traditional role in supporting cellular bioenergetic demands.

Metabolism in Invariant Natural Killer T Cells: An Overview

Cellular metabolism is critical for generating energy and macromolecules for cell growth and survival. In recent years, the importance of metabolism in mediating T cell differentiation, proliferation, and function has been a hot topic of investigation. However, very little is known about metabolic regulation in invariant natural killer T (iNKT) cells. In this viewpoint, we will discuss what is currently known about immunometabolism in iNKT cells and how these findings relate to CD4 T cells.

Nrf2-A Molecular Target for Sepsis Patients in Critical Care

The transcription factor NF-E2 p45-related factor 2 (Nrf2) is an established master regulator of the anti-oxidative and detoxifying cellular response. Thus, a role in inflammatory diseases associated with the generation of large amounts of reactive oxygen species (ROS) seems obvious. In line with this, data obtained in cell culture experiments and preclinical settings have shown that Nrf2 is important in regulating target genes that are necessary to ensure cellular redox balance. Additionally, Nrf2 is involved in the induction of phase II drug metabolizing enzymes, which are important both in degrading and converting drugs into active forms, and into putative carcinogens. Therefore, Nrf2 has also been implicated in tumorigenesis. This must be kept in mind when new therapy approaches are planned for the treatment of sepsis. Therefore, this review highlights the function of Nrf2 in sepsis with a special focus on the translation of rodent-based results into sepsis patients in the intensive care unit (ICU).

Hippo/Mst signaling coordinates cellular quiescence with terminal maturation in iNKT cell development and fate decisions

Invariant natural killer T (iNKT) cells acquire effector functions during development by mechanisms that remain poorly understood. Here, we show that the Hippo kinases Mst1 and Mst2 act as molecular rheostats for the terminal maturation and effector differentiation programs of iNKT cells. Loss of Mst1 alone or together with Mst2 impedes iNKT cell development, associated with defective IL-15-dependent cell survival. Mechanistically, Mst1 enforces iNKT cellular and transcriptional quiescence associated with maturation and commitment to iNKT1 cells by suppressing proliferation and Opa1-related mitochondrial metabolism that are dynamically regulated during iNKT cell development. Furthermore, Mst1 shapes the reciprocal fate decisions between iNKT1 and iNKT17 effector cells, which respectively depend upon mitochondrial dynamics and ICOS-mTORC2 signaling. Collectively, these findings establish Mst1 as a crucial regulator of mitochondrial homeostasis and quiescence in iNKT cell development and effector lineage differentiation and highlight that establishment of quiescence programs underlies iNKT cell development and effector maturation.

A focus on natural killer T-cell subset characterization and developmental stages

Almost 20 years ago, CD1d tetramers were developed to track invariant natural killer T (NKT) cells based on their specificity, and to define developmental steps during which differentiation markers and functional features are progressively acquired from early NKT cell precursor to fully mature NKT cell subsets. Based on these findings, a linear developmental model was proposed and subsequently used by all studies investigating the specific role of factors that control NKT cell development. More recently, based on intracellular staining patterns of lineage-specific transcription factors such as T-bet, GATA-3, promyelocytic leukemia zinc finger and RORγt, a lineage differentiation model was proposed for NKT cell development. Currently, studies on NKT cells development present lineage differentiation model data in addition to the linear maturation model. In the perspective presented here, we discuss current knowledge relating to NKT cell developmental models and particularly focus on the approaches and strategies, some of which appear nebulous, used to define NKT cell developmental stages and subsets.