Th2 skewing by activation of Nrf2 in CD4(+) T cells

2-Substituted-4,7-dihydro-4-ethylpyrazolo[1,5-a]pyrimidin-7-ones alleviate LPS-induced inflammation by modulating cell metabolism via CD73 upon macrophage polarization

Macrophage polarization towards the M1 phenotype under bacterial product-related exposure (LPS) requires a rapid change in gene expression patterns and cytokine production along with a metabolic rewiring. Metabolic pathways and redox reactions are such tightly connected, giving rise to an area of research referred to as immunometabolism. A role in this context has been paid to the master redox-sensitive regulator Nuclear factor erythroid 2-related factor 2 (Nrf2) and to the 5'-ectonucleotidase CD73, a marker related to macrophage metabolism rearrangement under pro-inflammatory conditions. In this light, a cell model of LPS-stimulated macrophages has been established and nine 4,7-dihydro-4-ethylpyrazolo[l,5-a]pyrimidin-7-ones with a potential anti-inflammatory effect have been administered. Our data highlight that two selected compounds (namely, 5 and 8) inhibit the LPS-induced Nrf2 nuclear translocation and ameliorate the activity rate of the antioxidant enzyme catalase. Additionally, the pyridine-containing compound (8) promotes the shift from the pro-inflammatory immunophenotype M1 to the pro-resolving M2 one, by downregulating CD80 and iNOS and by enhancing CD163 and TGFβ1 expression. Most importantly, CD73 is modulated by these compounds as well as the lactate production. Our data demonstrate that pyrazolo[l,5-a]pyrimidine derivatives are effective as anti-inflammatory compounds. Furthermore, these pyrazolo[l,5-a]pyrimidines exert their action via CD73-related signaling and modulation of cell metabolism of activated macrophages.

The role of ROS in tumor infiltrating immune cells and cancer immunotherapy

Reactive oxygen species (ROS) are a group of short-lived highly reactive molecules formed intracellularly from molecular oxygen. ROS can alter biochemical, transcriptional, and epigenetic programs and have an indispensable role in cellular function. In immune cells, ROS are mediators of specialized functions such as phagocytosis, antigen presentation, activation, cytolysis, and differentiation. ROS have a fundamental role in the tumor microenvironment (TME) where they are produced by immune cell-intrinsic and -extrinsic mechanisms. ROS can act as a double-edged sword with short exposures leading to activation in various innate and adaptative immune cells, and prolonged exposures, unopposed by redox balancing antioxidants leading to exhaustion, immunosuppression, and unresponsiveness to cancer immunotherapy. Due to its plasticity and impact on the anti-tumor function of immune cells, attempts are currently in process to harness ROS biology with the purpose to improve contemporary strategies of cancer immunotherapy. Here, we provide a short overview how ROS and various antioxidant systems impact on the function of innate and adaptive immune system cells with emphasis on the TME and immune-based therapies for cancer.

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.

Sphingosine 1-phosphate combining with S1PR4 promotes regulatory T cell differentiation related to FAO through Nrf2/PPARα

Metabolism and metabolic processes have long been considered to shape the tumour immunosuppressive microenvironment. Recent research has demonstrated that T regulatory cells (Tregs) display high rates of fatty acid oxidation (FAO) and a relatively low rate of glycolysis. Sphingosine 1-phosphate (S1P), which is a G protein signalling activator involved in immune regulation and FAO modulation, has been implicated in Treg differentiation. However, the precise relation between Treg differentiation and S1P remains unclear. In this study, we isolated naïve CD4+ T cells from the spleens of 6-8-week-old BALB/c mice using magnetic bead sorting, which was used in our study for Treg differentiation. S1P stimulation was performed during Treg differentiation. We examined the oxygen consumption and palmitic acid metabolism of the differentiated Tregs and evaluated the expression levels of various proteins, including Nrf2, CPT1A, Glut1, ACC1 and PPARα, through Western blotting. Our results demonstrate that S1P promotes Treg differentiation and enhances FAO, and that the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and peroxisome proliferator-activated receptor α (PPARα) is upregulated. Furthermore, Nrf2 or PPARα knockdown dampened the Treg differentiation and FAO that were promoted by S1P, confirming that S1P can bind with S1PR4 to promote Treg differentiation through the Nrf2/PPARα signalling pathway, which may be related to FAO facilitation.

Chronic application of alcohol-soluble gluten extract over undamaged skin causes clinical sensitization for life-threatening anaphylaxis via activation of systemic Th2 immune responses in mice

Introduction

Gluten allergy is a major public health problem that is growing at an alarming rate. Specific mechanisms underlying sensitization to gluten remain incompletely understood. Currently, it is unclear whether chronic exposure to alcohol-soluble gluten extract via undamaged skin has the capacity to clinically sensitize mice for life-threatening anaphylaxis. Using an adjuvant-free mouse model, here we tested the hypothesis that chronic application of alcohol-soluble durum gluten (ASDG) extract will clinically sensitize mice for life-threatening anaphylaxis.

Methods

This study was conducted in a gluten-free Balb/c mouse colony that was established and maintained on a plant protein-free diet. Groups of adult female mice were exposed dermally to ASDG extract or vehicle once a week for 9-weeks. Specific (s) and total (t) IgE levels were quantified. Mice were challenged systemically with ASDG to measure symptoms of systemic anaphylaxis. Hypothermic shock response (HSR) and mucosal mast cell degranulation response (MMCR) were determined upon challenge. Spleen Th1, Th2, and other immune markers were quantified.

Results

We found that chronic exposure to ASDG elicited robust elevation of sIgE and tIgE. Systemic challenge with ASDG, but not vehicle, elicited life-threatening anaphylaxis associated with dramatic HSR and MMCR. Correlation analysis demonstrated direct positive inter-relationships among IgE, HSR, and MMCR. Anaphylaxis was associated with significant elevation of prototypic Th2 but not Th1 immune markers in the spleen.

Discussion/Conclusion

Our study collectively demonstrates that ASDG is intrinsically allergenic; and chronic exposure to ASDG via undamaged skin can clinically sensitize mice for life-threatening anaphylaxis via activating the systemic Th2 immune responses.

The SWI/SNF chromatin-remodeling subunit DPF2 facilitates NRF2-dependent antiinflammatory and antioxidant gene expression

During emergency hematopoiesis, hematopoietic stem cells (HSCs) rapidly proliferate to produce myeloid and lymphoid effector cells, a response that is critical against infection or tissue injury. If unresolved, this process leads to sustained inflammation, which can cause life-threatening diseases and cancer. Here, we identify a role of double PHD fingers 2 (DPF2) in modulating inflammation. DPF2 is a defining subunit of the hematopoiesis-specific BAF (SWI/SNF) chromatin-remodeling complex, and it is mutated in multiple cancers and neurological disorders. We uncovered that hematopoiesis-specific Dpf2-KO mice developed leukopenia, severe anemia, and lethal systemic inflammation characterized by histiocytic and fibrotic tissue infiltration resembling a clinical hyperinflammatory state. Dpf2 loss impaired the polarization of macrophages responsible for tissue repair, induced the unrestrained activation of Th cells, and generated an emergency-like state of HSC hyperproliferation and myeloid cell-biased differentiation. Mechanistically, Dpf2 deficiency resulted in the loss of the BAF catalytic subunit BRG1 from nuclear factor erythroid 2-like 2-controlled (NRF2-controlled) enhancers, impairing the antioxidant and antiinflammatory transcriptional response needed to modulate inflammation. Finally, pharmacological reactivation of NRF2 suppressed the inflammation-mediated phenotypes and lethality of Dpf2Δ/Δ mice. Our work establishes an essential role of the DPF2-BAF complex in licensing NRF2-dependent gene expression in HSCs and immune effector cells to prevent chronic inflammation.

The role of Nrf2 in the pathogenesis and treatment of ulcerative colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease involving mainly the colorectal mucosa and submucosa, the incidence of which has been on the rise in recent years. Nuclear factor erythroid 2-related factor 2 (Nrf2), known for its key function as a transcription factor, is pivotal in inducing antioxidant stress and regulating inflammatory responses. Numerous investigations have demonstrated the involvement of the Nrf2 pathway in maintaining the development and normal function of the intestine, the development of UC, and UC-related intestinal fibrosis and carcinogenesis; meanwhile, therapeutic agents targeting the Nrf2 pathway have been widely investigated. This paper reviews the research progress of the Nrf2 signaling pathway in UC.

Combined Supplementation of Clostridium butyricum and Bifidobacterium infantis Diminishes Chronic Unpredictable Mild Stress-Induced Intestinal Alterations via Activation of Nrf-2 Signaling Pathway in Rats

Exposure to long-term chronic unpredictable mild stress (CUMS) can cause redox imbalance and inflammation, which may affect the integrity of the gut barrier. The present study was conducted to investigate the effects of a probiotics bacterium mixture, including Clostridium butyricum (C. butyricum) and Bifidobacterium infantis (B. infantis), on the intestinal homeostasis in rats exposed to multiple low-intensity stressors for 28 days. The mechanism of CUMS-induced altered intestinal homeostasis was evaluated by focusing on the nuclear factor-E2-related factor-2 (Nrf-2) pathway. In contrast to the CUMS group, probiotic mixture supplementation significantly (p < 0.01) reversed the stress-induced elevated corticosterone level, protein and lipid oxidation, and increased enzymatic and non-enzymatic antioxidant levels, as well as upregulated Nrf-2/HO-1 pathway. Probiotics supplementation further significantly (p < 0.01) decreased the CUMS-induced inflammation, altered T-lymphocyte levels, and suppressed the protein expression of nuclear factor kappa B (NF-κB) in rat intestines. Improvement in histological changes and intestinal barrier integrity further validate the beneficial effects of probiotic mixtures on CUMS-induced altered intestinal morphology. In conclusion, our results suggest that the combination of C. butyricum and B. infantis significantly attenuated CUMS-induced oxidative stress, inflammation, and T-lymphocyte modulation by upregulating Nrf-2/HO-1 signaling and inhibiting NF-κB expression in rat intestine.

The role of metabolic reprogramming of tumor-associated macrophages in shaping the immunosuppressive tumor microenvironment

Macrophages are potent immune effector cells in innate immunity and exert dual-effects in the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) make up a significant portion of TME immune cells. Similar to M1/M2 macrophages, TAMs are also highly plastic, and their functions are regulated by cytokines, chemokines and other factors in the TME. The metabolic changes in TAMs are significantly associated with polarization towards a protumour or antitumour phenotype. The metabolites generated via TAM metabolic reprogramming in turn promote tumor progression and immune tolerance. In this review, we explore the metabolic reprogramming of TAMs in terms of energy, amino acid and fatty acid metabolism and the potential roles of these changes in immune suppression.

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.

CD4+ T Cell NRF2 Signaling Improves Liver Transplantation Outcomes by Modulating T Cell Activation and Differentiation

Aims: Innate and adaptive immune responses regulate hepatic ischemia-reperfusion injury (IRI) in orthotopic liver transplantation (OLT). While the mechanism of how nuclear factor erythroid 2-related factor 2 (NRF2) plays a role in liver IRI has been studied, the contribution of T cell-specific NRF2 in OLT remains unknown. In the current translational study, we investigated whether and how CD4+ T cell-specific NRF2 signaling affects liver transplant outcomes in mice and humans. Results: In the experimental arm, cold-stored (4°C/18 h) wild-type (WT) mouse livers transplanted to NRF2-deficient (NRF2-knockout [NRF2-KO]) recipients experienced greater hepatocellular damage than those in Nrf2-proficient (WT) counterparts, evidenced by Suzuki's histological scores, frequency of TdT-mediated dUTP nick end labeling (TUNEL)+ cells, and elevated serum aspartate aminotransferase/alanine aminotransferase (AST/ALT) levels. In vitro studies showed that NRF2 signaling suppressed CD4+ T cell differentiation to a proinflammatory phenotype (Th1, Th17) while promoting the regulatory (Foxp3+) T cell lineage. Furthermore, OLT injury deteriorated in immune-compromised RAG2-KO test recipients repopulated with CD4+ T cells from NRF2-KO compared with WT donor mice. In the clinical arm of 45 human liver transplant patients, the perioperative increase of NRF2 expression in donor livers negatively regulated innate and adaptive immune activation, resulting in reduced hepatocellular injury in NRF2-proficient OLT. Innovation and Conclusion: CD4+ T cell population expressing NRF2 attenuated ischemia and reperfusion (IR)-triggered hepatocellular damage in a clinically relevant mouse model of extended donor liver cold storage, followed by OLT, whereas the perioperative increase of NRF2 expression reduced hepatic injury in human liver transplant recipients. Thus, CD4+ T cell NRF2 may be a novel cytoprotective sentinel against IR stress in OLT recipients. Antioxid. Redox Signal. 38, 670-683.

Effects of Medicinal Plants and Phytochemicals in Nrf2 Pathways during Inflammatory Bowel Diseases and Related Colorectal Cancer: A Comprehensive Review

Inflammatory bowel diseases (IBDs) are related to nuclear factor erythroid 2-related factor 2 (Nrf2) dysregulation. In vitro and in vivo studies using phytocompounds as modulators of the Nrf2 signaling in IBD have already been published. However, no existing review emphasizes the whole scenario for the potential of plants and phytocompounds as regulators of Nrf2 in IBD models and colitis-associated colorectal carcinogenesis. For these reasons, this study aimed to build a review that could fill this void. The PubMed, EMBASE, COCHRANE, and Google Scholar databases were searched. The literature review showed that medicinal plants and phytochemicals regulated the Nrf2 on IBD and IBD-associated colorectal cancer by amplifying the expression of the Nrf2-mediated phase II detoxifying enzymes and diminishing NF-κB-related inflammation. These effects improve the bowel environment, mucosal barrier, colon, and crypt disruption, reduce ulceration and microbial translocation, and consequently, reduce the disease activity index (DAI). Moreover, the modulation of Nrf2 can regulate various genes involved in cellular redox, protein degradation, DNA repair, xenobiotic metabolism, and apoptosis, contributing to the prevention of colorectal cancer.

The different facets of heme-oxygenase 1 in innate and adaptive immunity

Heme oxygenase (HO) enzymes are responsible for the main oxidative step in heme degradation, generating equimolar amounts of free iron, biliverdin and carbon monoxide. HO-1 is induced as a crucial stress response protein, playing protective roles in physiologic and pathological conditions, due to its antioxidant, anti-apoptotic and anti-inflammatory effects. The mechanisms behind HO-1-mediated protection are being explored by different studies, affecting cell fate through multiple ways, such as reduction in intracellular levels of heme and ROS, transcriptional regulation, and through its byproducts generation. In this review we focus on the interplay between HO-1 and immune-related signaling pathways, which culminate in the activation of transcription factors important in immune responses and inflammation. We also discuss the dual interaction of HO-1 and inflammatory mediators that govern resolution and tissue damage. We highlight the dichotomy of HO-1 in innate and adaptive immune cells development and activation in different disease contexts. Finally, we address different known anti-inflammatory pharmaceuticals that are now being described to modulate HO-1, and the possible contribution of HO-1 in their anti-inflammatory effects.

NRF2 Mediates Cellular Resistance to Transformation, Radiation, and Inflammation in Mice

Nuclear factor erythroid 2-related factor 2 (NRF2) is recognized as a master transcription factor that regulates expression of numerous detoxifying and antioxidant cytoprotective genes. In fact, models of NRF2 deficiency indicate roles not only in redox regulation, but also in metabolism, inflammatory/autoimmune disease, cancer, and radioresistancy. Since ionizing radiation (IR) generates reactive oxygen species (ROS), it is not surprising it activates NRF2 pathways. However, unexpectedly, activation is often delayed for many days after the initial ROS burst. Here, we demonstrate that, as assayed by γ-H2AX staining, rapid DNA double strand break (DSB) formation by IR in primary mouse Nrf2-/- MEFs was not affected by loss of NRF2, and neither was DSB repair to any great extent. In spite of this, basal and IR-induced transformation was greatly enhanced, suggesting that NRF2 protects against late IR-induced genomic instability, at least in murine MEFs. Another possible IR- and NRF2-related event that could be altered is inflammation and NRF2 deficiency increased IR-induced NF-κB pro-inflammatory responses mostly late after exposure. The proclivity of NRF2 to restrain inflammation is also reflected in the reprogramming of tumor antigen-specific lymphocyte responses in mice where Nrf2 k.o. switches Th2 responses to Th1 polarity. Delayed NRF2 responses to IR may be critical for the immune transition from prooxidant inflammation to antioxidant healing as well as in driving cellular radioresistance and survival. Targeting NRF2 to reprogram immunity could be of considerable therapeutic benefit in radiation and immunotherapy.

Role of Nuclear Factor Erythroid 2 (Nrf2) in the Recovery of Long COVID-19 Using Natural Antioxidants: A Systematic Review

Coronavirus disease 2019 (COVID-19) is an infectious disease with approximately 517 million confirmed cases, with the average number of cases revealing that patients recover immediately without hospitalization. However, several other cases found that patients still experience various symptoms after 3–12 weeks, which is known as a long COVID syndrome. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can activate nuclear factor kappa beta (NF-κβ) and unbind the nuclear factor erythroid 2-related factor 2 (Nrf2) with Kelch-like ECH-associated protein 1 (Keap1), causing inhibition of Nrf2, which has an important role in antioxidant response and redox homeostasis. Disrupting the Keap1–Nrf2 pathway enhances Nrf2 activity, and has been identified as a vital approach for the prevention of oxidative stress and inflammation. Hence, natural antioxidants from various sources have been identified as a promising strategy to prevent oxidative stress, which plays a role in reducing the long COVID-19 symptoms. Oxygen-rich natural antioxidant compounds provide an effective Nrf2 activation effect that interact with the conserved amino acid residues in the Keap1-binding pocket, such as Ser602, Ser363, Ser508, and Ser555. In this review, the benefits of various natural antioxidant compounds that can modulate the Nrf2 signaling pathway, which is critical in reducing and curing long COVID-19, are highlighted and discussed.

The Role of KEAP1-NRF2 System in Atopic Dermatitis and Psoriasis

The Kelch-like erythroid cell-derived protein with cap‘n’collar homology-associated protein 1 (KEAP1)-nuclear factor erythroid-2-related factor 2 (NRF2) system, a thiol-based sensor-effector apparatus, exerts antioxidative and anti-inflammatory effects and maintains skin homeostasis. Thus, NRF2 activation appears to be a promising treatment option for various skin diseases. However, NRF2-mediated defense responses may deteriorate skin inflammation in a context-dependent manner. Atopic dermatitis (AD) and psoriasis are two common chronic inflammatory skin diseases caused by a defective skin barrier, dysregulated immune responses, genetic predispositions, and environmental factors. This review focuses on the role of the KEAP1-NRF2 system in the pathophysiology of AD and psoriasis and the therapeutic approaches that utilize this system.

The Flavonoid Hesperidin Methyl Chalcone Targets Cytokines and Oxidative Stress to Reduce Diclofenac-Induced Acute Renal Injury: Contribution of the Nrf2 Redox-Sensitive Pathway

Hesperidin is derived from citrus fruits among other plants. Hesperidin was methylated to increase its solubility, generating hesperidin methyl chalcone (HMC), an emerging flavonoid that possess anti-inflammatory and antioxidant properties. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a powerful regulator of cellular resistance to oxidant products. Previous data evidenced HMC can activate Nrf2 signaling, providing antioxidant protection against diverse pathological conditions. However, its effects on kidney damage caused by non-steroidal anti-inflammatory drugs (NSAIDs) have not been evaluated so far. Mice received a nephrotoxic dose of diclofenac (200 mg/kg) orally followed by intra-peritoneal (i.p.) administration of HMC (0.03–3 mg/kg) or vehicle. Plasmatic levels of urea, creatinine, oxidative stress, and cytokines were assessed. Regarding the kidneys, oxidative parameters, cytokine production, kidney swelling, urine NGAL, histopathology, and Nrf2 mRNA expression and downstream targets were evaluated. HMC dose-dependently targeted diclofenac systemic alterations by decreasing urea and creatinine levels, and lipid peroxidation, as well as IL-6, IFN-γ, and IL-33 production, and restored antioxidant properties in plasma samples. In kidney samples, HMC re-established antioxidant defenses, inhibited lipid peroxidation and pro-inflammatory cytokines and upregulated IL-10, reduced kidney swelling, urine NGAL, and histopathological alterations. Additionally, HMC induced mRNA expression of Nrf2 and its downstream effectors HO-1 and Nqo1, as well as reduced the levels of Keap1 protein detected in renal tissue. The present data demonstrate HMC is a potential compound for the treatment of acute renal damage caused by diclofenac, a routinely prescribed non-steroidal anti-inflammatory drug.

Chronic Exposure to the Food Additive tBHQ Modulates Expression of Genes Related to SARS-CoV-2 and Influenza Viruses

Background. tert-butylhydroquinone (tBHQ) is an antioxidant commonly used as a food additive. Studies suggest that tBHQ could modulate immune responses to influenza and SARS-CoV-2 infection. In our transcriptomic analysis we explored the molecular mechanisms behind tBHQ’s modulatory properties and the relationships to respiratory viral infections. Methods. tBHQ was administered per os to BALB/c mice (1.5% [w/w]) for 20 days. Splenic T cells were isolated with magnetic separation and subjected to transcriptomic analysis. Gene-set enrichment analysis and g:Profiler was conducted to provide a functional interpretation of significantly changed genes. Further analysis for AHR/NRF2 binding sites was performed with GeneHancer. Results. In CD4⁺ cells, we found significantly altered expression of 269 genes by tBHQ. Of them, many had relevance in influenza infection such as genes responsible for virus entry (Anxa1/2, Cd14), interferon signaling (Dusp10, Tnfsf13), or prostaglandin synthesis (Ptgs1/2). In SARS-CoV-2 infections, interferon signaling (Ifitm1), proteolytic enzymes (CtsB), and also cell-surface proteins (Cd14, Cd151) were among the prominent alterations after tBHQ exposure. Of these genes, many had one or more binding sites for AHR and NRF2, two major xenosensors triggered by tBHQ. Conclusions. Our results strongly suggest that a common food additive, tBHQ, can modulate virus-dependent processes in both influenza and SARS-CoV-2 infections.

The Complicated Role of Nuclear Factor Erythroid-Derived 2-Like 2 in Allergy and Asthma

Nuclear factor erythroid-derived 2-like 2 (Nrf2) is a stress-activated transcription factor that is highly responsive to oxidative stress and electrophilic stimuli. Upon activation, Nrf2 upregulates a battery of cytoprotective genes meant to prevent cell death or damage. In many models of inflammation, Nrf2 protects against the immune response and decreases injury, including in the context of asthma and allergy. However, in some models of asthma and allergy, Nrf2 either does not play a role or can even exacerbate inflammation. In general, the reasons behind these discrepancies are not clear and the mechanisms by which Nrf2 modulates immune response are largely uncharacterized. The aim of this review is to highlight current literature assessing the role of Nrf2 in allergy and asthma to understand Nrf2 as a potential therapeutic target. SIGNIFICANCE STATEMENT: Nuclear factor erythroid-derived 2-like 2 (Nrf2) is an important immune mediator that modulates numerous immune cell types in various inflammatory diseases, including allergy and asthma. There is considerable interest in Nrf2 as a drug target in inflammation, which is complicated by the complex nature of Nrf2 in the immune system. This review focuses on the role of Nrf2 in asthma and allergy, including in regulating immune cell function and in detoxifying xenobiotics that exacerbate these diseases.

The Dangerous Liaisons in the Oxidative Stress Response to Leishmania Infection

Leishmania parasites preferentially invade macrophages, the professional phagocytic cells, at the site of infection. Macrophages play conflicting roles in Leishmania infection either by the destruction of internalized parasites or by providing a safe shelter for parasite replication. In response to invading pathogens, however, macrophages induce an oxidative burst as a mechanism of defense to promote pathogen removal and contribute to signaling pathways involving inflammation and the immune response. Thus, oxidative stress plays a dual role in infection whereby free radicals protect against invading pathogens but can also cause inflammation resulting in tissue damage. The induced oxidative stress in parasitic infections triggers the activation in the host of the antioxidant response to counteract the damaging oxidative burst. Consequently, macrophages are crucial for disease progression or control. The ultimate outcome depends on dangerous liaisons between the infecting Leishmania spp. and the type and strength of the host immune response.

Aberrant HO-1/NQO1-Reactive Oxygen Species-ERK Signaling Pathway Contributes to Aggravation of TPA-Induced Irritant Contact Dermatitis in Nrf2-Deficient Mice

NF-erythroid 2-related factor 2 (Nrf2) is a major transcription factor to protect cells against reactive oxygen species (ROS) and reactive toxicants. Meanwhile, Nrf2 can inhibit contact dermatitis through redox-dependent and -independent pathways. However, the underlying mechanisms of how Nrf2 mediates irritant contact dermatitis (ICD) are still unclear. In this article, we elucidated the role of Nrf2 in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced acute ICD. Our study demonstrated that the ear thickness, redness, swelling, and neutrophil infiltration were significantly increased, accompanied by increased expression of inflammatory cytokines (IL-1α, IL-1β, IL-6, etc.) and decreased expression of antioxidant genes (HO-1 and NQO1) in Nrf2 knockout mice. Moreover, ERK phosphorylation was elevated in mouse embryonic fibroblasts (MEFs) from Nrf2 knockout mouse. Inhibition of ERK significantly alleviated TPA-induced cutaneous inflammation and ROS accumulation in MEFs derived from mouse. Conversely, ROS scavenging inhibited the ERK activation and TPA-induced inflammation in MEFs. Taken together, the findings illustrate the key role of the Nrf2/ROS/ERK signaling pathway in TPA-induced acute ICD.

Recent Advances in Understanding Nrf2 Agonism and Its Potential Clinical Application to Metabolic and Inflammatory Diseases

Oxidative stress is a major component of cell damage and cell fat, and as such, it occupies a central position in the pathogenesis of metabolic disease. Nuclear factor-erythroid-derived 2-related factor 2 (Nrf2), a key transcription factor that coordinates expression of genes encoding antioxidant and detoxifying enzymes, is regulated primarily by Kelch-like ECH-associated protein 1 (Keap1). However, involvement of the Keap1–Nrf2 pathway in tissue and organism homeostasis goes far beyond protection from cellular stress. In this review, we focus on evidence for Nrf2 pathway dysfunction during development of several metabolic/inflammatory disorders, including diabetes and diabetic complications, obesity, inflammatory bowel disease, and autoimmune diseases. We also review the beneficial role of current molecular Nrf2 agonists and summarize their use in ongoing clinical trials. We conclude that Nrf2 is a promising target for regulation of numerous diseases associated with oxidative stress and inflammation. However, more studies are needed to explore the role of Nrf2 in the pathogenesis of metabolic/inflammatory diseases and to review safety implications before therapeutic use in clinical practice.

The Potential of Nrf2 Activation as a Therapeutic Target in Systemic Lupus Erythematosus

Inflammation and oxidative stress are well established in systemic lupus erythematosus (SLE) and are critical to the pathogenesis of autoimmune diseases. The transcription factor NF-E2 related factor 2 (Nrf2) is a central regulator of cellular anti-oxidative responses, inflammation, and restoration of redox balance. Accumulating reports support an emerging role for the regulation of Nrf2 in SLE. These include findings on the development of lupus-like autoimmune nephritis and altered immune cell populations in mice lacking Nrf2, as well as decreased Nrf2 abundance in the dendritic cells of patients with SLE. Nrf2-inducing agents have been shown to alleviate oxidative and inflammatory stress and reduce tissue injury in SLE mouse models. Since Nrf2 expression can be increased in activated T cells, the precise role of Nrf2 activation in different immune cell types and their function remains to be defined. However, targeting Nrf2 for the treatment of diseases associated with oxidative stress and inflammation, such as SLE, is promising. As investigation of Nrf2-inducing agents in clinical trials grows, defining the signaling and molecular mechanisms of action and downstream effects in response to different Nrf2-inducing agents in specific cells, tissues, and diseases, will be critical for effective clinical use.

IL-33-induced metabolic reprogramming controls the differentiation of alternatively activated macrophages and the resolution of inflammation

Alternatively activated macrophages (AAMs) contribute to the resolution of inflammation and tissue repair. However, molecular pathways that govern their differentiation have remained incompletely understood. Here, we show that uncoupling protein-2-mediated mitochondrial reprogramming and the transcription factor GATA3 specifically controlled the differentiation of pro-resolving AAMs in response to the alarmin IL-33. In macrophages, IL-33 sequentially triggered early expression of pro-inflammatory genes and subsequent differentiation into AAMs. Global analysis of underlying signaling events revealed that IL-33 induced a rapid metabolic rewiring of macrophages that involved uncoupling of the respiratory chain and increased production of the metabolite itaconate, which subsequently triggered a GATA3-mediated AAM polarization. Conditional deletion of GATA3 in mononuclear phagocytes accordingly abrogated IL-33-induced differentiation of AAMs and tissue repair upon muscle injury. Our data thus identify an IL-4-independent and GATA3-dependent pathway in mononuclear phagocytes that results from mitochondrial rewiring and controls macrophage plasticity and the resolution of inflammation.

Targeting Mitochondrial-Derived Reactive Oxygen Species in T Cell-Mediated Autoimmune Diseases

Mitochondrial dysfunction resulting in oxidative stress could be associated with tissue and cell damage common in many T cell-mediated autoimmune diseases. Autoreactive CD4 T cell effector subsets (Th1,Th17) driving these diseases require increased glycolytic metabolism to upregulate key transcription factors (TF) like T-bet and RORγt that drive differentiation and proinflammatory responses. However, research in immunometabolism has demonstrated that mitochondrial-derived reactive oxygen species (ROS) act as signaling molecules contributing to T cell fate and function. Eliminating autoreactive T cells by targeting glycolysis or ROS production is a potential strategy to inhibit autoreactive T cell activation without compromising systemic immune function. Additionally, increasing self-tolerance by promoting functional immunosuppressive CD4 T regulatory (Treg) cells is another alternative therapeutic for autoimmune disease. Tregs require increased ROS and oxidative phosphorylation (OxPhos) for Foxp3 TF expression, differentiation, and anti-inflammatory IL-10 cytokine synthesis. Decreasing glycolytic activity or increasing glutathione and superoxide dismutase antioxidant activity can also be beneficial in inhibiting cytotoxic CD8 T cell effector responses. Current treatment options for T cell-mediated autoimmune diseases such as Type 1 diabetes (T1D), multiple sclerosis (MS), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE) include global immunosuppression, antibodies to deplete immune cells, and anti-cytokine therapy. While effective in diminishing autoreactive T cells, they can also compromise other immune responses resulting in increased susceptibility to other diseases and complications. The impact of mitochondrial-derived ROS and immunometabolism reprogramming in autoreactive T cell differentiation could be a potential target for T cell-mediated autoimmune diseases. Exploiting these pathways may delay autoimmune responses in T1D.

hPMSCs inhibit the expression of PD-1 in CD4+IL-10+ T cells and mitigate liver damage in a GVHD mouse model by regulating the crosstalk between Nrf2 and NF-κB signaling pathway

Background

The activation of T cells and imbalanced redox metabolism enhances the development of graft-versus-host disease (GVHD). Human placenta-derived mesenchymal stromal cells (hPMSCs) can improve GVHD through regulating T cell responses. However, whether hPMSCs balance the redox metabolism of CD4⁺IL-10⁺ T cells and liver tissue and alleviate GVHD remains unclear. This study aimed to investigate the effect of hPMSC-mediated treatment of GVHD associated with CD4⁺IL-10⁺ T cell generation via control of redox metabolism and PD-1 expression and whether the Nrf2 and NF-κB signaling pathways were both involved in the process.

Methods

A GVHD mouse model was induced using 6–8-week-old C57BL/6 and Balb/c mice, which were treated with hPMSCs. In order to observe whether hPMSCs affect the generation of CD4⁺IL-10⁺ T cells via control of redox metabolism and PD-1 expression, a CD4⁺IL-10⁺ T cell culture system was induced using human naive CD4⁺ T cells. The percentage of CD4⁺IL-10⁺ T cells and their PD-1 expression levels were determined in vivo and in vitro using flow cytometry, and Nrf2, HO-1, NQO1, GCLC, GCLM, and NF-κB levels were determined by western blotting, qRT-PCR, and immunofluorescence, respectively. Hematoxylin-eosin, Masson’s trichrome, and periodic acid-Schiff staining methods were employed to analyze the changes in hepatic tissue.

Results

A decreased activity of superoxide dismutase (SOD) and a proportion of CD4⁺IL-10⁺ T cells with increased PD-1 expression were observed in GVHD patients and the mouse model. Treatment with hPMSCs increased SOD activity and GCL and GSH levels in the GVHD mouse model. The percentage of CD4⁺IL-10⁺ T cells with decreased PD-1 expression, as well as Nrf2, HO-1, NQO1, GCLC, and GCLM levels, both in the GVHD mouse model and in the process of CD4⁺IL-10⁺ T cell generation, were also increased, but NF-κB phosphorylation and nuclear translocation were inhibited after treatment with hPMSCs, which was accompanied by improvement of hepatic histopathological changes.

Conclusions

The findings suggested that hPMSC-mediated redox metabolism balance and decreased PD-1 expression in CD4⁺IL-10⁺ T cells were achieved by controlling the crosstalk between Nrf2 and NF-κB, which further provided evidence for the application of hPMSC-mediated treatment of GVHD.

The Redox-Metabolic Couple of T Lymphocytes: Potential Consequences for Hypertension

Significance: T lymphocytes, as part of the adaptive immune system, possess the ability to activate and function in extreme cellular microenvironments, which requires these cells to remain highly malleable. One mechanism in which T lymphocytes achieve this adaptability is by responding to cues from both reactive oxygen and nitrogen species, as well as metabolic flux, which together fine-tune the functional fate of these adaptive immune cells. Recent Advances: To date, examinations of the redox and metabolic effects on T lymphocytes have primarily investigated these biological processes as separate entities. Given that the redox and metabolic environments possess significant overlaps of pathways and molecular species, it is inevitable that perturbations in one environment affect the other. Recent consideration of this redox-metabolic couple has demonstrated the strong link and regulatory consequences of these two systems in T lymphocytes. Critical Issues: The redox and metabolic control of T lymphocytes is essential to prevent dysregulated inflammation, which has been observed in cardiovascular diseases such as hypertension. The role of the adaptive immune system in hypertension has been extensively investigated, but the understanding of how the redox and metabolic environments control T lymphocytes in this disease remains unclear. Future Directions: Herein, we provide a discussion of the redox and metabolic control of T lymphocytes as separate entities, as well as coupled to one another, to regulate adaptive immunity. While investigations examining this pair together in T lymphocytes are sparse, we speculate that T lymphocyte destiny is shaped by the redox-metabolic couple. In contrast, disrupting this duo may have inflammatory consequences such as hypertension.

Ursodeoxycholic acid impairs liver-infiltrating T-cell chemotaxis through IFN-γ and CX3CL1 production in primary biliary cholangitis

Ursodeoxycholic acid (UDCA) is the primary treatment for primary biliary cholangitis (PBC), but its mechanism of action remains unclear. Studies suggest that UDCA enhances NF erythroid 2-related factor 2 (NFE2L2) expression and that the interaction between IFN-γ and C-X3-C motif chemokine ligand 1 (CX3CL1) facilitates biliary inflammation in PBC. Therefore, we examined the effects of UDCA on the expression of IFN-γ and CX3CL1 in in vitro and in vivo PBC models such as human liver tissue, a murine model, cell lines, and isolated human intrahepatic biliary epithelial cells (IHBECs). We observed a significant decrease in IFN-γ mRNA levels and positive correlations between IFN-γ and CX3CL1 mRNA levels post-UDCA treatment in PBC livers. NFE2L2-mediated transcriptional activation was significantly enhanced in UDCA-treated Jurkat cells. In 2-octynoic acid-immunized mice, IFN-γ production by liver-infiltrating T cells was dependent on NFE2L2 activation. IFN-γ significantly and dose-dependentlyinduced CX3CL1 expression, which was significantly decreased in HuCC-T1 cells and IHBECs upon UDCA treatment. These results suggest that UDCA-induced suppression of IFN-γ and CX3CL1 production attenuates the chemotactic and adhesive abilities of liver-infiltrating T cells in PBC.

The role of Nrf2 in autoimmunity and infectious disease: Therapeutic possibilities

Nrf2 is a cytoprotective transcription factor which is involved in ameliorating oxidative stress and toxic insults. Recently, an immunomodulatory role for Nrf2 has gained appreciation as it has been shown to protect cells and hosts alike in a variety of immune and inflammatory disorders. However, Nrf2 utilizes numerous distinct pathways to elicit its immunomodulatory effects. In this review, we summarize the literature discussing the roles of Nrf2 in autoimmunity and infectious diseases with a goal of understanding the potential to therapeutically target Nrf2.

Nrf2 through Aryl Hydrocarbon Receptor Regulates IL-22 Response in CD4+ T Cells

IL-17A and IL-22 derived from Th17 cells play a significant role in mucosal immunity and inflammation. TGF-β and IL-6 promote Th17 differentiation; however, these cytokines have multiple targets. The identification and screening of additional molecules that regulate IL-17A and IL-22 responses in certain inflammatory conditions is of great clinical significance. In this study, we show that CDDO-Im, a specific Nrf2 activator, promotes IL-17A and IL-22 responses in murine Th17 cells. In contrast, CDDO-Im inhibits IL-17A response in multiple sclerosis patient-derived PBMCs. However, Nrf2 specifically regulates IL-22 response in vivo. Nrf2 acts through the regulation of antioxidant response element (ARE) binding motifs in target genes to induce or repress transcription. Promoter analysis revealed that Il17a, Rorc, and Ahr genes have several ARE motifs. We showed that Nrf2 bound to ARE repressor (ARE-R2) of Rorc and inhibited Rorc-dependent IL-17A transactivation. The luciferase reporter assay data showed that CDDO-Im regulated Ahr promoter activity. Chromatin immunoprecipitation quantitative PCR data showed that Nrf2 bound to ARE of AhR. Finally, we confirmed that the CDDO-Im-mediated induction of IL-22 production in CD4+ T cells was abrogated in CD4-specific Ahr knockout mice (AhrCD4 ). CH-223191, a specific AhR antagonist, inhibits CDDO-Im-induced IL-22 production in CD4+ T cells, which further confirmed the AhR-dependent regulation. Collectively, our data showed that Nrf2 via AhR pathways regulated IL-22 response in CD4+ T cells.

Investigating Molecular Mechanisms of Immunotoxicity and the Utility of ToxCast for Immunotoxicity Screening of Chemicals Added to Food

The development of high-throughput screening methodologies may decrease the need for laboratory animals for toxicity testing. Here, we investigate the potential of assessing immunotoxicity with high-throughput screening data from the U.S. Environmental Protection Agency ToxCast program. As case studies, we analyzed the most common chemicals added to food as well as per- and polyfluoroalkyl substances (PFAS) shown to migrate to food from packaging materials or processing equipment. The antioxidant preservative tert-butylhydroquinone (TBHQ) showed activity both in ToxCast assays and in classical immunological assays, suggesting that it may affect the immune response in people. From the PFAS group, we identified eight substances that can migrate from food contact materials and have ToxCast data. In epidemiological and toxicological studies, PFAS suppress the immune system and decrease the response to vaccination. However, most PFAS show weak or no activity in immune-related ToxCast assays. This lack of concordance between toxicological and high-throughput data for common PFAS indicates the current limitations of in vitro screening for analyzing immunotoxicity. High-throughput in vitro assays show promise for providing mechanistic data relevant for immune risk assessment. In contrast, the lack of immune-specific activity in the existing high-throughput assays cannot validate the safety of a chemical for the immune system.

Redox regulation of immunometabolism

Metabolic pathways and redox reactions are at the core of life. In the past decade(s), numerous discoveries have shed light on how metabolic pathways determine the cellular fate and function of lymphoid and myeloid cells, giving rise to an area of research referred to as immunometabolism. Upon activation, however, immune cells not only engage specific metabolic pathways but also rearrange their oxidation-reduction (redox) system, which in turn supports metabolic reprogramming. In fact, studies addressing the redox metabolism of immune cells are an emerging field in immunology. Here, we summarize recent insights revealing the role of reactive oxygen species (ROS) and the differential requirement of the main cellular antioxidant pathways, including the components of the thioredoxin (TRX) and glutathione (GSH) pathways, as well as their transcriptional regulator NF-E2-related factor 2 (NRF2), for proliferation, survival and function of T cells, B cells and macrophages.

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).

Protection against acute renal injury by naturally occurring medicines which act through Nrf2 signaling pathway

The cellular defense pathway plays a key role in maintaining the homeostasis, tissues and organisms. Nuclear factor E2-related factor 2 (Nrf2), as a key cell signaling pathway, plays an important role in encoding detoxification enzymes and other stress response mediators. Recent studies have shown that it is closely related to the prevention and treatment of acute kidney injury (AKI). Therefore, this article reviews the protective effects of Nrf2-related signaling pathways on acute kidney injury, and summarizes the strategies of natural pharmaceutical ingredients such as flavonoids, alkaloids, terpenes, phenylpropionic acid, polyphenols, and polysaccharides to prevent and treat acute kidney injury. It is of great significance to further study the relationship between Nrf2 regulated signal pathway and kidney disease and the development of new medicines for acute kidney injury treatment. It can also provide new ideas and treatment strategies for clinical treatment of acute kidney injury. PRACTICAL APPLICATIONS: This article reviewed the mechanisms by which the active ingredients of natural medicines slow down acute kidney injury through the Nrf2 pathway. It will help us to understand the regulatory role of the Nrf2 pathway in AKI more comprehensively, and provide a theoretical basis for further exploring the mechanism of more natural drugs to reduce acute kidney injury.

Environmental pollutants and the immune response

Environmental pollution is one of the most serious challenges to health in the modern world. Pollutants alter immune responses and can provoke immunotoxicity. In this Review, we summarize the major environmental pollutants that are attracting wide-ranging concern and the molecular basis underlying their effects on the immune system. Xenobiotic receptors, including the aryl hydrocarbon receptor (AHR), sense and respond to a subset of environmental pollutants by activating the expression of detoxification enzymes to protect the body. However, chronic activation of the AHR leads to immunotoxicity. KEAP1-NRF2 is another important system that protects the body against environmental pollutants. KEAP1 is a sensor protein that detects environmental pollutants, leading to activation of the transcription factor NRF2. NRF2 protects the body from immunotoxicity by inducing the expression of genes involved in detoxification, antioxidant and anti-inflammatory activities. Intervening in these sensor-response systems could protect the body from the devastating immunotoxicity that can be induced by environmental pollutants.

NRF-2 and nonalcoholic fatty liver disease

Currently, chronic liver diseases have conditioned morbidity and mortality, many of these with a metabolic, toxicologic, immunologic, viral, or other etiology. Thus, a transcription factor that has been of huge importance for biomedical research is NRF-2. The latter is considered a principal component of the antioxidant mechanism, and it has been acknowledged that it impairs the function of NRF-2 in many liver diseases and that it forms an essential part of the pathologic changes that occur in the liver to contain inflammation and damage. Within the investigations and experiments carried out, there are isolated drugs, many of them related to plants and natural extracts that possess antioxidant properties through the NRF-2 signaling pathway, or even involving the stimulation of the transcription target proteins of NRF-2. Notwithstanding all of these experimental findings, to date there is not sufficient clinical evidence to justify the use of NRF-2 in medical practice.

Nrf2-dependent and -independent effects of tBHQ in activated murine B cells

Nrf2 is a transcription factor that regulates cytoprotective cellular responses to oxidative and electrophilic stress. Nrf2 is potently activated by the synthetic food additive, tert-butylhydroquinone (tBHQ), which is widely used as a preservative in oils and processed foods. Previously published studies have established that tBHQ has numerous effects on T cell function. The purpose of this study was to determine the effect of tBHQ on B cell function and the role of Nrf2 in these effects. Specifically, we investigated T cell-independent B cell activation, differentiation, and IgM antibody production. Murine wild-type and Nrf2-null splenocytes were isolated, treated with tBHQ (0.25-2.5 μm), and activated by lipopolysaccharide (LPS), a T cell-independent B cell activator. Our findings indicate that tBHQ significantly enhanced IgM production in activated wild-type, but not Nrf2-null, B cells, suggesting this effect is Nrf2-dependent. In contrast, tBHQ significantly decreased the induction of CD69, CD25, CD22, and CD138 in both wild-type and Nrf2-null splenocytes. These findings indicate that the tBHQ-mediated increase in IgM is Nrf2-dependent, whereas the inhibition of CD69, CD25, CD22 and CD138 is Nrf2-independent. Overall, this study demonstrates that in addition to its effects on T cells, tBHQ also has potent effects on T cell-independent B cell function.

NRF2, a Transcription Factor for Stress Response and Beyond

Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that regulates the cellular defense against toxic and oxidative insults through the expression of genes involved in oxidative stress response and drug detoxification. NRF2 activation renders cells resistant to chemical carcinogens and inflammatory challenges. In addition to antioxidant responses, NRF2 is involved in many other cellular processes, including metabolism and inflammation, and its functions are beyond the originally envisioned. NRF2 activity is tightly regulated through a complex transcriptional and post-translational network that enables it to orchestrate the cell’s response and adaptation to various pathological stressors for the homeostasis maintenance. Elevated or decreased NRF2 activity by pharmacological and genetic manipulations of NRF2 activation is associated with many metabolism- or inflammation-related diseases. Emerging evidence shows that NRF2 lies at the center of a complex regulatory network and establishes NRF2 as a truly pleiotropic transcription factor. Here we summarize the complex regulatory network of NRF2 activity and its roles in metabolic reprogramming, unfolded protein response, proteostasis, autophagy, mitochondrial biogenesis, inflammation, and immunity.

The Influence of Reactive Oxygen Species in the Immune System and Pathogenesis of Multiple Sclerosis

Multiple roles have been indicated for reactive oxygen species (ROS) in the immune system in recent years. ROS have been extensively studied due to their ability to damage DNA and other subcellular structures. Noticeably, they have been identified as a pivotal second messenger for T-cell receptor signaling and T-cell activation and participate in antigen cross-presentation and chemotaxis. As an agent with direct toxic effects on cells, ROS lead to the initiation of the autoimmune response. Moreover, ROS levels are regulated by antioxidant systems, which include enzymatic and nonenzymatic antioxidants. Enzymatic antioxidants include superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase. Nonenzymatic antioxidants contain vitamins C, A, and E, glutathione, and thioredoxin. Particularly, cellular antioxidant systems have important functions in maintaining the redox system homeostasis. This review will discuss the significant roles of ROS generation and antioxidant systems under normal conditions, in the immune system, and pathogenesis of multiple sclerosis.

Nrf2 Activator RTA-408 Protects Against Ozone-Induced Acute Asthma Exacerbation by Suppressing ROS and γδT17 Cells

Ozone is a strong oxidant in air pollution that exacerbates respiratory disorders and is a major risk factor for acute asthma exacerbation. Ozone can induce reactive oxygen species (ROS) and airway neutrophilic inflammation. In addition, γδT17 cells contribute to IL-17A production upon ozone challenge, resulting in neutrophilic inflammation. It is known, however, that Nrf2 can ameliorate oxidative stress. We therefore investigated whether RTA-408, an Nrf2 activator, can attenuate airway inflammation and inhibit ROS production and whether this effect involves γδT17 cells. Balb/c mice were sensitized/challenged with ovalbumin (OVA) and followed by ozone exposure. We investigated the effect of Nrf2 activator RTA-408 on airway hyperresponsiveness, neutrophilic airway inflammation, cytokine/chemokine production, and OVA-specific IgE level in a mouse model of O3 induced asthma exacerbation. Furthermore, malondialdehyde (MDA) and glutathione (GSH) levels in lung and intracellular ROS were measured. IL-17⁺ γδT cell percentage by flow cytometer was determined. Nrf2 protein expression by western blot was also examined. We observed that RTA-408 attenuated ROS release during ozone-induced asthma exacerbation and suppressed neutrophil lung infiltration. RTA-408 decreased pro-inflammatory cytokine production and reduced the percentage of IL-17⁺ γδT cells. Thus, our results suggest that RTA-408 does attenuate airway inflammation in a murine model of ozone-induced asthma exacerbation.

CRISPR/Cas9-Induced Loss of Keap1 Enhances Anti-oxidation in Rat Adipose-Derived Mesenchymal Stem Cells

Stem cells have become a powerful tool in the treatment of many diseases owing to their regenerative ability and rapid promotion of development in regenerative medicine such as in traumatic brain injury. However, the high level of oxidant micro-environment in lesion region leads to more than 99% cells into death. In this study, we used genetic methods to edit Keap1 gene in mesenchymal stem cells, we and observed their antioxidative ability. First, we disturbed the start codon and the 376th amino acid codon of Keap1 in adipose-derived mesenchymal stem cells (Ad-MSCs) with CRISPR/Cas9, respectively, to release Nrf2 from the binding of Keap1. As a result, Nrf2 was activated and localized into nuclei and regulated cellular anti-oxidation. We observed that the cells lacking Keap1 ATG codon showed obvious nuclear localization of Nrf2. Besides lower expression of Bax-1 and lower content of malondialdehyde (MDA) were detected after H₂O₂ treatment, we also found higher expression of Bcl-2 in Keap1 ATG codon knock-out cells, whereas a higher expression of PCNA was observed only in the Keap1 376th codon-edited cells, whose Bax-1 expression was lower than that in the control cells. Our study revealed that loss of Keap1 resulted in anti-oxidative ability in Ad-MSCs, suggesting that our strategy can hopefully increase the viability of mesenchymal stem cells after grafting. This study is also a frontier exploration to the application of CRISPR/Cas9 in Ad-MSCs.

The Potential Role of Nrf2 Signaling in Leishmania Infection Outcomes

Nrf2 [nuclear factor erythroid 2-related factor 2 (Nrf2)] regulates the expression of a plethora of genes involved in the response to oxidative stress due to inflammation, aging, and tissue damage, among other pathological conditions. Deregulation of this cytoprotective system may also interfere with innate and adaptive immune responses. Oxidative burst, one of the main microbicidal mechanisms, could be impaired during initial phagocytosis of parasites, which could lead to the successful establishment of infection and promote susceptibility to diseases. A wide diversity of infections, mainly those caused by intracellular pathogens such as viruses, bacteria, and protozoan parasites, modulate the activation of Nrf2 by interfering with post-translational modifications, interactions between different protein complexes and the immune response. Nrf2 may be induced by pathogens via distinct pathways such as those involving the engagement of Toll-like receptors, the activation of PI3K/Akt, and endoplasmic reticulum stress. Recent studies have revealed the importance of Nrf2 on leishmaniasis. This mini-review discusses relevant findings that reveal the connection between Leishmania-induced modifications of the host pathways and their relevance to the modulation of the Nrf2-dependent antioxidative response to the infection.

Clonal copy-number mosaicism in autoreactive T lymphocytes in diabetic NOD mice

Concordance for type 1 diabetes (T1D) is far from 100% in monozygotic twins and in inbred nonobese diabetic (NOD) mice, despite genetic identity and shared environment during incidence peak years. This points to stochastic determinants, such as postzygotic mutations (PZMs) in the expanding antigen-specific autoreactive T cell lineages, by analogy to their role in the expanding tumor lineage in cancer. Using comparative genomic hybridization of DNA from pancreatic lymph-node memory CD4⁺ T cells of 25 diabetic NOD mice, we found lymphocyte-exclusive mosaic somatic copy-number aberrations (CNAs) with highly nonrandom independent involvement of the same gene(s) across different mice, some with an autoimmunity association (e.g., Ilf3 and Dgka). We confirmed genes of interest using the gold standard approach for CNA quantification, multiplex ligation-dependent probe amplification (MLPA), as an independent method. As controls, we examined lymphocytes expanded during normal host defense (17 NOD and BALB/c mice infected with Leishmania major parasite). Here, CNAs found were fewer and significantly smaller compared to those in autoreactive cells (P = 0.0019). We determined a low T cell clonality for our samples suggesting a prethymic formation of these CNAs. In this study, we describe a novel, unexplored phenomenon of a potential causal contribution of PZMs in autoreactive T cells in T1D pathogenesis. We expect that exploration of point mutations and studies in human T cells will enable the further delineation of driver genes to target for functional studies. Our findings challenge the classical notions of autoimmunity and open conceptual avenues toward individualized prevention and therapeutics.

The critical role of Bach2 in regulating type 2 chronic airway inflammation

Although Bach2 (broad complex-tramtrack-bric a brac and Cap'n'collar homology 2) plays an important role in regulating Th2 cell differentiation and type 2 immune responses, the underlying molecular mechanisms remain unclear. Our current studies demonstrate that Bach2 associates with Batf (basic leucine zipper transcription factor ATF-like) family transcription factors and binds to the regulatory regions of the Th2 cytokine gene loci. The Bach2-Batf complex antagonizes the recruitment of the interferon regulatory factor 4 (Irf4)-containing Batf complex to activator protein 1 (AP-1) motifs in the Th2 cytokine gene locus and suppresses Th2 cytokine production and/or Th2 cell differentiation. The deletion of Batf ameliorated the spontaneous development of type 2 airway inflammation that is found in mice with Bach2 deficiency specifically in T cells. Interestingly, Bach2 regulates Batf and Batf3 expression via two distinct pathways. First, the Bach2-Batf complex directly binds to the Batf and Batf3 gene loci and reduces transcription by interfering with the Batf-Irf4 complex. Second, Bach2 suppresses interleukin 4 (IL-4)-induced augmentation of Batf and Batf3 expression through the regulation of IL-4 production. These findings suggest that IL-4 and Batf family transcription factors form a positive feedback amplification loop to induce Th2 cell differentiation and that Bach2-Batf interactions block the formation of this amplification loop. Furthermore, we found that reductions in Bach2 confer an innate immunological function on CD4 T cells to induce antigen-independent cytokine production. Some Bach2-deficient lung CD4 T cells showed characteristic features similar to pathogenic Th2 cells, including IL-33 receptor expression and IL-33-dependent Th2 cytokine production. These results suggest a critical role for Bach2 in regulating Th2 cell differentiation and the subsequent onset of chronic type 2 inflammation.

A Protective Role of the NRF2-Keap1 Pathway in Maintaining Intestinal Barrier Function

Nrf2 (NF-E2-related factor 2) is a master regulator of cellular oxidative levels against environmental stresses. Nrf2 induces the expression of metabolic detoxification and antioxidant enzymes to eliminate reactive oxygen species (ROS). The gastrointestinal tract is a key source of ROS. Intestinal barrier is critical to maintain the healthy steady state of the human gastrointestinal tract. Nrf2 has been shown to play important roles in maintaining the integrity of intestinal mucosal barrier. Here, we made a systematic review on the roles of Nrf2 in maintaining intestinal barrier, including the following: (1) NRF2 reduced intestinal mucosal injury by suppressing oxidative stress; (2) NRF2 decreased intestinal inflammation by inhibiting the inflammatory pathway; (3) NRF2 affected intestinal tight junction proteins and apoptosis of cells to regulate intestinal permeability; (4) NRF2 affected T cell differentiation and functions; (5) the crossregulation between the KEAP1-NRF2 pathway and autophagy controlled intestinal oxidative stress.

Effects of Absence of Constitutive Androstane Receptor (CAR) on Bile Acid Homeostasis in Male and Female Mice

Accumulation of BAs in hepatocytes has a role in liver disease and also in drug-induced liver injury. The Constitutive Androstane Receptor (CAR) has been shown to protect against BA-induced liver injury. The polymorphism of CAR has recently been shown to modify the pharmacokinetics and pharmacodynamics of various drugs. Thus it was hypothesized that polymorphism of CAR may also influence BA homeostasis. Using CAR-null and WT mice, this study modeled the potential consequences of CAR polymorphism on BA homeostasis. Our previous study showed that chemical activation of CAR decreases the total BA concentrations in livers of mice. Surprisingly the absence of CAR also decreased the BA concentrations in livers of mice, but to a lesser extent than in CAR-activated mice. Neither CAR activation nor elimination of CAR altered the biliary excretion of total BAs, but CAR activation increased the proportion of 6-OH BAs (TMCA), whereas the lack of CAR increased the excretion of TCA, TCDCA and TDCA. Serum BA concentrations did not parallel the decrease in BA concentrations in the liver in either the mice after CAR activation or mice lacking CAR. Gene expression of BA synthesis, transporter and regulator genes were mainly similar in livers of CAR-null and WT mice. In summary, CAR activation decreases primarily the 12-OH BA concentrations in liver, whereas lack of CAR decreases the concentrations of 6-OH BAs in liver. In bile, CAR activation increases the biliary excretion of 6-OH BAs, whereas absence of CAR increases the biliary excretion of 12-OH BAs and TCDCA.

Oxidative stress pathways in pancreatic β-cells and insulin-sensitive cells and tissues: importance to cell metabolism, function, and dysfunction

It is now accepted that nutrient abundance in the blood, especially glucose, leads to the generation of reactive oxygen species (ROS), ultimately leading to increased oxidative stress in a variety of tissues. In the absence of an appropriate compensatory response from antioxidant mechanisms, the cell, or indeed the tissue, becomes overwhelmed by oxidative stress, leading to the activation of intracellular stress-associated pathways. Activation of the same or similar pathways also appears to play a role in mediating insulin resistance, impaired insulin secretion, and late diabetic complications. The ability of antioxidants to protect against the oxidative stress induced by hyperglycemia and elevated free fatty acid (FFA) levels in vitro suggests a causative role of oxidative stress in mediating the latter clinical conditions. In this review, we describe common biochemical processes associated with oxidative stress driven by hyperglycemia and/or elevated FFA and the resulting clinical outcomes: β-cell dysfunction and peripheral tissue insulin resistance.

Advances in Molecular Mechanisms of Wheat Allergenicity in Animal Models: A Comprehensive Review

The prevalence of wheat allergy has reached significant levels in many countries. Therefore, wheat is a major global food safety and public health issue. Animal models serve as critical tools to advance the understanding of the mechanisms of wheat allergenicity to develop preventive and control methods. A comprehensive review on the molecular mechanisms of wheat allergenicity using animal models is unavailable at present. There were two major objectives of this study: To identify the lessons that animal models have taught us regarding the molecular mechanisms of wheat allergenicity and to identify the strengths, challenges, and future prospects of animal models in basic and applied wheat allergy research. Using the PubMed and Google Scholar databases, we retrieved and critically analyzed the relevant articles and excluded celiac disease and non-celiac gluten sensitivity. Our analysis shows that animal models can provide insight into the IgE epitope structure of wheat allergens, effects of detergents and other chemicals on wheat allergenicity, and the role of genetics, microbiome, and food processing in wheat allergy. Although animal models have inherent limitations, they are critical to advance knowledge on the molecular mechanisms of wheat allergenicity. They can also serve as highly useful pre-clinical testing tools to develop safer genetically modified wheat, hypoallergenic wheat products, novel pharmaceuticals, and vaccines.

Nrf2 regulates CD4+ T cell-induced acute graft-versus-host disease in mice

Nuclear factor erythroid-derived 2-like 2 (Nrf2) is a ubiquitously expressed transcription factor that is well known for its role in regulating the cellular redox pathway. Although there is mounting evidence suggesting a critical role for Nrf2 in hematopoietic stem cells and innate leukocytes, little is known about its involvement in T-cell biology. In this study, we identified a novel role for Nrf2 in regulating alloreactive T-cell function during allogeneic hematopoietic cell transplantation (allo-HCT). We observed increased expression and nuclear translocation of Nrf2 upon T-cell activation in vitro, especially in CD4+ donor T cells after allo-HCT. Allo-HCT recipients of Nrf2 -/- donor T cells had significantly less acute graft-versus-host disease (GVHD)-induced mortality, morbidity, and pathology. This reduction in GVHD was associated with the persistence of Helios+ donor regulatory T cells in the allograft, as well as defective upregulation of the gut-homing receptor LPAM-1 on alloreactive CD8+ T cells. Additionally, Nrf2 -/- donor CD8+ T cells demonstrated intact cytotoxicity against allogeneic target cells. Tumor-bearing allo-HCT recipients of Nrf2 -/- donor T cells had overall improved survival as a result of preserved graft-versus-tumor activity and reduced GVHD activity. Our findings characterized a previously unrecognized role for Nrf2 in T-cell function, as well as revealed a novel therapeutic target to improve the outcomes of allo-HCT.