Nitric oxide modulates TGF-beta-directive signals to suppress Foxp3+ regulatory T cell differentiation and potentiate Th1 development

Enhanced eNOS/nitric oxide production by nebivolol interferes with TGF-β1/Smad3 signaling and collagen I deposition in the kidney after prolonged tacrolimus administration

AIMS

Tacrolimus is an effective immunosuppressant commonly used post-transplantation and in certain autoimmune diseases. However, its long-term administration is associated with renal fibrosis through transforming growth factor-beta/suppressor of mother against decapentaplegic (TGF-β/Smad) signaling that could be partly attributed to endothelial dysfunction alongside decreased nitric oxide (NO) release. Our study aimed to investigate the prospective renal anti-fibrotic effect of enhanced NO production by nebivolol against tacrolimus-stimulated TGF-β1/Smad3 signaling.

MATERIALS AND METHODS

To illustrate the proposed mechanism of nebivolol, Nω-nitro-L-arginine methyl ester (L-NAME); nitric oxide synthase inhibitor; was co-administered with nebivolol. Rats were treated for 30 days as control, tacrolimus, tacrolimus/nebivolol, tacrolimus/L-NAME, and tacrolimus/nebivolol/L-NAME groups.

KEY FINDINGS

Our results revealed that renal NO content was reduced in tacrolimus-treated rats, while treatment with tacrolimus/nebivolol enhanced NO content via up-regulated endothelial nitric oxide synthase (eNOS), but down-regulated inducible nitric oxide synthase (iNOS) expression. That participated in the inhibition of TGF-β1/Smad3 signaling induced by tacrolimus, where the addition of L-NAME abolished the defensive effects of nebivolol. Subsequently, the deposition of collagen I and alpha-smooth muscle actin (α-SMA) was retarded by nebivolol, emphasized by reduced Masson's trichrome staining. In accordance, there was a strong negative correlation between eNOS and both TGF-β1 and collagen I protein expression. The protective effects of nebivolol were further confirmed by the improvement in kidney function biomarkers and histological features.

SIGNIFICANCE

It can be suggested that treatment with nebivolol along with tacrolimus could effectively suppress renal TGF-β1/Smad3 fibrotic signaling via the enhancement of endothelial NO production, thus curbing renal fibrosis development.

Gut redox and microbiome: charting the roadmap to T-cell regulation

The gastrointestinal (GI) tract redox environment, influenced by commensal microbiota and bacterial-derived metabolites, is crucial in shaping T-cell responses. Specifically, metabolites from gut microbiota (GM) exhibit robust anti-inflammatory effects, fostering the differentiation and regulation of CD8+ tissue-resident memory (TRM) cells, mucosal-associated invariant T (MAIT) cells, and stabilizing gut-resident Treg cells. Nitric oxide (NO), a pivotal redox mediator, emerges as a central regulator of T-cell functions and gut inflammation. NO impacts the composition of the gut microbiome, driving the differentiation of pro-inflammatory Th17 cells and exacerbating intestinal inflammation, and supports Treg expansion, showcasing its dual role in immune homeostasis. This review delves into the complex interplay between GI redox balance and GM metabolites, elucidating their profound impact on T-cell regulation. Additionally, it comprehensively emphasizes the critical role of GI redox, particularly reactive oxygen species (ROS) and NO, in shaping T-cell phenotype and functions. These insights offer valuable perspectives on disease mechanisms and potential therapeutic strategies for conditions associated with oxidative stress. Understanding the complex cross-talk between GI redox, GM metabolites, and T-cell responses provides valuable insights into potential therapeutic avenues for immune-mediated diseases, underscoring the significance of maintaining GI redox balance for optimal immune health.

Targeting amino acid-metabolizing enzymes for cancer immunotherapy

Despite the immune system's role in the detection and eradication of abnormal cells, cancer cells often evade elimination by exploitation of various immune escape mechanisms. Among these mechanisms is the ability of cancer cells to upregulate amino acid-metabolizing enzymes, or to induce these enzymes in tumor-infiltrating immunosuppressive cells. Amino acids are fundamental cellular nutrients required for a variety of physiological processes, and their inadequacy can severely impact immune cell function. Amino acid-derived metabolites can additionally dampen the anti-tumor immune response by means of their immunosuppressive activities, whilst some can also promote tumor growth directly. Based on their evident role in tumor immune escape, the amino acid-metabolizing enzymes glutaminase 1 (GLS1), arginase 1 (ARG1), inducible nitric oxide synthase (iNOS), indoleamine 2,3-dioxygenase 1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and interleukin 4 induced 1 (IL4I1) each serve as a promising target for immunotherapeutic intervention. This review summarizes and discusses the involvement of these enzymes in cancer, their effect on the anti-tumor immune response and the recent progress made in the preclinical and clinical evaluation of inhibitors targeting these enzymes.

Biopterin metabolism and nitric oxide recoupling in cancer

Tetrahydrobiopterin is a cofactor necessary for the activity of several enzymes, the most studied of which is nitric oxide synthase. The role of this cofactor-enzyme relationship in vascular biology is well established. Recently, tetrahydrobiopterin metabolism has received increasing attention in the field of cancer immunology and immunotherapy due to its involvement in the cytotoxic T cell response. Past research has demonstrated that when the availability of BH4 is low, as it is in chronic inflammatory conditions and tumors, electron transfer in the active site of nitric oxide synthase becomes uncoupled from the oxidation of arginine. This results in the production of radical species that are capable of a direct attack on tetrahydrobiopterin, further depleting its local availability. This feedforward loop may act like a molecular switch, reinforcing low tetrahydrobiopterin levels leading to altered NO signaling, restrained immune effector activity, and perpetual vascular inflammation within the tumor microenvironment. In this review, we discuss the evidence for this underappreciated mechanism in different aspects of tumor progression and therapeutic responses. Furthermore, we discuss the preclinical evidence supporting a clinical role for tetrahydrobiopterin supplementation to enhance immunotherapy and radiotherapy for solid tumors and the potential safety concerns.

Opportunities for Nitric Oxide in Potentiating Cancer Immunotherapy

Despite nearly 30 years of development and recent highlights of nitric oxide (NO) donors and NO delivery systems in anticancer therapy, the limited understanding of exogenous NO's effects on the immune system has prevented their advancement into clinical use. In particular, the effects of exogenously delivered NO differing from that of endogenous NO has obscured how the potential and functions of NO in anticancer therapy may be estimated and exploited despite the accumulating evidence of NO's cancer therapy-potentiating effects on the immune system. After introducing their fundamentals and characteristics, this review discusses the current mechanistic understanding of NO donors and delivery systems in modulating the immunogenicity of cancer cells as well as the differentiation and functions of innate and adaptive immune cells. Lastly, the potential for the complex modulatory effects of NO with the immune system to be leveraged for therapeutic applications is discussed in the context of recent advancements in the implementation of NO delivery systems for anticancer immunotherapy applications. SIGNIFICANCE STATEMENT: Despite a 30-year history and recent highlights of nitric oxide (NO) donors and delivery systems as anticancer therapeutics, their clinical translation has been limited. Increasing evidence of the complex interactions between NO and the immune system has revealed both the potential and hurdles in their clinical translation. This review summarizes the effects of exogenous NO on cancer and immune cells in vitro and elaborates these effects in the context of recent reports exploiting NO delivery systems in vivo in cancer therapy applications.

Leishmania guyanensis suppressed inducible nitric oxide synthase provoked by its viral endosymbiont

Inducible nitric oxide synthase (iNOS) is essential to the production of nitric oxide (NO), an efficient effector molecule against intracellular human pathogens such as Leishmania protozoan parasites. Some strains of Leishmania are known to bear a viral endosymbiont termed Leishmania RNA virus 1 (LRV1). Recognition of LRV1 by the innate immune sensor Toll-like receptor-3 (TLR3) leads to conditions worsening the disease severity in mice. This process is governed by type I interferon (type I IFNs) arising downstream of TLR3 stimulation and favoring the formation of secondary metastatic lesions. The formation of these lesions is mediated by the inflammatory cytokine IL-17A and occurs in the absence, or low level of, protective cytokine IFN-γ. Here, we described that the presence of LRV1 led to the initial expression of iNOS and low production of NO that failed to control infection. We subsequently showed that LRV1-triggered type I IFN was essential but insufficient to induce robust iNOS induction, which requires strong activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Leishmania guyanensis carrying LRV1 (LgyLRV1+) parasites mitigated strong iNOS production by limiting NF-kB activation via the induction of tumor necrosis factor-alpha-induced protein 3 (TNFAIP3), also known as A20. Moreover, our data suggested that production of LRV1-induced iNOS could be correlated with parasite dissemination and metastasis via elevated secretion of IL-17A in the draining lymph nodes. Our findings support an additional strategy by which LRV1-bearing Leishmania guyanensis evaded killing by nitric oxide and suggest that low levels of LRV1-induced NO might contribute to parasite metastasis.

The effects of post-translational modifications on Th17/Treg cell differentiation

Regulatory T (Treg) cells and Th17 cells are subsets of CD4⁺ T cells which play an essential role in immune homeostasis and infection. Dysregulation of the Th17/Treg cell balance was shown to be implicated in the development and progression of several disorders such as autoimmune disease, inflammatory disease, and cancer. Multiple factors, including T cell receptor (TCR) signals, cytokines, metabolic and epigenetic regulators can influence the differentiation of Th17 and Treg cells and affect their balance. Accumulating evidence indicates that the activity of key molecules such as forkhead box P3 (Foxp3), the retinoic acid-related orphan receptor gamma t (RORγt), and signal transducer and activator of transcription (STAT)s are modulated by the number of post-translational modifications (PTMs) such as phosphorylation, methylation, nitrosylation, acetylation, glycosylation, lipidation, ubiquitination, and SUMOylation. PTMs might affect the protein folding efficiency and protein conformational stability, and consequently determine protein structure, localization, and function. Here, we review the recent progress in our understanding of how PTMs modify the key molecules involved in the Th17/Treg cell differentiation, regulate the Th17/Treg balance, and initiate autoimmune diseases caused by dysregulation of the Th17/Treg balance. A better understanding of Th17/Treg regulation may help to develop novel potential therapeutics to treat immune-related diseases.

Tumor-Acidity and Bioorthogonal Chemistry-Mediated On-Site Size Transformation Clustered Nanosystem to Overcome Hypoxic Resistance and Enhance Chemoimmunotherapy

Hypoxia, a common feature of most solid tumors, causes severe tumor resistance to chemotherapy and immunotherapy. Herein, a tumor-acidity and bioorthogonal chemistry-mediated on-site size transformation clustered nanosystem is designed to overcome hypoxic resistance and enhance chemoimmunotherapy. The nanosystem utilized the tumor-acidity responsive group poly(2-azepane ethyl methacrylate) with a rapid response rate and highly efficient bioorthogonal click chemistry to form large-sized aggregates in tumor tissue to enhance accumulation and retention. Subsequently, another tumor-acidity responsive group of the maleic acid amide with a slow response rate was cleaved allowing the aggregates to slowly dissociate into ultrasmall nanoparticles with better tumor penetration ability for the delivery of doxorubicin (DOX) and nitric oxide (NO) to a hypoxic tumor tissue. NO can reverse a hypoxia-induced DOX resistance and boost the antitumor immune response through a reprogrammed tumor immune microenvironment. This tumor-acidity and bioorthogonal chemistry-mediated on-site size transformation clustered nanosystem not only helps to counteract a hypoxia-induced chemoresistance and enhance antitumor immune responses but also provides a general drug delivery strategy for enhanced tumor accumulation and penetration.

Regulation of T Cells in Cancer by Nitric Oxide

The T cell-mediated immune response is primarily involved in the fight against infectious diseases and cancer and its underlying mechanisms are complex. The anti-tumor T cell response is regulated by various T cell subsets and other cells and tissues in the tumor microenvironment (TME). Various mechanisms are involved in the regulation of these various effector cells. One mechanism is the iNOS/.NO that has been reported to be intimately involved in the regulation and differentiation of the various cells that regulate the anti-tumor CD8 T cells. Both endogenous and exogenous .NO are implicated in this regulation. Importantly, the exposure of T cells to .NO had different effects on the immune response, depending on the .NO concentration and time of exposure. For instance, iNOS in T cells regulates activation-induced cell death and inhibits Treg induction. Effector CD8 T cells exposed to .NO result in the upregulation of death receptors and enhance their anti-tumor cytotoxic activity. .NO-Tregs suppress CD4 Th17 cells and their differentiation. Myeloid-derived suppressor cells (MDSCs) expressing iNOS inhibit T cell functions via .NO and inhibit anti-tumor CD8 T cells. Therefore, both .NO donors and .NO inhibitors are potential therapeutics tailored to specific target cells that regulate the T cell effector anti-tumor response.

Knockout of NOS2 Promotes Adipogenic Differentiation of Rat MSCs by Enhancing Activation of JAK/STAT3 Signaling

Mesenchymal stromal cells (MSCs) are a heterogeneous population of cells that possess multilineage differentiation potential and extensive immunomodulatory properties. In mice and rats, MSCs produce nitric oxide (NO), as immunomodulatory effector molecule that exerts an antiproliferative effect on T cells, while the role of NO in differentiation was less clear. Here, we investigated the role of NO synthase 2 (NOS2) on adipogenic and osteogenic differentiation of rat MSCs. MSCs isolated from NOS2-null (NOS2^–/–) and wild type (WT) Sprague–Dawley (SD) rats exhibited homogenous fibroblast-like morphology and characteristic phenotypes. However, after induction, adipogenic differentiation was found significantly promoted in NOS2^–/– MSCs compared to WT MSCs, but not in osteogenic differentiation. Accordingly, qRT-PCR revealed that the adipogenesis-related genes PPAR-γ, C/EBP-α, LPL and FABP4 were markedly upregulated in NOS2^–/– MSCs, but not for osteogenic transcription factors or marker genes. Further investigations revealed that the significant enhancement of adipogenic differentiation in NOS2^–/– MSCs was due to overactivation of the STAT3 signaling pathway. Both AG490 and S3I-201, small molecule inhibitors that selectively inhibit STAT3 activation, reversed this adipogenic effect. Furthermore, after high-fat diet (HFD) feeding, knockout of NOS2 in rat MSCs resulted in significant obesity. In summary, NOS2 is involved in the regulation of rat MSC adipogenic differentiation via the STAT3 signaling pathway.

Hypertensive female Sprague-Dawley rats require an intact nitric oxide synthase system for compensatory increases in renal regulatory T cells

We have previously shown that hypertensive female rats have more regulatory T cells (Tregs), which contribute more to blood pressure (BP) control in female versus male rats. Based on known protective properties of Tregs, the goal of the present study was to investigate the mechanisms by which female rats maintain Tregs. The present study was designed to 1) compare the impact of three hypertension models on the percentage of renal Tregs and 2) test the hypothesis that nitric oxide synthase (NOS) inhibition prevents increases in renal Tregs and exacerbates renal damage in female Sprague-Dawley rats. Rats (11-14 wk old) were randomized to one of the following four groups: control, norepinephrine (NE) infusion, angiotensin II infusion, or the NOS inhibitor N^ω-nitro-l-arginine methyl ester (l-NAME) in drinking water. BP was measured via tail cuff. After 2 wk of treatment, kidneys were isolated and processed to measure Tregs via flow cytometric analysis and renal injury via urinary albumin excretion, plasma creatinine, and histological analyses. Hypertensive treatments increased BP in all experimental animals. Increases in BP in norepinephrine-and angiotensin II-treated rats were associated with increases in renal Tregs versus control. In contrast, l-NAME treatment decreased Tregs compared with all groups. l-NAME treatment modestly increased albumin excretion. However, plasma creatinine was comparable among the groups, and there was no histological evidence of glomerular or tubular injury. This study provides insights into the mechanisms regulating renal Tregs and supports that an intact NOS system is crucial for female rats to have BP-related increases in renal Tregs.

Poly(cyclodextrin)-Polydrug Nanocomplexes as Synthetic Oncolytic Virus for Locoregional Melanoma Chemoimmunotherapy

Despite the approval of oncolytic virus therapy for advanced melanoma, its intrinsic limitations that include the risk of persistent viral infection and cost-intensive manufacturing motivate the development of analogous approaches that are free from the disadvantages of virus-based therapies. Herein, we report a nanoassembly comprised of multivalent host-guest interactions between polymerized paclitaxel (pPTX) and nitric oxide incorporated polymerized β-cyclodextrin (pCD-pSNO) that through its bioactive components and when used locoregionally recapitulates the therapeutic effects of oncolytic virus. The resultant pPTX/pCD-pSNO exhibits significantly enhanced cytotoxicity, immunogenic cell death, dendritic cell activation and T cell expansion in vitro compared to free agents alone or in combination. In vivo, intratumoral administration of pPTX/pCD-pSNO results in activation and expansion of dendritic cells systemically, but with a corresponding expansion of myeloid-derived suppressor cells and suppression of CD8+ T cell expansion. When combined with antibody targeting cytotoxic T lymphocyte antigen-4 that blunts this molecule's signaling effects on T cells, intratumoral pPTX/pCD-pSNO treatment elicits potent anticancer effects that significantly prolong animal survival. This formulation thus leverages the chemo- and immunotherapeutic synergies of paclitaxel and nitric oxide and suggests the potential for virus-free nanoformulations to mimic the therapeutic action and benefits of oncolytic viruses.

Metabolic Checkpoints in Differentiation of Helper T Cells in Tissue Inflammation

Naïve CD4⁺ T cell differentiate into effector and regulatory subsets of helper T (Th) cells in various pathophysiological conditions and modulate tissue inflammation in autoimmune diseases. While cytokines play a key role in determining the fate of Th cells differentiation, metabolites, and metabolic pathways profoundly influence Th cells fate and their functions. Emerging literature suggests that interplay between metabolic pathways and cytokines potentiates T cell differentiation and functions in tissue inflammation in autoimmune diseases. Metabolic pathways, which are essential for the differentiation and functions of Th cell subsets, are regulated by cytokines, nutrients, growth factors, local oxygen levels, co-activation receptors, and metabolites. Dysregulation of metabolic pathways not only alters metabolic regulators in Th cells but also affect the outcome of tissue inflammation in autoimmune and allergic diseases. Understanding the modulation of metabolic pathways during T cells differentiation may potentially lead to a therapeutic strategy for immune-modulation of autoimmune and allergic diseases. In this review, we summarize the role of metabolic checkpoints and their crosstalk with different master transcription factors and signaling molecules in differentiation and function of Th subsets, which may potentially unravel novel therapeutic interventions for tissue inflammation and autoimmune disorders.

Effect of recombinant human thrombopoietin on immune thrombocytopenia in pregnancy in a murine model

Primary immune thrombocytopenia (ITP) is a serious medical disorder that has the potential for maternal and fetal mortality. Corticosteroids, intravenous immunoglobulin, or both are the first-line treatments for ITP in pregnancy, but choices are limited if patients fail to respond. Recombinant human thrombopoietin (rhTPO) has been proved effective and safe in management of chronic ITP. However, the efficacy and safety of rhTPO for pregnant ITP patients still need to be explored. Here we developed an ideal murine model that simulated human ITP in pregnancy and evaluated the efficacy and safety of rhTPO in management of ITP in pregnancy. Model mice were subcutaneously administered with 0, 150, 1,500 and 15,000 U/kg rhTPO for 14 days. Significant higher platelet counts were noted in rhTPO-treated groups on Day 7, 10 and 14. On Day 20, half the maternal mice were sacrificed. Frequencies of Tregs in CD4⁺ T cells in rhTPO-treated groups were statistically higher than control. Significant higher plasma levels of TGF-β1 were observed in rhTPO-treated groups than control. There was no significant abnormality in gross or visceral examination of fetuses. The remaining half maternal mice and their pups were observed for at least three weeks to assess vital signs. No abnormal signs were noted. Furthermore, we investigated the underlying mechanisms. Results showed that Tregs were negative for c-Mpl and rhTPO had no direct effect on Tregs. Additionally, the Treg frequency in splenic CD4⁺ T cells in LY2109761-treated model mice was statistically lower than control. Thus, rhTPO may be a safe and effective option for treatment of pregnant ITP patients.

Regulation of iNOS on Immune Cells and Its Role in Diseases

In recent years, there have been many studies on the function of nitric oxide synthase (NOS) in experimental animals and humans. This review analyzes and explores the relationship between inducible nitric oxide synthase (iNOS) and T cells, macrophages, and dendritic cell et al. differentiation using data based on laboratory research, highlighting recent NOS laboratory research. Our insights into research prospects and directions are also presented.

Nitric Oxide Signaling in T Cell-Mediated Immunity

Nitric oxide (NO) is a key messenger in the pathogenesis of inflammation, linking innate and adaptive immunity. By targeting signaling molecules, NO from inducible NO synthase (iNOS) and endothelial (e)NOS affects T helper cell differentiation and the effector functions of T lymphocytes, and is a potential target for therapeutic manipulation. In this review we discuss the regulatory actions exerted by NO on T cell functions, focusing on S-nitrosylation as an important post-translational modification by which NO acts as a signaling molecule during T cell-mediated immunity. We also present recent findings showing novel mechanisms through which NO regulates the activation of human T cells, and consider their potential in strategies to treat tumoral, allergic, and autoimmune diseases.

Effects of ginsenosides on regulatory T cell differentiation

Regulatory T cells (Treg cells) are a subpopulation of T cells defined as CD4+Foxp3+CD25+. They mainly function as immunosuppressive T cells by downregulating the induction and proliferation of effector T cells, but also modulate the immune system by maintaining self-tolerance and preventing autoimmune disease. In this study, the regulatory roles of ginsenosides, one of the active components in ginseng, Panax ginseng C. A. Meyer, in Treg cell differentiation were examined. The results demonstrated that ginsenoside Rd induced Treg differentiation by upregulating Foxp3 expression and increased the generation of TGF-β1, IL-10 and IL-35. The data suggest that ginsenoside Rd may be a potential immunomodulating agent or supplement that can be applied for transplantation and autoimmune disorders.

LPS priming in early life decreases antigen uptake of dendritic cells via NO production

Immunological mechanisms of hygiene hypothesis are expected to develop a novel strategy for allergy prevention. Although a large number of studies has investigated the relation between allergies and infection, little is known about the influence of the exposure to infections on antigen uptake by dendritic cells (DCs). In this study, we examined the effect of lipopolysaccharide (LPS) priming in early life on the antigen uptake ability of DCs by using an original mouse model. LPS priming in juvenile mice decreased the migration of antigen-capturing CD11c⁺ cells in the lymph nodes, but not in aged mice. Besides, the bone marrow-derived DCs (BMDCs) from juvenile LPS-primed mice had the poor antigen uptake ability, and constitutively produced NO through the inducible nitric oxide synthase (iNOS). Interestingly, the LPS priming-induced poor antigen uptake of BMDCs was mimicked by the NO donor, and recovered by the iNOS inhibitor. Additionally, LPS priming in juvenile mice prevented the allergic reactions, but not in aged mice. Our results suggested that an exposure to infections in early life prevents allergy through the alteration of the BM cells fate that is to induce the differentiation of BM cells into inhibitory DCs such as NO-producing DCs.

Interaction of Cholera Toxin B-subunit with Human T-lymphocytes

In this work, ¹²⁵I-labeled cholera toxin B-subunit (CT-B) (specific activity 98 Ci/mmol) was prepared, and its high-affinity binding to human blood T-lymphocytes (K_d = 3.3 nM) was determined. The binding of the ¹²⁵I-labeled CT-B was inhibited by unlabeled interferon-α₂ (IFN-α₂), thymosin-α₁ (TM-α₁), and by the synthetic peptide LKEKK, which corresponds to sequences 16-20 of human TM-α₁ and 131-135 of IFN-α₂ (K_i 0.8, 1.2, and 1.6 nM, respectively), but was not inhibited by the unlabeled synthetic peptide KKEKL with inverted sequence (K_i > 1 µM). In the concentration range of 10-1000 nM, both CT-B and peptide LKEKK dose-dependently increased the activity of soluble guanylate cyclase (sGC) but did not affect the activity of membrane-bound guanylate cyclase. The KKEKL peptide tested in parallel did not affect sGC activity. Thus, the CT-B and peptide LKEKK binding to a common receptor on the surface of T-lymphocytes leads to an increase in sGC activity.

Immunobiology of Nitric Oxide and Regulation of Inducible Nitric Oxide Synthase

Nitric oxide (NO) is a bioactive gas that has multiple roles in innate and adaptive immune responses. In macrophages, nitric oxide is produced by inducible nitric oxide synthase upon microbial and cytokine stimulation. It is needed for host defense against pathogens and for immune regulation. This review will summarize the role of NO and iNOS in inflammatory and immune responses and will discuss the regulatory mechanisms that control inducible nitric oxide synthase expression and activity.

Lack of Association between Genetic Polymorphisms of JAK-STAT Signaling Pathway Genes and Acute Anterior Uveitis in Han Chinese

Purpose. This study aimed to investigate the association between single nucleotide polymorphisms (SNPs) of JAK-STAT signaling pathway genes and acute anterior uveitis (AAU) with or without ankylosing spondylitis (AS) in the Han Chinese population. Methods. Eleven SNPs of the JAK1, JAK2, STAT1, IRF1, and NOS2 genes were analyzed in 443 AAU patients with AS, 486 AAU patients without AS, and 714 healthy controls. Genotyping was performed by PCR-RFLP assay or TaqMan® probe assay. The Chi-squared (χ²) test and multivariate logistic regression analysis were used to compare the distributions of alleles and genotypes between patients and controls. P values were adjusted using Bonferroni correction. Results. We did not observe significant differences in the genotype and allele frequencies of any SNP between AAU patients with or without AS and healthy controls. Stratification analyses by gender and HLA-B27 status showed a boundary significant association between two SNPs (rs10975003 and rs10758669) in JAK2 and AAU (P = 0.052 and P = 0.053, resp.). Conclusions. Our results indicated that genetic polymorphisms of the JAK-STAT signaling pathway genes may not be associated with AAU in the Han Chinese population.

Dual targeting of the thioredoxin and glutathione systems in cancer and HIV

Although the use of antioxidants for the treatment of cancer and HIV/AIDS has been proposed for decades, new insights gained from redox research have suggested a very different scenario. These new data show that the major cellular antioxidant systems, the thioredoxin (Trx) and glutathione (GSH) systems, actually promote cancer growth and HIV infection, while suppressing an effective immune response. Mechanistically, these systems control both the redox- and NO-based pathways (nitroso-redox homeostasis), which subserve innate and cellular immune defenses. Dual inhibition of the Trx and GSH systems synergistically kills neoplastic cells in vitro and in mice and decreases resistance to anticancer therapy. Similarly, the population of HIV reservoir cells that constitutes the major barrier to a cure for AIDS is exquisitely redox sensitive and could be selectively targeted by Trx and GSH inhibitors. Trx and GSH inhibition may lead to a reprogramming of the immune response, tilting the balance between the immune system and cancer or HIV in favor of the former, allowing elimination of diseased cells. Thus, therapies based on silencing of the Trx and GSH pathways represent a promising approach for the cure of both cancer and AIDS and warrant further investigation.

Involvement of the janus kinase/signal transducer and activator of transcription signaling pathway in multiple sclerosis and the animal model of experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) and its animal model of experimental autoimmune encephalomyelitis (EAE) are characterized by focal inflammatory infiltrates into the central nervous system, demyelinating lesions, axonal damage, and abundant production of cytokines that activate immune cells and damage neurons and oligodendrocytes, including interleukin-12 (IL-12), IL-6, IL-17, IL-21, IL-23, granulocyte macrophage-colony stimulating factor, and interferon-gamma. The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathway mediates the biological activities of these cytokines and is essential for the development and regulation of immune responses. Dysregulation of the JAK/STAT pathway contributes to numerous autoimmune diseases, including MS/EAE. The JAK/STAT pathway is aberrantly activated in MS/EAE because of excessive production of cytokines, loss of expression of negative regulators such as suppressors of cytokine signaling proteins, and significant enrichment of genes encoding components of the JAK/STAT pathway, including STAT3. Specific JAK/STAT inhibitors have been used in numerous preclinical models of MS and demonstrate beneficial effects on the clinical course of disease and attenuation of innate and adaptive immune responses. In addition, other drugs such as statins, glatiramer acetate, laquinimod, and fumarates have beneficial effects that involve inhibition of the JAK/STAT pathway. We conclude by discussing the feasibility of the JAK/STAT pathway as a target for neuroinflammatory diseases.

Nitric oxide sustains IL-1β expression in human dendritic cells enhancing their capacity to induce IL-17-producing T-cells

The role played by lung dendritic cells (DCs) which are influenced by external antigens and by their redox state in controlling inflammation is unclear. We studied the role played by nitric oxide (NO) in DC maturation and function. Human DCs were stimulated with a long-acting NO donor, DPTA NONOate, prior to exposure to lipopolysaccharide (LPS). Dose-and time-dependent experiments were performed with DCs with the aim of measuring the release and gene expression of inflammatory cytokines capable of modifying T-cell differentiation, towardsTh1, Th2 and Th17 cells. NO changed the pattern of cytokine release by LPS-matured DCs, dependent on the concentration of NO, as well as on the timing of its addition to the cells during maturation. Addition of NO before LPS-induced maturation strongly inhibited the release of IL-12, while increasing the expression and release of IL-23, IL-1β and IL-6, which are all involved in Th17 polarization. Indeed, DCs treated with NO efficiently induced the release of IL-17 by T-cells through IL-1β. Our work highlights the important role that NO may play in sustaining inflammation during an infection through the preferential differentiation of the Th17 lineage.

Nitric oxide synthase in innate and adaptive immunity: an update

Thirty years after the discovery of its production by activated macrophages, our appreciation of the diverse roles of nitric oxide (NO) continues to grow. Recent findings have not only expanded our understanding of the mechanisms controlling the expression of NO synthases (NOS) in innate and adaptive immune cells, but have also revealed new functions and modes of action of NO in the control and escape of infectious pathogens, in T and B cell differentiation, and in tumor defense. I discuss these findings, in the context of a comprehensive overview of the various sources and multiple reaction partners of NO, and of the regulation of NOS2 by micromilieu factors, antisense RNAs, and 'unexpected' cytokines.

iNOS expression in CD4+ T cells limits Treg induction by repressing TGFβ1: combined iNOS inhibition and Treg depletion unmask endogenous antitumor immunity

PURPOSE

Expression of inducible nitric oxide synthase (iNOS) in different cellular compartments may have divergent effects on immune function. We used a syngeneic tumor model to functionally characterize the role of iNOS in regulation of CD4(+)FOXP3(+) regulatory T cells (Treg), and optimize the beneficial effects of iNOS inhibition on antitumor immunity.

EXPERIMENTAL DESIGN

Wild-type (WT) or iNOS knockout mice bearing established MT-RET-1 melanoma were treated with the small-molecule iNOS inhibitor L-NIL and/or cyclophosphamide alone or in combination. The effect of iNOS inhibition or knockout on induction of Treg from mouse and human CD4(+) T cells in ex vivo culture was determined in parallel in the presence or absence of TGFβ1-depleting antibodies, and TGFβ1 levels were assessed by ELISA.

RESULTS

Whereas intratumoral myeloid-derived suppressor cells (MDSC) were suppressed by iNOS inhibition or knockout, systemic and intratumoral FOXP3(+) Treg levels increased in tumor-bearing mice. iNOS inhibition or knockout similarly enhanced induction of Treg from activated cultured mouse splenocytes or purified human or mouse CD4(+) T cells in a TGFβ1-dependent manner. Although either iNOS inhibition or Treg depletion with low-dose cyclophosphamide alone had little effect on growth of established MT-RET1 melanoma, combination treatment potently inhibited MDSC and Treg, boosted tumor-infiltrating CD8(+) T-cell levels, and arrested tumor growth in an immune-dependent fashion.

CONCLUSIONS

iNOS expression in CD4(+) T cells suppresses Treg induction by inhibiting TGFβ1 production. Our data suggest that iNOS expression has divergent effects on induction of myeloid and lymphoid-derived regulatory populations, and strongly support development of combinatorial treatment approaches that target these populations simultaneously.

Technical advance: ascorbic acid induces development of double-positive T cells from human hematopoietic stem cells in the absence of stromal cells

The efficacy of donor HSCT is partly reduced as a result of slow post-transplantation immune recovery. In particular, T cell regeneration is generally delayed, resulting in high infection-related mortality in the first years post-transplantation. Adoptive transfer of in vitro-generated human T cell progenitors seems a promising approach to accelerate T cell recovery in immunocompromised patients. AA may enhance T cell proliferation and differentiation in a controlled, feeder-free environment containing Notch ligands and defined growth factors. Our experiments show a pivotal role for AA during human in vitro T cell development. The blocking of NOS diminished this effect, indicating a role for the citrulline/NO cycle. AA promotes the transition of proT1 to proT2 cells and of preT to DP T cells. Furthermore, the addition of AA to feeder cocultures resulted in development of DP and SP T cells, whereas without AA, a preT cell-stage arrest occurred. We conclude that neither DLL4-expressing feeder cells nor feeder cell conditioned media are required for generating DP T cells from CB and G-CSF-mobilized HSCs and that generation and proliferation of proT and DP T cells are greatly improved by AA. This technology could potentially be used to generate T cell progenitors for adoptive therapy.

Metformin aggravates immune-mediated liver injury in mice

Hepatotoxicity of the antidiabetic drug metformin has been reported, but the underlying mechanisms remain unclear. We here investigated the effect of metformin in immune-mediated liver damage. While not hepatotoxic alone, metformin (200 mg/kg) aggravated concanavalin A (Con A, 12 mg/kg)-induced hepatitis, an experimental model of T cell-mediated liver injury, in both relatively resistant BALB/c and highly susceptible C57Bl/6 mice. Metformin + Con A-treated mice had elevated serum levels of pro-inflammatory cytokines TNF-α and IFN-γ, accompanied by a massive mononuclear cell infiltration in the liver. This was associated with the higher numbers of CD4(+) T cells producing TNF-α, IFN-γ and IL-17, CD4(+) T cells expressing chemokine receptor CXCR3 and activation marker CD27, CD4(+)CD62L(-)CCR7(-) and CD8(+)CD62L(-)CCR7(-) effector memory cells, IFN-γ producing NK cells, IL-4 and IL-17 producing NKT cells and IL-12 producing macrophages/dendritic cells. The percentage of CD4(+)CXCR3(+)Tbet(+)IL-10(+) and CD4(+)CD69(+)CD25(-) regulatory T cells was reduced. Metformin stimulated inducible nitric oxide synthase (iNOS) expression in the liver and spleen, and genetic deletion of iNOS attenuated the hepatotoxicity of metformin. Metformin increased the autophagic light chain 3 conversion and mRNA expression of important autophagy-inducing (beclin-1, Atg5 and GABARAP) and pro-apoptotic (p21, p27, Puma, Noxa, Bax, Bad, Bak1, Bim and Apaf1), but not anti-apoptotic molecules (Bcl-xL, survivin and XIAP), which correlated with the apoptotic caspase-3/PARP cleavage in the liver. The autophagy inhibitor chloroquine (20 mg/kg) prevented liver injury and apoptotic changes induced by metformin. Therefore, metformin aggravates immune-mediated hepatitis by promoting autophagy and activation of immune cells, affecting effector, as well as liver-specific regulatory T cells and iNOS expression.

The implications of hyponitroxia in cancer

Tumors are spatially heterogeneous, with regions of relative hypoxia and normoxia. The tumor microenvironment is an important determinant of both tumor growth and response to a variety of cytotoxic and targeted therapies. In the tumor microenvironment, reactive oxygen species and nitric oxide (NO) are important mediators of the level of expression of many transcription factors and signaling cascades that affect tumor growth and responses to therapy. The primary objective of this review is to explore and discuss the seemingly dichotomous actions of NO in cancer biology as both a tumor promoter and suppressor with an emphasis on understanding the role of persistently low NO concentrations or hyponitroxia as a key mediator in tumor progression. This review will also discuss the potential role of hyponitroxia as a novel therapeutic target to treat cancer and outline an approach that provides new opportunities for pharmacological intervention.

T cell–derived inducible nitric oxide synthase switches off Th17 cell differentiation

Nitric oxide derived from iNOS in activated T cells negatively regulates Th17 cell differentiation.

RORγt is necessary for the generation of T_H17 cells but the molecular mechanisms for the regulation of T_H17 cells are still not fully understood. We show that activation of CD4⁺ T cells results in the expression of inducible nitric oxide synthase (iNOS). iNOS-deficient mice displayed enhanced T_H17 cell differentiation but without major effects on either T_H1 or T_H2 cell lineages, whereas endothelial NOS (eNOS) or neuronal NOS (nNOS) mutant mice showed comparable T_H17 cell differentiation compared with wild-type control mice. The addition of N6-(1-iminoethyl)-l-lysine dihydrochloride (L-NIL), the iNOS inhibitor, significantly enhanced T_H17 cell differentiation, and S-nitroso-N-acetylpenicillamine (SNAP), the NO donor, dose-dependently reduced the percentage of IL-17–producing CD4⁺ T cells. NO mediates nitration of tyrosine residues in RORγt, leading to the suppression of RORγt-induced IL-17 promoter activation, indicating that NO regulates IL-17 expression at the transcriptional level. Finally, studies of an experimental model of colitis showed that iNOS deficiency results in more severe inflammation with an enhanced T_H17 phenotype. These results suggest that NO derived from iNOS in activated T cells plays a negative role in the regulation of T_H17 cell differentiation and highlight the importance of intrinsic programs for the control of T_H17 immune responses.

CD8 T cells regulate allergic contact dermatitis by modulating CCR2-dependent TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells

Monocytes and their derived cells have critical roles in inflammation and immune defense. However, their function in skin diseases such as allergic contact dermatitis remains poorly defined. Using a model of contact hypersensitivity (CHS) toward 2,4-dinitrochlorobenzene, we show that Ly6C+ CD11b+ monocytic cells participate in the pathophysiology of CHS and their accumulation is regulated by effector CD8 T cells. These Ly6C+ CD11b+ monocytic cells are the primary contributors of tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) and derive from Ly6C(hi)CCR2+ monocytes, as they were absent in non-inflamed skin and accumulate as a consequence of inflammation in a C-C chemokine receptor type 2 (CCR2)-dependent manner. Importantly, CCR2(-/-) mice, or wild-type mice depleted of monocytes via clodronate liposomes, display a marked decrease in TNF-α and iNOS expression accompanied by attenuated skin inflammation. Using transgenic mice and antibody depletion, we show that effector CD8 T cells regulate the accumulation of Ly6C+ CD11b+ monocytic cells through IL-17 and activate them for TNF-α and iNOS through IFN-γ. CD8 T cell-derived IFN-γ was also critical for the accumulation of the major histocompatibility complex II-expressing Ly6C+ CD11b+ subset, which expressed intermediate levels of CD11c and costimulatory molecules. Taken together, our findings provide further insight into the pathophysiology of allergic contact dermatitis by showing that CD8 T cells regulate the inflammatory cascade through TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells.

CTLA4Ig inhibits effector T cells through regulatory T cells and TGF-β

The CD28 costimulatory receptor is a critical regulator of T cell function, making it an attractive therapeutic target for the treatment of immune-mediated diseases. CTLA4Ig, now approved for use in humans, prevents naive T cell activation by binding to B7 proteins and blocking engagement of CD28. However, CTLA4Ig suppresses inflammation even if administered when disease is established, suggesting alternative mechanisms. We identified a novel, CD28-independent mechanism by which CTLA4Ig inhibits activated T cells. We show that in vitro, CTLA4Ig synergizes with NO from bone marrow-derived macrophages to inhibit T cell proliferation. Depletion of regulatory T cells (Tregs) or interference with TGF-β signaling abrogated the inhibitory effect of CTLA4Ig. Parallel in vivo experiments using an allergic airway inflammation model demonstrated that this novel mechanism required both macrophages and regulatory T cells. Furthermore, CTLA4Ig was ineffective in SMAD3-deficient mice, supporting a requirement for TGF-β signaling. Thus, in addition to preventing naive T cells from being fully activated, CTLA4Ig can turn off already activated effector T cells by an NO/regulatory T cell/TGF-β-dependent pathway. This mechanism is similar to cell-extrinsic effects of endogenous CTLA4 and may be particularly important in the ability of CTLA4Ig to treat chronic inflammatory disease.

Induction and stability of human Th17 cells require endogenous NOS2 and cGMP-dependent NO signaling

Nitric oxide (NO) is a ubiquitous mediator of inflammation and immunity, involved in the pathogenesis and control of infectious diseases, autoimmunity, and cancer. We observed that the expression of nitric oxide synthase-2 (NOS2/iNOS) positively correlates with Th17 responses in patients with ovarian cancer (OvCa). Although high concentrations of exogenous NO indiscriminately suppress the proliferation and differentiation of Th1, Th2, and Th17 cells, the physiological NO concentrations produced by patients’ myeloid-derived suppressor cells (MDSCs) support the development of RORγt(Rorc)+IL-23R⁺IL-17⁺ Th17 cells. Moreover, the development of Th17 cells from naive-, memory-, or tumor-infiltrating CD4+ T cells, driven by IL-1β/IL-6/IL-23/NO-producing MDSCs or by recombinant cytokines (IL-1β/IL-6/IL-23), is associated with the induction of endogenous NOS2 and NO production, and critically depends on NOS2 activity and the canonical cyclic guanosine monophosphate (cGMP)–cGMP-dependent protein kinase (cGK) pathway of NO signaling within CD4⁺ T cells. Inhibition of NOS2 or cGMP–cGK signaling abolishes the de novo induction of Th17 cells and selectively suppresses IL-17 production by established Th17 cells isolated from OvCa patients. Our data indicate that, apart from its previously recognized role as an effector mediator of Th17-associated inflammation, NO is also critically required for the induction and stability of human Th17 responses, providing new targets to manipulate Th17 responses in cancer, autoimmunity, and inflammatory diseases.

Foxp3 expression and nitric oxide production in peripheral blood mononuclear cells of communicants with pulmonary tuberculosis

The understanding of the mechanisms involved in the immune response is of significant relevance to the control of tuberculosis (TB), especially in individuals living with patients with TB. To characterize the nitric oxide (NO) production and the Foxp3 marker expression in this population, peripheral blood mononuclear cells of intradomiciliary contacts of individuals with pulmonary tuberculosis with (CTb, susceptible) and without (STb, resistant) previous history of active infection were stimulated in vitro with Mycobacterium tuberculosis antigen (TbAg) and with the mitogen Concanavalin A for 24 and 48 h. The groups analysed did not present significant difference in the Foxp3 mRNA expression nor in the NO production. Negative correlation (P = 0.09) between NO and Foxp3 after a 48-h stimulation with TbAg was observed in the STb group. In this group, after a 24-h culture stimulated with TbAg (P = 0.03), this same correlation was observed. In comparison with the cytokines previously studied by our group (Cavalcanti et al., 2009), a positive correlation was observed between IL-10 and Foxp3 after a 48-h culture of cells from communicants susceptible to tuberculosis (STb) stimulated with TbAg (P = 0.04). Evaluating the entire population, a positive correlation was observed between the cytokine TNF-α and the Foxp3 marker in the cultures stimulated for 24 (P = 0.03) and 48 (P = 0.02) hours with TbAg. Therefore, considering the similarity in the exposure and the individual capacity of responding to the contact with M. tuberculosis, the present study contributes to the comprehension of the immune regulation in individuals living with patients with TB.

Nitrosothiols in the immune system: signaling and protection

SIGNIFICANCE

In the immune system, nitric oxide (NO) has been mainly associated with antibacterial defenses exerted through oxidative, nitrosative, and nitrative stress and signal transduction through cyclic GMP-dependent mechanisms. However, S-nitrosylation is emerging as a post-translational modification (PTM) involved in NO-mediated cell signaling.

RECENT ADVANCES

Precise roles for S-nitrosylation in signaling pathways have been described both for innate and adaptive immunity. Denitrosylation may protect macrophages from their own S-nitrosylation, while maintaining nitrosative stress compartmentalized in the phagosomes. Nitrosothiols have also been shown to be beneficial in experimental models of autoimmune diseases, mainly through their role in modulating T-cell differentiation and function.

CRITICAL ISSUES

Relationship between S-nitrosylation, other thiol redox PTMs, and other NO-signaling pathways has not been always taken into account, particularly in the context of immune responses. Methods for assaying S-nitrosylation in individual proteins and proteomic approaches to study the S-nitrosoproteome are constantly being improved, which helps to move this field forward.

FUTURE DIRECTIONS

Integrated studies of signaling pathways in the immune system should consider whether S-nitrosylation/denitrosylation processes are among the PTMs influencing the activity of key signaling and adaptor proteins. Studies in pathophysiological scenarios will also be of interest to put these mechanisms into broader contexts. Interventions modulating nitrosothiol levels in autoimmune disease could be investigated with a view to developing new therapies.

Apoptotic programs are determined during lineage commitment of CD4+ T effectors: selective regulation of T effector-memory apoptosis by inducible nitric oxide synthase

Lineage-committed T effectors generated in response to Ag during the inflammatory phase are destined to die during termination of the immune response. We present evidence to suggest that molecular signatures of lineage commitment are reflected in apoptotic cascades activated in CD4(+) T effectors. Exemplifying this, ablation of inducible NO synthase (iNOS) protected effector-memory T (TEM) cells, but not T(Naive) or central-memory T cells, activated in vitro, from apoptosis triggered by cytokine deprivation. Furthermore, attrition of T effectors generated in the secondary, but not the primary, response to Ag was substantially reduced in mice, which received iNOS inhibitors. Distinct patterns of iNOS expression were revealed in wild-type TEM effectors undergoing apoptosis, and ablation of iNOS protein in primary and TEM wild-type effectors confirmed observations made in iNOS(-/-) cells. Describing molecular correlates of this dependence, mitochondrial damage, activation of the protein Bax, and release from mitochondria of the apoptosis-inducing factor were selectively abrogated in iNOS(-/-) TEM effectors. Suggesting that iNOS dependence was linked to the functional identity of T cell subsets, both iNOS induction and apoptosis were compromised in IFN-γ(-/-) TEM effectors, which mirrored the response patterns of iNOS(-)(/)(-) TEM. Collectively, these observations suggest that programs regulating deletion and differentiation are closely integrated and likely encoded during lineage commitment of T effectors.

Nitric oxide inhibits the accumulation of CD4+CD44hiTbet+CD69lo T cells in mycobacterial infection

Animals lacking the inducible nitric oxide synthase gene (nos2(-/-)) are less susceptible to Mycobacterium avium strain 25291 and lack nitric oxide-mediated immunomodulation of CD4(+) T cells. Here we show that the absence of nos2 results in increased accumulation of neutrophils and both CD4(+) and CD8(+) T cells within the M. avium containing granuloma. Examination of the T-cell phenotype in M. avium infected mice demonstrated that CD4(+)CD44(hi) effector T cells expressing the Th1 transcriptional regulator T-bet (T-bet(+)) were specifically reduced by the presence of nitric oxide. Importantly, the T-bet(+) effector population could be separated into CD69(hi) and CD69(lo) populations, with the CD69(lo) population only able to accumulate during chronic infection within infected nos2(-/-) mice. Transcriptomic comparison between CD4(+)CD44(hi)CD69(hi) and CD4(+)CD44(hi)CD69(lo) populations revealed that CD4(+)CD44(hi)CD69(lo) cells had higher expression of the integrin itgb1/itga4 (VLA-4, CD49d/CD29). Inhibition of Nos2 activity allowed increased accumulation of the CD4(+) CD44(hi)T-bet(+)CD69(lo) population in WT mice as well as increased expression of VLA-4. These data support the hypothesis that effector T cells in mycobacterial granulomata are not a uniform effector population but exist in distinct subsets with differential susceptibility to the regulatory effects of nitric oxide.

CD28 ligation increases macrophage suppression of T-cell proliferation

When compared to spleen or lymph node cells, resident peritoneal cavity cells respond poorly to T-cell activation in vitro. The greater proportional representation of macrophages in this cell source has been shown to actively suppress the T-cell response. Peritoneal macrophages exhibit an immature phenotype (MHC class II(lo), B7(lo)) that reduces their efficacy as antigen-presenting cells. Furthermore, these cells readily express inducible nitric oxide synthase (iNOS), an enzyme that promotes T-cell tolerance by catabolism of the limiting amino acid arginine. Here, we investigate the ability of exogenous T-cell costimulation to recover the peritoneal T-cell response. We show that CD28 ligation failed to recover the peritoneal T-cell response and actually suppressed responses that had been recovered by inhibiting iNOS. As indicated by cytokine ELISpot and neutralizing monoclonal antibody (mAb) treatment, this 'cosuppression' response was due to CD28 ligation increasing the number of interferon (IFN)-γ-secreting cells. Our results illustrate that cellular composition and cytokine milieu influence T-cell costimulation biology.Cellular & Molecular Immunology advance online publication, 23 April 2012; doi:10.1038/cmi.2012.13.