Deficiency of Nuclear Factor-κB c-Rel Accelerates the Development of Autoimmune Diabetes in NOD Mice

NF-κB c-Rel is a critical regulator of TLR7-induced inflammation in psoriasis

BACKGROUND

Nuclear factor kappa B (NF-κB) c-Rel is a psoriasis susceptibility locus, however mechanisms underlying c-Rel transactivation during disease are poorly understood. Inflammation in psoriasis can be triggered following Toll-like Receptor 7 (TLR7) signalling in dendritic cells (DCs), and c-Rel is a critical regulator of DC function. Here, we studied the mechanism of TLR7-induced c-Rel-mediated inflammation in DCs.

METHODS

The overall expression of c-Rel was analysed in skin sections from patients with psoriasis in human transcriptomics datasets as well as the imiquimod-induced psoriasis mouse model. The function of c-Rel in DCs following TLR7 stimulation was determined by c-Rel CRISPR/Cas9 knockout DC2.4 immortalised cells and primary bone marrow derived dendritic cells from c-Rel knockout C57BL6/J mice.

FINDINGS

c-Rel is highly expressed in lesional skin of patients with psoriasis and TLR7-induced psoriatic lesions in mice. c-Rel deficiency protected mice from the disease, and specifically compromised TLR7-induced, and not TLR9- or TLR3-induced, inflammation in dendritic cells. Mechanistically, c-Rel deficiency disrupted activating NF-κB dimers and allowed binding of inhibitory NF-κB homodimers to the IL-1β and IL-6 promoters thus inhibiting their expression. This functionally compromises the ability of c-Rel deficient DCs to induce Th17 polarisation, which is critical in psoriasis pathogenesis.

INTERPRETATION

Our findings reveal that c-Rel is a key regulator of TLR7-mediated dendritic cell-dependent inflammation, and that targeting c-Rel-dependent signalling could prove an effective strategy to dampen excessive inflammation in TLR7-related skin inflammation.

FUNDING

A complete list of funding sources that contributed to this study can be found in the Acknowledgements section.

The significance of glutaredoxins for diabetes mellitus and its complications

Diabetes mellitus is a non-communicable metabolic disease hallmarked by chronic hyperglycemia caused by beta-cell failure. Diabetic complications affect the vasculature and result in macro- and microangiopathies, which account for a significantly increased morbidity and mortality. The rising incidence and prevalence of diabetes is a major global health burden. There are no feasible strategies for beta-cell preservation available in daily clinical practice. Therefore, patients rely on antidiabetic drugs or the application of exogenous insulin. Glutaredoxins (Grxs) are ubiquitously expressed and highly conserved members of the thioredoxin family of proteins. They have specific functions in redox-mediated signal transduction, iron homeostasis and biosynthesis of iron-sulfur (FeS) proteins, and the regulation of cell proliferation, survival, and function. The involvement of Grxs in chronic diseases has been a topic of research for several decades, suggesting them as therapeutic targets. Little is known about their role in diabetes and its complications. Therefore, this review summarizes the available literature on the significance of Grxs in diabetes and its complications. In conclusion, Grxs are differentially expressed in the endocrine pancreas and in tissues affected by diabetic complications, such as the heart, the kidneys, the eye, and the vasculature. They are involved in several pathways essential for insulin signaling, metabolic inflammation, glucose and fatty acid uptake and processing, cell survival, and iron and mitochondrial metabolism. Most studies describe significant changes in glutaredoxin expression and/or activity in response to the diabetic metabolism. In general, mitigated levels of Grxs are associated with oxidative distress, cell damage, and even cell death. The induced overexpression is considered a potential part of the cellular stress-response, counteracting oxidative distress and exerting beneficial impact on cell function such as insulin secretion, cytokine expression, and enzyme activity.

MBD2 acts as a repressor to maintain the homeostasis of the Th1 program in type 1 diabetes by regulating the STAT1-IFN-γ axis

The methyl-CpG-binding domain 2 (MBD2) interprets DNA methylome-encoded information through binding to the methylated CpG DNA, by which it regulates target gene expression at the transcriptional level. Although derailed DNA methylation has long been recognized to trigger or promote autoimmune responses in type 1 diabetes (T1D), the exact role of MBD2 in T1D pathogenesis, however, remains poorly defined. Herein, we generated an Mbd2 knockout model in the NOD background and found that Mbd2 deficiency exacerbated the development of spontaneous T1D in NOD mice. Adoptive transfer of Mbd2^-/- CD4 T cells into NOD.scid mice further confirmed the observation. Mechanistically, Th1 stimulation rendered the Stat1 promoter to undergo a DNA methylation turnover featured by the changes of DNA methylation levels or patterns along with the induction of MBD2 expression, which then bound to the methylated CpG DNA within the Stat1 promoter, by which MBD2 maintains the homeostasis of Th1 program to prevent autoimmunity. As a result, ectopic MBD2 expression alleviated CD4 T cell diabetogenicity following their adoptive transfer into NOD.scid mice. Collectively, our data suggest that MBD2 could be a viable target to develop epigenetic-based therapeutics against T1D in clinical settings.

Targeting NF-κB c-Rel in regulatory T cells to treat corneal transplantation rejection

The relevance of Tregs in the induction of tolerance against corneal allografts has been well established. Although it is well known that the conversion of Tregs into effector-like cells contributes to the loss of corneal immune privilege, the underlying mechanism is still not fully understood. Using heterologous penetrating keratoplasty model, we found that Tregs from corneal allograft rejected mice (inflam-Tregs) exhibit impaired function and characteristics of effector T cells. Further study showed that the expression of NF-κB c-Rel, a key mediator of effector T cell function, was significantly increased in inflam-Tregs. Mechanistic study revealed that elevated NF-κB c-Rel level in inflam-Tregs impaired Treg function through the promotion of inflammatory cytokine production and glycolysis. More importantly, we demonstrated that targeting NF-κB c-Rel was able to improve the immune suppressive function of inflam-Tregs in vitro and enhance the potential of them to suppress corneal transplantation rejection. Therefore, our current study identified NF-κB c-Rel as a key mediator of the conversion of Tregs into effector-like cells when under inflammatory environment.

Regulatory T Cells and Diabetes Mellitus

Immune system dysfunction causes dysregulation of immune homeostasis, which in turn leads to autoimmune diseases. Regulatory T cells (Tregs) are a specialized T cell subpopulation that maintain peripheral tolerance and immune homeostasis. Diabetic patients are at an increased risk of developing cardiovascular diseases; thus, in terms of coronary risk, diabetes mellitus (DM) is considered coronary heart disease equivalent. Accumulating evidence indicates that Tregs play an important role in protecting against the development of various cardiovascular diseases. In this review, we provide an overview of the role of Tregs in the pathogenesis of DM, including type 1 DM, type 2 DM, latent autoimmune diabetes of adults, and gestational DM. In addition, we discuss the role of Tregs in diabetic complications, including cardiovascular diseases, nephropathy, neuropathy, and retinopathy. Tregs play a beneficial role in the pathogenesis of DM and diabetic complications, although the precise molecular mechanisms underlying the protective effect of Tregs against DM are still obscure. Collectively, modification of Tregs may provide a promising and novel future strategy for the prevention and therapy of DM and diabetic complications.

NF-κB c-Rel Is Dispensable for the Development but Is Required for the Cytotoxic Function of NK Cells

Natural Killer (NK) cells are cytotoxic lymphocytes critical to the innate immune system. We found that germline deficiency of NF-κB c-Rel results in a marked decrease in cytotoxic function of NK cells, both in vitro and in vivo, with no significant differences in the stages of NK cell development. We found that c-Rel binds to the promoters of perforin and granzyme B, two key proteins required for NK cytotoxicity, and controls their expression. We generated a NK cell specific c-Rel conditional knockout to study NK cell intrinsic role of c- Rel and found that both global and conditional c-Rel deficiency leads to decreased perforin and granzyme B expression and thereby cytotoxic function. We also confirmed the role of c-Rel in perforin and granzyme B expression in human NK cells. c-Rel reconstitution rescued perforin and granzyme B expressions in c-Rel deficient NK cells and restored their cytotoxic function. Our results show a previously unknown role of c-Rel in transcriptional regulation of perforin and granzyme B expressions and control of NK cell cytotoxic function.

Innate immune receptors in type 1 diabetes: the relationship to cell death-associated inflammation

The importance of innate immunity in host defense and inflammatory responses has been clearly demonstrated after the discovery of innate immune receptors such as Toll-like receptors (TLRs) or Nucleotide-binding oligomerization domain-containing protein (Nod)-like receptors (NLRs). Innate immunity also plays a critical role in diverse pathological conditions including autoimmune diseases such as type 1 diabetes (T1D). In particular, the role of a variety of innate immune receptors in T1D has been demonstrated using mice with targeted disruption of such innate immune receptors. Here, we discuss recent findings showing the role of innate immunity in T1D that were obtained mostly from studies of genetic mouse models of innate immune receptors. In addition, the role of innate immune receptors involved in the pathogenesis of T1D in sensing death-associated molecular patterns (DAMPs) released from dead cells or pathogen-associated molecular patterns (PAMPs) will also be covered. Elucidation of the role of innate immune receptors in T1D and the nature of DAMPs sensed by such receptors may lead to the development of new therapeutic modalities against T1D.

Negative regulation of FOXP3 expression by c-Rel O-GlcNAcylation

O-GlcNAcylation is a reversible post-translational protein modification that regulates fundamental cellular processes including immune responses and autoimmunity. Previously, we showed that hyperglycemia increases O-GlcNAcylation of the transcription factor, nuclear factor kappaB c-Rel at serine residue 350 and enhances the transcription of the c-Rel-dependent proautoimmune cytokines interleukin-2, interferon gamma and granulocyte macrophage colony stimulating factor in T cells. c-Rel also plays a critical role in the transcriptional regulation of forkhead box P3 (FOXP3)-the master transcription factor that governs development and function of Treg cells. Here we show that the regulatory effect of c-Rel O-GlcNAcylation is gene-dependent, and in contrast to its role in enhancing the expression of proautoimmune cytokines, it suppresses the expression of FOXP3. Hyperglycemia-induced O-GlcNAcylation-dependent suppression of FOXP3 expression was found in vivo in two mouse models of autoimmune diabetes; streptozotocin-induced diabetes and spontaneous diabetes in nonobese diabetic mice. Mechanistically, we show that both hyperglycemia-induced and chemically enhanced cellular O-GlcNAcylation decreases c-Rel binding at the FOXP3 promoter and negatively regulates FOXP3 expression. Mutation of the O-GlcNAcylation site in c-Rel, (serine 350 to alanine), augments T cell receptor-induced FOXP3 expression and resists the O-GlcNAcylation-dependent repression of FOXP3 expression. This study reveals c-Rel S350 O-GlcNAcylation as a novel molecular mechanism inversely regulating immunosuppressive FOXP3 expression and proautoimmune gene expression in autoimmune diabetes with potential therapeutic implications.

The many-sided contributions of NF-κB to T-cell biology in health and disease

T cells (or T lymphocytes) exhibit a myriad of functions in immune responses, ranging from pathogen clearance to autoimmunity, cancer and even non-lymphoid tissue homeostasis. Therefore, deciphering the molecular mechanisms orchestrating their specification, function and gene expression pattern is critical not only for our comprehension of fundamental biology, but also for the discovery of novel therapeutic targets. Among the master regulators of T-cell identity, the functions of the NF-κB family of transcription factors have been under scrutiny for several decades. However, a more precise understanding of their pleiotropic functions is only just emerging. In this review we will provide a global overview of the roles of NF-κB in the different flavors of mature T cells. We aim at highlighting the complex and sometimes diverging roles of the five NF-κB subunits in health and disease.

NF-κB c-Rel Dictates the Inflammatory Threshold by Acting as a Transcriptional Repressor

NF-κB/Rel family of transcription factors plays a central role in initiation and resolution of inflammatory responses. Here, we identified a function of the NF-κB subunit c-Rel as a transcriptional repressor of inflammatory genes. Genetic deletion of c-Rel substantially potentiates the expression of several TNF-α-induced RelA-dependent mediators of inflammation. v-Rel, the viral homologue of c-Rel, but not RelB, also possesses this repressive function. Mechanistically, we found that c-Rel selectively binds to the co-repressor HDAC1 and competitively binds to the DNA mediating HDAC1 recruitment to the promoters of inflammatory genes. A specific point mutation at tyrosine25 in c-Rel's DNA-binding domain, for which a missense single nucleotide variation (Y25H) exists in humans, completely abrogated its ability to bind DNA and repress TNF-α-induced, RelA-mediated transcription. Our findings reveal that the transactivator NF-κB subunit c-Rel also plays a role as a transcriptional repressor in the maintenance of inflammatory homeostasis.

Regulation of B-cell function by NF-kappaB c-Rel in health and disease

B cells mediate humoral immune response and contribute to the regulation of cellular immune response. Members of the Nuclear Factor kappaB (NF-κB) family of transcription factors play a major role in regulating B-cell functions. NF-κB subunit c-Rel is predominantly expressed in lymphocytes, and in B cells, it is required for survival, proliferation, and antibody production. Dysregulation of c-Rel expression and activation alters B-cell homeostasis and is associated with B-cell lymphomas and autoimmune pathologies. Based on its essential roles, c-Rel may serve as a potential prognostic and therapeutic target. This review summarizes the current understanding of the multifaceted role of c-Rel in B cells and B-cell diseases.

Toll-like receptor 9 negatively regulates pancreatic islet beta cell growth and function in a mouse model of type 1 diabetes

AIMS/HYPOTHESIS

Innate immune effectors interact with the environment to contribute to the pathogenesis of the autoimmune disease, type 1 diabetes. Although recent studies have suggested that innate immune Toll-like receptors (TLRs) are involved in tissue development, little is known about the role of TLRs in tissue development, compared with autoimmunity. We aimed to fill the knowledge gap by investigating the role of TLR9 in the development and function of islet beta cells in type 1 diabetes, using NOD mice.

METHODS

We generated Tlr9^-/- NOD mice and examined them for type 1 diabetes development and beta cell function, including insulin secretion and glucose tolerance. We assessed islet and beta cell number and characterised CD140a expression on beta cells by flow cytometry. We also tested beta cell function in Tlr9^-/- C57BL/6 mice. Finally, we used TLR9 antagonists to block TLR9 signalling in wild-type NOD mice to verify the role of TLR9 in beta cell development and function.

RESULTS

TLR9 deficiency promoted pancreatic islet development and beta cell differentiation, leading to enhanced glucose tolerance, improved insulin sensitivity and enhanced first-phase insulin secretory response. This was, in part, mediated by upregulation of CD140a (also known as platelet-derived growth factor receptor-α [PDGFRα]). In the absence of TLR9, induced by either genetic targeting or treatment with TLR9 antagonists, which had similar effects on ontogenesis and function of beta cells, NOD mice were protected from diabetes.

CONCLUSIONS/INTERPRETATION

Our study links TLR9 and the CD140a pathway in regulating islet beta cell development and function and indicates a potential therapeutic target for diabetes prevention and/or treatment.

A Hypermorphic Nfkbid Allele Contributes to Impaired Thymic Deletion of Autoreactive Diabetogenic CD8+ T Cells in NOD Mice

In both NOD mice and humans, the development of type 1 diabetes (T1D) is dependent in part on autoreactive CD8+ T cells recognizing pancreatic β cell peptides presented by often quite common MHC class I variants. Studies in NOD mice previously revealed that the common H2-Kd and/or H2-Db class I molecules expressed by this strain aberrantly lose the ability to mediate the thymic deletion of pathogenic CD8+ T cell responses through interactions with T1D susceptibility genes outside the MHC. A gene(s) mapping to proximal chromosome 7 was previously shown to be an important contributor to the failure of the common class I molecules expressed by NOD mice to mediate the normal thymic negative selection of diabetogenic CD8+ T cells. Using an inducible model of thymic negative selection and mRNA transcript analyses, we initially identified an elevated Nfkbid expression variant as a likely NOD-proximal chromosome 7 region gene contributing to impaired thymic deletion of diabetogenic CD8+ T cells. CRISPR/Cas9-mediated genetic attenuation of Nfkbid expression in NOD mice resulted in improved negative selection of autoreactive diabetogenic AI4 and NY8.3 CD8+ T cells. These results indicated that allelic variants of Nfkbid contribute to the efficiency of intrathymic deletion of diabetogenic CD8+ T cells. However, although enhancing thymic deletion of pathogenic CD8+ T cells, ablating Nfkbid expression surprisingly accelerated T1D onset that was associated with numeric decreases in both regulatory T and B lymphocytes in NOD mice.

NF-κB is weakly activated in the NOD mouse model of type 1 diabetes

Type 1 diabetes is an autoimmune disease characterised by selective destruction of pancreatic beta cells by the immune system. The transcription factor nuclear factor-kappa B (NF-κB) regulates innate and adaptive immune responses. Using gene targeting and in vitro analysis of pancreatic islets and immune cells, NF-κB activation has been implicated in type 1 diabetes development. Here we use a non-obese diabetic (NOD) mouse model that expresses a luciferase reporter of transcriptionally active NF-κB to determine its activation in vivo during development of diabetes. Increased luciferase activity was readily detected upon treatment with Toll-like receptor ligands in vitro and in vivo, indicating activation of NF-κB. However, activated NF-κB was detectable at low levels above background in unmanipulated NOD mice, but did not vary with age, despite the progression of inflammatory infiltration in islets over time. NF-κB was highly activated in an accelerated model of type 1 diabetes that requires CD4⁺ T cells and inflammatory macrophages. These data shed light on the nature of the inflammatory response in the development of type 1 diabetes.

Feruloylated oligosaccharides from maize bran alleviate the symptoms of diabetes in streptozotocin-induced type 2 diabetic rats

This study investigated the therapeutic effect of feruloylated oligosaccharides (FOs) extracted from maize bran on type 2 diabetic rats and its potential mechanism. Streptozotocin (STZ) induced type 2 diabetic male rats were orally administered with different levels of FOs for 8 weeks, and ferulic acid (FA) treatment was conducted as the positive control. Among all the treatments, the oral administration of 600 mg per kg bw per d FOs showed the best therapeutic effects on the diabetic rats by significantly lowering the levels of fasting plasma glucose (FPG), fasting insulin, TG, LDL-c, aspartate transaminase, creatine kinase and lactate dehydrogenase in plasma, while increasing the level of plasma HDL-c. In addition, the intake of FOs at 600 mg per kg bw per d exhibited the best antioxidant effects in the plasma, liver, kidney and heart of the diabetic rats, and the highest inhibitory effects on the formation of AGEs and CML in the organs, which might explain the alleviating effects of FOs on abdominal aorta injury observed in the current study. FOs presented better regulation effects on FPG, plasma lipid and the protection of abdominal aorta than FA under the same administered dosage. Based on these outcomes, FOs from maize bran could be beneficial for prevention or early treatment of diabetes mellitus.

Rediscovery of NF-κB signaling in nasopharyngeal carcinoma: How genetic defects of NF-κB pathway interplay with EBV in driving oncogenesis?

Nasopharyngeal carcinoma (NPC) is a unique EBV-associated subtype of head and neck cancer, which has the highest incidence in Southern China and eastern South Asia. The interaction between genetic risk factors and environmental challenge, have been considered to contribute to the development of nasopharyngeal carcinogenesis. Constitutive activation of NF-κB signaling has been seen in NPC tissues and is associated with unfavorable prognosis. Recently, several whole exome sequencing study consistently revealed that high frequency mutations of NF-κB pathway negative regulators is common in nasopharyngeal carcinoma, which reinforce the importance of NF-κB driving oncogenesis. This review focuses on the current state of research in role of NF-κB in NPC carcinogenesis. We summarized the newly identified loss of function (LOF) mutations on NF-κB negative regulators leading to it's activation bypass LMP-1 stimulation. We discussed the critical role of NF-κB activation in immortalization and transformation of nasopharygeal epithelium. We also depicted how NF-κB signaling mediated chronic inflammation contribute to persistent EBV infection, immune evasion of EBV infected cells, metabolic reprogramming, and cancer stem cells (CSCs) formation in NPC. Lastly, we discussed the clinical resonance of targeting NF-κB for NPC precise therapy.

Self-Transducible Bimodal PDX1-FOXP3 Protein Lifts Insulin Secretion and Curbs Autoimmunity, Boosting Tregs in Type 1 Diabetic Mice

Type 1 diabetes (T1D) is characterized by massive destruction of insulin-producing β cells by autoreactive T lymphocytes, arising via defective immune tolerance. Therefore, effective anti-T1D therapeutics should combine autoimmunity-preventing and insulin production-restoring properties. We constructed a cell-permeable PDX1-FOXP3-TAT fusion protein (FP) composed of two transcription factors: forkhead box P3 (FOXP3), the master regulator of differentiation and functioning of self-tolerance-promoting Tregs, and pancreatic duodenal homeobox-1 (PDX1), the crucial factor supporting β cell development and maintenance. The FP was tested in vitro and in a non-obese diabetic mouse T1D model. In vitro, FP converted naive CD4⁺ T cells into a functional "Treg-like" subset, which suppressed cytokine secretion, downregulated antigen-specific responses, and curbed viability of diabetogenic effector cells. In hepatic stem-like cells, FP potentiated endocrine transdifferentiation, inducing expression of Insulin2 and other β lineage-specific genes. In vivo, FP administration to chronically diabetic mice triggered (1) a significant elevation of insulin and C-peptide levels, (2) the formation of insulin-containing cell clusters in livers, and (3) a systemic anti-inflammatory shift (higher Foxp3⁺CD4⁺CD25⁺ T cell frequencies, elevated rates of IL-10-producing cells, and reduced rates of IFN-γ-secreting cells). Overall, in accordance with its design, PDX1-FOXP3-TAT FP delivered both Treg-stabilizing anti-autoimmune and de novo insulin-producing effects, proving its anti-T1D therapeutic potential.