NUR77 exerts a protective effect against inflammatory bowel disease by negatively regulating the TRAF6/TLR-IL-1R signalling axis

Controversy and multiple roles of the solitary nucleus receptor Nur77 in disease and physiology

Neuron-derived clone 77 (Nur77), a member of the orphan nuclear receptor family, is expressed and activated rapidly in response to diverse physiological and pathological stimuli. It exerts complex biological functions, including roles in the nervous system, genome integrity, cell differentiation, homeostasis, oxidative stress, autophagy, aging, and infection. Recent studies suggest that Nur77 agonists alleviate symptoms of neurodegenerative diseases, highlighting its potential as a therapeutic target in such conditions. In cancer, Nur77 demonstrates dual roles, acting as both a tumor suppressor and promoter, depending on the cancer type and stage, making it a controversial yet promising anticancer target. This review provides a structured analysis of the functions of Nur77, focusing on its physiological and pathological roles, therapeutic potential, and existing controversies. Emphasis is placed on its emerging applications in neurodegenerative diseases and cancer, offering key insights for future research and clinical translation.

Childhood obesity and risk of inflammatory bowel disease in adulthood: A Mendelian randomization study

It is well-known that childhood obesity is associated with various adult gastrointestinal diseases, inflammatory bowel disease (IBD) being no exception. However, previous epidemiological observational studies, while reporting a correlation between the 2, have left the question of a causal relationship inconclusive. This study aims to use a 2-sample Mendelian randomization (MR) analysis to assess the causal relationship between childhood obesity and IBD as well as its subtypes (ulcerative colitis [UC] and Crohn disease [CD]). Data on childhood obesity, IBD, and its subtypes (UC and CD) were sourced from IEU OpenGWAS (https://gwas.mrcieu.ac.uk/datasets/ieu-a-1096/) and IIBDGC (https://www.ibdgenetics.org/). The data were analyzed using the inverse variance weighted (IVW), MR-Egger, weighted median, simple mode, and weighted mode methods. The MR analysis indicates no causal relationship between childhood obesity and IBD or its subtypes (UC and CD). The consistency of the results across the IVW, MR-Egger, weighted median, simple mode, and weighted mode methods suggests the reliability of the findings. We found that childhood obesity is not causally related to IBD or its subtypes (UC and CD). This differs from prior studies. The observed discrepancies may be due to common biological or environmental confounding factors.

The phthalide compound tokinolide B from Angelica sinensis exerts anti-inflammatory effects through Nur77 binding

BACKGROUND

Nur77, an orphan member of the nuclear receptor superfamily, regulates inflammatory diseases and is a therapeutic target for treating inflammation. Phthalides in Angelica sinensis exhibit anti-inflammatory activity.

PURPOSE

This study aimed to screen compounds from A. sinensis phthalide extract that could exert anti-inflammatory activity by targeting Nur77. To provide new theoretical support for better elucidation of Chinese medicine targeting mitochondria to achieve multiple clinical efficacies.

METHODS

The anti-inflammatory capacity of phthalides was assessed in tumor necrosis factor-alpha (TNF-α)-stimulated HepG2 cells using western blotting. The interaction between phthalides and Nur77 was verified by molecular docking, surface plasmon resonance, and cellular thermal shift assay. Co-immunoprecipitation, western blotting, and immunostaining were performed to determine the molecular mechanisms. The in vivo anti-inflammatory activity of the phthalides was evaluated in a lipopolysaccharide (LPS)/d-galactosamine (d-GalN)-induced acute hepatitis and liver injury mouse model of acute hepatitis and liver injury. Finally, the toxicity of phthalide toxicity was assessed in zebrafish experiments.

RESULTS

Among the 27 phthalide compounds isolated from A. sinensis, tokinolide B (TB) showed the best Nur77 binding capacity and, the best anti-inflammatory activity, which was induced without apoptosis. In vivo and in vitro experiments showed that TB promoted Nur77 translocation from the nucleus to the mitochondria and interacted with tumor necrosis factor receptor-associated factor 2 (TRAF2) and sequestosome 1 (p62) to induce mitophagy for anti-inflammatory functions. TB substantially inhibited LPS/d-GalN-induced acute hepatitis and liver injury in mice. TB also exhibited significantly lower toxicity than celastrol in zebrafish experiments.

CONCLUSION

These findings suggested that TB inhibits inflammation by promoting Nur77 interaction with TRAF2 and p62, thereby inducing mitophagy. These findings offer promising directions for developing novel anti-inflammatory agents, enhance the understanding of phthalide compounds, and highlight the therapeutic potential of traditional Chinese herbs.

Nur77 as a novel regulator of Paneth cell differentiation and function

Serving as a part of intestinal innate immunity, Paneth cells play an important role in intestinal homeostasis maintenance via their multiple functions. However, the regulation of Paneth cells has been proven to be complex and diverse. Here, we identified nuclear receptor Nur77 as a novel regulator of Paneth cell differentiation and function. Nur77 deficiency led to the loss of Paneth cells in murine ileal crypts. Intestinal tissues or organoids with Nur77 deficiency exhibited the impaired intestinal stem cell niche and failed to enhance antimicrobial peptide expression after Paneth cell degranulation. The defects in Paneth cells and antimicrobial peptides in Nur7-/- mice led to intestinal microbiota disorders. Nur77 deficiency rendered postnatal mice susceptible to necrotizing enterocolitis. Mechanistically, Nur77 transcriptionally inhibited Dact1 expression to activate Wnt signaling activity, thus promoting Paneth cell differentiation and function. Taken together, our data suggest the regulatory role of Nur77 in Paneth cell differentiation and function and reveal a novel Dact1-mediated Wnt inhibition mechanism in Paneth cell development.

Exploring the versatility of miRNA-128: a comprehensive review on its role as a biomarker and therapeutic target in clinical pathways

MicroRNAs (miRNAs/ miRs) are short, noncoding RNAs, usually consisting of 18 to 24 nucleotides, that control gene expression after the process of transcription and have crucial roles in several clinical processes. This article seeks to provide an in-depth review and evaluation of the many activities of miR-128, accentuating its potential as a versatile biomarker and target for therapy; The circulating miR-128 has garnered interest because of its substantial influence on gene regulation and its simplicity in extraction. Several miRNAs, such as miR-128, have been extracted from circulating blood cells, cerebrospinal fluid, and plasma/serum. The miR-128 molecule can specifically target a diverse range of genes, enabling it to have intricate physiological impacts by concurrently regulating many interrelated pathways. It has a vital function in several biological processes, such as modulating the immune system, regulating brain plasticity, organizing the cytoskeleton, and inducing neuronal death. In addition, miR-128 modulates genes associated with cell proliferation, the cell cycle, apoptosis, plasma LDL levels, and gene expression regulation in cardiac development. The dysregulation of miR-128 expression and activity is associated with the development of immunological responses, changes in neural plasticity, programmed cell death, cholesterol metabolism, and heightened vulnerability to autoimmune illnesses, neuroimmune disorders, cancer, and cardiac problems; The paper highlights the importance of studying the consequences of miR-128 dysregulation in these specific locations. By examining the implications of miRNA-128 dysregulation in these areas, the article underscores its significance in diagnosis and treatment, providing a foundation for research and clinical applications.

Nuclear receptor Nur77 regulates immunomechanics of macrophages

Nuclear receptor Nur77 plays a pivotal role in immune regulation across various tissues, influencing pro-inflammatory signaling pathways and cellular metabolism. While cellular mechanics have been implicated in inflammation, the contribution of Nur77 to these mechanical processes remains elusive. Macrophages exhibit remarkable plasticity in their morphology and mechanics, enabling them to adapt and execute essential inflammatory functions, such as navigating through inflamed tissue and pathogen engulfment. However, the precise regulatory mechanisms governing these dynamic changes in macrophage mechanics during inflammation remain poorly understood. To establish the potential correlation of Nur77 with cellular mechanics, we compared bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Nur77-deficient (Nur77-KO) mice and employed cytoskeletal imaging, single-cell acoustic force spectroscopy (AFS), migration and phagocytosis assays, and RNA-sequencing. Our findings reveal that Nur77-KO BMDMs exhibit changes to their actin networks compared to WT BMDMs, which is associated with a stiffer and more rigid phenotype. Subsequent in vitro experiments validated our observations, showcasing that Nur77 deficiency leads to enhanced migration, reduced adhesion, and increased phagocytic activity. The transcriptomics data confirmed altered mechanics-related pathways in Nur77-deficient macrophage that are accompanied by a robust pro-inflammatory phenotype. Utilizing previously obtained ChIP-data, we revealed that Nur77 directly targets differentially expressed genes associated with cellular mechanics. In conclusion, while Nur77 is recognized for its role in reducing inflammation of macrophages by inhibiting the expression of pro-inflammatory genes, our study identifies a novel regulatory mechanism where Nur77 governs macrophage inflammation through the modulation of expression of genes involved in cellular mechanics. Our findings suggest that immune regulation by Nur77 may be partially mediated through alterations in cellular mechanics, highlighting a potential avenue for therapeutic targeting.

Lactic acid induces transcriptional repression of macrophage inflammatory response via histone acetylation

Lactic acid has emerged as an important modulator of immune cell function. It can be produced by both gut microbiota and the host metabolism at homeostasis and during disease states. The production of lactic acid in the gut microenvironment is vital for tissue homeostasis. In the present study, we examined how lactic acid integrates cellular metabolism to shape the epigenome of macrophages during pro-inflammatory response. We found that lactic acid serves as a primary fuel source to promote histone H3K27 acetylation, which allows the expression of immunosuppressive gene program including Nr4a1. Consequently, macrophage pro-inflammatory function was transcriptionally repressed. Furthermore, the histone acetylation induced by lactic acid promotes a form of long-term immunosuppression ("trained immunosuppression"). Pre-exposure to lactic acid induces lipopolysaccharide tolerance. These findings thus indicate that lactic acid sensing and its effect on chromatin remodeling in macrophages represent a key homeostatic mechanism that can provide a tolerogenic tissue microenvironment.

Histone lactylation inhibits RARγ expression in macrophages to promote colorectal tumorigenesis through activation of TRAF6-IL-6-STAT3 signaling

Macrophages are phenotypically and functionally diverse in the tumor microenvironment (TME). However, how to remodel macrophages with a protumor phenotype and how to manipulate them for therapeutic purposes remain to be explored. Here, we show that in the TME, RARγ is downregulated in macrophages, and its expression correlates with poor prognosis in patients with colorectal cancer (CRC). In macrophages, RARγ interacts with tumor necrosis factor receptor-associated factor 6 (TRAF6), which prevents TRAF6 oligomerization and autoubiquitination, leading to inhibition of nuclear factor κB signaling. However, tumor-derived lactate fuels H3K18 lactylation to prohibit RARγ gene transcription in macrophages, consequently enhancing interleukin-6 (IL-6) levels in the TME and endowing macrophages with tumor-promoting functions via activation of signal transducer and activator of transcription 3 (STAT3) signaling in CRC cells. We identified that nordihydroguaiaretic acid (NDGA) exerts effective antitumor action by directly binding to RARγ to inhibit TRAF6-IL-6-STAT3 signaling. This study unravels lactate-driven macrophage function remodeling by inhibition of RARγ expression and highlights NDGA as a candidate compound for treating CRC.

Identification of key genes as potential diagnostic and therapeutic targets for comorbidity of myasthenia gravis and COVID-19

Introduction

Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder. Coronavirus disease 2019 (COVID-19) has a significant impact on the health and quality of life of MG patients and may even trigger the onset of MG in some cases. With the worldwide development of the COVID-19 vaccination, several new-onset MG cases and exacerbations following the COVID-19 vaccines have been acknowledged. The potential link between myasthenia gravis (MG) and COVID-19 has prompted the need for further investigation into the underlying molecular mechanism.

Methods and results

The differential expression analysis identified six differentially expressed genes (DEGs) shared by myasthenia gravis (MG) and COVID-19, namely SAMD9, PLEK, GZMB, JUNB, NR4A1, and NR1D1. The relationship between the six common genes and immune cells was investigated in the COVID-19 dataset. The predictive value of the shared genes was assessed and a nomogram was constructed using machine learning algorithms. The regulatory miRNAs, transcription factors and small molecular drugs were predicted, and the molecular docking was carried out by AutoDock.

Discussion

We have identified six common DEGs of MG and COVID-19 and explored their immunological effects and regulatory mechanisms. The result may provide new insights for further mechanism research.

OTUB1-mediated inhibition of ubiquitination: a growing list of effectors, multiplex mechanisms, and versatile functions

Protein ubiquitination plays a pivotal role in protein homeostasis. Ubiquitination may regulate the stability, activity, protein-protein interaction, and localization of a protein. Ubiquitination is subject to regulation by two groups of counteracting enzymes, the E3 ubiquitin ligases and deubiquitinases. Consistently, deubiquitinases are involved in essentially all biological processes. OTUB1, an OTU-family deubiquitinase, is a critical regulator of development, cancer, DNA damage response, and immune response. OTUB1 antagonizes the ubiquitination of a wide-spectrum of proteins through at least two different mechanisms. Besides direct deubiquitination, OTUB1 can also inhibit ubiquitination by non-canonically blocking ubiquitin transfer from certain ubiquitin-conjugases (E2). In this review, we start with a general background of protein ubiquitination and deubiquitination. Next, we introduce the basic characteristics of OTUB1 and then elaborate on the updated biological functions of OTUB1. Afterwards, we discuss potential mechanisms underlying the versatility and specificity of OTUB1 functions. In the end, we discuss the perspective that OTUB1 can be a potential therapeutic target for cancer.

Oxysophocarpine suppresses TRAF6 level to ameliorate oxidative stress and inflammatory factors secretion in mice with dextran sulphate sodium (DSS) induced-ulcerative colitis

PURPOSE

Ulcerative colitis is an inflammation-related disease with a high recurrence risk. Oxysophocarpine (OSC) is a traditional Chinese medicine isolated from legumes and exerts vital functions on many human diseases. However, the OSC's role in ulcerative colitis has not been fully elucidated. This research aimed to investigate the OSC's impact on ulcerative colitis and its mechanisms.

METHODS

A mouse model of ulcerative colitis was induced by dextran sulphate sodium (DSS). The effect of OSC on ulcerative colitis was examined using Disease Activity Index detection, hematoxylin-eosin (HE) staining, and enzyme-linked immunosorbent assay (ELISA). Meanwhile, the mechanism of OSC in ulcerative colitis was assessed by immunohistochemistry assay, Western blot, HE staining, and ELISA.

RESULTS

For the OSC's function in ulcerative colitis, OSC increased the mice weight, decreased Disease Activity Index scores, and alleviated colitis cell infiltration and epithelial cell destruction in DSS-induced ulcerative colitis. Also, OSC mitigated oxidative stress (decreased PGE2, MPO levels, and increased SOD levels) and inflammation (decreased IL-6, TNF-α and IL-1β levels) in DSS-induced ulcerative colitis. For the OSC's mechanism in ulcerative colitis, OSC inhibited the level of tumor necrosis factor receptor-associated Factor 6 (TRAF6) and the phosphorylation of nuclear factor-κB (NF-κB). TRAF6 overexpression abolished the effect of OSC on DSS-induced colon injury and its associated oxidative stress and inflammatory properties in ulcerative colitis.

CONCLUSION

OSC decreased the TRAF6 level to reduce oxidative stress and inflammatory factors secretion in mice with DSS induced-ulcerative colitis.

Exploring the impact of miR-128 in inflammatory diseases: A comprehensive study on autoimmune diseases

microRNAs (miRNAs) play a crucial role in various biological processes, including immune system regulation, such as cell proliferation, tolerance (central and peripheral), and T helper cell development. Dysregulation of miRNA expression and activity can disrupt immune responses and increase susceptibility to neuroimmune disorders. Conversely, miRNAs have been shown to have a protective role in modulating immune responses and preventing autoimmunity. Specifically, reducing the expression of miRNA-128 (miR-128) in an Alzheimer's disease (AD) mouse model has been found to improve cognitive deficits and reduce neuropathology. This comprehensive review focuses on the significance of miR-128 in the pathogenesis of neuroautoimmune disorders, including multiple sclerosis (MS), AD, Parkinson's disease (PD), Huntington's disease (HD), epilepsy, as well as other immune-mediated diseases such as inflammatory bowel disease (IBD) and rheumatoid arthritis (RA). Additionally, we present compelling evidence supporting the potential use of miR-128 as a diagnostic or therapeutic biomarker for neuroimmune disorders. Collectively, the available literature suggests that targeting miR-128 could be a promising strategy to alleviate the behavioral symptoms associated with neuroimmune diseases. Furthermore, further research in this area may uncover new insights into the molecular mechanisms underlying these disorders and potentially lead to the development of novel therapeutic approaches.

Inhibition of Nur77 expression and translocation by compound B6 reduces ER stress and alleviates cigarette smoke-induced inflammation and injury in bronchial epithelial cells

Chronic obstructive pulmonary disease (COPD) is a leading cause of death worldwide with inflammation and injury in airway epithelial cells. However, few treatment options effectively reduce severity. We previously found that Nur77 is involved in lipopolysaccharide-induced inflammation and injury of lung tissue. Here, we established an in vitro model of COPD-related inflammation and injury in 16-HBE cells induced by cigarette smoke extract (CSE). In these cells, Nur77 expression and localization to the endoplasmic reticulum (ER) increased following CSE treatment, as did ER stress marker (BIP, ATF4, CHOP) expression, inflammatory cytokine expression, and apoptosis. The flavonoid derivative, named B6, which was shown to be a modulator of Nur77 in previous screen, molecular dynamics simulation revealed that B6 binds strongly to Nur77 through hydrogen bonding and hydrophobic interactions. Treating CSE-stimulated 16-HBE cells with B6 resulted in a reduction of both inflammatory cytokine expression and secretion, as well as attenuated apoptosis. Furthermore, B6 treatment resulted in a decrease in Nur77 expression and translocation to the ER, which was accompanied by a concentration-dependent reduction in the expression of ER stress markers. Meanwhile, B6 played a similar role in CSE-treated BEAS-2B cells. These combined effects suggest that B6 could inhibit inflammation and apoptosis in airway epithelial cells after cigarette smoke stimulation, and support its further development as a candidate intervention for treating COPD-related airway inflammation.

Virtual screening-molecular docking-activity evaluation of Ailanthus altissima (Mill.) swingle bark in the treatment of ulcerative colitis

BACKGROUND

The dried bark of Ailanthus altissima (Mill.) Swingle is widely used in traditional Chinese medicine for the treatment of ulcerative colitis. The objective of this study was to explore the therapeutic basis of the dried bark of Ailanthus altissima (Mill.) Swingle for the treatment of ulcerative colitis based on Virtual Screening-Molecular Docking-Activity Evaluation technology.

METHODS

By searching the Traditional Chinese Medicine Systems Pharmacology TCMSP Database and Analysis Platform, 89 compounds were obtained from the chemical components of the dried bark of Ailanthus altissima (Mill.) Swingle. Then, after preliminarily screening the compounds based on Lipinski's rule of five and other relevant conditions, the AutoDock Vina molecular docking software was used to evaluate the affinity of the compounds to ulcerative colitis-related target proteins and their binding modes through use of the scoring function to identify the best candidate compounds. Further verification of the compound's properties was achieved through in vitro experiments.

RESULTS

Twenty-two compounds obtained from the secondary screening were molecularly docked with ulcerative colitis-related target proteins (IL-1R, TLR, EGFR, TGFR, and Wnt) using AutoDock Vina. The free energies of the highest scoring compounds binding to the active cavity of human IL-1R, TLR, EGFR, TGFR, and Wnt proteins were - 8.7, - 8.0, - 9.2, - 7.7, and - 8.5 kcal/mol, respectively. The potential compounds, dehydrocrebanine, ailanthone, and kaempferol, were obtained through scoring function and docking mode analysis. Furthermore, the potential compound ailanthone (1, 3, and 10 µM) was found to have no significant effect on cell proliferation, though at 10 µM it reduced the level of pro-inflammatory factors caused by lipopolysaccharide.

CONCLUSION

Among the active components of the dried bark of Ailanthus altissima (Mill.) Swingle, ailanthone plays a major role in its anti-inflammatory properties. The present study shows that ailanthone has advantages in cell proliferation and in inhibiting of inflammation, but further animal research is needed to confirm its pharmaceutical potential.

Sennoside A restrains TRAF6 level to modulate ferroptosis, inflammation and cognitive impairment in aging mice with Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a common neurodegenerative disease and a momentous cause of dementia in the elderly. Sennoside A (SA) is an anthraquinone compound and possesses decisive protective functions in various human diseases. The purpose of this research was to elucidate the protective effect of SA against AD and investigate its mechanism.

METHODS

Male APPswe/PS1dE9 (APP/PS1) transgenic mice with a C57BL/6J background were chosen as AD model. Age-matched nontransgenic littermates (C57BL/6 mice) were negative controls. SA's functions in AD in vivo were estimated by cognitive function analysis, Western blot, hematoxylin-eosin staining, TUNEL staining, Nissl staining, detection of Fe²⁺ levels, glutathione and malondialdehyde contents, and quantitative real-time PCR. Also, SA's functions in AD in LPS-induced BV2 cells were examined using Cell Counting Kit-8 assay, flow cytometry, quantitative real-time PCR, Western blot, enzyme-linked immunosorbent assay, and analysis of reactive oxygen species levels. Meanwhile, SA's mechanisms in AD were assessed by several molecular experiments.

RESULTS

Functionally, SA mitigated cognitive function, hippocampal neuronal apoptosis, ferroptosis, oxidative stress, and inflammation in AD mice. Furthermore, SA reduced BV2 cell apoptosis, ferroptosis, oxidative stress, and inflammation induced by LPS. Rescue assay revealed that SA abolished the high expressions of TRAF6 and p-P65 (NF-κB pathway-related proteins) induced by AD, and this impact was reversed after TRAF6 overexpression. Conversely, this impact was further enhanced after TRAF6 knockdown.

CONCLUSIONS

SA relieved ferroptosis, inflammation and cognitive impairment in aging mice with AD through decreasing TRAF6.

Distinct transcriptional signatures in purified circulating immune cells drive heterogeneity in disease location in IBD

OBJECTIVE

To infer potential mechanisms driving disease subtypes among patients with inflammatory bowel disease (IBD), we profiled the transcriptome of purified circulating monocytes and CD4 T-cells.

DESIGN

RNA extracted from purified monocytes and CD4 T-cells derived from the peripheral blood of 125 endoscopically active patients with IBD was sequenced using Illumina HiSeq 4000NGS. We used complementary supervised and unsupervised analytical methods to infer gene expression signatures associated with demographic/clinical features. Expression differences and specificity were validated by comparison with publicly available single cell datasets, tissue-specific expression and meta-analyses. Drug target information, druggability and adverse reaction records were used to prioritise disease subtype-specific therapeutic targets.

RESULTS

Unsupervised/supervised methods identified significant differences in the expression profiles of CD4 T-cells between patients with ileal Crohn's disease (CD) and ulcerative colitis (UC). Following a pathway-based classification (Area Under Receiver Operating Characteristic - AUROC=86%) between ileal-CD and UC patients, we identified MAPK and FOXO pathways to be downregulated in UC. Coexpression module/regulatory network analysis using systems-biology approaches revealed mediatory core transcription factors. We independently confirmed that a subset of the disease location-associated signature is characterised by T-cell-specific and location-specific expression. Integration of drug-target information resulted in the discovery of several new (BCL6, GPR183, TNFAIP3) and repurposable drug targets (TUBB2A, PRKCQ) for ileal CD as well as novel targets (NAPEPLD, SLC35A1) for UC.

CONCLUSIONS

Transcriptomic profiling of circulating CD4 T-cells in patients with IBD demonstrated marked molecular differences between the IBD-spectrum extremities (UC and predominantly ileal CD, sandwiching colonic CD), which could help in prioritising particular drug targets for IBD subtypes.

The effects of esketamine on the intestinal microenvironment and intestinal microbiota in mice

OBJECTIVE

This study aimed to investigate the impact of esketamine on the intestinal flora and microenvironment in mice using mRNA transcriptome sequencing and 16S rRNA sequencing.

METHODS

Ten female mice were randomly assigned to two groups. One group received daily intramuscular injections of sterile water, while the other group received esketamine. After 24 days, the mice were sacrificed, and their intestinal tissues and contents were collected for 16S rRNA sequencing and mRNA transcriptome sequencing. The intergroup differences in the mouse intestinal flora were analyzed. Differentially expressed genes were utilized to construct ceRNA networks and transcription factor regulatory networks to assess the effects of esketamine on the intestinal flora and intestinal tissue genes.

RESULTS

Esketamine significantly altered the abundance of intestinal microbiota, including Adlercreutzia equolifaciens and Akkermansia muciniphila. Differential expression analysis revealed 301 significantly upregulated genes and 106 significantly downregulated genes. The ceRNA regulatory network consisted of 6 lncRNAs, 44 miRNAs, and 113 mRNAs, while the regulatory factor network included 13 transcription factors and 53 target genes. Gene Ontology enrichment analysis indicated that the differentially expressed genes were primarily associated with immunity, including B-cell activation and humoral immune response mediation. The biological processes in the ceRNA regulatory network primarily involved transport, such as organic anion transport and monocarboxylic acid transport. The functional annotation of target genes in the TF network was mainly related to epithelial cells, including epithelial cell proliferation and regulation.

CONCLUSION

Esketamine induces changes in gut microbiota and the intestinal microenvironment, impacting the immune environment and transport modes.

NR4A1 modulates intestinal smooth muscle cell phenotype and dampens inflammation-associated intestinal remodeling

Stricture formation is a common complication of Crohn's disease (CD), driven by enhanced deposition of extracellular matrix (ECM) and expansion of the intestinal smooth muscle layers. Nuclear receptor subfamily 4 group A member 1 (NR4A1) is an orphan nuclear receptor that exhibits anti-proliferative effects in smooth muscle cells (SMCs). We hypothesized that NR4A1 regulates intestinal SMC proliferation and muscle thickening in the context of inflammation. Intestinal SMCs isolated from Nr4a1^+/+ and Nr4a1^-/- littermates were subjected to shotgun proteomic analysis, proliferation, and bioenergetic assays. Proliferation was assessed in the presence and absence of NR4A1 agonists, cytosporone-B (Csn-B) and 6-mercaptopurine (6-MP). In vivo, we compared colonic smooth muscle thickening in Nr4a1^+/+ and Nr4a1^-/- mice using the chronic dextran sulfate sodium (DSS) model of colitis. Second, SAMP1/YitFc mice (a model of spontaneous ileitis) were treated with Csn-B and small intestinal smooth muscle thickening was assessed. SMCs isolated from Nr4a1^-/- mice exhibited increased abundance of proteins related to cell proliferation, metabolism, and ECM production, whereas Nr4a1^+/+ SMCs highly expressed proteins related to the regulation of the actin cytoskeleton and contractile processes. SMCs isolated from Nr4a1^-/- mice exhibited increased proliferation and alterations in cellular metabolism, whereas activation of NR4A1 attenuated proliferation. In vivo, Nr4a1^-/- mice exhibited increased colonic smooth muscle thickness following repeated cycles of DSS. Activating NR4A1 with Csn-B, in the context of established inflammation, reduced ileal smooth muscle thickening in SAMP1/YitFc mice. Targeting NR4A1 may provide a novel approach to regulate intestinal SMC phenotype, limiting excessive proliferation that contributes to stricture development in CD.

m6A methyltransferase METTL3 participated in sympathetic neural remodeling post-MI via the TRAF6/NF-κB pathway and ROS production

OBJECTIVE

Sudden cardiac death caused by ventricular arrhythmias (VAs) is the main cause of high mortality in patients with myocardial infarction (MI). Sympathetic neural remodeling caused by inflammation after MI is closely associated with the occurrence of VAs. METTL3, the earliest identified m⁶A methyltransferase, is critical in mediating inflammatory responses. Our aim was to investigate whether the m⁶A methyltransferase METTL3 was involved in sympathetic remodeling post-MI and its specific mechanism.

METHODS AND RESULTS

A rat MI model was established via left coronary artery ligation. The expression of METTL3, TRAF6, NOX2, and NF-κB increased at 3 days and remained elevated at 7 days after MI, as determined via Western blotting. METTL3 was primarily present in macrophages, as determined via immunofluorescence. Intramyocardial injection of lentivirus carrying METTL3-shRNA inhibited METTL3 expression in vivo. Methylated immunoprecipitation-qPCR determined the METTL3 knockdown inhibited the m⁶A level of TRAF6 mRNA 3'-UTR. The co-immunoprecipitation experiment proved that METTL3 combines with TRAF6. Western blotting showed that silencing METTL3 inhibited TRAF6 level, NF-κB activation, and ROS production; decreased cytokine release (TNF-α and IL-1β); and downregulated nerve growth factor expression. Finally, METTL3 knockdown reduced sympathetic remodeling after MI, as determined via immunofluorescence assays of tyrosine hydroxylase and growth-associated protein 43. Programmed electrical stimulation, renal sympathetic nerve activity recording, and haemodynamic measurements showed that METTL3 inhibition decreased sympathetic activity and improved cardiac function.

CONCLUSIONS

Downregulation of METTL3 expression attenuated the excessive sympathetic neural remodeling induced by MI, further reducing the incidence of VAs and improving cardiac function. This was partly associated with the inhibition of the TRAF6/NF-κB pathway and ROS production.

Expression of TRAF6 in peripheral blood B cells of patients with myasthenia gravis

Background

Tumor necrosis factor receptor-associated factor 6 (TRAF6) can regulate the activation of inflammatory signaling pathways by acting as an E3 ubiquitin ligase, which enhances B cell activation. This study aimed to evaluate the expression of TRAF6 in the peripheral blood B cells of myasthenia gravis (MG) patients and analyze the relationships between TRAF6 expression and clinical characteristics.

Method

In our study, the expression level of TRAF6 in peripheral blood B cells of 89 patients was measured by flow cytometry compared with that of healthy subjects. The effects of disease severity, MG classification and immunotherapy on TRAF6 expression level were also analyzed.

Results

In our study, TRAF6 expression was elevated in CD19⁺ B cells and CD19⁺CD27⁺ memory B cells in generalized MG (GMG) patients compared with ocular MG (OMG) patients (p = 0.03 and p = 0.03, respectively). There was a significant positive correlation between the TRAF6 expression level and disease severity in both OMG patients and GMG patients (CD19⁺ B cells: OMG: p < 0.001, r = 0.89; GMG: p = 0.001, r = 0.59; CD29⁺CD27⁺ B cells: OMG: p = 0.001, r = 0.80; GMG: p = 0.048, r = 0.38). TRAF6 expression was significantly elevated in CD19⁺ B cells and CD19⁺CD27⁺ memory B cells in GMG with acute aggravation compared with GMG in MMS (p = 0.009 and p = 0.028, respectively). In the eleven MG patients who were followed, TRAF6 expression in B cells and memory B cells was significantly decreased after treatment (p = 0.03 and p < 0.01, respectively).

Conclusion

TRAF6 is potentially a useful biomarker of inflammation in patients with MG, and might be used to evaluate the effectiveness of treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02833-9.

Essential Roles of the Transcription Factor NR4A1 in Regulatory T Cell Differentiation under the Influence of Immunosuppressants

Calcineurin inhibitors (CNIs), used as immunosuppressants, have revolutionized transplantation medicine with their strong suppressive activity on alloreactive T lymphocytes; however, they may also cause various adverse effects, including an increased risk for infection and nephrotoxicity. Regulatory T (Treg) cells can complement the deleterious side effects of CNIs with their effective Ag-specific suppressive activities. However, several studies have shown that CNIs suppress Treg cell differentiation. Therefore, an understanding of the mechanisms by which CNIs suppress Treg cell differentiation, as well as an approach for promoting the differentiation of Treg cells in the presence of CNIs, has significant clinical value. In this article, we report that the nuclear orphan receptor Nr4a1 plays a pivotal role in Treg cell differentiation in the presence of CNIs. Unlike that of its family members, Nr4a2 and Nr4a3, the expression of Nr4a1 was not suppressed by CNI treatment, thereby mediating Treg cell differentiation in the presence of CNIs. In a mouse allogeneic graft-versus-host disease model, Nr4a1 mediated tolerance by promoting Treg cell differentiation in mice administered cyclosporine A, prolonging the survival of recipients. Furthermore, activation of Nr4a1 via its agonist partially restored Treg cell differentiation, which was suppressed by cyclosporine A treatment. Finally, we found that the rs2701129 single-nucleotide polymorphism, which was shown to downregulate NR4A1 expression, showed a trend toward a higher incidence of chronic graft-versus-host disease in patients undergoing hematopoietic stem cell transplantation. Therefore, our study will be of clinical significance because we demonstrated the role of Nr4a1 in Treg cell differentiation in the presence of CNIs.

Oncogenic potential of BEST4 in colorectal cancer via activation of PI3K/Akt signaling

BEST4 is a member of the bestrophin protein family that plays a critical role in human intestinal epithelial cells. However, its role and mechanism in colorectal cancer (CRC) remain largely elusive. Here, we investigated the role and clinical significance of BEST4 in CRC. Our results demonstrate that BEST4 expression is upregulated in clinical CRC samples and its high-level expression correlates with advanced TNM (tumor, lymph nodes, distant metastasis) stage, LNM (lymph node metastasis), and poor survival. Functional studies revealed that ectopic expression of BEST4 promoted CRC cell proliferation and metastasis, whereas the depletion of BEST4 had the opposite effect both in vitro and in vivo. Mechanistically, BEST4 binds to the p85α regulatory subunit of phosphatidylinositol-3-kinase (PI3K) and promotes p110 kinase activity; this leads to activation of Akt signaling and expression of MYC and CCND1, which are critical regulators of cell proliferation and metastasis. In clinical samples, the expression of BEST4 is positively associated with the expression of phosphorylated Akt, MYC and CCND1. Pharmacological inhibition of Akt activity markedly repressed BEST4-mediated Akt signaling and proliferation and metastasis of CRC cells. Importantly, the interaction between BEST4 and p85α was also enhanced by epidermal growth factor (EGF) in CRC cells. Therapeutically, BEST4 suppression effectively sensitized CRC cells to gefitinib treatment in vivo. Taken together, our findings indicate the oncogenic potential of BEST4 in colorectal carcinogenesis and metastasis by modulating BEST4/PI3K/Akt signaling, highlighting a potential strategy for CRC therapy.

Inflammatory Monocyte Counts Determine Venous Blood Clot Formation and Resolution

BACKGROUND

Monocytes are thought to be involved in venous thrombosis but the role of individual monocyte subpopulations on thrombus formation, clot inflammation, and degradation is an important unresolved issue. We investigate the role of inflammatory Ly6Chi monocytes in deep vein thrombosis and their potential therapeutic impact.

METHODS

Frequencies and compositions of blood monocytes were analyzed by flow cytometry in CCR2-/- (C-C chemokine receptor type 2) and wild-type mice of different ages and after treatment with the NR4A1 (nuclear receptor group 4 family A member 1, Nur77) agonist CnsB (cytosporone B). TF (tissue factor) sufficient and deficient Ly6Chi monocytes were adoptively transferred into aged CCR2-/- mice. Thrombus formation and size were followed by ultrasound over a 3-week period after surgical reduction of blood flow (stenosis) in the inferior vena cava.

RESULTS

Reduced numbers of peripheral monocytes in aged (>30 w) CCR2-/- mice are accompanied by reduced thrombus formation after inferior vena cava ligation. Reducing the number of inflammatory Ly6Chi monocytes in wild-type mice by CsnB treatment before ligation, similarly suspends clotting, while later treatment (d1 or d4) reduces thrombus growth and accelerates resolution. We describe how changes in inflammatory monocyte numbers affect the gradual differentiation of monocytes in thrombi and show that only tissue factor-competent Ly6Chi monocytes restore thrombosis in aged CCR2-/- mice.

CONCLUSIONS

We conclude that the number of inflammatory Ly6Chi monocytes controls deep vein thrombosis formation, growth, and resolution and can be therapeutically manipulated with a NR4A1 agonist at all disease stages.

TRIP6 promotes inflammatory damage via the activation of TRAF6 signaling in a murine model of DSS-induced colitis

Background

TRIP6 is a zyxin family member that serves as an adaptor protein to regulate diverse biological processes. In prior reports, TRIP6 was shown to play a role in regulating inflammation. However, its in vivo roles and mechanistic importance in colitis remain largely elusive. Herein, we therefore employed TRIP6-deficient (TRIP6^−/−) mice in order to explore the mechanistic importance of TRIP6 in a dextran sodium sulfate (DSS)-induced model of murine colitis.

Findings

Wild-type (TRIP6^+/+) mice developed more severe colitis following DSS-mediated disease induction relative to TRIP6^−/− mice, as evidenced by more severe colonic inflammation and associated crypt damage. TRIP6 expression in wild-type mice was significantly elevated following DSS treatment. Mechanistically, TRIP6 binds to TRAF6 and enhances oligomerization and autoubiquitination of TRAF6. This leads to the activation of NF-κB signaling and the expression of pro-inflammatory cytokines such as TNFα and IL-6, in the in vivo mouse model of colitis.

Conclusions

These in vivo data demonstrate that TRIP6 serves as a positive regulator of DSS-induced colitis through interactions with TRAF6 resulting in the activation of inflammatory TRAF6 signaling, highlighting its therapeutic promise as a protein that theoretically can be targeted to prevent or treat colitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12950-021-00298-0.

Cx32 inhibits the autophagic effect of Nur77 in SH-SY5Y cells and rat brain with ischemic stroke

The pathogenesis of cerebral ischemia-reperfusion (I/R) is complex. Cx32 expression has been reported to be up-regulated in ischemic lesions of aged human brain. Nevertheless, the function of Cx32 during cerebral I/R is poorly understood. Autophagy is of vital importance in the pathogenesis of cerebral I/R. In the current study, we found that oxygen-glucose deprivation/reoxygenation (OGD/R) or I/R insult significantly induced the up-regulation of Cx32 and activation of autophagy. Inhibition of Cx32 alleviated OGD/R or I/R injury, and further activated autophagy. In addition, Nur77 expression was found to be up-regulated after OGD/R or I/R. After inhibiting Cx32, the expression of Nur77 was further increased and Nur77 was translocated from nucleus to mitochondrial. Inhibition of Cx32 also activated mitophagy by promoting autophagosome formation and up-regulating the expression of mitochondrial autophagy marker molecules. Of note, in the siNur77-transfected cells, the number of dysfunctional mitochondrial was increased, and mitophagy was suppressed, which aggravated OGD/R-induced neuronal injury. In conclusion, Cx32 might act as a regulatory factor of Nur77 controlling neuronal autophagy in the brains. Understanding the mechanism of this regulatory pathway will provide new insight into the role Cx32 and Nur77 in cerebral ischemia, offering new opportunities for therapeutics.

Nr4A1 modulates inflammation-associated intestinal fibrosis and dampens fibrogenic signaling in myofibroblasts

Intestinal fibrosis is a common complication of the inflammatory bowel diseases (IBDs), contributing to tissue stiffening and luminal narrowing. Human nuclear receptor 4A 1 (NR4A1) was previously reported to regulate mesenchymal cell function and dampen fibrogenic signaling. NR4A1 gene variants are associated with IBD risk, and it has been shown to regulate intestinal inflammation. Here, we tested the hypothesis that NR4A1 acts as a negative regulator of intestinal fibrosis through regulating myofibroblast function. Using the SAMP1/YitFc mouse, we tested whether two pharmacological agents known to enhance NR4A1 signaling, cytosporone B (Csn-B) or 6-mercaptopurine (6-MP), could reduce fibrosis. We also used the dextran sulfate sodium (DSS) model of colitis and assessed the magnitude of colonic fibrosis in mouse nuclear receptor 4A 1 (Nr4a1^-/-) and their wild-type littermates (Nr4a1^+/+). Lastly, intestinal myofibroblasts isolated from Nr4a1^-/- and Nr4a1^+/+ mice or primary human intestinal myofibroblasts were stimulated with transforming growth factor-β1 (TGF-β1), in the presence or absence of Csn-B or 6-MP, and proliferation and ECM gene expression assessed. Csn-B or 6-MP treatment significantly reduced ileal thickness, collagen, and overall ECM content in SAMP1/YitFc mice. This was associated with a reduction in proliferative markers within the mesenchymal compartment. Nr4a1^-/- mice exposed to DSS exhibited increased colonic thickening and ECM content. Nr4a1^-/- myofibroblasts displayed enhanced TGF-β1-induced proliferation. Furthermore, Csn-B or 6-MP treatment was antiproliferative in Nr4a1^+/+ but not Nr4a1^-/- cells. Lastly, activating NR4A1 in human myofibroblasts reduced TGF-β1-induced collagen deposition and fibrosis-related gene expression. Our data suggest that NR4A1 can attenuate fibrotic processes in intestinal myofibroblasts and could provide a valuable clinical target to treat inflammation-associated intestinal fibrosis.NEW & NOTEWORTHY Fibrosis and increased muscle thickening contribute to stricture formation and intestinal obstruction, a complication that occurs in 30%-50% of patients with CD within 10 yr of disease onset. More than 50% of those who undergo surgery to remove the obstructed bowel will experience stricture recurrence. To date, there are no drug-based approaches approved to treat intestinal strictures. In the current submission, we identify NR4A1 as a novel target to treat inflammation-associated intestinal fibrosis.

Nuclear receptor Nur77: its role in chronic inflammatory diseases

Nur77 is a nuclear receptor that has been implicated as a regulator of inflammatory disease. The expression of Nur77 increases upon stimulation of immune cells and is differentially expressed in chronically inflamed organs in human and experimental models. Furthermore, in a variety of animal models dedicated to study inflammatory diseases, changes in Nur77 expression alter disease outcome. The available studies comprise a wealth of information on the function of Nur77 in diverse cell types and tissues. Negative cross-talk of Nur77 with the NFκB signaling complex is an example of Nur77 effector function. An alternative mechanism of action has been established, involving Nur77-mediated modulation of metabolism in macrophages as well as in T cells. In this review, we summarize our current knowledge on the role of Nur77 in atherosclerosis, inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and sepsis. Detailed insight in the control of inflammatory responses will be essential in order to advance Nur77-targeted therapeutic interventions in inflammatory disease.

The role of nuclear receptor 4A1 (NR4A1) in drug-induced gingival overgrowth

Drug-induced gingival overgrowth (DIGO) is a side effect of cyclosporine A (CsA), nifedipine (NIF), and phenytoin (PHT). Nuclear receptor 4A1 (NR4A1) plays a role in fibrosis in multiple organs. However, the relationship between NR4A1 and DIGO remains unclear. We herein investigated the involvement of NR4A1 in DIGO. In the DIGO mouse model, CsA inhibited the up-regulation of Nr4a1 expression induced by periodontal disease (PD) in gingival tissue, but not that of Col1a1 and Pai1. We detected gingival overgrowth (GO) in Nr4a1 knock out (KO) mice with PD. A NR4A1 agonist inhibited the development of GO in DIGO model mice. TGF-β increased Col1a1 and Pai1 expression levels in KO mouse gingival fibroblasts (mGF) than in wild-type mice, while the overexpression of NR4A1 in KO mGF suppressed the levels. NR4A1 expression levels in gingival tissue were significantly lower in DIGO patients than in PD patients. We also investigated the relationship between nuclear factor of activated T cells (NFAT) and NR4A1. NFATc3 siRNA suppressed the TGF-β-induced up-regulation of NR4A1 mRNA expression in human gingival fibroblasts (hGF). CsA suppressed the TGF-β-induced translocation of NFATc3 into the nuclei of hGF. Furthermore, NIF and PHT also decreased NR4A1 mRNA expression levels and suppressed the translocation of NFATc3 in hGF. We confirmed that CsA, NIF, and PHT reduced cytosolic calcium levels increased by TGF-β, while CaCl₂ enhanced the TGF-β-up-regulated NR4A1 expression. We propose that the suppression of the calcium-NFATc3-NR4A1 cascade by these three drugs plays a role in the development of DIGO.

Novel NR4A1 Arg293Ser Mutation in Patients With Familial Crohn's Disease

BACKGROUND/AIM

The underlying etiology of Crohn's disease remains unknown. The aim of this study was to identify genomic alterations associated with the development of Crohn's disease in one Japanese family with a family history of Crohn's disease.

MATERIALS AND METHODS

We performed whole-exome sequence and pedigree analysis of a Japanese family in which both sisters developed Crohn's disease. Whole-exome sequencing was performed using the Ion Torrent Proton™ system. Data from the Proton runs were initially processed using the Ion Torrent platform-specific pipeline software Ion Reporter. An autosomal dominant mode of inheritance was assumed, and stringent selection criteria were applied.

RESULTS

A substitution in the NR4A1 gene at codon 293 resulting in an amino acid change from arginine to serine was identified only in the affected sisters.

CONCLUSION

The impaired DNA-binding capacity of the NR4A1 protein due to an NR4A1 germline mutation may be a possible cause of Crohn's disease.

MiR-128-3p alleviates TNBS-induced colitis through inactivating TRAF6/NF-κB signaling pathway in rats

miR-128-3p is reported to involve in pathogenesis of several autoimmune diseases, yet the role of miR-128-3p in inflammatory bowel disease (IBD) remains unknown. To investigate miR-128-3p in IBD, experimental colitis animal model was generated by 2,4,6-Trinitrobenzenesulfonic acid solution (TNBS). miR-128-3p agomir was used to overexpress miR-128-3p in rats. Histological assessment and myeloperoxidase activity were conducted to evaluate the TNBS-induced colitis. Effect of miR-128-3p overexpression on levels of TNF-α, IL-1β, ICAM-1, and MCP-1 was tested by ELISA assay. The target of miR-128-3p was predicted and further confirmed by dual-luciferase reporter assay. The expressions of TRAF6, p-NF-κB, and NF-κB were determined by western blot. The miR-128-3p level was significantly decreased in rats with TNBS-induced colitis. miR-128-3p could alleviate TNBS-induced colitis and inhibit production of inflammatory factors. We found TRAF6 was a direct target of miR-128-3p using bioinformatics and luciferase assay. By western blot, we discovered miR-128-3p activates NF-κB by targeting TRAF6. Our data reveal a novel mechanism that a decreased miR-128-3p level in TNBS-induced colitis could inhibit production of inflammatory factors, which activates NF-κB signaling by targeting TRAF6. Our findings might provide a novel therapeutic target for drug design and development for IBD therapeutics.

The NR4A agonist, Cytosporone B, attenuates pro-inflammatory mediators in human colorectal cancer tissue ex vivo

Inflammation is a pivotal pathological factor in colorectal cancer (CRC) initiation and progression, and modulating this inflammatory state has the potential to ameliorate disease progression. NR4A receptors have emerged as key regulators of inflammatory pathways that are important in CRC. Here, we have examined the effect of NR4A agonist, Cytosporone B (CsnB), on colorectal tissue integrity and its effect on the inflammatory profile in CRC tissue ex vivo. Here, we demonstrate concentrations up 100 μM CsnB did not adversely affect tissue integrity as measured using transepithelial electrical resistance, histology and crypt height. Subsequently, we reveal through the use of a cytokine/chemokine array, ELISA and qRT-PCR analysis that multiple pro-inflammatory mediators were significantly increased in CRC tissue compared to control tissue, which were then attenuated with the addition of CsnB (such as IL-1β, IL-8 and TNFα). Lastly, stratification of the data revealed that CsnB especially alters the inflammatory profile of tumours derived from males who had not undergone chemoradiotherapy. Thus, this study demonstrates that NR4A agonist CsnB does not adversely affect colon tissue structure or functionality and can attenuate the pro-inflammatory state of human CRC tissue ex vivo.

Posttranslational modifications as therapeutic targets for intestinal disorders

A variety of biological processes are regulated by posttranslational modifications. Posttranslational modifications including phosphorylation, ubiquitination, glycosylation, and proteolytic cleavage, control diverse physiological functions in the gastrointestinal tract. Therefore, a better understanding of their implications in intestinal diseases, including inflammatory bowel disease, irritable bowel syndrome, celiac disease, and colorectal cancer would provide a basis for the identification of novel biomarkers as well as attractive therapeutic targets. Posttranslational modifications can be common denominators, as well as distinct biomarkers, characterizing pathological differences of various intestinal diseases. This review provides experimental evidence that identifies changes in posttranslational modifications from patient samples, primary cells, or cell lines in intestinal disorders, and a summary of carefully selected information on the use of pharmacological modulators of protein modifications as therapeutic options.

Roles of protein ubiquitination in inflammatory bowel disease

Inflammatory bowel disease (IBD) including Crohn's disease (CD) and ulcerative colitis (UC) seriously affects the quality of life for patients. The pathogenesis of IBD contains the environmental, host genetic and epigenetic factors. In recent years, the studies of protein ubiquitination, an important protein post-translational modification as an epigenetic factor, have emerged in the pathogenesis and development of IBD. In the past few years, accumulative evidence illustrated that six E3 ubiquitin ligases, namely, ring finger protein (RNF) 183, RNF 20, A20, Pellino 3, TRIM62 and Itch, exhibited clear mechanisms in the development of IBD. They regulate the intestinal inflammation by facilitating the ubiquitination of targeted proteins which participate in different inflammatory signaling pathways. Besides, it was reported that some deubiquitinating enzymes such as Cylindromatosis and USP7 were involved in the development of IBD, but the molecular mechanism was still unclear. This review summarized the role and regulatory mechanism of protein ubiquitination in the pathogenesis and development of IBD, providing insights to develop a new therapeutic strategy in IBD treatments.

'Nur'turing tumor T cell tolerance and exhaustion: novel function for Nuclear Receptor Nur77 in immunity

The nuclear receptor Nur77 is expressed in a multitude of tissues, regulating cell differentiation and homeostasis. Dysregulation of Nur77 signaling is associated with cancer, cardiovascular disease, and disorders of the CNS. The role of Nur77 in T cells has been studied for almost 30 years now. There is a clear appreciation that Nur77 is crucial for apoptosis of self‐reactive T cells. However, the regulation and function of Nur77 in mature T cells remains largely unclear. In an exciting development, Nur77 has been recently demonstrated to impinge on cancer immunotherapy involving chimeric antigen receptor (CAR) T cells and tumor infiltrating lymphocytes (TILs). These studies indicated that Nur77 deficiency reduced T cell tolerance and exhaustion, thus raising the effectiveness of immune therapy in mice. Based on these novel insights, it may be proposed that regulation of Nur77 activity holds promise for innovative drug development in the field of cellular immunotherapy in cancer. In this review, we therefore summarize the role of Nur77 in T cell selection and maturation; and further develop the idea of targeting its activity in these cells as a potential strategy to augment current cancer immunotherapy treatments.

GPA peptide enhances Nur77 expression in intestinal epithelial cells to exert a protective effect against DSS-induced colitis

Ulcerative colitis (UC) is a widespread inflammatory bowel disease that causes long-lasting inflammation and ulcers in the colon and rectum. In the inflamed tissue of patients with UC, the tight junctions are disrupted and large amounts of pro-inflammatory cytokines are produced, resulting in immune dysregulation. The expression of Nur77 is significantly reduced in the colon of inflammatory bowel disease, while Nur77 deficiency increases the susceptibility to DSS-induced colitis. Here, we report that Gly-Pro-Ala (GPA) peptide isolated from fish skin gelatin hydrolysate can significantly alleviate intestinal inflammation and damage caused by DSS-induced mice colitis. Besides maintaining the intestinal epithelial barrier, GPA alleviates intestinal inflammation and oxidative stress by inhibiting NF-κB activation. Interestingly, GPA binds to the ligand-binding domain of Nur77 and stimulates its autotranscriptional activity to enhance its expression in intestinal epithelial cells. Furthermore, GPA activates the promoter of IκBα to increase its expression, resulting in the abolishment of the NF-κB pathway. In contrast, the inhibitory effects of GPA on colitis are abolished in Nur77^-/- mice. Our results suggest that as a Nur77 modulator, GPA may be applied to the prevention of intestinal inflammation.

GPA Peptide-Induced Nur77 Localization at Mitochondria Inhibits Inflammation and Oxidative Stress through Activating Autophagy in the Intestine

Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), is a chronic inflammatory disease affecting the colon, and its incidence is rising worldwide. Nur77, belongs to the NR4A subfamily of nuclear hormone receptors, plays a critical role in controlling the pathology of colitis. The aim of this study is to investigate the protection effect and mechanism of Gly-Pro-Ala (GPA) peptide, isolated from fish skin gelatin hydrolysate, in a mouse model of dextran sulfate sodium- (DSS-) induced colitis and intestinal epithelial cells (IECs) stimulated by lipopolysaccharide (LPS). In vivo, GPA treatment alleviates DSS-induced weight loss, disease activity index (DAI) increase, colon length shortening, and colonic pathological damage. Production of proinflammatory cytokines, ROS, and MDA is significantly decreased by GPA treatment. In vitro, GPA significantly inhibits proinflammatory cytokine production, cytotoxicity, ROS, and MDA in IECs. Furthermore, GPA induces autophagy to suppress inflammation and oxidative stress. GPA promotes Nur77 translocation from the nucleus to mitochondria where it facilitates Nur77 interaction with TRAF6 and p62, leading to the induction of autophagy. In addition, GPA contributed to the maintenance of tight junction architecture in vivo and in vitro. Taken together, GPA, as a Nur77 modulator, could exert anti-inflammatory and antioxidant effects by inducing autophagy in IECs, suggesting that GPA may be promising for the prevention of colitis.

Calcipotriol and iBRD9 reduce obesity in Nur77 knockout mice by regulating the gut microbiota, improving intestinal mucosal barrier function

Objective

The orphan nuclear receptor Nur77 is an important factor regulating metabolism. Nur77 knockout mice become obese with age, but the cause of obesity in these mice has not been fully ascertained. We attempted to explain the cause of obesity in Nur77 knockout mice from the perspective of the gut microbiota and to investigate the inhibitory effect of calcipotriol combined with BRD9 inhibitor (iBRD9) on obesity.

Methods

Eight-week-old wild-type mice and Nur77 knockout C57BL/6J mice were treated with calcipotriol combined with iBRD9 for 12 weeks. Mouse feces were collected and the gut microbiota was assessed by analyzing 16S rRNA gene sequences. The bacterial abundance difference was analyzed, and the intestinal mucosal tight junction protein, antimicrobial peptide, and inflammatory cytokine mRNA levels of the colon and serum LPS and inflammatory cytokine levels were measured.

Results

Calcipotriol combined with iBRD9 treatment reduced the body weight and body fat percentage in Nur77 knockout mice. In the gut microbiota of Nur77 knockout mice, the relative abundances of Lachnospiraceae and Prevotellaceae decreased, and Rikenellaceae increased; while Rikenellaceae decreased after treatment (p < 0.05). Correspondingly, the mRNA levels of intestinal mucosal tight junction proteins (occludin (Ocln), claudin3 (Cldn3)) in the colons of Nur77 knockout mice were significantly decreased, and they increased significantly after treatment (p < 0.001). The mRNA levels of inflammatory cytokines (tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β)) were significantly increased in Nur77 knockout mice, and TNF-α and IL-6 levels were significantly decreased after treatment (p < 0.05, <0.01, or <0.001). The levels of serum LPS, TNF-α, and IL-1β in Nur77 knockout mice were significantly increased (p < 0.05). Serum LPS, TNF-α, and IL-6 levels were significantly decreased after treatment (p < 0.05 or <0.01).

Conclusions

Calcipotriol combined with iBRD9 can regulate the gut microbiota, improve intestinal mucosal barrier function, reduce LPS absorption into the blood, and alleviate obesity in Nur77 knockout mice.

A miR-146a-5p/TRAF6/NF-kB p65 axis regulates pancreatic cancer chemoresistance: functional validation and clinical significance

Background: Dysregulated microRNA (miRNA) expression in cancer can act as a key factor that modifies biological processes, including chemoresistance. Our study aimed to identify the miRNAs associated with gemcitabine (GEM) resistance in pancreatic ductal adenocarcinoma (PDAC) and to explore the potential mechanisms. Methods: The miRNA microarray was used to identify miRNAs associated with GEM resistance. Quantitative real-time PCR was used to examine miR-146a-5p expression in paired PDAC and adjacent normal tissues. Bioinformatics analysis, luciferase reporter assays, and chromatin immunoprecipitation assays were used to confirm tumor necrosis factor receptor-associated factor 6 (TRAF6) as a direct target of miR-146a-5p and to explore the potential transcription factor binding and regulation by miR-146a-5p. In vitro and in vivo experiments were performed to investigate the mechanisms. Results: MiR-146a-5p expression was significantly decreased in PDAC tissues compared with adjacent normal tissues, and miR-146a-5p expression correlated with prognosis in PDAC patients. Functional studies indicated that miR-146a-5p suppressed PDAC cell proliferation and sensitized PDAC cells to GEM chemotherapy by targeting the 3'-untranslated region (3'-UTR) of TRAF6. MiR-146a-5p was also observed to downregulate the TRAF6/NF-κB p65/P-gp axis, which regulates PDAC cell growth and chemoresistance. Conclusions: Taken together, the results indicate that the miR-146a-5p/TRAF6/NF-κB p65 axis drives pancreatic chemoresistance by regulating P-gp, suggesting that miR-146a-5p may be utilized as a new therapeutic target and prognostic marker in PDAC patients.

Cigarette smoke downregulates Nur77 to exacerbate inflammation in chronic obstructive pulmonary disease (COPD)

Cigarette smoke (CS) contains multiple gaseous and particulate materials that can cause lung inflammation, and smoking is the major cause of chronic obstructive pulmonary disease (COPD). We sought to determine the mechanisms of how CS triggers lung inflammation. Nur77, a nuclear hormone receptor belonging to the immediate-early response gene family, controls inflammatory responses, mainly by suppressing the NF-κB signaling pathway. Because it is unknown if Nur77's anti-inflammatory role modulates COPD, we assessed if and how Nur77 expression and activity are altered in CS-induced airway inflammation. In lung tissues and bronchial epithelial cells from COPD patients, we found Nur77 was downregulated. In a murine model of CS-induced airway inflammation, CS promoted lung inflammation and also reduced Nur77 activity in wild type (WT) mice, whereas lungs of Nur77-deficient mice showed exaggerated CS-induced inflammatory responses. Our findings in in vitro studies of human airway epithelial cells complemented those in vivo data in mice, together showing that CS induced threonine-phosphorylation of Nur77, which is known to interfere with its anti-inflammatory functions. In summary, our findings point to Nur77 as an important regulator of CS-induced inflammatory responses and support the potential benefits of Nur77 activation for COPD treatment.

Tumor Necrosis Factor Receptor-Associated Factor 6 Promotes Hepatocarcinogenesis by Interacting With Histone Deacetylase 3 to Enhance c-Myc Gene Expression and Protein Stability

The oncogene c-Myc is aberrantly expressed and plays a key role in malignant transformation and progression of hepatocellular carcinoma (HCC). Here, we report that c-Myc is significantly up-regulated by tumor necrosis factor receptor-associated factor 6 (TRAF6), an E3 ubiquitin ligase, in hepatocarcinogenesis. High TRAF6 expression in clinical HCC samples correlates with poor prognosis, and the loss of one copy of the Traf6 gene in Traf6^+/- mice significantly impairs liver tumorigenesis. Mechanistically, TRAF6 first interacts with and ubiquitinates histone deacetylase 3 (HDAC3) with K63-linked ubiquitin chains, which leads to the dissociation of HDAC3 from the c-Myc promoter and subsequent acetylation of histone H3 at K9, thereby epigenetically enhancing the mRNA expression of c-Myc. Second, the K63-linked ubiquitination of HDAC3 impairs the HDAC3 interaction with c-Myc and promotes c-Myc protein acetylation, which thereby enhances c-Myc protein stability by inhibiting carboxyl terminus of heat shock cognate 70-kDa-interacting protein-mediated c-Myc ubiquitination and degradation. Importantly, TRAF6/HDAC3/c-Myc signaling is also primed in hepatitis B virus-transgenic mice, unveiling a critical role for a mechanism in inflammation-cancer transition. In clinical specimens, TRAF6 positively correlates with c-Myc at both the mRNA and protein levels, and high TRAF6 and c-Myc expression is associated with an unfavorable prognosis, suggesting that TRAF6 collaborates with c-Myc to promote human hepatocarcinogenesis. Consistently, curbing c-Myc expression by inhibition of TRAF6 activity with a TRAF6 inhibitor peptide or the silencing of c-Myc by small interfering RNA significantly suppressed tumor growth in mice. Conclusion: These findings demonstrate the oncogenic potential of TRAF6 during hepatocarcinogenesis by modulating TRAF6/HDAC3/c-Myc signaling, with potential implications for HCC therapy.

Glucocorticoids Oppose Thymocyte Negative Selection by Inhibiting Helios and Nur77

Glucocorticoid (GC) signaling in thymocytes shapes the TCR repertoire by antagonizing thymocyte negative selection. The transcription factors Nur77 and Helios, which are upregulated in TCR-signaled thymocytes, have been implicated in negative selection. In this study, we found that GCs inhibited Helios and, to a lesser extent, Nur77 upregulation in TCR-stimulated mouse thymocytes. Inhibition was increased by GC preincubation, and reductions in mRNA were prevented by a protein synthesis inhibitor, suggesting that GCs suppress indirectly via an intermediary factor. Upregulation of Helios in TCR-stimulated thymocytes was unaffected by deletion of Nur77, indicating Nur77 and Helios are regulated independently. Whereas CD4⁺ thymocytes are positively selected in wild-type AND TCR-transgenic B6 mice, loss of GC receptor expression resulted in increased negative selection. Correspondingly, Helios and Nur77 levels were elevated in TCR^hiCD4⁺CD8⁺ (TCR-signaled) thymocytes. Notably, deletion of Helios fully reversed this negative selection, whereas deletion of Nur77 had no effect on CD4⁺CD8⁺ cell numbers but reversed the loss of mature CD4⁺ thymocytes. Thus, Nur77 and Helios are GC targets that play nonredundant roles in setting the signaling threshold for thymocyte negative selection.

Nuclear Receptors Regulate Intestinal Inflammation in the Context of IBD

Gastrointestinal (GI) homeostasis is strongly dependent on nuclear receptor (NR) functions. They play a variety of roles ranging from nutrient uptake, sensing of microbial metabolites, regulation of epithelial intestinal cell integrity to shaping of the intestinal immune cell repertoire. Several NRs are associated with GI pathologies; therefore, systematic analysis of NR biology, the underlying molecular mechanisms, and regulation of target genes can be expected to help greatly in uncovering the course of GI diseases. Recently, an increasing number of NRs has been validated as potential drug targets for therapeutic intervention in patients with inflammatory bowel disease (IBD). Besides the classical glucocorticoids, especially PPARγ, VDR, or PXR-selective ligands are currently being tested with promising results in clinical IBD trials. Also, several pre-clinical animal studies are being performed with NRs. This review focuses on the complex biology of NRs and their context-dependent anti- or pro-inflammatory activities in the regulation of gastrointestinal barrier with special attention to NRs already pharmacologically targeted in clinic and pre-clinical IBD treatment regimens.

Oncogenic potential of truncated RXRα during colitis-associated colorectal tumorigenesis by promoting IL-6-STAT3 signaling

Retinoid X receptor-alpha (RXRα) is a potent regulator of inflammatory responses; however, its therapeutic potential for inflammatory cancer remains to be explored. We previously discovered that RXRα is abnormally cleaved in tumor cells and tissues, producing a truncated RXRα (tRXRα). Here, we show that transgenic expression of tRXRα in mice accelerates the development of colitis-associated colon cancer (CAC). The tumorigenic effect of tRXRα is primarily dependent on its expression in myeloid cells, which results in interleukin-6 (IL-6) induction and STAT3 activation. Mechanistic studies reveal an extensive interaction between tRXRα and TRAF6 in the cytoplasm of macrophages, leading to TRAF6 ubiquitination and subsequent activation of the NF-κB inflammatory pathway. K-80003, a tRXRα modulator derived from nonsteroidal anti-inflammatory drug (NSAID) sulindac, suppresses the growth of tRXRα-mediated colorectal tumor by inhibiting the NF-κB-IL-6-STAT3 signaling cascade. These results provide new insight into tRXRα action and identify a promising tRXRα ligand for treating CAC.

Ovarian tumor domain-containing ubiquitin aldehyde binding protein 1 inhibits inflammation by regulating Nur77 stability

Nur77 (NR4A1) plays an important role in various inflammatory responses. Nur77 is rapidly degraded in cells and its protein level is critically controlled. Although few E3 ligases regulating the Nur77 protein have been defined, the deubiquitinase (DUB) responsible for Nur77 stability has not been reported to date. We identified ovarian tumor domain-containing ubiquitin aldehyde binding protein 1 (OTUB1) as a DUB that stabilizes Nur77 by preventing its proteasomal degradation. We found that OTUB1 interacted with Nur77 to deubiquitinate it, thereby stabilizing Nur77 in an Asp88-dependent manner. This suggests that OTUB1 targets Nur77 for deubiquitination via a non-canonical mechanism. Functionally, OTUB1 inhibited TNFα-induced IL-6 production by promoting Nur77 protein stability. OTUB1 modulated the stability of Nur77 as a counterpart of tripartite motif 13 (Trim13). That is, OTUB1 reduced the ubiquitination and degradation of Nur77 potentiated by Trim13. In addition, this DUB also inhibited IL-6 production, which was further amplified by Trim13 in TNFα-induced responses. These findings suggest that OTUB1 is an important regulator of Nur77 stability and plays a role in controlling the inflammatory response.

TRAF6 inhibits colorectal cancer metastasis through regulating selective autophagic CTNNB1/β-catenin degradation and is targeted for GSK3B/GSK3β-mediated phosphorylation and degradation

Aberrant CTNNB1 signaling is one of the fundamental processes in cancers, especially colorectal cancer (CRC). Here, we reported that TRAF6, an E3 ubiquitin ligase important for inflammatory signaling, inhibited epithelial-mesenchymal transition (EMT) and CRC metastasis through driving a selective autophagic CTNNB1 degradation machinery. Mechanistically, TRAF6 interacted with MAP1LC3B/LC3B through its LC3-interacting region 'YxxL' and catalyzed K63-linked polyubiquitination of LC3B. The K63-linked ubiquitination of LC3B promoted the formation of the LC3B-ATG7 complex and was critical to the subsequent recognition of CTNNB1 by LC3B for the selective autophagic degradation. However, TRAF6 was phosphorylated at Thr266 by GSK3B in most clinical CRC, which triggered K48-linked polyubiquitination and degradation of TRAF6 and thereby attenuated its inhibitory activity towards the autophagy-dependent CTNNB1 signaling. Clinically, decreased expression of TRAF6 was associated with elevated GSK3B protein levels and activity and reduced overall survival in CRC patients. Pharmacological inhibition of GSK3B activity stabilized the TRAF6 protein, promoted CTNNB1 degradation, and effectively suppressed EMT and CRC metastasis. Thus, targeting TRAF6 and its pathway may be meaningful for treating advanced CRC. Abbreviations: AMBRA1: autophagy and beclin 1 regulator 1; AOM: azoxymethane; ATG5: autophagy related 5; ATG7: autophagy related 7; Baf A1: bafilomycin A₁; BECN1: beclin 1; CoIP: co-immunoprecipitation; CQ: chloroquine; CRC: colorectal cancer; CTNNB1/β-catenin: catenin beta 1; DSS: dextran sodium sulfate; EMT: epithelial-mesenchymal transition; FBS: fetal bovine serum; GFP: green fluorescent protein; GSK3B/GSK3β: glycogen synthase kinase 3 beta; IgG: Immunoglobulin G; IHC: immunohistochemistry; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; RFP: red fluorescent protein; RT: room temperature; shRNA: short hairpin RNA; siRNA: small interfering RNA; TRAF6: TNF receptor-associated factor 6; WT: wild-type; ZEB1: zinc finger E-box binding homeobox 1.

Nuclear Receptors in the Pathogenesis and Management of Inflammatory Bowel Disease

Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the transcription of target genes. Previous epidemiological and genetic studies have documented the association of NRs with the risk of inflammatory bowel disease (IBD). Although the mechanisms of action of NRs in IBD have not been fully established, accumulating evidence has demonstrated that NRs play complicated roles in regulating intestinal immunity, mucosal barriers, and intestinal flora. As one of the first-line medications for the treatment of IBD, 5-aminosalicylic acid (5-ASA) activates peroxisome proliferator-activated receptor gamma (PPARγ) to attenuate colitis. The protective roles of rifaximin and rifampicin partly depend on promoting pregnane X receptor (PXR) expression. The aims of this review are to discuss the roles of several important NRs, such as PPARγ, PXR, vitamin D receptor (VDR), farnesoid X receptor (FXR), and RAR-related orphan receptor gammat (RORγt), in the pathogenesis of IBD and management strategies based on targeting these receptors.

Caspase-1-dependent mechanism mediating the harmful impacts of the quorum-sensing molecule N-(3-oxo-dodecanoyl)-l-homoserine lactone on the intestinal cells

N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C12-HSL), a quorum-sensing (QS) molecule produced by Gram-negative bacteria in the gastrointestinal tract, adversly impacts host cells. Our previous study demonstrated that 3-oxo-C12-HSL induced a decrease in cell viability via cell apoptosis and eventually disrupted mucin synthesis from LS174T goblet cells. However, the molecular mechanism underlying cell apoptosis and whether pyroptosis was involved in this process are still unknown. In this study, we emphasized on the caspases signal pathway and sterile inflammation to reveal the harmful effects of 3-oxo-C12-HSL on LS174T goblet cells. Our data showed that 3-oxo-C12-HSL is a major inducer of oxidative stress indicated by a high level of intracellular reactive oxygen species (ROS). However, TQ416, an inhibitor of paraoxonase 2, can effectively block oxidative stress. A higher ROS level is the trigger for activating the caspase-1 and 3 cascade signal pathways. Blockade of ROS synthesis and caspase-1 and 3 cascades can obviously rescue the viability of LS174T cells after 3-oxo-C12-HSL treatment. We also found that paralleled with a higher level of ROS and caspases activation, an abnormal expression of proinflammatory cytokines was induced by 3-oxo-C12-HSL treatment; however, the blockage of TLRs-NF-κB pathway cannot restore cell viability and secretary function. These data collectively indicate that 3-oxo-C12-HSL exposure induces damages to cell viability and secretary function of LS174T goblet cells, which is mediated by oxidative stress, cell apoptosis, and sterile inflammation. Overall, the data in this study will provide a better understanding of the harmful impacts of some QS molecules on host cells and their underlying mechanism.