Nuclear Receptor Nur77 Attenuates Airway Inflammation in Mice by Suppressing NF-κB Activity in Lung Epithelial Cells

HPGD: An Intermediate Player in Microglial Polarization and Multiple Sclerosis Regulated by Nr4a1

HPGD encodes 15-Hydroxyprostaglandin dehydrogenase catalyzing the decomposition of prostaglandin E2 and has not been reported in multiple sclerosis (MS). We previously found that Nr4a1 regulated microglia polarization and inhibited the progression of experimental autoimmune encephalomyelitis (EAE). Bioinformatics analysis suggested that HPGD might be regulated by Nr4a1. Therefore, this study aimed to explore the role of HPGD in microglia polarization and determine whether HPGD mediates the inhibition of EAE by Nr4a1. C57BL/6 mice were treated with MOG35-55 peptide to induce EAE. BV-2 cells were treated with LPS/IL-4 to induce M1/M2 polarization. We then analyzed the pathological changes of spinal cord tissue, detected the expression levels of M1/M2 genes in tissues and cells, and explored the effect of HPGD on PPARγ activation to clarify the role of HPGD in EAE. The interaction between HPGD and Nr4a1 was verified by ChIP and pull-down assay. HPGD was downregulated in the spinal cord of EAE mice and HPGD overexpression alleviated the progression of EAE. Experiments in vitro and in vivo revealed that HPGD inhibited M1 polarization, promoted M2 polarization and increased PPARγ-DNA complex level. Nr4a1 could bind to the promoter of HPGD and its overexpression increased HPGD level. HPGD overexpression (or knockdown) reversed the effect of Nr4a1 knockdown (or overexpression) on M1/2 polarization. HPGD is regulated by Nr4a1 and inhibits the progression of EAE through shifting the M1/M2 polarization and promoting the activation of PPARγ signaling pathway. This study provides potential targets and basis for the development of MS therapeutic drugs.

Lung Gene Expression Suggests Roles for Interferon-Stimulated Genes and Adenosine Deaminase Acting against RNA-1 in Pathologic Responses to Diisocyanate

Mechanisms underlying methylene diphenyl diisocyanate (MDI) and other low molecular weight chemical-induced asthma are unclear and appear distinct from those of high molecular weight (HMW) allergen-induced asthma. We sought to elucidate molecular pathways that differentiate asthma-like pathogenic vs nonpathogenic responses to respiratory tract MDI exposure in a murine model. Lung gene expression differences in MDI exposed immune-sensitized and nonsensitized mice vs unexposed controls were measured by microarrays, and associated molecular pathways were identified through bioinformatic analyses and further compared with published studies of a prototypic HMW asthmagen (ovalbumin). Respiratory tract MDI exposure significantly altered lung gene expression in both nonsensitized and immune-sensitized mice, vs controls. Fifty-three gene transcripts were altered in all MDI exposed lung tissue vs controls, with levels up to 10-fold higher in immune-sensitized vs nonsensitized mice. Gene transcripts selectively increased in MDI exposed immune-sensitized animals were dominated by chitinases and chemokines and showed substantial overlap with those increased in ovalbumin-induced asthma. In contrast, MDI exposure of nonsensitized mice increased type I interferon stimulated genes (ISGs) in a pattern reflecting deficiency in adenosine deaminase acting against RNA (ADAR-1), an important regulator of innate, as well as "sterile" or autoimmunity triggered by tissue damage. Thus, MDI-induced changes in lung gene expression were identified that differentiate nonpathogenic innate responses in nonsensitized hosts from pathologic adaptive responses in immune-sensitized hosts. The data suggest that MDI alters unique biological pathways involving ISGs and ADAR-1, potentially explaining its unique immunogenicity/allergenicity.

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.

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.

Silencing lncRNA CDKN2B-AS1 Alleviates Childhood Asthma Progression Through Inhibiting ZFP36 Promoter Methylation and Promoting NR4A1 Expression

LncRNA cyclin-dependent kinase inhibitor 2B antisense RNA 1 (CDKN2B-AS1) was found to be upregulated in plasma of patients with bronchial asthma. This study aimed to explore the roles and mechanisms of CDKN2B-AS1 in childhood asthma. We found that CDKN2B-AS1 was upregulated and zinc finger protein 36 (ZFP36) mRNA was downregulated in blood samples of children with asthma compared with healthy controls as measured by RT-qPCR. Human bronchial epithelial cell line BEAS-2B was treated with LPS to induce inflammation model. Small interfering RNA against CDKN2B-AS1 (si-CDKN2B-AS1) was transfected into LPS-treated BEAS-2B cells, and we observed that CDKN2B-AS1 silencing increased cell viability and inhibited apoptosis and inflammation cytokine levels in LPS-treated BEAS-2B cells. Methylation-specific PCR, ChIP, and RIP assays indicated that CDKN2B-AS1 inhibited ZFP36 expression by recruiting DNMT1 to promote ZFP36 promoter methylation. Co-immunoprecipitation (Co-IP) assay verified the interaction between ZFP36 and nuclear receptor subfamily 4 group A member 1 (NR4A1) proteins. Then rescue experiments revealed that ZFP36 knockdown reversed the effects of CDKN2B-AS1 silencing on BEAS-2B cell functions. ZFP36 overexpression facilitated apoptosis, inflammation, and p-p65 expression in BEAS-2B cells, while NR4A1 knockdown reversed these effects. Additionally, CDKN2B-AS1 silencing alleviated airway hyperresponsiveness and inflammation in ovalbumin (OVA)-induced asthma mice. In conclusion, silencing lncRNA CDKN2B-AS1 enhances BEAS-2B cell viability, reduces apoptosis and inflammation in vitro, and alleviated asthma symptoms in OVA-induced asthma mice in vivo through inhibiting ZFP36 promoter methylation and NR4A1-mediated NF-κB signaling pathway.

NDRG1 Signaling Is Essential for Endothelial Inflammation and Vascular Remodeling

BACKGROUND

NDRG-1 (N-myc downstream-regulated gene 1) is a member of NDRG family that plays essential roles in cell differentiation, proliferation, and stress responses. Although the expression of NDRG1 is regulated by fluid shear stress, its roles in vascular biology remain poorly understood. The purpose of the study is to determine the functional significance of NDRG1 in vascular inflammation and remodeling.

METHODS AND RESULTS

By using quantitative polymerase chain reaction, western blot, and immunohistochemistry, we demonstrate that the expression of NDRG1 is markedly increased in cytokine-stimulated endothelial cells and in human and mouse atherosclerotic lesions. To determine the role of NDRG1 in endothelial activation, we performed loss-of-function studies using NDRG1 short hairpin RNA. Our results demonstrate that NDRG1 knockdown by lentivirus bearing NDRG1 short hairpin RNA substantially attenuates both IL-1β (interleukin-1β) and TNF-α (tumor necrosis factor-α)-induced expression of cytokines/chemokines and adhesion molecules. Intriguingly, inhibition of NDRG1 also significantly attenuates the expression of procoagulant molecules, such as PAI-1 (plasminogen activator inhibitor type 1) and TF (tissue factor), and increases the expression of TM (thrombomodulin) and t-PA (tissue-type plasminogen activator), thus exerting potent antithrombotic effects in endothelial cells. Mechanistically, we showed that NDRG1 interacts with orphan Nur77 (nuclear receptor) and functionally inhibits the transcriptional activity of Nur77 and NF-κB (nuclear factor Kappa B) in endothelial cells. Moreover, in NDRG1 knockdown cells, both cytokine-induced mitogen-activated protein kinase activation, c-Jun phosphorylation, and AP-1 (activator protein 1) transcriptional activity are substantially inhibited. Neointima and atherosclerosis formation induced by carotid artery ligation and arterial thrombosis were markedly attenuated in endothelial cell-specific NDRG1 knockout mice compared with their wild-type littermates.

CONCLUSIONS

Our results for the first time identify NDRG1 as a critical mediator implicated in regulating endothelial inflammation, thrombotic responses, and vascular remodeling, and suggest that inhibition of NDRG1 may represent a novel therapeutic strategy for inflammatory vascular diseases, such as atherothrombosis and restenosis.

Conformationally Restricted Dipeptide-Based Nanoparticles for Delivery of siRNA in Experimental Liver Cirrhosis

Liver cirrhosis is a major health problem with multiple associated complications. The presently available drug delivery systems showed moderate site-specific delivery of antifibrotic molecules to the diseased liver; therefore, research on more effective and selective delivery systems in the context of liver cirrhosis remains a necessity in clinical investigation. The aim of the present study was to develop a peptide-based targeted nanocarrier to deliver an oligonucleotide to the hepatic sinusoidal and perivascular regions of the cirrhotic liver. We have synthesized and characterized a conformationally restricted targeted pentapeptide (RΔFRGD), which contains an unnatural amino acid, α,β-dehydrophenylalanine (ΔF). The RΔFRGD self-assembled into spherical nanoparticles (NPs) and was characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Next, we investigated the delivery potential of the pentapeptide-based NPs to make a stable complex with a well-established small interference RNA and studied its site-specific delivery in experimental liver cirrhosis. We used siNR4A1 of the orphan nuclear receptor 4A1 (NR4A1), a well-known regulatory checkpoint for controlling liver fibrosis. Peptide NPs and their complex with siNR4A1 showed high biocompatibility against various mammalian cell lines. Hepatic tissue biodistribution analysis illustrated that targeted NPs predominantly accumulated in the cirrhotic liver compared to normal rats, specifically in sinusoidal and perivascular areas. A significant downregulation of the NR4A1 mRNA expression (-70%) andlower levels of the NR4A1/GAPDH ratio (-55%) were observed in the RΔFRGD-siNR4A1 nanocomplex-treated group in comparison to the RΔFRGD-vehicle group (RΔFRGD-Veh) at the gene and protein levels, respectively. In addition, in vivo inhibition of NR4A1 produced a significant aggravation in hepatic fibrosis compared with siRNA-vehicle-treated rats (+41% in the MT stain). The novel pentapeptide-based targeted delivery system can be further evaluated and validated for therapeutic purposes in various pathological conditions.

Fragment-based discovery of orphan nuclear receptor Nur77/NGFI-B ligands

The transcription factor nerve growth factor-induced clone B (NGFI-B, Nur77, NR4A1) is an orphan nuclear receptor playing a role in cell survival and apoptosis regulation. Pharmacological Nur77 modulation holds promise for cancer and (neuro-)inflammatory disease treatment. The available Nur77 ligand scaffolds based on highly lipophilic natural products cytosporone B, celastrol and isoalantolactone are inadequate for the development of potent Nur77 modulators with favorable properties as chemical tools and future drugs. By fragment library screening and subsequent modeling for fragment extension, we have obtained a set of new Nur77 ligands offering alternative chemotypes for the development of Nur77 agonists and inverse agonists. Computer-aided fragment extension in a second stage screening yielded a Nur77 agonist with significant activation efficacy and preference over the related NR4A receptors.

Arc Regulates Transcription of Genes for Plasticity, Excitability and Alzheimer’s Disease

The immediate early gene Arc is a master regulator of synaptic function and a critical determinant of memory consolidation. Here, we show that Arc interacts with dynamic chromatin and closely associates with histone markers for active enhancers and transcription in cultured rat hippocampal neurons. Both these histone modifications, H3K27Ac and H3K9Ac, have recently been shown to be upregulated in late-onset Alzheimer’s disease (AD). When Arc induction by pharmacological network activation was prevented using a short hairpin RNA, the expression profile was altered for over 1900 genes, which included genes associated with synaptic function, neuronal plasticity, intrinsic excitability, and signalling pathways. Interestingly, about 100 Arc-dependent genes are associated with the pathophysiology of AD. When endogenous Arc expression was induced in HEK293T cells, the transcription of many neuronal genes was increased, suggesting that Arc can control expression in the absence of activated signalling pathways. Taken together, these data establish Arc as a master regulator of neuronal activity-dependent gene expression and suggest that it plays a significant role in the pathophysiology of AD.

Nuclear receptor Nr1d1 alleviates asthma by abating GATA3 gene expression and Th2 cell differentiation

Nuclear receptors are a unique family of transcription factors that play cardinal roles in physiology and plethora of human diseases. The adopted orphan nuclear receptor Nr1d1 is a constitutive transcriptional repressor known to modulate several biological processes. In this study, we found that Nr1d1 plays a decisive role in T helper (Th)-cell polarization and transcriptionally impedes the formation of Th2 cells by directly binding to the promoter region of GATA binding protein 3 (GATA3) gene. Nr1d1 interacts with its cellular companion, the nuclear receptor corepressor and histone deacetylase 3 to form a stable repression complex on the GATA3 promoter. The presence of Nr1d1 also imparts protection against associated inflammatory responses in murine model of asthma and its ligand SR9011 eased disease severity by suppressing Th2 responses. Moreover, Chip-seq profiling uncovered Nr1d1 interactions with other gene subsets that impedes Th2-linked pathways and regulates metabolism, immunity and brain functions, therefore, providing empirical evidence regarding the genetic link between asthma and other comorbid conditions. Thus, Nr1d1 emerges as a molecular switch that could be targeted to subdue asthma.

Design and synthesis of adamantyl-substituted flavonoid derivatives as anti-inflammatory Nur77 modulators: Compound B7 targets Nur77 and improves LPS-induced inflammation in vitro and in vivo

In continuing our study on discovering new Nur77-targeting anti-inflammatory agents with natural skeletons, we combined adamantyl group and hydroxamic acid moiety with flavonoid nucleus, synthesized three series of flavonoid derivatives with a similar structure like CD437, and evaluated their activities against LPS-induced inflammation. Compound B7 was found to be an excellent Nur77 binder (K_d = 3.55 × 10^-7 M) and a potent inhibitor of inflammation, which significantly decreased the production of cytokines in vitro, such as NO, IL-6, IL-1β, and TNF-α, at concentrations of 1.25, 2.5, and 5 μM. Mechanistically, B7 modulated the colocalization of Nur77 at mitochondria and inhibited the lipopolysaccharides (LPS)-induced inflammation via the blockade of NF-κB activation in a Nur77-dependent manner. Additionally, B7 showed in vivo anti-inflammatory activity in the LPS-induced mice model of acute lung injury (ALI). These data suggest that the Nur77-targeting flavonoid derivatives can be particularly useful for further pharmaceutical development for the treatment of inflammatory diseases such as ALI.

The upregulation of Nur77 decreases ketamine-induced hippocampal neurons toxicity in rats

Ketamine is clinically used as a narcotic. However, ketamine has certain deficits and produces toxicity to neurons. As a member of the NR4A receptor subfamily, Nur77 decreases neurodegenerative disorders. The study aims to investigate the effects of upregulated Nur77 on ketamine-induced rat hippocampal neurons damage and the active mechanism. Neurons were obtained from rat hippocampal and identified by immunofluorescence assays. The treatment groups contained ketamine group, Nur77 group, ketamine + Nur77 group and ketamine + L-cam group. Neurons apoptosis and reactive oxygen species (ROS) were determined by a related kit using flow cytometry. Enzyme NAD(P)H quinone oxidoreductase 1 (NQO1), enzyme heme oxygenase 1 (HO1), Nur77, the expression of Bax, Bcl-2 and cleaved-caspase-3 and inflammatory cytokines were measured using western blot assays and reverse transcription-quantitative PCR (RT-qPCR) assays. Ketamine-induced neurons apoptosis; however, Nur77 decreased ketamine-induced neurons apoptosis. A low level of ROS was observed in two combination groups. Neurons treated by ketamine only had the lowest levels of Nur77, NQO1 and HO1, compared with other treatment groups. The levels of Bax and cleaved-caspase-3 in two combination groups were lower than those in the ketamine group. Furthermore, the ketamine group had higher levels of tumor necrosis factor alpha, IL-1β and IL-6 but the lowest level of IL-4. Upregulated Nur77 reduced the ketamine-induced toxicity in neurons. The mechanism of Nur77 involved antioxidation, apoptosis signaling pathway and inflammation signaling pathway. Our study provides a novel therapy that could attenuate ketamine-induced toxicity.

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.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

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.

Nuclear Receptors in Asthma: Empowering Classical Molecules Against a Contemporary Ailment

The escalation in living standards and adoption of 'Western lifestyle' has an allied effect on the increased allergy and asthma burden in both developed and developing countries. Current scientific reports bespeak an association between allergic diseases and metabolic dysfunction; hinting toward the critical requirement of organized lifestyle and dietary habits. The ubiquitous nuclear receptors (NRs) translate metabolic stimuli into gene regulatory signals, integrating diet inflences to overall developmental and physiological processes. As a consequence of such promising attributes, nuclear receptors have historically been at the cutting edge of pharmacy world. This review discusses the recent findings that feature the cardinal importance of nuclear receptors and how they can be instrumental in modulating current asthma pharmacology. Further, it highlights a possible future employment of therapy involving dietary supplements and synthetic ligands that would engage NRs and aid in eliminating both asthma and linked comorbidities. Therefore, uncovering new and evolving roles through analysis of genomic changes would represent a feasible approach in both prevention and alleviation of asthma.

Regulatory Effects of Nur77 on Airway Remodeling and ASMC Proliferation in House Dust Mite-Induced Asthma

Airway remodeling played a vital role in the development of asthma, and airway smooth muscle (ASM) mass was its hallmark. However, few strategies targeting ASM remodeling were developed in treating asthma. Nur77 was the transcription factor nuclear receptor involved in the pathogenesis of several lung diseases. Nur77 distribution and expression were determined in an HDM-mediated allergic asthma model. Its effect on airway hyperresponsiveness (AHR), chronic inflammation, and ASM remodeling in asthmatic mice was evaluated using a lentivirus-mediated shRNA. Possible mechanisms were explored by examining Nur77 actions and its underlying pathways in primary human AMC cells (ASMCs). In this study, we reported that Nur77 expression was mainly distributed along ASM and increased in lungs of HDM-challenged mice. Nur77 depletion by lentivirus-mediated shRNA ameliorated AHR, chronic inflammation, goblet cell hyperplasia, and airway remodeling in the asthmatic mouse model. By means of primary human ASMC, we discovered that Nur77 upregulation by HDM stimulation promoted cell proliferation and ROS production, as well as reduced antioxidant gene expression. These alterations might associate with MFN2/MAPK/AKT pathways. These findings broadened our understanding of airway remodeling and ASMC proliferation, which might provide a novel therapeutic target for asthma patients.

'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.

Early immune suppression leads to uncontrolled mite proliferation and potent host inflammatory responses in a porcine model of crusted versus ordinary scabies

Scabies is a neglected tropical disease of global significance. Our understanding of host-parasite interactions has been limited, particularly in crusted scabies (CS), a severe clinical manifestation involving hyper-infestation of Sarcoptes scabiei mites. Susceptibility to CS may be associated with immunosuppressive conditions but CS has also been seen in cases with no identifiable risk factor or immune deficit. Due to ethical and logistical difficulties with undertaking research on clinical patients with CS, we adopted a porcine model which parallels human clinical manifestations. Transcriptomic analysis using microarrays was used to explore scabies pathogenesis, and to identify early events differentiating pigs with ordinary (OS) and crusted scabies. Pigs with OS (n = 4), CS (n = 4) and non-infested controls (n = 4) were compared at pre-infestation, weeks 1, 2, 4 and 8 post-infestation. In CS relative to OS, there were numerous differentially expressed genes including pro-inflammatory cytokines (IL17A, IL8, IL19, IL20 and OSM) and chemokines involved in immune cell activation and recruitment (CCL20, CCL27 and CXCL6). The influence of genes associated with immune regulation (CD274/PD-L1 and IL27), immune signalling (TLR2, TLR8) and antigen presentation (RFX5, HLA-5 and HLA-DOB) were highlighted in the early host response to CS. We observed similarities with gene expression profiles associated with psoriasis and atopic dermatitis and confirmed previous observations of Th2/17 pronounced responses in CS. This is the first comprehensive study describing transcriptional changes associated with the development of CS and significantly, the distinction between OS and CS. This provides a basis for clinical follow-up studies, potentially identifying new control strategies for this severely debilitating disease.

The immune response to Sarcoptes scabiei infestation is poorly defined. There have been few studies of crusted scabies, a debilitating clinical variant of the disease characterised by extremely high mite numbers. In this study, we used a pig model to explore differences in gene expression between clinical variants of scabies, including a focus on immune events occurring prior to the development of clinical signs. In early infestation, genes relating to inflammation, immune recognition and cell migration were potently suppressed in pigs with crusted scabies. This suggests that these pigs lacked the ability to mount a timely, effective immune response, allowing mites to proliferate unchecked. In later infestation, the large numbers of mites then triggered a strong inflammatory response leading to severe skin pathology. Gene expression profiles in crusted scabies shared similarities with other inflammatory skin diseases such as psoriasis. This is the first study to compare immune responses in crusted and ordinary scabies in early infestation and reveals new insights into the progression of disease. Findings may lead to the development of new approaches to diagnose and treat this important, but neglected disease.

Lindera obtusiloba Attenuates Oxidative Stress and Airway Inflammation in a Murine Model of Ovalbumin-Challenged Asthma

Lindera obtusiloba is widespread in northeast Asia and used for treatment of improvement of blood circulation and anti-inflammation. In this study, we investigated anti-inflammatory and anti-oxidant effects of the methanolic extract of L. obtusiloba leaves (LOL) in an ovalbumin (OVA)-challenged allergic asthma model and tumor necrosis factor (TNF)-α-stimulated NCI-H292 cell. Female BALB/c mice were sensitized with OVA by intraperitoneal injection on days 0 and 14, and airway-challenged with OVA from days 21 to 23. Mice were administered 50 and 100 mg/kg of LOL by oral gavage 1 h before the challenge. LOL treatment effectively decreased airway hyper-responsiveness and inhibited inflammatory cell recruitment, Th2 cytokines, mucin 5AC (MUC5AC) in bronchoalveolar lavage fluid in OVA-challenged mice, which were accompanied by marked suppression of airway inflammation and mucus production in the lung tissue. LOL pretreatment inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) with suppression of activator protein (AP)-1 and MUC5AC in the lung tissue. LOL also down-regulated expression of inflammatory cytokines, and inhibited the activation of NF-κB in TNF-α-stimulated NCI-H292 cells. LOL elevated the translocation of nuclear factor-erythroid 2-related factor (Nrf-2) into nucleus concurrent with increase of heme oxyngenase-1 (HO-1) and NAD(P)H quinine oxidoreductase 1 (NQO1). Moreover, LOL treatment exhibited a marked increase in the anti-oxidant enzymes activities, whereas effectively suppressed the production of reactive oxygen species and nitric oxide, as well as lipid peroxidation in lung tissue of OVA-challenged mice and TNF-α-stimulated NCI-H292 cells. These findings suggest that LOL might serve as a therapeutic agent for the treatment of allergic asthma.

Deficiency of the Transcription Factor NR4A1 Enhances Bacterial Clearance and Prevents Lung Injury During Escherichia Coli Pneumonia

BACKGROUND

Bacterial pneumonia is one of the most common diagnoses and a leading cause of death in the intensive care unit. NR4A1 is an early response gene that has been identified as a vital regulator of immune and inflammatory responses. This study aims to explore the role of NR4A1 in Escherichia coli (E. coli) pneumonia.

METHODS

Alveolar macrophages (AMs) were isolated from wild-type (WT) and NR4A1 knock out (Nr4a1) mice, and the NR4A1 expression and phagocytic capacity against E. coli were measured in vitro. WT and Nr4a1 mice were subjected to E. coli or sham pneumonia. Bacterial load, lung injury severity, inflammatory cell infiltration, and cytokines were assessed at 0, 4, and 18 h after surgery. Survival rates within 48 h were evaluated in WT and Nr4a1 mice. In addition, NR4A1 antagonist (DIM-C-pPhCO2Me) was also used to confirm the role of NR4A1 in vivo and ex vivo.

RESULTS

NR4A1 was rapidly induced in AMs at 15 min after E. coli stimulation. Compared with untreated WT AMs, NR4A1 deficiency and DIM-C-pPhCO2Me treatment showed an enhanced phagocytic function (47.72 ± 0.74% vs. 62.3 ± 0.9%, P < 0.001; 11.79 ± 1.21% vs. 30.08 ± 0.79%, P < 0.001, respectively) at 30 min after the E. coli challenge in vitro. NR4A1 deficiency significantly improved the survival rate (33.3% in WT vs. 82.4% in Nr4a1, P < 0.01), which is comparable with DIM-C-pPhCO2Me pretreatment. The survival advantage of Nr4a1 mice was associated with decreased bacterial burden and inflammation and alleviated lung damage.

CONCLUSIONS

These data demonstrate that NR4A1 impairs the phagocytic capacity of AMs and disrupts the host defense against invading bacteria, worsening the outcome of E. coli pneumonia in mice.

Nur77 attenuates inflammatory responses and oxidative stress by inhibiting phosphorylated IκB-α in Parkinson's disease cell model

Neuroinflammation and oxidative stress play key roles in the pathological development of Parkinson’s disease (PD). Nerve growth factor-induced gene B (Nur77) is closely related to dopamine neurotransmission, and its pathogenesis is unclear. This study aims to investigate the role and mechanism of Nur77 in a cell model of Parkinson’s disease. Silencing Nur77 with siRNA can aggravate intracellular LDH release, increase the expression of pro-inflammatory genes (such as tumor necrosis factor α, nuclear factor κB (p65), monocyte chemotactic protein 1, interleukin-6), and decrease cell survival, decrease expression of nuclear factor E2-related factor(Nrf2), heme oxygenase 1, NADPH quinineoxidoreductase-1. Cytosporone B (Nur77 agonist) has the opposite effect to Nur77 silencing. PDTC (NF-κB inhibitor / antioxidant) can also inhibit pro-inflammatory genes to a similar degree as Cytosporone B. Phosphorylated IκB-α can be inhibited by Cytosporone B, while silencing Nur77 can increase the protein expression level of phosphorylated IκB-α. After silencing IκB-α, both Cytosporone B and siNur77 did not affect pro-inflammatory genes and antioxidant stress. These findings reveal the first evidence that Nur77 exerts anti-inflammatory and antioxidant stress effects by inhibiting IκB-α phosphorylation expression in a Parkinson cell model. Nur77 may be a potential therapeutic target for Parkinson’s disease.

FSTL-1 Attenuation Causes Spontaneous Smoke-Resistant Pulmonary Emphysema

Rationale: The role of FSTL-1 (follistatin-like 1) in lung homeostasis is unknown.Objectives: We aimed to define the impact of FSTL-1 attenuation on lung structure and function and to identify FSTL-1-regulated transcriptional pathways in the lung. Further, we aimed to analyze the association of FSTL-1 SNPs with lung disease.Methods: FSTL-1 hypomorphic (FSTL-1 Hypo) mice underwent lung morphometry, pulmonary function testing, and micro-computed tomography. Fstl1 expression was determined in wild-type lung cell populations from three independent research groups. RNA sequencing of wild-type and FSTL-1 Hypo mice identified FSTL-1-regulated gene expression, followed by validation and mechanistic in vitro examination. FSTL1 SNP analysis was performed in the COPDGene (Genetic Epidemiology of Chronic Obstructive Pulmonary Disease) cohort.Measurements and Main Results: FSTL-1 Hypo mice developed spontaneous emphysema, independent of smoke exposure. Fstl1 is highly expressed in the lung by mesenchymal and endothelial cells but not immune cells. RNA sequencing of whole lung identified 33 FSTL-1-regulated genes, including Nr4a1, an orphan nuclear hormone receptor that negatively regulates NF-κB (nuclear factor-κB) signaling. In vitro, recombinant FSTL-1 treatment of macrophages attenuated NF-κB p65 phosphorylation in an Nr4a1-dependent manner. Within the COPDGene cohort, several SNPs in the FSTL1 region corresponded to chronic obstructive pulmonary disease and lung function.Conclusions: This work identifies a novel role for FSTL-1 protecting against emphysema development independent of smoke exposure. This FSTL-1-deficient emphysema implicates regulation of immune tolerance in lung macrophages through Nr4a1. Further study of the mechanisms involving FSTL-1 in lung homeostasis, immune regulation, and NF-κB signaling may provide additional insight into the pathophysiology of emphysema and inflammatory lung diseases.

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.

Inhibition of IRF4 in dendritic cells by PRR-independent and -dependent signals inhibit Th2 and promote Th17 responses

Cyclic AMP (cAMP) is involved in many biological processes but little is known regarding its role in shaping immunity. Here we show that cAMP-PKA-CREB signaling (a pattern recognition receptor [PRR]-independent mechanism) regulates conventional type-2 Dendritic Cells (cDC2s) in mice and reprograms their Th17-inducing properties via repression of IRF4 and KLF4, transcription factors essential for cDC2-mediated Th2 induction. In mice, genetic loss of IRF4 phenocopies the effects of cAMP on Th17 induction and restoration of IRF4 prevents the cAMP effect. Moreover, curdlan, a PRR-dependent microbial product, activates CREB and represses IRF4 and KLF4, resulting in a pro-Th17 phenotype of cDC2s. These in vitro and in vivo results define a novel signaling pathway by which cDC2s display plasticity and provide a new molecular basis for the classification of novel cDC2 and cDC17 subsets. The findings also reveal that repressing IRF4 and KLF4 pathway can be harnessed for immuno-regulation.

Accelerated aging induced by deficiency of Zmpste24 protects old mice to develop bleomycin-induced pulmonary fibrosis

Idiopathic pulmonary fibrosis is a devastating aging-associated disease of unknown etiology. Despite that aging is a major risk factor, the mechanisms linking aging with this disease are uncertain, and experimental models to explore them in lung fibrosis are scanty. We examined the fibrotic response to bleomycin-induced lung injury in Zmpste24-deficient mice, which exhibit nuclear lamina defects developing accelerated aging. We found that young WT and Zmpste24(-/-) mice developed a similar fibrotic response to bleomycin. Unexpectedly, while old WT mice developed severe lung fibrosis, accelerated aged Zmpste24-/- mice were protected showing scant lung damage. To investigate possible mechanisms associated with this resistance to fibrosis, we compared the transcriptome signature of the lungs and found that Zmpste24(-/-) mice showed downregulation of several core and associated matrisome genes compared with WT mice. Interestingly, some microRNAs that target extracellular matrix molecules such as miR23a, miR27a, miR29a, miR29b-1, miR145a, and miR491 were dysregulated resulting in downregulation of profibrotic pathways such as TGF-β/SMAD3/NF-κB and Wnt3a/β-catenin signaling axis. These results indicate that the absence of Zmpste24 in aging mice results in impaired lung fibrotic response after injury, which is likely associated to the dysregulation of fibrosis-related miRNAs.

Interleukin-16 aggravates ovalbumin-induced allergic inflammation by enhancing Th2 and Th17 cytokine production in a mouse model

Asthma is a chronic inflammatory disease that involves a variety of cytokines and cells. Interleukin-16 (IL-16) is highly expressed during allergic airway inflammation and is involved in its development. However, its specific mechanism of action remains unclear. In the present study, we used an animal model of ovalbumin (OVA)-induced allergic asthma with mice harboring an IL-16 gene deletion to investigate the role of this cytokine in asthma, in addition to its underlying mechanism. Increased IL-16 expression was observed during OVA-induced asthma in C57BL/6J mice. However, when OVA was used to induce asthma in IL-16^-/- mice, a diminished inflammatory reaction, decreased bronchoalveolar lavage fluid (BALF) eosinophil numbers, and the suppression of OVA-specific IgE levels in the serum and BALF were observed. The results also demonstrated decreased levels of T helper type 2 (Th2) and Th17 cytokines upon OVA-induced asthma in IL-16^-/- mice. Hence, we confirmed that IL-16 enhances the lung allergic inflammatory response and suggest a mechanism possibly associated with the up-regulation of IgE and the promotion of Th2 and Th17 cytokine production. This work explored the mechanism underlying the regulation of IL-16 in asthma and provides a new target for the clinical treatment of asthma.

Nur77 protects against adverse cardiac remodelling by limiting neuropeptide Y signalling in the sympathoadrenal-cardiac axis

Aims

Cardiac remodelling and heart failure are promoted by persistent sympathetic activity. We recently reported that nuclear receptor Nur77 may protect against sympathetic agonist-induced cardiac remodelling in mice. The sympathetic co-transmitter neuropeptide Y (NPY) is co-released with catecholamines and is a known cardiac modulator and predictor of heart failure mortality. Recently, transcriptome analyses revealed NPY as a putative target of Nur77. In this study, we assess whether Nur77 modulates adverse cardiac remodelling via NPY signalling.

Methods and results

Nur77 represses NPY expression in the PC12 adrenal chromaffin cell line. Accordingly, NPY levels are higher in adrenal gland, plasma, and heart from Nur77-KO compared to wild-type mice. Conditioned medium from Nur77-silenced chromaffin cells and serum from Nur77-KO mice induce marked hypertrophy in cultured neonatal rat cardiomyocytes, which is inhibited by the NPY type 1 receptor (NPY1R) antagonist BIBO3304. In cardiomyocytes from Nur77-KO mice, intracellular Ca2+ is increased partially via the NPY1R. This is independent from elevated circulating NPY since cardiomyocyte-specific Nur77-deficient mice (CM-KO) do not have elevated circulating NPY, but do exhibit BIBO3304-sensitive, increased cardiomyocyte intracellular Ca2+. In vivo, this translates to NPY1R antagonism attenuating cardiac calcineurin activity and isoproterenol-induced cardiomyocyte hypertrophy and fibrosis in full-body Nur77-KO mice, but not in CM-KO mice.

Conclusions

The cardioprotective action of Nur77 can be ascribed to both inhibition of circulating NPY levels and to cardiomyocyte-specific modulation of NPY-NPY1R signalling. These results reveal the underlying mechanism of Nur77 as a promising modifier gene in heart failure.

Prevention of progression of pulmonary hypertension by the Nur77 agonist 6-mercaptopurine: role of BMP signalling

Pulmonary arterial hypertension (PAH) is a progressive fatal disease characterised by abnormal remodelling of pulmonary vessels, leading to increased vascular resistance and right ventricle failure. This abnormal vascular remodelling is associated with endothelial cell dysfunction, increased proliferation of smooth muscle cells, inflammation and impaired bone morphogenetic protein (BMP) signalling. Orphan nuclear receptor Nur77 is a key regulator of proliferation and inflammation in vascular cells, but its role in impaired BMP signalling and vascular remodelling in PAH is unknown.

We hypothesised that activation of Nur77 by 6-mercaptopurine (6-MP) would improve PAH by inhibiting endothelial cell dysfunction and vascular remodelling.

Nur77 expression is decreased in cultured pulmonary microvascular endothelial cells (MVECs) and lungs of PAH patients. Nur77 significantly increased BMP signalling and strongly decreased proliferation and inflammation in MVECs. In addition, conditioned medium from PAH MVECs overexpressing Nur77 inhibited the growth of healthy smooth muscle cells. Pharmacological activation of Nur77 by 6-MP markedly restored MVEC function by normalising proliferation, inflammation and BMP signalling. Finally, 6-MP prevented and reversed abnormal vascular remodelling and right ventricle hypertrophy in the Sugen/hypoxia rat model of severe angioproliferative PAH.

Our data demonstrate that Nur77 is a critical modulator in PAH by inhibiting vascular remodelling and increasing BMP signalling, and activation of Nur77 could be a promising option for the treatment of PAH.

Nur77 promotes cigarette smoke‑induced autophagic cell death by increasing the dissociation of Bcl2 from Beclin-1

Chronic obstructive pulmonary disease (COPD) is characterized by partially reversible airflow limitation and persistent alveolar destruction, and autophagy is involved in the pathogenesis of cigarette smoke (CS)‑induced COPD. Nuclear receptor 77 (Nur77) participates in a number of biological processes, including apoptosis, autophagy and in disease pathogenesis; however, the role of Nur77 in COPD remains unknown. Thus, in this study, we aimed to elucidate the role of Nur77 in COPD. We report that CS promotes Nur77 expression and nuclear export in vivo and in vitro, which increases cigarette smoke extract (CSE)‑induced autophagy. In addition, we found that lung tissues, human bronchial epithelial (HBE) cells and A549 cells exposed to CS or CSE expressed lower levels of LC3 and Beclin‑1 and contained fewer autophagosomes following Nur77 knockdown with siRNA‑Nur77. Moreover, a co‑immunoprecipitation assay demonstrated that CSE promoted autophagy, partly by accelerating the interaction between Nur77 and Bcl2, in turn leading to the increased dissociation of Bcl2 from Beclin‑1; by contrast, leptomycin B (LMB) suppressed the dissociation of Bcl2 from Beclin‑1. Taken together, the findings of this study demonstrate that Nur77 is involved in the CSE‑induced autophagic death of lung cells, and that this process is partially dependent on the increased interaction between Nur77 and Bcl2, and on the dissociation of Bcl2 from Beclin‑1. This study illustrates the role of Nur77 in bronchial and alveolar destruction following exposure to CS.

Insights into the Signal Transduction Pathways of Mouse Lung Type II Cells Revealed by Transcription Factor Profiling in the Transcriptome

Alveolar type II cells constitute a small fraction of the total lung cell mass. However, they play an important role in many cellular processes including trans-differentiation into type I cells as well as repair of lung injury in response to toxic chemicals and respiratory pathogens. Transcription factors are the regulatory proteins dynamically modulating DNA structure and gene expression. Transcription factor profiling in microarray datasets revealed that several members of AP1, ATF, NF-kB, and C/EBP families involved in diverse responses were expressed in mouse lung type II cells. A transcriptional factor signature consisting of Cebpa, Srebf1, Stat3, Klf5, and Elf3 was identified in lung type II cells, Sox9+ pluripotent lung stem cells as well as in mouse lung development. Identification of the transcription factor profile in mouse lung type II cells will serve as a useful resource and facilitate the integrated analysis of signal transduction pathways and specific gene targets in a variety of physiological conditions.

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.

Macrophage nuclear receptors: Emerging key players in infectious diseases

Nuclear receptors (NRs) are ligand-activated transcription factors that are expressed in a variety of cells, including macrophages. For decades, NRs have been therapeutic targets because their activity can be pharmacologically modulated by specific ligands and small molecule inhibitors. NRs regulate a variety of processes, including those intersecting metabolic and immune functions, and have been studied in regard to various autoimmune diseases. However, the complex roles of NRs in host response to infection are only recently being investigated. The NRs peroxisome proliferator-activated receptor γ (PPARγ) and liver X receptors (LXRs) have been most studied in the context of infectious diseases; however, recent work has also linked xenobiotic pregnane X receptors (PXRs), vitamin D receptor (VDR), REV-ERBα, the nuclear receptor 4A (NR4A) family, farnesoid X receptors (FXRs), and estrogen-related receptors (ERRs) to macrophage responses to pathogens. Pharmacological inhibition or antagonism of certain NRs can greatly influence overall disease outcome, and NRs that are protective against some diseases can lead to susceptibility to others. Targeting NRs as a novel host-directed treatment approach to infectious diseases appears to be a viable option, considering that these transcription factors play a pivotal role in macrophage lipid metabolism, cholesterol efflux, inflammatory responses, apoptosis, and production of antimicrobial byproducts. In the current review, we discuss recent findings concerning the role of NRs in infectious diseases with an emphasis on PPARγ and LXR, the two most studied. We also highlight newer work on the activity of emerging NRs during infection.

NR4A nuclear receptors in cardiac remodeling and neurohormonal regulation

Heart failure is characterized by the constant interplay between the underlying cardiac insult, degree of myocardial dysfunction and the activity of compensatory neurohormonal mechanisms. The sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS) become activated to maintain cardiac output; however, their chronic hyperactivity will eventually become deleterious. Several nuclear hormone receptors, including the mineralocorticoid receptor and estrogen receptor, are well-known to modulate cardiac disease. Recently, the subfamily of NR4A nuclear receptors i.e. Nur77, Nurr1 and NOR-1, are emerging as key players in cardiac stress responses, as well as pivotal regulators of neurohormonal mechanisms. In this review, we summarize current literature on NR4A nuclear receptors in the heart and in various components of the SNS, RAAS and immune system and discuss the functional implications for NR4As in cardiac function and disease.

Key Functions and Therapeutic Prospects of Nur77 in Inflammation Related Lung Diseases

The transcription factor Nur77 belongs to the NR4A subfamily of nuclear hormone receptors. It features an atypical ligand-binding site that precludes canonical ligand binding, leading to the designation orphan nuclear receptor. However, recent studies show that small molecules can interact with the receptor and modulate its activity by inducing a conformational change in the Nur77 ligand-binding site. Nur77 expression and activation are rapidly induced by various physiological and pathologic stimuli. Once expressed, Nur77 initiates transcriptional activity and modulates expression of its target genes. Both in vitro and in vivo evidence shows that Nur77 dampens the immune response to proinflammatory stimuli, such as tumor necrosis factor-α, Toll-like receptor ligands, and oxidized lipids, primarily by suppressing NF-κB signaling. Although studies focusing on Nur77's role in lung pathophysiology are currently incomplete, available data support its involvement in the pathogenesis of lung diseases, including asthma, acute lung injury, and pulmonary fibrosis, and thus suggest a therapeutic potential for Nur77 activation in these diseases. This review addresses the mechanisms that control Nur77 as well as its known roles in inflammation-related lung diseases. Evidence regarding the therapeutic potential of Nur77-targeting molecules will also be presented. Although current knowledge is limited, additional research followed by clinical studies may firmly identify Nur77 as a pharmacologic target for inflammation-related lung diseases.

The E3 ubiquitin ligase Trim13 regulates Nur77 stability via casein kinase 2α

Nur77 is a member of the NR4A subfamily of nuclear receptors and has been shown to regulate various biological processes such as apoptosis and inflammation. Here, we show that Nur77 ubiquitination is mediated by the tripartite motif 13 (Trim13), a RING-type E3 ubiquitin ligase. The interaction between Nur77 and Trim13 was confirmed by co-immunoprecipitation. Moreover, we found that Lys539 in Nur77 ubiquitination is targeted for Trim13, which leads to Nur77 degradation. The Trim13-mediated ubiquitination of Nur77 was optimal in the presence of the E2 enzyme UbcH5. Importantly, in addition to Trim13-mediated ubiquitination, the stability of Nur77 was also regulated by casein kinase 2α (CK2α). Pharmacological inhibition of CK2 markedly increased Nur77 levels, whereas overexpression of CK2α, but not its inactive mutant, dramatically decreased Nur77 levels by promoting Nur77 ubiquitination. CK2α phosphorylated Ser154 in Nur77 and thereby regulated Nur77 protein levels by promoting its ubiquitin-mediated degradation. Importantly, we also show that degradation of Nur77 is involved in TNFα-mediated IL-6 production via CK2α and Trim13. Taken together, these results suggest that the sequential phosphorylation and ubiquitination of Nur77 controls its degradation, and provide a therapeutic approach for regulating Nur77 activity through the CK2α-Trim13 axis as a mechanism to control the inflammatory response.

Nur77 variants solely comprising the amino-terminal domain activate hypoxia-inducible factor-1α and affect bone marrow homeostasis in mice and humans

Gene targeting via homologous recombination can occasionally result in incomplete disruption of the targeted gene. Here, we show that a widely used Nur77-deficient transgenic mouse model expresses a truncated protein encoding for part of the N-terminal domain of nuclear receptor Nur77. This truncated Nur77 protein is absent in a newly developed Nur77-deficient mouse strain generated using Cre-Lox recombination. Comparison of these two mouse strains using immunohistochemistry, flow cytometry, and colony-forming assays shows that homologous recombination-derived Nur77-deficient mice, but not WT or Cre-Lox-derived Nur77-deficient mice, suffer from liver immune cell infiltrates, loss of splenic architecture, and increased numbers of bone marrow hematopoietic stem cells and splenic colony-forming cells with age. Mechanistically, we demonstrate that the truncated Nur77 N-terminal domain protein maintains the stability and activity of hypoxia-inducible factor (HIF)-1, a transcription factor known to regulate bone marrow homeostasis. Additionally, a previously discovered, but uncharacterized, human Nur77 transcript variant that encodes solely for its N-terminal domain, designated TR3β, can also stabilize and activate HIF-1α. Meta-analysis of publicly available microarray data sets shows that TR3β is highly expressed in human bone marrow cells and acute myeloid leukemia samples. In conclusion, our study provides evidence that a transgenic mouse model commonly used to study the biological function of Nur77 has several major drawbacks, while simultaneously identifying the importance of nongenomic Nur77 activity in the regulation of bone marrow homeostasis.

Loss of the zona pellucida-binding protein 2 (Zpbp2) gene in mice impacts airway hypersensitivity and lung lipid metabolism in a sex-dependent fashion

The human chromosomal region 17q12-q21 is one of the best replicated genome-wide association study loci for childhood asthma. The associated SNPs span a large genomic interval that includes several protein-coding genes. Here, we tested the hypothesis that the zona pellucida-binding protein 2 (ZPBP2) gene residing in this region contributes to asthma pathogenesis using a mouse model. We tested the lung phenotypes of knock-out (KO) mice that carry a deletion of the Zpbp2 gene. The deletion attenuated airway hypersensitivity (AHR) in female, but not male, mice in the absence of allergic sensitization. Analysis of the lipid profiles of their lungs showed that female, but not male, KO mice had significantly lower levels of sphingosine-1-phosphate (S1P), very long-chain ceramides (VLCCs), and higher levels of long-chain ceramides compared to wild-type controls. Furthermore, in females, lung resistance following methacholine challenge correlated with lung S1P levels (Pearson correlation coefficient 0.57) suggesting a link between reduced AHR in KO females, Zpbp2 deletion, and S1P level regulation. In livers, spleens and blood plasma, however, VLCC, S1P, and sphingosine levels were reduced in both KO females and males. We also find that the Zpbp2 deletion was associated with gain of methylation in the adjacent DNA regions. Thus, we demonstrate that the mouse ortholog of ZPBP2 has a role in controlling AHR in female mice. Our data also suggest that Zpbp2 may act through regulation of ceramide metabolism. These findings highlight the importance of phospholipid metabolism for sexual dimorphism in AHR.

The neuropeptide NMU amplifies ILC2-driven allergic lung inflammation

Type 2 innate lymphoid cells (ILC2s) both contribute to mucosal homeostasis and initiate pathologic inflammation in allergic asthma. However, the signals that direct ILC2s to promote homeostasis versus inflammation are unclear. To identify such molecular cues, we profiled mouse lung-resident ILCs using single-cell RNA sequencing at steady state and after in vivo stimulation with the alarmin cytokines IL-25 and IL-33. ILC2s were transcriptionally heterogeneous after activation, with subpopulations distinguished by expression of proliferative, homeostatic and effector genes. The neuropeptide receptor Nmur1 was preferentially expressed by ILC2s at steady state and after IL-25 stimulation. Neuromedin U (NMU), the ligand of NMUR1, activated ILC2s in vitro, and in vivo co-administration of NMU with IL-25 strongly amplified allergic inflammation. Loss of NMU-NMUR1 signalling reduced ILC2 frequency and effector function, and altered transcriptional programs following allergen challenge in vivo. Thus, NMUR1 signalling promotes inflammatory ILC2 responses, highlighting the importance of neuro-immune crosstalk in allergic inflammation at mucosal surfaces.

Celastrol-Induced Nur77 Interaction with TRAF2 Alleviates Inflammation by Promoting Mitochondrial Ubiquitination and Autophagy

Mitochondria play an integral role in cell death, autophagy, immunity, and inflammation. We previously showed that Nur77, an orphan nuclear receptor, induces apoptosis by targeting mitochondria. Here, we report that celastrol, a potent anti-inflammatory pentacyclic triterpene, binds Nur77 to inhibit inflammation and induce autophagy in a Nur77-dependent manner. Celastrol promotes Nur77 translocation from the nucleus to mitochondria, where it interacts with tumor necrosis factor receptor-associated factor 2 (TRAF2), a scaffold protein and E3 ubiquitin ligase important for inflammatory signaling. The interaction is mediated by an LxxLL motif in TRAF2 and results not only in the inhibition of TRAF2 ubiquitination but also in Lys63-linked Nur77 ubiquitination. Under inflammatory conditions, ubiquitinated Nur77 resides at mitochondria, rendering them sensitive to autophagy, an event involving Nur77 interaction with p62/SQSTM1. Together, our results identify Nur77 as a critical intracellular target for celastrol and unravel a mechanism of Nur77-dependent clearance of inflamed mitochondria to alleviate inflammation.

MicroRNA-34/449 targets IGFBP-3 and attenuates airway remodeling by suppressing Nur77-mediated autophagy

Autophagy plays critical roles in airway inflammation and fibrosis-mediated airway remodeling and many factors including proinflammatory cytokines and inflammation related pathways are involved in the process. The aim of the present study was to examine the role of epithelial microRNAs (miRNAs) in autophagy-mediated airway remodeling and to identify the factors involved and the underlying mechanisms. Serum miR-34/449, inflammatory factors, and autophagy and fibrosis-related proteins were determined by real-time PCR, enzyme-linked immunosorbent assay and western blotting in 46 subjects with asthma and 10 controls and in the lung epithelial cell line BEAS-2B induced with IL-13 and treated with miRNA mimics. Luciferase assays were used to verify IGFBP-3 as a target of miR-34/449, and immunohistochemistry, immunofluorescence and co-immunoprecipitation were used in vitro and in vivo study. miR-34/449 were downregulated in patients with asthma in parallel with the upregulation of autophagy-related proteins. Proinflammatory factors and fibrosis-related proteins were significantly higher in asthma patients than in healthy controls. IL-13 induction promoted autophagy and upregulated miR-34/449 in BEAS-2B cells, and these effects were restored by IGFBP-3 silencing. miR-34/449 overexpression suppressed autophagy, decreased fibrosis, activated Akt, downregulated fibrosis-related factors, and downregulated proinflammatory cytokines and nuclear factor κB by targeting IGFBP-3. In vivo experiments showed that miR-34/449 overexpression was associated with Nur77 nuclear translocation and IGFBP-3 downregulation in parallel with decreased airway remodeling by decreased autophagy. miR-34/449 are potential biomarkers and therapeutic targets in asthma. miR-34/449 may contribute to airway inflammation and fibrosis by modulating IGFBP-3 mediated autophagy activation.

Tonic LAT-HDAC7 Signals Sustain Nur77 and Irf4 Expression to Tune Naive CD4 T Cells

CD4+ T cells differentiate into T helper cell subsets in feedforward manners with synergistic signals from the T cell receptor (TCR), cytokines, and lineage-specific transcription factors. Naive CD4+ T cells avoid spontaneous engagement of feedforward mechanisms but retain a prepared state. T cells lacking the adaptor molecule LAT demonstrate impaired TCR-induced signals yet cause a spontaneous lymphoproliferative T helper 2 (TH2) cell syndrome in mice. Thus, LAT constitutes an unexplained maintenance cue. Here, we demonstrate that tonic signals through LAT constitutively export the repressor HDAC7 from the nucleus of CD4+ T cells. Without such tonic signals, HDAC7 target genes Nur77 and Irf4 are repressed. We reveal that Nur77 suppresses CD4+ T cell proliferation and uncover a suppressive role for Irf4 in TH2 polarization; halving Irf4 gene-dosage leads to increases in GATA3+ and IL-4+ cells. Our studies reveal that naive CD4+ T cells are dynamically tuned by tonic LAT-HDAC7 signals.

Orphan nuclear receptor Nur77 inhibits poly (I:C)-triggered acute liver inflammation by inducing the ubiquitin-editing enzyme A20

Inflammation is a key contributor to various types of acute and chronic liver disease. We recently reported that lack of Nur77, an orphan nuclear receptor, contributes to the pathogenesis of inflammatory diseases including inflammatory bowel disease and sepsis. However, whether Nur77 plays a critical role in liver inflammation remains to be fully understood. Employing in vivo acute liver inflammation model in wild-type (Nur77^+/+) and Nur77^-/- mice, we here found that Nur77 deficiency dramatically increased the production of pro-inflammatory cytokines and accelerated liver injury induced by poly (I:C)/D-GalN in Nur77^-/- mice. Mechanistically, Nur77 acts as a negative regulator of NF-κB signaling by inducing the expression of ubiquitin-editing enzyme A20, a novel target gene of Nur77. Notably, in inflammatory cells, overexpression of A20 enhanced, whereas knockdown of A20 by siRNA approach impaired, the inhibitory effect of Nur77 on poly (I:C)-triggered inflammation. Collectively, our data suggest that the orphan nuclear receptor Nur77 plays a protective role in poly (I:C)-triggered liver inflammation by inducing A20, thus making it a promising target for the prevention and treatment of liver inflammation.

Rheb1 deletion in myeloid cells aggravates OVA-induced allergic inflammation in mice

The small GTPase ras homolog enriched in brain (Rheb) is a downstream target of tuberous sclerosis complex 1/2 (TSC1/2) and an upstream activator of the mechanistic target of rapamycin complex 1 (mTORC1), the emerging essential modulator of M1/M2 balance in macrophages. However, the role and regulatory mechanisms of Rheb in macrophage polarization and allergic asthma are not known. In the present study, we utilized a mouse model with myeloid cell-specific deletion of the Rheb1 gene and an ovalbumin (OVA)-induced allergic asthma model to investigate the role of Rheb1 in allergic asthma and macrophage polarization. Increased activity of Rheb1 and mTORC1 was observed in myeloid cells of C57BL/6 mice with OVA-induced asthma. In an OVA-induced asthma model, Rheb1-KO mice demonstrated a more serious inflammatory response, more mucus production, enhanced airway hyper-responsiveness, and greater eosinophil numbers in bronchoalveolar lavage fluid (BALF). They also showed increased numbers of bone marrow macrophages and BALF myeloid cells, elevated M2 polarization and reduced M1 polarization of macrophages. Thus, we have established that Rheb1 is critical for the polarization of macrophages and inhibition of allergic asthma. Deletion of Rheb1 enhances M2 polarization but decreases M1 polarization in alveolar macrophages, leading to the aggravation of OVA-induced allergic asthma.

Effect of a retinoid X receptor partial agonist on airway inflammation and hyperresponsiveness in a murine model of asthma

Background

Retinoid X receptors (RXRs) are members of the nuclear receptor (NR) superfamily that mediate signaling by 9-cis retinoic acid, a vitamin A (retinol) derivative. RXRs play key roles not only as homodimers but also as heterodimeric partners—e.g., retinoic acid receptors (RARs), vitamin D receptors (VDRs), liver X receptors (LXRs), and peroxisome proliferator-activated receptors (PPARs). The NR family was recently associated with allergic diseases, but the role of RXRs in allergen-induced airway responses is not well defined.

The goal of this study is to elucidate the role of RXRs in asthma pathogenesis and the potency of RXR partial agonist in the treatment of allergic airway inflammation and airway hyperresponsiveness using a murine model of asthma.

Methods

We investigated the effect of a novel RXR partial agonist (NEt-4IB) on the development of allergic airway inflammation and airway hyperresponsiveness (AHR) in a murine model of asthma. Balb/c mice were sensitized (days 0 and 14) and challenged (days 28–30) with ovalbumin (OVA), and airway inflammation and airway responses were monitored 48 h after the last OVA challenge. NEt-4IB was administered orally on days 25 to 32.

Results

Oral administration of NEt-4IB significantly suppressed AHR and inflammatory cell accumulation in the airways and attenuated the levels of TNF-α in the lung and IL-5, IL-13 and NO levels in bronchoalveolar lavage (BAL) fluid and the number of periodic acid Schiff (PAS)-positive goblet cells in lung tissue. Treatment with NEt-4IB also significantly suppressed NF-κB expression.

Conclusion

These data suggest that RXRs may be of crucial importance in the mechanism of allergic asthma and that the novel RXR partial agonist NEt-4IB may be a promising candidate for the treatment of allergic airway inflammation and airway hyperresponsiveness in a model of allergic asthma.

Nur77 attenuates endothelin-1 expression via downregulation of NF-κB and p38 MAPK in A549 cells and in an ARDS rat model

Acute respiratory distress syndrome (ARDS) is characterized by inflammatory injury to the alveolar and capillary barriers that results in impaired gas exchange and severe acute respiratory failure. Nuclear orphan receptor Nur77 has emerged as a regulator of gene expression in inflammation, and its role in the pathogenesis of ARDS is not clear. The objective of this study is to investigate the potential role of Nur77 and its underlying mechanism in the regulation of endothelin-1 (ET-1) expression in lipopolysaccharide (LPS)-induced A549 cells and an ARDS rat model. We demonstrate that LPS induced Nur77 expression and nuclear export in A549 cells. Overexpression of Nur77 markedly decreased basal and LPS-induced ET-1 expression in A549 cells, whereas knockdown of Nur77 increased the ET-1 expression. LPS-induced phosphorylation and nuclear translocation of NF-κB and p38 MAPK were blocked by Nur77 overexpression and augmented by Nur77 knockdown in A549 cells. In vivo, LPS induced Nur77 expression in lung in ARDS rats. Pharmacological activation of Nur77 by cytosporone B (CsnB) inhibited ET-1 expression in ARDS rats, decreased LPS-induced phosphorylation of NF-κB and p38 MAPK, and relieved lung, liver, and kidney injury. Pharmacological deactivation of Nur77 by 1,1-bis-(3'-indolyl)-1-(p-hydroxyphenyl)methane (DIM-C-pPhOH, C-DIM8) had no effect on ET-1 expression and lung injury. These results indicated that Nur77 decreases ET-1 expression by suppressing NF-κB and p38 MAPK in LPS-stimulated A549 cells in vitro, and, in an LPS-induced ARDS rat model, CsnB reduced ET-1 expression and lung injury in ARDS rats.

Targeted inhibition of Six1 attenuates allergic airway inflammation and remodeling in asthmatic mice

Asthma is an inflammatory disease of the airways, characterized by lung eosinophilia, mucus hypersecretion by goblet cells and airway hyperresponsiveness to inhaled allergens. The purpose of this study was to evaluate the effects of Six1 on airway inflammation and remodeling and the underlying mechanisms in a murine model of chronic asthma. Female BALB/c mice were randomly divided into four groups: phosphate-buffered saline control, ovalbumin (OVA)-induced asthma group, OVA+siNC and OVA+siSix1. In this mice model, Six1 expression level was significantly elevated in OVA-induced asthma of mice. Additionally, downregulation of Six1 dramatically decreased OVA-challenged inflammation, infiltration, and mucus production. Moreover, silencing of Six1 resulted in decreased levels of immunoglobulin E and inflammatory mediators and reduced inflammatory cell accumulation, as well as inhibiting the expression of important mediators including matrix metalloproteinase MMP-2 and MMP-9, which is related to airway remodeling. Further analysis indicated that silencing of Six1 can significantly inhibit NF-kB pathway activation in the lungs. .In conclusion, these findings indicated that the downregulation of Six1 effectively inhibited airway inflammation and reversed airway remodeling, which suggest that Six1 represents a promising therapeutic strategy for human allergic asthma.

Macrolactins from Marine-Derived Bacillus subtilis B5 Bacteria as Inhibitors of Inducible Nitric Oxide and Cytokines Expression

In order to find new natural products with anti-inflammatory activity, chemical investigation of a 3000-meter deep-sea sediment derived bacteria Bacillus subtilis B5 was carried out. A new macrolactin derivative was isolated and identified as 7,13-epoxyl-macrolactin A (1). Owing to the existence of the epoxy ring, 1 exhibited a significant inhibitory effect on the expression of inducible nitric oxide and cytokines, compared with previously isolated known macrolactins (2-5). Real-time Polymerase Chain Reaction (PCR) analysis showed that the new compound significantly inhibited the mRNA expressions of inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and interleukin-6 (IL-6) in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Reverse transcription-PCR analysis demonstrated that the new compound reduced the mRNA expression level of IL-1β in a concentration-dependent manner.