Nurr1 dependent regulation of pro-inflammatory mediators in immortalised synovial fibroblasts

Advances in NURR1-Regulated Neuroinflammation Associated with Parkinson's Disease

Neuroinflammation plays a crucial role in the progression of neurodegenerative disorders, particularly Parkinson's disease (PD). Glial cell activation and subsequent adaptive immune involvement are neuroinflammatory features in familial and idiopathic PD, resulting in the death of dopaminergic neuron cells. An oxidative stress response, inflammatory mediator production, and immune cell recruitment and activation are all hallmarks of this activation, leading to chronic neuroinflammation and progressive neurodegeneration. Several studies in PD patients' cerebrospinal fluid and peripheral blood revealed alterations in inflammatory markers and immune cell populations that may lead to or exacerbate neuroinflammation and perpetuate the neurodegenerative process. Most of the genes causing PD are also expressed in astrocytes and microglia, converting their neuroprotective role into a pathogenic one and contributing to disease onset and progression. Nuclear receptor-related transcription factor 1 (NURR1) regulates gene expression linked to dopaminergic neuron genesis and functional maintenance. In addition to playing a key role in developing and maintaining neurotransmitter phenotypes in dopaminergic neurons, NURR1 agonists have been shown to reverse behavioral and histological abnormalities in animal PD models. NURR1 protects dopaminergic neurons from inflammation-induced degeneration, specifically attenuating neuronal death by suppressing the expression of inflammatory genes in microglia and astrocytes. This narrative review highlights the inflammatory changes in PD and the advances in NURR1-regulated neuroinflammation associated with PD. Further, we present new evidence that targeting this inflammation with a variety of potential NURR1 target therapy medications can effectively slow the progression of chronic neuroinflammation-induced PD.

NR4A1-3 nuclear receptor activity and immune cell dysregulation in rheumatic diseases

The development and progression of immune-mediated rheumatic disease (IMRD) involves dysfunction of innate and adaptive immune cell populations leading to altered responses including inflammasome activation, dysregulated cytokine networks, increased immune cell numbers and multifaceted cell-cell communication. Several rheumatic diseases are further characterized by the presence of autoantibodies, immune complex mediated complement activation and the deficit of peripheral immune tolerance due to reduced regulatory T-lymphocyte cell function. Ultimately, in rheumatic disease the loss in cellular and tissue homeostasis culminates in the advancement of chronic inflammation. The three members of the NR4A subfamily of nuclear receptors are immediate early genes, and act as potent transcriptional responders to changes in the cellular and tissue microenvironment. Subfamily members are rapidly expressed in diseases characterized by inflammation and function to control the differentiation and activity of innate and adaptive immune cells in a cell-type and cell-context specific manner. Rheumatic disease including rheumatoid-, psoriatic-, osteo-arthritis and systemic sclerosis display altered NR4A1-3 activity in controlling immune cell migration and function, production of paracrine signaling molecules, synovial tissue hyperplasia, and regulating cartilage turn-over in vivo. Additionally, NR4A1-3 activities mediate cytokine, prostanoid and growth factor signaling to control angiogenesis, modulate the regulatory functions of mesenchymal stromal cells, alter the activation status of dendritic cells, influence the generation of peripheral myeloid and T-lymphocyte lineages and promote the maintenance of functional regulatory T-cells. Further reports uncover the potential of moderating NR4A 1-3 receptors as therapeutic targets in altering immune tolerance, pathological angiogenesis and controlling inflammation in several models of disease.

NURR1 expression regulates retinal pigment epithelial-mesenchymal transition and age-related macular degeneration phenotypes

Phenotypic variations in the retinal pigment epithelial (RPE) layer are often a predecessor and driver of ocular degenerative diseases, such as age-related macular degeneration (AMD), the leading cause of vision loss in the elderly. We previously identified the orphan nuclear receptor-related 1 (NURR1), from a nuclear receptor atlas of human RPE cells, as a candidate transcription factor potentially involved in AMD development and progression. In the present study we characterized the expression of NURR1 as a function of age in RPE cells harvested from human donor eyes and in donor tissue from AMD patients. Mechanistically, we found an age-dependent shift in NURR1 dimerization from NURR1-RXRα heterodimers toward NURR1-NURR1 homodimers in primary human RPE cells. Additionally, overexpression and activation of NURR1 attenuated TNF-α-induced epithelial-to-mesenchymal transition (EMT) and migration, and modulated EMT-associated gene and protein expression in human RPE cells independent of age. In vivo, oral administration of IP7e, a potent NURR1 activator, ameliorated EMT in an experimental model of wet AMD and improved retinal function in a mouse model that presents with dry AMD features, impacting AMD phenotype, structure, and function of RPE cells, inhibiting accumulation of immune cells, and diminishing lipid accumulation. These results provide insight into the mechanisms of action of NURR1 in the aging eye, and demonstrate that the relative expression levels and activity of NURR1 is critical for both physiological and pathological functions of human RPE cells through RXRα-dependent regulation, and that targeting NURR1 may have therapeutic potential for AMD by modulating EMT, inflammation, and lipid homeostasis.

Nurr1 Is Not an Essential Regulator of BDNF in Mouse Cortical Neurons

Nurr1 and brain-derived neurotrophic factor (BDNF) play major roles in cognition. Nurr1 regulates BDNF in midbrain dopaminergic neurons and cerebellar granule cells. Nurr1 and BDNF are also highly expressed in the cerebral cortex, a brain area important in cognition. Due to Nurr1 and BDNF tissue specificity, the regulatory effect of Nurr1 on BDNF in different brain areas cannot be generalized. The relationship between Nurr1 and BDNF in the cortex has not been investigated previously. Therefore, we examined Nurr1-mediated BDNF regulation in cortical neurons in activity-dependent and activity-independent states. Mouse primary cortical neurons were treated with the Nurr1 agonist, amodiaquine (AQ). Membrane depolarization was induced by KCl or veratridine and reversed by nimodipine. AQ and membrane depolarization significantly increased Nurr1 (p < 0.001) and BDNF (pAQ < 0.001, pKCl < 0.01) as assessed by real-time qRT-PCR. However, Nurr1 knockdown did not affect BDNF gene expression in resting or depolarized neurons. Accordingly, the positive correlation between Nurr1 and BDNF expression in AQ and membrane depolarization experiments does not imply co-regulation because Nurr1 knockdown did not affect BDNF gene expression in resting or depolarized cortical neurons. Therefore, in contrast to midbrain dopaminergic neurons and cerebellar granule cells, Nurr1 does not regulate BDNF in cortical neurons.

Orphan Nuclear Receptor NR4A2 Is Constitutively Expressed in Cartilage and Upregulated in Inflamed Synovium From hTNF-Alpha Transgenic Mice

Orphan nuclear receptor 4A2 (NR4A2/Nurr1) is a constitutively active transcription factor with potential roles in the onset and progression of inflammatory arthropathies. NR4A2 is overexpressed in synovium and cartilage from individuals with rheumatoid arthritis (RA), psoriatic arthritis, and osteoarthritis. This study documents the expression and tissue localization of NR4A2 and upstream regulator nuclear factor kappa B (NF-κB) in the human tumor necrosis factor-alpha (hTNF-α) transgenic mouse model of RA. Since TNF-α is a potent inducer of NR4A2 in vitro, we hypothesized that NR4A2 would also be upregulated and active during disease progression in this model. Expression levels of NR4A2, related receptors NR4A1 (Nur77) and 3 (NOR1), and NF-κB₁ transcripts were quantified by RT-qPCR in hTNF-α and wild-type joints at three stages of disease. The protein distribution of NR4A2 and NF-κB subunit RelA (p65) was analyzed by quantitative immunohistochemistry. Global gene expression of 88 RA-related genes was also screened and compared between groups. Consistent with previous reports on the hTNF-α model, transgenic mice exhibited significant weight loss and severely swollen paws by 19 weeks of age compared to age-matched wild-type controls. NR4A1-3 and NF-κB₁ were constitutively expressed at disease onset and in healthy joints. NF-κB₁ transcript levels increased 2-fold in hTNF-α paws with established disease (12 weeks), followed by a 2-fold increase in NR4A2 at the late disease stage (19 weeks). NR4A2 and RelA proteins were overexpressed in inflamed synovium prior to symptoms of arthritis, suggesting that gene expression changes documented in whole paws were largely driven by elevated expression in diseased synovium. Broader screening of RA-related genes by RT-qPCR identified several differentially expressed genes in hTNF-α joints including those encoding inflammatory cytokines and chemokines, matrix-degrading enzymes and inhibitors, cell surface receptors, intracellular signaling proteins and transcription factors. Consensus binding sites for NR4A receptors and NF-κB₁ were enriched in the promoters of differentially expressed genes suggesting central roles for these transcription factors in this model. This study is the first comprehensive analysis of NR4A2 in an animal model of RA and validates the hTNF-α model for testing of small molecules and genetic strategies targeting this transcription factor.

The function of nuclear hormone receptor 4A signaling in the human reproductive system: A review

AIM

This review aims to summarize the research focused upon the functions of nuclear hormone receptor 4A (NR4A) in the human reproductive system. The research questions addressed are to decipher what role the NR4A subfamily plays in the regulation of the human reproductive system and effects upon fertility issues through regulation of the expression of the NR4A subfamily.

METHODS

The electronic database PubMed was searched for studies published before November 2021. Keywords included "NR4A," "trophoblast," "decidualization," "folliculogenesis," "estrogen," "pregnancy," "Leydig cells," "fertility," and "reproductive." Relevant references from retrieved manuscripts and review articles were also searched manually.

RESULTS

NR4A subfamily are involved in trophoblast differentiation, endometrial decidualization, embryo adhesion, secretion of related hormones, and regulation of spontaneous term labor. Besides, many studies have provided strong evidence that they play critical roles in spermatogenesis. Furthermore, Multiple mechanisms can affect the expression of NR4As. Broadly, NR4A family receptors affect the human reproductive system in multiple ways.

CONCLUSIONS

Further research is needed to specifically dissect the functions and regulatory mechanisms of these receptors and their pharmaceutical antagonists and agonists. The connection between the NR4A subfamily and a variety of reproductive disorders needs to be proven experimentally such that further examination of human tissue is required to assess the role of these receptors in human reproductive diseases.

Recent Advances in Drug Repurposing for Parkinson's Disease

As a long-term degenerative disorder of the central nervous system that mostly affects older people, Parkinson's disease is a growing health threat to our ever-aging population. Despite remarkable advances in our understanding of this disease, all therapeutics currently available only act to improve symptoms but cannot stop the disease progression. Therefore, it is essential that more effective drug discovery methods and approaches are developed, validated, and used for the discovery of disease-modifying treatments for Parkinson's disease. Drug repurposing, also known as drug repositioning, or the process of finding new uses for existing or abandoned pharmaceuticals, has been recognized as a cost-effective and timeefficient way to develop new drugs, being equally promising as de novo drug discovery in the field of neurodegeneration and, more specifically for Parkinson's disease. The availability of several established libraries of clinical drugs and fast evolvement in disease biology, genomics and bioinformatics has stimulated the momentums of both in silico and activity-based drug repurposing. With the successful clinical introduction of several repurposed drugs for Parkinson's disease, drug repurposing has now become a robust alternative approach to the discovery and development of novel drugs for this disease. In this review, recent advances in drug repurposing for Parkinson's disease will be discussed.

Organogermanium suppresses cell death due to oxidative stress in normal human dermal fibroblasts

Reactive oxygen species (ROS) are very harmful to dermal cells, and it is thus important to develop cosmetics that protect the skin from ROS and other stimuli. Repagermanium is a synthetic water-soluble organogermanium polymer, and in this study, we attempted to visualize the incorporation of germanium into normal human dermal fibroblasts (NHDFs) using isotope microscopy. In addition, the content of 3-(trihydroxygermyl)propanoic acid (THGP), a hydrolyzed monomer of repagermanium, in NHDFs was determined through liquid chromatography mass spectrometry (LC-MS/MS), and the dose-dependent incorporation of THGP was confirmed. We then evaluated the preventive effects of THGP against ROS-induced NHDF death and confirmed the observed preventive effects through gene profiling and expression analysis. The addition of 0.59–5.9 mM THGP reduced cell death resulting from ROS damage caused by the reaction between xanthine oxidase and hypoxanthine and the direct addition of H₂O₂. Furthermore, this study provides the first demonstration that the effect of THGP was not due to the direct scavenging of ROS, which indicates that the mechanism of THGP differs from that of general antioxidants, such as ascorbic acid. The gene profiling and expression analysis showed that THGP suppressed the expression of the nuclear receptor subfamily 4 group A member 2 (NR4A2) gene, which is related to cell death, and the interleukin 6 (IL6) and chemokine (C-X-C motif) ligand 2 (CXCL2) genes, which are related to the inflammatory response. Furthermore, the production of IL6 induced by H₂O₂ was suppressed by the THGP treatment. Our data suggest that the preventive effect of THGP against ROS-induced cell death is not due to antioxidant enzymes or ROS scavenging.

Molecular Insights into NR4A2(Nurr1): an Emerging Target for Neuroprotective Therapy Against Neuroinflammation and Neuronal Cell Death

NR4A2 is a nuclear receptor and a transcription factor, with distinctive physiological features. In the cell nuclei of the central nervous system, it is widely expressed and identified as a crucial regulator of dopaminergic (DA) neuronal differentiation, survival, and maintenance. Importantly, it has regulated different genes crucial for dopaminergic signals, and its expression has been diminished in both aged and PD post-mortem brains and reduced in PD patients. In microglia and astrocytes, the expression of NR4A2 has been found where it can be capable of inhibiting the expression of proinflammatory mediators; hence, it protected inflammation-mediated DA neuronal death. In addition, NR4A2 plays neuroprotective role via regulating different signals. However, NR4A2 has been mainly focused on Parkinson's research, but, in recent times, it has been studied in Alzheimer's disease (AD), multiple sclerosis (MS), and stroke. Altered expression of NR4A2 is connected to AD progression, and activation of its may improve cognitive function. It is downregulated in peripheral blood mononuclear cells of MS patients; nonetheless, its role in MS has not been fully clear. miR-145-5p known as a putative regulator of NR4A2 and in a middle cerebral artery occlusion/reperfusion model, anti-miR-145-5p administration promoted neurological outcomes in rat. To date, various activators and modulators of NR4A2 have been discovered and investigated as probable therapeutic drugs in neuroinflammatory and neuronal cell death models. The NR4A2 gene and cell-based therapy are described as promising drug candidates for neurodegenerative diseases. Moreover, microRNA might have a crucial role in neurodegeneration via affecting NR4A2 expression. Herein, we present the role of NR4A2 in neuroinflammation and neuronal cell death focusing on neurodegenerative conditions and display NR4A2 as a promising therapeutic target for the therapy of neuroprotection.

A novel diindolylmethane analog, 1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane, inhibits the tumor necrosis factor-induced inflammatory response in primary murine synovial fibroblasts through a Nurr1-dependent mechanism

The progression of rheumatoid arthritis involves the thickening of the synovial lining due to the proliferation of fibroblast-like synoviocytes (FLS) and infiltration by inflammatory cells. Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine involved in progression of the disease. Under rheumatoid conditions, FLS express the tumor necrosis factor (TNF)-recognition complex (TNFR1, TNFR2, VCAM-1 and ICAM-1), which induces local macrophage activation and leads to downstream nuclear factor κB (NF-κB) signaling. The NF-κB-regulated inflammatory gene, cyclooxygenase (COX), increases synthesis of prostaglandins that contribute to the propagation of inflammatory damage within the joint. Because the nuclear orphan receptor, NR4A2 (Nurr1), can negatively regulate NF-κB-dependent inflammatory gene expression in macrophages, we postulated that activation of this receptor by the Nurr1 ligand 1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane (C-DIM12) would modulate inflammatory gene expression in synovial fibroblasts by inhibiting NF-κB. Treatment with C-DIM12 suppressed TNFα-induced expression of adhesion molecules and NF-κB regulated genes in primary synovial fibroblasts including vascular adhesion molecule 1 (VCAM-1), PGE2 and COX-2. Immunofluorescence studies indicated that C-DIM12 did not prevent translocation of p65 and stabilized nuclear localization of Nurr1 in synovial fibroblasts. Knockdown of Nurr1 expression by RNA interference prevented the inhibitory effects of C-DIM12 on inflammatory gene expression, indicating that the anti-inflammatory effects of this compound are Nurr1-dependent. Collectively, these data suggest that this receptor may be a viable therapeutic target in RA.

Effect of spontaneous term labour on the expression of the NR4A receptors nuclear receptor related 1 protein (Nurr1), neuron-derived clone 77 (Nur77) and neuron-derived orphan receptor 1 (NOR1) in human fetal membranes and myometrium

Inflammation has been implicated in the mechanisms responsible for human labour. Emerging evidence indicates that nuclear receptor subfamily 4A (NR4A) receptors regulate the transcription of genes involved in inflammation. The aim of the present study was to determine the effect of spontaneous term labour, Toll-like receptor (TLR) ligands and nucleotide-binding oligomerisation domain-containing (NOD) ligands on the expression of nuclear receptor related 1 protein (Nurr1), neuron-derived clone 77 (Nur77) and neuron-derived orphan receptor 1 (NOR1) in human fetal membranes and myometrium. Human fetal membranes and myometrium were collected from term non-labouring women and women after spontaneous labour onset. Tissue explants were used to determine the effect of the bacterial products lipopolysaccharide (LPS; TLR4 ligand), flagellin (TLR5 ligand), fibroblast-stimulating lipopeptide (FSL-1) (TLR2 ligand), γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP) (NOD1 ligand) or minimal peptidoglycan muramyl dipeptide (MDP; NOD2 ligand) on Nurr1, Nur77 and NOR1 expression. Term labour was associated with significantly higher Nurr1 and Nur77, but not NOR1, expression in fetal membranes and myometrium. LPS and MDP increased Nurr1, Nur77 and NOR in fetal membranes; flagellin increased Nurr1 in fetal membranes and the myometrium, as well as NOR1 in the myometrium; and FSL-1 increased Nurr1 expression in fetal membranes. In summary, human labour and bacterial products increase Nurr1, Nur77 and/or NOR1 expression in human fetal membranes and myometrium. This increase in NR4A receptors may contribute to the expression of proinflammatory and pro-labour genes associated with fetal membrane rupture and myometrial contractions.

A purine antimetabolite attenuates toll-like receptor-2, -4, and subarachnoid hemorrhage-induced brain apoptosis

BACKGROUND

Upregulation of high-level toll-like receptors (TLRs) is observed in the serum of animals following experimental subarachnoid hemorrhage (SAH) and is highly related to SAH-induced early brain injury (EBI). The present study was of interest to examine the effect of 6-mercaptopurine (6-MP) on alternation of TLR-2, -3, and -4 in this model.

METHODS

A rodent SAH model was used. Administration with 6-MP (0.5/1/2 mg/kg/d) was initiated 1 h after the induction of SAH via an osmotic minipump. Cerebral cortex was harvested to measure TLRs messenger RNA and protein (reverse transcription polymerase chain reaction [rt-PCR] and Western blot). Cerebral cortex was harvested for activated caspases (rt-PCR) measurement.

RESULTS

Cellular evaluation revealed increased neuronal nuclei(+) neurons with vacuolated nuclear and glial fibrillary acidic protein(+) astrocytes in the SAH group, but absent in the 6-MP treatment and healthy controls. The TLR-3 levels were not significantly increased in animals subject to SAH, compared with the controls (no SAH). The levels of TLR-2 and -4 in the SAH only and SAH plus vehicle groups were significantly elevated (P < 0.01), and treatment with 6-MP reduced TLR-2, -3 (at 2 mg/kg), and -4 (dose-dependently) protein expression following SAH. Likewise, the TLR-4 messenger RNA levels were also significantly reduced in the 6-MP (at 1 mg/kg and 2 mg/kg) groups. Cleaved caspase-3 and caspase-9a were reduced at 2-mg/kg 6-MP treatment group.

CONCLUSIONS

These results show that 6-MP attenuates the expression of TLR-2, -4, especially TLR-4, which play an antiapoptotic effect on SAH-induced EBI. This finding supported that through modulating TLRs, 6-MP can attenuate SAH-induced EBI. Those results offer credit to the neuroprotective effect of 6-MP.

Orphan nuclear receptor NR4A2 induces transcription of the immunomodulatory peptide hormone prolactin

Background

Nuclear receptor 4A2 (NR4A2) is an orphan nuclear receptor and constitutively active transcription factor expressed at elevated levels in inflamed joint tissues from patients with arthritis. Inflammatory mediators rapidly and potently induce NR4A2 expression in resident joint cells and infiltrating immune cells. This receptor promotes synovial hyperplasia by increasing proliferation of synoviocytes and inducing transcription of matrix degrading enzymes and pro-inflammatory mediators. In order to further elucidate the molecular mechanisms of NR4A2, we conducted a gene expression screen to identify novel transcriptional targets of NR4A2 that may contribute to arthritis progression.

Methods

NR4A2 was over-expressed in human synoviocytes by lentiviral transduction and gene expression changes were measured using qPCR arrays specific for inflammation, proliferation, adhesion, and migration pathways. Subsequent analysis focused on the most potently induced gene prolactin (PRL). Messenger RNA levels of PRL and PRL receptor (PRL-R) were measured by RT-qPCR and protein levels were measured by ELISA. PRL promoter studies were conducted in synoviocytes transiently transfected with NR4A2 and PRL reporter constructs. Molecular responses to PRL in synoviocytes were addressed using qPCR arrays specific for JAK/STAT signaling pathways.

Results

PRL was the most potently induced gene on the qPCR arrays, exhibiting a 68-fold increase in response to ectopic NR4A2. This gene encodes an immunomodulatory peptide hormone with roles in autoimmune diseases and inflammation. Induction of PRL mRNA and secreted protein by NR4A2 was confirmed in subsequent experiments, with increases of 300-fold and 18-fold respectively. Depletion of endogenous NR4A receptors with shRNA reduced basal and PGE₂-induced PRL levels by 95%. At the transcriptional level, NR4A2 requires a functional DNA binding domain to transactivate the distal PRL promoter. Deletional analysis indicates that NR4A2 targets a region of the distal PRL promoter spanning −270 to -32 bp. In synoviocytes, recombinant PRL regulates several genes involved in inflammation, proliferation, and cell survival, suggesting that NR4A2 induced PRL may also impact these pathways and contribute to arthritis progression.

Conclusions

These results provide the first evidence for transcriptional regulation of the immunomodulatory peptide hormone PRL by NR4A2 in synoviocytes, and highlight a novel molecular pathway in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-015-0059-2) contains supplementary material, which is available to authorized users.

Chemoprevention of skin cancer with 1,1-Bis (3'-indolyl)-1-(aromatic) methane analog through induction of the orphan nuclear receptor, NR4A2 (Nurr1)

Background

The objective of this study was to demonstrate the anti-skin cancer and chemopreventive potential of 1,1-bis(3′-indolyl)-1-(p-chlorophenyl methane) (DIM-D) using an in vitro model.

Methods

In vitro cell cytotoxicity and viability assays were carried out in A431 human epidermoid carcinoma cell line and normal human epidermal keratinocytes (NHEK) respectively by crystal violet staining. Apoptosis induction in A431 cells (DIM-D treated) and NHEK cells pretreated with DIM-D (2 hr) prior to UVB irradiation, were assessed. The accumulation of reactive oxygen species (ROS) in DIM-D pretreated NHEK cells (2 hr) prior to UVB exposure was also determined. Immunocytochemistry and western blot analysis was performed to determine cleaved caspase 3 and DNA damage markers in DIM-D treated A431 cells and in DIM-D pretreated NHEK cells prior to UVB irradiation.

Results

The IC50 values of DIM-D were 68.7±7.3, 48.3±10.1 and 11.5±3.1 μM whilst for Epigallocatechin gallate (EGCG) were 419.1±8.3, 186.1±5.2 and 56.7±3.1 μM for 24, 48 and 72 hr treatments respectively. DIM-D exhibited a significantly (p<0.05) greater induction of DNA fragmentation in A431 cells compared to EGCG with percent cell death of 38.9. In addition, DIM-D induced higher expression in A431 cells compared to EGCG of cleaved caspase 3 (3.0-fold vs. 2.4-fold changes), Nurr1 (2.7-fold vs. 1.7-fold changes) and NFκB (1.3-fold vs. 1.1-fold changes). DIM-D also exhibited chemopreventive activity in UVB-irradiated NHEK cells by significantly (p<0.05) reducing UVB-induced ROS formation and apoptosis compared to EGCG. Additionally, DIM-D induced expression of Nurr1 but reduced expression of 8-OHdG significantly in UVB-irradiated NHEK cells compared to EGCG and UV only.

Conclusion

Our results suggest that DIM-D exhibits Nurr1-dependent transactivation in the induction of apoptosis in A431 cells and it protects NHEK cells against UVB-induced ROS formation and DNA damage.

Tumor necrosis factor inhibition modulates thrombospondin-1 expression in human inflammatory joint disease through altered NR4A2 activity

We examined thrombospondin-1 (THBS1, alias TSP-1) expression in human synovial tissue (ST) during the resolution phase of chronic inflammation and elucidated its transcriptional regulation by the orphan receptor 4A2 (NR4A2). In vivo, rheumatoid arthritis (RA) serum and ST revealed altered expression levels and tissue distribution of TSP-1. After anti-tumor necrosis factor therapy, a reciprocal relationship between TSP-1 and NR4A2 expression levels was measured in patients with clinical and ST responses to biological treatment. In vitro, primary RA fibroblast-like synoviocytes (FLSs) expressed minimal TSP-1 mRNA levels with high transcript levels of NR4A2, vascular endothelial growth factor (VEGF), and IL-8 measured. Hypoxic modulation of RA FLSs resulted in inverse expression levels of TSP-1 compared with NR4A2, IL-8, and VEGF. Ectopic NR4A2 expression led to reduced TSP-1 mRNA and protein levels with concomitant increases in proangiogenic mediators. NR4A2 transcriptional activity, independent of DNA binding, repressed the hTSP-1 promoter leading to reduced mRNA and protein release in immortalized K4IM FLSs. Bioinformatic and deletion studies identified a 5' region of the TSP-1 promoter repressed by NR4A2 and proangiogenic transcription factors, including NF-κB and Ets1/2. Stable depletion of NR4A2 levels resulted in a shift in the TSP-1/VEGF expression ratio. Thus, modulation of TSP-1 expression is achieved through anti-tumor necrosis factor therapy effects on specific transcriptional networks, suggesting that enhanced TSP-1 expression may help restore tissue homeostasis during resolution of inflammation.

Gene expression profiling and association studies implicate the neuregulin signaling pathway in Behçet's disease susceptibility

Behçet's disease (BD) is a complex disease with genetic and environmental risk factors implicated in its etiology; however, its pathophysiology is poorly understood. To decipher BD's genetic underpinnings, we combined gene expression profiling with pathway analysis and association studies. We compared the gene expression profiles in peripheral blood mononuclear cells (PBMCs) of 15 patients and 14 matched controls using Affymetrix microarrays and found that the neuregulin signaling pathway was over-represented among the differentially expressed genes. The Epiregulin (EREG), Amphiregulin (AREG), and Neuregulin-1 (NRG1) genes of this pathway stand out as they are also among the top differentially expressed genes. Twelve haplotype tagging SNPs at the EREG-AREG locus and 15 SNPs in NRG1 found associated in at least one published BD genome-wide association study were tested for association with BD in a dataset of 976 Iranian patients and 839 controls. We found a novel association with BD for the rs6845297 SNP located downstream of EREG, and replicated three associations at NRG1 (rs4489285, rs383632, and rs1462891). Multifactor dimensionality reduction analysis indicated the existence of epistatic interactions between EREG and NRG1 variants. EREG-AREG and NRG1, which are members of the epidermal growth factor (EGF) family, seem to modulate BD susceptibility through main effects and gene-gene interactions. These association findings support a role for the EGF/ErbB signaling pathway in BD pathogenesis that warrants further investigation and highlight the importance of combining genetic and genomic approaches to dissect the genetic architecture of complex diseases.

Early life permethrin exposure induces long-term brain changes in Nurr1, NF-kB and Nrf-2

Pesticide exposure during brain development represents an important risk factor for the onset of brain-aging processes. Here, the impact of permethrin administered to rats from 6th to 21st day of life, at a dose near to "no observed adverse effect level" (NOAEL), was studied when animals reached 500 day-old. The permethrin treatment induced a decrease in Nurr1 gene expression in striatum, an increase in hippocampus and cerebellum, while the protein level changed only in striatum where it was increased. NF-kB p65 gene expression was increased in cerebellum, while its protein level augmented in cerebellum and in prefrontal cortex and decreased in hippocampus of treated rats compared to control ones. Nrf-2 gene expression resulted significantly higher only in cerebellum of treated animals. The results suggest that early life permethrin treatment induces long-lasting effects leading to dopaminergic neuronal disorders, monitored by Nurr1 alteration. Moreover the impairment of NF-kB and Nrf-2, important for the balance between pro- and anti-inflammatory systems, confirms that the neonatal permethrin treatment can influence genes involved with the onset of brain-ageing processes.

Orphan nuclear receptor NR4A2 induces synoviocyte proliferation, invasion, and matrix metalloproteinase 13 transcription

OBJECTIVE

To address the role of the nuclear receptor 4A (NR4A) family of orphan nuclear receptors in synoviocyte transformation, hyperplasia, and regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in models of inflammatory arthritis.

METHODS

NR4A messenger RNA levels in synovial tissue and primary synoviocytes were measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR). NR4A2 was stably overexpressed in normal synoviocytes, and cell proliferation, survival, anchorage-independent growth, migration, and invasion were monitored in vitro. MMP and TIMP expression levels were analyzed by quantitative RT-PCR, and MMP-13 promoter activity was measured using reporter assays. Stable depletion of endogenous NR4A levels was achieved by lentiviral transduction of NR4A short hairpin RNA (shRNA), and the effects on proliferation, migration, and MMP-13 expression were analyzed.

RESULTS

NR4A2 was expressed at elevated levels in normal, OA, and RA synovial tissue and in primary RA synoviocytes. Tumor necrosis factor α (TNFα) rapidly and selectively induced expression of NR4A2 in synoviocytes. Ectopic expression of NR4A2 in normal synoviocytes significantly increased proliferation and survival, promoted anchorage-independent growth, and induced migration and invasion. MMP-13 gene expression was synergistically induced by NR4A2 and TNFα, while expression of TIMP-2 was antagonized. NR4A2 directly transactivated the proximal MMP-13 promoter, and a point mutation in the DNA binding domain of NR4A2 abolished transcriptional activation. Depletion of endogenous NR4A receptors with shRNA reduced synoviocyte proliferation, migration, and MMP-13 expression.

CONCLUSION

The orphan nuclear receptor NR4A2 is a downstream mediator of TNFα signaling in synovial tissue. NR4A2 transcriptional activity contributes to the hyperplastic and invasive phenotype of synoviocytes that leads to cartilage destruction, suggesting that this receptor may show promise as a therapeutic target in inflammatory arthritis.

Efficacy of concurrent administration of cilostazol and methotrexate in rheumatoid arthritis: pharmacologic and clinical significance

AIMS

This study aimed to assess the beneficial effects of the concurrent administration of cilostazol and methotrexate (MTX) on the synovial fibroblasts obtained from patients with rheumatoid arthritis (RA), and in a mouse model of collagen-induced arthritis (CIA).

MAIN METHODS

Production of TNF-α, IL-1β, IL-6 and MCP-1 on synovial fibroblasts from RA patients was determined by RT-PCR. Cell proliferation, viability and apoptosis were measured. Anti-arthritic effects were evaluated in CIA mice.

KEY FINDING

Concurrent use of cilostazol and MTX effectively suppressed proliferation and cell viability associated with enhanced apoptosis of synovial fibroblasts and significantly suppressed cytokine production, including TNF-α, IL-1β, IL-6, and MCP-1 in an additive manner. In line with these findings, LPS-induced increased expression of NURR1 mRNA and protein were suppressed by cilostazol and MTX in accordance with suppression of NF-κB p65 activity. These suppressed effects were reversed by KT5720 (cAMP-protein kinase inhibitor) and ZM 241385 (A(2A) receptor antagonist), respectively. In CIA mice, treatment with cilostazol, MTX and their combination significantly decreased clinical signs with improvement of histopathological status in the paw of mice, accompanied by reduced serum cytokine levels. Likewise, following concurrent administration, CD68 (+)-cell recruitment, proteoglycan depletion and osteoclast formation were significantly suppressed in association with repressed RANKL expression in the joints of CIA mice.

SIGNIFICANCE

In conclusion, a combination of cilostazol and MTX may provide an effective therapeutic strategy for the suppression of inflammation and the prevention of joint damage in RA via activation of the cAMP-dependent protein kinase in the synovial fibroblasts.

The Transcription Factor NURR1 Exerts Concentration-Dependent Effects on Target Genes Mediating Distinct Biological Processes

The transcription factor NURR1 plays a pivotal role in the development and maintenance of neurotransmitter phenotype in midbrain dopamine neurons. Conversely, decreased NURR1 expression is associated with a number of dopamine-related CNS disorders, including Parkinson's disease and drug addiction. In order to better understand the nature of NURR1-responsive genes and their potential roles in dopamine neuron differentiation and survival, we used a human neural cellular background (SK-N-AS cells) in which to generate a number of stable clonal lines with graded NURR1 gene expression that approximated that seen in DA cell-rich human substantia nigra. Gene expression profiling data from these NURR1-expressing clonal lines were validated by quantitative RT-PCR and subjected to bioinformatic analyses. The present study identified a large number of NURR1-responsive genes and demonstrated the potential importance of concentration-dependent NURR1 effects in the differential regulation of distinct NURR1 target genes and biological pathways. These data support the promise of NURR1-based CNS therapeutics for the neuroprotection and/or functional restoration of DA neurons.

Research resource: nuclear receptor atlas of human retinal pigment epithelial cells: potential relevance to age-related macular degeneration

Retinal pigment epithelial (RPE) cells play a vital role in retinal physiology by forming the outer blood-retina barrier and supporting photoreceptor function. Retinopathies including age-related macular degeneration (AMD) involve physiological and pathological changes in the epithelium, severely impairing the retina and effecting vision. Nuclear receptors (NRs), including peroxisome proliferator-activated receptor and liver X receptor, have been identified as key regulators of physiological pathways such as lipid metabolic dysregulation and inflammation, pathways that may also be involved in development of AMD. However, the expression levels of NRs in RPE cells have yet to be systematically surveyed. Furthermore, cell culture lines are widely used to study the biology of RPE cells, without knowledge of the differences or similarities in NR expression and activity between these in vitro models and in vivo RPE. Using quantitative real-time PCR, we assessed the expression patterns of all 48 members of the NR family plus aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator in human RPE cells. We profiled freshly isolated cells from donor eyes (in vivo), a spontaneously arising human cell line (in vitro), and primary cell culture lines (in vitro) to determine the extent to which NR expression in the cultured cell lines reflects that of in vivo. To evaluate the validity of using cell culture models for investigating NR receptor biology, we determined transcriptional activity and target gene expression of several moderately and highly expressed NRs in vitro. Finally, we identified a subset of NRs that may play an important role in pathobiology of AMD.

Expression of pro-inflammatory TACE-TNF-α-amphiregulin axis in Sjögren's syndrome salivary glands

The tumor-necrosis-factor-converting-enzyme (TACE)-TNF-α-Amphiregulin (AREG) axis plays an important pathogenic role in inflammatory and autoimmune disorders. However, the pathological roles of these proteins in the chronic autoimmune disease Sjögren's syndrome (SS) remain to be elucidated. It is known that the TACE-AREG axis is clearly part of a larger cascade of signals that starts with the activation of Furin, responsible for maturation of TACE that, in turn, determines the production of active TNF-α, directly involved in the up-regulation of AREG expression. This study showed that Furin, TACE, TNF-α, and AREG proteins, detected in acinar and ductal cells of human salivary glands from SS patients, increased remarkably in comparison with biopsies of labial salivary glands from healthy controls. The changes in Furin, TACE, TNF- α, and AREG proteins' level detected in salivary glands biopsies of SS patients could be responsible for pro-inflammatory cytokines overexpression characterizing Sjögren's syndrome.

6-Mercaptopurine attenuates adhesive molecules in experimental vasospasm

OBJECTIVE

Adhesion molecules, including intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin, are important inflammatory mediators which are elevated in the serum of patients following aneurysmal subarachnoid hemorrhage (SAH). The authors previously found that 6-mercaptopurine (6-mp) was effective in preventing and reversing arterial narrowing in a rodent SAH model. The present study was to examine whether levels of adhesion molecules were altered after treatment with 6-mp in this animal model.

MATERIALS AND METHODS

Animals were each injected with autologous blood into the cisterna magna, and intraperitoneal treatment with 6-mp (2 mg/kg) was initiated 1 h before (prevention) or later (treatment). The compound was subsequently administered at 24 and 48 h post-SAH. Blood samples were collected at 72 h post-SAH to measure ICAM-1, VCAM-1, and E-selectin levels. The basilar arteries were harvested and sliced, and their cross-sectional areas were measured. Morphologically, convolution of the internal elastic lamina, distorted endothelial wall, and myonecrosis of the smooth muscle were prominently observed in the SAH only and vehicle-treated SAH groups, but not in the 6-mp-treated SAH group or in healthy controls. No significant differences were found in the levels of VCAM-1 among all groups. However, the levels of E-selectin were increased in all animals subjected to SAH (SAH only and SAH plus vehicle groups) compared with healthy controls (no SAH), but not in the 6-mp group (SAH plus 6-mp treatment and preventive treatment with 6-mp).Likewise, the levels of ICAM-1 in the SAH only and SAH plus vehicle groups were significantly elevated (p < 0.001), and pretreatment and treatment with 6-mp reduced ICAM-1 to control levels.

CONCLUSION

These results show that ICAM-1 and E-selectin may play a role in mediating SAH-induced vasospasm and that a reduction of both adhesive molecules after SAH may partly contribute to the antispastic effect of 6-mp.

Dexamethasone-pDMAEMA polymeric conjugates reduce inflammatory biomarkers in human intestinal epithelial monolayers

The mucoadhesive polymer, poly(dimethylamino)ethyl methacrylate, (pDMAEMA), was synthesised by living radical polymerisation and subsequently conjugated by quaternisation reaction to a functionalised anti-inflammatory corticosteroid dexamethasone, to separately yield two conjugates with either 9:1 or 18:1 molar ratios of dexamethasone:polymer respectively. The hypothesis was to test whether the active agent maintained in vitro bioactivity when exposed to the apical side of human intestinal epithelial monolayers, Caco-2 and mucus-covered HT29-MTX-E12 (E12). HPLC analysis indicated high conjugate purity. Similar to pDMAEMA, fluorescently-labelled dexamethasone-pDMAEMA conjugates were bioadhesive to Caco-2 and mucoadhesive to E12. Apical addition of conjugates suppressed mRNA expression of the inflammatory markers, NURR1 and ICAM-1 in E12 following stimulation by PGE(2) and TNF-alpha, respectively. Conjugates also suppressed TNF-alpha stimulated cytokine secretion to the basolateral side of Caco-2 monolayers. Measurement of dexamethasone permeability from conjugates across monolayers suggested that conjugation reduced permeability compared to free dexamethasone. LDH assay indicated that conjugates were not cytotoxic to monolayers. Anti-inflammatory agents can therefore be successfully conjugated to polymers and they retain adhesion and bioactivity and have potential to be formulated for topical administration.

Increased Expression of the Orphan Nuclear Receptor NURR1 in Psoriasis and Modulation following TNF-α Inhibition

The orphan nuclear receptor NURR1 belongs to the NR4A subfamily of transcription factors which are emerging as important mediators of cytokine and growth factor signaling. The transcriptional function of these ligand-independent and constitutively active receptors is controlled at the level of expression and nuclear localization. This study examines the expression of NURR1 in psoriasis and biological effects on this receptor following inhibition of tumor necrosis factor-alpha (TNF-alpha) signaling. We report increased expression of NURR1 mRNA and protein in involved psoriasis skin compared with uninvolved and normal skin, which correlates significantly (P=0.0055) with clinical measures of the psoriasis area and severity index. Enhanced NURR1 expression localizes to both nucleus and cytoplasm of cells of involved epidermis, blood vessels, and inflammatory infiltrates, in contrast to predominant cytoplasmic distribution in uninvolved and normal skin. Endogenous NURR1 levels are rapidly and selectively increased in response to proinflammatory agonists and growth factors in normal dermal endothelial cells. Following TNF-alpha inhibition with infliximab or etanercept, NURR1 mRNA and protein levels in involved skin are significantly decreased and cytoplasmic distribution is restored. These findings establish the aberrant expression and distribution of NURR1 in psoriasis and suggest that clinical benefits of TNF-alpha inhibition may be mediated through altered NURR1 activity.

Transcriptional repression of matrix metalloproteinase gene expression by the orphan nuclear receptor NURR1 in cartilage

The NR4A orphan receptors (Nur77, NURR1, and NOR-1) are emerging as key regulators of cytokine and growth factor action in chronic inflammatory diseases. In this study, we address the role of these receptors in cartilage homeostasis during inflammatory joint disease. We document for the first time expression of the NR4A receptors in osteoarthritic cartilage. Relative to Nur77 and NOR-1, NURR1 is expressed at the highest level and correlates with cyclooxygenase-2 levels in cartilage. Consistent with this observation, cyclooxygenase-2-derived prostaglandin E(2) (PGE(2)) rapidly and potently induces NURR1 expression in chondrocytes, suggesting that this receptor may regulate PGE(2)-mediated processes in cartilage. We demonstrate that PGE(2) represses interleukin-1beta-induced matrix metalloproteinase (MMP)-1 and that transient overexpression of NURR1 is sufficient to antagonize expression of this gene. Furthermore, MMP-1 promoter activity is potently suppressed by NURR1, resulting in a significant reduction in endogenous MMP-1 mRNA and secreted pro-MMP-1 protein. In addition, NURR1 selectively antagonizes cytokine-induced MMP-3 and -9 expression with minimal effects on MMP-2 and -13 and tissue inhibitor of matrix metalloproteinases-1 and -2. To explore the molecular mechanisms of NURR1 transrepression, we reveal that this receptor targets a critical region of the MMP-1 promoter (-1772 to -1546 bp) and that repression does not require consensus binding sites for NURR1. We confirm that NURR1 targets a 40-bp promoter sequence that is also positively regulated by ETS transcription factors. Finally, functional studies indicate that transcriptional antagonism exists between NURR1 and ETS1 on the MMP-1 promoter. We propose a protective function for NURR1 in cartilage homeostasis by selectively repressing MMP gene expression during inflammation.