NR4A2 as a Novel Target Gene for Developmental and Epileptic Encephalopathy: A Systematic Review of Related Disorders and Therapeutic Strategies.

The NR4A2 gene encodes an orphan transcription factor of the steroid-thyroid hormone-retinoid receptor superfamily. This review focuses on the clinical findings associated with the pathogenic variants so far reported, including three unreported cases. Also, its role in neurodegenerative diseases, such as Parkinson's or Alzheimer's disease, is examined, as well as a brief exploration on recent proposals to develop novel therapies for these neurological diseases based on small molecules that could modulate NR4A2 transcriptional activity. The main characteristic shared by all patients is mild to severe developmental delay/intellectual disability. Moderate to severe disorder of the expressive and receptive language is present in at least 42%, while neuro-psychiatric issues were reported in 53% of patients. Movement disorders, including dystonia, chorea or ataxia, are described in 37% patients, although probably underestimated because of its frequent onset in late adolescence-young adulthood. Finally, epilepsy was surprisingly present in 42% of patients, being drug-resistant in three of them. The age at onset varied widely, from five months to twenty-six years, as did the classification of epilepsy, which ranged from focal epilepsy to infantile spasms or Lennox-Gastaut syndrome. Accordingly, we propose that NR4A2 should be considered as a first-tier target gene for the genetic diagnosis of developmental and epileptic encephalopathy.

Albiflorin ameliorates thioacetamide-induced hepatic fibrosis: The involvement of NURR1-mediated inflammatory signaling cascades in hepatic stellate cells activation.

Thioacetamide (TAA) within the liver generates hepatotoxic metabolites that can be induce hepatic fibrosis, similar to the clinical pathological features of chronic human liver disease. The potential protective effect of Albiflorin (ALB), a monoterpenoid glycoside found in Paeonia lactiflora Pall, against hepatic fibrosis was investigated. The mouse hepatic fibrosis model was induced with an intraperitoneal injection of TAA. Hepatic stellate cells (HSCs) were subjected to treatment with transforming growth factor-beta (TGF-ß), while lipopolysaccharide/adenosine triphosphate (LPS/ATP) was added to stimulate mouse peritoneal macrophages (MPMs), leading to the acquisition of conditioned medium. For TAA-treated mice, ALB reduced ALT, AST, HYP levels in serum or liver. The administration of ALB reduced histopathological abnormalities, and significantly regulated the expressions of nuclear receptor-related 1 protein (NURR1) and the P2X purinoceptor 7 receptor (P2×7r) in liver. ALB could suppress HSCs epithelial-mesenchymal transition (EMT), extracellular matrix (ECM) deposition, and pro-inflammatory factor level. ALB also remarkably up-regulated NURR1, inhibited P2×7r signaling pathway, and worked as working as C-DIM12, a NURR1 agonist. Moreover, deficiency of NURR1 in activated HSCs and Kupffer cells weakened the regulatory effect of ALB on P2×7r inhibition. NURR1-mediated inhibition of inflammatory contributed to the regulation of ALB ameliorates TAA-induced hepatic fibrosis, especially based on involving in the crosstalk of HSCs-macrophage. Therefore, ALB plays a significant part in the mitigation of TAA-induced hepatotoxicity this highlights the potential of ALB as a protective intervention for hepatic fibrosis.

PON3::LCN1 and HTN3::MSANTD3 Gene Fusions With NR4A3/NR4A2 Expression in Salivary Acinic Cell Carcinoma.

Acinic cell carcinoma of the salivary gland (AciCC) is a low-grade carcinoma characterized by the overexpression of the transcription factor nuclear receptor subfamily 4 group A member 3 (NR4A3). AciCC has been the subject of a few molecular research projects. This study delves into AciCC's molecular landscape to identify additional alterations and explore their clinical implications. RNA sequencing and immunohistochemical staining for markers NR4A3/NR4A2, DOG-1, S100, and mammaglobin were utilized on 41 AciCCs and 11 secretory carcinoma (SC) samples. NR4A3 was evident in 35 AciCCs, while the residual 6 were NR4A3-negative and NR4A2-positive; SC samples were consistently NR4A3-negative. A novel fusion, PON3 exon 1- LCN1 exon 5, was detected in 9/41 (21.9%) AciCCs, exhibiting a classical histologic pattern with serous cell components growing in solid sheets alongside the intercalated duct-like component. Clinical follow-up of 39 patients over a median of 59 months revealed diverse prognostic outcomes: 34 patients exhibited no disease evidence, whereas the remaining 5 experienced poorer prognosis, involving local recurrence, lymph node, and distant metastasis, and disease-associated death, 4 of which harbored the PON3::LCN1 fusion. In addition, the HTN3::MSANTD3 fusion was recurrently identified in 7/41 AciCC cases. SC patients lacked both fusions. Immunohistochemistry uncovered differential expression of DOG-1, S100, and mammaglobin across samples, providing nuanced insights into their roles in AciCC. This study accentuates PON3::LCN1 and HTN3::MSANTD3 fusions as recurrent molecular events in AciCC, offering potential diagnostic and prognostic utility and propelling further research into targeted therapeutic strategies.

Unveiling the methionine cycle: a key metabolic signature and NR4A2 as a methionine-responsive oncogene in esophageal squamous cell carcinoma.

Esophageal squamous cell carcinoma (ESCC) is a deadly malignancy with notable metabolic reprogramming, yet the pivotal metabolic feature driving ESCC progression remains elusive. Here, we show that methionine cycle exhibits robust activation in ESCC and is reversely associated with patient survival. ESCC cells readily harness exogenous methionine to generate S-adenosyl-methionine (SAM), thus promoting cell proliferation. Mechanistically, methionine augments METTL3-mediated RNA m6A methylation through SAM and revises gene expression. Integrative omics analysis highlights the potent influence of methionine/SAM on NR4A2 expression in a tumor-specific manner, mediated by the IGF2BP2-dependent stabilization of methylated NR4A2 mRNA. We demonstrate that NR4A2 facilitates ESCC growth and negatively impacts patient survival. We further identify celecoxib as an effective inhibitor of NR4A2, offering promise as a new anti-ESCC agent. In summary, our findings underscore the active methionine cycle as a critical metabolic characteristic in ESCC, and pinpoint NR4A2 as a novel methionine-responsive oncogene, thereby presenting a compelling target potentially superior to methionine restriction.

Bis-Indole Derivatives as Dual Nuclear Receptor 4A1 (NR4A1) and NR4A2 Ligands.

Bis-indole derived compounds such as 1,1-bis(3'-indolyl)-1-(3,5-disubstitutedphenyl) methane (DIM-3,5) and the corresponding 4-hydroxyl analogs (DIM8-3,5) are NR4A1 ligands that act as inverse NR4A1 agonists and are potent inhibitors of tumor growth. The high potency of several DIM-3,5 analogs (IC50 < 1 mg/kg/day), coupled with the >60% similarity of the ligand-binding domains (LBDs) of NR4A1 and NR4A2 and the pro-oncogenic activities of both receptors lead us to hypothesize that these compounds may act as dual NR4A1 and NR4A2 ligands. Using a fluorescence binding assay, it was shown that 22 synthetic DIM8-3,5 and DIM-3,5 analogs bound the LBD of NR4A1 and NR4A2 with most KD values in the low µM range. Moreover, the DIM-3,5 and DIM8-3,5 analogs also decreased NR4A1- and NR4A2-dependent transactivation in U87G glioblastoma cells transfected with GAL4-NR4A1 or GAL4-NR4A2 chimeras and a UAS-luciferase reporter gene construct. The DIM-3,5 and DIM8-3,5 analogs were cytotoxic to U87 glioblastoma and RKO colon cancer cells and the DIM-3,5 compounds were more cytotoxic than the DIM8-3,5 compounds. These studies show that both DIM-3,5 and DIM8-3,5 compounds previously identified as NR4A1 ligands bind both NR4A1 and NR4A2 and are dual NR4A1/2 ligands.

Orphan Nuclear Receptor Family 4A (NR4A) Members NR4A2 and NR4A3 Selectively Modulate Elements of the Monocyte Response to Buffered Hypercapnia.

Hypercapnia occurs when the partial pressure of carbon dioxide (CO2) in the blood exceeds 45 mmHg. Hypercapnia is associated with several lung pathologies and is transcriptionally linked to suppression of immune and inflammatory signalling through poorly understood mechanisms. Here we propose Orphan Nuclear Receptor Family 4A (NR4A) family members NR4A2 and NR4A3 as potential transcriptional regulators of the cellular response to hypercapnia in monocytes. Using a THP-1 monocyte model, we investigated the sensitivity of NR4A family members to CO2 and the impact of depleting NR4A2 and NR4A3 on the monocyte response to buffered hypercapnia (10% CO2) using RNA-sequencing. We observed that NR4A2 and NR4A3 are CO2-sensitive transcription factors and that depletion of NR4A2 and NR4A3 led to reduced CO2-sensitivity of mitochondrial and heat shock protein (Hsp)-related genes, respectively. Several CO2-sensitive genes were, however, refractory to depletion of NR4A2 and NR4A3, indicating that NR4As regulate certain elements of the cellular response to buffered hypercapnia but that other transcription factors also contribute. Bioinformatic analysis of conserved CO2-sensitive genes implicated several novel putative CO2-sensitive transcription factors, of which the ETS Proto-Oncogene 1 Transcription Factor (ETS-1) was validated to show increased nuclear expression in buffered hypercapnia. These data give significant insights into the understanding of immune responses in patients experiencing hypercapnia.

PROKR1-CREB-NR4A2 axis for oxidative muscle fiber specification and improvement of metabolic function.

Metabolic disorders are characterized by an imbalance in muscle fiber composition, and a potential therapeutic approach involves increasing the proportion of oxidative muscle fibers. Prokineticin receptor 1 (PROKR1) is a G protein-coupled receptor that plays a role in various metabolic functions, but its specific involvement in oxidative fiber specification is not fully understood. Here, we investigated the functions of PROKR1 in muscle development to address metabolic disorders and muscular diseases. A meta-analysis revealed that the activation of PROKR1 upregulated exercise-responsive genes, particularly nuclear receptor subfamily 4 group A member 2 (NR4A2). Further investigations using ChIP-PCR, luciferase assays, and pharmacological interventions demonstrated that PROKR1 signaling enhanced NR4A2 expression by Gs-mediated phosphorylation of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) in both mouse and human myotubes. Genetic and pharmacological interventions showed that the PROKR1-NR4A2 axis promotes the specification of oxidative muscle fibers in both myocytes by promoting mitochondrial biogenesis and metabolic function. Prokr1-deficient mice displayed unfavorable metabolic phenotypes, such as lower lean mass, enlarged muscle fibers, impaired glucose, and insulin tolerance. These mice also exhibited reduced energy expenditure and exercise performance. The deletion of Prokr1 resulted in decreased oxidative muscle fiber composition and reduced activity in the Prokr1-CREB-Nr4a2 pathway, which were restored by AAV-mediated Prokr1 rescue. In summary, our findings highlight the activation of the PROKR1-CREB-NR4A2 axis as a mechanism for increasing the oxidative muscle fiber composition, which positively impacts overall metabolic function. This study lays an important scientific foundation for the development of effective muscular-metabolic therapeutics with unique mechanisms of action.

A role of NR4A2 in Graves' disease: regulation of Th17/Treg.

PURPOSE: This study aimed to explore the molecular pathogenesis of Graves' disease (GD). METHODS: The gene expression profile in CD4+ T cells from GD patients and healthy controls were analyzed through mRNA-sequencing. The expression of NR4A2 was determined by quantitative real-time PCR and western blot. The levels of Th17 and Treg were determined by flow cytometry. ELISA was employed to detect the levels of IL-10, IL-17A, IL-17F and IL-22. RESULTS: In the CD4+ T cells from GD patients, there were 128 up-regulated and 510 down-regulated genes. Subsequently, we focused on the role of nuclear receptor 4 group A member 2 (NR4A2) in GD. NR4A2 was lowly expressed in the CD4+ T cells from GD patients. Its expression was negatively correlated with free triiodothyronine and tetraiodothyronine, but positively correlated with thyroid stimulating hormone. NR4A2 knockdown decreased the percentage of Treg cells, with a decreased IL-10 level. While its over-expression augmented the Treg differentiation, with an elevated IL-10 level. In addition, knockdown or over-expression of NR4A2 showed no significant influence on Th17 differentiation. CONCLUSION: These results indicate that the low level of NR4A2 in GD patients may suppress Treg differentiation, but have no influence on Th17 differentiation, leading to the imbalance of Th17/Treg and contributing to the development of GD. Revealing the role of NR4A2 in GD provides a novel insight for the treatment of GD.

The nuclear receptor Nurr1 is preferentially expressed in human pro-inflammatory macrophages and limits their inflammatory profile.

Nurr1 is a member of the orphan nuclear receptor family NR4A (nuclear receptor subfamily 4 group A) that modulates inflammation in several cell lineages, both positively and negatively. Macrophages are key regulators of inflammatory responses, yet information about the role of Nurr1 in human macrophages is scarce. Here we examined Nurr1 expression and activity in steady state and activated human macrophages. Pro- and anti-inflammatory macrophages were generated in vitro by culture of blood monocytes with granulocyte/macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF), respectively. Nurr1 expression was predominant in macrophages with the pro-inflammatory phenotype. Nurr1 activation with the agonists 1,1-bis(3'-indolyl)-1-(p-chlorophenyl) methane (C-DIM12) or isoxazolo-pyridinone 7e (IP7e) did not globally modify the polarization status of pro-inflammatory macrophages, but they decreased their production of TNF, IL-1ß, IL-6, IL-8, IL-12 p40, CCL2, IFN-ß, and reactive oxygen species, with variable potencies. Conversely, Nurr1 deficient macrophages increased the expression of transcripts encoding inflammatory mediators, particularly that of IL6, IFNB1, and CCL2. Mechanistically, endogenous Nurr1 interacted with NF-κB p65 in basal conditions and upon lipopolysaccharide (LPS)-mediated activation. C-DIM12 stabilized those complexes in cells exposed to LPS and concurrently decreased NF-κB transcriptional activity and p65 nuclear translocation. Expression of high levels of Nurr1 was associated with a subset of dermal macrophages that display enhanced levels of TNF and lower expression of the anti-inflammatory marker CD163L1 in skin lesions from patients with bullous pemphigoid (BP), a chronic inflammatory autoimmune blistering disorder. These results suggest that Nurr1 expression is linked with the pro-inflammatory phenotype of human macrophages, both in vivo and in vitro, where it may constitute a brake to attenuate the synthesis of inflammatory mediators.

Natural products and synthetic analogs as selective orphan nuclear receptor 4A (NR4A) modulators.

Although endogenous ligands for the orphan nuclear receptor 4A1 (NR4A1, Nur77), NR4A2 (Nurr1), and NR4A3 (Nor-1) have not been identified, several natural products and synthetic analogs bind NR4A members. These studies are becoming increasingly important since members of the NR4A subfamily of 3 receptors are potential drug targets for treating cancer and non-cancer endpoints and particularly those conditions associated with inflammatory diseases. Ligands that bind NR4A1, NR4A2, and NR4A3 including Cytosporone B, celastrol, bis-indole derived (CDIM) compounds, tryptophan/indolic, metabolites, prostaglandins, resveratrol, piperlongumine, fatty acids, flavonoids, alkaloids, peptides, and drug families including statins and antimalarial drugs. The structural diversity of NR4A ligands and their overlapping and unique effects on NR4A1, NR4A2, and NR4A3 suggest that NR4A ligands are selective NR4A modulators (SNR4AMs) that exhibit tissue-, structure-, and response-specific activities. The SNR4AM activities of NR4A ligands are exemplified among the Cytosporone B analogs where n-pentyl-2-[3,5-dihydroxy-2-(nonanoyl)]phenyl acetate (PDNPA) binds NR4A1, NR4A2 and NR4A3 but activates only NR4A1 and exhibits significant functional differences with other Cytosporone B analogs. The number of potential clinical applications of agents targeting NR4A is increasing and this should spur future development of SNR4AMs as therapeutics that act through NR4A1, NR4A2 and NR4A3.

Exploring Fatty Acid Mimetics as NR4A Ligands.

The ligand-activated transcription factors Nur77, Nurr1, and NOR-1 forming the NR4A family of nuclear receptors are considered as potential targets in various pathologies, including neurodegeneration and cancer. However, chemical tools for pharmacological NR4A modulation as a prerequisite for target validation are rare. Recent findings suggest that NR4As bind fatty acid metabolites and fatty acid mimetic (FAM) drugs, opening new opportunities for NR4A modulator development. We have explored the chemical space of FAM NR4A ligands by using fragment screening, in silico analysis, and systematic structure-activity relationship evaluation. From a chemically diverse library of 92 fragments, we identified 11 new FAM NR4A agonist and inverse agonist scaffolds. Structural optimization of the most active FAM fragment yielded NR4A agonists with submicromolar potency and binding affinity, demonstrating remarkable potential of FAM as NR4A-modulating tools and drugs.

Structure-Guided Design of Nurr1 Agonists Derived from the Natural Ligand Dihydroxyindole.

The neuroprotective transcription factor Nurr1 was recently found to bind the dopamine metabolite 5,6-dihydroxyindole (DHI) providing access to Nurr1 ligand design from a natural template. We screened a custom set of 14 k extended DHI analogues in silico for optimized descendants to select 24 candidates for microscale synthesis and in vitro testing. Three out of six primary hits were validated as novel Nurr1 agonists with up to sub-micromolar binding affinity, highlighting the druggability of the Nurr1 surface region lining helix 12. In vitro profiling confirmed cellular target engagement of DHI descendants and demonstrated remarkable additive effects of combined Nurr1 agonist treatment, indicating diverse binding sites mediating Nurr1 activation, which may open new avenues in Nurr1 modulation.

(-)-Epigallocatechin-3-gallate promotes intestinal epithelial proliferation and barrier function after ischemia/reperfusion injury via activation of Nurr1.

CONTEXT: (-)-Epigallocatechin-3-gallate (EGCG) is involved in cell proliferation and ischemia/reperfusion (I/R) injury of several organs. OBJECTIVE: To identify the role of EGCG in intestinal epithelial proliferation and barrier exposed to I/R injury. MATERIAL AND METHODS: Fifty Sprague-Dawley rats were divided into sham, I/R, I/R + EGCG (12.5 mg/kg), I/R + EGCG (25 mg/kg) and I/R + EGCG (50 mg/kg). I/R group rats were subjected to intestinal ischemia for 1 h and 6 h reperfusion. The rats were supplemented with EGCG 12.5, 25 and 50 mg/kg daily for 3 days via intraperitoneal injection before surgery. We used IEC-6 to expose to hypoxia/reoxygenation (H/R) injury to mimic I/R in vivo. IEC-6 cells were divided into control, H/R and H/R + EGCG (40 µmol/L). The effects of EGCG and its mechanism was explored. RESULTS: Pharmacological treatment with EGCG notably improves intestinal epithelial proliferation (12.5 mg/kg, 1.74-fold; 25 mg/kg, 2.93-fold, and 50 mg/kg, 4.33-fold) and barrier function after I/R injury. EGCG promoted cell proliferation (2.99-fold) and increased the expression of occludin (2.36-fold) and ZO-1 (1.64-fold) in IEC-6 cells after H/R injury. EGCG promoted proliferation of IEC-6 cells with ED50 values of 18.16 µmol/L. Further investigations indicated that EGCG activated Nurr1 expression in intestine after I/R injury. EGCG promote cell proliferation and increased the expression of occludin and ZO-1 in IEC-6 cells after H/R injury were abrogated in the knockdown of Nurr1 by siRNA. DISCUSSION AND CONCLUSION: Our findings indicate that EGCG promotes intestinal epithelial cell proliferation and barrier function after I/R injury in vitro and in vivo via activation of Nurr1.

Mechanisms of NURR1 Regulation: Consequences for Its Biological Activity and Involvement in Pathology.

NURR1 (Nuclear receptor-related 1 protein or NR4A2) is a nuclear protein receptor transcription factor with an essential role in the development, regulation, and maintenance of dopaminergic neurons and mediates the response to stressful stimuli during the perinatal period in mammalian brain development. The dysregulation of NURR1 activity may play a role in various diseases, including the onset and progression of neurodegenerative diseases, and several other pathologies. NURR1 is regulated by multiple mechanisms, among which phosphorylation by kinases or SUMOylation are the best characterized. Both post-translational modifications can regulate the activity of NURR1, affecting its stability and transcriptional activity. Other non-post-translational regulatory mechanisms include changes in its subcellular distribution or interaction with other protein partners by heterodimerization, also affecting its transcription activity. Here, we summarize the currently known regulatory mechanisms of NURR1 and provide a brief overview of its participation in pathological alterations.

Smoke and Spike: Benzo[a]pyrene Enhances SARS-CoV-2 Infection by Boosting NR4A2-Induced ACE2 and TMPRSS2 Expression.

Cigarette smoke aggravates severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the underlying mechanisms remain unclear. Here, they show that benzo[a]pyrene in cigarette smoke extract facilitates SARS-CoV-2 infection via upregulating angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2). Benzo[a]pyrene trans-activates the promoters of ACE2 and TMPRSS2 by upregulating nuclear receptor subfamily 4 A number 2 (NR4A2) and promoting its binding of NR4A2 to their promoters, which is independent of functional genetic polymorphisms in ACE2 and TMPRSS2. Benzo[a]pyrene increases the susceptibility of lung epithelial cells to SARS-CoV-2 pseudoviruses and facilitates the infection of authentic Omicron BA.5 in primary human alveolar type II cells, lung organoids, and lung and testis of hamsters. Increased expression of Nr4a2, Ace2, and Tmprss2, as well as decreased methylation of CpG islands at the Nr4a2 promoter are observed in aged mice compared to their younger counterparts. NR4A2 knockdown or interferon-λ2/λ3 stimulation downregulates the expression of NR4A2, ACE2, and TMPRSS2, thereby inhibiting the infection. In conclusion, benzo[a]pyrene enhances SARS-CoV-2 infection by boosting NR4A2-induced ACE2 and TMPRSS2 expression. This study elucidates the mechanisms underlying the detrimental effects of cigarette smoking on SARS-CoV-2 infection and provides prophylactic options for coronavirus disease 2019, particularly for the elderly population.

An optimized Nurr1 agonist provides disease-modifying effects in Parkinson's disease models.

The nuclear receptor, Nurr1, is critical for both the development and maintenance of midbrain dopamine neurons, representing a promising molecular target for Parkinson's disease (PD). We previously identified three Nurr1 agonists (amodiaquine, chloroquine and glafenine) that share an identical chemical scaffold, 4-amino-7-chloroquinoline (4A7C), suggesting a structure-activity relationship. Herein we report a systematic medicinal chemistry search in which over 570 4A7C-derivatives were generated and characterized. Multiple compounds enhance Nurr1's transcriptional activity, leading to identification of an optimized, brain-penetrant agonist, 4A7C-301, that exhibits robust neuroprotective effects in vitro. In addition, 4A7C-301 protects midbrain dopamine neurons in the MPTP-induced male mouse model of PD and improves both motor and non-motor olfactory deficits without dyskinesia-like behaviors. Furthermore, 4A7C-301 significantly ameliorates neuropathological abnormalities and improves motor and olfactory dysfunctions in AAV2-mediated α-synuclein-overexpressing male mouse models. These disease-modifying properties of 4A7C-301 may warrant clinical evaluation of this or analogous compounds for the treatment of patients with PD.

Development of a Potent Nurr1 Agonist Tool for In Vivo Applications.

Nuclear receptor related 1 (Nurr1) is a neuroprotective transcription factor and an emerging target in neurodegenerative diseases. Despite strong evidence for a role in Parkinson's and Alzheimer's disease, pharmacological control and validation of Nurr1 are hindered by a lack of suitable ligands. We have discovered considerable Nurr1 activation by the clinically studied dihydroorotate dehydrogenase (DHODH) inhibitor vidofludimus calcium and systematically optimized this scaffold to a Nurr1 agonist with nanomolar potency, strong activation efficacy, and pronounced preference over the highly related receptors Nur77 and NOR1. The optimized compound induced Nurr1-regulated gene expression in astrocytes and exhibited favorable pharmacokinetics in rats, thus emerging as a superior chemical tool to study Nurr1 activation in vitro and in vivo.

The nuclear receptor subfamily 4 group A1 in human disease.

Nuclear receptor 4A1 (NR4A1), a member of the NR4A subfamily, acts as a gene regulator in a wide range of signaling pathways and responses to human diseases. Here, we provide a brief overview of the current functions of NR4A1 in human diseases and the factors involved in its function. A deeper understanding of these mechanisms can potentially improve drug development and disease therapy.

Protective effect of Nr4a2 (Nurr1) against LPS-induced depressive-like behaviors via regulating activity of microglia and CamkII neurons in anterior cingulate cortex.

Neuroinflammation is tightly associated with onset of depression. The nuclear receptor related 1 protein (Nurr1, also called Nr4a2), its roles in dopaminergic neurons is well understood, which can alleviate inflammation. Nevertheless, potential effects of Nr4a2 on neuroinflammation associated with depression still remains unclear. Chronic lipopolysaccharides (LPS) stress induced depressive-behaviors were confirmed via behavioral tests. Differentially expressed genes were detected by using RNA-sequencing. The anterior cingulate cortex (ACC) tissues were collected for biochemical experiments. The Golgi-Cox staining and virus labeling were used to evaluate the dendritic spines. We applied fluoxetine (FLX) and amodiaquine dihydrochloride (AQ, a highly selective agonist of Nr4a2) in mice. Overexpression experiments were performed by injecting with AAV-Nr4a2-EGFP into ACC. Chemogenetic activation of CamkII neurons via injecting the hM3Dq virus. Mice treated with LPS displayed depressive- and anxiety-like behaviors. The reduction of Nr4a2 and FosB induced by LPS were rescued by pretreatment with FLX or AQ. More importantly, LPS-induced behavior deficits in mice were also alleviated via fluoxetine treatment and pharmacological activation the expression of Nr4a2. Meanwhile, enhancing the level of Nr4a2 could improve dendritic spines loss of neuron and morphological changes in microglia. Overexpression of Nr4a2 in ACC reversed the depressive- and anxiety-like behaviors caused by LPS administration. Activation of CamkII neurons in ACC could robustly increase the expression of Nr4a2 and improve LPS-induced behavior deficits. Our findings demonstrate that the Nr4a2 may regulate depressive-like behaviors via alleviating the impairment of morphology and function on microglia and CamkII neurons induced by chronic neuroinflammation.

Activity-Dependent Nr4a2 Induction Modulates Synaptic Expression of AMPA Receptors and Plasticity via a Ca2+/CRTC1/CREB Pathway.

Transcription factors have a pivotal role in synaptic plasticity and the associated modification of neuronal networks required for memory formation and consolidation. The nuclear receptors subfamily 4 group A (Nr4a) have emerged as possible modulators of hippocampal synaptic plasticity and cognitive functions. However, the molecular and cellular mechanisms underlying Nr4a2-mediated hippocampal synaptic plasticity are not completely known. Here, we report that neuronal activity enhances Nr4a2 expression and function in cultured mouse hippocampal neurons (both sexes) by an ionotropic glutamate receptor/Ca2+/cAMP response element-binding protein/CREB-regulated transcription factor 1 (iGluR/Ca2+/CREB/CRTC1) pathway. Nr4a2 activation mediates BDNF production and increases expression of iGluRs, thereby affecting LTD at CA3-CA1 synapses in acute mouse hippocampal slices (both sexes). Together, our results indicate that the iGluR/Ca2+/CREB/CRTC1 pathway mediates activity-dependent expression of Nr4a2, which is involved in glutamatergic synaptic plasticity by increasing BDNF and synaptic GluA1-AMPARs. Therefore, Nr4a2 activation could be a therapeutic approach for brain disorders associated with dysregulated synaptic plasticity.SIGNIFICANCE STATEMENT A major factor that regulates fast excitatory synaptic transmission and plasticity is the modulation of synaptic AMPARs. However, despite decades of research, the underlying mechanisms of this modulation remain poorly understood. Our study identified a molecular pathway that links neuronal activity with AMPAR modulation and hippocampal synaptic plasticity through the activation of Nr4a2, a member of the nuclear receptor subfamily 4. Since several compounds have been described to activate Nr4a2, our study not only provides mechanistic insights into the molecular pathways related to hippocampal synaptic plasticity and learning, but also identifies Nr4a2 as a potential therapeutic target for pathologic conditions associated with dysregulation of glutamatergic synaptic function.