Role of c-Myc haploinsufficiency in the maintenance of HSCs in mice.

This study was conducted to determine the dosage effect of c-Myc on hematopoiesis and its distinct role in mediating the Wnt/ß-catenin pathway in hematopoietic stem cell (HSC) and bone marrow niche cells. c-Myc haploinsufficiency led to ineffective hematopoiesis by inhibiting HSC self-renewal and quiescence and by promoting apoptosis. We have identified Nr4a1, Nr4a2, and Jmjd3, which are critical for the maintenance of HSC functions, as previously unrecognized downstream targets of c-Myc in HSCs. c-Myc directly binds to the promoter regions of Nr4a1, Nr4a2, and Jmjd3 and regulates their expression. Our results revealed that Nr4a1 and Nr4a2 mediates the function of c-Myc in regulating HSC quiescence, whereas all 3 genes contribute to the function of c-Myc in the maintenance of HSC survival. Adenomatous polyposis coli (Apc) is a negative regulator of the Wnt/ß-catenin pathway. We have provided the first evidence that Apc haploinsufficiency induces a blockage of erythroid lineage differentiation through promoting secretion of IL6 in bone marrow endothelial cells. We found that c-Myc haploinsufficiency failed to rescue defective function of Apc-deficient HSCs in vivo but it was sufficient to prevent the development of severe anemia in Apc-heterozygous mice and to significantly prolong the survival of those mice. Furthermore, we showed that c-Myc-mediated Apc loss induced IL6 secretion in endothelial cells, and c-Myc haploinsufficiency reversed the negative effect of Apc-deficient endothelial cells on erythroid cell differentiation. Our studies indicate that c-Myc has a context-dependent role in mediating the function of Apc in hematopoiesis.

Role of the Orphan Nuclear Receptor NR4A Family in T-Cell Biology.

The nuclear orphan receptors NR4A1, NR4A2, and NR4A3 are immediate early genes that are induced by various signals. They act as transcription factors and their activity is not regulated by ligand binding and are thus regulated via their expression levels. Their expression is transiently induced in T cells by triggering of the T cell receptor following antigen recognition during both thymic differentiation and peripheral T cell responses. In this review, we will discuss how NR4A family members impact different aspects of the life of a T cell from thymic differentiation to peripheral response against infections and cancer.

Alpha synuclein deficiency increases CD4+ T-cells pro-inflammatory profile in a Nurr1-dependent manner.

It has been suggested that extracellular alpha synuclein (αSyn) can mediate neuroinflammation in Parkinson's disease, and that αSyn affects B-cell maturation. However, the function of αSyn in T cells is poorly understood. We hypothesized that αSyn can affect CD4+ T-cell proliferation and activity. We found that αSyn deficiency exacerbates disease progression in 8 weeks old C57BL6/J EAE-induced mice, and that αSyn-deficient CD4+ T cells have increased pro-inflammatory response to myelin antigen relative to wild-type cells, as measured by cytokine secretion of interleukin IL-17 and interferon gamma. Furthermore, expression of αSyn on a background of αSyn knockout mitigates the inflammatory responses in CD4+ T cells. We discovered that elevated levels of Nurr1, a transcription factor belonging to the orphan nuclear receptor family, are associated with the pro-inflammatory profile of αSyn-deficient CD4+ T cells. In addition, we demonstrated that silencing of Nurr1 expression using an siRNA reduces IL-17 levels and increases the levels of IL-10, an anti-inflammatory cytokine. Study of αSyn-mediated cellular pathways in CD4+ T cells may provide useful insights into the development of pro-inflammatory responses in immunity, providing future avenues for therapeutic intervention.

HX600, a synthetic agonist for RXR-Nurr1 heterodimer complex, prevents ischemia-induced neuronal damage.

Ischemic stroke is amongst the leading causes of death and disabilities. The available treatments are suitable for only a fraction of patients and thus novel therapies are urgently needed. Blockage of one of the cerebral arteries leads to massive and persisting inflammatory reaction contributing to the nearby neuronal damage. Targeting the detrimental pathways of neuroinflammation has been suggested to be beneficial in conditions of ischemic stroke. Nuclear receptor 4A-family (NR4A) member Nurr1 has been shown to be a potent modulator of harmful inflammatory reactions, yet the role of Nurr1 in cerebral stroke remains unknown. Here we show for the first time that an agonist for the dimeric transcription factor Nurr1/retinoid X receptor (RXR), HX600, reduces microglia expressed proinflammatory mediators and prevents inflammation induced neuronal death in in vitro co-culture model of neurons and microglia. Importantly, HX600 was protective in a mouse model of permanent middle cerebral artery occlusion and alleviated the stroke induced motor deficits. Along with the anti-inflammatory capacity of HX600 in vitro, treatment of ischemic mice with HX600 reduced ischemia induced Iba-1, p38 and TREM2 immunoreactivities, protected endogenous microglia from ischemia induced death and prevented leukocyte infiltration. These anti-inflammatory functions were associated with reduced levels of brain lysophosphatidylcholines (lysoPCs) and acylcarnitines, metabolites related to proinflammatory events. These data demonstrate that HX600 driven Nurr1 activation is beneficial in ischemic stroke and propose that targeting Nurr1 is a novel candidate for conditions involving neuroinflammatory component.

Correlation between Nurr1 expression and drug resistance in the brain of rats with epilepsy.

OBJECTIVE: To investigate the correlation between nuclear receptor related 1 (Nurr1) expression and drug resistance in the brain of rats with epilepsy. MATERIALS AND METHODS: A total of 60 adult male Sprague-Dawley rats were selected, and the animal model of epilepsy was established by electrical stimulation. These rats were randomly divided into the control group and the drug-resistant group. The model of drug-resistant epilepsy was screened with phenytoin (PHT) and phenobarbital (PB); the hippocampus and temporal lobe cortex tissues were isolated from rats; the messenger ribonucleic acid (mRNA) and protein levels of Nurr1 in the hippocampus and cortex tissues of the two groups of rats were detected by reverse transcription polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry, respectively. The budding tissue marker growth-associated protein-43 (GAP43) in hippocampus tissues were labeled by immunofluorescence staining; the mRNA and protein levels of indicators related to drug-resistant epilepsy, including leukemia-associated phenotype (LAP), multi-drug resistance protein (MRP), P-glycoprotein (P-gp) and monocyte chemoattractant protein-1 (MCP-1), were further detected. Pearson correlation analysis was used to analyze the correlations of the protein level of Nurr1 with drug-resistant indicators. RESULTS: The mRNA and protein levels of Nurr1 in hippocampus tissues of the drug-resistant group were significantly increased compared with those of the control group (p < 0.05). In temporal lobe cortex tissues, there was no significant difference in the mRNA level of Nurr1 between the control group and the drug-resistant group (p > 0.05). The immunohistochemistry results showed that the fluorescence intensity of GAP3 in hippocampus tissues of the drug-resistant group was significantly higher than that of the control group. The mRNA and protein levels of epilepsy-related indicators, LAP, MRP, P-gp and MCP-1 in hippocampus tissues of drug-resistant group were significantly up-regulated compared with those of the control group (p < 0.05). Pearson correlation analysis indicated that the protein level of Nurr1 in hippocampus tissues was positively correlated with those of LAP, MRP, P-gp and MCP-1 in the corresponding regions (p < 0.05). CONCLUSIONS: Nurr1 enhances the drug resistance of epilepsy in rats by up-regulating the expression of proteins related to drug resistance.

Relevance of the NR4A sub-family of nuclear orphan receptors in trophoblastic BeWo cell differentiation.

Nur-77, a member of the NR4A sub-family of nuclear orphan receptors, is downregulated in the placentae of pre-eclamptic women. Here, we investigate the relevance of Nor-1, Nurr-1 and Nur-77 in trophoblastic cell differentiation. Their transcript levels were found to be significantly upregulated in BeWo cells treated with forskolin. The maximum increase was observed after 2 h, with a second peak in the expression levels after 48 h. The expression of NR4A sub-family members was also found to be upregulated in BeWo cells after treatment with hCG and GnRH. A similar significant increase was observed at the respective protein levels after 2 and 48 h of treatment with forskolin, hCG or GnRH. Silencing Nor-1, Nurr-1 or Nur-77 individually did not show any effect on forskolin-, hCG- and/or GnRH-mediated BeWo cell fusion and/or hCG secretion. After silencing any one member of the NR4A sub-family, an increase in the transcript levels of the other sub-family members was observed, indicating a compensatory effect due to their functional redundancy. Simultaneously silencing all three NR4A sub-family members significantly downregulated forskolin- and hCG-mediated BeWo cell fusion and/or hCG secretion. However, a considerable amount of cell death occurred after forskolin or hCG treatment as compared to the control siRNA-transfected cells. These results suggest that the NR4A sub-family of nuclear orphan receptors has a role in trophoblastic cell differentiation.

Pathological mechanism of secondary-progressive multiples sclerosis and its animal model.

Development of acute experimental autoimmune encephalomyelitis (EAE) depends on Th17 cells expressing the nuclear factor NR4A2, which we have previously reported to be upregulated in peripheral blood T cells from patients of multiple sclerosis (MS). EAE induced in mice lacking NR4A2 in T cells showed a great reduction in Th17-mediated acute symptoms, whereas a late-onset disease independent of NR4A2 was still inducible. We identified cytotoxic T-cell-like CD4+ T cells expressing the T-box transcription factor Eomesodermin (Eomes) as a pathogenic component for the development of the late-onset disease. Furthermore, T cell-specific deletion of the Eomes gene or Eomes-specific RNA interference in vivo remarkably ameliorated the late-onset EAE. Intriguingly, similar Eomes-expressing CD4+ T cells are increased in the peripheral blood and cerebrospinal fluid only from patients with secondary-progressive MS accompanied by neurodegenerative symptoms, but not in relapsing-remitting MS. Mechanistic analysis revealed that granzyme B was secreted by Eomes-expressing CD4+ T cells and the activation of protease-activated receptor-1 by granzyme B is involved in the neuroinflammation observed in the late-onset EAE.

Role of Nurr1 in the Generation and Differentiation of Dopaminergic Neurons from Stem Cells.

NURR1 is an essential transcription factor for the differentiation, maturation, and maintenance of midbrain dopaminergic neurons (DA neurons) as it has been demonstrated using knock-out mice. DA neurons of the substantia nigra pars compacta degenerate in Parkinson's disease (PD) and mutations in the Nurr1 gene have been associated with this human disease. Thus, the study of NURR1 actions in vivo is fundamental to understand the mechanisms of neuron generation and degeneration in the dopaminergic system. Here, we present and discuss findings indicating that NURR1 is a valuable molecular tool for the in vitro generation of DA neurons which could be used for modeling and studying PD in cell culture and in transplantation approaches. Transduction of Nurr1 alone or in combination with other transcription factors such as Foxa2, Ngn2, Ascl1, and Pitx3, induces the generation of DA neurons, which upon transplantation have the capacity to survive and restore motor behavior in animal models of PD. We show that the survival of transplanted neurons is increased when the Nurr1-transduced olfactory bulb stem cells are treated with GDNF. The use of these and other factors with the induced pluripotent stem cell (iPSC)-based technology or the direct reprogramming of astrocytes or fibroblasts into human DA neurons has produced encouraging results for the study of the cellular and molecular mechanisms of neurodegeneration in PD and for the search of new treatments for this disease.

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.

Correlation between orphan nuclear receptor Nurr1 expression and amyloid deposition in 5XFAD mice, an animal model of Alzheimer's disease.

The functional roles of the orphan nuclear receptor, Nurr1, have been extensively studied and well established in the development and survival of midbrain dopamine neurons. As Nurr1 and other NR4A members are widely expressed in the brain in overlapping and distinct manners, it has been an open question whether Nurr1 has important function(s) in other brain areas. Recent studies suggest that up-regulation of Nurr1 expression is critical for cognitive functions and/or long-term memory in forebrain areas including hippocampal formation. Questions remain about the association between Nurr1 expression and Alzheimer's disease (AD) brain pathology. Here, using our newly developed Nurr1-selective antibody, we report that Nurr1 protein is prominently expressed in brain areas with Aß accumulation, that is, the subiculum and the frontal cortex, in the 5XFAD mouse and that Nurr1 is highly co-expressed with Aß at early stages. Furthermore, the number of Nurr1-expressing cells significantly declines in the 5XFAD mouse in an age-dependent manner, accompanied by increased plaque deposition. Thus, our findings suggest that altered expression of Nurr1 is associated with AD progression. Using our newly developed Nurr1-selective antibody, we show that Nurr1 protein is prominently expressed in brain areas accumulating amyloid-beta (Aß) in the transgenic mouse model of Alzheimer's disease (AD) and that Nurr1 is highly co-expressed with Aß at early stages (upper panel). Furthermore, in the AD brain the number of Nurr1-expressing cells significantly declines in an age-dependent manner concomitant with increased Aß accumulation (lower diagram) highlighting a possible Nurr1 involvement in AD pathology.

Efficient reprogramming of mouse fibroblasts to neuronal cells including dopaminergic neurons.

Somatic cells were directly converted to functional neurons through the use of a combination of transcription factors, including Ascl1, Brn2, and Myt1l. However, a major limitation is the lack of a reliable source of cell-replacement therapy for neurological diseases. Here, we show that a combination of the transcription factors Ascl1 and Nurr1 (AN) and neurotrophic factors including SHH and FGF8b directly reprogrammed embryonic mouse fibroblasts to induced neuronal (iN) cells: pan-neuronal cells and dopaminergic (DA) neurons under our systematic cell culture conditions. Reprogrammed cells showed the morphological properties of neuronal cells. Additionally, cells were analyzed using various markers, including Tuj1 and Map2 for neuronal cells and Lmx1a, Th, Aadc and Vmat2 for DA neurons in our immunostaining and reverse transcription (RT)-PCR experiments. We found that a combination of transcription factors and neurotrophic factors could directly reprogram fibroblasts to neuronal cells including DA neurons. Various types of reprogrammed cells are promising cell sources for cell-based therapy of neurological disorders like Parkinson's disease and spinal cord injury.

Low dose bexarotene treatment rescues dopamine neurons and restores behavioral function in models of Parkinson's disease.

Nurr1 is a nuclear hormone receptor (NucHR) strongly implicated in the growth, maintenance, and survival of dopaminergic neurons. Nurr1 may be unable to bind ligands directly, but it forms heterodimers with other NucHRs that do. Using bioluminescence resonance energy transfer (BRET) assays to directly monitor interactions of Nurr1 with other NucHRs, we found the cancer drug bexarotene (Targretin, also LGD1069) displayed biased interactions with Nurr1-RXR heterodimers compared with RXR-RXR homodimers. Remarkably, at doses up to 100-fold lower than those effective in rodent cancer models, bexarotene rescued dopamine neurons and reversed behavioral deficits in 6-hydroxydopamine (6-OHDA) lesioned rats. Compared to the high doses used in cancer therapy, low doses of bexarotene have significantly milder side effects including a reduced increase in plasma triglycerides and less suppression of thyroid function. On the basis of extrapolations from rat to human doses, we hypothesize that low oral doses of bexarotene may provide an effective and tolerated therapy for Parkinson's disease (PD).

Nr4a receptors are essential for thymic regulatory T cell development and immune homeostasis.

Regulatory T cells (T(reg) cells) develop from progenitor thymocytes after the engagement of T cell antigen receptors (TCRs) with high-affinity ligands, but the underlying molecular mechanisms are still unclear. Here we show that the Nr4a nuclear receptors, which are encoded by immediate-early genes upregulated by TCR stimulation in thymocytes, have essential roles in T(reg) cell development. Mice that lacked all Nr4a factors could not produce T(reg) cells and died early owing to systemic autoimmunity. Nr4a receptors directly activated the promoter of the gene encoding the transcription factor Foxp3, and forced activation of Nr4a receptors bypassed low-strength TCR signaling to drive the T(reg) cell developmental program. Our results suggest that Nr4a receptors have key roles in determining CD4(+) T cell fates in the thymus and thus contribute to immune homeostasis.

NR4A nuclear receptors support memory enhancement by histone deacetylase inhibitors.

The formation of a long-lasting memory requires a transcription-dependent consolidation period that converts a short-term memory into a long-term memory. Nuclear receptors compose a class of transcription factors that regulate diverse biological processes, and several nuclear receptors have been implicated in memory formation. Here, we examined the potential contribution of nuclear receptors to memory consolidation by measuring the expression of all 49 murine nuclear receptors after learning. We identified 13 nuclear receptors with increased expression after learning, including all 3 members of the Nr4a subfamily. These CREB-regulated Nr4a genes encode ligand-independent "orphan" nuclear receptors. We found that blocking NR4A activity in memory-supporting brain regions impaired long-term memory but did not impact short-term memory in mice. Further, expression of Nr4a genes increased following the memory-enhancing effects of histone deacetylase (HDAC) inhibitors. Blocking NR4A signaling interfered with the ability of HDAC inhibitors to enhance memory. These results demonstrate that the Nr4a gene family contributes to memory formation and is a promising target for improving cognitive function.

Vitamin D and Parkinson's disease.

Parkinson's disease (PD) is the second most common form of neurodegeneration among the elderly population. PD is clinically characterized by tremors, rigidity, slowness of movement, and postural imbalance. Interestingly, a significant association has been demonstrated between PD and low levels of vitamin D in the serum, and vitamin D supplement appears to have a beneficial clinical effect on PD. Genetic studies have provided the opportunity to determine which proteins link vitamin D to PD pathology, e.g., Nurr1 gene, toll-like receptor, gene related to lipid disorders, vascular endothelial factor, tyrosine hydroxylase, and angiogenin. Vitamin D also exerts its effects on cancer through nongenomic factors, e.g., bacillus Calmette-Guerin vaccination, interleukin-10, Wntß-catenin signaling pathways, mitogen-activated protein kinase pathways, and the reduced form of the nicotinamide adenine dinucleotide phosphate. In conclusion, vitamin D might have a beneficial role in PD. Calcitriol is best used for PD because it is the active form of the vitamin D(3) metabolite and modulates inflammatory cytokine expression. Further investigation with calcitriol in PD is needed.

The function and mechanisms of Nurr1 action in midbrain dopaminergic neurons, from development and maintenance to survival.

Nurr1 is critical for the development and maintenance of midbrain dopaminergic (DA) neurons in mouse. Loss of Nurr1 function early during development in mice leads to the absence of midbrain DA neurons. Reduction of Nurr1 function in adulthood leads to a slowly progressive loss of striatal DA and markers for DAergic neurons, supporting its selective roles in the maintenance of DAergic neuronal survival and function. To understand the molecular mechanisms of Nurr1 action, our group has identified VIP as a potential target gene of Nurr1. Nurr1 regulates VIP mRNA and protein levels, and transactivates the VIP promoter through Nurr1-responsive cis elements. Nurr1 loss of function leads to the decrease of VIP mRNA level in developing midbrain, suggesting that Nurr1 is involved in the in vivo regulation of VIP expression in midbrain. Our group has also cloned a novel protein interactor for Nurr1. We identified a family of gene products that interact and regulate the activity of Nurr1 by screening yeast two-hybrid library and termed the longest splicing form, NuIP. In vivo NuIP protein is largely colocalized with Nurr1 in adult midbrain dopaminergic neurons. NuIP interacts and positively regulates the activity of Nurr1 protein and could also possibly mediate cross talk between Nurr1 and GTPase mediated signaling pathways. Other recently identified potential target genes and interacting proteins of Nurr1 are also summarized and discussed in this review.

The synergistic effect of beta-boswellic acid and Nurr1 overexpression on dopaminergic programming of antioxidant glutathione peroxidase-1-expressing murine embryonic stem cells.

Parkinson's disease (PD) is a neurodegenerative disorder in which the nigro-striatal dopaminergic (DAergic) neurons have been selectively lost. Due to side effects of levodopa, a dopamine precursor drug, recently cell replacement therapy for PD has been considered. Lack of sufficient amounts of, embryos and ethical problems regarding the use of dopamine-rich embryonic neural cells have limited the application of these cells for PD cell therapy. Therefore, many investigators have focused on using the pluripotent stem cells to generate DAergic neurons. This study is aimed first to establish a mouse embryonic stem (mES) cell line that can stably co-express Nurr1 (Nuclear receptor subfamily 4, group A, member 2) transcription factor in order to efficiently generate DAergic neurons, and glutathione peroxidase-1 (GPX-1) to protect the differentiated DAergic-like cells against oxidative stress. In addition to genetic engineering of ES cells, the effect of Beta-boswellic acid (BBA) on DAergic differentiation course of mES cells was sought in the present study. To that end, the feeder-independent CGR8 mouse embryonic stem cells were transduced by Nurr1- and GPX-1-harboring Lentiviruses and the generated Nurr1/GPX-1-expresssing ES clones were characterized and verified. Gene expression analyses demonstrated that BBA treatment and overexpression of Nurr1 has a synergistic effect on derivation of DAergic neurons from Nurr1/GPX-1-expressing ES cells. The differentiated cells could exclusively synthesize and secrete dopamine in response to stimuli. Overexpression of GPX-1 in genetically engineered Nurr1/GPX-1-ES cells increased the viability of these cells during their differentiation into CNS stem cells. In conclusion, the results demonstrated that Nurr1-overexpressing feeder-independent ES cells like the feeder-dependent ES cells, can be efficiently programmed into functional DAergic neurons and additional treatment of cells by BBA can even augment this efficiency. GPX-1 overexpression in Nurr1/GPX-1-ES cells increases the viability of differentiated CNS stem-like cells. The result of this study may have impact on future stem cell therapy of PD.

Age-related changes in dopamine signaling in Nurr1 deficient mice as a model of Parkinson's disease.

The nuclear receptor related 1 (Nurr1) transcription factor contributes to the development and maintenance of dopamine (DA) neurons in the brain. We found that heterozygous Nurr1 knockout (Nurr1 +/-) influenced the age-dependent decline in the number of DA neurons and influenced DA signaling. We examined the DA marker, tyrosine hydroxylase, using immunohistochemistry, and we measured DA signaling using fast-scan cyclic voltammetry in 3 age groups of wild-type (Nurr1 +/+) and mutant (Nurr1 +/-) mice: 3-6, 9-12, and 15-23 mo old. Prior to significant loss of DA neurons and to the onset of parkinsonian symptoms, young Nurr1 +/- mice (3-6 mo) exhibited a decrease in peak evoked DA release that was partially countered by a decrease in the rate of DA reuptake. As peak evoked DA release declined with age for both the wild-type and Nurr1 +/- mice, both genotypes manifested decreased DA reuptake. As the DA release fell further with age, decreased DA reuptake eventually could not adequately compensate the Nurr1 +/- mice. The results indicated that Nurr1 deficiency led to impaired DA release even before significant DA neuron loss.