Decreased NURR1 and PITX3 gene expression in Chinese patients with Parkinson's disease

The Crucial Roles of Pitx3 in Midbrain Dopaminergic Neuron Development and Parkinson's Disease-Associated Neurodegeneration

The degeneration of midbrain dopaminergic (mDA) neurons, particularly in the substantia nigra pars compacta (SNc), is one of the most prominent pathological hallmarks of Parkinson's disease (PD). To uncover the pathogenic mechanisms of mDA neuronal death during PD may provide therapeutic targets to prevent mDA neuronal loss and slow down the disease's progression. Paired-like homeodomain transcription factor 3 (Pitx3) is selectively expressed in the mDA neurons as early as embryonic day 11.5 and plays a critical role in mDA neuron terminal differentiation and subset specification. Moreover, Pitx3-deficient mice exhibit some canonical PD-related features, including the profound loss of SNc mDA neurons, a dramatic decrease in striatal dopamine (DA) levels, and motor abnormalities. However, the precise role of Pitx3 in progressive PD and how this gene contributes to mDA neuronal specification during early stages remains unclear. In this review, we updated the latest findings on Pitx3 by summarizing the crosstalk between Pitx3 and its associated transcription factors in mDA neuron development. We further explored the potential benefits of Pitx3 as a therapeutic target for PD in the future. To better understand the transcriptional network of Pitx3 in mDA neuron development may provide insights into Pitx3-related clinical drug-targeting research and therapeutic approaches.

Want of Wnt in Parkinson's disease: Could sFRP disrupt interplay between Nurr1 and Wnt signaling?

Nuclear receptor related 1 (Nurr1) is a transcription factor known to regulate the development and maintenance of midbrain dopaminergic (mDA) neurons. Reports have confirmed that defect or obliteration of Nurr1 results in neurodegeneration and motor function impairment leading to Parkinson's disease (PD). Studies have also indicated that Nurr1 regulates the expression of alpha-synuclein (α-SYN) and mutations in Nurr1 cause α-SYN overexpression, thereby increasing the risk of PD. Nurr1 is modulated via various pathways including Wnt signaling pathway which is known to play an important role in neurogenesis and deregulation of it contributes to PD pathogenesis. Both Wnt/β-catenin dependent and independent pathways are implicated in the activation of Nurr1 and subsequent downregulation of α-SYN. This review highlights the interaction between Nurr1 and Wnt signaling pathways in mDA neuronal development. We further hypothesize how modulation of Wnt signaling pathway by its antagonist, secreted frizzled related proteins (sFRPs) could be a potential route to treat PD.

The Gene Expression of Proteins Involved in Intercellular Signaling and Neurodegeneration in the Substantia Nigra in a Mouse Subchronic Model of Parkinson's Disease

Given the limited access to clinical material for studying the pathogenesis of Parkinson's disease (PD), these studies should be carried out on experimental models. We have recently developed a subchronic model of the progressive development of PD with a gradual transition from the preclinical (asymptomatic) stage to the clinical (symptomatic) one. The aim of this study was to evaluate changes in the expression of a wide range of genes in the substantia nigra (SN), the central link in the regulation of motor function, in mice in our subchronic model of PD. We have found changes in the expression of a number of genes encoding enzymes involved in the synthesis and degradation of dopamine as well as proteins involved in the vesicular cycle, axonal transport, protein degradation in the proteasome system, neuroinflammation, and cell death in the SN of our mouse model of the clinical stage of PD. Similar changes in gene expression were previously demonstrated in patients (postmortem), indicating good reproducibility of PD in our model. Further analysis of the gene expression in the SN of mice has shown that the expression of some genes also changes in the model of the preclinical stage, when dopaminergic neurons have not yet died. Thus, this study opens up broad prospects for further evaluation of the molecular mechanisms of PD pathogenesis and the development of a test system for drug screening.

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.

Recruitment of the CoREST transcription repressor complexes by Nerve Growth factor IB-like receptor (Nurr1/NR4A2) mediates silencing of HIV in microglial cells

Human immune deficiency virus (HIV) infection in the brain leads to chronic neuroinflammation due to the production of pro-inflammatory cytokines, which in turn promotes HIV transcription in infected microglial cells. However, powerful counteracting silencing mechanisms in microglial cells result in the rapid shutdown of HIV expression after viral reactivation to limit neuronal damage. Here we investigated whether the Nerve Growth Factor IB-like nuclear receptor Nurr1 (NR4A2), which is a repressor of inflammation in the brain, acts directly to restrict HIV expression. HIV silencing following activation by TNF-α, or a variety of toll-like receptor (TLR) agonists, in both immortalized human microglial cells (hμglia) and induced pluripotent stem cells (iPSC)-derived human microglial cells (iMG) was enhanced by Nurr1 agonists. Similarly, overexpression of Nurr1 led to viral suppression, while conversely, knock down (KD) of endogenous Nurr1 blocked HIV silencing. The effect of Nurr1 on HIV silencing is direct: Nurr1 binds directly to the specific consensus binding sites in the U3 region of the HIV LTR and mutation of the Nurr1 DNA binding domain blocked its ability to suppress HIV-1 transcription. Chromatin immunoprecipitation (ChIP) assays also showed that after Nurr1 binding to the LTR, the CoREST/HDAC1/G9a/EZH2 transcription repressor complex is recruited to the HIV provirus. Finally, transcriptomic studies demonstrated that in addition to repressing HIV transcription, Nurr1 also downregulated numerous cellular genes involved in inflammation, cell cycle, and metabolism, further promoting HIV latency and microglial homoeostasis. Nurr1 therefore plays a pivotal role in modulating the cycles of proviral reactivation by potentiating the subsequent proviral transcriptional shutdown. These data highlight the therapeutic potential of Nurr1 agonists for inducing HIV silencing and microglial homeostasis and ultimately for the amelioration of the neuroinflammation associated with HIV-associated neurocognitive disorders (HAND).

Mitochondrial function and dynamics in neural stem cells and neurogenesis: Implications for neurodegenerative diseases

Mitochondria have been largely described as the powerhouse of the cell and recent findings demonstrate that this organelle is fundamental for neurogenesis. The mechanisms underlying neural stem cells (NSCs) maintenance and differentiation are highly regulated by both intrinsic and extrinsic factors. Mitochondrial-mediated switch from glycolysis to oxidative phosphorylation, accompanied by mitochondrial remodeling and dynamics are vital to NSCs fate. Deregulation of mitochondrial proteins, mitochondrial DNA, function, fission/fusion and metabolism underly several neurodegenerative diseases; data show that these impairments are already present in early developmental stages and NSC fate decisions. However, little is known about mitochondrial role in neurogenesis. In this Review, we describe the recent evidence covering mitochondrial role in neurogenesis, its impact in selected neurodegenerative diseases, for which aging is the major risk factor, and the recent advances in stem cell-based therapies that may alleviate neurodegenerative disorders-related neuronal deregulation through improvement of mitochondrial function and dynamics.

NURR1-deficient mice have age- and sex-specific behavioral phenotypes

The transcription factor NURR1 is essential to the generation and maintenance of midbrain dopaminergic (mDA) neurons and its deregulation is involved in the development of dopamine (DA)‐associated brain disorders, such as Parkinson's disease (PD). The old male NURR1 heterozygous knockout (NURR1‐KO) mouse has been proposed as a model of PD due to its altered motor performance that was, however, not confirmed in a subsequent study. Based on these controversial results, we explored the effects of the NURR1 deficiency on locomotor activity, motor coordination, brain and plasma DA levels, blood pressure and heart rate of old mice, also focusing on the potential effect of sex. As a probable consequence of the role of NURR1 in DA pathway, we observed that the old NURR1‐KO mouse is characterized by motor impairment, and increased brain DA level and heart rate, independently from sex. However, we also observed an alteration in spontaneous locomotor activity that only affects males. In conclusion, NURR1 deficiency triggers sex‐ and age‐specific alterations of behavioral responses, of DA levels and cardiovascular abnormalities. Further studies in simplified systems will be necessary to dissect the mechanism underlying these observations.

Genome-Wide DNA Methylation in Policemen Working in Cities Differing by Major Sources of Air Pollution

DNA methylation is the most studied epigenetic mechanism that regulates gene expression, and it can serve as a useful biomarker of prior environmental exposure and future health outcomes. This study focused on DNA methylation profiles in a human cohort, comprising 125 nonsmoking city policemen (sampled twice), living and working in three localities (Prague, Ostrava and Ceske Budejovice) of the Czech Republic, who spent the majority of their working time outdoors. The main characterization of the localities, differing by major sources of air pollution, was defined by the stationary air pollution monitoring of PM2.5, B[a]P and NO₂. DNA methylation was analyzed by a genome-wide microarray method. No season-specific DNA methylation pattern was discovered; however, we identified 13,643 differentially methylated CpG loci (DML) for a comparison between the Prague and Ostrava groups. The most significant DML was cg10123377 (log₂FC = −1.92, p = 8.30 × 10⁻⁴) and loci annotated to RPTOR (total 20 CpG loci). We also found two hypomethylated loci annotated to the DNA repair gene XRCC5. Groups of DML annotated to the same gene were linked to diabetes mellitus (KCNQ1), respiratory diseases (PTPRN2), the dopaminergic system of the brain and neurodegenerative diseases (NR4A2). The most significant possibly affected pathway was Axon guidance, with 86 potentially deregulated genes near DML. The cluster of gene sets that could be affected by DNA methylation in the Ostrava groups mainly includes the neuronal functions and biological processes of cell junctions and adhesion assembly. The study demonstrates that the differences in the type of air pollution between localities can affect a unique change in DNA methylation profiles across the human genome.

The essential role of transcription factor Pitx3 in preventing mesodiencephalic dopaminergic neurodegeneration and maintaining neuronal subtype identities during aging

Pituitary homeobox 3 (Pitx3) is required for the terminal differentiation of nigrostriatal dopaminergic neurons during neuronal development. However, whether Pitx3 contributes to the normal physiological function and cell-type identity of adult neurons remains unknown. To explore the role of Pitx3 in maintaining mature neurons, we selectively deleted Pitx3 in the mesodiencephalic dopaminergic (mdDA) neurons of Pitx3fl/fl/DATCreERT2 bigenic mice using a tamoxifen inducible CreERT2/loxp gene-targeting system. Pitx3fl/fl/DATCreERT2 mice developed age-dependent progressive motor deficits, concomitant with a rapid reduction of striatal dopamine (DA) content and a profound loss of mdDA neurons in the substantia nigra pars compacta (SNc) but not in the adjacent ventral tegmental area (VTA), recapitulating the canonical neuropathological features of Parkinson's disease (PD). Mechanistic studies showed that Pitx3-deficiency significantly increased the number of cleaved caspase-3+ cells in SNc, which likely underwent neurodegeneration. Meanwhile, the vulnerability of SNc mdDA neurons was increased in Pitx3fl/fl/DATCreERT2 mice, as indicated by an early decline in glial cell line-derived neurotrophic factor (GDNF) and aldehyde dehydrogenase 1a1 (Aldh1a1) levels. Noticeably, somatic accumulation of α-synuclein (α-syn) was also significantly increased in the Pitx3-deficient neurons. Together, our data demonstrate that the loss of Pitx3 in fully differentiated mdDA neurons results in progressive neurodegeneration, indicating the importance of the Pitx3 gene in adult neuronal survival. Our findings also suggest that distinct Pitx3-dependent pathways exist in SNc and VTA mdDA neurons, correlating with the differential vulnerability of SNc and VTA mdDA neurons in the absence of Pitx3.

Failure of Glial Cell-Line Derived Neurotrophic Factor (GDNF) in Clinical Trials Orchestrated By Reduced NR4A2 (NURR1) Transcription Factor in Parkinson's Disease. A Systematic Review

Parkinson’s disease (PD) is one of the most common neurodegenerative maladies with unforeseen complex pathologies. While this neurodegenerative disorder’s neuropathology is reasonably well known, its etiology remains a mystery, making it challenging to aim therapy. Glial cell-line derived neurotrophic factor (GDNF) remains an auspicious therapeutic molecule for treating PD. Neurotrophic factor derived from glial cell lines is effective in rodents and nonhuman primates, but clinical findings have been equivocal. Laborious exertions have been made over the past few decades to improve and assess GDNF in treating PD (clinical studies). Definitive clinical trials have, however, failed to demonstrate a survival advantage. Consequently, there seemed to be a doubt as to whether GDNF has merit in the potential treatment of PD. The purpose of this cutting edge review is to speculate as to why the clinical trials have failed to meet the primary endpoint. We introduce a hypothesis, “Failure of GDNF in clinical trials succumbed by nuclear receptor-related factor 1 (Nurr1) shortfall.” We demonstrate how Nurr1 binds to GDNF to induce dopaminergic neuron synthesis. Due to its undisputable neuro-protection aptitude, we display Nurr1 (also called Nr4a2) as a promising therapeutic target for PD.

Neurodevelopmental defects and neurodegenerative phenotypes in human brain organoids carrying Parkinson's disease-linked DNAJC6 mutations

Loss-of-function mutations of DNAJC6, encoding HSP40 auxilin, have recently been identified in patients with early-onset Parkinson's disease (PD). To study the roles of DNAJC6 in PD pathogenesis, we used human embryonic stem cells with CRISPR-Cas9-mediated gene editing. Here, we show that DNAJC6 mutations cause key PD pathologic features, i.e., midbrain-type dopamine (mDA) neuron degeneration, pathologic α-synuclein aggregation, increase of intrinsic neuronal firing frequency, and mitochondrial and lysosomal dysfunctions in human midbrain-like organoids (hMLOs). In addition, neurodevelopmental defects were also manifested in hMLOs carrying the mutations. Transcriptomic analyses followed by experimental validation revealed that defects in DNAJC6-mediated endocytosis impair the WNT-LMX1A signal during the mDA neuron development. Furthermore, reduced LMX1A expression during development caused the generation of vulnerable mDA neurons with the pathologic manifestations. These results suggest that the human model of DNAJC6-PD recapitulates disease phenotypes and reveals mechanisms underlying disease pathology, providing a platform for assessing therapeutic interventions.

Nurr1 performs its anti-inflammatory function by regulating RasGRP1 expression in neuro-inflammation

Nurr1, a transcription factor belonging to the orphan nuclear receptor, has an essential role in the generation and maintenance of dopaminergic neurons and is important in the pathogenesis of Parkinson’ disease (PD). In addition, Nurr1 has a non-neuronal function, and it is especially well known that Nurr1 has an anti-inflammatory function in the Parkinson’s disease model. However, the molecular mechanisms of Nurr1 have not been elucidated. In this study, we describe a novel mechanism of Nurr1 function. To provide new insights into the molecular mechanisms of Nurr1 in the inflammatory response, we performed Chromatin immunoprecipitation sequencing (ChIP-Seq) on LPS-induced inflammation in BV2 cells and finally identified the RasGRP1 gene as a novel target of Nurr1. Here, we show that Nurr1 directly binds to the RasGRP1 intron to regulate its expression. Moreover, we also identified that RasGRP1 regulates the Ras-Raf-MEK-ERK signaling cascade in LPS-induced inflammation signaling. Finally, we conclude that RasGRP1 is a novel regulator of Nurr1’s mediated inflammation signaling.

The transcription factor Nurr1 is upregulated in amyotrophic lateral sclerosis patients and SOD1-G93A mice

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that affects both lower and upper motor neurons (MNs) in the central nervous system. ALS etiology is highly multifactorial and multifarious, and an effective treatment is still lacking. Neuroinflammation is a hallmark of ALS and could be targeted to develop new therapeutic approaches. Interestingly, the transcription factor Nurr1 has been demonstrated to have an important role in the inflammatory process in several neurological disorders, such as Parkinson's disease and multiple sclerosis. In the present paper, we demonstrate for the first time that Nurr1 expression levels are upregulated in the peripheral blood of ALS patients. Moreover, we investigated Nurr1 function in the SOD1-G93A mouse model of ALS. Nurr1 was strongly upregulated in the spinal cord during the asymptomatic and early symptomatic phases of the disease, where it promoted the expression of brain-derived neurotrophic factor mRNA and the repression of NFκB pro-inflammatory targets, such as inducible nitric oxide synthase. Therefore, we hypothesize that Nurr1 is activated in an early phase of the disease as a protective endogenous anti-inflammatory mechanism, although not sufficient to reverse disease progression. On the basis of these observations, Nurr1 could represent a potential biomarker for ALS and a promising target for future therapies.

The Critical Role of Nurr1 as a Mediator and Therapeutic Target in Alzheimer's Disease-related Pathogenesis

Several studies have revealed that the transcription factor nuclear receptor related 1 (Nurr1) plays several roles not only in the regulation of gene expression related to dopamine synthesis, but also in alternative splicing, and miRNA targeting. Moreover, it regulates cognitive functions and protects against inflammation-induced neuronal death. In particular, the role of Nurr1 in the pathogenesis of Parkinson's disease (PD) has been well investigated; for example, it has been shown that it restores behavioral and histological impairments in PD models. Although many studies have evaluated the connection between Nurr1 and PD pathogenesis, the role of Nurr1 in Alzheimer's disease (AD) remain to be studied. There have been several studies describing Nurr1 protein expression in the AD brain. However, only a few studies have examined the role of Nurr1 in the context of AD. Therefore, in this review, we highlight the overall effects of Nurr1 under the neuropathologic conditions related to AD. Furthermore, we suggest the possibility of using Nurr1 as a therapeutic target for AD or other neurodegenerative disorders.

Nurr1Cd11bcre conditional knockout mice display inflammatory injury to nigrostriatal dopaminergic neurons

Nuclear receptor-related 1 protein (NURR1) is essential for the development and maintenance of midbrain dopaminergic (DAergic) neurons. NURR1 also protects DAergic neurons against neuroinflammation. However, it remains to be determined to what extent does NURR1 exerts its protective function through acting autonomously in the microglia. Using Cre/lox gene targeting system, we deleted Nurr1 in the microglia of Nurr1^Cd11bcre conditional knockout (cKO) mice. The Nurr1^Cd11bcre cKO mice displayed age-dependent motor abnormalities and increased microglial activation, but with no obvious DAergic neurodegeneration. To boost the inflammatory injury, we systemically administered endotoxin lipopolysaccharide (LPS) to Nurr1^Cd11bcre mice. As expected, LPS treatment exacerbated the motor phenotypes and inflammatory reactions in Nurr1^Cd11bcre cKO mice. More importantly, LPS administration caused DAergic neuron loss and α-synuclein aggregation, two pathological hallmarks of Parkinson's disease (PD). Therefore, our findings provide in vivo evidence supporting a critical protective role of NURR1 in the microglia against inflammation-induced degeneration of DAergic neurons in PD.

NURR1 Impairment in Multiple Sclerosis

The transcription factor NURR1 is a constitutively active orphan receptor belonging to the steroid hormone receptor class NR4A. Although a genetic association between NURR1 and autoimmune inflammatory diseases has never emerged from genome-wide association studies (GWAS), alterations in the expression of NURR1 have been observed in various autoimmune diseases. Specifically, its role in autoimmune inflammatory diseases is mainly related to its capability to counteract inflammation. In fact, NURR1 exerts anti-inflammatory functions inhibiting the transcription of the molecules involved in proinflammatory pathways, not only in the peripheral blood compartment, but also in the cerebral parenchyma acting in microglial cells and astrocytes. In parallel, NURR1 has been also linked to dopamine-associated brain disorders, such as Parkinson’s disease (PD) and schizophrenia, since it is involved in the development and in the maintenance of midbrain dopaminergic neurons (mDA). Considering its role in neuro- and systemic inflammatory processes, here we review the evidences supporting its contribution to multiple sclerosis (MS), a chronic inflammatory autoimmune disease affecting the central nervous system (CNS). To date, the specific role of NURR1 in MS is still debated and few authors have studied this topic. Here, we plan to clarify this issue analyzing the reported association between NURR1 and MS in human and murine model studies.

Altered Expression Levels of MicroRNA-132 and Nurr1 in Peripheral Blood of Parkinson's Disease: Potential Disease Biomarkers

MicroRNAs (miRNAs) are small and evolutionary conserved noncoding RNAs that are involved in post-transcriptional gene regulation. Differential expression levels of miRNAs can be used as potential biomarkers of disease. Previous animal studies have indicated that the expression level of miR-132 is negatively correlated with its downstream molecule nuclear receptor related 1 protein (Nurr1), which is one of the key factors for the maintenance of dopaminergic function and is particularly vulnerable in Parkinson's disease (PD). However, this correlation has not been confirmed in human patients with PD. Moreover, the possible involvement of miR-132 during the pathogenesis and progression of PD is not fully investigated. Therefore, in the present study, we determined the peripheral circulation levels of miR-132 and Nurr1 in patients with PD, neurological disease controls (NDC) and healthy controls (HC) by reverse transcription real-time quantitative PCR (RT-qPCR). Our data clearly demonstrated that the plasma miR-132 level in PD was significantly higher than those in HC (178%, p < 0.05) and NDC (188%, p < 0.001). When adjusted for gender and age, higher level of miR-132 expression was associated with the significantly increased risk for PD in males and was closely related with the disease stages and disease severity. Furthermore, peripheral Nurr1 was significantly decreased in PD compared with HC (56%, p < 0.001) and NDC (58%, p < 0.001). Much more interestingly, further analysis revealed a negative correlation between the decreased Nurr1 level and the elevated miR-132 level in PD. All these findings indicated that the combination of a high miR-132 level with the low level of its downstream Nurr1 might be a potential biomarker aiding in the diagnosis of PD and monitoring disease progression.

Alterations of NURR1 and Cytokines in the Peripheral Blood Mononuclear Cells: Combined Biomarkers for Parkinson's Disease

Nuclear receptor related 1 protein (NURR1), a transcription factor as key player for maintaining dopamine neuron functions and regulating neuroinflammation in the central nerves system, is a potential susceptibility gene for Parkinson’s disease (PD). To ascertain whether the expression levels of NURR1 gene and inflammatory cytokines are altered in patients with PD, we measured their mRNA levels in the peripheral blood mononuclear cells (PBMCs) in 312 PD patients, 318 healthy controls (HC), and 332 non-PD neurological disease controls (NDCs) by quantitative real-time PCR. Our data showed that NURR1 gene expression was significantly decreased in the PBMCs of PD as compared with that of HC and NDC (p < 0.01). Since NURR1 was reported to have regulating effects on neuroinflammation, we assessed the expression levels of cytokines (TNF-α, IL-1β, IL-4, IL-6, and IL-10) in the PBMCs of PD and controls (HC and NDC). Our results showed that the expression levels of those cytokines were significantly higher than those of controls. Statistical analysis revealed that NURR1 expression presented a negative correlation with the expression of TNF-α, IL-1β, IL-6, and IL-10, and collectively the measurements of NURR1 plus those cytokines significantly improve the diagnostic accuracy. All these findings suggested that NURR1 is likely to be involved in the process of PD by mediating the neuroinflammation, and the combination of NURR1 and cytokines assessment in the PBMCs can be potential biomarkers for PD diagnosis.

Age-dependent decrease of Nurr1 protein expression in the gerbil hippocampus

Nuclear receptor related-1 protein (Nurr1) serves important roles in hippocampal-dependent cognitive process. In the present study, the protein expression of Nurr1 was compared in the hippocampi of young [postnatal month 3 (PM 3)], adult (PM 12) and aged (PM 24) gerbils using western blot analysis and immunohistochemistry. Results indicated that the protein level of Nurr1 was significantly and gradually decreased in the gerbil hippocampus with increasing age. In addition, strong Nurr1 immunoreactivity was primarily observed in pyramidal neurons and granule cells of the hippocampus in the young group, which was determined to be reduced in the adult group and to a greater extent in the aged group. Collectively the data demonstrated that Nurr1 immunoreactivity was gradually and markedly decreased during normal aging. These results indicate that gradual decrease of Nurr1 expression in the hippocampus may be associated with the normal aging process and a decline in hippocampus-dependent cognitive function.

Transcription Factors: Potential Cell Death Markers in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease with a long preclinical phase. The continuous loss of dopaminergic (DA) neurons is one of the pathogenic hallmarks of PD. Diagnosis largely depends on clinical observation, but motor dysfunctions do not emerge until 70%-80% of the nigrostriatal nerve terminals have been destroyed. Therefore, a biomarker that indicates the degeneration of DA neurons is urgently needed. Transcription factors are sequence-specific DNA-binding proteins that regulate RNA synthesis from a DNA template. The precise control of gene expression plays a critical role in the development, maintenance, and survival of cells, including DA neurons. Deficiency of certain transcription factors has been associated with DA neuron loss and PD. In this review, we focus on some transcription factors and discuss their structure, function, mechanisms of neuroprotection, and their potential for use as biomarkers indicating the degeneration of DA neurons.

Association of polymorphisms and reduced expression levels of the NR4A2 gene with Parkinson's disease in a Mexican population

INTRODUCTION

The NR4A2 transcription factor is important in the development, survival and phenotype of dopaminergic neurons and it is postulated as a possible biomarker for Parkinson's disease (PD). Therefore, our aim was to analyze in a sample of a Mexican population with idiopathic PD, mutations (in two hotspot mutation regions) and two polymorphisms (rs34884856 in promotor and rs35479735 intronic regions) of the NR4A2 gene. We also evaluate the levels of NR4A2 gene expression in peripheral blood for a Mexican population, and identify whether they are associated with NR4A2 gene polymorphisms.

METHODS

We conducted a case-control study, which included 227 idiopathic PD cases and 454 unrelated controls. Genetic variants of the NR4A2 gene were genotyped by high-resolution melting (HRM) and validated by an automated sequencing method. The gene expression was performed in peripheral blood using a real-time polymerase chain reaction.

RESULTS

The rs35479735 polymorphism was associated with a higher risk of developing PD. In addition, NR4A2 gene expression was significantly decreased in patients with PD. Linkage disequilibrium analysis showed a haplotype H4 (3C-3G) that showed lower levels of expression, and contained the risk alleles for both polymorphisms.

CONCLUSIONS

In summary, this is the first study in a Mexican population that considers the analysis of NR4A2 in patients with PD. An association was identified between genotype and mRNA expression levels of NR4A2 in patients with PD. These results suggest that polymorphisms and expression of the NR4A2 gene could play an important role in the risk of developing PD in Mexican populations.

In vivo expression of Nurr1/Nr4a2a in developing retinal amacrine subtypes in zebrafish Tg(nr4a2a:eGFP) transgenics

The Nuclear receptor subfamily 4 group A member 2 (Nr4a2) is crucial for the formation or maintenance of dopaminergic neurons in the central nervous system including the retina, where dopaminergic amacrine cells contribute to visual function. Little is known about which cells express Nr4a2 at which developmental stage. Furthermore, whether Nr4a2 functions in combination with other genes is poorly understood. Thus, we generated a novel transgenic to visualize Nr4a2 expression in vivo during zebrafish retinogenesis. A 4.1 kb fragment of the nr4a2a promoter was used to drive green fluorescent protein expression in this Tg(nr4a2a:eGFP) line. In situ hybridization showed that transgene expression follows endogenous RNA expression at a cellular level. Temporal expression and lineages were quantified using in vivo time-lapse imaging in embryos. Nr4a2 expressing retinal subtypes were characterized immunohistochemically. Nr4a2a:eGFP labeled multiple neuron subtypes including 24.5% of all amacrine interneurons. Nr4a2a:eGFP labels all tyrosine hydroxylase labeled dopaminergic amacrine cells, and other nondopaminergic GABAergic amacrine populations. Nr4a2a:eGFP is confined to a specific progenitor lineage identified by sequential expression of the bhlh transcription factor Atonal7 (Atoh7) and Pancreas transcription factor 1a (Ptf1a), and labels postmitotic postmigratory amacrine cells. Thus, developmental Nr4a2a expression indicates a role during late differentiation of specific amacrine interneurons. Tg(nr4a2a:eGFP) is an early marker of distinct neurons including dopaminergic amacrine cells. It can be utilized to assess consequences of gene manipulations and understand whether Nr4a2 only carries out its role in the presence of specific coexpressed genes. This will allow Nr4a2 use to be refined for regenerative approaches.

Identification of NURR1 (Exon 4) and FOXA1 (Exon 3) Haplotypes Associated with mRNA Expression Levels in Peripheral Blood Lymphocytes of Parkinson's Patients in Small Indian Population

Here, we study the expression of NURR1 and FOXA1 mRNA in peripheral blood lymphocytes and its haplotypes in coding region in a small Chennai population of India. Thirty cases of Parkinson's patients (PD) with anti-PD medications (20 males aged 65.85 ± 1.19 and 10 females aged 65.7 ± 1.202) and 30 age matched healthy people (20 males aged 68.45 ± 1.282 and 10 females aged 65.8 ± 1.133) were included. The expression of NURR1 and FOXA1 in PBL was detected by Q-PCR and haplotypes were identified by PCR-SSCP. In the 30 PD cases examined, NURR1 and FOXA1 expression was significantly reduced in both male and female PD patients. However, NURR1 (57.631% reduced in males; 28.93% in females) and FOXA1 (64.42% in males; 55.76% in females) mRNA expression did differ greatly between male and female PD patients. Polymorphisms were identified at exon 4 of the NURR1 and at exon 3 of the FOXA1, respectively, in both male and female patients. A near significant difference in SSCP patterns between genders of control and PD population was analyzed suggesting that further investigations of more patients, more molecular markers, and coding regions should be performed. Such studies could potentially reveal peripheral molecular marker of early PD and different significance to the respective genders.

DNA methylome changes by estradiol benzoate and bisphenol A links early-life environmental exposures to prostate cancer risk

Developmental exposure to endocrine-disrupting chemicals (EDCs), 17β-estradiol-3-benzoate (EB) and bisphenol A (BPA), increases susceptibility to prostate cancer (PCa) in rodent models. Here, we used the methylated-CpG island recovery assay (MIRA)-assisted genomic tiling and CpG island arrays to identify treatment-associated methylome changes in the postnatal day (PND)90 dorsal prostate tissues of Sprague-Dawley rats neonatally (PND1, 3, and 5) treated with 25 µg/pup or 2,500 µg EB/kg body weight (BW) or 0.1 µg BPA/pup or 10 µg BPA/kg BW. We identified 111 EB-associated and 86 BPA-associated genes, with 20 in common, that have significant differentially methylated regions. Pathway analysis revealed cancer as the top common disease pathway. Bisulfite sequencing validated the differential methylation patterns observed by array analysis in 15 identified candidate genes. The methylation status of 7 (Pitx3, Wnt10b, Paqr4, Sox2, Chst14, Tpd52, Creb3l4) of these 15 genes exhibited an inverse correlation with gene expression in tissue samples. Cell-based assays, using 5-aza-cytidine-treated normal (NbE-1) and cancerous (AIT) rat prostate cells, added evidence of DNA methylation-mediated gene expression of 6 genes (exception: Paqr4). Functional connectivity of these genes was linked to embryonic stem cell pluripotency. Furthermore, clustering analyses using the dataset from The Cancer Genome Atlas revealed that expression of this set of 7 genes was associated with recurrence-free survival of PCa patients. In conclusion, our study reveals that gene-specific promoter methylation changes, resulting from early-life EDC exposure in the rat, may serve as predictive epigenetic biomarkers of PCa recurrence, and raises the possibility that such exposure may impact human disease.

Efficient generation of dopaminergic-like neurons by overexpression of Nurr1 and Pitx3 in mouse induced Pluripotent Stem Cells

Parkinson's disease (PD) is a neurodegenerative disorder, in which the nigro-striatal Dopaminergic (DAergic) neurons are selectively lost. Treatment of neurodegenerative diseases with Pluripotent Stem Cells (PSCs) is a big interest in cell therapy. Here, we used induced Pluripotent Stem Cells (iPSCs) expressing two master Dopaminergic (DAergic) transcription factors, i.e. Nurr1 and Pitx3, to generate functional in vitro DAergic-like neurons. After establishment and characterization of Doxycycline-inducible iPSCs from mouse fibroblasts, the cells were transduced by NURR1- and PITX3-harboring lentiviruses. The Nurr1/Pitx3 -iPSCs were differentiated through a five-stage protocol to generate DAergic-like neurons. The results confirmed the efficient expression of DAergic neuron markers in the end of protocol. Beside, the generated cells could exclusively synthesize and secrete Dopamine in response to secretagogues. In conclusion, overexpression of Nurr1 and Pitx3 in iPSCs could efficiently program iPSCs into functional DAergic-like neurons. This finding may have an impact on future stem cell therapy of PD.

Long Non-coding RNAs in the Cytoplasm

An enormous amount of long non-coding RNAs (lncRNAs) transcribed from eukaryotic genome are important regulators in different aspects of cellular events. Cytoplasm is the residence and the site of action for many lncRNAs. The cytoplasmic lncRNAs play indispensable roles with multiple molecular mechanisms in animal and human cells. In this review, we mainly talk about functions and the underlying mechanisms of lncRNAs in the cytoplasm. We highlight relatively well-studied examples of cytoplasmic lncRNAs for their roles in modulating mRNA stability, regulating mRNA translation, serving as competing endogenous RNAs, functioning as precursors of microRNAs, and mediating protein modifications. We also elaborate the perspectives of cytoplasmic lncRNA studies.

Efficient and biologically relevant consensus strategy for Parkinson's disease gene prioritization

BACKGROUND

The systemic information enclosed in microarray data encodes relevant clues to overcome the poorly understood combination of genetic and environmental factors in Parkinson's disease (PD), which represents the major obstacle to understand its pathogenesis and to develop disease-modifying therapeutics. While several gene prioritization approaches have been proposed, none dominate over the rest. Instead, hybrid approaches seem to outperform individual approaches.

METHODS

A consensus strategy is proposed for PD related gene prioritization from mRNA microarray data based on the combination of three independent prioritization approaches: Limma, machine learning, and weighted gene co-expression networks.

RESULTS

The consensus strategy outperformed the individual approaches in terms of statistical significance, overall enrichment and early recognition ability. In addition to a significant biological relevance, the set of 50 genes prioritized exhibited an excellent early recognition ability (6 of the top 10 genes are directly associated with PD). 40 % of the prioritized genes were previously associated with PD including well-known PD related genes such as SLC18A2, TH or DRD2. Eight genes (CCNH, DLK1, PCDH8, SLIT1, DLD, PBX1, INSM1, and BMI1) were found to be significantly associated to biological process affected in PD, representing potentially novel PD biomarkers or therapeutic targets. Additionally, several metrics of standard use in chemoinformatics are proposed to evaluate the early recognition ability of gene prioritization tools.

CONCLUSIONS

The proposed consensus strategy represents an efficient and biologically relevant approach for gene prioritization tasks providing a valuable decision-making tool for the study of PD pathogenesis and the development of disease-modifying PD therapeutics.

Contra-directional Coupling of Nur77 and Nurr1 in Neurodegeneration: A Novel Mechanism for Memantine-Induced Anti-inflammation and Anti-mitochondrial Impairment

Recent evidence suggests that nerve growth factor IB (Nur77) and nuclear receptor related1 (Nurr1) are differentially involved in dopaminergic neurodegeneration. Since memantine has shown clinically relevant efficacy in Parkinson's disease (PD) and displayed a potent protective effect on dopaminergic neurons in experimental PD models, we asked if it exerts its neuroprotection by regulating Nur77 and Nurr1 signaling. We adopted a well-established in vitro PD model, 6-hydroxydopamine (OHDA)-lesioned PC12 cells, to test our hypothesis. Different concentrations of memantine were incubated with 6-OHDA-lesioned PC12 cells, and Nur77/Nurr1 and their related signaling molecules were examined by Western blot and immunocytochemistry. Nur77-deficient PC12 cells were used to verify the influences of Nur77 on neurodegeneration and memantine-mediated neuroprotection. We found that memantine reversed Nur77 upregulation and restored Nurr1 downregulation in 6-OHDA-lesioned PC12 cells. 6-OHDA incubation caused Nur77 translocation from the nucleus to cytosol and induced co-localization of Cyt c/HSP60/Nur77 in the cytosol. Memantine strongly reduced the sub-cellular translocations of Nur77/Cyt c/HSP60 under 6-OHDA-induced oxidative condition. Knockdown of Nur77 enhanced the viability of PC12 cells exposed to 6-OHDA, while memantine-induced neuroprotection was much less in the cells with Nur77 knockdown than in those without it. We conclude that Nur77 plays a crucial role in modulating mitochondrial impairment and contributes to neurodegeneration under the experimental PD condition. Memantine effectively suppresses such Nur77-mediated neurodegeneration and promotes survival signaling through post-translational modification of Nurr1. Nur77 and Nurr1 present a contra-directionally coupling interaction in memantine-mediated neuroprotection.

A novel synthetic activator of Nurr1 induces dopaminergic gene expression and protects against 6-hydroxydopamine neurotoxicity in vitro

Degeneration of dopaminergic neurons in Parkinson's disease (PD) is associated with decreased expression of the orphan nuclear receptor Nurr1 (NR4A2), which is critical for both homeostasis and development of dopamine (DA) neurons. The synthetic, phytochemical-based compound, 1,1-bis (3'-indolyl)-1-(p-chlorophenyl) methane (C-DIM12) activates Nurr1 in cancer cells and prevents loss of dopaminergic neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD in mice. In the present study, we examined the capacity of C-DIM12 to induce expression of Nurr1-regulated genes in two dopaminergic neuronal cell lines (N2A, N27) and to protect against 6-hydroxydopamine (6-OHDA) neurotoxicity. C-DIM12 induced expression of Nurr1-regulated genes that was abolished by Nurr1 knockdown. C-DIM12 increased expression of transfected human Nurr1, induced Nurr1 protein expression in primary dopaminergic neurons and enhanced neuronal survival from exposure to 6-OHDA. These data indicate that C-DIM12 stimulates neuroprotective expression Nurr1-regulated genes in DA neurons.

Age-related gene expression changes in substantia nigra dopamine neurons of the rat

Ageing affects most, if not all, functional systems in the body. For example, the somatic motor nervous system, responsible for initiating and regulating motor output to skeletal musculature, is vulnerable to ageing. The nigrostriatal dopamine pathway is one component of this system, with deficits in dopamine signalling contributing to major motor dysfunction, as exemplified in Parkinson's disease (PD). However, while the dopamine deficit in PD is due to degeneration of substantia nigra (SN) dopamine (DA) neurons, it is unclear whether there is sufficient loss of SN DA neurons with ageing to explain observed motor impairments. Instead, evidence suggests that age-related loss of DA neuron function may be more important than frank cell loss. To further elucidate the mechanisms of functional decline, we have investigated age-related changes in gene expression specifically in laser microdissected SN DA neurons. There were significant age-related changes in the expression of genes associated with neurotrophic factor signalling and the regulation of tyrosine hydroxylase activity. Furthermore, reduced expression of the DA neuron-associated transcription factor, Nurr1, may contribute to these changes. Together, these results suggest that altered neurotrophic signalling and tyrosine hydroxylase activity may contribute to altered DA neuron signalling and motor nervous system regulation in ageing.

Dopaminergic control of autophagic-lysosomal function implicates Lmx1b in Parkinson's disease

The role of developmental transcription factors in maintenance of neuronal properties and in disease remains poorly understood. Lmx1a and Lmx1b are key transcription factors required for the early specification of ventral midbrain dopamine (mDA) neurons. Here we show that conditional ablation of Lmx1a and Lmx1b after mDA neuron specification resulted in abnormalities that show striking resemblance to early cellular abnormalities seen in Parkinson's disease. We found that Lmx1b was required for the normal execution of the autophagic-lysosomal pathway and for the integrity of dopaminergic nerve terminals and long-term mDA neuronal survival. Notably, human LMX1B expression was decreased in mDA neurons in brain tissue affected by Parkinson's disease. Thus, these results reveal a sustained and essential requirement of Lmx1b for the function of midbrain mDA neurons and suggest that its dysfunction is associated with Parkinson's disease pathogenesis.

Expression analysis of the long non-coding RNA antisense to Uchl1 (AS Uchl1) during dopaminergic cells' differentiation in vitro and in neurochemical models of Parkinson's disease

Antisense (AS) transcripts are RNA molecules that are transcribed from the opposite strand to sense (S) genes forming S/AS pairs. The most prominent configuration is when a lncRNA is antisense to a protein coding gene. Increasing evidences prove that antisense transcription may control sense gene expression acting at distinct regulatory levels. However, its contribution to brain function and neurodegenerative diseases remains unclear. We have recently identified AS Uchl1 as an antisense to the mouse Ubiquitin carboxy-terminal hydrolase L1 (Uchl1) gene (AS Uchl1), the synthenic locus of UCHL1/PARK5. This is mutated in rare cases of early-onset familial Parkinson's Disease (PD) and loss of UCHL1 activity has been reported in many neurodegenerative diseases. Importantly, manipulation of UchL1 expression has been proposed as tool for therapeutic intervention. AS Uchl1 induces UchL1 expression by increasing its translation. It is the representative member of SINEUPs (SINEB2 sequence to UP-regulate translation), a new functional class of natural antisense lncRNAs that activate translation of their sense genes. Here we take advantage of FANTOM5 dataset to identify the transcription start sites associated to S/AS pair at Uchl1 locus. We show that AS Uchl1 expression is under the regulation of Nurr1, a major transcription factor involved in dopaminergic cells' differentiation and maintenance. Furthermore, AS Uch1 RNA levels are strongly down-regulated in neurochemical models of PD in vitro and in vivo. This work positions AS Uchl1 RNA as a component of Nurr1-dependent gene network and target of cellular stress extending our understanding on the role of antisense transcription in the brain.

Retinoic acid-loaded polymeric nanoparticles induce neuroprotection in a mouse model for Parkinson's disease

Retinoic acid (RA) plays an important role in the commitment, maturation and survival of neural cells. Recently, RA was pointed as a therapeutic option for some neurodegenerative diseases, including Parkinson's disease (PD). The administration of RA has been defying, and in this sense we have previously developed novel RA-loaded polymeric nanoparticles (RA-NPs) that ensure the efficient intracellular transport and controlled release of RA. Herein, we show that nanoformulation as an efficient neuroprotective effect on dopaminergic (DA) neurons in the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) induced mouse model for PD. The results showed that the RA-NPs administration induced a significant reduction of DA neuron loss in the substantia nigra (SN) as well as their neuronal fiber/axonal innervations in the striatum. Furthermore, we observed an increase in the expression levels of the transcription factors Pitx3 and Nurr1 induced by RA-NPs, showing its supportive effect on the development and functional maintenance of DA neurons in PD. This is the first study showing that RA-NPs can be an innovative strategy to halt the progression of PD pathogenesis, suggesting that this nanoformulation could be of particular interest for the development of new approaches for PD therapeutics.

Association of Nurr1 gene mutations with Parkinson's disease in the Han population living in the Hubei province of China

Nurr1 defects could in part underlie Parkinson's disease pathogenesis, and Nurr1 gene polymorphism has been found in Caucasian patients with Parkinson's disease. In this study, heteroduplex technology was applied to compare the DNA sequences of eight exons of Nurr1 among 200 sporadic Parkinson's disease patients and 200 healthy controls in the Han population in the Hubei province, China. One allele amplified from exon 3 of Nurr1 was polymorphic in five Parkinson's disease patients (2.5%, 5/200), and two individuals had a polymorphic allele amplified from exon 2 (1%, 2/200). The anomalous electrophoresis fragment in exon 3 of Nurr1 gene contained a 709C/A missense mutation, and a polymorphic single nucleotide polymorphism at 388G/A was identified in exon 2. Compared with the control group, the Nurr1 gene expression level in the Parkinson's disease group was decreased, and the Nurr1 gene expression levels in Parkinson's disease patients carrying the polymorphisms at exons 2 and 3 were significantly decreased. Our data indicate that the single nucleotide polymorphism 388G/A in exon 2 and the 709C/A missense mutation in exon 3 of the Nurr1 gene in the Chinese population might affect the pathogenesis of Parkinson's disease.

A high-efficiency induction of dopaminergic cells from human umbilical mesenchymal stem cells for the treatment of hemiparkinsonian rats

The success rate in previous attempts at transforming human umbilical mesenchymal stem cells (HUMSCs) isolated from Wharton's jelly of the umbilical cord into dopaminergic cells was a mere 12.7%. The present study was therefore initiated to establish a more effective procedure for better yield of dopaminergic cells in such transformation for more effective HUMSC-based therapy for parkinsonism. To examine, in vitro, the effects of enhanced Nurr1 expression in HUMSCs on their differentiation, cells were processed through the three-stage differentiation protocol. The capacity of such cells to synthesize and release dopamine was measured by HPLC. The therapeutic effects of Nurr1-overexppressed HUMSCs were examined in 6-hydroxydopamine-lesioned rats by quantification of rotations in response to amphetamine. Enhanced Nurr1 expression in HUMSCs promoted the transformation into dopaminergic cells in vitro through stepwise culturing in sonic hedgehog, fibroblast growth factor-8, and neuron-conditioned medium. The success rate was about 71%, as determined by immunostaining for tyrosine hydroxylase and around 94 nM dopamine synthesis (intracellular and released into the culture medium), as measured by HPLC. Additionally, transplantation of such cells into the striatum of hemiparkinsonian rats resulted in improvement of their behavioral deficits, as indicated by amphetamine-evoked rotation scores. Viability of the transplanted cells lasted for at least 3 months as verified by positive staining for tyrosine hydroxylase. Nurr1, FGF8, Shh, and NCM can synergistically enhance the differentiation of HUMSCs into dopaminergic cells and may pave the way for HUMSC-based treatments for Parkinson's disease.

L-dopa reverses behavioral deficits in the Pitx3 mouse fetus

Studies of fetal rodents have provided evidence that early emerging behaviors, such as the suckling response, are dependent on the developing dopaminergic system. Although connections have been made between manipulations of dopamine and altered behavioral responses, the specific neural pathways involved have yet to be discovered. In this study, we examined the neurobehavioral output of the nigrostriatal pathway, using the Pitx3ak/2J mouse model (Pitx3). Used extensively in the study of Parkinson's disease, the Pitx3 mouse has very specific prenatal loss of dopaminergic neurons solely in the nigrostriatal pathway. Because of this specificity, we hypothesized that behavioral deficits specific to the nigrostriatal pathway would be reversed with administration of the dopamine precursor 3,4-dihydroxyphenylalanine (L-dopa). To test this hypothesis, homozygous mutant and heterozygous control fetal subjects were administered 1 of 4 doses (0, 25, 50, or 75 mg/kg) of L-dopa on the day before birth. Quantification of fetal behavior was scored from video recordings of behavioral observations. The behavioral measures used were (a) spontaneous movement activity; (b) state organization, from quantifications of high- and low-amplitude movements; (c) interlimb movement synchrony, a measure of limb coordination; and (d) oral grasp, similar to a newborn infant suckling response. Specific behavioral deficits observed in the Pitx3 mutants were reversed by L-dopa administration in a dose-dependent manner. However, different deficits required dissimilar doses for reversal, suggesting that some early emerging behaviors may be more sensitive to the administration of L-dopa. Taken together, this study provides valuable information about prenatal behaviors dependent on the nigrostriatal pathway.

The lifelong maintenance of mesencephalic dopaminergic neurons by Nurr1 and engrailed

Specific vulnerability and degeneration of the dopaminergic neurons in the substantia nigra pars compacta of the midbrain is the pathological hallmark of Parkinson’s disease. A number of transcription factors regulate the birth and development of this set of neurons and some remain constitutively expressed throughout life. These maintenance transcription factors are closely associated with essential neurophysiological functions and are required ultimately for the long-term survival of the midbrain dopaminergic neurons. The current review describes the role of two such factors, Nurr1 and engrailed, in differentiation, maturation, and in normal physiological functions including acquisition of neurotransmitter identity. The review will also elucidate the relationship of these factors with life, vulnerability, degeneration and death of mesencephalic dopaminergic neurons in the context of Parkinson’s disease.

NURR1 in Parkinson disease--from pathogenesis to therapeutic potential

In Parkinson disease (PD), affected midbrain dopamine (DA) neurons lose specific dopaminergic properties before the neurons die. How the phenotype of DA neurons is normally established and the ways in which pathology affects the maintenance of cell identity are, therefore, important considerations. Orphan nuclear receptor NURR1 (NURR1, also known as NR4A2) is involved in the differentiation of midbrain DA neurons, but also has an important role in the adult brain. Emerging evidence indicates that impaired NURR1 function might contribute to the pathogenesis of PD: NURR1 and its transcriptional targets are downregulated in midbrain DA neurons that express high levels of the disease-causing protein α-synuclein. Clinical and experimental data indicate that disrupted NURR1 function contributes to induction of DA neuron dysfunction, which is seen in early stages of PD. The likely involvement of NURR1 in the development and progression of PD makes this protein a potentially interesting target for therapeutic intervention.

Transcription factor Nurr1 maintains fiber integrity and nuclear-encoded mitochondrial gene expression in dopamine neurons

Developmental transcription factors important in early neuron specification and differentiation often remain expressed in the adult brain. However, how these transcription factors function to mantain appropriate neuronal identities in adult neurons and how transcription factor dysregulation may contribute to disease remain largely unknown. The transcription factor Nurr1 has been associated with Parkinson's disease and is essential for the development of ventral midbrain dopamine (DA) neurons. We used conditional Nurr1 gene-targeted mice in which Nurr1 is ablated selectively in mature DA neurons by treatment with tamoxifen. We show that Nurr1 ablation results in a progressive pathology associated with reduced striatal DA, impaired motor behaviors, and dystrophic axons and dendrites. We used laser-microdissected DA neurons for RNA extraction and next-generation mRNA sequencing to identify Nurr1-regulated genes. This analysis revealed that Nurr1 functions mainly in transcriptional activation to regulate a battery of genes expressed in DA neurons. Importantly, nuclear-encoded mitochondrial genes were identified as the major functional category of Nurr1-regulated target genes. These studies indicate that Nurr1 has a key function in sustaining high respiratory function in these cells, and that Nurr1 ablation in mice recapitulates early features of Parkinson's disease.

Ginkgo biloba extract (EGb 761) modulates the expression of dopamine-related genes in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity and behavioral impairment in rodents similar to Parkinson's disease. The MPTP mouse model is widely used to evaluate new protective agents. EGb 761 is a well-defined mixture of active compounds extracted from Ginkgo biloba leaves according to a standardized procedure. We have shown that EGb 761 attenuates the loss of striatal dopamine levels and prevents the neurodegeneration of the nigrostriatal pathway induced by MPTP. This finding shows that neuroprotective effects of EGb 761 act, in part, on the dopamine system. Therefore, this study investigates whether EGb 761 exerts dopaminergic neuroprotection through the regulation of dopamine-related gene expression in MPTP-induced Parkinsonism. Male C57BL/6J mice were injected with MPTP (30 mg/kg, i.p.) for 5 days and later with EGb 761 (40 mg/kg, i.p.) daily for 18 days. The expression of selected genes was evaluated in the striatum and midbrain by quantitative PCR. The genes for tyrosine hydroxylase (Th), vesicular monoamine transporter 2 (Vmat2), dopamine transporter (Dat), dopamine D2 receptor (Da-d2r), and transcription factors (Pitx3 and Nurr1) related to dopamine neurotransmission were selected for the analysis. EGb 761 administration to MPTP-treated mice protected Th (41%), Vmat2 (15%), Dat (102%), Da-d2r (46%), Pitx3 (63%), and Nurr1 (148%) mRNA levels in the midbrain, all of which were up-regulated. However, EGb 761 partially reversed the MPTP effect exclusively for Th (48%) and Nurr1 (96%) mRNA in the striatum. Only Th and Nurr1 mRNA and protein levels were regulated by EGb 761 in both regions of the nigrostriatal pathway. This result could be related to the regulation of their transcription. Our results suggest that EGb 761-associated neuroprotection against MPTP neurotoxicity is related to the regulation of the dopamine genes. Moreover, this neuroprotection also involves the regulation of transcription factors such as Nurr1 that are important for the functional maintenance of dopaminergic neurons.

Altered transcription factor trafficking in oxidatively-stressed neuronal cells

Age-related neurodegenerative diseases are associated with alterations in gene expression in affected neurons. One of the mechanisms that could account for this is altered subcellular localization of transcription factors, which has been observed in human post-mortem brains of each of the major neurodegenerative diseases, including Parkinson's disease (PD). The specific mechanisms are yet to be elucidated; however a potential mechanism involves alterations in nuclear transport. In this study, we examined the nucleocytoplasmic trafficking of select transcription factors in response to a PD-relevant oxidative injury, 6-hydroxydopamine (6OHDA). Utilizing a well-established model of ligand-regulated nucleocytoplasmic shuttling, the glucocorticoid receptor, we found that 6OHDA selectively impaired nuclear import through an oxidative mechanism without affecting nuclear export or nuclear retention. Interestingly, impaired nuclear import was selective as Nrf2 (nuclear factor E2-related factor 2) nuclear localization remained intact in 6OHDA-treated cells. Thus, oxidative stress specifically impacts the subcellular localization of some but not all transcription factors, which is consistent with observations in post-mortem PD brains. Our data further implicate a role for altered microtubule dependent trafficking in the differential effects of 6OHDA on transcription factor import. Oxidative disruption of microtubule-dependent nuclear transport may contribute to selective declines in transcriptional responses of aging or diseased dopaminergic cells.