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

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.

Roles of Transcription Factors in the Development and Reprogramming of the Dopaminergic Neurons

The meso-diencephalic dopaminergic (mdDA) neurons regulate various critical processes in the mammalian nervous system, including voluntary movement and a wide range of behaviors such as mood, reward, addiction, and stress. mdDA neuronal loss is linked with one of the most prominent human movement neurological disorders, Parkinson’s disease (PD). How these cells die and regenerate are two of the most hotly debated PD research topics. As for the latter, it has been long known that a series of transcription factors (TFs) involves the development of mdDA neurons, specifying cell types and controlling developmental patterns. In vitro and in vivo, TFs regulate the expression of tyrosine hydroxylase, a dopamine transporter, vesicular monoamine transporter 2, and L-aromatic amino acid decarboxylase, all of which are critical for dopamine synthesis and transport in dopaminergic neurons (DA neurons). In this review, we encapsulate the molecular mechanism of TFs underlying embryonic growth and maturation of mdDA neurons and update achievements on dopaminergic cell therapy dependent on knowledge of TFs in mdDA neuronal development. We believe that a deeper understanding of the extrinsic and intrinsic factors that influence DA neurons’ fate and development in the midbrain could lead to a better strategy for PD cell therapy.

Synergistic Effects of Combined Nurr1 Overexpression and Natural Inducers on the More Efficient Production of Dopaminergic Neuron-Like Cells From Stem Cells

The development of dopaminergic (DA) neurons is a very complex process, and a combination of extrinsic and intrinsic factors involves their differentiation. Transcription factor, Nurr1 plays an essential role in the differentiation and maintenance of midbrain DA neurons. Nurr1-based therapies may restore DA function in Parkinson's disease (PD) by replacing damaged cells with differentiated cells derived from stem cells. Providing tissue-specific microenvironments such as brain extract can effectively induce dopaminergic gene expression in stem cells. The present study aimed to investigate the combined effects of Nurr1 gene overexpression and a neonatal rat brain extract (NRBE) induction on dopaminergic differentiation of P19 stem cells. In order to neural differentiation induction, stably Nurr1-transfected cells were treated with 100 μg/ml of NRBE. The differentiation potential of the cells was then evaluated during a period of 1–3 weeks via various methods. The initial evaluation of the cells by direct observation under a light microscope and cresyl violet specific staining, confirmed neuron-like morphology in the differentiated cells. In addition, different molecular and cellular techniques, including real-time PCR, immunofluorescence, and flow cytometry, demonstrated that the treated cells expressed pan-neuronal and dopaminergic markers. In all experimental groups, neuronal phenotype with dopaminergic neuron-like cells characteristics mainly appeared in the second week of the differentiation protocol. Overall, the results of the present study revealed for the first time the synergistic effects of Nurr1 gene overexpression and possible soluble factors that existed in NRBE on the differentiation of P19 stem cells into dopaminergic neuron-like cells.

Regulation of Glutamate, GABA and Dopamine Transporter Uptake, Surface Mobility and Expression

Neurotransmitter transporters limit spillover between synapses and maintain the extracellular neurotransmitter concentration at low yet physiologically meaningful levels. They also exert a key role in providing precursors for neurotransmitter biosynthesis. In many cases, neurons and astrocytes contain a large intracellular pool of transporters that can be redistributed and stabilized in the plasma membrane following activation of different signaling pathways. This means that the uptake capacity of the brain neuropil for different neurotransmitters can be dynamically regulated over the course of minutes, as an indirect consequence of changes in neuronal activity, blood flow, cell-to-cell interactions, etc. Here we discuss recent advances in the mechanisms that control the cell membrane trafficking and biophysical properties of transporters for the excitatory, inhibitory and modulatory neurotransmitters glutamate, GABA, and dopamine.

Current State-of-the-Art and Unresolved Problems in Using Human Induced Pluripotent Stem Cell-Derived Dopamine Neurons for Parkinson's Disease Drug Development

Human induced pluripotent stem (iPS) cells have the potential to give rise to a new era in Parkinson's disease (PD) research. As a unique source of midbrain dopaminergic (DA) neurons, iPS cells provide unparalleled capabilities for investigating the pathogenesis of PD, the development of novel anti-parkinsonian drugs, and personalized therapy design. Significant progress in developmental biology of midbrain DA neurons laid the foundation for their efficient derivation from iPS cells. The introduction of 3D culture methods to mimic the brain microenvironment further expanded the vast opportunities of iPS cell-based research of the neurodegenerative diseases. However, while the benefits for basic and applied studies provided by iPS cells receive widespread coverage in the current literature, the drawbacks of this model in its current state, and in particular, the aspects of differentiation protocols requiring further refinement are commonly overlooked. This review summarizes the recent data on general and subtype-specific features of midbrain DA neurons and their development. Here, we review the current protocols for derivation of DA neurons from human iPS cells and outline their general weak spots. The associated gaps in the contemporary knowledge are considered and the possible directions for future research that may assist in improving the differentiation conditions and increase the efficiency of using iPS cell-derived neurons for PD drug development are discussed.

Extracellular Vesicles as Nanotherapeutics for Parkinson's Disease

Extracellular vesicles (EVs) are naturally occurring membranous structures secreted by normal and diseased cells, and carrying a wide range of bioactive molecules. In the central nervous system (CNS), EVs are important in both homeostasis and pathology. Through receptor-ligand interactions, direct fusion, or endocytosis, EVs interact with their target cells. Accumulating evidence indicates that EVs play crucial roles in the pathogenesis of many neurodegenerative disorders (NDs), including Parkinson's disease (PD). PD is the second most common ND, characterized by the progressive loss of dopaminergic (DAergic) neurons within the Substantia Nigra pars compacta (SNpc). In PD, EVs are secreted by both neurons and glial cells, with either beneficial or detrimental effects, via a complex program of cell-to-cell communication. The functions of EVs in PD range from their etiopathogenetic relevance to their use as diagnostic tools and innovative carriers of therapeutics. Because they can cross the blood-brain barrier, EVs can be engineered to deliver bioactive molecules (e.g., small interfering RNAs, catalase) within the CNS. This review summarizes the latest findings regarding the role played by EVs in PD etiology, diagnosis, prognosis, and therapy, with a particular focus on their use as novel PD nanotherapeutics.

Regulation of Social Stress and Neural Degeneration by Activity-Regulated Genes and Epigenetic Mechanisms in Dopaminergic Neurons

Transcriptional and epigenetic regulation of both dopaminergic neurons and their accompanying glial cells is of great interest in the search for therapies for neurodegenerative disorders such as Parkinson’s disease (PD). In this review, we collate transcriptional and epigenetic changes identified in adult Drosophila melanogaster dopaminergic neurons in response to either prolonged social deprivation or social enrichment, and compare them with changes identified in mammalian dopaminergic neurons during normal development, stress, injury, and neurodegeneration. Surprisingly, a small set of activity-regulated genes (ARG) encoding transcription factors, and a specific pattern of epigenetic marks on gene promoters, are conserved in dopaminergic neurons over the long evolutionary period between mammals and insects. In addition to their classical function as immediate early genes to mark acute neuronal activity, these ARG transcription factors are repurposed in both insects and mammals to respond to chronic perturbations such as social enrichment, social stress, nerve injury, and neurodegeneration. We suggest that these ARG transcription factors and epigenetic marks may represent important targets for future therapeutic intervention strategies in various neurodegenerative disorders including PD.

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.

Transcription Factor-Based Fate Specification and Forward Programming for Neural Regeneration

Traditionally, in vitro generation of donor cells for brain repair has been dominated by the application of extrinsic growth factors and morphogens. Recent advances in cell engineering strategies such as reprogramming of somatic cells into induced pluripotent stem cells and direct cell fate conversion have impressively demonstrated the feasibility to manipulate cell identities by the overexpression of cell fate-determining transcription factors. These strategies are now increasingly implemented for transcription factor-guided differentiation of neural precursors and forward programming of pluripotent stem cells toward specific neural subtypes. This review covers major achievements, pros and cons, as well as future prospects of transcription factor-based cell fate specification and the applicability of these approaches for the generation of donor cells for brain repair.

Epigenetic Regulation of the Ontogenic Expression of the Dopamine Transporter

The dopamine transporter (DAT) is a plasma membrane transport protein responsible for regulating the duration and intensity of dopaminergic signaling. Altered expression of DAT is linked to neurodevelopmental disorders, including attention deficit hyperactivity disorder and autism spectrum disorder, and is shown to contribute to the response of psychotropic drugs and neurotoxicants. Although the postnatal levels of DAT have been characterized, there are few data regarding the mechanisms that regulate postnatal DAT expression. Here, we examine the ontogeny of DAT mRNA from postnatal days 0 to 182 in the rat brain and define a role for epigenetic mechanisms regulating DAT expression. DAT mRNA and protein significantly increased between PND 0 and 6 months in rat midbrain and striatum, respectively. The epigenetic modifiers Dnmt1, Dnmt3a, Dnmt3b, and Hdac2 demonstrated age associated decreases in mRNA expression whereas Hdac5 and Hdac8 showed increased mRNA expression with age. Chromatin immunoprecipitation studies revealed increased protein enrichment of acetylated histone 3 at lysines 9 and 14 and the dopaminergic transcription factors Nurr1 and Pitx3 within the DAT promoter in an age-related manner. Together these studies provide evidence for the role of epigenetic modifications in the regulation of DAT during development. The identification of these mechanisms may contribute to potential therapeutic interventions aimed at neurodevelopmental disorders of the dopaminergic system.

In Vitro Generation of Glucose-Responsive Insulin-Secreting Cells from PDX1-Overexpressing Human-Induced Pluripotent Stem Cell Derived from Diabetic Patient

Pancreatic and duodenal homeobox 1 (PDX1), a member of the homeodomain-containing transcription factor family, is a key transcription factor for pancreas development and mature β-cell function. In this study, induced overexpression of PDX1 resulted in producing susceptible cells for pancreatic differentiation and was well beneficial to enhance β-cell production, maturation, function, and survival. Induced PDX1 overexpression in harmony with a set of signaling molecules involves in guiding the signaling pathways toward pancreas development, leaded to high-efficient in vitro generation of ectopic insulin-producing cells (IPCs) with the effectively reduced number of polyhormonal cells and increased number of insulin (INS) single-positive cells. This strategy yielded 85.61% glucose-responsive insulin-positive cells in vitro, which was seven times higher than the basal level, and electron microscopy images revealed the presence of mature β-cell secretory granules. The generation of glucose-responsive insulin-secreting β-like cells from human-induced pluripotent stem cells (hiPSCs) in vitro would provide a promising approach to produce an unprecedented cell source for cell transplantation therapy in diabetes without the ethical obstacle of embryonic stem cells and would bypass immune rejection. These cells are an invaluable source for disease modeling, drug discovery, and pharmacogenomics studies as well.

Sequential Application of Discrete Topographical Patterns Enhances Derivation of Functional Mesencephalic Dopaminergic Neurons from Human Induced Pluripotent Stem Cells

Parkinson’s Disease is a progressive neurodegenerative disorder attributed to death of mesencephalic dopaminergic (DA) neurons. Pluripotent stem cells have great potential in the study for this late-onset disease, but acquirement of cells that are robust in quantity and quality is still technically demanding. Biophysical cues have been shown to direct stem cell fate, but the effect of different topographies in the lineage commitment and subsequent maturation stages of cells have been less examined. Using human induced pluripotent stem cells (iPSCs), we applied topographical patterns sequentially during differentiation stages and examined their ability to influence derivation yield and functionality of regionalized subtype-specific DA neurons. Gratings showed higher yield of DA neurons and may be beneficial for initial lineage commitment. Cells derived on pillars in the terminal differentiation stage have increased neuronal complexity, and were more capable of firing repetitive action potentials, showing that pillars yielded better network formation and functionality. Our topography platform can be applied to patient-derived iPSCs as well, and that cells harbouring LRRK2 mutation were more functionally mature when optimal topographies were applied sequentially. This will hopefully accelerate development of robust cell models that will provide novel insights into discovering new therapeutic approaches for Parkinson’s Disease.

Liver X receptors agonist promotes differentiation of rat bone marrow derived mesenchymal stem cells into dopaminergic neuron-like cells

Dopaminergic (DA) neurons derived from bone marrow derived mesenchymal stem cells (BMSCs) maybe a valuable source for cell replacement therapy in Parkinson disease. Recent studies showed that new functions of LXR and their ligands have been proposed to prevent PD in the adult nervous system. The present study was designed to observe the effect of liver X receptors (LXR) agonist on differentiation of rat BMSCs into DA neurons. Expressions of the neuronal markers (Tuj1 and Nestin), the specific marker of DA neurons (tyrosine hydroxylase, TH), LXR α and LXR β were measured by immunocytochemical assay and TH/Tuj1 positive cells were determined by quantitative cell count analyses. mRNA expressions of LXR α, LXR β, TH, DAT, Nurr1, Pitx3, En1 and Lmx1b were measured by qPCR. Compared with growth factors (GF) treated group, combined use of LXR and GF induced rat BMSCs to TH-expressing cells with 87.42% of efficiency in 6 days of period of induction. LXR agonist alone did not induce the differentiation. Compared with GF alone, combined use of LXR and GF increased expressions of LXR α and LXR β protein and mRNA and TH, DAT, Nurr1, and Pitx3 mRNA, decreased expressions of En1 and Lmx1b mRNA. Our experimental results indicated that LXR activation leads to improve induction efficiency and shorten induction period of rat BMSCs into DA neuron-like cells through regulating DA development-related genes expressions and that LXR can be considered as a candidate target for drug development to improve differentiation of BMSCs into DA neurons.

Region Specific Effects of Aging and the Nurr1-Null Heterozygous Genotype on Dopamine Neurotransmission

The transcription factor Nurr1 is essential for dopamine neuron differentiation and is important in maintaining dopamine synthesis and neurotransmission in the adult. Reduced Nurr1 function, due to the Nurr1-null heterozygous genotype (+/-), impacts dopamine neuron function in a region specific manner resulting in a decrease in dopamine synthesis in the dorsal and ventral striatum and a decrease in tissue dopamine levels in the ventral striatum. Additionally, maintenance of tissue dopamine levels in the dorsal striatum and survival of nigrostriatal dopamine neurons with aging (>15 months) or after various toxicant treatments are impaired. To further investigate the effects of aging and the Nurr1-null heterozygous genotype, we measured regional tissue dopamine levels, dopamine neuron numbers, body weight, open field activity and rota-rod performance in young (3-5 months) and aged (15-17 months) wild-type +/+ and +/- mice. Behavioral tests revealed no significant differences in rota-rod performance or basal open field activity as a result of aging or genotype. The +/- mice did show a significant increase in open field activity after 3 min of restraint stress. No differences in tissue dopamine levels were found in the dorsal striatum. However, there were significant reductions in tissue dopamine levels in the ventral striatum, which was separated into the nucleus accumbens core and shell, in the aged +/- mice. These data indicate that the mesoaccumbens system is more susceptible to the combination of aging and the +/- genotype than the nigrostriatal system. Additionally, the effects of aging and the +/- genotype may be dependent on genetic background or housing conditions. As Nurr1 mutations have been implicated in a number of diseases associated with dopamine neurotransmission, further data is needed to understand why and how Nurr1 can have differential functions across different dopamine neuron populations in aging.

NR4A2 genetic variation and Parkinson's disease: Evidence from a systematic review and meta-analysis

INTRODUCTION

The homo sapiens nuclear receptor subfamily 4, group A (NR4A2) genetic variation has been implicated as a risk factor for Parkinson's disease (PD). Nevertheless, the results are inconclusive. We conducted a comprehensive systematic review and meta-analysis to quantify the impact of NR4A2 variation on the risk of PD.

METHODS

All eligible case-control studies published up to June 2016 by searching Pubmed, OVID, EBSCO, PsycINFO, ISI Web of Knowledge, Chinese Biomedical Literature Database and China Academic Journals Database were identified. Pooled odds ratio (OR) with 95% confidence interval (CI) were used to access the strength of the association in fixed- or random-effects model.

RESULTS

Eighteen studies reported 24 genetic variants with a total of 6150 cases and 5919 controls were included. Twelve studies for NR4A2 rs35479735 polymorphism and 4 studies for rs12803 were available for meta-analysis. A significant association was observed for rs35479735 under the homozygous model (OR=1.31, 95% CI: 1.10-1.56, P=0.003), whereas no significant association for rs12803 was detected. In subgroup analysis stratified by ethnicity, age onset and familial history, we found no significant association except one in sporadic PD subgroup under the recessive (OR=3.30, 95% CI: 1.23-8.84, P=0.02) and homozygous model (OR=3.43, 95% CI: 1.26-9.33, P=0.02) for rs35479735.

CONCLUSION

The study comprehensively evaluated the association of NR4A2 variation with PD, and the results failed to demonstrate that the NR4A2 polymorphisms significantly associated with PD except for rs35479735, suggesting that more studies are needed to elucidate if NR4A2 is a risk of PD.