Foxa2 and Nurr1 synergistically yield A9 nigral dopamine neurons exhibiting improved differentiation, function, and cell survival

Activating Wnt1/β-Catenin signaling pathway to restore Otx2 expression in the dopaminergic neurons of ventral midbrain

Parkinson's disease (PD) is the world's second most prevalent neurodegenerative disease. Currently, aside from levodopa, there are no other effective drugs clinically available to slow its progression. Otx2 plays a critical role in the differentiation of midbrain dopaminergic neurons (mDANs) during midbrain development. However, in adulthood, Otx2 is primarily expressed in the ventral tegmental area (VTA)-ventral part, and mDANs in the dorsal part of the VTA and the substantia nigra pars compacta (SNc) show no Otx2 expression. Research indicates that Otx2 is essential not only for the development of mDANs but also for their protection against the toxicity of MPTP and rotenone. Consequently, Otx2 is a potential clinical target for mDANs protection. Identifying the upstream mechanism that regulates Otx2 expression is crucial to restoring its expression in the SNc and enhancing its levels in the entire ventral midbrain mDANs. In this study, we have demonstrated the safety of Otx2 overexpression in vitro by using adeno-associate virus (AAV) and explored the feasibility of promoting Otx2 expression through the Wnt/β-Catenin signaling pathway using various drugs, a miR-34 mimic, and an inhibitor. Our results showed that Otx2 overexpression via AAV in the SNc is relatively safe, and CHIR99021 can induce Otx2 expression in mouse mDANs, thereby, alleviating PD-liked motor symptoms induced by MPTP. These findings suggest that modulating Otx2 expression through the Wnt/β-Catenin signaling pathway holds a therapeutic approach for Parkinson's disease.

Alpha-Synuclein drives NURR1 and NLRP3 Inflammasome dysregulation in Parkinson's disease: From pathogenesis to potential therapeutic strategies

Parkinson's disease (PD), a progressive neurodegenerative disorder, is characterized by the loss of dopaminergic neurons and pathological aggregation of α-synuclein (α-Syn). Emerging evidence highlights the interplay between genetic susceptibility, neuroinflammation, and transcriptional dysregulation in driving PD pathogenesis. This review brings together the latest information on three important players: α-Syn, the transcription factor Orphan nuclear receptor (NURR1), and the NOD-like receptor 3 (NLRP3) inflammasome. Pathogenic α-syn aggregates cause damage to neurons by disrupting mitochondria and lysosomes and spreading in a way similar to prion proteins. They also turn on the NLRP3 inflammasome, which is a key player in neuroinflammation. NLRP3-driven release of pro-inflammatory cytokines exacerbates neurodegeneration and creates a self-sustaining inflammatory milieu. Meanwhile, reduced NURR1 activity, a pivotal modulator of dopaminergic neuron survival and development, exposes neurons to oxidative stress, neuroinflammation, and α-Syn toxicity, hence exacerbating disease progression. So, targeting this trio exhibits transformative potential against PD pathogenesis.

Rapid effects of valproic acid on the fetal brain transcriptome: Implications for brain development and autism

There is an increased incidence of autism among the children of women who take the anti-epileptic, mood stabilizing drug, valproic acid (VPA) during pregnancy; moreover, exposure to VPA in utero causes autistic-like symptoms in rodents and non-human primates. Analysis of RNAseq data ob-tained from E12.5 fetal mouse brains 3 hours after VPA administration revealed that VPA significant-ly increased or decreased the expression of approximately 7,300 genes. No significant sex differ-ences in VPA-induced gene expression were observed. Expression of genes associated with neu-rodevelopmental disorders (NDDs) such as autism as well as neurogenesis, axon growth and syn-aptogenesis, GABAergic, glutaminergic and dopaminergic synaptic transmission, perineuronal nets, and circadian rhythms was dysregulated by VPA. Moreover, expression of 399 autism risk genes was significantly altered by VPA as was expression of 252 genes that have been reported to play fundamental roles in the development of the nervous system but are not otherwise linked to autism. The goal of this study was to identify mouse genes that are: (a) significantly up- or down-regulated by VPA in the fetal brain and (b) known to be associated with autism and/or to play a role in embryonic neurodevelopmental processes, perturbation of which has the potential to alter brain connectivity in the postnatal and adult brain. The set of genes meeting these criteria pro-vides potential targets for future hypothesis-driven approaches to elucidating the proximal underly-ing causes of defective brain connectivity in NDDs such as autism.

Directional induction of neural stem cells, a new therapy for neurodegenerative diseases and ischemic stroke

Due to the limited capacity of the adult mammalian brain to self-repair and regenerate, neurological diseases, especially neurodegenerative disorders and stroke, characterized by irreversible cellular damage are often considered as refractory diseases. Neural stem cells (NSCs) play a unique role in the treatment of neurological diseases for their abilities to self-renew and form different neural lineage cells, such as neurons and glial cells. With the increasing understanding of neurodevelopment and advances in stem cell technology, NSCs can be obtained from different sources and directed to differentiate into a specific neural lineage cell phenotype purposefully, making it possible to replace specific cells lost in some neurological diseases, which provides new approaches to treat neurodegenerative diseases as well as stroke. In this review, we outline the advances in generating several neuronal lineage subtypes from different sources of NSCs. We further summarize the therapeutic effects and possible therapeutic mechanisms of these fated specific NSCs in neurological disease models, with special emphasis on Parkinson's disease and ischemic stroke. Finally, from the perspective of clinical translation, we compare the strengths and weaknesses of different sources of NSCs and different methods of directed differentiation, and propose future research directions for directed differentiation of NSCs in regenerative medicine.

Genes critical for development and differentiation of dopaminergic neurons are downregulated in Parkinson's disease

We performed transcriptome analysis using RNA sequencing on substantia nigra pars compacta (SNpc) from mice after acute and chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment and from Parkinson's disease (PD) patients. Acute and chronic exposure to MPTP resulted in decreased expression of genes involved in sodium channel regulation. However, upregulation of pro-inflammatory pathways was seen after single dose but not after chronic MPTP treatment. Dopamine biosynthesis and synaptic vesicle recycling pathways were downregulated in PD patients and after chronic MPTP treatment in mice. Genes essential for midbrain development and determination of dopaminergic phenotype such as, LMX1B, FOXA1, RSPO2, KLHL1, EBF3, PITX3, RGS4, ALDH1A1, RET, FOXA2, EN1, DLK1, GFRA1, LMX1A, NR4A2, GAP43, SNCA, PBX1, and GRB10 were downregulated in human PD and overexpression of GFP tagged LMX1B rescued MPP⁺ induced death in SH-SY5Y neurons. Downregulation of gene ensemble involved in development and differentiation of dopaminergic neurons indicate their potential involvement in pathogenesis and progression of human PD.

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.

Timing of MeCP2 Expression Determines Midbrain Dopamine Neuron Phenotype Specification

Midbrain dopamine (DA) neurons are associated with locomotor and psychiatric disorders. DA phenotype is specified in ancestral neural precursor cells (NPCs) and maintained throughout neuronal differentiation. Here we show that endogenous expression of MeCP2 coincides with DA phenotype specification in mouse mesencephalon, and premature expression of MeCP2 prevents in vitro cultured NPCs from acquiring DA phenotype through interfering NURR1 transactivation of DA phenotype genes. By contrast, ectopic MeCP2 expression does not disturb DA phenotype in the DA neurons. By analyzing the dynamic change of DNA methylation along DA neuronal differentiation at the promoter of DA phenotype gene tyrosine hydroxylase (Th), we show that Th expression is determined by TET1-mediated de-methylation of NURR1 binding sites within Th promoter. Chromatin immunoprecipitation assays demonstrate that premature MeCP2 dominates the DNA binding of the corresponding sites thereby blocking TET1 function in DA NPCs, whereas TET1-mediated de-methylation prevents excessive MeCP2 binding in DA neurons. The significance of temporal DNA methylation status is further confirmed by targeted methylation/demethylation experiments showing that targeted de-methylation in DA NPCs protects DA phenotype specification from ectopic MeCP2 expression, whereas targeted methylation disturbs phenotype maintenance in MeCP2-overexpressed DA neurons. These findings suggest the appropriate timing of MeCP2 expression as a novel determining factor for guiding NPCs into DA lineage.

Newly regenerated dopaminergic neurons in 6-OHDA-lesioned adult zebrafish brain proliferate in the Olfactory bulb and telencephalon, but migrate to, differentiate and mature in the diencephalon

In order to understand the biological processes underlying dopaminergic neurons (DpN) regeneration in a 6-hydroxydopamine(6-OHDA)-induced adult zebrafish-based Parkinson's disease model, this study investigated the specific phases of neuroregeneration in a time-based manner. Bromodeoxyuridine (BrdU) was administered 24 h before the harvest of brain tissues at day three, five, seven, nine, 12 and 14 postlesion. Potential migration of proliferative cells was tracked over 14 days postlesion through double-pulse tracking [BrdU and 5-ethynyl-2'-deoxyuridine (EdU)] of cells and immunohistostaining of astrocytes [glial fibrillary acidic protein (GFAP)]. Gene expression of foxa2 and nurr1 (nr4a2a) at day three, nine, 14, 18, 22 and 30 postlesion was quantified using qPCR. Protein expression of foxa2 at day three, seven, 14 and 22 postlesion was validated using the western blot technique. Double labelling [EdU and tyrosine hydroxylase (TH)] of proliferative cells was performed to ascertain their fate after the neuroregeneration processes. It was found that whilst cell proliferation remained unchanged in the area of substantial DpN loss, the ventral diencephalon (vDn), there was a transient increase of cell proliferation in the olfactory bulb (OB) and telencephalon (Tel) seven days postlesion. BrdU-immunoreactive (ir)/ EdU-ir cells and activated astrocytes were later found to be significantly increased in the vDn and its nearby area (Tel) 14 days postlesion. There was a significant but transient downregulation of foxa2 at day three and nine postlesion, and nr4a2a at day three, nine and 14 postlesion. The expression of both genes remained unchanged in the OB and Tel. There was a transient downregulation of foxa2 protein expression at day three and seven postlesion. The significant increase of EdU-ir/ TH-ir cells in the vDn 30 days postlesion indicates maturation of proliferative cells (formed between day five-seven postlesion) into DpN. The present findings warrant future investigation of critical factors that govern the distinctive phases of DpN regeneration.

Chromatin architecture in addiction circuitry identifies risk genes and potential biological mechanisms underlying cigarette smoking and alcohol use traits

Cigarette smoking and alcohol use are among the most prevalent substances used worldwide and account for a substantial proportion of preventable morbidity and mortality, underscoring the public health significance of understanding their etiology. Genome-wide association studies (GWAS) have successfully identified genetic variants associated with cigarette smoking and alcohol use traits. However, the vast majority of risk variants reside in non-coding regions of the genome, and their target genes and neurobiological mechanisms are unknown. Chromosomal conformation mappings can address this knowledge gap by charting the interaction profiles of risk-associated regulatory variants with target genes. To investigate the functional impact of common variants associated with cigarette smoking and alcohol use traits, we applied Hi-C coupled MAGMA (H-MAGMA) built upon cortical and newly generated midbrain dopaminergic neuronal Hi-C datasets to GWAS summary statistics of nicotine dependence, cigarettes per day, problematic alcohol use, and drinks per week. The identified risk genes mapped to key pathways associated with cigarette smoking and alcohol use traits, including drug metabolic processes and neuronal apoptosis. Risk genes were highly expressed in cortical glutamatergic, midbrain dopaminergic, GABAergic, and serotonergic neurons, suggesting them as relevant cell types in understanding the mechanisms by which genetic risk factors influence cigarette smoking and alcohol use. Lastly, we identified pleiotropic genes between cigarette smoking and alcohol use traits under the assumption that they may reveal substance-agnostic, shared neurobiological mechanisms of addiction. The number of pleiotropic genes was ~26-fold higher in dopaminergic neurons than in cortical neurons, emphasizing the critical role of ascending dopaminergic pathways in mediating general addiction phenotypes. Collectively, brain region- and neuronal subtype-specific 3D genome architecture helps refine neurobiological hypotheses for smoking, alcohol, and general addiction phenotypes by linking genetic risk factors to their target genes.

Psychological impacts of COVID-19 pandemic on the mode choice behaviour: A hybrid choice modelling approach

The COVID-19 pandemic is a pivotal moment in the history of mankind, which had a huge impact on the fast-paced world. The uncertainty associated with the plight of the pandemic, pushed the world towards a sense of insecurity and panic. Apart from the disease, the psychological problems connected to the lockdowns has caused an unprecedented change in the thought process of people towards travel. In the present study, we aim to statistically illustrate the change, the pandemic and lockdowns brought upon the travel mode choice behaviour. An Integrated choice and latent variable (ICLV) framework was adapted to understand the impact of the novel behavioural constructs, such as awareness of the disease and people's perception of the strictness of lockdown towards the mode choice in the post pandemic scenario. Different trip types were characterized according to the nature of the trip and their mode choice were assessed separately for the impact of the latent constructs. The results suggest that the awareness of the disease and the perception of strictness of the lockdown implemented play a major role in affecting the change of the mode choice of people. Further, the perception of safety in public transport, characterized by the social distancing and sanitization measures, determine the willingness of people towards the choice of public transit systems. The study concludes with a focus on the policies, which could be implemented for a safe travel in the post lockdown stage.

On the Road from Phenotypic Plasticity to Stem Cell Therapy

In 1981, I published a paper in the first issue of The Journal of Neuroscience with my postdoctoral mentor, Richard Bunge. At that time, the long-standing belief that each neuron expressed only one neurotransmitter, known as Dale's Principle (Dale, 1935), was being hotly debated following a report by French embryologist Nicole Le Douarin showing that neural crest cells destined for one transmitter phenotype could express characteristics of another if transplanted to alternate sites in the developing embryo (Le Douarin, 1980). In the Bunge laboratory, we were able to more directly test the question of phenotypic plasticity in the controlled environment of the tissue culture dish. Thus, in our paper, we grew autonomic catecholaminergic neurons in culture under conditions which promoted the acquisition of cholinergic traits and showed that cells did not abandon their inherited phenotype to adopt a new one but instead were capable of dual transmitter expression. In this Progressions article, I detail the path that led to these findings and how this study impacted the direction I followed for the next 40 years. This is my journey from phenotypic plasticity to the promise of a stem cell therapy.

Direct conversion of human fibroblasts into dopaminergic neuron-like cells using small molecules and protein factors

BACKGROUND

Generation of neurons is essential in cell replacement therapy for neurodegenerative disorders like Parkinson's disease. Several studies have reported the generation of dopaminergic (DA) neurons from mouse and human fibroblasts by ectopic expression of transcription factors, in which genetic manipulation is associated with potential risks.

METHODS

The small molecules and protein factors were selected based on their function to directly induce human fetal lung IMR-90 fibroblasts into DA neuron-like cells. Microscopical, immunocytochemical, and RT-qPCR analyses were used to characterize the morphology, phenotype, and gene expression features of the induced cells. The whole-cell patch-clamp recordings were exploited to measure the electrophysiological properties.

RESULTS

Human IMR-90 fibroblasts were rapidly converted into DA neuron-like cells after the chemical induction using small molecules and protein factors, with a yield of approximately 95% positive TUJ1-positive cells. The induced DA neuron-like cells were immunopositive for pan-neuronal markers MAP2, NEUN, and Synapsin 1 and DA markers TH, DDC, DAT, and NURR1. The chemical induction process did not involve a neural progenitor/stem cell intermediate stage. The induced neurons could fire single action potentials, which reflected partially the electrophysiological properties of neurons.

CONCLUSION

We developed a chemical cocktail of small molecules and protein factors to convert human fibroblasts into DA neuron-like cells without passing through a neural progenitor/stem cell intermediate stage. The induced DA neuron-like cells from human fibroblasts might provide a cellular source for cell-based therapy of Parkinson's disease in the future.

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.

How Eudaimonic Aspect of Subjective Well-Being Affect Transport Mode Choice? The Case of Thessaloniki, Greece

In recent years, the relationship between transportation and subjective well-being has been a major subject. Well-being is a factor that can affect travelers’ psychology and transport mode choice. For this reason, policymakers have attempted to improve travelers’ subjective well-being and promote sustainable modes of transport. For a better understanding of these factors, a questionnaire-based survey was conducted to identify the travel eudaimonia aspect of subjective well-being (comfort, safety, autonomy, self-confidence, physical, and mental health), for the various means of transport in the city of Thessaloniki. During the survey, 300 valid questionnaires were completed. The collection of the above data was followed by statistical analysis. The aim of the analysis was to identify the factors of travel eudaimonia that contributed to the mode choice. For that reason, four ordinal regression models were developed to determine how travel eudaimonia affected the usage frequency of the four available means of transport in the city of Thessaloniki (i.e., private car, bicycle, public transport, walking). Walking was rated higher than other modes in all factors, whilst cycling was rated high in physical and mental health, self-confidence, and autonomy, but low in comfort and safety. Public transport scored very low in all factors, demonstrating the poor quality of service provided by the city’s public transport. Moreover, from the ordinal regression models’ results, it could be demonstrated that travel eudaimonia factors had a significant role to play in mode choice. Recognizing the impact of these factors on transport mode choice is particularly useful for policymakers, researchers, and engineers, as it helps them to make informed decisions about what improvements are needed to promote sustainable modes of transport (mainly walking, cycling, and secondarily, public transport).

Direct conversion of mouse astrocytes into neural progenitor cells and specific lineages of neurons

BACKGROUND

Cell replacement therapy has been envisioned as a promising treatment for neurodegenerative diseases. Due to the ethical concerns of ESCs-derived neural progenitor cells (NPCs) and tumorigenic potential of iPSCs, reprogramming of somatic cells directly into multipotent NPCs has emerged as a preferred approach for cell transplantation.

METHODS

Mouse astrocytes were reprogrammed into NPCs by the overexpression of transcription factors (TFs) Foxg1, Sox2, and Brn2. The generation of subtypes of neurons was directed by the force expression of cell-type specific TFs Lhx8 or Foxa2/Lmx1a.

RESULTS

Astrocyte-derived induced NPCs (AiNPCs) share high similarities, including the expression of NPC-specific genes, DNA methylation patterns, the ability to proliferate and differentiate, with the wild type NPCs. The AiNPCs are committed to the forebrain identity and predominantly differentiated into glutamatergic and GABAergic neuronal subtypes. Interestingly, additional overexpression of TFs Lhx8 and Foxa2/Lmx1a in AiNPCs promoted cholinergic and dopaminergic neuronal differentiation, respectively.

CONCLUSIONS

Our studies suggest that astrocytes can be converted into AiNPCs and lineage-committed AiNPCs can acquire differentiation potential of other lineages through forced expression of specific TFs. Understanding the impact of the TF sets on the reprogramming and differentiation into specific lineages of neurons will provide valuable strategies for astrocyte-based cell therapy in neurodegenerative diseases.

Combinatorial programming of human neuronal progenitors using magnetically-guided stoichiometric mRNA delivery

Identification of optimal transcription factor expression patterns to direct cellular differentiation along a desired pathway presents significant challenges. We demonstrate massively combinatorial screening of temporally-varying mRNA transcription factors to direct differentiation of neural progenitor cells using a dynamically-reconfigurable magnetically-guided spotting technology for localizing mRNA, enabling experiments on millimetre size spots. In addition, we present a time-interleaved delivery method that dramatically reduces fluctuations in the delivered transcription factor copy numbers per cell. We screened combinatorial and temporal delivery of a pool of midbrain-specific transcription factors to augment the generation of dopaminergic neurons. We show that the combinatorial delivery of LMX1A, FOXA2 and PITX3 is highly effective in generating dopaminergic neurons from midbrain progenitors. We show that LMX1A significantly increases TH-expression levels when delivered to neural progenitor cells either during proliferation or after induction of neural differentiation, while FOXA2 and PITX3 increase expression only when delivered prior to induction, demonstrating temporal dependence of factor addition.

Comparative review of adult midbrain and striatum neurogenesis with classical neurogenesis

Parkinson's Disease (PD) motor symptoms are caused by loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc) of the midbrain. Dopamine cell replacement therapy (DA CRT), either by cell transplantation or endogenous repair, has been a potential treatment to replace dead cells and improve PD motor symptoms. Adult midbrain and striatum have been studied for many years to find evidence of neurogenesis. Although the literature is controversial, recent research has revived the possibility of neurogenesis here. This paper aims to review the process of neurogenesis (by focusing on gene expression patterns) in the adult midbrain/striatum and compare it with classical neurogenesis that occurs in developing midbrain, Sub Ventricular Zone (SVZ) and Sub Granular Zone (SGZ) of the adult brain.

Nuclear receptors in neural stem/progenitor cell homeostasis

In the central nervous system, embryonic and adult neural stem/progenitor cells (NSCs) generate the enormous variety and huge numbers of neuronal and glial cells that provide structural and functional support in the brain and spinal cord. Over the last decades, nuclear receptors and their natural ligands have emerged as critical regulators of NSC homeostasis during embryonic development and adult life. Furthermore, substantial progress has been achieved towards elucidating the molecular mechanisms of nuclear receptors action in proliferative and differentiation capacities of NSCs. Aberrant expression or function of nuclear receptors in NSCs also contributes to the pathogenesis of various nervous system diseases. Here, we review recent advances in our understanding of the regulatory roles of steroid, non-steroid, and orphan nuclear receptors in NSC fate decisions. These studies establish nuclear receptors as key therapeutic targets in brain diseases.

Exogenous stem cells pioneer a biobridge to the advantage of host brain cells following stroke: New insights for clinical applications

Stroke continues to maintain its status as one of the top causes of mortality within the United States. Currently, the only Food and Drug Administration (FDA)-approved drug in place for stroke patients, tissue plasminogen activator (tPA), has a rigid therapeutic window, closing at approximately 4.5 h after stroke onset. Due to this short time frame and other restrictions, such as any condition that increases a patient's risk for hemorrhaging, it has been predicted that <5% of ischemic stroke patients benefit from tPA. Given that rehabilitation therapy remains the only other option for stroke victims, there is a clear unmet clinical need for treatment available for the remaining 95%. While still considered an experimental treatment, the utilization of stem cell therapies for stroke holds consistent promise. Copious preclinical studies report the capacity for transplanted stem cells to rescue the brain parenchyma surrounding the stroke-induced infarct core. At present, the exact mechanisms in which stem cells contribute a robust therapeutic benefit remains unclear. Following stem cell administration, researchers have observed cell replacement, an increase in growth factors, and a reduction in inflammation. With a deeper understanding of the precise mechanism of stem cells, these therapies can be optimized in the clinic to afford the greatest therapeutic benefit. Recent studies have depicted a unique method of endogenous stem cell activation as a result of stem cell therapy. In both traumatic brain injury and stroke models, transplanted mesenchymal stromal cells (MSCs) facilitated a pathway between the neurogenic niches of the brain and the damaged area through extracellular matrix remodeling. The biobridge pioneered by the MSCs was utilized by the endogenous stem cells, and these cells were able to travel to the damaged areas distal to the neurogenic niches, a feat unachievable without prior remodeling. These studies broaden our understanding of stem cell interactions within the injured brain and help to guide both researchers and clinicians in developing an effective stem cell treatment for stroke. This paper is a review article. Referred literature in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors’ experiences.

Valproate increases dopamine transporter expression through histone acetylation and enhanced promoter binding of Nurr1

The dopamine transporter (DAT) is the key regulator of dopaminergic transmission and is a target of several xenobiotics, including pesticides and pharmacological agents. Previously, we identified a prominent role for histone deacetylases in the regulation of DAT expression. Here, we utilized a rat dopaminergic cell line (N27) to probe the responsiveness of DAT mRNA expression to inhibitors of histone acetylation. Inhibition of histone deacetylases (HDACs) by valproate, butyrate and Trichostatin A led to a 3-10-fold increase in DAT mRNA expression, a 50% increase in protein levels, which were accompanied by increased H3 acetylation levels. To confirm the mechanism of valproate-mediated increase in DAT mRNA, chromatin immunoprecipitation (ChIP) assays were used and demonstrated a significant increase in enrichment of acetylation of histone 3 on lysines 9 and 14 (H3K9/K14ac) in the DAT promoter. Expression of Nurr1 and Pitx3, key regulators of DAT expression, were increased following valproate treatment and Nurr1 binding was enriched in the DAT promoter. Together, these results indicate that histone acetylation and subsequent enhancement of transcription factor binding are plausible mechanisms for DAT regulation by valproate and, perhaps, by other xenobiotics.

Efficient Generation of Dopamine Neurons by Synthetic Transcription Factor mRNAs

Generation of functional dopamine (DA) neurons is an essential step for the development of effective cell therapy for Parkinson's disease (PD). The generation of DA neurons can be accomplished by overexpression of DA-inducible genes using virus- or DNA-based gene delivery methods. However, these gene delivery methods often cause chromosomal anomalies. In contrast, mRNA-based gene delivery avoids this problem and therefore is considered safe to use in the development of cell-based therapy. Thus, we used mRNA-based gene delivery method to generate safe DA neurons. In this study, we generated transformation-free DA neurons by transfection of mRNA encoding DA-inducible genes Nurr1 and FoxA2. The delivery of mRNA encoding dopaminergic fate inducing genes proved sufficient to induce naive rat forebrain precursor cells to differentiate into neurons exhibiting the biochemical, electrophysiological, and functional properties of DA neurons in vitro. Additionally, the generation efficiency of DA neurons was improved by the addition of small molecules, db-cAMP, and the adjustment of transfection timing. The successful generation of DA neurons using an mRNA-based method offers the possibility of developing clinical-grade cell sources for neuronal cell replacement treatment for PD.

Stem Cell-Induced Biobridges as Possible Tools to Aid Neuroreconstruction after CNS Injury

Notch-induced mesenchymal stromal cells (MSCs) mediate a distinct mechanism of repair after brain injury by forming a biobridge that facilitates biodistribution of host cells from a neurogenic niche to the area of injury. We have observed the biobridge in an area between the subventricular zone and the injured cortex using immunohistochemistry and laser capture. Cells in the biobridge express high levels of extracellular matrix metalloproteinases (MMPs), specifically MMP-9, which co-localized with a trail of MSCs graft. The transplanted stem cells then become almost undetectable, being replaced by newly recruited host cells. This stem cell-paved biobridge provides support for distal migration of host cells from the subventricular zone to the site of injury. Biobridge formation by transplanted stem cells seems to have a fundamental role in initiating endogenous repair processes. Two major stem cell-mediated repair mechanisms have been proposed thus far: direct cell replacement by transplanted grafts and bystander effects through the secretion of trophic factors including fibroblast growth factor 2 (FGF-2), epidermal growth factor (EGF), stem cell factor (SCF), erythropoietin, and brain-derived neurotrophic factor (BDNF) among others. This groundbreaking observation of biobridge formation by transplanted stem cells represents a novel mechanism for stem cell mediated brain repair. Future studies on graft-host interaction will likely establish biobridge formation as a fundamental mechanism underlying therapeutic effects of stem cells and contribute to the scientific pursuit of developing safe and efficient therapies not only for traumatic brain injury but also for other neurological disorders. The aim of this review is to hypothetically extend concepts related to the formation of biobridges in other central nervous system disorders.

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.

In vitro generation of mature midbrain-type dopamine neurons by adjusting exogenous Nurr1 and Foxa2 expressions to their physiologic patterns

Developmental information aids stem cell biologists in producing tissue-specific cells. Recapitulation of the developmental profile of a specific cell type in an in vitro stem cell system provides a strategy for manipulating cell-fate choice during the differentiation process. Nurr1 and Foxa2 are potential candidates for genetic engineering to generate midbrain-type dopamine (DA) neurons for experimental and therapeutic applications in Parkinson's disease (PD), as forced expression of these genes in neural stem/precursor cells (NPCs) yields cells with a complete battery of midbrain DA neuron-specific genes. However, simple overexpression without considering their expression pattern in the developing midbrain tends to generate DA cells without adequate neuronal maturation and long-term maintenance of their phenotype in vitro and in vivo after transplantation. We here show that the physiological levels and timing of Nurr1 and Foxa2 expression can be replicated in NPCs by choosing the right vectors and promoters. Controlled expression combined with a strategy for transgene expression maintenance induced generation of fully mature midbrain-type DA neurons. These findings demonstrate the feasibility of cellular engineering for artificial cell-fate specification.

Dual delivery of siRNA and plasmid DNA using mesoporous silica nanoparticles to differentiate induced pluripotent stem cells into dopaminergic neurons

Nurr1 plasmid and Rex1 siRNA were complexed with positively charged FITC-conjugated mesoporous silica nanoparticles. The pNurr1–siRex1–FMSN(+) was delivered to induced pluripotent stem cells to enhance their differentiation into dopaminergic neurons.

Dopaminergic neurons differentiating from LRRK2 G2019S induced pluripotent stem cells show early neuritic branching defects

Some mutations of the LRRK2 gene underlie autosomal dominant form of Parkinson’s disease (PD). The G2019S is a common mutation that accounts for about 2% of PD cases. To understand the pathophysiology of this mutation and its possible developmental implications, we developed an in vitro assay to model PD with human induced pluripotent stem cells (hiPSCs) reprogrammed from skin fibroblasts of PD patients suffering from the LRKK2 G2019S mutation. We differentiated the hiPSCs into neural stem cells (NSCs) and further into dopaminergic neurons. Here we show that NSCs bearing the mutation tend to differentiate less efficiently into dopaminergic neurons and that the latter exhibit significant branching defects as compared to their controls.

Migration of bone marrow progenitor cells in the adult brain of rats and rabbits

Neurogenesis takes place in the adult mammalian brain in three areas: Subgranular zone of the dentate gyrus (DG); subventricular zone of the lateral ventricle; olfactory bulb. Different molecular markers can be used to characterize the cells involved in adult neurogenesis. It has been recently suggested that a population of bone marrow (BM) progenitor cells may migrate to the brain and differentiate into neuronal lineage. To explore this hypothesis, we injected recombinant SV40-derived vectors into the BM and followed the potential migration of the transduced cells. Long-term BM-directed gene transfer using recombinant SV40-derived vectors leads to expression of the genes delivered to the BM firstly in circulating cells, then after several months in mature neurons and microglial cells, and thus without central nervous system (CNS) lesion. Most of transgene-expressing cells expressed NeuN, a marker of mature neurons. Thus, BM-derived cells may function as progenitors of CNS cells in adult animals. The mechanism by which the cells from the BM come to be neurons remains to be determined. Although the observed gradual increase in transgene-expressing neurons over 16 mo suggests that the pathway involved differentiation of BM-resident cells into neurons, cell fusion as the principal route cannot be totally ruled out. Additional studies using similar viral vectors showed that BM-derived progenitor cells migrating in the CNS express markers of neuronal precursors or immature neurons. Transgene-positive cells were found in the subgranular zone of the DG of the hippocampus 16 mo after intramarrow injection of the vector. In addition to cells expressing markers of mature neurons, transgene-positive cells were also positive for nestin and doublecortin, molecules expressed by developing neuronal cells. These cells were actively proliferating, as shown by short term BrdU incorporation studies. Inducing seizures by using kainic acid increased the number of BM progenitor cells transduced by SV40 vectors migrating to the hippocampus, and these cells were seen at earlier time points in the DG. We show that the cell membrane chemokine receptor, CCR5, and its ligands, enhance CNS inflammation and seizure activity in a model of neuronal excitotoxicity. SV40-based gene delivery of RNAi targeting CCR5 to the BM results in downregulating CCR5 in circulating cells, suggesting that CCR5 plays an important role in regulating traffic of BM-derived cells into the CNS, both in the basal state and in response to injury. Furthermore, reduction in CCR5 expression in circulating cells provides profound neuroprotection from excitotoxic neuronal injury, reduces neuroinflammation, and increases neuronal regeneration following this type of insult. These results suggest that BM-derived, transgene-expressing, cells can migrate to the brain and that they become neurons, at least in part, by differentiating into neuron precursors and subsequently developing into mature neurons.

Nemo-like kinase as a negative regulator of nuclear receptor Nurr1 gene transcription in prostate cancer

Background

Nurr1, a member of the orphan receptor family, plays an important role in several types of cancer. Our previous work demonstrated that increased expression of Nurr1 plays a significant role in the initiation and progression of prostate cancer (PCa), though the mechanisms for regulation of Nurr1 expression remain unknown. In this study, we investigated the hypothesis that Nemo-like kinase (NLK) is a key regulator of Nurr1 expression in PCa.

Methods

Immunohistochemistry and Western blot analysis were used to evaluate levels of NLK and Nurr1 in prostatic tissues and cell lines. The effects of overexpression or knockdown of Nurr1 were evaluated in PCa cells through use of PCR, Western blots and promoter reporter assays. The role of Nurr1 promoter cis element was studied by creation of two mutant Nurr1 promoter luciferase constructs, one with a mutated NF-κB binding site and one with a mutated CREB binding site. In addition, three specific inhibitors were used to investigate the roles of these proteins in transcriptional activation of Nurr1, including BAY 11–7082 (NF-κB inhibitor), KG-501 (CREB inhibitor) and ICG-001 (CREB binding protein, CBP, inhibitor). The function of CBP in NLK-mediated regulation of Nurr1 expression was investigated using immunofluorescence, co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation assays (ChIPs).

Results

NLK expression was inversely correlated with Nurr1 expression in prostate cancer tissues and cell lines. Overexpression of NLK suppressed Nurr1 promoter activity, leading to downregulation of Nurr1 expression. In contrast, knockdown of NLK demonstrated opposite results, leading to upregulation of Nurr1. When compared with the wild-type Nurr1 promoter, mutation of NF-κB- and CREB-binding sites of the Nurr1 promoter region significantly reduced the upregulation of Nurr1 induced by knockdown of NLK in LNCaP cells; treatment with inhibitors of CREB, CBP and NF-κB led to similar results. We also found that NLK directly interacts with CBP, that knockdown of NLK significantly increases the recruitment of CBP to both NF-κB- and CREB-binding sites, and that regulation of NLK on Nurr1 expression is abrogated by knockdown of CBP.

Conclusions

Our results suggest that NLK inhibits transcriptional activation of Nurr1 gene by impeding CBP’s role as a co-activator of NF-κB and CREB in prostate cancer.

Epigenetic regulation contributes to urocortin-enhanced midbrain dopaminergic neuron differentiation

The production of midbrain dopaminergic (mDA) neurons requires precise extrinsic inductive signals and intrinsic transcriptional cascade at a specific time point in development. Urocortin (UCN) is a peptide of the corticotropin-releasing hormone family that mediates various responses to stress. UCN was first cloned from adult rat midbrain. However, the contribution of UCN to the development of mDA neurons is poorly understood. Here, we show that UCN is endogenously expressed in the developing ventral midbrain (VM) and its receptors are exhibited in Nurr1(+) postmitotic mDA precursors and TH(+) neurons, suggesting possible roles in regulating their terminal differentiation. UCN treatment increased DA cell numbers in rat VM precursor cultures by promoting the conversion of Nurr1(+) precursors into DA neurons. Furthermore, neutralization of secreted UCN with anti-UCN antibody resulted in a reduction in the number of DA neurons. UCN induced an abundance of acetylated histone H3 and enhanced late DA regulator Nurr1, Foxa2, and Pitx3 expressions. Using pharmacological and RNA interference approaches, we further demonstrated that histone deacetylase (HDAC) inhibition and late transcriptional factors upregulation contribute to UCN-mediated DA neuron differentiation. Chromatin immunoprecipitation analyses revealed that UCN promoted histone acetylation of chromatin surrounding the TH promoter by directly inhibiting HDAC and releasing of methyl CpG binding protein 2-CoREST-HDAC1 repressor complex from the promoter, ultimately leading to an increase in Nurr1/coactivators-mediated transcription of TH gene. Moreover, UCN treatment in vivo also resulted in increased DA neuron differentiation. These findings suggest that UCN might contribute to regulate late mDA neuron differentiation during VM development.

Nurr1-Based Therapies for Parkinson's Disease

Previous studies have documented that orphan nuclear receptor Nurr1 (also known as NR4A2) plays important roles in the midbrain dopamine (DA) neuron development, differentiation, and survival. Furthermore, it has been reported that the defects in Nurr1 are associated with Parkinson's disease (PD). Thus, Nurr1 might be a potential therapeutic target for PD. Emerging evidence from in vitro and in vivo studies has recently demonstrated that Nurr1-activating compounds and Nurr1 gene therapy are able not only to enhance DA neurotransmission but also to protect DA neurons from cell injury induced by environmental toxin or microglia-mediated neuroinflammation. Moreover, modulators that interact with Nurr1 or regulate its function, such as retinoid X receptor, cyclic AMP-responsive element-binding protein, glial cell line-derived neurotrophic factor, and Wnt/β-catenin pathway, have the potential to enhance the effects of Nurr1-based therapies in PD. This review highlights the recent progress in preclinical studies of Nurr1-based therapies and discusses the outlook of this emerging therapy as a promising new generation of PD medication.

Combined Nurr1 and Foxa2 roles in the therapy of Parkinson's disease

Use of the physiological mechanisms promoting midbrain DA (mDA) neuron survival seems an appropriate option for developing treatments for Parkinson's disease (PD). mDA neurons are specifically marked by expression of the transcription factors Nurr1 and Foxa2. We show herein that Nurr1 and Foxa2 interact to protect mDA neurons against various toxic insults, but their expression is lost during aging and degenerative processes. In addition to their proposed cell-autonomous actions in mDA neurons, forced expression of these factors in neighboring glia synergistically protects degenerating mDA neurons in a paracrine mode. As a consequence of these bimodal actions, adeno-associated virus (AAV)-mediated gene delivery of Nurr1 and Foxa2 in a PD mouse model markedly protected mDA neurons and motor behaviors associated with nigrostriatal DA neurotransmission. The effects of the combined gene delivery were dramatic, highly reproducible, and sustained for at least 1 year, suggesting that expression of these factors is a promising approach in PD therapy.

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.

Dynamic Trk and G Protein Signalings Regulate Dopaminergic Neurodifferentiation in Human Trophoblast Stem Cells

Understanding the mechanisms in the generation of neural stem cells from pluripotent stem cells is a fundamental step towards successful management of neurodegenerative diseases in translational medicine. Albeit all-trans retinoic acid (RA) has been associated with axon outgrowth and nerve regeneration, the maintenance of differentiated neurons, the association with degenerative disease like Parkinson's disease, and its regulatory molecular mechanism from pluripotent stem cells to neural stem cells remain fragmented. We have previously reported that RA is capable of differentiation of human trophoblast stem cells to dopamine (DA) committed progenitor cells. Intracranial implantation of such neural progenitor cells into the 6-OHDA-lesioned substantia nigra pars compacta successfully regenerates dopaminergic neurons and integrity of the nigrostriatal pathway, ameliorating the behavioral deficits in the Parkinson’s disease rat model. Here, we demonstrated a dynamic molecular network in systematic analysis by addressing spatiotemporal molecular expression, intracellular protein-protein interaction and inhibition, imaging study, and genetic expression to explore the regulatory mechanisms of RA induction in the differentiation of human trophoblast stem cells to DA committed progenitor cells. We focused on the tyrosine receptor kinase (Trk), G proteins, canonical Wnt2B/β-catenin, genomic and non-genomic RA signaling transductions with Tyrosine hydroxylase (TH) gene expression as the differentiation endpoint. We found that at the early stage, integration of TrkA and G protein signalings aims for axonogenesis and morphogenesis, involving the novel RXRα/Gα_q/11 and RARβ/Gβ signaling pathways. While at the later stage, five distinct signaling pathways together with epigenetic histone modifications emerged to regulate expression of TH, a precursor of dopamine. RA induction generated DA committed progenitor cells in one day. Our results provided substantial mechanistic evidence that human trophoblast stem cell-derived neural stem cells can potentially be used for neurobiological study, drug discovery, and as an alternative source of cell-based therapy in neurodegenerative diseases like Parkinson’s disease.

Development and function of the midbrain dopamine system: what we know and what we need to

The past two decades have seen an explosion in our understanding of the origin and development of the midbrain dopamine system. Much of this work has been focused on the aspects of dopamine neuron development related to the onset of movement disorders such as Parkinson's disease, with the intent of hopefully delaying, preventing or fixing symptoms. While midbrain dopamine degeneration is a major focus for treatment and research, many other human disorders are impacted by abnormal dopamine, including drug addiction, autism and schizophrenia. Understanding dopamine neuron ontogeny and how dopamine connections and circuitry develops may provide us with key insights into potentially important avenues of research for other dopamine-related disorders. This review will provide a brief overview of the major molecular and genetic players throughout the development of midbrain dopamine neurons and what we know about the behavioral- and disease-related implications associated with perturbations to midbrain dopamine neuron development. We intend to combine the knowledge of two broad fields of neuroscience, both developmental and behavioral, with the intent on fostering greater discussion between branches of neuroscience in the service of addressing complex cognitive questions from a developmental perspective and identifying important gaps in our knowledge for future study.

Generation of Dopamine Neurons from Rodent Fibroblasts through the Expandable Neural Precursor Cell Stage

Recent groundbreaking work has demonstrated that combined expression of the transcription factors Brn2, Ascl1, and Myt1L (BAM; also known as Wernig factors) convert mouse fibroblasts into postmitotic neuronal cells. However, questions remain regarding whether trans-conversion is achieved directly or involves an intermediary precursor stage. Trans-conversion toward expandable neural precursor cells (NPCs) is more useful than direct one-step neuron formation with respect to yielding a sufficient number of cells and the feasibility of manipulating NPC differentiation toward certain neuron subtypes. Here, we show that co-expression of Wernig factors and Bcl-xL induces fibroblast conversion into NPCs (induced NPCs (iNPCs)) that are highly expandable for >100 passages. Gene expression analyses showed that the iNPCs exhibited high expression of common NPC genes but not genes specific to defined embryonic brain regions. This finding indicated that a regional identity of iNPCs was not established. Upon induction, iNPCs predominantly differentiated into astrocytes. However, the differentiation potential was not fixed and could be efficiently manipulated into general or specific subtypes of neurons by expression of additional genes. Specifically, overexpression of Nurr1 and Foxa2, transcription factors specific for midbrain dopamine neuron development, drove iNPCs to yield mature midbrain dopamine neurons equipped with presynaptic DA neuronal functions. We further assessed the therapeutic potential of iNPCs in Parkinson disease model rats.

Autologous iPSC-derived dopamine neuron transplantation in a nonhuman primate Parkinson's disease model

Autologous dopamine (DA) neurons are a new cell source for replacement therapy of Parkinson's disease (PD). In this study, we tested the safety and efficacy of autologous induced pluripotent stem cell (iPSC)-derived DA cells for treatment of a cynomolgus monkey PD model. Monkey bone marrow mesenchymal cells were isolated and induced to iPSCs, followed by differentiation into DA cells using a method with high efficiency. Autologous DA cells were introduced into the brain of a cynomolgus monkey PD model without immunosuppression; three PD monkeys that had received no grafts served as controls. The PD monkey that had received autologous grafts experienced behavioral improvement compared with that of controls. Histological analysis revealed no overgrowth of grafts and a significant number of surviving A9 region-specific graft-derived DA neurons. The study provided a proof-of-principle to employ iPSC-derived autologous DA cells for PD treatment using a nonhuman primate PD model.

Stem cell-paved biobridges facilitate stem transplant and host brain cell interactions for stroke therapy

Distinguished by an infarct core encased within a penumbra, stroke remains a primary source of mortality within the United States. While our scientific knowledge regarding the pathology of stroke continues to improve, clinical treatment options for patients suffering from stroke are extremely limited. Tissue plasminogen activator (tPA) remains the sole FDA-approved drug proven to be helpful following stroke. However, due to the need to administer the drug within 4.5h of stroke onset its usefulness is constrained to less than 5% of all patients suffering from ischemic stroke. One experimental therapy for the treatment of stroke involves the utilization of stem cells. Stem cell transplantation has been linked to therapeutic benefit by means of cell replacement and release of growth factors; however the precise means by which this is accomplished has not yet been clearly delineated. Using a traumatic brain injury model, we recently demonstrated the ability of transplanted mesenchymal stromal cells (MSCs) to form a biobridge connecting the area of injury to the neurogenic niche within the brain. We hypothesize that MSCs may also have the capacity to create a similar biobridge following stroke; thereby forming a conduit between the neurogenic niche and the stroke core and peri-infarct area. We propose that this biobridge could assist and promote interaction of host brain cells with transplanted stem cells and offer more opportunities to enhance the effectiveness of stem cell therapy in stroke. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Stem cell therapy in neurodegenerative diseases: From principles to practice

The lack of curative therapies for neurodegenerative diseases has high economic impact and places huge burden on the society. The contribution of stem cells to cure neurodegenerative diseases has been unraveled and explored extensively over the past few years. Beyond substitution of the lost neurons, stem cells act as immunomodulators and neuroprotectors. A large number of preclinical and a small number of clinical studies have shown beneficial outcomes in this context. In this review, we have summarized the current concepts of stem cell therapy in neurodegenerative diseases and the recent advances in this field, particularly between 2010 and 2012. Further studies should be encouraged to resolve the clinical issues and vague translational findings for maximum optimization of the efficacy of stem cell therapy in neurodegenerative diseases.

High cytoplasmic expression of the orphan nuclear receptor NR4A2 predicts poor survival in nasopharyngeal carcinoma

OBJECTIVE

This study aimed at investigating whether the orphan nuclear receptor NR4A2 is significantly associated with clinicopathologic features and overall survival of patients with nasopharyngeal carcinoma (NPC).

METHODS

Immunohistochemistry was performed to determine NR4A2 protein expression in 84 NPC tissues and 20 non-cancerous nasopharyngeal (NP) tissues. The prognostic significance of NR4A2 protein expression was evaluated using Cox proportional hazards regression models and Kaplan-Meier survival analysis.

RESULTS

We did not find a significant association between total NR4A2 expression and clinicopathological variables in 84 patients with NPC. However, we observed that high cytoplasmic expression of NR4A2 was significantly associated with tumor size (T classification) (P = 0.006), lymph node metastasis (N classification) (P = 0.002) and clinical stage (P = 0.017). Patients with higher cytoplasmic NR4A2 expression had a significantly lower survival rate than those with lower cytoplasmic NR4A2 expression (P = 0.004). Multivariate Cox regression analysis analysis suggested that the level of cytoplasmic NR4A2 expression was an independent prognostic indicator for overall survival of patients with NPC (P = 0.033).

CONCLUSIONS

High cytoplasmic expression of NR4A2 is a potential unfavorable prognostic factor for patients with NPC.

Nurr1 blocks the mitogenic effect of FGF-2 and EGF, inducing olfactory bulb neural stem cells to adopt dopaminergic and dopaminergic-GABAergic neuronal phenotypes

The transcription factor Nurr1 is expressed in the mouse olfactory bulb (OB), although it remains unknown whether it influences the generation of dopaminergic neurons (DA) (DA neurons) in cells isolated from this brain region. We found that expressing Nurr1 in proliferating olfactory bulb stem cells (OBSCs) produces a marked inhibition of cell proliferation and the generation of immature neurons immunoreactive for tyrosine hydroxylase (TH) concomitant with marked upregulations of Th, Dat, Gad, and Fgfr2 transcripts. In long-term cultures, these cells develop neurochemical and synaptic markers of mature-like mesencephalic DA neurons, expressing GIRK2, VMAT2, DAT, calretinin, calbindin, synapsin-I, and SV2. Concurring with the increase in both Th and Gad expression, a subpopulation of induced cells was both TH- and GAD-immunoreactive indicating that they are dopaminergic-GABAergic neurons. Indeed, these cells could mature to express VGAT, suggesting they can uptake and store GABA in vesicles. Remarkably, the dopamine D1 receptor agonist SKF-38393 induced c-Fos in TH(+) cells and dopamine release was detected in these cultures under basal and KCl-evoked conditions. By contrast, cotransducing the Neurogenin2 and Nurr1 transcription factors produced a significant decrease in the number of TH-positive neurons. Our results indicate that Nurr1 overexpression in OBSCs induces the formation of two populations of mature dopaminergic neurons with features of the ventral mesencephalon or of the OB, capable of responding to functional dopaminergic stimuli and of releasing dopamine. They also suggest that the accumulation of Fgfr2 by Nurr1 in OBSCs may be involved in the generation of DA neurons.

Epigenetic activation of the Foxa2 gene is required for maintaining the potential of neural precursor cells to differentiate into dopaminergic neurons after expansion

Dysregulation of forkhead box protein A2 (Foxa2) expression in fetal ventral mesencephalon (VM)-derived neural precursor cells (NPCs) appears to be associated with the loss of their potential to differentiate into dopaminergic (DA) neurons after mitogenic expansion in vitro, hindering their efficient use as a transplantable cell source. Here, we report that epigenetic activation of Foxa2 in VM-derived NPCs by inducing histone hyperacetylation rescues the mitogenic-expansion-dependent decrease of differentiation potential to DA neurons. The silencing of Foxa2 gene expression after expansion is accompanied by repressive histone modifications, including hypoacetylation of histone H3 and H4 and trimethylation of H3K27 on the Foxa2 promoter, as well as on the global level. In addition, histone deacetylase 7 (HDAC7) is highly expressed during differentiation and recruited to the Foxa2 promoter. Induction of histone acetylation in VM-derived NPCs by either knockdown of HDAC7 or treatment with the HDAC inhibitor apicidin upregulates Foxa2 expression via hyperacetylation of H3 and a decrease in H3K27 trimethylation on the promoter regions, leading to the expression of DA neuron developmental genes and enhanced differentiation of DA neurons. These effects are antagonized by the expression of shRNAs specific for Foxa2 but enhanced by shRNA for HDAC7. Collectively, these findings indicate that loss of differentiation potential of expanded VM-derived NPCs is attributed to a decrease in Foxa2 expression and suggest that activation of the endogenous Foxa2 gene by epigenetic regulation might be an approach to enhance the generation of DA neurons.

PINK1 positively regulates HDAC3 to suppress dopaminergic neuronal cell death

Deciphering the molecular basis of neuronal cell death is a central issue in the etiology of neurodegenerative diseases, such as Parkinson's and Alzheimer's. Dysregulation of p53 levels has been implicated in neuronal apoptosis. The role of histone deacetylase 3 (HDAC3) in suppressing p53-dependent apoptosis has been recently emphasized; however, the molecular basis of modulation of p53 function by HDAC3 remains unclear. Here we show that PTEN-induced putative kinase 1 (PINK1), which is linked to autosomal recessive early-onset familial Parkinson's disease, phosphorylates HDAC3 at Ser-424 to enhance its HDAC activity in a neural cell-specific manner. PINK1 prevents H2O2-induced C-terminal cleavage of HDAC3 via phosphorylation of HDAC3 at Ser-424, which is reversed by protein phosphatase 4c. PINK1-mediated phosphorylation of HDAC3 enhances its direct association with p53 and causes subsequent hypoacetylation of p53. Genetic deletion of PINK1 partly impaired the suppressive role of HDAC3 in regulating p53 acetylation and transcriptional activity. However, depletion of HDAC3 fully abolished the PINK1-mediated p53 inhibitory loop. Finally, ectopic expression of phosphomometic-HDAC3(S424E) substantially overcomes the defective action of PINK1 against oxidative stress in dopaminergic neuronal cells. Together, our results uncovered a mechanism by which PINK1-HDAC3 network mediates p53 inhibitory loop in response to oxidative stress-induced damage.

Transcription factors Foxa1 and Foxa2 are required for adult dopamine neurons maintenance

The proteins Foxa1 and Foxa2 belong to the forkhead family of transcription factors and are involved in the development of several tissues, including liver, pancreas, lung, prostate, and the neural system. Both Foxa1 and Foxa2 are also crucial for the specification and differentiation of dopamine (DA) neurons during embryonic development, while about 30% of mice with an embryonic deletion of a single allele of the Foxa2 gene exhibit an age-related asymmetric loss of DA neurons and develop locomotor symptoms resembling Parkinson's disease (PD). Notably, both Foxa1 and Foxa2 factors continue to be expressed in the adult dopamine system. To directly assess their functions selectively in adult DA neurons, we induced genetic deletions of Foxa1/2 transcription factors in mice using a tamoxifen inducible tissue-specific CreERT2 recombinase expressed under control of the dopamine transporter (DAT) promoter (DATCreERT2). The conditional DA neurons-specific ablation of both genes, but not of Foxa2 alone, in early adulthood, caused a decline of striatal dopamine and its metabolites, along with locomotor deficits. At early pre-symptomatic stages, we observed a decline in aldehyde dehydrogenase family 1, subfamily A1 (Aldh1a1) protein expression in DA neurons. Further analyses revealed a decline of aromatic amino acid decarboxylase (AADC) and a complete loss of DAT expression in these neurons. These molecular changes ultimately led to a reduction of DA neuron numbers in the substantia nigra pars compacta (SNpc) of aged cFoxa1/2^−/− mice, resembling the progressive course of PD in humans. Altogether, in this study, we address the molecular, cellular, and functional role of both Foxa1 and Foxa2 factors in the maintenance of the adult dopamine system which may help to find better approaches for PD treatment.

The Shh coreceptor Cdo is required for differentiation of midbrain dopaminergic neurons

Sonic hedgehog (Shh) signaling is required for numerous developmental processes including specification of ventral cell types in the central nervous system such as midbrain dopaminergic (DA) neurons. The multifunctional coreceptor Cdo increases the signaling activity of Shh which is crucial for development of forebrain and neural tube. In this study, we investigated the role of Cdo in midbrain DA neurogenesis. Cdo and Shh signaling components are induced during neurogenesis of embryonic stem (ES) cells. Cdo(-/-) ES cells show reduced neuronal differentiation accompanied by increased cell death upon neuronal induction. In addition, Cdo(-/-) ES cells form fewer tyrosine hydroxylase (TH) and microtubule associated protein 2 (MAP2)-positive DA neurons correlating with the decreased expression of key regulators of DA neurogenesis, such as Shh, Neurogenin2, Mash1, Foxa2, Lmx1a, Nurr1 and Pitx3, relative to the Cdo(+/+) ES cells. Consistently, the Cdo(-/-) embryonic midbrain displays a reduction in expression of TH and Nurr1. Furthermore, activation of Shh signaling by treatment with Purmorphamine (Pur) restores the DA neurogenesis of Cdo(-/-) ES cells, suggesting that Cdo is required for the full Shh signaling activation to induce efficient DA neurogenesis.

Stem cell-paved biobridge facilitates neural repair in traumatic brain injury

Modified mesenchymal stromal cells (MSCs) display a unique mechanism of action during the repair phase of traumatic brain injury by exhibiting the ability to build a biobridge between the neurogenic niche and the site of injury. Immunohistochemistry and laser capture assay have visualized this biobridge in the area between the neurogenic subventricular zone and the injured cortex. This biobridge expresses high levels of extracellular matrix metalloproteinases (MMPs), which are initially co-localized with a stream of transplanted MSCs, but later this region contains only few to non-detectable grafts and becomes overgrown by newly recruited host cells. We have reported that long-distance migration of host cells from the neurogenic niche to the injured brain site can be attained via these transplanted stem cell-paved biobridges, which serve as a key regenerative process for the initiation of endogenous repair mechanisms. Thus, far the two major schools of discipline in stem cell repair mechanisms support the idea of "cell replacement" and the bystander effects of "trophic factor secretion." Our novel observation of stem cell-paved biobridges as pathways for directed migration of host cells from neurogenic niche toward the injured brain site adds another mode of action underlying stem cell therapy. More in-depth investigations on graft-host interaction will likely aid translational research focused on advancing this stem cell-paved biobridge from its current place, as an equally potent repair mechanism as cell replacement and trophic factor secretion, into a new treatment strategy for traumatic brain injury and other neurological disorders.

Potential for cell therapy in Parkinson's disease using genetically programmed human embryonic stem cell-derived neural progenitor cells

Neural transplantation is a promising strategy for restoring dopaminergic dysfunction and modifying disease progression in Parkinson's disease (PD). Human embryonic stem cells (hESCs) are a potential resource in this regard because of their ability to provide a virtually limitless supply of homogenous dopaminergic progenitors and neurons of appropriate lineage. The recent advances in developing robust cell culture protocols for directed differentiation of hESCs to near pure populations of ventral mesencephalic (A9-type) dopaminergic neurons has heightened the prospects for PD cell therapy. Here, we focus our review on current state-of-the-art techniques for harnessing hESC-based strategies toward development of a stem cell therapeutic for PD. Importantly, we also briefly describe a novel genetic-programming approach that may address many of the key challenges that remain in the field and that may hasten clinical translation.

Foxa2 acts as a co-activator potentiating expression of the Nurr1-induced DA phenotype via epigenetic regulation

Understanding how dopamine (DA) phenotypes are acquired in midbrain DA (mDA) neuron development is important for bioassays and cell replacement therapy for mDA neuron-associated disorders. Here, we demonstrate a feed-forward mechanism of mDA neuron development involving Nurr1 and Foxa2. Nurr1 acts as a transcription factor for DA phenotype gene expression. However, Nurr1-mediated DA gene expression was inactivated by forming a protein complex with CoREST, and then recruiting histone deacetylase 1 (Hdac1), an enzyme catalyzing histone deacetylation, to DA gene promoters. Co-expression of Nurr1 and Foxa2 was established in mDA neuron precursor cells by a positive cross-regulatory loop. In the presence of Foxa2, the Nurr1-CoREST interaction was diminished (by competitive formation of the Nurr1-Foxa2 activator complex), and CoREST-Hdac1 proteins were less enriched in DA gene promoters. Consequently, histone 3 acetylation (H3Ac), which is responsible for open chromatin structures, was strikingly increased at DA phenotype gene promoters. These data establish the interplay of Nurr1 and Foxa2 as the crucial determinant for DA phenotype acquisition during mDA neuron development.

Orphan nuclear receptor nurr1 as a potential novel marker for progression in human prostate cancer

A number of studies have indicated that Nurr1, which belongs to a novel class of orphan nuclear receptors (the NR4A family), is important for carcinogenesis. Here we investigated expression of Nurr1 protein in benign and malignant human prostate tissues and association with clinicopathologic features using immunohistochemical techniques. Moreover, we also investigated the ability of Nurr1 to influence proliferation, migration, invasion and apoptosis of human prostate cancer cells using small interfering RNA silencing. Immunohistochemical analysis revealed that the expression of Nurr1 protein was higher in prostate cancer tissues than in benign prostate tissue (P < 0.001), levels being positively correlated with tumor T classification (P = 0.003), N classification (P = 0.017), M classification (P = 0.011) and the Gleason score (P = 0.020) of prostate cancer patients. In vitro, silencing of endogenous Nurr1 attenuated cell proliferation, migration and invasion, and induced apoptosis of prostate cancer cells. These results suggest that Nurr1 may be used as an indicator for prostate cancer progression and be useful for novel potential therapeutic strategies.