Generation of tyrosine hydroxylase-producing neurons from precursors of the embryonic and adult forebrain

Combining physical & cognitive training with iPSC-derived dopaminergic neuron transplantation promotes graft integration & better functional outcome in parkinsonian marmosets

Parkinson's disease (PD) is a relentlessly progressive and currently incurable neurodegenerative disease with significant unmet medical needs. Since PD stems from the degeneration of midbrain dopaminergic (DA) neurons in a defined brain location, PD patients are considered optimal candidates for cell replacement therapy. Clinical trials for cell transplantation in PD are beginning to re-emerge worldwide with a new focus on induced pluripotent stem cells (iPSCs) as a source of DA neurons since they can be derived from adult somatic cells and produced in large quantities under current good manufacturing practices. However, for this therapeutic strategy to be realized as a viable clinical option, fundamental translational challenges need to be addressed including the manufacturing process, purity and efficacy of the cells, the method of delivery, the extent of host reinnervation and the impact of patient-centered adjunctive interventions. In this study we report on the impact of physical and cognitive training (PCT) on functional recovery in the nonhuman primate (NHP) model of PD after cell transplantation. We observed that at 6 months post-transplant, the PCT group returned to normal baseline in their daily activity measured by actigraphy, significantly improved in their sensorimotor and cognitive tasks, and showed enhanced synapse formation between grafted cells and host cells. We also describe a robust, simple, efficient, scalable, and cost-effective manufacturing process of engraftable DA neurons derived from iPSCs. This study suggests that integrating PCT with cell transplantation therapy could promote optimal graft functional integration and better outcome for patients with PD.

Mepirapim, a novel synthetic cannabinoid, induces Parkinson's disease-related behaviors by causing maladaptation of the dopamine system in the brain

Mepirapim is a novel synthetic cannabinoid that first appeared on the illicit drug market in 2013. In recent years, recreational abuse of Mepirapim has caused serious emergencies, posing a threat to public health. However, there are no legal regulations to prohibit the use of Mepirapim, as there is no scientific evidence for the dangerous pharmacological effects of the drug. In the present study, we investigated the dangerous neurotoxic effects of Mepirapim through behavioral and molecular experiments in mice (ICR/CD1, male, 25-30 g). In particular, based on a previous study that Mepirapim activates the dopamine system, we evaluated whether high-dose Mepirapim [single (15, 30, or 60 mg·kg^-1, i.p.) or multiple (8, 15, or 30 mg·kg^-1, i.p. × 4 at 2 h intervals)] treatment causes Parkinson's disease-related symptoms through damage to the dopamine system. In the result, we found that Mepirapim treatment caused comprehensive Parkinson's disease-related symptoms, including motor impairment, cognitive deficits and mood disorders. Furthermore, we confirmed the maladaptation in dopamine-related neurochemicals, including decreased dopamine levels, decreased tyrosine hydroxylase expression, and increased α-synuclein expression, in the brains of mice treated with Mepirapim. Taken together, these results indicate that Mepirapim has dangerous neurotoxic effects that induces Parkinson's disease-related behaviors by causing maladaptation of the dopamine system in the brain. Based on these findings, we propose the strict regulation of recreational abuse and therapeutic misuse of Mepirapim.

Single-Cell Profiling of Coding and Noncoding Genes in Human Dopamine Neuron Differentiation

Dopaminergic (DA) neurons derived from human pluripotent stem cells (hPSCs) represent a renewable and available source of cells useful for understanding development, developing disease models, and stem-cell therapies for Parkinson's disease (PD). To assess the utility of stem cell cultures as an in vitro model system of human DA neurogenesis, we performed high-throughput transcriptional profiling of ~20,000 ventral midbrain (VM)-patterned stem cells at different stages of maturation using droplet-based single-cell RNA sequencing (scRNAseq). Using this dataset, we defined the cellular composition of human VM cultures at different timepoints and found high purity DA progenitor formation at an early stage of differentiation. DA neurons sharing similar molecular identities to those found in authentic DA neurons derived from human fetal VM were the major cell type after two months in culture. We also developed a bioinformatic pipeline that provided a comprehensive long noncoding RNA landscape based on temporal and cell-type specificity, which may contribute to unraveling the intricate regulatory network of coding and noncoding genes in DA neuron differentiation. Our findings serve as a valuable resource to elucidate the molecular steps of development, maturation, and function of human DA neurons, and to identify novel candidate coding and noncoding genes driving specification of progenitors into functionally mature DA neurons.

Current Status of Stem Cell-Derived Therapies for Parkinson's Disease: From Cell Assessment and Imaging Modalities to Clinical Trials

Curative therapies or treatments reversing the progression of Parkinson’s disease (PD) have attracted considerable interest in the last few decades. PD is characterized by the gradual loss of dopaminergic (DA) neurons and decreased striatal dopamine levels. Current challenges include optimizing neuroprotective strategies, developing personalized drug therapy, and minimizing side effects from the long-term prescription of pharmacological drugs used to relieve short-term motor symptoms. Transplantation of DA cells into PD patients’ brains to replace degenerated DA has the potential to change the treatment paradigm. Herein, we provide updates on current progress in stem cell-derived DA neuron transplantation as a therapeutic alternative for PD. We briefly highlight cell sources for transplantation and focus on cell assessment methods such as identification of genetic markers, single-cell sequencing, and imaging modalities used to access cell survival and function. More importantly, we summarize clinical reports of patients who have undergone cell-derived transplantation in PD to better perceive lessons that can be drawn from past and present clinical outcomes. Modifying factors include (1) source of the stem cells, (2) quality of the stem cells, (3) age of the patient, (4) stage of disease progression at the time of cell therapy, (5) surgical technique/practices, and (6) the use of immunosuppression. We await the outcomes of joint efforts in clinical trials around the world such as NYSTEM and CiRA to further guide us in the selection of the most suitable parameters for cell-based neurotransplantation in PD.

Non-cell autonomous mechanism of Parkinson's disease pathology caused by G2019S LRRK2 mutation in Ashkenazi Jewish patient: Single cell analysis

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease, characterized by the loss of the midbrain dopaminergic neurons, which leads to impaired motor and cognitive functions. PD is predominantly an idiopathic disease, however about 5% of cases are linked to hereditary mutations. The most common mutation in both familial and sporadic PD is the G2019S mutation of leucine-rich repeat kinase 2 (LRRK2) with high prevalence in Ashkenazi Jewish patients and in North African Berber and Arab patients. It is still not fully understood how this mutation leads to PD pathology. In this study, we derived induced pluripotent stem cells (iPSCs) from an Ashkenazi Jewish patient with G2019S LRRK2 mutation to isolate self-renewable multipotent neural stem cells (NSCs) and to model this form of PD in vitro. To investigate the cellular diversity and disease pathology in the NSCs, we used single cell RNA-seq transcriptomic profiling. The evidence suggests there are three subpopulations within the NSCs: a committed neuronal population, intermediate stage population and undifferentiated stage population. Unbiased single-cell transcriptomic analysis revealed differential expression and dysregulation of genes involved in PD pathology. The significantly affected genes were involved in mitochondrial function, DNA repair, protein degradation, oxidative stress, lysosome biogenesis, ubiquitination, endosome function, autophagy and mitochondrial quality control. The results suggest that G2019S LRRK2 mutation may affect multiple cell types in a non-cell autonomous mechanism of PD pathology and that unbiased single-cell transcriptomics holds promise for personalized medicine.

Generation of Neural Stem Cells from Induced Pluripotent Stem Cells

Neural stem cells (NSCs) are defined by three necessary but not sufficient criteria: (1) self-renewable, (2) ability to generate a large number of progeny, and (3) ability to differentiate into the principal central nervous system (CNS) cell types, neurons, astrocytes, and oligodendrocytes. There are various approaches to derive neural lineages from pluripotent stem cells. It is well recognized that the chosen method of NSC derivation is critical to answering the basic biology question under investigation, to the success rate in drug discovery and to the efficacy of the therapeutic cells intended for repairing the CNS. There are three critical attributes of NSCs: (1) well-defined and stable cellular composition, (2) consistent process of perpetuation that avoids drift in composition, and (3) stable phenotype or therapeutic activity of the NSCs or their differentiated progeny. Over the past decades, we have been continuously developing consistent processes for generating stable, multipotent self-renewable NSCs from various sources. In this chapter, we report a method to generate NSCs from induced pluripotent stem cells.

Standards for Deriving Nonhuman Primate-Induced Pluripotent Stem Cells, Neural Stem Cells and Dopaminergic Lineage

Humans and nonhuman primates (NHP) are similar in behavior and in physiology, specifically the structure, function, and complexity of the immune system. Thus, NHP models are desirable for pathophysiology and pharmacology/toxicology studies. Furthermore, NHP-derived induced pluripotent stem cells (iPSCs) may enable transformative developmental, translational, or evolutionary studies in a field of inquiry currently hampered by the limited availability of research specimens. NHP-iPSCs may address specific questions that can be studied back and forth between in vitro cellular assays and in vivo experimentations, an investigational process that in most cases cannot be performed on humans because of safety and ethical issues. The use of NHP model systems and cell specific in vitro models is evolving with iPSC-based three-dimensional (3D) cell culture systems and organoids, which may offer reliable in vitro models and reduce the number of animals used in experimental research. IPSCs have the potential to give rise to defined cell types of any organ of the body. However, standards for deriving defined and validated NHP iPSCs are missing. Standards for deriving high-quality iPSC cell lines promote rigorous and replicable scientific research and likewise, validated cell lines reduce variability and discrepancies in results between laboratories. We have derived and validated NHP iPSC lines by confirming their pluripotency and propensity to differentiate into all three germ layers (ectoderm, mesoderm, and endoderm) according to standards and measurable limits for a set of marker genes. The iPSC lines were characterized for their potential to generate neural stem cells and to differentiate into dopaminergic neurons. These iPSC lines are available to the scientific community. NHP-iPSCs fulfill a unique niche in comparative genomics to understand gene regulatory principles underlying emergence of human traits, in infectious disease pathogenesis, in vaccine development, and in immunological barriers in regenerative medicine.

Functional dissection of astrocyte-secreted proteins: Implications in brain health and diseases

Astrocytes, which are homeostatic cells of the central nervous system (CNS), display remarkable heterogeneity in their morphology and function. Besides their physical and metabolic support to neurons, astrocytes modulate the blood-brain barrier, regulate CNS synaptogenesis, guide axon pathfinding, maintain brain homeostasis, affect neuronal development and plasticity, and contribute to diverse neuropathologies via secreted proteins. The identification of astrocytic proteome and secretome profiles has provided new insights into the maintenance of neuronal health and survival, the pathogenesis of brain injury, and neurodegeneration. Recent advances in proteomics research have provided an excellent catalog of astrocyte-secreted proteins. This review categorizes astrocyte-secreted proteins and discusses evidence that astrocytes play a crucial role in neuronal activity and brain function. An in-depth understanding of astrocyte-secreted proteins and their pathways is pivotal for the development of novel strategies for restoring brain homeostasis, limiting brain injury/inflammation, counteracting neurodegeneration, and obtaining functional recovery.

Kisspeptin innervation of the hypothalamic paraventricular nucleus: sexual dimorphism and effect of estrous cycle in female mice

The hypothalamic paraventricular nucleus (PVN) is the major autonomic output area of the hypothalamus and a critical regulatory center for energy homeostasis. The organism's energetic balance is very important for both the regular onset of puberty and regulation of fertility. Several studies have suggested a relationship among neural circuits controlling food intake, energy homeostasis and the kisspeptin peptide. The kisspeptin system is clustered in two main groups of cell bodies [the anterior ventral periventricular region (AVPV) and the arcuate nucleus (ARC)] projecting mainly to gonadotropin-releasing hormone (GnRH) neurons and to a few other locations, including the PVN. In the present study, we investigated the distribution of the kisspeptin fibers within the PVN of adult CD1 mice. We observed a significant sexual dimorphism for AVPV and ARC, as well as for the PVN innervation. Kisspeptin fibers showed a different density within the PVN, being denser in the medial part than in the lateral one; moreover, in female, the density changed, according to different phases of the estrous cycle (the highest density being in estrus phase). The presence of a profound effect of estrous cycle on the kisspeptin immunoreactivity in AVPV (with a higher signal in estrus) and ARC, and the strong co-localization between kisspeptin and NkB only in ARC and not in PVN suggested that the majority of the kisspeptin fibers found in the PVN might arise directly from AVPV.

Predictive Markers Guide Differentiation to Improve Graft Outcome in Clinical Translation of hESC-Based Therapy for Parkinson's Disease

Stem cell treatments for neurodegenerative diseases are expected to reach clinical trials soon. Most of the approaches currently under development involve transplantation of immature progenitors that subsequently undergo phenotypic and functional maturation in vivo, and predicting the long-term graft outcome already at the progenitor stage remains a challenge. Here, we took an unbiased approach to identify predictive markers expressed in dopamine neuron progenitors that correlate with graft outcome in an animal model of Parkinson's disease through gene expression analysis of >30 batches of grafted human embryonic stem cell (hESC)-derived progenitors. We found that many of the commonly used markers did not accurately predict in vivo subtype-specific maturation. Instead, we identified a specific set of markers associated with the caudal midbrain that correlate with high dopaminergic yield after transplantation in vivo. Using these markers, we developed a good manufacturing practice (GMP) differentiation protocol for highly efficient and reproducible production of transplantable dopamine progenitors from hESCs.

Activated astrocytes enhance the dopaminergic differentiation of stem cells and promote brain repair through bFGF

Astrocytes provide neuroprotective effects against degeneration of dopaminergic (DA) neurons and play a fundamental role in DA differentiation of neural stem cells. Here we show that light illumination of astrocytes expressing engineered channelrhodopsin variant (ChETA) can remarkably enhance the release of basic fibroblast growth factor (bFGF) and significantly promote the DA differentiation of human embryonic stem cells (hESCs) in vitro. Light activation of transplanted astrocytes in the substantia nigra (SN) also upregulates bFGF levels in vivo and promotes the regenerative effects of co-transplanted stem cells. Importantly, upregulation of bFGF levels, by specific light activation of endogenous astrocytes in the SN, enhances the DA differentiation of transplanted stem cells and promotes brain repair in a mouse model of Parkinson's disease (PD). Our study indicates that astrocyte-derived bFGF is required for regulation of DA differentiation of the stem cells and may provide a strategy targeting astrocytes for treatment of PD.

Allopregnanolone and neurogenesis in the nigrostriatal tract

Reinstalling the neurobiological circuits to effectively change the debilitating course of neurodegenerative diseases is of utmost importance. This reinstallation requires generation of new cells which are able to differentiate into specific types of neurons and modification of the local environment suitable for integration of these new neurons into the neuronal circuits. Allopregnanolone (APα) seems to be involved in both of these processes, and therefore, is a potential neurotrophic agent. Loss of dopamine neurons in the substantia nigra (SN) is one of the main pathological features of Parkinson’s and also in, at least, a subset of Alzheimer’s patients. Therefore, reinstallation of the dopamine neurons in nigrostriatal tract is of unique importance for these neurodegenerative diseases. However, for the neurogenic status and the roles of allopregnanolone in the nigrostriatal tract, the evidence is accumulating and debating. This review summarizes recent studies regarding the neurogenic status in the nigrostriatal tract. Furthermore, special attention is placed on evidence suggesting that reductions in allopregnenalone levels are one of the major pathological features in PD and AD. This evidence has also been confirmed in brains of mice that were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or those bearing neurodegenerative mutations. Lastly, we highlight studies showing that allopregnanalone can augment the number of total cells and dopaminergic neurons via peripheral exogenous administration.

Imaging neural stem cell graft-induced structural repair in stroke

Stem cell therapy ameliorates motor deficits in experimental stroke model. Multimodal molecular imaging enables real-time longitudinal monitoring of infarct location, size, and transplant survival. In the present study, we used magnetic resonance imaging (MRI) and positron emission tomography (PET) to track the infarct evolution,tissue repair, and the fate of grafted cells. We genetically engineered embryonic stem cell-derived neural stem cells (NSCs) with a triple fusion reporter gene to express monomeric red fluorescence protein and herpes simplex virus-truncated thymidine kinase for multimodal molecular imaging and SPIO labeled for MRI. The infarct size as well as fate and function of grafted cells were tracked in real time for 3 months using MRI and PET. We report that grafted NSCs reduced the infarct size in animals with less than 0.1 cm(3) initial infarct in a dose-dependent manner, while larger stroke was not amenable to such beneficial effects. PET imaging revealed increased metabolic activity in grafted animals and visualized functioning grafted cells in vivo. Immunohistopathological analysis demonstrated that, after a 3-month survival period, grafted NSCs dispersed in the stroke-lesioned parenchyma and differentiated into neurons, astrocytes, and oligodendrocytes. Longitudinal multimodal imaging provides insights into time course dose-dependent interactions between NSC grafts and structural changes in infarcted tissue.

Allopregnanolone reinstates tyrosine hydroxylase immunoreactive neurons and motor performance in an MPTP-lesioned mouse model of Parkinson's disease

Restorative/protective therapies to restore dopamine neurons in the substantia nigra pars compacta (SNpc) are greatly needed to effectively change the debilitating course of Parkinson's disease. In this study, we tested the therapeutic potential of a neurogenic neurosteroid, allopregnanolone, in the restoration of the components of the nigrostriatal pathway in MPTP-lesioned mice by measuring striatal dopamine levels, total and tyrosine hydroxylase immunoreactive neuron numbers and BrdU-positive cells in the SNpc. An acute treatment (once/week for two weeks) with allopregnanolone restored the number of tyrosine hydroxylase-positive and total cell numbers in the SNpc of MPTP-lesioned mice, even though this did not increase striatal dopamine. It was also noted that MPTP treated mice to which allopregnanolone was administered had an increase in BrdU-positive cells in the SNpc. The effects of allopregnanolone in MPTP-lesioned mice were more apparent in mice that underwent behavioral tests. Interestingly, mice treated with allopregnanolone after MPTP lesion were able to perform at levels similar to that of non-lesioned control mice in a rotarod test. These data demonstrate that allopregnanolone promotes the restoration of tyrosine hydroxylase immunoreactive neurons and total cells in the nigrostriatal tract, improves the motor performance in MPTP-treated mice, and may serve as a therapeutic strategy for Parkinson's disease.

Dopaminergic neurons from midbrain-specified human embryonic stem cell-derived neural stem cells engrafted in a monkey model of Parkinson's disease

The use of human embryonic stem cells (hESCs) to repair diseased or injured brain is promising technology with significant humanitarian, societal and economic impact. Parkinson’s disease (PD) is a neurological disorder characterized by the loss of midbrain dopaminergic (DA) neurons. The generation of this cell type will fulfill a currently unmet therapeutic need. We report on the isolation and perpetuation of a midbrain-specified self-renewable human neural stem cell line (hNSCs) from hESCs. These hNSCs grew as a monolayer and uniformly expressed the neural precursor markers nestin, vimentin and a radial glial phenotype. We describe a process to direct the differentiation of these hNSCs towards the DA lineage. Glial conditioned media acted synergistically with fibroblastic growth factor and leukemia inhibitory factor to induce the expression of the DA marker, tyrosine hydroxylase (TH), in the hNSC progeny. The glial-derived neurotrophic factor did not fully mimic the effects of conditioned media. The hNSCs expressed the midbrain-specific transcription factors Nurr1 and Pitx3. The inductive effects did not modify the level of the glutamic acid decarboxylase (GAD) transcript, a marker for GABAergic neurons, while the TH transcript increased 10-fold. Immunocytochemical analysis demonstrated that the TH-expressing cells did not co-localize with GAD. The transplantation of these DA-induced hNSCs into the non-human primate MPTP model of PD demonstrated that the cells maintain their DA-induced phenotype, extend neurite outgrowths and express synaptic markers.

Progress on stem cell research towards the treatment of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive accumulation of Lewy body inclusions along with selective destruction of dopaminergic (DA) neurons in the nigrostriatal tract of the brain. Genetic studies have revealed much about the pathophysiology of PD, enabling the identification of both biomarkers for diagnosis and genetic targets for therapeutic treatment, which are evolved in tandem with the development of stem cell technologies. The discovery of induced pluripotent stem (iPS) cells facilitates the derivation of stem cells from adult somatic cells for personalized treatment and thus overcomes not only the limited availability of human embryonic stem cells but also ethical concerns surrounding their use. Non-viral, non-integration, or non-DNA-mediated reprogramming technologies are being developed. Protocols for generating midbrain DA neurons are undergoing constant refinement. The iPS cell-derived DA neurons provide cellular models for investigating disease progression in vitro and for screening molecules of novel therapeutic potential and have beneficial effects on improving the behavior of parkinsonian animals. Further progress in the development of safer non-viral/non-biased reprogramming strategies and the subsequent generation of homogenous midbrain DA neurons shall pave the way for clinical trials. A combined approach of drugs, cell replacement, and gene therapy to stop disease progression and to improve treatment may soon be within our reach.

Building authentic midbrain dopaminergic neurons from stem cells - lessons from development

The challenge with controlling the differentiation of human pluripotent cells to generate functional dopaminergic neurons for the treatment of Parkinson’s disease has undergone significant progress in recent years. Here, we summarize the differences between newer and older protocols for generating midbrain dopaminergic neurons from human pluripotent stem cells, and we highlight the importance of following developmental pathways during differentiation. The field has now developed to a point where it is timely to take human pluripotent stem cells one step closer to clinical use, and cell criteria to be fulfilled for such developments are outlined in this review.

The enhancement of neural stem cell survival and growth by coculturing with expanded Sertoli cells in vitro

Sertoli cells (SCs) have been described as the "nurse cells" of testis to provide essential growth factors and to create a proper environment for the development of other cells (e.g., germinal and neural stem cell). However, the physiological functions of the SCs obtained from different culture conditions are different in a coculturing system, and thus the optimal SC culturing condition should be investigated in vitro. In this paper, primary Sertoli cells were isolated from a 12-day-old mouse and expanded in two different culture conditions: a two dimensional (2D) plastic tissue disc and a three dimensional (3D) microcarrier culture system. They were then cocultured with neural stem cells (NSCs) isolated from 14-day-old mouse embryos. The metabolic activities of SCs(2D) (SCs in 2D) and SCs(3D) (SCs in 3D) and the amount of proteins secreted from two culturing systems were compared. The results show that the metabolic activity and the amount of secreted proteins from SCs(3D) were higher than both from SCs(2D). Three coculturing groups: NSCs+SC(2D), NSCs+SC(3D), and NSCs +SC-conditioned medium (SCCM, control group) were also compared regarding cell morphology and the numbers of neurons, neural outgrowths and neurospheres. The quantity of neurons, neural outgrowths and neurospheres were the highest in the NSCs+SC(3D) group. SCs cultured in the 3D system had a strong trophic effect on NSCs and enhanced their survival and growth. Besides, the mRNA of trophic and nutritive factors such as Glial-cell-line-derived neurotrophic factor (GDNF) and Interleukin-1 α (IL-1 α) secreted by the SCs from both 2D and 3D culture system were analyzed by real time-PCR and gel assay. The mRNA transcription of GDNF and IL-1α is more apparent in the 3D culture system than that from the 2D one. The coculturing system of NSCs+SC(3D) is a promising candidate for future neural stem cell transplantation.

Oct4-induced reprogramming is required for adult brain neural stem cell differentiation into midbrain dopaminergic neurons

Neural stem cells (NSCs) lose their competency to generate region-specific neuronal populations at an early stage during embryonic brain development. Here we investigated whether epigenetic modifications can reverse the regional restriction of mouse adult brain subventricular zone (SVZ) NSCs. Using a variety of chemicals that interfere with DNA methylation and histone acetylation, we showed that such epigenetic modifications increased neuronal differentiation but did not enable specific regional patterning, such as midbrain dopaminergic (DA) neuron generation. Only after Oct-4 overexpression did adult NSCs acquire a pluripotent state that allowed differentiation into midbrain DA neurons. DA neurons derived from Oct4-reprogrammed NSCs improved behavioural motor deficits in a rat model of Parkinson's disease (PD) upon intrastriatal transplantation. Here we report for the first time the successful differentiation of SVZ adult NSCs into functional region-specific midbrain DA neurons, by means of Oct-4 induced pluripotency.

Cell transplantation and gene therapy in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disorder affecting, in part, dopaminergic motor neurons of the ventral midbrain and their terminal projections that course to the striatum. Symptomatic strategies focused on dopamine replacement have proven effective at remediating some motor symptoms during the course of disease but ultimately fail to deliver long-term disease modification and lose effectiveness due to the emergence of side effects. Several strategies have been experimentally tested as alternatives for Parkinson's disease, including direct cell replacement and gene transfer through viral vectors. Cellular transplantation of dopamine-secreting cells was hypothesized as a substitute for pharmacotherapy to directly provide dopamine, whereas gene therapy has primarily focused on restoration of dopamine synthesis or neuroprotection and restoration of spared host dopaminergic circuitry through trophic factors as a means to enhance sustained controlled dopamine transmission. This seems now to have been verified in numerous studies in rodents and nonhuman primates, which have shown that grafts of fetal dopamine neurons or gene transfer through viral vector delivery can lead to improvements in biochemical and behavioral indices of dopamine deficiency. However, in clinical studies, the improvements in parkinsonism have been rather modest and variable and have been plagued by graft-induced dyskinesias. New developments in stem-cell transplantation and induced patient-derived cells have opened the doors for the advancement of cell-based therapeutics. In addition, viral-vector-derived therapies have been developed preclinically with excellent safety and efficacy profiles, showing promise in clinical trials thus far. Further progress and optimization of these therapies will be necessary to ensure safety and efficacy before widespread clinical use is deemed appropriate.

Enhanced proliferation and dopaminergic differentiation of ventral mesencephalic precursor cells by synergistic effect of FGF2 and reduced oxygen tension

Effective numerical expansion of dopaminergic precursors might overcome the limited availability of transplantable cells in replacement strategies for Parkinson's disease. Here we investigated the effect of fibroblast growth factor-2 (FGF2) and FGF8 on expansion and dopaminergic differentiation of rat embryonic ventral mesencephalic neuroblasts cultured at high (20%) and low (3%) oxygen tension. More cells incorporated bromodeoxyuridine in cultures expanded at low as compared to high oxygen tension, and after 6 days of differentiation there were significantly more neuronal cells in low than in high oxygen cultures. Low oxygen during FGF2-mediated expansion resulted also in a significant increase in tyrosine hydroxylase-immunoreactive (TH-ir) dopaminergic neurons as compared to high oxygen tension, but no corresponding effect was observed for dopamine release into the culture medium. However, switching FGF2-expanded cultures from low to high oxygen tension during the last two days of differentiation significantly enhanced dopamine release and intracellular dopamine levels as compared to all other treatment groups. In addition, the short-term exposure to high oxygen enhanced in situ assessed TH enzyme activity, which may explain the elevated dopamine levels. Our findings demonstrate that modulation of oxygen tension is a recognizable factor for in vitro expansion and dopaminergic differentiation of rat embryonic midbrain precursor cells.

Telencephalic neural precursor cells show transient competence to interpret the dopaminergic niche of the embryonic midbrain

Neural Precursor Cells (NPCs) generate complex stereotypic arrays of neuronal subtypes in the brain. This process involves the integration of patterning cues that progressively restrict the fate of specific NPCs. Yet the capacity of NPCs to interpret foreign microenvironments during development remains poorly defined. The aim of this work was to test the competence of mouse telencephalic NPCs to respond to the dopaminergic niche of the mesencephalon. Telencephalic NPCs isolated from midgestation mouse embryos (E10.5) and transplanted to age-matched mesencephalic explants efficiently differentiated into neurons but were largely unable to produce midbrain dopaminergic (mDA) neurons. Instead, E10.5 telencephalic NPCs behaved as restricted gabaergic progenitors that maintained ectopic expression of Foxg1 and Pax6. In contrast, E8.5 telencephalic NPCs were able to differentiate into Lmx1a(+)/Foxa2(+)/TH(+) neurons in the dopaminergic niche of the mesencephalic explants. In addition, these early telencephalic NPCs showed region-dependent expression of Nkx6.1, Nkx2.2 and site-specific differentiation into gabaergic neurons within the mesencephalic tissue. Significant dopaminergic differentiation of E8.5 telencephalic NPCs was not observed after transplantation to E12.5 mesencephalic explants, suggesting that inductive signals in the dopaminergic niche rapidly decay after midgestation. Moreover, we employed transplantation of embryonic stem cells-derived precursors to demonstrate that extinction of inductive signals within the telencephalon lags behind the commitment of residing NPCs. Our data indicate that the plasticity to interpret multiple instructive niches is an early and ephemeral feature of the telencephalic neural lineage.

Skin-derived precursors differentiating into dopaminergic neuronal cells in the brains of Parkinson disease model rats

OBJECT

In the authors' previous study, they observed that amino acids 157-171 of von Hippel-Lindau protein (VHL peptide) induced neuronal differentiation of skin-derived precursors. They also noted that transplantation of these differentiated cells into the striata of a Parkinson disease (PD) rat model reduced apomorphine-induced rotations. In the present study, they investigated if these cells produce dopamine in the striatum.

METHODS

Skin-derived precursors were differentiated into neurons using VHL peptide and transplanted into the striata of a PD model of rats. Four weeks after transplantation, a probe was inserted into rat striata and extracellular dopamine was extracted by microdialysis. Dopamine levels were measured by high-pressure liquid chromatography. Brain sections were assessed by immunohistochemical analysis for the presence of tyrosine hydroxylase and dopamine transporter.

RESULTS

Increased dopamine levels in the striata of the rats were observed after transplantation (p < 0.01), and these were correlated with a reduction in the number of apomorphine-induced rotations (p < 0.05). Skin-derived precursors observed along the tract of transplantation were positive for tyrosine hydroxylase and dopamine transporter.

CONCLUSIONS

This study suggests that transplantation of skin-derived precursors, differentiated into neuronal cells using VHL peptide, can improve PD-like symptoms by enabling production of dopamine in the striata in a PD model of rats.

Lovastatin induces neuronal differentiation and apoptosis of embryonal carcinoma and neuroblastoma cells: enhanced differentiation and apoptosis in combination with dbcAMP

Differentiation-based therapeutics are an underutilized but a potentially significant treatment option for cancer patients. We show that lovastatin, a competitive inhibitor of the rate-limiting enzyme of mevalonate synthesis HMG-CoA reductase, is able to induce tumour cell differentiation and apoptosis in vitro. We used embryonal carcinoma (EC) and neuroblastoma (NB) cell lines and found that lovastatin promoted apoptosis and induced expression of the neuronal differentiation markers, tyrosine hydroxylase (TH), and growth-associated protein 43. The apoptotic and differentiation responses were time and dose-dependant and rescued by the co-administration of mevalonate. The expression of TH is regulated primarily by a cyclic AMP (cAMP) response element (CRE) in its promoter. Lovastatin enhanced the expression of a CRE-driven luciferase construct in P19 cells. Furthermore, combining lovastatin with 1 mM dibutyryladenosine 3',5'-cyclic monophosphate treatments induced higher expression from the CRE construct, enhanced differentiation and cytotoxicity. This study suggests the potential of combining these therapeutic approaches in EC and NB patients.

Expansion of mouse sertoli cells on microcarriers

BACKGROUND

Sertoli cells (SCs) have been described as the 'nurse cells' of the testis whose primary function is to provide essential growth factors and create an appropriate environment for development of other cells [for example, germinal and nerve stem cells (NSCs), used here]. However, the greatest challenge at present is that it is difficult to obtain sufficient SCs of normal physiological function for cell transplantation and biological medicine, largely due to traditional static culture parameter difficult to be monitored and scaled up.

OBJECTIVE

Operational stirred culture conditions for in vitro expansion and differentiation of SCs need to be optimized for large-scale culture.

MATERIALS AND METHODS

In this study, the culturing process for primary SC expansion and maintaining lack of differentiation was optimized for the first time, by using microcarrier bead technology in spinner flask culture. Effects of various feeding/refreshing regimes, stirring speeds, seed inoculum levels of SCs, and concentrations of microcarrier used for expansion of mouse SCs were also explored. In addition, pH, osmotic pressure and metabolic variables including consumption rates of glucose, glutamine, amino acids, and formation rates of lactic acid and ammonia, were investigated in culture.

RESULTS

After 6 days, maximal cell densities achieved were 4.6 x 10(6) cells/ml for Cytodex-1 in DMEM/FBS compared to 4.8 x 10(5) cells/ml in static culture. Improved expansion was achieved using an inoculum of 1 x 10(5) cells/ml and microcarrier concentration of 3 mg/ml at stirring speed of 30 rpm. RESULTS indicated that medium replacement (50% changed everyday) resulted in supply of nutrients and removal of waste products inhibiting cell growth, that lead to maintenance of cultures in steady state for several days. These conditions favoured preservation of SCs in the undifferentiated state and significantly increased their physiological activity and trophic function, which were assessed by co-culturing with NSCs and immunostaining.

CONCLUSION

Data obtained in this study demonstrate the vast potential of this stirred culture system for efficient, reproducible and cost-effective expansion of SCs in vitro. The system has advantages over static culture, which has major obstacles such as lower cell density, is time-consuming and susceptible to contamination.

Human neural stem cell grafts modify microglial response and enhance axonal sprouting in neonatal hypoxic-ischemic brain injury

BACKGROUND AND PURPOSE

Hypoxic-ischemic (HI) brain injury in newborn infants represents a major cause of cerebral palsy, development delay, and epilepsy. Stem cell-based therapy has the potential to rescue and replace the ischemic tissue caused by HI and to restore function. However, the mechanisms by which stem cell transplants induce functional recovery are yet to be elucidated. In the present study, we sought to investigate the efficacy of human neural stem cells derived from human embryonic stem cells in a rat model of neonatal HI and the mechanisms enhancing brain repair.

METHODS

The human neural stem cells were genetically engineered for in vivo molecular imaging and for postmortem histological tracking. Twenty-four hours after the induction of HI, animals were grafted with human neural stem cells into the forebrain. Motor behavioral tests were performed the fourth week after transplantation. We used immunocytochemistry and neuroanatomical tracing to analyze neural differentiation, axonal sprouting, and microglia response. Treatment-induced changes in gene expression were investigated by microarray and quantitative polymerase chain reaction.

RESULTS

Bioluminescence imaging permitted real time longitudinal tracking of grafted human neural stem cells. HI transplanted animals significantly improved in their use of the contralateral impeded forelimb and in the Rotorod test. The grafts showed good survival, dispersion, and differentiation. We observed an increase of uniformly distributed microglia cells in the grafted side. Anterograde neuroanatomical tracing demonstrated significant contralesional sprouting. Microarray analysis revealed upregulation of genes involved in neurogenesis, gliogenesis, and neurotrophic support.

CONCLUSIONS

These results suggest that human neural stem cell transplants enhance endogenous brain repair through multiple modalities in response to HI.

A synergistic approach for neural repair: cell transplantation and induction of endogenous precursor cell activity

Stem cell research offers enormous potential for treating many diseases of the nervous system. At present, therapeutic strategies in stem cell research segregate into two approaches: cell transplantation or endogenous cell stimulation. Realistically, future cell therapies will most likely involve a combination of these two approaches, a theme of our current research. Here, we propose that there exists a 'synergy' between exogenous (transplanted) and endogenous stem cell actions that can be utilized to achieve therapeutic ends. Elucidating mechanisms underlying this exogenous-endogenous stem cell synergism may lead to the development of optimal cell therapies for neural disorders.

Effects of Epimedium flavonoids on proliferation and differentiation of neural stem cells in vitro

OBJECTIVE

The purpose of this study is to investigate the effects of Epimedium flavonoids (EF), which is extracted from a traditional Chinese Epimedium herb, and its effect on the proliferation and differentiation of neural stem cells (NSCs) in vitro.

METHODS

The single cells isolated from the hippocampi of 1 day old neonatal rats were cultured in a serum-free condition medium DMEM/F12 (1 : 1) with different concentrations of EF or 20 ng/ml epidermal growth factor (EGF) and 10 ng/ml basic fibroblast growth factor (bFGF). After 7 and 28 days, the neurospheres' diameters were measured. The formed neurospheres were cultured in the differentiation medium containing EF or 10% fetal bovine serum (FBS). After 12 hours and 7 days, immunofluorescent studies for nestin, Musashi-1, BrdU, beta-III-tubulin, NF-200 and GFAP were performed. The number and lengths of 10-15 axons of NF-200 immunopositive cells were measured.

RESULTS

The results showed that the isolated cells had the ability to propagate as neurospheres in the medium with 200 and 400 m g/ml EF, but without any EGF or bFGF, and the volume of neurospheres increase gradually from 7 to 28 days. In comparison with FBS control, the number of NF-200 positive neurons had significantly increased in the EF groups where the newborn neurons were morphologically more mature and able to migrate farther away from neurospheres than in the FBS control.

DISCUSSION

The results demonstrate that EF effectively promotes the proliferation and differentiation of NSCs in vitro, suggesting that EF may have new properties of regulating central nervous system function by neurogenesis.

Transplantation of subventricular zone neural precursors induces an endogenous precursor cell response in a rat model of Parkinson's disease

Realistically, future stem cell therapies for neurological conditions including Parkinson's disease (PD) will most probably entail combination treatment strategies, involving both the stimulation of endogenous cells and transplantation. Therefore, this study investigates these two modes of neural precursor cell (NPC) therapy in concert in order to determine their interrelationships in a rat PD model. Human placental alkaline phosphatase (hPAP)-labeled NPCs were transplanted unilaterally into host rats which were subsequently infused ipsilaterally with 6-hydroxydopamine (6-OHDA). The reaction of host NPCs to the transplantation and 6-OHDA was tracked by bromodeoxyuridine (BrdU) labeling. Two weeks after transplantation, in animals transplanted with NPCs we found evidence of elevated host subventricular zone NPC proliferation, neurogenesis, and migration to the graft site. In these animals, we also observed a significant preservation of striatal tyrosine hydroxylase (TH) expression and substantia nigra TH cell number. We have seen no evidence that neuroprotection is a product of dopamine neuron replacement by NPC-derived cells. Rather, the NPCs expressed glial cell line-derived neurotrophic factor (GDNF), sonic hedgehog (Shh), and stromal cell-derived factor 1 alpha (SDF1alpha), providing a molecular basis for the observed neuroprotection and endogenous NPC response to transplantation. In summary, our data suggests plausible synergy between exogenous and endogenous NPC actions, and that NPC implantation before the 6-OHDA insult can create a host microenvironment conducive to stimulation of endogenous NPCs and protection of mature nigral neurons.

Important precautions when deriving patient-specific neural elements from pluripotent cells

Multipotent human neural stem cells (hNSC) have traditionally been isolated directly from the central nervous system (CNS). To date, as a therapeutic tool in the treatment of neurologic disorders, the most promising results have been obtained using hNSC isolated directly from the human fetal neuroectoderm. The propagation ability of such tissue-derived hNSC is often limited, however, making it difficult to establish a large-scale culture. Following engraftment, these hNSC often show low efficiency in generating the desired neuronal cells necessary for reconstruction of the damaged host milieu and, as a result, have failed to give satisfactory results in clinical trials so far. Alternatively, human embryonic stem cells (hESC) offer a pluripotent reservoir for in vitro derivation of a rich spectrum of well-characterized neural-lineage committed stem/progenitor/precursor cells that can, theoretically, be picked at precisely their safest and most efficacious state of plasticity to meet a given clinical challenge. However, the need for 'foreign' biologic additives and multilineage differentiation inclination may make direct use of such cell-derived hNSC in patients problematic. The hNSC, when derived from pluripotent cells under protocols presently employed in the field, tend to display not only a low efficiency in neuronal differentiation, but also an inclination for phenotypic heterogeneity and instability and, hence, increased risk of tumorigenesis following engraftment. For hNSC derived in vitro to be used safely in therapeutic paradigms, it requires conversion of human pluripotent cells uniformly to cells that are restricted to the neural lineage in need of repair. Developing strategies for direct induction of human pluripotent cells exclusively into neural-committed progenies at a broad range of developmental stages will allow a large supply of optimal therapeutic hNSC tailor-made for safe and effective treatment of particular neurologic diseases and injuries in patients.

Neurodevelopmental abnormalities in neurosphere-derived neural stem cells from SMN-depleted mice

Spinal muscular atrophy (SMA) is a genetic disorder caused by depletion of survival motor neuron (SMN) protein and characterized by degeneration of alpha-motor neurons in the spinal cord. We investigated the morphology and differentiation of neurosphere-derived neural stem cells (NSCs) generated from the brains of a hypomorphic series of SMA mice. Neurospheres from the Smn(-/-);SMN2 mice, which represent a model of very severe SMA, produced NSCs with increased proliferation during growth and differentiation. These cells produced fewer Tuj1-positive neuronal cells, which displayed morphological alterations and had fewer and shorter neurites. The decrease in the number of Tuj1-positive cells was not a result of enhanced apoptosis but was accompanied by an increase in the number of nestin-positive cells. These results provide insight into the most severe model of SMA, in which SMN is nearly completely depleted, and suggest that SMN has a role in neurodevelopment as well as in neuromaintenance. Our work raises the possibility that SMN depletion affects neurodevelopment and neuromaintenance to varying extents, leading to SMA pathogenesis.

Glial Cells as Players in Parkinsonism: The “Good,” the “Bad,” and the “Mysterious” Glia

The role of glia in Parkinson's disease (PD) is very interesting because it may open new therapeutic strategies in this disease. Traditionally it has been considered that astrocytes and microglia play different roles in PD: Astroglia are considered the “good” glia and have traditionally been supposed to be neuroprotective due to their capacity to quench free radicals and secrete neurotrophic factors, whereas microglia, considered the “bad” glia, are thought to play a critical role in neuroinflammation. The proportion of astrocytes surrounding dopamine (DA) neurons in the substantia nigra, the target nucleus for neurodegeneration in PD, is the lowest for any brain area, suggesting that DA neurons are more vulnerable in terms of glial support than any neuron in other brain areas. Astrocytes are critical in the modulation of the neurotoxic effects of many toxins that induce experimental parkinsonism and they produce substances in vitro that could modify the effects of L-DOPA from neurotoxic to neurotrophic. There is a great interest in the role of inflammation in PD, and in the brains of these patients there is evidence for microglial production of cytokines and other substances that could be harmful to neurons, suggesting that microglia of the substantia nigra could be actively involved, primarily or secondarily, in the neurodegeneration process. There is, however, evidence in favor of the role of neurotoxic diffusible signals from microglia to DA neurons. More recently a third glial player, oligodendroglia, has been implicated in the pathogenesis of PD. Oligodendroglia play a key role in myelination of the nervous system. Recent neuropathological studies suggested that the nigrostriatal dopamine neurons, which were considered classically as the primary target for neurodegeneration in PD, degenerate at later stages than other neurons with poor myelination. Therefore, the role of oligodendroglia, which also secrete neurotrophic factors, has entered the center of interest of neuroscientists.

In vitro assays for neural stem cell differentiation: induction of dopaminergic phenotype

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra. Symptoms include tremors, rigidity, bradykinesia, and instability. Neural transplantation is a promising strategy for improving dopaminergic dysfunction in PD provided that the dopaminergic neurons are consistently generated from a renewable source of cells. Neural stem cells (NSCs) have the ability to self-renew, generate a large number of progeny, and differentiate into the principal nervous system cell types. As such, stem cells provide an exciting opportunity to understand the basic mechanisms involved in cell differentiation and histogenesis. These mechanisms have translational applications in tissue engineering and biomedicine in general. In vitro differentiation assays are important in cell characterization, in assaying for novel instructive molecules, and in generating specific cell types. We describe differentiation techniques to test NSCs for multipotency and to induce the dopaminergic phenotype in neural stem cell progeny by coculturing them with astrocytes and treating them with conditioned media and basic fibroblastic growth factor.

Behavioral improvement in a primate Parkinson's model is associated with multiple homeostatic effects of human neural stem cells

Stem cells have been widely assumed to be capable of replacing lost or damaged cells in a number of diseases, including Parkinson's disease (PD), in which neurons of the substantia nigra (SN) die and fail to provide the neurotransmitter, dopamine (DA), to the striatum. We report that undifferentiated human neural stem cells (hNSCs) implanted into 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated Parkinsonian primates survived, migrated, and had a functional impact as assessed quantitatively by behavioral improvement in this DA-deficit model, in which Parkinsonian signs directly correlate to reduced DA levels. A small number of hNSC progeny differentiated into tyrosine hydroxylase (TH) and/or dopamine transporter (DAT) immunopositive cells, suggesting that the microenvironment within and around the lesioned adult host SN still permits development of a DA phenotype by responsive progenitor cells. A much larger number of hNSC-derived cells that did not express neuronal or DA markers was found arrayed along the persisting nigrostriatal path, juxtaposed with host cells. These hNSCs, which express DA-protective factors, were therefore well positioned to influence host TH+ cells and mediate other homeostatic adjustments, as reflected in a return to baseline endogenous neuronal number-to-size ratios, preservation of extant host nigrostriatal circuitry, and a normalizing effect on alpha-synuclein aggregation. We propose that multiple modes of reciprocal interaction between exogenous hNSCs and the pathological host milieu underlie the functional improvement observed in this model of PD.

Genetically engineered human neural stem cells for brain repair in neurological diseases

Neural stem cells (NSCs)of the central nervous system (CNS) have recently received a great deal of attention and interest for their therapeutic potential for neurological disorders. NSCs are defined as CNS progenitor cells that have the capacity for self-renewal and multipotent potential to become neurons or glial cells. Recent studies have shown that NSCs isolated from mammalian CNS including human can be propagated in vitro and then implanted into the brain of animal models of human neurological disorders. Recently, we have generated clonally derived immortalized human NSC cell lines via a retroviral vector encoded with v-myc oncogene. One of the human NSC lines, HB1.F3, was utilized in stem-cell based therapy in animal models of human neurological disorders. When F3 human NSCs were implanted into the brain of murine models of lysosomal storage diseases, stroke, Parkinson disease, Huntington disease or stroke, implanted F3 NSCs were found to migrate to the lesion sites, differentiate into neurons and glial cells, and restore functional deficits found in these neurological disorders. In animal models of brain tumors, F3 NSCs could deliver a bioactive therapeutically relevant molecules to effect a significant anti-tumor response intracranial tumor mass. Since these genetically engineered human NSCs are immortalized and continuously multiplying, there would be limitless supply of human neurons for treatment for patients suffering from neurological disorders including stroke, Parkinson disease, Huntington disease, ALS, multiple sclerosis and spinal cord injury. The promising field of stem cell research as it applies to regenerative medicine is still in infancy, but its potential appears limitless, and we are blessed to be involved in this exciting realm of research.

Human fetal cortical and striatal neural stem cells generate region-specific neurons in vitro and differentiate extensively to neurons after intrastriatal transplantation in neonatal rats

Human fetal brain is a potential source of neural stem cells (NSCs) for cell replacement therapy in neurodegenerative diseases. We explored whether NSCs isolated from cortex and striatum of human fetuses, aged 6-9 weeks post-conception, maintain their regional identity and differentiate into specific neuron types in culture and after intrastriatal transplantation in neonatal rats. We observed no differences between cortex- and striatum-derived NSCs expanded as neurospheres in proliferative capacity, growth rate, secondary sphere formation, and expression of neural markers. After 4 weeks of differentiation in vitro, cortical and striatal NSCs gave rise to similar numbers of GABAergic and VMAT2- and parvalbumin-containing neurons. However, whereas cortical NSCs produced higher number of glutamatergic and tyrosine hydroxylase- and calretinin-positive neurons, several-fold more neurons expressing the striatal projection neuron marker, DARPP-32, were observed in cultures of striatal NSCs. Human cortical and striatal NSCs survived and migrated equally well after transplantation. The two NSC types also generated similar numbers of mature NeuN-positive neurons, which were several-fold higher at 4 months as compared to at 1 month after grafting. At 4 months, the grafts contained cells with morphologic characteristics of neurons, astrocytes, and oligodendrocytes. Many of neurons were expressing parvalbumin. Our data show that NSCs derived from human fetal cortex and striatum exhibit region-specific differentiation in vitro, and survive, migrate, and form mature neurons to the same extent after intrastriatal transplantation in newborn rats.

Astrocyte-like cells as a main target for estrogen action during neuronal differentiation

Neurospheres from the subventricular zone of adult mice were used as an experimental model to analyse the early differential effects of 17beta-estradiol (17beta-E2). Both floating and differentiating neurospheres expressed estrogen receptors (ERs) alpha and beta. The initial phases of differentiation coincided with a peak of ERalpha expression as by Western blot analysis. Treatment with 10 nM 17beta-E2 induced a significant increase in the glial fibrillary acidic protein (GFAP)-positive population and a greater expression of GFAP, an effect sensitive to the estrogen receptor antagonist ICI 182,780. The GFAP-positive cell population induced by 17beta-E2 was characterized by a highly differentiated phenotype and intense immunostaining as by immunocytochemistry and flow cytometry. These cells co-expressed ERalpha and were positive to BrdU. 17beta-E2 also affected neuronal differentiation by rapidly and transiently increasing the percentage of polysialylated-neural cell adhesion molecule (PSA-NCAM)-positive progenitors, and by accelerating the appearance of a mature neuronal phenotype, as evaluated by microtubule-associated protein 2 (MAP2) staining. Our results point to a key role for ERalpha during initial phases of differentiation of brain cells and to an effect of 17beta-E2 that sequentially involves both glia and neurons.

Engineering a Dopaminergic Phenotype in Stem/Precursor Cells: Role of Nurr1, Glia-Derived Signals, and Wnts

Recent results from clinical trials using fetal tissue grafts in patients with Parkinson's disease (PD) have indicated that current surgical strategies for dopamine cell replacement therapy need to be improved in order to achieve better functional integration of the grafts and to avoid dyskinesias. Previous studies using rich dopaminergic (DA) cell suspensions have provided proof-of-concept that PD patients can benefit from cell replacement therapy. Stem cells have been proposed as better candidates for cell replacement therapy in PD since they can be standardized, expanded, and engineered in vitro. Recent developments indicate that cell preparations enriched in DA neurons can be generated in vitro, but their functional integration in animal models of disease is still far from optimal. This is not entirely surprising considering our limited knowledge of the development of DA neurons and the reduced number of factors that have been implemented in stem cell differentiation protocols. This review will focus on three aspects of DA neuron development: (1) the function of Nurr1 and retinoid X receptors (RXR) in the differentiation of DA precursors and in the survival of DA neurons; (2) the role of glia in DA neurogenesis and the differentiation of DA precursors; and (3) the function of the Wnt family of lipoproteins in the proliferation and differentiation of DA precursors. A greater understanding of the cellular and molecular mechanisms that control DA neuron development, as well as their functional integration in vivo, are likely to ultimately contribute to the development of novel stem cell replacement therapies for PD.

Ontogeny of tyrosine hydroxylase mRNA expression in mid- and forebrain: neuromeric pattern and novel positive regions

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamines and, thus, critical in determining the catecholaminergic phenotype. In this study, we have examined the expression of TH mRNA by in situ hybridization in the embryonic mouse forebrain and midbrain and have mapped its localization according to the neuromeric pattern. We find that early in embryonic development, 10 to 12 days post coitum (dpc), TH mRNA is expressed in ample continuous regions of the neuroepithelium, extending across several neuromeres. However, from 12.5 dpc onward, the expression becomes restricted to discrete regions, which correspond to the dopaminergic nuclei (A8 to A15). In addition to these nuclei previously described, TH mRNA is also observed in regions that do not express this enzyme according to immunohistochemical studies. This difference in relation to protein expression pattern is consequent with the known posttranscriptional regulation of TH expression. The most representative example of a novel positive region is the conspicuous mRNA expression in both medial and lateral ganglionic eminences. This result agrees with reports describing the capacity of striatal stem cells (that is, located at the lateral ganglionic eminence) to become dopaminergic in vitro. Other regions include the isthmic mantle layer and the early floor plate of the midbrain-caudal forebrain. On the whole, the expression map we have obtained opens new perspectives for evolutionary/comparative studies, as well as for therapeutic approaches looking for potentially dopaminergic cells. Developmental Dynamics 234:709-717, 2005. (c) 2005 Wiley-Liss, Inc.

Aberrant cortical neurogenesis in a pediatric neuroAIDS model: neurotrophic effects of growth hormone

OBJECTIVE

To study the effects of HIV-1 and feline immunodeficiency virus (FIV) on neural stem cell viability, together with the neurotrophic properties of growth hormone (GH) in models of pediatric neuroAIDS.

DESIGN AND METHODS

Mouse neural stem cells were infected in vitro with a Sindbis virus vector (SIN-HIVenv) expressing the envelope protein from the brain-derived HIV-1 strain JR-FL using a vector expressing enhanced green fluorescent protein (SIN-EGFP) as control. Cell survival and alterations in expression of neural stem cell markers upon GH treatment was assessed. Neonatal cats were infected with a neurovirulent FIV strain and 6 weeks after infection treated with GH for 6 weeks. Twelve weeks post-infection, neural progenitor cell marker expression, neuronal loss and neuroinflammation in brain were examined using real time reverse transcription-PCR and immunohistochemical analyses.

RESULTS

HIV-1 envelope expression in neural stem cells reduced nestin expression (P < 0.05) and induced cell death (P < 0.001), which was blocked by GH. In the frontal cortex of FIV-infected cats neuroinflammation, loss of differentiated neurons (P < 0.01) and aberrant neuronal progenitor cell gene expression (P < 0.05) were observed. FIV envelope expression was detected in neural progenitor and monocytoid cells. GH treatment of FIV-infected animals induced insulin-like growth factor-1 expression in neurons (P < 0.01), enhanced neuronal survival (P < 0.01) and increased nestin expression (P < 0.05). Moreover, improved neurobehavioral performance (P < 0.01) and immunological status (P < 0.001) were observed, among GH-treated animals infected with FIV.

CONCLUSION

GH protects neural stem cells that are susceptible to lentivirus-mediated injury. Thus, GH may be a potential treatment for pediatric neuroAIDS because of its neurotrophic actions.

Directed differentiation of dopaminergic neuronal subtypes from human embryonic stem cells

How dopamine (DA) neuronal subtypes are specified remains unknown. In this study we show a robust generation of functional DA neurons from human embryonic stem cells (hESCs) through a specific sequence of application of fibroblast growth factor 8 (FGF8) and sonic hedgehog (SHH). Treatment of hESC-derived Sox1+ neuroepithelial cells with FGF8 and SHH resulted in production of tyrosine hydroxylase (TH)-positive neurons that were mostly bipolar cells, coexpression with gamma-aminobutyric acid, and lack of midbrain marker engrailed 1 (En1) expression. However, FGF8 treatment of precursor cells before Sox1 expression led to the generation of a similar proportion of TH+ neurons characteristic of midbrain projection DA neurons with large cell bodies and complex processes and coexpression of En1. This suggests that one mechanism of generating neuronal subtypes is temporal availability of morphogens to a specific group of precursors. The in vitro-generated DA neurons were electrophysiologically active and released DA in an activity-dependent manner. They may thus provide a renewable source of functional human DA neurons for drug screening and development of sustainable therapeutics for disorders affecting the DA system.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

Estrogen promotes differentiation and survival of dopaminergic neurons derived from human neural stem cells

To investigate the effect of estrogen on neuronal differentiation, especially on dopaminergic (DA) neurons, human neural stem cells (NSCs) were differentiated in the presence of 17beta-estradiol. NSCs gave rise to tyrosine hydroxylase (TH)-positive neurons in vitro, the proportion of which was increased by 17beta-estradiol. Increase in TH-positive neurons was abrogated by an estrogen receptor (ER) antagonist, ICI182780, suggesting ERs play a role in differentiation of DA neurons. The observation that ERs were expressed in both proliferating NSCs and postmitotic DA neurons suggested that increase in TH-positive neurons was due to induction and support of DA neurons. 17beta-Estradiol also increased the number of DA neurons derived from human NSCs in vivo when the cells were grafted into mouse brains. These results support a possible role for estrogen in the transplantation of NSCs for Parkinson's disease.

Human neural stem cells genetically modified for brain repair in neurological disorders

Existence of multipotent neural stem cells (NSC) has been known in developing or adult mammalian CNS, including humans. NSC have the capacity to grow indefinitely and have multipotent potential to differentiate into three major cell types of CNS, neurons, astrocytes and oligodendrocytes. Stable clonal lines of human NSC have recently been generated from the human fetal telencephalon using a retroviral vector encoding v-myc. One of the NSC lines, HB1.F3, carries normal human karyotype of 46XX and has the ability to self-renew, differentiate into cells of neuronal and glial lineages, and integrate into the damaged CNS loci upon transplantation into the brain of animal models of Parkinson disease, HD, stroke and mucopolysaccharidosis. F3 human NSC were genetically engineered to produce L-dihydroxyphenylalanine (L-DOPA) by double transfection with cDNA for tyrosine hydroxylase and guanosine triphosphate cylohydrolase-1, and transplantation of these cells in the brain of Parkinson disease model rats led to L-DOPA production and functional recovery. Proactively transplanted F3 human NSC in rat striatum, supported the survival of host striatal neurons against neuronal injury caused by 3-nitropro-pionic acid in rat model of HD. Intravenously introduced through the tail vein, F3 human NSC were found to migrate into ischemic lesion sites, differentiate into neurons and glial cells, and improve functional deficits in rat stroke models. These results indicate that human NSC should be an ideal vehicle for cell replacement and gene transfer therapy for patients with neurological diseases. In addition to immortalized human NSC, immortalized human bone marrow mesenchymal stem cell lines have been generated from human embryonic bone marrow issues with retroviral vectors encording v-myc or teromerase gene. These immortalized cell lines of human bone marrow mesenchymal stem cells differentiated into neurons/glial cells, bone, cartilage and adipose tissue when they were grown in selective inducing media. There is further need for investigation into the neurogenic potential of the human bone marrow stem cell lines and their utility in animal models of neurological diseases.