From bench to bed: the potential of stem cells for the treatment of Parkinson's disease

Pharmacological and stem cell therapy of stroke in animal models: Do they accurately reflect the response of humans?

Cerebrovascular diseases are the second leading cause of death worldwide. Despite significant research investment, the only available therapeutic options are mechanical thrombectomy and tissue plasminogen activator thrombolysis. None of the more than a thousand drugs tested on animal models have proven successful in human clinical trials. Several factors contribute to this poor translation of data from stroke-related animal models to human stroke patients. Firstly, our understanding of the molecular and cellular processes involved in recovering from an ischemic stroke is severely limited. Secondly, although the risk of stroke is particularly high among older patients with comorbidities, most drugs are tested on young, healthy animals in controlled laboratory conditions. Furthermore, in animal models, the tracking of post-stroke recovery typically spans only 3 to 28 days, with occasional extensions to 60 days, whereas human stroke recovery is a more extended and complex process. Thirdly, young animal models often exhibit a considerably higher rate of spontaneous recovery compared to humans following a stroke. Fourth, only a very limited number of animals are utilized for each condition, including control groups. Another contributing factor to the much smaller beneficial effects in humans is that positive outcomes from numerous animal studies are more readily accepted than results reported in human trials that do not show a clear benefit to the patient. Useful recommendations for conducting experiments in animal models, with increased chances of translatability to humans, have been issued by both the STEPS investigative team and the STAIR committee. However, largely, due to economic factors, these recommendations are largely ignored. Furthermore, one might attribute the overall failures in predicting and subsequently developing effective acute stroke therapies beyond thrombolysis to potential design deficiencies in clinical trials.

Clinical Ageing

Ageing is generally characterised by the declining ability to respond to stress, increasing homeostatic imbalance, and increased risk of ageing-associated diseases . Mechanistically, the lifelong accumulation of a wide range of molecular and cellular impairments leads to organismal senescence. The aging population poses a severe medical concern due to the burden it places on healthcare systems and the general public as well as the prevalence of diseases and impairments associated with old age. In this chapter, we discuss organ failure during ageing as well as ageing of the hypothalamic-pituitary-adrenal axis and drugs that can regulate it. A much-debated subject is about ageing and regeneration. With age, there is a gradual decline in the regenerative properties of most tissues. The goal of regenerative medicine is to restore cells, tissues, and structures that are lost or damaged after disease, injury, or ageing. The question arises as to whether this is due to the intrinsic ageing of stem cells or, rather, to the impairment of stem-cell function in the aged tissue environment. The risk of having a stroke event doubles each decade after the age of 55. Therefore, it is of great interest to develop neurorestorative therapies for stroke which occurs mostly in elderly people. Initial enthusiasm for stimulating restorative processes in the ischaemic brain with cell-based therapies has meanwhile converted into a more balanced view, recognising impediments related to survival, migration, differentiation, and integration of therapeutic cells in the hostile aged brain environment. Therefore, a current lack of understanding of the fate of transplanted cells means that the safety of cell therapy in stroke patients is still unproven. Another issue associated with ischaemic stroke is that patients at risk for these sequels of stroke are not duly diagnosed and treated due to the lack of reliable biomarkers. However, recently neurovascular unit-derived exosomes in response to Stroke and released into serum are new plasma genetic and proteomic biomarkers associated with ischaemic stroke. The second valid option, which is also more economical, is to invest in prevention.

Progress in treatment of neuromyelitis optica spectrum disorders (NMOSD): Novel insights into therapeutic possibilities in NMOSD

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune inflammatory demyelinating disorder of the central nervous system (CNS), which is a severely disabling disorder leading to devastating sequelae or even death. Repeated acute attacks and the presence of aquaporin-4 immunoglobulin G (AQP4-IgG) antibody are the typical characteristics of NMOSD. Recently, the phase III trials of the newly developed biologicals therapies have shown their effectiveness and good tolerance to a certain extent when compared with the traditional therapy with the first- and second-line drugs. However, there is still a lack of large sample, double-blind, randomized, clinical studies to confirm their efficacy, safety, and tolerability. Especially, these drugs have no clear effect on NMOSD patients without AQP4-IgG and refractory patients. Therefore, it is of strong demand to further conduct large sample, double-blind, randomized, clinical trials, and novel therapeutic possibilities in NMOSD are discussed briefly here.

Comparisons of clinical phenotype, radiological and laboratory features, and therapy of neuromyelitis optica spectrum disorder by regions: update and challenges

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory demyelinating disease of the central nervous system (CNS) associated with autoantibody (ab) to aquaporin-4 (AQP4). There is obvious variation between regions and countries in the epidemiology, clinical features and management in NMOSD. Based on published population-based observation and cohort studies, the different clinical pattern of NMOSD has been seen in several geographical regions and some of these patients with NMOSD-like features do not fully meet the current diagnostic criteria, which is needed to consider the value of recently revised diagnostic criteria. At present, all treatments applied in NMOSD have made great progress, however, these treatments failed in AQP4 ab negative and refractory patients. Therefore, it is necessary to turn into an innovative idea and to open a new era of NMOSD treatment to develop novel and diverse targets and effective therapeutic drugs in NMOSD and to conduct the trails in large clinical samples and case-control studies to confirm their therapeutic effects on NMOSD in the future, which still remain a challenge.

Epigenetic plasticity and redox regulation of neural stem cell state and fate

The neural stem cells (NSCs) are essential for normal brain development and homeostasis. The cell state (i.e. quiescent versus activated) and fate (i.e. the cell lineage of choice upon differentiation) of NSCs are tightly controlled by various redox and epigenetic regulatory mechanisms. There is an increasing appreciation that redox and epigenetic regulations are intimately linked, but how this redox-epigenetics crosstalk affects NSC activity remains poorly understood. Another unresolved topic is whether the NSCs actually contribute to brain ageing and neurodegenerative diseases. In this review, we aim to 1) distill concepts that underlie redox and epigenetic regulation of NSC state and fate; 2) provide examples of the redox-epigenetics crosstalk in NSC biology; and 3) highlight potential redox- and epigenetic-based therapeutic opportunities to rescue NSC dysfunctions in ageing and neurodegenerative diseases.

Recent Advances in the Treatment of Cerebellar Disorders

Various etiopathologies affect the cerebellum, resulting in the development of cerebellar ataxias (CAs), a heterogeneous group of disorders characterized clinically by movement incoordination, affective dysregulation, and cognitive dysmetria. Recent progress in clinical and basic research has opened the door of the ‘‘era of therapy” of CAs. The therapeutic rationale of cerebellar diseases takes into account the capacity of the cerebellum to compensate for pathology and restoration, which is collectively termed cerebellar reserve. In general, treatments of CAs are classified into two categories: cause-cure treatments, aimed at arresting disease progression, and neuromodulation therapies, aimed at potentiating cerebellar reserve. Both forms of therapies should be introduced as soon as possible, at a time where cerebellar reserve is still preserved. Clinical studies have established evidence-based cause-cure treatments for metabolic and immune-mediated CAs. Elaborate protocols of rehabilitation and non-invasive cerebellar stimulation facilitate cerebellar reserve, leading to recovery in the case of controllable pathologies (metabolic and immune-mediated CAs) and delay of disease progression in the case of uncontrollable pathologies (degenerative CAs). Furthermore, recent advances in molecular biology have encouraged the development of new forms of therapies: the molecular targeting therapy, which manipulates impaired RNA or proteins, and the neurotransplantation therapy, which delays cell degeneration and facilitates compensatory functions. The present review focuses on the therapeutic rationales of these recently developed therapeutic modalities, highlighting the underlying pathogenesis.

Task Force Paper On Cerebellar Transplantation: Are We Ready to Treat Cerebellar Disorders with Cell Therapy?

Restoration of damaged central nervous system structures, functional recovery, and prevention of neuronal loss during neurodegenerative diseases are major objectives in cerebellar research. The highly organized anatomical structure of the cerebellum with numerous inputs/outputs, the complexity of cerebellar functions, and the large spectrum of cerebellar ataxias render therapies of cerebellar disorders highly challenging. There are currently several therapeutic approaches including motor rehabilitation, neuroprotective drugs, non-invasive cerebellar stimulation, molecularly based therapy targeting pathogenesis of the disease, and neurotransplantation. We discuss the goals and possible beneficial mechanisms of transplantation therapy for cerebellar damage and its limitations and factors determining outcome.

Exogenous neural stem cell transplantation for cerebral ischemia

Cerebral ischemic injury is the main manifestation of stroke, and its incidence in stroke patients is 70–80%. Although ischemic stroke can be treated with tissue-type plasminogen activator, its time window of effectiveness is narrow. Therefore, the incidence of paralysis, hypoesthesia, aphasia, dysphagia, and cognitive impairment caused by cerebral ischemia is high. Nerve tissue regeneration can promote the recovery of the aforementioned dysfunction. Neural stem cells can participate in the reconstruction of the damaged nervous system and promote the recovery of nervous function during self-repair of damaged brain tissue. Neural stem cell transplantation for ischemic stroke has been a hot topic for more than 10 years. This review discusses the treatment of ischemic stroke with neural stem cells, as well as the mechanisms of their involvement in stroke treatment.

Neurotransplantation therapy

Neurotransplantation may be a promising approach for therapy of cerebellar diseases characterized by a substantial loss of neurons. Neurotransplantation could rescue neurons from degeneration and maintain cerebellar reserve, facilitate cerebellar compensation, or help reconstruct damaged neural circuits by cell substitution. These mechanisms of action can be of varying importance according to the type of cerebellar disease. Neurotransplantation therapy in cerebellar ataxias is still at the stage of experimental studies. There is currently little knowledge regarding cerebellar patients. Nevertheless, data provided by experiments in animal models of cerebellar degeneration and both clinical studies and experiences in patients with other neurologic diseases enable us to suggest basic principles, expectations, limitations, and future directions of neurotransplantation therapy for cerebellar diseases.

Neural stem cell therapy for neurodegenerative disorders: The role of neurotrophic support

Neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and Huntington's disease currently affect tens of millions of people worldwide. Unfortunately, as the world's population ages, the incidence of many of these diseases will continue to rise and is expected to more than double by 2050. Despite significant research and a growing understanding of disease pathogenesis, only a handful of therapies are currently available and all of them provide only transient benefits. Thus, there is an urgent need to develop novel disease-modifying therapies to prevent the development or slow the progression of these debilitating disorders. A growing number of pre-clinical studies have suggested that transplantation of neural stem cells (NSCs) could offer a promising new therapeutic approach for neurodegeneration. While much of the initial excitement about this strategy focused on the use of NSCs to replace degenerating neurons, more recent studies have implicated NSC-mediated changes in neurotrophins as a major mechanism of therapeutic efficacy. In this mini-review we will discuss recent work that examines the ability of NSCs to provide trophic support to disease-effected neuronal populations and synapses in models of neurodegeneration. We will then also discuss some of key challenges that remain before NSC-based therapies for neurodegenerative diseases can be translated toward potential clinical testing.

Immunomodulatory effects of stem cells: Therapeutic option for neurodegenerative disorders

Stem cells have the capability of self-renewal and can differentiate into different cell types that might be used in regenerative medicine. Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS) currently lack effective treatments. Although stem cell therapy is still on the way from bench to bedside, we consider that it might provide new hope for patients suffering with neurodegenerative diseases. In this article, we will give an overview of recent studies on the potential therapeutic use of mesenchymal stem cells (MSCs), neural stem cells (NSCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and perinatal stem cells to neurodegenerative disorders and we will describe their immunomodulatory mechanisms of action in specific therapeutic modalities.

Generation of Neural Progenitor Spheres from Human Pluripotent Stem Cells in a Suspension Bioreactor

Conventional two-dimensional (2-D) culture systems cannot provide large numbers of human pluripotent stem cells (hPSCs) and their derivatives that are demanded for commercial and clinical applications in in vitro drug screening, disease modeling, and potentially cell therapy. The technologies that support three-dimensional (3-D) suspension culture, such as a stirred bioreactor, are generally considered as promising approaches to produce the required cells. Recently, suspension bioreactors have also been used to generate mini-brain-like structure from hPSCs for disease modeling, showing the important role of bioreactor in stem cell culture. This chapter describes a detailed culture protocol for neural commitment of hPSCs into neural progenitor cell (NPC) spheres using a spinner bioreactor. The basic steps to prepare hPSCs for bioreactor inoculation are illustrated from cell thawing to cell propagation. The method for generating NPCs from hPSCs in the spinner bioreactor along with the static control is then described. The protocol in this study can be applied to the generation of NPCs from hPSCs for further neural subtype specification, 3-D neural tissue development, or potential preclinical studies or clinical applications in neurological diseases.

Different Tissue-Derived Stem Cells: A Comparison of Neural Differentiation Capability

BACKGROUND

Stem cells are capable of self-renewal and differentiation into a wide range of cell types with multiple clinical and therapeutic applications. Stem cells are providing hope for many diseases that currently lack effective therapeutic methods, including strokes, Huntington's disease, Alzheimer's and Parkinson's disease. However, the paucity of suitable cell types for cell replacement therapy in patients suffering from neurological disorders has hampered the development of this promising therapeutic approach.

AIM

The innovative aspect of this study has been to evaluate the neural differentiation capability of different tissue-derived stem cells coming from different tissue sources such as bone marrow, umbilical cord blood, human endometrium and amniotic fluid, cultured under the same supplemented media neuro-transcription factor conditions, testing the expression of neural markers such as GFAP, Nestin and Neurofilaments using the immunofluorescence staining assay and some typical clusters of differentiation such as CD34, CD90, CD105 and CD133 by using the cytofluorimetric test assay.

RESULTS

Amniotic fluid derived stem cells showed a more primitive phenotype compared to the differentiating potential demonstrated by the other stem cell sources, representing a realistic possibility in the field of regenerative cell therapy suitable for neurodegenerative diseases.

The effect of Young's modulus on the neuronal differentiation of mouse embryonic stem cells

There is substantial evidence that cells produce a diverse response to changes in ECM stiffness depending on their identity. Our aim was to understand how stiffness impacts neuronal differentiation of embryonic stem cells (ESC's), and how this varies at three specific stages of the differentiation process. In this investigation, three effects of stiffness on cells were considered; attachment, expansion and phenotypic changes during differentiation. Stiffness was varied from 2 kPa to 18 kPa to finally 35 kPa. Attachment was found to decrease with increasing stiffness for both ESC's (with a 95% decrease on 35 kPa compared to 2 kPa) and neural precursors (with a 83% decrease on 35 kPa). The attachment of immature neurons was unaffected by stiffness. Expansion was independent of stiffness for all cell types, implying that the proliferation of cells during this differentiation process was independent of Young's modulus. Stiffness had no effect upon phenotypic changes during differentiation for mESC's and neural precursors. 2 kPa increased the proportion of cells that differentiated from immature into mature neurons. Taken together our findings imply that the impact of Young's modulus on attachment diminishes as neuronal cells become more mature. Conversely, the impact of Young's modulus on changes in phenotype increased as cells became more mature.

Stem cell transplantation for treating Parkinson's disease: Literature analysis based on the Web of Science

OBJECTIVE:

To identify global research trends of stem cell transplantation for treating Parkinson's disease using a bibliometric analysis of the Web of Science.

DATA RETRIEVAL:

We performed a bibliometric analysis of data retrievals for stem cell transplantation for treating Parkinson's disease from 2002 to 2011 using the Web of Science.

SELECTION CRITERIA:

Inclusion criteria: (a) peer-reviewed articles on stem cell transplantation for treating Parkinson's disease which were published and indexed in the Web of Science; (b) type of articles: original research articles, reviews, meeting abstracts, proceedings papers, book chapters, editorial material and news items; (c) year of publication: 2002–2011. Exclusion criteria: (a) articles that required manual searching or telephone access; (b) we excluded documents that were not published in the public domain; (c) we excluded a number of corrected papers from the total number of articles.

MAIN OUTCOME MEASURES:

(1) Type of literature; (2) annual publication output; (3) distribution according to journals; (4) distribution according to subject areas; (5) distribution according to country; (6) distribution according to institution; (7) comparison of countries that published the most papers on stem cell transplantation from different cell sources for treating Parkinson's disease; (8) comparison of institutions that published the most papers on stem cell transplantation from different cell sources for treating Parkinson's disease in the Web of Science from 2002 to 2011; (9) comparison of studies on stem cell transplantation from different cell sources for treating Parkinson's disease

RESULTS:

In total, 1 062 studies on stem cell transplantation for treating Parkinson's disease appeared in the Web of Science from 2002 to 2011, almost one third of which were from American authors and institutes. The number of studies on stem cell transplantation for treating Parkinson's disease had gradually increased over the past 10 years. Papers on stem cell transplantation for treating Parkinson's disease appeared in journals such as Stem Cells and Experimental Neurology. Although the United States published more articles addressing neural stem cell and embryonic stem cell transplantation for treating Parkinson's disease, China ranked first for articles published on bone marrow mesenchymal stem cell transplantation for treating Parkinson's disease.

CONCLUSION:

From our analysis of the literature and research trends, we found that stem cell transplantation for treating Parkinson's disease may offer further benefits in regenerative medicine.

Stem cell therapies in preclinical models of stroke associated with aging

Stroke has limited treatment options, demanding a vigorous search for new therapeutic strategies. Initial enthusiasm to stimulate restorative processes in the ischemic brain by means of cell-based therapies has meanwhile converted into a more balanced view recognizing impediments related to unfavorable environments that are in part related to aging processes. Since stroke afflicts mostly the elderly, it is highly desirable and clinically important to test the efficacy of cell therapies in aged brain microenvironments. Although widely believed to be refractory to regeneration, recent studies using both neural precursor cells and bone marrow-derived mesenchymal stem cells for stroke therapy suggest that the aged rat brain is not refractory to cell-based therapy, and that it also supports plasticity and remodeling. Yet, important differences exist in the aged compared with young brain, i.e., the accelerated progression of ischemic injury to brain infarction, the reduced rate of endogenous neurogenesis and the delayed initiation of neurological recovery. Pitfalls in the development of cell-based therapies may also be related to age-associated comorbidities, e.g., diabetes or hyperlipidemia, which may result in maladaptive or compromised brain remodeling, respectively. These age-related aspects should be carefully considered in the clinical translation of restorative therapies.

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.

Natural killer cell-activating receptor NKG2D mediates innate immune targeting of allogeneic neural progenitor cell grafts

Cell replacement therapy holds promise for a number of untreatable neurological or psychiatric diseases but the immunogenicity of cellular grafts remains controversial. Emerging stem cell and reprogramming technologies can be used to generate autologous grafts that minimize immunological concerns but autologous grafts may carry an underlying genetic vulnerability that reduces graft efficacy or survival. Healthy allogeneic grafts are an attractive and commercially scalable alternative if immunological variables can be controlled. Stem cells and immature neural progenitor cells (NPC) do not express major histocompatibility complex (MHC) antigens and can evade adaptive immune surveillance. Nevertheless, in an experimental murine model, allogeneic NPCs do not survive and differentiate as well as syngeneic grafts, even when traditional immunosuppressive treatments are used. In this study, we show that natural killer (NK) cells recognize the lack of self-MHC antigens on NPCs and pose a barrier to NPC transplantation. NK cells readily target both syngeneic and allogeneic NPC, and killing is modulated primarily by NK-inhibiting "self" class I MHC and NK-activating NKG2D-ligand expression. The absence of NKG2D signaling in NK cells significantly improves NPC-derived neuron survival and differentiation. These data illustrate the importance of innate immune mechanisms in graft outcome and the potential value of identifying and targeting NK cell-activating ligands that may be expressed by stem cell derived grafts.

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.

Primate adult brain cell autotransplantation produces behavioral and biological recovery in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonian St. Kitts monkeys

The potential for "replacement cells" to restore function in Parkinson's disease has been widely reported over the past 3 decades, rejuvenating the central nervous system rather than just relieving symptoms. Most such experiments have used fetal or embryonic sources that may induce immunological rejection and generate ethical concerns. Autologous sources, in which the cells to be implanted are derived from recipients' own cells after reprogramming to stem cells, direct genetic modifications, or epigenetic modifications in culture, could eliminate many of these problems. In a previous study on autologous brain cell transplantation, we demonstrated that adult monkey brain cells, obtained from cortical biopsies and kept in culture for 7 weeks, exhibited potential as a method of brain repair after low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) caused dopaminergic cell death. The present study exposed monkeys to higher MPTP doses to produce significant parkinsonism and behavioral impairments. Cerebral cortical cells were biopsied from the animals, held in culture for 7 weeks to create an autologous neural cell "ecosystem" and reimplanted bilaterally into the striatum of the same six donor monkeys. These cells expressed neuroectodermal and progenitor markers such as nestin, doublecortin, GFAP, neurofilament, and vimentin. Five to six months after reimplantation, histological analysis with the dye PKH67 and unbiased stereology showed that reimplanted cells survived, migrated bilaterally throughout the striatum, and seemed to exert a neurorestorative effect. More tyrosine hydroxylase-immunoreactive neurons and significant behavioral improvement followed reimplantation of cultured autologous neural cells as a result of unknown trophic factors released by the grafts.

Efficient and scalable expansion of human pluripotent stem cells under clinically compliant settings: a view in 2013

Human pluripotent stem cells (hPSCs) hold great promise for revolutionizing regenerative medicine for their potential applications in disease modeling, drug discovery, and cellular therapy. Many their applications require robust and scalable expansion of hPSCs, even under settings compliant to good clinical practices. Rapid evolution of media and substrates provided safer and more defined culture conditions for long-term expansion of undifferentiated hPSCs in either adhesion or suspension. With well-designed automatic systems or fully controlled bioreactors, production of a clinically relevant quantity of hPSCs could be achieved in the near future. The goal is to find a scalable, xeno-free, chemically defined, and economic culture system for clinical-grade expansion of hPSCs that complies the requirements of current good manufacturing practices. This review provides an updated overview of the current development and challenges on the way to accomplish this goal, including discussions on basic principles for bioprocess design, serum-free media, extracellular matric or synthesized substrate, microcarrier- or cell aggregate-based suspension culture, and scalability and practicality of equipment.

Interplay between human microglia and neural stem/progenitor cells in an allogeneic co-culture model

Experimental neural cell therapies, including donor neural stem/progenitor cells (NPCs) have been reported to offer beneficial effects on the recovery after an injury and to counteract inflammatory and degenerative processes in the central nervous system (CNS). The interplay between donor neural cells and the host CNS still to a large degree remains unclear, in particular in human allogeneic conditions. Here, we focused our studies on the interaction of human NPCs and microglia utilizing a co-culture model. In co-cultures, both NPCs and microglia showed increased survival and proliferation compared with mono-cultures. In the presence of microglia, a larger subpopulation of NPCs expressed the progenitor cell marker nestin, whereas a smaller group of NPCs expressed the neural markers polysialylated neural cell adhesion molecule, A2B5 and glial fibrillary acidic protein compared with NPC mono-cultures. Microglia thus hindered differentiation of NPCs. The presence of human NPCs increased microglial phagocytosis of latex beads. Furthermore, we observed that the expression of CD200 molecules on NPCs and the CD200 receptor protein on microglia was enhanced in co-cultures, whereas the release of transforming growth factor-β was increased suggesting anti-inflammatory features of the co-cultures. To conclude, the interplay between human allogeneic NPCs and microglia, significantly affected their respective proliferation and phenotype. Neural cell therapy including human donor NPCs may in addition to offering cell replacement, modulate host microglial phenotypes and functions to benefit neuroprotection and repair.

Concise review: Can stem cells be used to treat or model Alzheimer's disease?

Alzheimer's disease (AD) is the leading cause of age-related dementia, affecting over 5 million people in the U.S. alone. AD patients suffer from progressive neurodegeneration that gradually impairs their memory, ability to learn, and carry out daily activities. Unfortunately, current therapies for AD are largely palliative and several promising drug candidates have failed in recent clinical trials. There is therefore an urgent need to improve our understanding of AD pathogenesis, create innovative and predictive models, and develop new and effective therapies. In this review, we will discuss the potential of stem cells to aid in these challenging endeavors. Because of the widespread nature of AD pathology, cell-replacement strategies have been viewed as an incredibly challenging and unlikely treatment approach. Yet recent work shows that transplantation of neural stem cells (NSCs) can improve cognition, reduce neuronal loss, and enhance synaptic plasticity in animal models of AD. Interestingly, the mechanisms that mediate these effects appear to involve neuroprotection and trophic support rather than neuronal replacement. Stem cells may also offer a powerful new approach to model and study AD. Patient-derived induced pluripotent stem cells, for example, may help to advance our understanding of disease mechanisms. Likewise, studies of human embryonic and NSCs are helping to decipher the normal functions of AD-related genes; revealing intriguing roles in neural development.

Midbrain dopaminergic neurons: a review of the molecular circuitry that regulates their development

Dopaminergic (DA) neurons of the ventral midbrain (VM) play vital roles in the regulation of voluntary movement, emotion and reward. They are divided into the A8, A9 and A10 subgroups. The development of the A9 group of DA neurons is an area of intense investigation to aid the generation of these neurons from stem cell sources for cell transplantation approaches to Parkinson's disease (PD). This review discusses the molecular processes that are involved in the identity, specification, maturation, target innervation and survival of VM DA neurons during development. The complex molecular interactions of a number of genetic pathways are outlined, as well as recent advances in the mechanisms that regulate subset identity within the VM DA neuronal pool. A thorough understanding of the cellular and molecular mechanisms involved in the development of VM DA neurons will greatly facilitate the use of cell replacement therapy for the treatment of PD.

Human neural stem/progenitor cells derived from embryonic stem cells and fetal nervous system present differences in immunogenicity and immunomodulatory potentials in vitro

To develop cell therapies for damaged nervous tissue with human neural stem/progenitor cells (hNPCs), the risk of an immune response and graft rejection must be considered. There are conflicting results and lack of knowledge concerning the immunocompetence of hNPCs of different origin. Here, we studied the immunogenicity and immunomodulatory potentials of hNPCs cultured under equivalent conditions after derivation from human embryonic stem cells (hESC-NPCs) or human fetal spinal cord tissue (hfNPCs). The expression patterns of human leukocyte antigen, co-stimulatory and adhesion molecules in hESC-NPCs and hfNPCs were relatively similar and mostly not affected by inflammatory cytokines. Unstimulated hfNPCs secreted more transforming growth factor-β1 (TGF-β1) and β2 but similar level of interleukin (IL)-10 compared to hESC-NPCs. In contrast to hfNPCs, hESC-NPCs displayed 4-6 fold increases in TGF-β1, TGF-β2 and IL-10 under inflammatory conditions. Both hNPCs reduced the alloreaction between allogeneic peripheral blood mononuclear cells (PBMCs) and up-regulated CD4(+)CD25(+)forkhead box P3 (FOXP3)(+) T cells. However, hESC-NPCs but not hfNPCs dose-dependently triggered PBMC proliferation, which at least partly may be due to TGF-β signaling. To conclude, hESC-NPCs and hfNPCs displayed similarities but also significant differences in their immunocompetence and interaction with allogeneic PBMCs, differences may be crucial for the outcome of cell therapy.

Interaction of ES cell derived neural progenitor cells with natural killer cells and cytotoxic T cells

Knowing that human embryonic stem cells (HESC) can be derived into several different cells types render these cells very attractive to cure diseases. Unless these stem cells are originated from the patient itself, they will be isolated from a donor, who is genetically unrelated to the recipient. This situation will mimic an allogenic transplantation with an immune response against the transplanted cells. The immunogenicity of the HESC and the potential of NK and T-cells to target HESC and the lineage derived from HESC have to be addressed. Several different tests do exist to analyse NK cells and T-cells activity against HESC and its progenitor cells. In this chapter review the capacity of NK and T cells against neural progenitor derived from HESC, through a classical and a novel approach that combined the phenotype and also the functionality of the effector cells. In addition, we also demonstrate in the same test that we can determine the lysis of the progenitor cells by flow cytometry.

Neural tissue transplantation, repair, and rehabilitation

Transplants of cells and tissues to the central nervous system of adult mammals can, under appropriate conditions, survive, integrate, and function. In particular, the grafted cells can sustain functional recovery in animal models of a range of neurodegenerative conditions including genetic and idiopathic neurodegenerative diseases of adulthood and aging, ischemic stroke, and brain and spinal cord trauma. In a restricted subset of such conditions, cell transplantation has progressed to application in humans in early-stage clinical trials. At the present stage of play, there is clear evidence of clinical efficacy of fetal cell transplants in Parkinson disease (notwithstanding a range of technical difficulties still to be fully resolved), and preliminary claims of promising outcomes in several other severe neurodegenerative conditions, including Huntington disease and stroke. Moreover, the experimental literature is increasingly suggesting that the experience and training of the graft recipient materially affects the functional outcome. For example, environmental enrichment, behavioral activity, and specific training can enhance the recovery process to maximize functional recovery. There are even circumstances where the grafted cells have been demonstrated to restore the neural substrate for new learning. Consequently, it is not sufficient to replace lost cells anatomically; rather, for the grafts to be effective, they need to be integrated functionally into the host circuitry, and the host animal requires training and rehabilitation to maximize function of the reconstructed graft-host circuitry. Such observations require reconsideration of the design of the next generation of clinical trials and subsequent service delivery, to include physiotherapists, cognitive therapists, and rehabilitation experts as core members of the transplant team, along with the neurologists and neurosurgeons that have conventionally led the field.

Transplanting intact donor tissue enhances dopamine cell survival and the predictability of motor improvements in a rat model of Parkinson's disease

Primary cell transplantation is currently the gold standard for cell replacement in Parkinson's disease. However, the number of donors needed to treat a single patient is high, and the functional outcome is sometimes variable. The present work explores the possibility of enhancing the viability and/or functionality of small amounts of ventral mesencephalic (VM) donor tissue by reducing its perturbation during preparation and implantation. Briefly, unilaterally lesioned rats received either: (1) an intact piece of half an embryonic day 13 (E13) rat VM; (2) dissociated cells from half an E13 rat VM; or (3) no transplant. D-amphetamine- induced rotations revealed that animals receiving pieces of VM tissue or dissociated cells showed significant improvement in ipsilateral rotation 4 weeks post transplantation. By 6 weeks post transplantation, animals receiving pieces of VM tissue showed a trend for further improvement, while those receiving dissociated cells remained at their 4 week scores. Postmortem cell counts showed that the number of dopaminergic neurons in dissociated cell transplants was significantly lower than that surviving in transplants of intact tissue. When assessing the correlation between the number of dopamine cells in each transplant, and the improvement in rotation bias in experimental animals, it was shown that transplants of whole pieces of VM tissue offered greater predictability of graft function based on their dopamine cell content. Such results suggest that maintaining the integrity of VM tissue during implantation improves dopamine cell content, and that the dopamine cell content of whole tissue grafts offers a more predictable outcome of graft function in an animal model of Parkinson's disease.

Science to practice: genetic engineering meets cell tracking--a promising approach for cell-based therapies?

Cell-based therapies are gaining increasing importance and have been evaluated in many settings, including cancer, Parkinson disease, myocardial repair, stroke, and diabetes. In this context, it is of major importance that the cells are implanted into an optimal tissue environment and, correspondingly, that they reach the diseased region. Intravenous cell injection often is the route of choice, particularly if the cells are expected to circulate in the blood for longer periods of time and are able to actively migrate to the diseased tissue. Unfortunately, often only a small percentage of intravenously injected cells reach the target area. Higher accumulation can be achieved if the cells are injected into an artery that feeds the diseased area. However, in this case, fast blood velocities and substantial sheer stress make it difficult for the cells to adhere. In the study by Gorelik and colleagues (1), genetic engineering was used to overcome this limitation. Glial precursor cells were transiently transfected with very late antigen-4 (VLA-4) binding to vascular cell adhesion molecule-1 (VCAM-1), which is upregulated in inflamed endothelial cells. After labeling these cells with superparamagnetic iron oxide (SPIO) containing rhodamine, significantly increased binding to inflamed brain endothelial cells was shown and their homogeneous distribution over the inflamed brain tissue was convincingly demonstrated with magnetic resonance (MR) imaging and histologic examination. The authors concluded that transient transfection of SPIO-labeled cells with VLA-4 in combination with their arterial injection and the use of MR imaging monitoring may be an elegant way to increase the efficacy of cell-based treatments of inflammatory brain diseases.

The co-transduction of Nurr1 and Brn4 genes induces the differentiation of neural stem cells into dopaminergic neurons

Fetal brain tissue can be used in cell replacement therapy for PD (Parkinson's disease), but there is a poor donor supply of this tissue. NSCs (neural stem cells) may overcome this problem as they can be isolated and expanded in vitro. However, the usage of NSCs is limited because the differentiation of NSCs into specific dopaminergic neurons has proven difficult. In the present study, we investigated the effect of Nurr1 (nuclear receptor related factor 1), a transcription factor specific for the development and maintenance of the midbrain dopaminergic neurons on inducing the differentiation of NSCs into TH (tyrosine hydroxylase) immunoreactive dopaminergic neurons. Nonetheless, these cells exhibited an immature neuronal morphology with small cell bodies and short neurite processes, and they seldom expressed DAT (dopamine transporter), a late marker of mature dopaminergic neurons. However, forced co-expression of Nurr1 with Brn4, a member of the POU domain family of transcription factors, caused immature Nurr1-induced dopaminergic neurons to differentiate into morphologically and phenotypically more mature neurons. Thus the enriched generation of mature dopaminergic neurons by forced expression of Nurr1 with Brn4 may be of future importance in NSC-based cell replacement therapy for PD.

Prolonged membrane depolarization enhances midbrain dopamine neuron differentiation via epigenetic histone modifications

Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiological and clinical implications of this neuronal subtype. We show that prolonged membrane depolarization induced by KCl treatment promotes DA neuron differentiation from neural precursor cells (NPCs) derived from embryonic ventral midbrain (VM). Interestingly, the depolarization-induced increase of DA neuron yields was not abolished by L-type calcium channel blockers, along with no depolarization-mediated change of intracellular calcium level in the VM-derived NPCs (VM-NPCs), suggesting that the depolarization effect is due to a calcium-independent mechanism. Experiments with labeled DA neuron progenitors indicate that membrane depolarization acts at the differentiation fate determination stage and promotes the expression of DA phenotype genes (tyrosine hydroxylase [TH] and DA transporter [DAT]). Recruitment of Nurr1, a transcription factor crucial for midbrain DA neuron development, to the promoter of TH gene was enhanced by depolarization, along with increases of histone 3 acetylation (H3Ac) and trimethylation of histone3 on lysine 4 (H3K4m3), and decreases of H3K9m3 and H3K27m3 in the consensus Nurr1 binding regions of TH promoter. Depolarization stimuli on differentiating VM-NPCs also induced dissociation of methyl CpG binding protein 2 and related repressor complex molecules (repressor element-1 silencing transcription factor corepressor and histone deacetylase 1) from the CpG sites of TH and DAT promoters. Based on these findings, we suggest that membrane depolarization promotes DA neuron differentiation by opening chromatin structures surrounding DA phenotype genes and inhibiting the binding of corepressors, thus allowing transcriptional activators such as Nurr1 to access DA neuron differentiation gene promoter regions.

In vitro maturation of dopaminergic neurons derived from mouse embryonic stem cells: implications for transplantation

The obvious motor symptoms of Parkinson's disease result from a loss of dopaminergic neurons from the substantia nigra. Embryonic stem cell-derived neural progenitor or precursor cells, adult neurons and fetal midbrain tissue have all been used to replace dying dopaminergic neurons. Transplanted cell survival is compromised by factors relating to the new environment, for example; hypoxia, mechanical trauma and excitatory amino acid toxicity. In this study we investigate, using live-cell fluorescence Ca²⁺ and Cl⁻ imaging, the functional properties of catecholaminergic neurons as they mature. We also investigate whether GABA has the capacity to act as a neurotoxin early in the development of these neurons. From day 13 to day 21 of differentiation [Cl⁻]_i progressively dropped in tyrosine hydroxylase positive (TH⁺) neurons from 56.0 (95% confidence interval, 55.1, 56.9) mM to 6.9 (6.8, 7.1) mM. At days 13 and 15 TH⁺ neurons responded to GABA (30 µM) with reductions in intracellular Cl⁻ ([Cl⁻]_i); from day 21 the majority of neurons responded to GABA (30 µM) with elevations of [Cl⁻]_i. As [Cl⁻]_i reduced, the ability of GABA (30 µM) to elevate intracellular Ca²⁺ ([Ca²⁺]_i) did also. At day 13 of differentiation a three hour exposure to GABA (30 µM) or L-glutamate (30 µM) increased the number of midbrain dopaminergic (TH⁺ and Pitx3⁺) neurons labeled with the membrane-impermeable nuclear dye TOPRO-3. By day 23 cultures were resistant to the effects of both GABA and L-glutamate. We believe that neuronal susceptibility to amino acid excitotoxicity is dependent upon neuronal maturity, and this should be considered when isolating cells for transplantation studies.

Co-transplantation of macaque autologous Schwann cells and human embryonic nerve stem cells in treatment of macaque Parkinson's disease

OBJECTIVE

To investigate the therapeutic effects of co-transplantation with Schwann cells (SCs) and human embryonic nerve stem cells (NSCs) on macaque Parkinson's disease (PD).

METHODS

Macaque autologous SCs and human embryonic NSCs were adopted for the treatment of macaque PD.

RESULTS

Six months after transplantation, positron emission computerized tomography showed that (18)F-FP-β-CIT was significantly concentrated in the injured striatum in the co-transplanted group. Immunohistochemical staining of transplanted area tissue showed migration of tyroxine hydroxylase positive cells from the transplant area to the surrounding area was significantly increased in the co-transplanted group.

CONCLUSIONS

Co-transplantation of SCs and NSCs could effectively cure PD in macaques. SCs harvested from the autologous peripheral nerves can avoid rejection and the ethics problems, so it is expected to be applied clinically.

Efficient generation of A9 midbrain dopaminergic neurons by lentiviral delivery of LMX1A in human embryonic stem cells and induced pluripotent stem cells

Human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC) offer great hope for in vitro modeling of Parkinson's disease (PD), as well as for designing cell-replacement therapies. To realize these opportunities, there is an urgent need to develop efficient protocols for the directed differentiation of hESC/iPSC into dopamine (DA) neurons with the specific characteristics of the cell population lost to PD, i.e., A9-subtype ventral midbrain DA neurons. Here we use lentiviral vectors to drive the expression of LMX1A, which encodes a transcription factor critical for ventral midbrain identity, specifically in neural progenitor cells. We show that clonal lines of hESC engineered to contain one or two copies of this lentiviral vector retain long-term self-renewing ability and pluripotent differentiation capacity. Greater than 60% of all neurons generated from LMX1A-engineered hESC were ventral midbrain DA neurons of the A9 subtype, compared with ∼10% in green fluorescent protein-engineered controls, as judged by specific marker expression and functional analyses. Moreover, DA neuron precursors differentiated from LMX1A-engineered hESC were able to survive and differentiate when grafted into the brain of adult mice. Finally, we provide evidence that LMX1A overexpression similarly increases the yield of DA neuron differentiation from human iPSC. Taken together, our data show that stable genetic engineering of hESC/iPSC with lentiviral vectors driving controlled expression of LMX1A is an efficient way to generate enriched populations of human A9-subtype ventral midbrain DA neurons, which should prove useful for modeling PD and may be helpful for designing future cell-replacement strategies.

The colayer method as an efficient way to genetically modify mesencephalic progenitor cells transplanted into 6-OHDA rat model of Parkinson's disease

Exogenous cell replacement represents a potent treatment option for Parkinson's disease. However, the low survival rate of transplanted dopaminergic neurons (DA) calls for methodological improvements. Here we evaluated a method to combine transient genetic modification of neuronal progenitor cells with an optimized cell culture protocol prior to intrastriatal transplantation into 6-hydroxydopamine (6-OHDA) unilateral lesioned rats. Plasmid-based delivery of brain-derived neurotrophic factor (BDNF) increases the number of DA neurons, identified by tyrosine hydroxylase immunoreactivity (TH-ir), by 25% in vitro, compared to enhanced green fluorescence protein (EGFP)-transfected controls. However, the nucleofection itself, especially the cell detachment and reseeding procedure, decreases the TH-ir neuron number to 40% compared with nontransfected control cultures. To circumvent this drawback we established the colayer method, which contains a mix of nucleofected cells reseeded on top of an adherent sister culture in a ratio 1:3. In this setup TH-ir neuron number remains high and could be further increased by 25% after BDNF transfection. Comparison of both cell culture procedures (standard and colayer) after intrastriatal transplantation revealed a similar DA neuron survival as seen in vitro. Two weeks after grafting TH-ir neuron number was strongly reduced in animals receiving the standard EGFP-transfected cells (271 ± 62) compared to 1,723 ± 199 TH-ir neurons in the colayer group. In contrast to the in vitro results, no differences in the number of grafted TH-ir neurons were observed between BDNF, EGFP, and nontransfected colayer groups, neither 2 nor 13 weeks after transplantation. Likewise, amphetamine and apomorphine-induced rotational behavior improved similarly over time in all groups. Nevertheless, the colayer protocol provides an efficient way for neurotrophic factor release by transplanted progenitor cells and will help to study the effects of candidate factors on survival and integration of transplanted DA neurons.

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.

To be or not to be accepted: the role of immunogenicity of neural stem cells following transplantation into the brain in animal and human studies

Grafting of neural stem cells into the mammalian central nervous system (CNS) has been performed for some decades now, both in basic research and clinical applications for neurological disorders such as Parkinson's and Huntington's disease, stroke, and spinal cord injuries. Albeit the "proof of principle" status that neural grafts can reinstate functional deficits and rebuild damaged neuronal circuitries, many critical scientific questions are still open. Among them are the manifold immunological aspects that are encountered during the graft-host interaction in vivo. For example, the experience with allografted cells in absence of immunosuppressant drugs has raised serious doubts about an immunological privileged site within the CNS as compared to other engraftment sites in the body. This review discusses recent experimental and clinical findings demonstrating that neural stem cells have unique characteristics that help them modulate the host immunological defense, but, under some conditions, may still trigger a rejection process. Implications of these findings on neural grafting and potential new therapeutic applications are discussed.

A simple method for large-scale generation of dopamine neurons from human embryonic stem cells

Dopamine (DA) neurons derived from human embryonic stem cells (hESCs) are potentially valuable in drug screening and as a possible source of donor tissue for transplantation in Parkinson's disease. However, existing culture protocols that promote the differentiation of DA neurons from hESCs are complex, involving multiple steps and having unreliable results between cultures. Here we report a simple and highly reproducible culture protocol that induces expandable DA neuron progenitors from hESCs in attached cultures. We found that the hESC-derived neuronal progenitors retain their full capacity to generate DA neurons after repeated passaging in the presence of basic fibroblast growth factor (bFGF) and medium conditioned with PA6 stromal cells. Using immunocytochemistry and RT-PCR, we found that the differentiated DA neurons exhibit a midbrain phenotype and express, e.g., Aldh1a, Ptx3, Nurr1, and Lmx1a. Using HPLC, we monitored their production of DA. We then demonstrated that the expanded progenitors are possible to cryopreserve without loosing the dopaminergic phenotype. With our protocol, we obtained large and homogeneous populations of dopaminergic progenitors and neurons. We conclude that our protocol can be used to generate human DA neurons suitable for the study of disease mechanisms, toxicology, drug screening, and intracerebral transplantation.

Nucleotides affect neurogenesis and dopaminergic differentiation of mouse fetal midbrain-derived neural precursor cells

The fetal midbrain is a preferred source for isolating and producing dopaminergic neurons for subsequent grafting and replacement of damaged or lost dopaminergic midbrain neurons. We analysed the potential of a variety of nucleotides and of adenosine to support dopaminergic neuron formation from primary mouse fetal midbrain-derived cells, harvested at E10.5 and at E13.5 and subjected to adherent cell culture. In contrast to cells derived at E13.5, cells derived at E10.5 have the potential to produce dopaminergic neurons in culture. These neurons express tyrosine hydroxylase and the dopamine transporter. The fetal ventral midbrain contained mRNA encoding almost all P2X and P2Y receptors, all adenosine receptors as well as the ectonucleotidases nucleoside triphosphate diphosphohydrolase 2 and tissue nonspecific alkaline phosphatase. Essentially, all components of the purinergic signalling pathway were also expressed by the cultured cells. ATP, ADPβS, 2MeSATP, 2ClATP and adenosine increased neuron formation. There was, however, no preference for the formation of dopaminergic neurons-with the exception of 2ClATP that increased the relative contribution of tyrosine hydroxylase-positive neurons. In cells isolated at E13.5 UTP promoted neuron survival but ADPβS and ATPγS essentially eliminated neurons. These data showed that the outcome of nucleotide application was different even though cells isolated at E10.5 and E13.5 expressed very similar receptor mRNA profiles. They suggest that purinergic agonists carry potential for stimulating neurogenesis and enriching the contribution of dopaminergic neurons in vitro. Nucleotide receptor agonists may be of value for contributing to the formation and survival of dopaminergic neurons in vivo.

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

Effective dopamine (DA) neuron differentiation from neural precursor cells (NPCs) is prerequisite for precursor/stem cell-based therapy of Parkinson's disease (PD). Nurr1, an orphan nuclear receptor, has been reported as a transcription factor that can drive DA neuron differentiation from non-dopaminergic NPCs in vitro. However, Nurr1 alone neither induces full neuronal maturation nor expression of proteins found specifically in midbrain DA neurons. In addition, Nurr1 expression is inefficient in inducing DA phenotype expression in NPCs derived from certain species such as mouse and human. We show here that Foxa2, a forkhead transcription factor whose role in midbrain DA neuron development was recently revealed, synergistically cooperates with Nurr1 to induce DA phenotype acquisition, midbrain-specific gene expression, and neuronal maturation. Thus, the combinatorial expression of Nurr1 and Foxa2 in NPCs efficiently yielded fully differentiated nigral (A9)-type midbrain neurons with clearly detectable DA neuronal activities. The effects of Foxa2 in DA neuron generation were observed regardless of the brain regions or species from which NPCs were derived. Furthermore, DA neurons generated by ectopic Foxa2 expression were more resistant to toxins. Importantly, Foxa2 expression resulted in a rapid cell cycle exit and reduced cell proliferation. Consistently, transplantation of NPCs transduced with Nurr1 and Foxa2 generated grafts enriched with midbrain-type DA neurons but reduced number of proliferating cells, and significantly reversed motor deficits in a rat PD model. Our findings can be applied to ongoing attempts to develop an efficient and safe precursor/stem cell-based therapy for PD.

Nanotechnology for treatment of stroke and spinal cord injury

The use of nanotechnology in cell therapy and tissue engineering offers promising future perspectives for brain and spinal cord injury treatment. Stem cells have been shown to selectively target injured brain and spinal cord tissue and improve functional recovery. To allow cell detection, superparamagnetic iron-oxide nanoparticles can be used to label transplanted cells. MRI is then a suitable method for the in vivo tracking of grafted cells in the host organism. CNS, and particularly spinal cord, injury is accompanied by tissue damage and the formation of physical and biochemical barriers that prevent axons from regenerating. One aspect of nanomedicine is the development of biologically compatible nanofiber scaffolds that mimic the structure of the extracellular matrix and can serve as a permissive bridge for axonal regeneration or as a drug-delivery system. The incorporation of biologically active epitopes and/or the utilization of these scaffolds as stem cell carriers may further enhance their therapeutic efficacy.

In vitro and in vivo enhanced generation of human A9 dopamine neurons from neural stem cells by Bcl-XL

Human neural stem cells derived from the ventral mesencephalon (VM) are powerful research tools and candidates for cell therapies in Parkinson disease. Previous studies with VM dopaminergic neuron (DAn) precursors indicated poor growth potential and unstable phenotypical properties. Using the model cell line hVM1 (human ventral mesencephalic neural stem cell line 1; a new human fetal VM stem cell line), we have found that Bcl-X(L) enhances the generation of DAn from VM human neural stem cells. Mechanistically, Bcl-X(L) not only exerts the expected antiapoptotic effect but also induces proneural (NGN2 and NEUROD1) and dopamine-related transcription factors, resulting in a high yield of DAn with the correct phenotype of substantia nigra pars compacta (SNpc). The expression of key genes directly involved in VM/SNpc dopaminergic patterning, differentiation, and maturation (EN1, LMX1B, PITX3, NURR1, VMAT2, GIRK2, and dopamine transporter) is thus enhanced by Bcl-X(L). These effects on neurogenesis occur in parallel to a decrease in glia generation. These in vitro Bcl-X(L) effects are paralleled in vivo, after transplantation in hemiparkinsonian rats, where hVM1-Bcl-X(L) cells survive, integrate, and differentiate into DAn, alleviating behavioral motor asymmetry. Bcl-X(L) then allows for human fetal VM stem cells to stably generate mature SNpc DAn both in vitro and in vivo and is thus proposed as a helpful factor for the development of cell therapies for neurodegenerative conditions, Parkinson disease in particular.

Neuroprotective effects of laminin and its KDI domain

Successful treatment of neurodegenerative diseases and CNS trauma are the most intractable problems in modern medicine. Numerous reports have shown the strong role that laminins have on the survival, regeneration and development of various types of cells, including neural cells. It would be desirable to take advantage of laminin activities for therapeutic purposes. However, there are at least ten laminin variants and the trimeric molecules are of the order of 800,000 molecular weight. Furthermore, human laminins are not available in quantity. Therefore, we and others have taken the approach of determining which domains of the laminin molecules are functional in the CNS, and whether short peptides from these regions exhibit biological activities with the intent of testing their potential for therapeutic use. Understanding the role of laminins and their small biologically active peptide domains, such as the KDI (lysine–aspartic acid–isoleucine) peptide from γ1 laminin, in neuronal development, CNS trauma (spinal cord injury and stroke) and neurodegenerative disorders (amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease) may help to develop clinically applicable methods to treat the presently untreatable CNS diseases and trauma even in the near future.

Musings on genome medicine: is there hope for ethical and safe stem cell therapeutics?

Although most stem cell therapy has been non-controversial, therapy based on pluripotent stem cells has raised both ethical and safety concerns. Despite these concerns, the use of cells derived from pluripotent stem cells has recently been approved for clinical trials. We suggest that recent advances in the field have provided avenues to develop pluripotent cells that raise far fewer ethical concerns. Moreover, advances in cell sorting, gene modification and screening have allowed the development of safer therapeutic approaches. Continued advances in this rapidly evolving field are likely to allow therapy to be delivered in a safe and effective manner without socially divisive ethical controversy in the not-so-distant future.

Efficient production of mesencephalic dopamine neurons by Lmx1a expression in embryonic stem cells

Signaling factors involved in CNS development have been used to control the differentiation of embryonic stem cells (ESCs) into mesencephalic dopamine (mesDA) neurons, but tend to generate a limited yield of desired cell type. Here we show that forced expression of Lmx1a, a transcription factor functioning as a determinant of mesDA neurons during embryogenesis, effectively can promote the generation of mesDA neurons from mouse and human ESCs. Under permissive culture conditions, 75%-95% of mouse ESC-derived neurons express molecular and physiological properties characteristic of bona fide mesDA neurons. Similar to primary mesDA neurons, these cells integrate and innervate the striatum of 6-hydroxy dopamine lesioned neonatal rats. Thus, the enriched generation of functional mesDA neurons by forced expression of Lmx1a may be of future importance in cell replacement therapy of Parkinson disease.