Assessment of stromal-derived inducing activity in the generation of dopaminergic neurons from human embryonic stem cells

Proneurogenic actions of follicle-stimulating hormone on neurospheres derived from ovarian cortical cells in vitro

BACKGROUND

Neural stem and progenitor cells (NSPCs) from extra-neural origin represent a valuable tool for autologous cell therapy and research in neurogenesis. Identification of proneurogenic biomolecules on NSPCs would improve the success of cell therapies for neurodegenerative diseases. Preliminary data suggested that follicle-stimulating hormone (FSH) might act in this fashion. This study was aimed to elucidate whether FSH promotes development, self-renewal, and is proneurogenic on neurospheres (NS) derived from sheep ovarian cortical cells (OCCs). Two culture strategies were carried out: (a) long-term, 21-days NS culture (control vs. FSH group) with NS morphometric evaluation, gene expression analyses of stemness and lineage markers, and immunolocalization of NSPCs antigens; (b) NS assay to demonstrate FSH actions on self-renewal and differentiation capacity of NS cultured with one of three defined media: M1: positive control with EGF/FGF2; M2: control; and M3: M2 supplemented with FSH.

RESULTS

In long-term cultures, FSH increased NS diameters with respect to control group (302.90 ± 25.20 μm vs. 183.20 ± 7.63 on day 9, respectively), upregulated nestin (days 15/21), Sox2 (day 21) and Pax6 (days 15/21) and increased the percentages of cells immunolocalizing these proteins. During NS assays, FSH stimulated NSCPs proliferation, and self-renewal, increasing NS diameters during the two expansion periods and the expression of the neuron precursor transcript DCX during the second one. In the FSH-group there were more frequent cell-bridges among neighbouring NS.

CONCLUSIONS

FSH is a proneurogenic hormone that promotes OCC-NSPCs self-renewal and NS development. Future studies will be necessary to support the proneurogenic actions of FSH and its potential use in basic and applied research related to cell therapy.

Recent approaches in regenerative medicine in the fight against neurodegenerative disease

Neurodegenerative diseases arise due to slow and gradual loss of structure and/or function of neurons and glial cells and cause different degrees of loss of cognition abilities and sensation. The little success in developing effective treatments imposes a high and regressive economic impact on society, patients and their families. In recent years, regenerative medicine has provided a great opportunity to research new innovative strategies with strong potential to treatleva these diseases. These effects are due to the ability of suitable cells and biomaterials to regenerate damaged nerves with differentiated cells, creating an appropriate environment for recovering or preserving existing healthy neurons and glial cells from destruction and damage. Ultimately, a better understanding and thus a further investigation of stem cell technology, tissue engineering, gene therapy, and exosomes allows progress towards practical and effective treatments for neurodegenerative diseases. Therefore, in this review, advances currently being developed in regenerative medicine using animal models and human clinical trials in neurological disorders are summarized.

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

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

Introduction to stem cells

Stem cells have self-renewal capability and can proliferate and differentiate into a variety of functionally active cells that can serve in various tissues and organs. This review discusses the history, definition, and classification of stem cells. Human pluripotent stem cells (hPSCs) mainly include embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs). Embryonic stem cells are derived from the inner cell mass of the embryo. Induced pluripotent stem cells are derived from reprogramming somatic cells. Pluripotent stem cells have the ability to differentiate into cells derived from all three germ layers (endoderm, mesoderm, and ectoderm). Adult stem cells can be multipotent or unipotent and can produce tissue-specific terminally differentiated cells. Stem cells can be used in cell therapy to replace and regenerate damaged tissues or organs.

Development, wiring and function of dopamine neuron subtypes

The midbrain dopamine (mDA) system is composed of molecularly and functionally distinct neuron subtypes that mediate specific behaviours and are linked to various brain diseases. Considerable progress has been made in identifying mDA neuron subtypes, and recent work has begun to unveil how these neuronal subtypes develop and organize into functional brain structures. This progress is important for further understanding the disparate physiological functions of mDA neurons and their selective vulnerability in disease, and will ultimately accelerate therapy development. This Review discusses recent advances in our understanding of molecularly defined mDA neuron subtypes and their circuits, ranging from early developmental events, such as neuron migration and axon guidance, to their wiring and function, and future implications for therapeutic strategies.

Gradient biomimetic platforms for neurogenesis studies

There is a need for the development of new cellular therapies for the treatment of many diseases, with the central nervous system (CNS) currently an area of specific focus. Due to the complexity and delicacy of its biology, there is currently a limited understanding of neurogenesis and consequently a lack of reliable test platforms, resulting in several CNS based diseases having no cure. The ability to differentiate pluripotent stem cells into specific neuronal sub-types may enable scalable manufacture for clinical therapies, with a focus also on the purity and quality of the cell population. This focus is targeted towards an urgent need for the diseases that currently have no cure, e.g. Parkinson's disease. Differentiation studies carried out using traditional 2D cell culture techniques are designed using biological signals and morphogens known to be important for neurogenesis in vivo. However, such studies are limited by their simplistic nature, including a general poor efficiency and reproducibility, high reagent costs and an inability to scale-up the process to a manufacture-wide design for clinical use. Biomimetic approaches to recapitulate a more in vivo-like environment are progressing rapidly within this field, with application of bio(chemical) gradients presented both as 2D surfaces and within a 3D volume. This review focusses on the development and application of these advanced extracellular environments particularly for the neural niche. We emphasise the progress that has been made specifically in the area of stem cell derived neuronal differentiation. Increasing developments in biomaterial approaches to manufacture stem cells will enable the improvement of differentiation protocols, enhancing the efficiency and repeatability of the process with a move towards up-scaling. Progress in this area brings these techniques closer to enabling the development of therapies for the clinic.

A Step-by-Step Refined Strategy for Highly Efficient Generation of Neural Progenitors and Motor Neurons from Human Pluripotent Stem Cells

Limited access to human neurons, especially motor neurons (MNs), was a major challenge for studying neurobiology and neurological diseases. Human pluripotent stem cells (hPSCs) could be induced as neural progenitor cells (NPCs) and further multiple neural subtypes, which provide excellent cellular sources for studying neural development, cell therapy, disease modeling and drug screening. It is thus important to establish robust and highly efficient methods of neural differentiation. Enormous efforts have been dedicated to dissecting key signalings during neural commitment and accordingly establishing reliable differentiation protocols. In this study, we refined a step-by-step strategy for rapid differentiation of hPSCs towards NPCs within merely 18 days, combining the adherent and neurosphere-floating methods, as well as highly efficient generation (~90%) of MNs from NPCs by introducing refined sets of transcription factors for around 21 days. This strategy made use of, and compared, retinoic acid (RA) induction and dual-SMAD pathway inhibition, respectively, for neural induction. Both methods could give rise to highly efficient and complete generation of preservable NPCs, but with different regional identities. Given that the generated NPCs can be differentiated into the majority of excitatory and inhibitory neurons, but hardly MNs, we thus further differentiate NPCs towards MNs by overexpressing refined sets of transcription factors, especially by adding human SOX11, whilst improving a series of differentiation conditions to yield mature MNs for good modeling of motor neuron diseases. We thus refined a detailed step-by-step strategy for inducing hPSCs towards long-term preservable NPCs, and further specified MNs based on the NPC platform.

Replacing what's lost: a new era of stem cell therapy for Parkinson's disease

Background

Stem cells hold tremendous promise for regenerative medicine because they can be expanded infinitely, giving rise to large numbers of differentiated cells required for transplantation. Stem cells can be derived from fetal sources, embryonic origins (embryonic stem cells or ESCs) or reprogrammed from adult cell types (induced pluripotent stem cells or iPSCs). One unique property of stem cells is their ability to be directed towards specific cell types of clinical interest, and can mature into functional cell types in vivo. While transplantations of fetal or ESC-derived tissues are known to illicit a host immunogenic response, autologous transplantations using cell types derived from one’s own iPSCs eliminate risks of tissue rejection and reduce the need for immunosuppressants. However, even with these benefits, cell therapy comes with significant hurdles that researchers are starting to overcome. In this review, we will discuss the various steps to ensure safety, efficacy and clinical practicality of cell replacement therapy in neurodegenerative diseases, in particular, Parkinson’s disease.

Main body

Parkinson’s disease (PD) results from a loss of dopaminergic neurons from the substantia nigra and is an ideal target for cell replacement therapy. Early trials using fetal midbrain material in the late 1980s have resulted in long term benefit for some patients, but there were multiple shortcomings including the non-standardization and quality control of the transplanted fetal material, and graft-induced dyskinesia that some patients experience as a result. On the other hand, pluripotent stem cells such as ESCs and iPSCs serve as an attractive source of cells because they can be indefinitely cultured and is an unlimited source of cells. Stem cell technologies and our understanding of the developmental potential of ESCs and iPSCs have deepened in recent years and a clinical trial for iPSC-derived dopaminergic cells is currently undergoing for PD patients in Japan. In this focused review, we will first provide a historical aspect of cell therapies in PD, and then discuss the various challenges pertaining to the safety and efficacy of stem cell-based cell transplantations, and how these hurdles were eventually overcome.

Conclusion

With the maturity of the iPSC technology, cell transplantation appears to be a safe and effective therapy. Grafts in non-human primates survive and remain functional for more than 2 years after transplantation, with no signs of tumorigenesis, indicating safety and efficacy of the treatment. However, immunosuppressants are still required because of the lack of “universal stem cells” that would not evoke an immune response. The results of ongoing and upcoming trials by a global consortium known as GForce-PD would be highly anticipated because the success of these trials would open up possibilities for using cell therapy for the treatment of PD and other degenerative diseases.

Top-Down Inhibition (TDi) and Baseline Activation (BLa): Controlling Signal Transduction When Endogenous Cytokines are Ruining Your Differentiation

In the 20 years since the first human pluripotent stem cell (hPSC) lines were established, there have been a plethora of protocols developed that allow us to generate a wide range of human cell types in vitro. Efforts to achieve a greater degree of specificity and efficiency in generating desired cell types have resulted in increasingly complex approaches. The magnitude and timing of signals has become key, and the concept of a "fully defined" system is a forever sought-after goal with shifting goalposts. This overview discusses two related approaches that can be used to deliver a tightly regulated, intermediate-strength signal, and which can also manage the impact of endogenous signaling variation and enable a switch away from bovine serum albumin-containing medium to a better-defined system without suffering a subsequent loss of robustness or efficiency. The approaches, referred to as top-down inhibition and baseline activation, were developed to deliver intermediate levels of BMP and WNT signaling during neural crest induction from hPSC, but could be applied to a variety of other signals and differentiation systems. © 2019 by John Wiley & Sons, Inc.

Spheroids Spontaneously Generated In Vitro from Sheep Ovarian Cortical Cells Contain Integrating Cells That Exhibit Hallmarks of Neural Stem/Progenitor Cells

Cell spheroids are inducible or spontaneously generated cell aggregates produced in vitro that can provide a valuable model for developmental biology, stem cell biology, and cancer therapy research. This investigation aimed to define the cellular identity of spheroids spontaneously generated in vitro from sheep ovarian cortical cells cultured under specific serum-free conditions. Spheroids were characterized during 21 days of culture by morphometric evaluation, detection of alkaline phosphatase (AP) activity, gene expression analyses of stemness transcription factors and several lineage markers, immunolocalization analyses, as well as assessment of self-renewal and differentiation potential. Cell aggregation, evidenced from day 3 of culture onward, resulted in efficient generation of 65-75 spheroids for every 500,000 cells seeded. The spheroids reached maximum diameter (187 ± 15.9 μm) during the second week of culture and exhibited AP activity. Sox2, Oct4, and Nanog were expressed throughout the culture period, with upregulation of Sox2. Neural lineage specification genes (eg, nestin, vimentin, Pax6, and p75NTR) were expressed from day 10 onward at levels above that of Oct4, Nanog and those for endoderm [alpha-fetoprotein (AFP)], and mesoderm (brachyury) specification. Neural stem cell (NSC)/neural progenitor cell (NPC) markers, nestin, Pax6, p75NTR, and vimentin, were extensively localized in cells on day 10, 15 (44.75% ± 5.84%; 93.54% ± 1.35%; 78.90% ± 4.80%; 73.82% ± 3.40%, respectively), and 21 (49.98% ± 5.30%; 91.84% ± 1.9%; 76.74% ± 11.0%; 95.80% ± 3.60%, respectively). Spheroid cell self-renewal was evidenced by cell proliferation and the generation of new spheroids during two consecutive expansion periods. Culture of spheroid cells under differentiation conditions gave rise to cells showing immunolocalization of the neuron-specific antigen NeuN and the astroglial antigen GFAP (glial fibrillary acidic protein). Our results indicate that spheroids spontaneously generated in this culture system were comprised of cells with molecular characteristics of NSC/NPC that can self-renew and differentiate into neurons and glia, supporting the identity of spheroids as neurospheres.

Stem cell colony interspacing effect on differentiation to neural cells

Efforts to enhance the efficiency of neural differentiation of stem cells are primarily focused on exogenous modulation of physical niche parameters such as surface topography and extracellular matrix proteins, or addition of certain growth factors or small molecules to culture media. We report a novel neurogenic niche to enhance the neural differentiation of embryonic stem cells (ESCs) without any external intervention by micropatterning ESCs into spatially organized colonies of controlled size and interspacing. Using an aqueous two-phase system cell microprinting technology, we generated pairs of uniformly sized isolated ESC colonies at defined interspacing distances over a layer of differentiation-inducing stromal cells. Our comprehensive analysis of temporal expression of neural genes and proteins of cells in colony pairs showed that interspacing two colonies at approximately 0.66 times the colony diameter (0.66D) significantly enhanced neural differentiation of ESCs. Cells in these colonies displayed higher expression of neural genes and proteins and formed thick neurite bundles between the two colonies. A computational model of spatial distribution of soluble factors of cells in interspaced colony pairs showed that the enhanced neural differentiation is due to the presence of stable concentration gradients of soluble signalling factors between the two colonies. Our results indicate that culturing ESCs in colony pairs with defined interspacing is a promising approach to efficiently derive neural cells. Additionally, this approach provides a platform for quantitative studies of molecular mechanisms that regulate neurogenesis of stem cells.

Neural stem cell therapy-Brief review

Adult mammalian neural stem cells are unique because of their properties, such as differentiation capacity, self-renewal, quiescence, and also because they exist in specific niches, which are the subventricular zone (SVZ) and subgranular zone (SGZ) - the dentate gyrus of the hippocampus. SVZ is situated along the ependymal cell layer, dividing the ventricular area and subventricular zone. There are several sources of neural stem cells such as human embryonic stem cells, human fetal brain-derived neural stem/progenitor cells, human induced pluripotent stem cells, direct reprogrammed astrocytes. Stem cell sciences are a promising tool for research purposes as well as therapy. Induced pluripotent stem cells appear to be very useful for human neuron studies, allowing the creation of defined neuron populations, particularly for neurodevelopmental and neurodegenerative diseases as well as ischemic events. Neural stem cell sciences have a promising future in terms of stem cell therapy as well as research. There is, however, still a great need for further research to overcome obstacles.

Transplantation in the nonhuman primate MPTP model of Parkinson's disease: update and perspectives

In order to calibrate stem cell exploitation for cellular therapy in neurodegenerative diseases, fundamental and preclinical research in NHP (nonhuman primate) models is crucial. Indeed, it is consensually recognized that it is not possible to directly extrapolate results obtained in rodent models to human patients. A large diversity of neurological pathologies should benefit from cellular therapy based on neural differentiation of stem cells. In the context of this special issue of Primate Biology on NHP stem cells, we describe past and recent advances on cell replacement in the NHP model of Parkinson's disease (PD). From the different grafting procedures to the various cell types transplanted, we review here diverse approaches for cell-replacement therapy and their related therapeutic potential on behavior and function in the NHP model of PD.

Stem cell transplantation for Huntington's diseases

Therapeutic approaches based on stem cells have received considerable attention as potential treatments for Huntington's disease (HD), which is a fatal, inherited neurodegenerative disorder, caused by progressive loss of GABAergic medium spiny neurons (MSNs) in the striatum of the forebrain. Transplantation of stem cells or their derivatives in animal models of HD, efficiently improved functions by replacing the damaged or lost neurons. In particular, neural stem cells (NSCs) for HD treatments have been developed from various sources, such as the brain itself, the pluripotent stem cells (PSCs), and the somatic cells of the HD patients. However, the brain-derived NSCs are difficult to obtain, and the PSCs have to be differentiated into a population of the desired neuronal cells that may cause a risk of tumor formation after transplantation. In contrast, induced NSCs, derived from somatic cells as a new stem cell source for transplantation, are less likely to form tumors. Given that the stem cell transplantation strategy for treatment of HD, as a genetic disease, is to replace the dysfunctional or lost neurons, the correction of mutant genes containing the expanded CAG repeats is essential. In this review, we will describe the methods for obtaining the optimal NSCs for transplantation-based HD treatment and the differentiation conditions for the functional GABAergic MSNs as therapeutic cells. Also, we will discuss the valuable gene correction of the disease stem cells by the CRISPR/Cas9 system for HD treatment.

Self-regulatory factors of embryonic stem cells in co-culture with stromal cells enhance neural differentiation

Embryonic stem cells (ESCs), due to their intrinsic capability to generate somatic cells of all three germ layers, are potential sources of neural cells for cell replacement therapies. However, the empirical differentiation protocols and the lack of mechanistic understanding of the neural differentiation of ESCs have limited the utility of ESCs as a developmental model or as a cell source for neural cell populations for replacement therapies. Co-culturing ESCs with stromal cells is one of the extensively used methods to induce neural differentiation. Despite several studies to identify neural inducing factors in stromal cell induced neural differentiation, the self-regulatory effects of ESCs in the neural differentiation process remain unexplored. For the first time, we elucidate the self-regulatory role of mESCs in their neural cell differentiation by supplementing conditioned media from differentiating mESCs to mESC-PA6 co-cultures and quantitatively evaluating the change in neural differentiation. Moreover, we use statistical tools to analyze the expression of various growth and trophic factors and distinguish the factors produced primarily by PA6 cells versus mESCs in co-culture. We observe that addition of the medium containing mESC-secreted factors to a single mESC colony co-cultured with PA6 cells significantly enhances the neural differentiation of mESCs compares to the medium extracted from the stromal cells only. Hierarchical clustering of gene expression data from PA6 and co-cultured mESCs segregates two groups of factors that are produced by the stromal cells and differentiating mESCs. Identifying the major soluble factors that drive and regulate the neural differentiation process in the mESC-PA6 co-culture niche will help understand molecular mechanisms of neural development. Moreover, it can be a major step toward developing novel protocols to differentiate stem cells with mESC derived factor supplementation without using feeder cells and with greater efficiency compared to existing approaches.

Molecular Analysis of Stromal Cells-Induced Neural Differentiation of Mouse Embryonic Stem Cells

Deriving specific neural cells from embryonic stem cells (ESCs) is a promising approach for cell replacement therapies of neurodegenerative diseases. When co-cultured with certain stromal cells, mouse ESCs (mESCs) differentiate efficiently to neural cells. In this study, a comprehensive gene and protein expression analysis of differentiating mESCs is performed over a two-week culture period to track temporal progression of cells from a pluripotent state to specific terminally-differentiated neural cells such as neurons, astrocytes, and oligodendrocytes. Expression levels of 26 genes consisting of marker genes for pluripotency, neural progenitors, and specific neuronal, astroglial, and oligodendrocytic cells are tracked using real time q-PCR. The time-course gene expression analysis of differentiating mESCs is combined with the hierarchal clustering and functional principal component analysis (FPCA) to elucidate the evolution of specific neural cells from mESCs at a molecular level. These statistical analyses identify three major gene clusters representing distinct phases of transition of stem cells from a pluripotent state to a terminally-differentiated neuronal or glial state. Temporal protein expression studies using immunohistochemistry demonstrate the generation of neural stem/progenitor cells and specific neural lineages and show a close agreement with the gene expression profiles of selected markers. Importantly, parallel gene and protein expression analysis elucidates long-term stability of certain proteins compared to those with a quick turnover. Describing the molecular regulation of neural cells commitment of mESCs due to stromal signaling will help identify major promoters of differentiation into specific cell types for use in cell replacement therapy applications.

In Vitro Models for Neurogenesis

The process of generating new neurons of different phenotype and function from undifferentiated stem and progenitor cells starts at very early stages of development and continues in discrete regions of the mammalian nervous system throughout life. Understanding mechanisms underlying neuronal cell development, biology, function, and interaction with other cells, especially in the neurogenic niche of fully developed adults, is important in defining and developing new therapeutic regimes in regenerative neuroscience. Studying these complex and dynamic processes in vivo is challenging because of the complexity of the nervous system and the presence of many known and unknown confounding variables. However, the challenges could be overcome with simple and robust in vitro models that more or less recapitulate the in vivo events. In this work, we will present an overview of present available in vitro cell-based models of neurogenesis.

Cell reprogramming and neuronal differentiation applied to neurodegenerative diseases: Focus on Parkinson's disease

Adult cells from patients can be reprogrammed to induced pluripotent stem cells (iPSCs) which successively can be used to obtain specific cells such as neurons. This remarkable breakthrough represents a new way of studying diseases and brought new therapeutic perspectives in the field of regenerative medicine. This is particular true in the neurology field, where few techniques are amenable to study the affected tissue of the patient during illness progression, in addition to the lack of neuroprotective therapies for many diseases. In this review we discuss the advantages and unresolved issues of cell reprogramming and neuronal differentiation. We reviewed evidence using iPSCs-derived neurons from neurological patients. Focusing on data obtained from Parkinson's disease (PD) patients, we show that iPSC-derived neurons possess morphological and functional characteristics of this disease and build a case for the use of this technology to study PD and other neuropathologies while disease is in progress. These data show the enormous impact that this new technology starts to have on different purposes such as the study and design of future therapies of neurological disease, especially PD.

Moving stem cells to the clinic: potential and limitations for brain repair

Stem cell-based therapies hold considerable promise for many currently devastating neurological disorders. Substantial progress has been made in the derivation of disease-relevant human donor cell populations. Behavioral data in relevant animal models of disease have demonstrated therapeutic efficacy for several cell-based approaches. Consequently, cGMP grade cell products are currently being developed for first in human clinical trials in select disorders. Despite the therapeutic promise, the presumed mechanism of action of donor cell populations often remains insufficiently validated. It depends greatly on the properties of the transplanted cell type and the underlying host pathology. Several new technologies have become available to probe mechanisms of action in real time and to manipulate in vivo cell function and integration to enhance therapeutic efficacy. Results from such studies generate crucial insight into the nature of brain repair that can be achieved today and push the boundaries of what may be possible in the future.

The significance of membrane fluidity of feeder cell-derived substrates for maintenance of iPS cell stemness

The biological activity of cell-derived substrates to maintain undifferentiated murine-induced pluripotent stem (iPS) cells was correlated to membrane fluidity as a new parameter of cell culture substrates. Murine embryonic fibroblasts (MEFs) were employed as feeder cells and their membrane fluidity was tuned by chemical fixation using formaldehyde (FA). Membrane fluidity was evaluated by real-time single-molecule observations of green fluorescent protein-labeled epidermal growth factor receptors on chemically fixed MEFs. Biological activity was monitored by colony formation of iPS cells. Treatment with a low concentration of FA sustained the membrane fluidity and biological activity, which were comparable to those of mitomycin C-treated MEFs. The biological activity was further confirmed by sustained expression of alkaline phosphatase, SSEA-1, and other pluripotency markers in iPS cells after 3-5 days of culture on FA-fixed MEFs. Chemical fixation of feeder cells has several advantages such as providing ready-to-use culture substrates without contamination by proliferating feeder cells. Therefore, our results provide an important basis for the development of chemically fixed culture substrates for pluripotent stem cell culture as an alternative to conventional treatment by mitomycin C or x-ray irradiation.

Stem cells from human exfoliated deciduous tooth exhibit stromal-derived inducing activity and lead to generation of neural crest cells from human embryonic stem cells

OBJECTIVE

The neural crest is a transient structure of early vertebrate embryos that generates neural crest cells (NCCs). These cells can migrate throughout the body and produce a diverse array of mature tissue types. Due to the ethical and technical problems surrounding the isolation of these early human embryo cells, researchers have focused on in vitro studies to produce NCCs and increase their knowledge of neural crest development.

MATERIALS AND METHODS

In this experimental study, we cultured human embryonic stem cells (hESCs) on stromal stem cells from human exfoliated deciduous teeth (SHED) for a two-week period. We used different approaches to characterize these differentiated cells as neural precursor cells (NPCs) and NCCs.

RESULTS

In the first co-culture week, hESCs appeared as crater-like structures with marginal rosettes. NPCs derived from these structures expressed the early neural crest marker p75 in addition to numerous other genes associated with neural crest induction such as SNAIL, SLUG, PTX3 and SOX9. Flow cytometry analysis showed 70% of the cells were AP2/P75 positive. Moreover, the cells were able to self-renew, sustain multipotent differentiation potential, and readily form neurospheres in suspension culture.

CONCLUSION

SHED, as an adult stem cell with a neural crest origin, has stromal-derived inducing activity (SDIA) and can be used as an NCC inducer from hESCs. These cells provide an invaluable resource to study neural crest differentiation in both normal and disordered human neural crest development.

Physical cues of cell culture materials lead the direction of differentiation lineages of pluripotent stem cells

Differentiation methods of hPSCs into specific cell lineages. Differentiation of hPSCsviaEB formation (types AB, A–D) or without EB formation (types E–H).

Getting it right before transplantation: example of a stem cell model with regenerative potential for the CNS

The burden of neurodegenerative disorders in an aging population has become a challenge for the modern world. While the biomarkers available and the methods of diagnosis have improved to detect the onset of these diseases at early stages, the question of adapted and efficient therapies is still a major issue. The prospect of replacing the loss of functional neural cells remains an attractive but still audacious approach. A huge progress has been made in the generation of neurons derived from human stem cell lines and transplantation assays are tested in animals for a wide range of pathologies of the central nervous system. Here we take one step back and examine neuronal differentiation and the characterization of neural progenitors derived from human embryonic stem cells. We gather results from our previous studies and present a cell model that was successfully used in functional analyses and engraftment experiments. These neuronal precursors exhibit spontaneous and evoked activity, indicating that their electrophysiological and calcium handling properties are similar to those of matured neurons. Hence this summarized information will serve as a basis to design better stem cell-based therapies to improve neural regeneration.

Dopamine neuron generation from human embryonic stem cells

The capacity of pluripotency and self-renewal of human embryonic stem (hES) cells may provide unlimited cell source for cell replacement therapy. In this manuscript we summarize hES differentiation protocols coculture with PA6 or MS5 stromal cells. After 7∼ 9 days of differentiation, neural rosettes were robustly appeared followed by coculture with sonic hedgehog over-expressing stromal cells efficiently generated dopaminergic neural precursor cells. Using this protocol, the majority of differentiated hES cells contained nestin positive cells (＞95%) and after final differentiation a high percentage of TuJ1 positive neurons was tyrosine hydroxylase positive (＞40%).

Functional differentiation of midbrain neurons from human cord blood-derived induced pluripotent stem cells

Introduction

Human induced pluripotent stem cells (hiPSCs) offer great promise for regenerative therapies or in vitro modelling of neurodegenerative disorders like Parkinson’s disease. Currently, widely used cell sources for the generation of hiPSCs are somatic cells obtained from aged individuals. However, a critical issue concerning the potential clinical use of these iPSCs is mutations that accumulate over lifetime and are transferred onto iPSCs during reprogramming which may influence the functionality of cells differentiated from them. The aim of our study was to establish a differentiation strategy to efficiently generate neurons including dopaminergic cells from human cord blood-derived iPSCs (hCBiPSCs) as a juvenescent cell source and prove their functional maturation in vitro.

Methods

The differentiation of hCBiPSCs was initiated by inhibition of transforming growth factor-β and bone morphogenetic protein signaling using the small molecules dorsomorphin and SB 431542 before final maturation was carried out. hCBiPSCs and differentiated neurons were characterized by immunocytochemistry and quantitative real time-polymerase chain reaction. Since functional investigations of hCBiPSC-derived neurons are indispensable prior to clinical applications, we performed detailed analysis of essential ion channel properties using whole-cell patch-clamp recordings and calcium imaging.

Results

A Sox1 and Pax6 positive neuronal progenitor cell population was efficiently induced from hCBiPSCs using a newly established differentiation protocol. Neuronal progenitor cells could be further maturated into dopaminergic neurons expressing tyrosine hydroxylase, the dopamine transporter and engrailed 1. Differentiated hCBiPSCs exhibited voltage-gated ion currents, were able to fire action potentials and displayed synaptic activity indicating synapse formation. Application of the neurotransmitters GABA, glutamate and acetylcholine induced depolarizing calcium signal changes in neuronal cells providing evidence for the excitatory effects of these ligand-gated ion channels during maturation in vitro.

Conclusions

This study demonstrates for the first time that hCBiPSCs can be used as a juvenescent cell source to generate a large number of functional neurons including dopaminergic cells which may serve for the development of novel regenerative treatment strategies.

Adipocytes derived from PA6 cells reliably promote the differentiation of dopaminergic neurons from human embryonic stem cells

The PA6 stromal cell line comprises a heterogeneous population of cells that can induce both mouse and human embryonic stem cells to differentiate into dopaminergic neurons. This ability of PA6 cells has been termed stromal cell-derived inducing activity (SDIA). The level of SDIA has been found to vary considerably between and within batches of PA6 cells. Not only are the molecular mechanisms that underlie SDIA unknown but also the cell type(s) within the heterogeneous PA6 cultures that underlie SDIA remain poorly defined. In this study, we reveal that adipocytes, which are present within the heterogeneous PA6 cell population, robustly release the factors mediating SDIA. Furthermore, we report that the coculture of human embryonic stem cells with PA6-derived adipocytes reliably induces their differentiation into midbrain dopaminergic neurons.

Immortalization of neuronal progenitors using SV40 large T antigen and differentiation towards dopaminergic neurons

Transplantation is common in clinical practice where there is availability of the tissue and organ. In the case of neurodegenerative disease such as Parkinson's disease (PD), transplantation is not possible as a result of the non-availability of tissue or organ and therefore, cell therapy is an innovation in clinical practice. However, the availability of neuronal cells for transplantation is very limited. Alternatively, immortalized neuronal progenitors could be used in treating PD. The neuronal progenitor cells can be differentiated into dopaminergic phenotype. Here in this article, the current understanding of the molecular mechanisms involved in the differentiation of dopaminergic phenotype from the neuronal progenitors immortalized with SV40 LT antigen is discussed. In addition, the methods of generating dopaminergic neurons from progenitor cells and the factors that govern their differentiation are elaborated. Recent advances in cell-therapy based transplantation in PD patients and future prospects are discussed.

Stem cell culture using cell-derived substrates

There have been great efforts to develop cell culture systems using chemically-fixed cells or decellularized matrices to regulate stem cell functions.

Highly efficient differentiation of neural precursors from human embryonic stem cells and benefits of transplantation after ischemic stroke in mice

Introduction

Ischemic stroke is a leading cause of death and disability, but treatment options are severely limited. Cell therapy offers an attractive strategy for regenerating lost tissues and enhancing the endogenous healing process. In this study, we investigated the use of human embryonic stem cell-derived neural precursors as a cell therapy in a murine stroke model.

Methods

Neural precursors were derived from human embryonic stem cells by using a fully adherent SMAD inhibition protocol employing small molecules. The efficiency of neural induction and the ability of these cells to further differentiate into neurons were assessed by using immunocytochemistry. Whole-cell patch-clamp recording was used to demonstrate the electrophysiological activity of human embryonic stem cell-derived neurons. Neural precursors were transplanted into the core and penumbra regions of a focal ischemic stroke in the barrel cortex of mice. Animals received injections of bromodeoxyuridine to track regeneration. Neural differentiation of the transplanted cells and regenerative markers were measured by using immunohistochemistry. The adhesive removal test was used to determine functional improvement after stroke and intervention.

Results

After 11 days of neural induction by using the small-molecule protocol, over 95% of human embryonic stem-derived cells expressed at least one neural marker. Further in vitro differentiation yielded cells that stained for mature neuronal markers and exhibited high-amplitude, repetitive action potentials in response to depolarization. Neuronal differentiation also occurred after transplantation into the ischemic cortex. A greater level of bromodeoxyuridine co-localization with neurons was observed in the penumbra region of animals receiving cell transplantation. Transplantation also improved sensory recovery in transplant animals over that in control animals.

Conclusions

Human embryonic stem cell-derived neural precursors derived by using a highly efficient small-molecule SMAD inhibition protocol can differentiate into electrophysiologically functional neurons in vitro. These cells also differentiate into neurons in vivo, enhance regenerative activities, and improve sensory recovery after ischemic stroke.

Alginate microcapsule as a 3D platform for the efficient differentiation of human embryonic stem cells to dopamine neurons

Human embryonic stem cells (hESCs) are emerging as an attractive alternative source for cell replacement therapy since the cells can be expanded in culture indefinitely and differentiated into any cell types in the body. In order to optimize cell-to-cell interaction, cell proliferation and differentiation into specific lineages as well as tissue organization, it is important to provide a microenvironment for the hESCs which mimics the stem cell niche. One approach is to provide a three-dimensional (3D) environment such as encapsulation. We present an approach to culture and differentiate hESCs into midbrain dopamine (mdDA) neurons in a 3D microenvironment using alginate microcapsules for the first time. A detailed gene and protein expression analysis during neuronal differentiation showed an increased gene and protein expression of various specific DA neuronal markers, particularly tyrosine hydroxylase (TH) by >100 folds after 2 weeks and at least 50% higher expression after 4 weeks respectively, compared to cells differentiated under conventional two-dimensional (2D) platform. The encapsulated TH(+) cells co-expressed mdDA neuronal markers, forkhead box protein A-2 (FOXA2) and pituitary homeobox-3 (PITX3) after 4 weeks and secreted approximately 60pg/ml/10(6) cells higher DA level when induced. We propose that the 3D platform facilitated an early onset of DA neuronal generation compared to that with conventional 2D system which also secretes more DA under potassium-induction. It is a very useful model to study the proliferation and directed differentiation of hESCs to various lineages, particularly to mdDA neurons. This 3D system also allows the separation of feeder cells from hESCs during the process of differentiation and also has potential for immune-isolation during transplantation studies.

Lignin Induces ES Cells to Differentiate into Neuroectodermal Cells through Mediation of the Wnt Signaling Pathway

Embryonic stem cells (ES cells) are characterized by their pluripotency and infinite proliferation potential. Ever since ES cells were first established in 1981, there have been a growing number of studies aimed at clinical applications of ES cells. In recent years, various types of differentiation inducement systems using ES cells have been established. Further studies have been conducted to utilize differentiation inducement systems in the field of regenerative medicine. For cellular treatments using stem cells including ES cells, differentiation induction should be performed in a sufficient manner to obtain the intended cell lineages. Lignin is a high-molecular amorphous material that forms plants together with cellulose and hemicelluloses, in which phenylpropane fundamental units are complexly condensed. Lignin derivatives have been shown to have several bioactive functions. In spite of these findings, few studies have focused on the effects of lignin on stem cells. Our study aimed to develop a novel technology using lignin to effectively induce ES cells to differentiate into neuroectodermal cells including ocular cells and neural cells. Since lignin can be produced at a relatively low cost in large volumes, its utilization is expected for more convenient differentiation induction technologies and in the field of regenerative medicine in the future.

Simple generation of neurons from human embryonic stem cells using agarose multiwell dishes

Human embryonic stem cells (hESC) are potentially an unlimited source of neurons for study and therapy for human disease. Directed differentiation of hESC has been performed using many different methods, often via neural precursor intermediates generated from aggregates of hESC. We describe here a protocol based on commercially available reusable silicone micromolds and two small molecule growth factor inhibitors to simply and reproducibly generate human neurons from hESC. Hundreds of neurospheres were generated with a single pipettation of hESC into agarose multiwell plates made with the micromolds. This was followed by suspension culture with two medium changes, and plating of clumps cut from the neurospheres on laminin-coated coverslips. After two weeks of terminal differentiation, 90%+ of cells expressed neuronal proteins, and many of the neurons expressed markers of peripheral sensory neurons. The neurons made with this method underwent productive infection with the human-specific pathogenic virus varicella zoster, demonstrating the utility of the neurons for addressing clinically relevant research questions. This simple method should allow laboratories experienced in growing human pluripotent cells to easily generate neurons for studies of nerve cell biology and pathology.

Stromal factors SDF1α, sFRP1, and VEGFD induce dopaminergic neuron differentiation of human pluripotent stem cells

Human embryonic stem cell (hESC)-derived dopaminergic (DA) neurons hold potential for treating Parkinson's disease (PD) through cell replacement therapy. Generation of DA neurons from hESCs has been achieved by coculture with the stromal cell line PA6, a source of stromal cell-derived inducing activity (SDIA). However, the factors produced by stromal cells that result in SDIA are largely undefined. We previously reported that medium conditioned by PA6 cells can generate functional DA neurons from NTera2 human embryonal carcinoma stem cells. Here we show that PA6-conditioned medium can induce DA neuronal differentiation in both NTera2 cells and the hESC I6 cell line. To identify the factor(s) responsible for SDIA, we used large-scale microarray analysis of gene expression combined with mass spectrometric analysis of PA6-conditioned medium (CM). The candidate factors, hepatocyte growth factor (HGF), stromal cell-derived factor-1 α (SDF1α), secreted frizzled-related protein 1 (sFRP1), and vascular endothelial growth factor D (VEGFD) were identified, and their concentrations in PA6 CM were established by immunoaffinity capillary electrophoresis. Upon addition of SDF1α, sFRP1, and VEGFD to the culture medium, we observed an increase in the number of cells expressing tyrosine hydroxylase (a marker for DA neurons) and βIII-tubulin (a marker for immature neurons) in both the NTera2 and I6 cell lines. These results indicate that SDF1α, sFRP1, and VEGFD are major components of SDIA and suggest the potential use of these defined factors to elicit DA differentiation of pluripotent human stem cells for therapeutic intervention in PD.

Astrocytes generated from patient induced pluripotent stem cells recapitulate features of Huntington's disease patient cells

Background

Huntington’s Disease (HD) is a devastating neurodegenerative disorder that clinically manifests as motor dysfunction, cognitive impairment and psychiatric symptoms. There is currently no cure for this progressive and fatal disorder. The causative mutation of this hereditary disease is a trinucleotide repeat expansion (CAG) in the Huntingtin gene that results in an expanded polyglutamine tract. Multiple mechanisms have been proposed to explain the preferential striatal and cortical degeneration that occurs with HD, including non-cell-autonomous contribution from astrocytes. Although numerous cell culture and animal models exist, there is a great need for experimental systems that can more accurately replicate the human disease. Human induced pluripotent stem cells (iPSCs) are a remarkable new tool to study neurological disorders because this cell type can be derived from patients as a renewable, genetically tractable source for unlimited cells that are difficult to acquire, such as neurons and astrocytes. The development of experimental systems based on iPSC technology could aid in the identification of molecular lesions and therapeutic treatments.

Results

We derived iPSCs from a father with adult onset HD and 50 CAG repeats (F-HD-iPSC) and his daughter with juvenile HD and 109 CAG repeats (D-HD-iPSC). These disease-specific iPSC lines were characterized by standard assays to assess the quality of iPSC lines and to demonstrate their pluripotency. HD-iPSCs were capable of producing phenotypically normal, functional neurons in vitro and were able to survive and differentiate into neurons in the adult mouse brain in vivo after transplantation. Surprisingly, when HD-iPSCs were directed to differentiate into an astrocytic lineage, we observed the presence of cytoplasmic, electron clear vacuoles in astrocytes from both F-HD-iPSCs and D-HD-iPSCs, which were significantly more pronounced in D-HD-astrocytes. Remarkably, the vacuolation in diseased astrocytes was observed under basal culture conditions without additional stressors and increased over time. Importantly, similar vacuolation phenotype has also been observed in peripheral blood lymphocytes from individuals with HD. Together, these data suggest that vacuolation may be a phenotype associated with HD.

Conclusions

We have generated a unique in vitro system to study HD pathogenesis using patient-specific iPSCs. The astrocytes derived from patient-specific iPSCs exhibit a vacuolation phenotype, a phenomenon previously documented in primary lymphocytes from HD patients. Our studies pave the way for future mechanistic investigations using human iPSCs to model HD and for high-throughput therapeutic screens.

Small molecules greatly improve conversion of human-induced pluripotent stem cells to the neuronal lineage

Efficient in vitro differentiation into specific cell types is more important than ever after the breakthrough in nuclear reprogramming of somatic cells and its potential for disease modeling and drug screening. Key success factors for neuronal differentiation are the yield of desired neuronal marker expression, reproducibility, length, and cost. Three main neuronal differentiation approaches are stromal-induced neuronal differentiation, embryoid body (EB) differentiation, and direct neuronal differentiation. Here, we describe our neurodifferentiation protocol using small molecules that very efficiently promote neural induction in a 5-stage EB protocol from six induced pluripotent stem cells (iPSC) lines from patients with Parkinson's disease and controls. This protocol generates neural precursors using Dorsomorphin and SB431542 and further maturation into dopaminergic neurons by replacing sonic hedgehog with purmorphamine or smoothened agonist. The advantage of this approach is that all patient-specific iPSC lines tested in this study were successfully and consistently coaxed into the neural lineage.

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.

Alginate microcapsule as a 3D platform for propagation and differentiation of human embryonic stem cells (hESC) to different lineages

Human embryonic stem cells (hESC) are emerging as an attractive alternative source for cell replacement therapy since they can be expanded in culture indefinitely and differentiated to any cell types in the body. Various types of biomaterials have also been used in stem cell cultures to provide a microenvironment mimicking the stem cell niche(1-3). The latter is important for promoting cell-to-cell interaction, cell proliferation, and differentiation into specific lineages as well as tissue organization by providing a three-dimensional (3D) environment(4) such as encapsulation. The principle of cell encapsulation involves entrapment of living cells within the confines of semi-permeable membranes in 3D cultures(2). These membranes allow for the exchange of nutrients, oxygen and stimuli across the membranes, whereas antibodies and immune cells from the host that are larger than the capsule pore size are excluded(5). Here, we present an approach to culture and differentiate hESC DA neurons in a 3D microenvironment using alginate microcapsules. We have modified the culture conditions(2) to enhance the viability of encapsulated hESC. We have previously shown that the addition of p160-Rho-associated coiled-coil kinase (ROCK) inhibitor, Y-27632 and human fetal fibroblast-conditioned serum replacement medium (hFF-CM) to the 3D platform significantly enhanced the viability of encapsulated hESC in which the cells expressed definitive endoderm marker genes(1). We have now used this 3D platform for the propagation of hESC and efficient differentiation to DA neurons. Protein and gene expression analyses after the final stage of DA neuronal differentiation showed an increased expression of tyrosine hydroxylase (TH), a marker for DA neurons, >100 folds after 2 weeks. We hypothesized that our 3D platform using alginate microcapsules may be useful to study the proliferation and directed differentiation of hESC to various lineages. This 3D system also allows the separation of feeder cells from hESC during the process of differentiation and also has potential for immune-isolation during transplantation in the future.

DA neurons derived from hES cells that express HLA-G1 are capable of immunosuppression

Human embryonic stem (hES) cells have the capacity for self-renewal and exhibit multipotentiality. hES cells have promise for serving as an unlimited source of ideal seed cells for cell transplantation. However, the rejection that occurs between the transplant recipient and the transplanted cell poses a major challenge for therapeutic transplantation. This study was designed to devise methods to enhance immune tolerance in cell therapy. We established an hES cell line that could stably express human leukocyte antigen-G1 (HLA-G1). The established HLA-G1-H1 hES cells still retained all the characteristics of normal human embryonic stem cells. By using the SDIA method, we induced dopaminergic (DA) neurons by coculturing HLA-G1-H1 hES cells with the mouse stromal cell line PA6. Tyrosine hydroxylase (TH)+neurons were detected on the 10th day of differentiation, and 70% of the HLA-G1-H1 hES cells were TH+mature DA neurons because the differentiation time was only 3 weeks. Cells that had been differentiating for different periods of time still expressed HLA-G1, and these differentiated DA neurons released dopamine and other catecholamines in response to K+ depolarization as measured by HPLC. After careful study, we found that HLA-G1-H1 hES cells are capable of inhibiting the proliferation of mixed T-lymphocytes. DA neurons derived from HLA-G1-H1 hES attenuated the release of proinflammatory cytokines IL-1β and IFN-γ from lipopolysaccharide (LPS)-stimulated BV2 microglia. The efficiency of inhibition was significant and dose-dependent. This method might be used to treat Parkinson's patients via cell transplantation.

Microprinted feeder cells guide embryonic stem cell fate

We introduce a non-contact approach to microprint multiple types of feeder cells in a microarray format using immiscible aqueous solutions of two biopolymers. Droplets of cell suspension in the denser aqueous phase are printed on a substrate residing within a bath of the immersion aqueous phase. Due to their affinity to the denser phase, cells remain localized within the drops and adhere to regions of the substrate underneath the drops. We show the utility of this technology for creating duplex heterocellular stem cell niches by printing two different support cell types on a gel surface and overlaying them with mouse embryonic stem cells (mESCs). As desired, the type of printed support cell spatially direct the fate of overlaid mESCs. Interestingly, we found that interspaced mESCs colonies on differentiation-inducing feeder cells show enhanced neuronal differentiation and give rise to dense networks of neurons. This cell printing technology provides unprecedented capabilities to efficiently identify the role of various feeder cells in guiding the fate of stem cells.

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.

Embryonic stem cells in non-human primates: An overview of neural differentiation potential

Non-human primate (NHP) embryonic stem (ES) cells show unlimited proliferative capacities and a great potential to generate multiple cell lineages. These properties make them an ideal resource both for investigating early developmental processes and for assessing their therapeutic potential in numerous models of degenerative diseases. They share the same markers and the same properties with human ES cells, and thus provide an invaluable transitional model that can be used to address the safety issues related to the clinical use of human ES cells. Here, we review the available information on the derivation and the specific features of monkey ES cells. We comment on the capacity of primate ES cells to differentiate into neural lineages and the current protocols to generate self-renewing neural stem cells. We also highlight the signalling pathways involved in the maintenance of these neural cell types. Finally, we discuss the potential of monkey ES cells for neuronal differentiation.

Neural differentiation of induced pluripotent stem cells

The great potential of induced pluripotent cells (iPS) cells is that it allows the possibility of deriving pluripotent stem cells from any human patient. Generation of patient-derived stem cells serves as a great source for developing cell replacement therapies and also for creating human cellular model systems of specific diseases or disorders. This is only of benefit if there are well-established differentiation assay systems to generate the cell types of interest. This chapter describes robust and well-characterized protocols for differentiating iPS cells to neural progenitors, neurons, glia and neural crest cells. These established assays can be applied to iPS cell lines derived from patients with neurodegenerative disorders to study cellular mechanisms associated with neurodegeneration as well as investigating the regenerative potential of patient derived stem cells.

Small-molecule inhibitors of bone morphogenic protein and activin/nodal signals promote highly efficient neural induction from human pluripotent stem cells

The balance of bone morphogenic protein (BMP), transforming growth factor-β (TGFβ)/activin/nodal, and Wnt signals regulates the early lineage segregation of human embryonic stem cells (ESCs). Here we demonstrate that a combination of small-molecule inhibitors of BMP (Dorsomorphin) and TGFβ/activin/nodal (SB431542) signals promotes highly efficient neural induction from both human ESCs and induced pluripotent stem cells (iPSCs). The combination of small molecules had effects on both cell survival and purity of neural differentiation, under conditions of stromal (PA6) cell coculture and feeder-free floating aggregation culture, for all seven pluripotent stem cell lines that we studied, including three ESC and four iPSC lines. Small molecule compounds are stable and cost effective, so our findings provide a promising strategy for controlled production of neurons in regenerative medicine.

Human embryonic stem cells: derivation, culture, and differentiation: a review

The greatest therapeutic promise of human embryonic stem cells (hESC) is to generate specialized cells to replace damaged tissue in patients suffering from various degenerative diseases. However, the signaling mechanisms involved in lineage restriction of ESC to adopt various cellular phenotypes are still under investigation. Furthermore, for progression of hESC-based therapies towards clinical applications, appropriate culture conditions must be developed to generate genetically stable homogenous populations of cells, to hinder possible adverse effects following transplantation. Other critical challenges that must be addressed for successful cell implantation include problems related to survival and functional efficacy of the grafted cells. This review initially describes the derivation of hESC and focuses on recent advances in generation, characterization, and maintenance of these cells. We also give an overview of original and emerging differentiation strategies used to convert hESC to different cell types. Finally, we will discuss transplantation studies of hESC-derived cells with respect to safety and functional recovery.

Role of transcription factors in cell replacement therapies for neurodegenerative conditions

Parkinson's disease is the second most common neurological condition, behind dementia, for which there is currently no cure. A promising curative treatment approach is cell replacement therapy, which involves the introduction of new dopaminergic cells into a degenerative Parkinson's disease brain. The future progression of this field into a clinically viable treatment option is reliant on generating replacement dopaminergic cells. Furthermore, as the ability of transplanted dopaminergic neurons to form connections with host tissue is dependent on where the cells are derived from, the replacement dopaminergic cells will need to be phenotypically similar to substantia nigra dopaminergic neurons. This article focuses on how developmental transcription factors have been utilized to assist the progression of stem cell therapies for Parkinson's disease. Key transcription factor-mediated stages of substantia nigra dopaminergic neuronal development is described in the belief that a comprehensive understanding of this specific dopaminergic differentiation pathway is necessary for the progression of successful cell therapies for Parkinson's disease.

Stem cell-based models and therapies for neurodegenerative diseases

Multiple neurodegenerative disorders typically result from irrevocable damage and improper functioning of specialized neuronal cells or populations of neuronal cells. These disorders have the potential to contribute to an already overburdened health care system unless the progression of neurodegeneration can be altered. Progress in understanding neurodegenerative cell biology has been hampered by a lack of predictive and, some would claim, relevant cellular models. Additionally, the research needed to develop new drugs and determine methods for repair or replacement of damaged neurons is severely hampered by the lack of an adequate in vitro human neuron cell-based model. In this context, pluripotent stem cells and neural progenitors and their properties including unlimited proliferation, plasticity to generate other cell types, and a readily available source of cells--pose an excellent alternative to ex vivo primary cultures or established immortalized cell lines in contributing to our understanding of neurodegenerative cell biology and our ability to analyze the therapeutic or cytotoxic effects of chemicals, drugs, and xenobiotics. Many questions that define the underlying "genesis" of the neuronal death in these disorders also remain unanswered, with evidence suggesting a key role for mitochondrial dysfunction. The assessment of stem cells, neural progenitors, and engineered adult cells can provide useful insights into neuronal development and neurodegenerative processes. Finally, the potential for a combination of cell- and gene-based therapeutics for neurodegenerative disorders is also discussed.