Enhanced yield of neuroepithelial precursors and midbrain-like dopaminergic neurons from human embryonic stem cells using the bone morphogenic protein antagonist noggin

Induced pluripotent stem cells in the study of neurological diseases

Five years after their initial derivation from mouse somatic cells, induced pluripotent stem (iPS) cells are an important tool for the study of neurological diseases. By offering an unlimited source of patient-specific disease-relevant neuronal and glial cells, iPS cell-based disease models hold enormous promise for identification of disease mechanisms, discovery of molecular targets and development of phenotypic screens for drug discovery. The present review focuses on the recent advancements in modeling neurological disorders, including the demonstration of disease-specific phenotypes in iPS cell-derived neurons generated from patients with spinal muscular atrophy, familial dysautonomia, Rett syndrome, schizophrenia and Parkinson disease. The ability of this approach to detect treatment effects from known therapeutic compounds has also been demonstrated, providing proof of principle for the use of iPS cell-derived cells in drug discovery.

Enhanced production of neuroprogenitors, dopaminergic neurons, and identification of target genes by overexpression of sonic hedgehog in human embryonic stem cells

Molecular and cellular signaling pathways are involved in the process of neural differentiation from human embryonic stem cells (hESC) to terminally differentiated neurons. The Sonic hedgehog (SHH) morphogen is required to direct the differentiation of hESC to several neural subtypes, for example, dopaminergic (DA) or motor neurons. However, the roles of SHH signaling and the pathway target genes that regulate the diversity of cellular responses arising from SHH activation during neurogenesis of hESC have yet to be elucidated. In this study, we report that overexpression of SHH in hESC promotes the derivation of neuroprogenitors (NP), increases proliferation of NP, and subsequently increases the yield of DA neurons. Next, gene expression changes resulting from the overexpression of SHH in hESC-derived NP were examined by genome-wide transcriptional profiling. Categorizing the differentially expressed genes according to the Gene Ontology biological processes showed that they are involved in numerous cellular processes, including neural development, NP proliferation, and neural specification. In silico GLI-binding sites analysis of the differentially expressed genes also identified a set of putative novel direct target genes of SHH in hESC-derived NP, which are involved in nervous system development. Electrophoretic mobility shift assays and promoter-luciferase assays confirmed that GLI1 binds to the promoter region and activates transcription of HEY2, a NOTCH signaling target gene. Taken together, our data provide evidence for the first time that there is cross-talk between the NOTCH and SHH signaling pathways in hESC-derived NP and also provide significant new insights into transcriptional targets in SHH-mediated neural differentiation of hESC.

Specification of neuronal and glial subtypes from human pluripotent stem cells

Human pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide a dynamic tool for revealing early embryonic development, modeling pathological processes, and developing therapeutics through drug discovery and potential cell replacement. The first step toward the utilities of human PSCs is directed differentiation to functionally specialized cell/tissue types. Following developmental principles, human ESCs, and lately iPSCs, have been effectively differentiated to region- and/or transmitter-specific neuronal and glial types, including cerebral glutamatergic, striatal γ-aminobutyric acid (GABA)-ergic, forebrain cholinergic, midbrain dopaminergic, and spinal motor neurons, as well as astrocytes and oligodendrocytes. These studies also reveal unique aspects of human cell biology, including intrinsically programmed developmental course, differential uses of transcription factors for neuroectoderm specification, and distinct responses to extracellular signals in regulating cell fate. Such information will be instrumental in translating biological findings to therapeutic development.

E-cadherin-expressing feeder cells promote neural lineage restriction of human embryonic stem cells

Human embryonic stem cells (hESCs) represent a promising source of tissues of different cell lineages because of their high degree of self-renewal and their unique ability to give rise to most somatic cell lineages. In this article, we report on a new approach to differentiate hESCs into neural stem cells that can be differentiated further into neuronal restricted cells. We have rapidly and efficiently differentiated hESCs into neural stem cells by presenting the cell adhesion molecule, E-cadherin, to undifferentiated hESCs via E-cadherin transfected fibroblast monolayers. The neural restricted progenitor cells rapidly express nestin and beta-III-tubulin, but not glial fibrillary acidic protein (GFAP) during the 1-week E-cadherin induction phase, suggesting that E-cadherin promotes rapid neuronal differentiation. Further, these cells are able to achieve enhanced neuronal differentiation with the addition of exogenous growth factors. Cadherin-induced hESCs show a loss in Oct4 and nestin expression associated with positive staining for vimentin, neurofilament, and neural cell adhesion molecule. Moreover, blocking by functional E-cadherin antibody and failure of paracrine stimulation suggested that direct E-cadherin engagement is necessary to induce neural restriction. By providing hESCs with molecular cues to promote differentiation, we are able to utilize a specific cell-cell adhesion molecule, E-cadherin, to influence the nature and degree of neural specialization.

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.

Tracking stem cell differentiation in the setting of automated optogenetic stimulation

Membrane depolarization has been shown to play an important role in the neural differentiation of stem cells and in the survival and function of mature neurons. Here, we introduce a microbial opsin into ESCs and develop optogenetic technology for stem cell engineering applications, with an automated system for noninvasive modulation of ESC differentiation employing fast optogenetic control of ion flux. Mouse ESCs were stably transduced with channelrhodopsin-2 (ChR2)-yellow fluorescent protein and purified by fluorescence activated cell sorting (FACS). Illumination of resulting ChR2-ESCs with pulses of blue light triggered inward currents. These labeled ESCs retained the capability to differentiate into functional mature neurons, assessed by the presence of voltage-gated sodium currents, action potentials, fast excitatory synaptic transmission, and expression of mature neuronal proteins and neuronal morphology. We designed and tested an apparatus for optically stimulating ChR2-ESCs during chronic neuronal differentiation, with high-speed optical switching on a custom robotic stage with environmental chamber for automated stimulation and imaging over days, with tracking for increased expression of neural and neuronal markers. These data point to potential uses of ChR2 technology for chronic and temporally precise noninvasive optical control of ESCs both in vitro and in vivo, ranging from noninvasive control of stem cell differentiation to causal assessment of the specific contribution of transplanted cells to tissue and network function.

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.

Physiological properties of neurons derived from human embryonic stem cells using a dibutyryl cyclic AMP-based protocol

Neurons derived from human embryonic stem cells hold promise for the therapy of neurological diseases. Quality inspection of human embryonic stem cell-derived neurons has often been based on immunolabeling for neuronal markers. Here we put emphasis on their physiological properties. Electrophysiological measurements were carried out systematically at different stages of neuronal in vitro development, including the very early stage, neuroepithelial rosettes. Developing human neurons are able to generate action potentials (APs) as early as 10 days after the start of differentiation. Tyrosine hydroxylase (TH)-positive (putative dopaminergic, DA) neurons tend to aggregate into clumps, and their overall yield per coverslip is relatively low (8.3%) because of areas void of DA neurons. On the same in vitro day, neighboring neurons can be in very different stages of differentiation, including repetitive AP firing, single full-size AP, and abortive AP. Similarly, the basic electrophysiological parameters (resting membrane potential, input resistance, peak sodium, and peak potassium currents) are scattered in a wide range. Visual appearance of differentiating neurons, and number of primary and secondary dendrites cannot be used to predict the peak sodium current or AP firing properties of cultured neurons. Approximately 13% of neurons showed evidence of hyperpolarization-induced current (I(h)), a characteristic of DA neurons; however, no neurons with repetitive APs showed I(h). The electrophysiological measurements thus indicate that a standard DA differentiation (dibutyryl cyclic AMP-based) protocol, applied for 2-5 weeks, produces a heterogeneous ensemble of mostly immature neurons. The overall quality of human neurons under present conditions (survival factors were not used) begins to deteriorate after 12 days of differentiation.

Gli1 is an inducing factor in generating floor plate progenitor cells from human embryonic stem cells

Generation of mesencephalic dopamine (mesDA) neurons from human embryonic stem cells (hESCs) requires several stages of signaling from various extrinsic and intrinsic factors. To date, most methods incorporate exogenous treatment of Sonic hedgehog (SHH) to derive mesDA neurons. However, we and others have shown that this approach is inefficient for generating FOXA2+ cells, the precursors of mesDA neurons. As mesDA neurons are derived from the ventral floor plate (FP) regions of the embryonic neural tube, we sought to develop a system to derive FP cells from hESC. We show that forced expression of the transcription factor GLI1 in hESC at the earliest stage of neural induction, resulted in their commitment to FP lineage. The GLI1+ cells coexpressed FP markers, FOXA2 and Corin, and displayed exocrine SHH activity by ventrally patterning the surrounding neural progenitors. This system results in 63% FOXA2+ cells at the neural progenitor stage of hESC differentiation. The GLI1-transduced cells were also able to differentiate to neurons expressing tyrosine hydroxylase. This study demonstrates that GLI1 is a determinant of FP specification in hESC and describes a highly robust and efficient in vitro model system that mimics the ventral neural tube organizer. Stem Cells 2010;28:1805–1815

A small synthetic cripto blocking Peptide improves neural induction, dopaminergic differentiation, and functional integration of mouse embryonic stem cells in a rat model of Parkinson's disease

Cripto is a glycosylphosphatidylinositol-anchored coreceptor that binds Nodal and the activin type I (ALK)-4 receptor, and is involved in cardiac differentiation of mouse embryonic stem cells (mESCs). Interestingly, genetic ablation of cripto results in increased neuralization and midbrain dopaminergic (DA) differentiation of mESCs, as well as improved DA cell replacement therapy (CRT) in a model of Parkinson's disease (PD). In this study, we developed a Cripto specific blocking tool that would mimic the deletion of cripto, but could be easily applied to embryonic stem cell (ESC) lines without the need of genetic manipulation. We thus screened a combinatorial peptide library and identified a tetrameric tripeptide, Cripto blocking peptide (BP), which prevents Cripto/ALK-4 receptor interaction and interferes with Cripto signaling. Cripto BP treatment favored neuroectoderm formation and promoted midbrain DA neuron differentiation of mESCs in vitro and in vivo. Remarkably, Cripto BP-treated ESCs, when transplanted into the striatum of PD rats, enhanced functional recovery and reduced tumor formation, mimicking the effect of genetic ablation of cripto. We therefore suggest that specific blockers such as Cripto BP may be used to improve the differentiation of ESC-derived DA neurons in vitro and their engraftment in vivo, bringing us closer towards an application of ESCs in CRT.

Interaction of a specific population of human embryonic stem cell-derived progenitor cells with CD11b+ cells ameliorates sepsis-induced lung inflammatory injury

Human embryonic stem cells differentiated under mesoderm-inducing conditions have important therapeutic properties in sepsis-induced lung injury in mice. Single cell suspensions obtained from day 7 human embryoid bodies (d7EBs) injected i.v. 1 hour after cecal ligation and puncture significantly reduced lung inflammation and edema as well as production of tumor necrosis factor-α and interferon-γ in lungs compared with controls, whereas interleukin-10 production remained elevated. d7EB cell transplantation also reduced mortality to 50% from 90% in the control group. The protection was ascribed to d7EB cell interaction with lung resident CD11b+ cells, and was correlated with the ability of d7EB cells to reduce it also reduced production of proinflammatory cytokines by CD11+ cells, and to endothelial NO synthase–derived NO by d7EB cells, leading to inhibition of inducible macrophage-type NO synthase activation in CD11b+ cells. The protective progenitor cells were positive for the endothelial and hematopoietic lineage marker angiotensin converting enzyme (ACE). Only the ACE+ fraction modulated the proinflammatory profile of CD11b+ cells and reduced mortality in septic mice. In contrast to the nonprotective ACE-cell fraction, the ACE+ cell fraction also produced NO. These findings suggest that an ACE+ subset of human embryonic stem cell–derived progenitor cells has a highly specialized anti-inflammatory function that ameliorates sepsis-induced lung inflammation and reduces mortality.

Regulation of stem cell pluripotency and differentiation by G protein coupled receptors

Stem cell-based therapeutics have the potential to effectively treat many terminal and debilitating human diseases, but the mechanisms by which their growth and differentiation are regulated are incompletely defined. Recent data from multiple systems suggest major roles for G protein coupled receptor (GPCR) pathways in regulating stem cell function in vivo and in vitro. The goal of this review is to illustrate common ground between the growing field of stem cell therapeutics and the long-established field of G protein coupled receptor signaling. Herein, we briefly introduce basic stem cell biology and discuss how several conserved pathways regulate pluripotency and differentiation in mouse and human stem cells. We further discuss general mechanisms by which GPCR signaling may impact these pluripotency and differentiation pathways, and summarize specific examples of receptors from each of the major GPCR subfamilies that have been shown to regulate stem cell function. Finally, we discuss possible therapeutic implications of GPCR regulation of stem cell function.

Progress and prospects: stem cells and neurological diseases

The central nervous system has limited capacity of regenerating lost tissue in slowly progressive, degenerative neurological conditions such as Parkinson's disease (PD), Alzheimer's disease or Huntington's disease (HD), or in acute injuries resulting in rapid cell loss for example, in cerebrovascular damage (for example, stroke) or spinal cord injury. Although the adult brain contains small numbers of stem cells in restricted areas, they do not contribute significantly to functional recovery. Transplantation of stem cells or stem cell-derived progenitors has long been seen as a therapeutic solution to repair the damaged brain. With the advent of the induced pluripotent stem cells technique a new and potentially better source for transplantable cells may be available in future. This review aims to highlight current strategies to replace lost cellular populations in neurodegenerative diseases with the focus on HD and PD and traumatic brain injuries such as stroke, discussing many of the technical and biological issues associated with central nervous system cell transplantation.

Differentiated Parkinson patient-derived induced pluripotent stem cells grow in the adult rodent brain and reduce motor asymmetry in Parkinsonian rats

Recent advances in deriving induced pluripotent stem (iPS) cells from patients offer new possibilities for biomedical research and clinical applications, as these cells could be used for autologous transplantation. We differentiated iPS cells from patients with Parkinson's disease (PD) into dopaminergic (DA) neurons and show that these DA neurons can be transplanted without signs of neurodegeneration into the adult rodent striatum. The PD patient iPS (PDiPS) cell-derived DA neurons survived at high numbers, showed arborization, and mediated functional effects in an animal model of PD as determined by reduction of amphetamine- and apomorphine-induced rotational asymmetry, but only a few DA neurons projected into the host striatum at 16 wk after transplantation. We next applied FACS for the neural cell adhesion molecule NCAM on differentiated PDiPS cells before transplantation, which resulted in surviving DA neurons with functional effects on amphetamine-induced rotational asymmetry in a 6-OHDA animal model of PD. Morphologically, we found that PDiPS cell-derived non-DA neurons send axons along white matter tracts into specific close and remote gray matter target areas in the adult brain. Such findings establish the transplantation of human PDiPS cell-derived neurons as a long-term in vivo method to analyze potential disease-related changes in a physiological context. Our data also demonstrate proof of principle of survival and functional effects of PDiPS cell-derived DA neurons in an animal model of PD and encourage further development of differentiation protocols to enhance growth and function of implanted PDiPS cell-derived DA neurons in regard to potential therapeutic applications.

Human ES and iPS cells as cell sources for the treatment of Parkinson's disease: current state and problems

Cell therapy using human embryonic stem cells (hESCs) is a promising therapeutic option for Parkinson's disease (PD), an incurable neurodegenerative disease. A prerequisite for clinical application of hESCs for PD is an efficient and strict differentiation of hESCs into midbrain dopamine (mDA) neuron-like cells, which would be directly translated into high effectiveness of the therapy with minimum risk of undesirable side effects. Due to fruitful efforts from many laboratories, a variety of strategies for improving efficiency of dopaminergic differentiation from hESCs have been developed, mostly by optimizing culture conditions, genetic modification, and modulating intracellular signaling pathways. The rapid advances in the fields of dopaminergic differentiation of hESCs, prevention of tumor formation, and establishment of safe human induced pluripotent stem cells (hiPSCs) would open the door to highly effective, tumor-free, and immune rejection-free cell therapy for PD in the near future.

Comparison of Transplant Efficiency between Spontaneously Derived and Noggin-Primed Human Embryonic Stem Cell Neural Precursors in the Quinolinic Acid Rat Model of Huntington's Disease

Human neural precursors (hNP) derived from embryonic stem cells (hESC) may provide a viable cellular source for transplantation therapy for Huntington's disease (HD). However, developing effective transplantation therapy for the central nervous system (CNS) using hESC relies on optimizing the in vitro production of hNP to control appropriate in vivo posttransplantation neuronal differentiation. The current study provides the first direct in vivo comparison of the transplant efficiency and posttransplantation characteristics of spontaneously derived and noggin-primed hNP following transplantation into the quinolinic acid (QA) rat model of HD. We show that spontaneously derived and noggin-primed hNP both survived robustly up to 8 weeks after transplantation into the QA-lesioned striatum of the adult rat. Transplanted hNP underwent extensive migration and large-scale differentiation towards a predominantly neuronal fate by 8 weeks posttransplantation. Furthermore, in vitro noggin priming of hNP specifically increased the extent of neuronal differentiation at both 4 and 8 weeks posttransplantation when compared to spontaneously derived hNP grafts. The results of this study suggest that in vitro noggin priming provides an effective mechanism by which to enhance hNP transplant efficiency for the treatment of HD.

Differentiation of human ES and Parkinson's disease iPS cells into ventral midbrain dopaminergic neurons requires a high activity form of SHH, FGF8a and specific regionalization by retinoic acid

The cardinal motor symptoms of Parkinson's disease (PD) are caused by the vulnerability to dysfunction and degeneration of ventral midbrain (VM) dopaminergic (DA) neurons. A major limitation for experimental studies of current ES/iPS cell differentiation protocols is the lack of VM DA neurons with a stable phenotype as defined by an expression marker code of FOXA2/TH/β-tubulin. Here we demonstrate a combination of three modifications that were required to produce VM DA neurons. Firstly, early and specific exposure to 10(-)(8)M (low dose) retinoic acid improved the regional identity of neural progenitor cells derived from human ES cells, PD or healthy subject-specific iPS cells. Secondly, a high activity form of human sonic hedgehog established a sizeable FOXA2(+) neural progenitor cell population in vitro. Thirdly, early exposure to FGF8a, rather than Fgf8b, and WNT1 was required for robust differentiation of the FOXA2(+) floor plate-like human neural progenitor cells into FOXA2(+) DA neurons. FOXA2(+) DA neurons were also generated when this protocol was adapted to feeder-free conditions. In summary, this new human ES and iPS cell differentiation protocol using FGF8a, WNT1, low dose retinoic acid and a high activity form of SHH can generate human VM DA neurons that are required for relevant new bioassays, drug discovery and cell based therapies for PD.

Therapeutic potential of appropriately evaluated safe-induced pluripotent stem cells for spinal cord injury

Various types of induced pluripotent stem (iPS) cells have been established by different methods, and each type exhibits different biological properties. Before iPS cell-based clinical applications can be initiated, detailed evaluations of the cells, including their differentiation potentials and tumorigenic activities in different contexts, should be investigated to establish their safety and effectiveness for cell transplantation therapies. Here we show the directed neural differentiation of murine iPS cells and examine their therapeutic potential in a mouse spinal cord injury (SCI) model. "Safe" iPS-derived neurospheres, which had been pre-evaluated as nontumorigenic by their transplantation into nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mouse brain, produced electrophysiologically functional neurons, astrocytes, and oligodendrocytes in vitro. Furthermore, when the safe iPS-derived neurospheres were transplanted into the spinal cord 9 d after contusive injury, they differentiated into all three neural lineages without forming teratomas or other tumors. They also participated in remyelination and induced the axonal regrowth of host 5HT(+) serotonergic fibers, promoting locomotor function recovery. However, the transplantation of iPS-derived neurospheres pre-evaluated as "unsafe" showed robust teratoma formation and sudden locomotor functional loss after functional recovery in the SCI model. These findings suggest that pre-evaluated safe iPS clone-derived neural stem/progenitor cells may be a promising cell source for transplantation therapy for SCI.

Stem cells and cell replacement therapy for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by a progressive degeneration of the midbrain dopamine (DA) neurons in the substantia nigra pars compacta (SNc) that predominantly affects the ventral population projecting to the dorsal striatum and leads to a gradual dysfunction of the motor system. There is currently no cure for PD. Pharmacological and surgical (e.g. deep brain stimulation) interventions can alleviate some of the symptoms, but lose their efficacy over time. The distinct loss of DA neurons in the SN offers the opportunity to assay neuronal cell replacement, and the clinical transplantation of fetal midbrain neuroblasts in PD patients has shown that this approach is feasible. However, there are multiple problems associated with the use of fetus-derived material, including limited availability. DA neurons derived from stem cells (SC) represent an alternative and unlimited cell source for cell replacement therapies. Currently, human pluripotent SC, such as embryonic (ES), and most recently, induced pluripotent stem cells (iPS), and multipotent (tissue-specific) adult SC are available, although the methodology for a reliable and efficient production of DA neurons necessary for biomedical applications is still underdeveloped. Here, we discuss some essentials for SC and SC-derived DA neurons to become therapeutic agents.

Stage-specific role for shh in dopaminergic differentiation of human embryonic stem cells induced by stromal cells

Stromal cells have been used to induce dopaminergic differentiation of mouse, primate, and human embryonic stem cells (hESCs), but the mechanism that governs this induction is unknown. In this manuscript, we show that medium conditioned by the stromal cell line PA6 (PA6-CM) can induce dopaminergic differentiation in neural stem cells (NSCs) derived from hESCs but not directly from hESCs, indicating that soluble factors produced by PA6 cells act at the NSC stage to specify a dopaminergic fate. To identify such soluble factors, we analyzed the transcriptomes of PA6 cells, NSCs, and dopaminergic populations induced by PA6-CM from hESC-derived NSCs. We focused our analysis on growth factors expressed by PA6 and receptors expressed by NSCs, and generated a list of growth factors and receptors that are differentially expressed. Some of the growth factor/receptor pairs are categorized into the Shh, Wnt5A, TGFbeta, and IGF pathways. The expression of genes activated by these pathways in dopaminergic populations was analyzed to confirm that these signals were likely candidates for specifying dopaminergic fate. Results were verified for Shh by using perturbation agents such as cyclopamine to show that Shh is indeed one of the active agents in PA6-CM, and by showing that Shh and FGF8 can substitute for PA6-CM at the NSC induction stage. We conclude that PA6-CM can induce dopaminergic differentiation in hESCs in a stage-specific manner. Shh is likely an important soluble dopaminergic inducing factor secreted by stromal cells and acts after the neural fate determination.

CD15, CD24, and CD29 define a surface biomarker code for neural lineage differentiation of stem cells

Identification and use of cell surface cluster of differentiation (CD) biomarkers have enabled much scientific and clinical progress. We identify a CD surface antigen code for the neural lineage based on combinatorial flow cytometric analysis of three distinct populations derived from human embryonic stem cells: (1) CD15(+)/CD29(HI)/CD24(LO) surface antigen expression defined neural stem cells; (2) CD15(-)/CD29(HI)/CD24(LO) revealed neural crest-like and mesenchymal phenotypes; and (3) CD15(-)/CD29(LO)/CD24(HI) selected neuroblasts and neurons. Fluorescence-activated cell sorting (FACS) for the CD15(-)/CD29(LO)/CD24(HI) profile reduced proliferative cell types in human embryonic stem cell differentiation. This eliminated tumor formation in vivo, resulting in pure neuronal grafts. In conclusion, combinatorial CD15/CD24/CD29 marker profiles define neural lineage development of neural stem cell, neural crest, and neuronal populations from human stem cells. We believe this set of biomarkers enables analysis and selection of neural cell types for developmental studies and pharmacological and therapeutic applications.

Stem cell-derived dopamine neurons for brain repair in Parkinson’s disease

One of the prospects for a curative treatment for Parkinson’s disease is to replace the lost dopaminergic neurons. Preclinical and clinical trials have demonstrated that dissected fetal dopaminergic neurons have the potential to markedly improve motor function in animal models and Parkinson’s disease patients. However, this source of cells will never be sufficient to use as a widespread therapy. Over the last 20 years, scientists have been searching for other reliable sources of midbrain dopamine neurons, and stem cells appear to be strong candidates. This article reviews the potential of different types of stem cells, from embryonic to adult to induced pluripotent stem cells, to see how well the cells can be differentiated into fully functional dopamine neurons, which cells might be the best candidates and how much more research is required before stem cell technology might be translated to a clinical therapy for Parkinson’s disease.

Long-term, stable differentiation of human embryonic stem cell-derived neural precursors grafted into the adult mammalian neostriatum

Stem cell grafts have been advocated as experimental treatments for neurological diseases by virtue of their ability to offer trophic support for injured neurons and, theoretically, to replace dead neurons. Human embryonic stem cells (HESCs) are a rich source of neural precursors (NPs) for grafting, but have been questioned for their tendency to form tumors. Here we studied the ability of HESC-derived NP grafts optimized for cell number and differentiation stage prior to transplantation, to survive and stably differentiate and integrate in the basal forebrain (neostriatum) of young adult nude rats over long periods of time (6 months). NPs were derived from adherent monolayer cultures of HESCs exposed to noggin. After transplantation, NPs showed a drastic reduction in mitotic activity and an avid differentiation into neurons that projected via major white matter tracts to a variety of forebrain targets. A third of NP-derived neurons expressed the basal forebrain-neostriatal marker dopamine-regulated and cyclic AMP-regulated phosphoprotein. Graft-derived neurons formed mature synapses with host postsynaptic structures, including dendrite shafts and spines. NPs inoculated in white matter tracts showed a tendency toward glial (primarily astrocytic) differentiation, whereas NPs inoculated in the ventricular epithelium persisted as nestin(+) precursors. Our findings demonstrate the long-term ability of noggin-derived human NPs to structurally integrate tumor-free into the mature mammalian forebrain, while maintaining some cell fate plasticity that is strongly influenced by particular central nervous system (CNS) niches.

Regulation of neural specification from human embryonic stem cells by BMP and FGF

Inhibition of bone morphogenetic protein (BMP) signaling is required for vertebrate neural induction, and fibroblast growth factors (FGFs) may affect neural induction through phosphorylation at the linker region of Smad1, thus regulating BMP signaling. Here we show that human embryonic stem cells efficiently convert to neuroepithelial cells in the absence of BMP antagonists, or even when exposed to high concentrations of exogenous BMP4. Molecular and functional analyses revealed multiple levels of endogenous BMP signaling inhibition that may account for the efficient neural differentiation. Blocking FGF signaling inhibited neural induction, but did not alter the phosphorylation of the linker region of Smad1, suggesting that FGF enhances human neural specification independently of BMP signaling.

Human amniotic fluid stem cells do not differentiate into dopamine neurons in vitro or after transplantation in vivo

Although embryonic stem (ES) cells can generate dopamine (DA) neurons that are potentially useful as a cell replacement therapy in Parkinson's disease (PD), associated ethical and practical concerns remain major stumbling blocks to their eventual use in humans. In this study, we examined human amniotic fluid stem (hAFS) cells derived from routine amniocenteses for their potential to give rise to DA neurons in vitro and following transplantation into the 6-hydroxydopamine-lesioned rat brain. We show that undifferentiated hAFS cells constitutively expressed mRNAs and proteins typical of stem cells but also cell derivatives of all three germ layers, including neural progenitors/neurons (nestin, beta-tubulin III, neurofilament). Additionally, these cells expressed mRNAs of an immature DA phenotype (Lmx1a, Pitx-3, Nurr1, Aldh1a1) but not the corresponding proteins. Importantly, treatment with DA differentiation factors using a variety of protocols did not further promote the development of fully differentiated DA neurons from hAFS cells. Thus, Lmx1a, Aldh1a1, AADC, TH, and DAT proteins were not detected in hAFS cells in culture or after transplantation into the PD rat brain. Moreover, by 3 weeks after implantation, there were no surviving AFS cells in the graft, likely as a result of an acute immunorejection response, as evidenced by the abundant presence of CD11+ macrophage/microglia and reactive GFAP+ astrocytes in the host brain. Taken together, these results suggest that further studies will be needed to improve differentiation procedures in culture and to prolong cell survival in vivo if hAFS cells are to be useful as replacement cells in PD.

Isolation and culture of ventral mesencephalic precursor cells and dopaminergic neurons from rodent brains

The ability to isolate ventral midbrain (VM) precursor cells and neurons provides a powerful means to characterize their differentiation properties and to study their potential for restoring dopamine (DA) neurons degenerated in Parkinson's disease (PD). Preparation and maintenance of DA VM in primary culture involves a number of critical steps to yield healthy cells and appropriate data. Here, we offer a detailed description of protocols to consistently prepare VM DA cultures from rat and mouse embryonic fetal-stage midbrain. We also present methods for organotypic culture of midbrain tissue, for differentiation as aggregate cultures, and for adherent culture systems of DA differentiation and maturation, followed by a synopsis of relevant analytical read-out options. Isolation and culture of rodent VM precursor cells and DA neurons can be exploited for studies of DA lineage development, of neuroprotection, and of cell therapeutic approaches in animal models of PD.

Neuronal cell replacement in Parkinson's disease

Transplantation of foetal dopamine neurons into the striatum of Parkinson's disease patients can provide restoration of the dopamine system and alleviate motor deficits. However, cellular replacement is associated with several problems. As with pharmacological treatments, cell therapy can lead to disabling abnormal involuntary movements (dyskinesias). The exclusion of serotonin and GABA neurons, and enrichment of substantia nigra (A9) dopamine neurons, may circumvent this problem. Furthermore, although grafted foetal dopamine neurons can survive in Parkinson's patients for more than a decade, the occurrence of Lewy bodies within such transplanted cells and reduced dopamine transporter and tyrosine hydroxylase expression levels indicate that grafted cells are associated with pathology. It will be important to understand if such abnormalities are host- or graft induced and to develop methods to ensure survival of functional dopamine neurons. Careful preparation of cellular suspensions to minimize graft-induced inflammatory responses might influence the longevity of transplanted cells. Finally, a number of practical and ethical issues are associated with the use of foetal tissue sources. Thus, future cell therapy is aiming towards the use of embryonic stem cell or induced pluripotent stem cell derived dopamine neurons.

Future directions: use of interventional MRI for cell-based therapy of Parkinson disease

Transplantation of neural cells for the treatment of neurologic disorders has garnered much attention and considerable enthusiasm from patients and physicians alike. Cell-based therapies have been proposed for a wide range of central nervous system pathologies ranging from stroke and trauma to demyelinating disorders and neurodegenerative diseases. Notably, cell transplantation for Parkinson disease (PD) has become even more attractive with the rapid advances in derivation of dopaminergic neurons from human embryonic stem cells. This article briefly reviews some of the relevant issues regarding the transplantation of cells for treatment of PD and hypothesizes how interventional MRI may be useful to optimize the surgical delivery of cells for PD and other central nervous system disorders.

Cell-based therapies for Parkinson's disease: past, present, and future

Parkinson's disease (PD) researchers have pioneered the use of cell-based therapies (CBTs) in the central nervous system. CBTs for PD were originally envisioned as a way to replace the dopaminergic nigral neurons lost with the disease. Several sources of catecholaminergic cells, including autografts of adrenal medulla and allografts or xenografts of mesencephalic fetal tissue, were successfully assessed in animal models, but their clinical translation has yielded poor results and much controversy. Recent breakthroughs on cell biology are helping to develop novel cell lines that could be used for regenerative medicine. Their future successful clinical application depends on identifying and solving the problems encountered in previous CBTs trials. In this review, we critically analyze past CBTs' clinical translation, the impact of the host in graft survival, and the role of preclinical studies and emerging new cell lines. We propose that the prediction of clinical results from preclinical studies requires experimental designs that allow blind data acquisition and statistical analysis, assessment of the therapy in models that parallel clinical conditions, looking for sources of complications or side effects, and limiting optimism bias when reporting outcomes.

A novel combination of factors, termed SPIE, which promotes dopaminergic neuron differentiation from human embryonic stem cells

Background

Stromal-Derived Inducing Activity (SDIA) is one of the most efficient methods of generating dopaminergic (DA) neurons from embryonic stem cells (ESC). DA neuron induction can be achieved by co-culturing ESC with the mouse stromal cell lines PA6 or MS5. The molecular nature of this effect, which has been termed “SDIA” is so far unknown. Recently, we found that factors secreted by PA6 cells provided lineage-specific instructions to induce DA differentiation of human ESC (hESC).

Methodology/Principal Findings

In the present study, we compared PA6 cells to various cell lines lacking the SDIA effect, and employed genome expression analysis to identify differentially-expressed signaling molecules. Among the factors highly expressed by PA6 cells, and known to be associated with CNS development, were stromal cell-derived factor 1 (SDF-1/CXCL12), pleiotrophin (PTN), insulin-like growth factor 2 (IGF2), and ephrin B1 (EFNB1). When these four factors, the combination of which was termed SPIE, were applied to hESC, they induced differentiation to TH-positive neurons in vitro. RT-PCR and western blot analysis confirmed the expression of midbrain specific markers, including engrailed 1, Nurr1, Pitx3, and dopamine transporter (DAT) in cultures influenced by these four molecules. Electrophysiological recordings showed that treatment of hESC with SPIE induced differentiation of neurons that were capable of generating action potentials and forming functional synaptic connections.

Conclusions/Significance

The combination of SDF-1, PTN, IGF2, and EFNB1 mimics the DA phenotype-inducing property of SDIA and was sufficient to promote differentiation of hESC to functional midbrain DA neurons. These findings provide a method for differentiating hESC to form DA neurons, without a requirement for the use of animal-derived cell lines or products.

Development of human nervous tissue upon differentiation of embryonic stem cells in three-dimensional culture

Researches on neural differentiation using embryonic stem cells (ESC) require analysis of neurogenesis in conditions mimicking physiological cellular interactions as closely as possible. In this study, we report an air-liquid interface-based culture of human ESC. This culture system allows three-dimensional cell expansion and neural differentiation in the absence of added growth factors. Over a 3-month period, a macroscopically visible, compact tissue developed. Histological coloration revealed a dense neural-like neural tissue including immature tubular structures. Electron microscopy, immunochemistry, and electrophysiological recordings demonstrated a dense network of neurons, astrocytes, and oligodendrocytes able to propagate signals. Within this tissue, tubular structures were niches of cells resembling germinal layers of human fetal brain. Indeed, the tissue contained abundant proliferating cells expressing markers of neural progenitors. Finally, the capacity to generate neural tissues on air-liquid interface differed for different ESC lines, confirming variations of their neurogenic potential. In conclusion, this study demonstrates in vitro engineering of a human neural-like tissue with an organization that bears resemblance to early developing brain. As opposed to previously described methods, this differentiation (a) allows three-dimensional organization, (b) yields dense interconnected neural tissue with structurally and functionally distinct areas, and (c) is spontaneously guided by endogenous developmental cues.

Lentiviral delivery of LMX1a enhances dopaminergic phenotype in differentiated human bone marrow mesenchymal stem cells

Human mesenchymal stem cells (MSCs) reside in the bone marrow and are known for their ability to differentiate along the mesenchymal lineage (fat, bone, and cartilage). Recent works have suggested the possibility that these cells are also capable of differentiating toward the neuroectodermal lineage. Using lentiviral gene delivery, we sought to reprogram the bone marrow-derived MSCs toward dopaminergic differentiation through delivery of LMX1a, which was reported to be a key player in dopaminergic differentiation in both developmental animal models and embryonic stem cells. Transduction of cells with fluorescent reporter genes confirmed efficiency of gene delivery. On incubation of the LMX1a transduced cells in differentiation medium, the LMX1a protein was concentrated in the cells' nuclei and specific dopaminergic developmental genes were upregulated. Moreover, the transduced cells expressed higher levels of tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis, and secreted significantly higher level of dopamine in comparison to nontransduced cells. We hereby present a novel strategy to facilitate the dopaminergic differentiation of bone marrow-derived MSCs as a possible cell source for autologous transplantation for Parkinsonian patients in the future.

Conditions for tumor-free and dopamine neuron-enriched grafts after transplanting human ES cell-derived neural precursor cells

We have previously demonstrated derivation of neural precursor (NP) cells of a midbrain-type from human embryonic stem (hES) cells to yield an enriched population of dopamine (DA) neurons. These hES-derived NPs can be expanded in vitro through multiple passages without altering their DA neurogenic potential. Here, we studied two aspects of these hES-NP cells that are critical issues in cell therapeutic approaches for Parkinson's disease (PD): cell survival and tumorigenic potential. Neuroepithelial rosettes, a potentially tumorigenic structure, disappeared during hES-NP cell expansion in vitro. Although a minor population of cells positive for Oct3/4, a marker specific for undifferentiated hES cells, persisted in culture during hES-NP cell expansion, they could be completely eliminated by subculturing hES-NPs under differentiation-inducing conditions. Consistently, no tumors/teratomas are formed in rats grafted with multipassaged hES-NPs. However, extensively expanded hES-NP cells easily underwent cell death during differentiation in vitro and after transplantation in vivo. Transgenic expression of Bcl-XL and sonic hedgehog (SHH) completely overcame the cell survival problems without increasing tumor formation. These findings indicate that hES-NP cell expansion in conjunction with Bcl-XL+SHH transgene expression may provide a renewable and safe source of DA neurons for transplantation in PD.

Human embryonic stem cell differentiation toward regional specific neural precursors

Human embryonic stem cells (hESCs) are self-renewing pluripotent cells that have the capacity to differentiate into a wide variety of cell types. This potentiality represents a promising source to overcome many human diseases by providing an unlimited supply of all cell types, including cells with neural characteristics. Therefore, this review summarizes early neural development and the potential of hESCs to differentiate under in vitro conditions, examining at the same time the potential use of differentiated hESCs for therapeutic applications for neural tissue and cell regeneration.

Identification of transplantable dopamine neuron precursors at different stages of midbrain neurogenesis

Protocols used for generation of mesencephalic dopamine (mesDA) neurons from stem cells, or fetal brain tissue, invariably result in cell preparations that are highly mixed in composition, containing mesDA neuron precursors in various states of fate commitment and differentiation. For further optimisation and refinement of these procedures it is essential to determine the optimal stage of development and phenotypic characteristics of cells used for grafting. We have used fluorescence-activated cell sorting procedures to isolate mesDA precursors in defined stages of differentiation from mouse ventral mesencephalon (VM), at embryonic day 10.5 (E10.5), when the mesDA neuron domain consists of proliferative radial glia-like cells expressing the mesDA neuron determinant Lmx1a and the floorplate marker Corin, and at E12.5, when the VM has expanded to comprise a mixture of proliferative progenitors, neuroblasts and young neurons. The sorted cells were transplanted to the striatum of 6-hydroxydopamine-lesioned rats. Results show that the Lmx1a/Corin-expressing ventricular zone progenitors, which are the source of mesDA neurons in grafts from E10.5 VM, had lost this capacity at E12.5. At this later stage all transplantable mesDA precursors resided in the intermediate zone as postmitotic Nurr1-expressing neuroblasts. The more differentiated, TH-expressing cells survived sorting and transplantation poorly. We also provide evidence that, during early mesDA neurogenesis, the progenitors for nigral mesDA neurons segregate to lateral parts of the Lmx1a-expressing domain and can be selectively isolated based on their level of Corin expression. These results have implications for current efforts to develop well-characterized stem cell-derived mesDA progenitor cell preparations for cell therapy.

Noggin maintains pluripotency of human embryonic stem cells grown on Matrigel

OBJECTIVE

Spontaneous differentiation of human embryonic stem cell (hESC) cultures is a major concern in stem cell research. Physical removal of differentiated areas in a stem cell colony is the current approach used to keep the cultures in a pluripotent state for a prolonged period of time. All hESCs available for research require unidentified soluble factors secreted from feeder layers to maintain the undifferentiated state and pluripotency. Under experimental conditions, stem cells are grown on various matrices, the most commonly used being Matrigel.

MATERIALS AND METHODS

We propose an alternative method to prevent spontaneous differentiation of hESCs grown on Matrigel that uses low amounts of recombinant noggin. We make use of the porosity of Matrigel to serve as a matrix that traps noggin and gradually releases it into the culture to antagonize bone morphogenetic proteins (BMP). BMPs are known to initiate differentiation of hESCs and are either present in the conditioned medium or are secreted by hESCs themselves.

RESULTS

hESCs grown on Matrigel supplemented with noggin in conditioned medium from feeder layers (irradiated mouse embryonic fibroblasts) retained both normal karyotype and markers of hESC pluripotency for 14 days. In addition, these cultures were found to have increased cell proliferation of stem cells as compared to hESCs grown on Matrigel alone.

CONCLUSION

Noggin can be utilized for short term prevention of spontaneous differentiation of stem cells grown on Matrigel.

Human glioblastoma-derived cancer stem cells: establishment of invasive glioma models and treatment with oncolytic herpes simplex virus vectors

Glioblastoma, the most malignant type of primary brain tumor, is one of the solid cancers where cancer stem cells have been isolated, and studies have suggested resistance of those cells to chemotherapy and radiotherapy. Here, we report the establishment of CSC-enriched cultures derived from human glioblastoma specimens. They grew as neurospheres in serum-free medium with epidermal growth factor and fibroblast growth factor 2, varied in the level of CD133 expression and very efficiently formed highly invasive and/or vascular tumors upon intracerebral implantation into immunodeficient mice. As a novel therapeutic strategy for glioblastoma-derived cancer stem-like cells (GBM-SC), we have tested oncolytic herpes simplex virus (oHSV) vectors. We show that although ICP6 (UL39)-deleted mutants kill GBM-SCs as efficiently as wild-type HSV, the deletion of gamma34.5 significantly attenuated the vectors due to poor replication. However, this was significantly reversed by the additional deletion of alpha47. Infection with oHSV G47Delta (ICP6(-), gamma34.5(-), alpha47(-)) not only killed GBM-SCs but also inhibited their self-renewal as evidenced by the inability of viable cells to form secondary tumor spheres. Importantly, despite the highly invasive nature of the intracerebral tumors generated by GBM-SCs, intratumoral injection of G47Delta significantly prolonged survival. These results for the first time show the efficacy of oHSV against human GBM-SCs, and correlate this cytotoxic property with specific oHSV mutations. This is important for designing new oHSV vectors and clinical trials. Moreover, the new glioma models described in this study provide powerful tools for testing experimental therapeutics and studying invasion and angiogenesis.

Parkinson's disease patient-derived induced pluripotent stem cells free of viral reprogramming factors

Induced pluripotent stem cells (iPSCs) derived from somatic cells of patients represent a powerful tool for biomedical research and may provide a source for replacement therapies. However, the use of viruses encoding the reprogramming factors represents a major limitation of the current technology since even low vector expression may alter the differentiation potential of the iPSCs or induce malignant transformation. Here, we show that fibroblasts from five patients with idiopathic Parkinson's disease can be efficiently reprogrammed and subsequently differentiated into dopaminergic neurons. Moreover, we derived hiPSCs free of reprogramming factors using Cre-recombinase excisable viruses. Factor-free hiPSCs maintain a pluripotent state and show a global gene expression profile, more closely related to hESCs than to hiPSCs carrying the transgenes. Our results indicate that residual transgene expression in virus-carrying hiPSCs can affect their molecular characteristics and that factor-free hiPSCs therefore represent a more suitable source of cells for modeling of human disease.

Future of cell and gene therapies for Parkinson's disease

The experimental field of restorative neurology continues to advance with implantation of cells or transfer of genes to treat patients with neurological disease. Both strategies have generated a consensus that demonstrates their capacity for structural and molecular brain modification in the adult brain. However, both approaches have yet to successfully address the complexities to make such novel therapeutic modalities work in the clinic. Prior experimental cell transplantation to patients with PD utilized dissected pieces of fetal midbrain tissue, containing mixtures of cells and neuronal types, as donor cells. Stem cell and progenitor cell biology provide new opportunities for selection and development of large batches of specific therapeutic cells. This may allow for cell composition analysis and dosing to optimize the benefit to an individual patient. The biotechnology used for cell and gene therapy for treatment of neurological disease may eventually be as advanced as today's pharmaceutical drug-related design processes. Current gene therapy phase 1 safety trials for PD include the delivery of a growth factor (neurturin via the glial cell line-derived neurotrophic factor receptor) and a transmitter enzyme (glutamic acid decarboxylase and aromatic acid decarboxylase). Many new insights from cell biological and molecular studies provide opportunities to selectively express or suppress factors relevant to neuroprotection and improved function of neurons involved in PD. Future gene and cell therapies are likely to coexist with classic pharmacological therapies because their use can be tailored to individual patients' underlying disease process and need for neuroprotective or restorative interventions.

Stem cells in development of therapeutics for Parkinson's disease: a perspective

Using Parkinson's disease as a prototype of neurodegenerative diseases, we propose applications of human stem cells in the development of therapeutics for neurodegenerative diseases. First, in vitro differentiation of human stem cells offers a versatile model for dissecting molecular interactions underlying human dopamine (DA) neuron specification, which may form a foundation for instigating regeneration of DA neurons from progenitors that reside in the brain. Second, stem cells derived from diseased cells or through genetic modification can serve as a platform for unraveling biochemical processes that lead to the cellular pathogenesis of degeneration. This may in turn serve as a template for identifying or developing therapeutics for slowing, stopping, or reversing the disease process. And finally, stem cells, particularly those induced from patients' own cells, provide a reliable source of DA neurons for cell-based therapy.

Efficient derivation of functional dopaminergic neurons from human embryonic stem cells on a large scale

Cell-replacement therapy using human embryonic stem cells (hESCs) holds great promise in treating Parkinson's disease. We have recently reported a highly efficient method to generate functional dopaminergic (DA) neurons from hESCs. Our method includes a unique step, the formation of spherical neural masses (SNMs), and offers the highest yield of DA neurons ever achieved so far. In this report, we describe our method step by step, covering not only how to differentiate hESCs into DA neurons at a high yield, but also how to amplify, freeze and thaw the SNMs, which are the key structures that make our protocol unique and advantageous. Although the whole process of generation of DA neurons from hESCs takes about 2 months, only 14 d are needed to derive DA neurons from the SNMs.