Electrical and neurotransmitter activity of mature neurons derived from mouse embryonic stem cells by Sox-1 lineage selection and directed differentiation

SOX1 Is a Backup Gene for Brain Neurons and Glioma Stem Cell Protection and Proliferation

Failed neuroprotection leads to the initiation of several diseases. SOX1 plays many roles in embryogenesis, oncogenesis, and male sex determination, and can promote glioma stem cell proliferation, invasion, and migration due to its high expression in glioblastoma cells. The functional versatility of the SOX1 gene in malignancy, epilepsy, and Parkinson's disease, as well as its adverse effects on dopaminergic neurons, makes it an interesting research focus. Hence, we collate the most important discoveries relating to the neuroprotective effects of SOX1 in brain cancer and propose hypothesis worthy of SOX1's role in the survival of senescent neuronal cells, its roles in fibroblast cell proliferation, and cell fat for neuroprotection, and the discharge of electrical impulses for homeostasis. Increase in electrical impulses transmitted by senescent cells affects the synthesis of neurotransmitters, which will modify the brain cell metabolism and microenvironment.

Induced Pluripotent Stem Cell-Derived Podocyte-Like Cells as Models for Assessing Mechanisms Underlying Heritable Disease Phenotype: Initial Studies Using Two Alport Syndrome Patient Lines Indicate Impaired Potassium Channel Activity

Renal podocyte survival depends upon the dynamic regulation of a complex cell architecture that links the glomerular basement membrane to integrins, ion channels, and receptors. Alport syndrome is a heritable chronic kidney disease where mutations in α3, α4, or α5 collagen genes promote podocyte death. In rodent models of renal failure, activation of the calcium-sensing receptor (CaSR) can protect podocytes from stress-related death. In this study, we assessed CaSR function in podocyte-like cells derived from induced-pluripotent stem cells from two patients with Alport Syndrome (AS1 & AS2) and a renal disease free individual [normal human mesangial cell (NHMC)], as well as a human immortalized podocyte-like (HIP) cell line. Extracellular calcium elicited concentration-dependent elevations of intracellular calcium in all podocyte-like cells. NHMC and HIP, but not AS1 or AS2 podocyte-like cells, also showed acute reductions in intracellular calcium prior to elevation. In NHMC podocyte-like cells this acute reduction was blocked by the large-conductance potassium channel (KCNMA1) inhibitors iberiotoxin (10 nM) and tetraethylammonium (5 mM), as well as the focal adhesion kinase inhibitor PF562271 (N-methyl-N-(3-((2-(2-oxo-2,3-dihydro-1H-indol-5-ylamino)-5-trifluoromethyl-pyrimidin-4-ylamino)-methyl)-pyridin-2-yl)-methanesulfonamide, 10 nM). Quantitative polymerase chain reaction (qPCR) and immunolabeling showed the presence of KCNMA1 transcript and protein in all podocyte-like cells tested. Cultivation of AS1 podocytes on decellularized plates of NHMC podocyte-like cells partially restored acute reductions in intracellular calcium in response to extracellular calcium. We conclude that the AS patient-derived podocyte-like cells used in this study showed dysfunctional integrin signaling and potassium channel function, which may contribute to podocyte death seen in Alport syndrome.

HTS/HCS to screen molecules able to maintain embryonic stem cell self-renewal or to induce differentiation: overview of protocols

Embryonic stem (ES) cells, combining self-renewal ability with wide range tissue-specific cell differentiation, represent one of the most powerful model systems in basic research, drug discovery and biomedical applications. In the field of drug development, ES cells are instrumental in high-throughput/content screening (HTS/HCS) for the evaluation of large compound libraries to test biological activity and toxic properties. Since it is a high priority to test new compounds in vitro, before starting animal and human treatments, there is an increasing demand for new in vitro models that can be used in HTS/HCS to facilitate drug development. In order to achieve this objective, several methods for ES cell self-renewal or differentiation have been evaluated to assess their compatibility with HTS/HCS. This review describes protocols used to screen molecules able to maintain self-renewal or to induce differentiation in ectodermal, mesodermal, endodermal, and their derivative cell lines.

Human pluripotent stem cell derived midbrain PITX3(eGFP/w) neurons: a versatile tool for pharmacological screening and neurodegenerative modeling

PITX3 expression is confined to adult midbrain dopaminergic (mDA) neurons. In this study we describe the generation and basic functional characteristics of mDA neurons derived from a human pluripotent stem cell (hPSC) line expressing eGFP under the control of the PITX3 promoter. Flow cytometry showed that eGFP was evident in 15% of the neuron population at day 12 of differentiation and this level was maintained until at least day 80. From days 20 to 80 of differentiation intracellular chloride decreased and throughout this period around ∼20% of PITX3^eGFP/w neurons exhibited spontaneous Ca²⁺ transients (from 3.3 ± 0.3 to 5.0 ± 0.1 min^-1, respectively). These neurons also responded to any of ATP, glutamate, acetylcholine, or noradrenaline with elevations of intracellular calcium. As neuronal cultures matured more dopamine was released and single PITX3^eGFP/w neurons began to respond to more than one neurotransmitter. MPP⁺ and tumor necrosis factor (TNF), but not prostaglandin E₂, caused death of the ∼50% of PITX3^eGFP/w neurons (day 80). Tracking eGFP using time lapse confocal microscopy over 24 h demonstrated significant TNF-mediated neurite retraction over time. This work now shows that these PITX3^eGFP/w neurons are amenable to flow cytometry, release dopamine and respond to multiple neurotransmitters with elevations of intracellular calcium, we believe that they represent a versatile system for neuropharmacological and neurotoxicological studies.

GABAergic neurons from mouse embryonic stem cells possess functional properties of striatal neurons in vitro, and develop into striatal neurons in vivo in a mouse model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disease where GABAergic medium spiny neurons (MSNs) in the striatum degenerate. Embryonic stem cell-derived neural transplantation may provide an appropriate therapy for HD. Here we aimed to develop a suitable protocol to obtain a high percentage of functional GABAergic neurons from mouse embryonic stem cells (mESCs), and then tested their differentiation potential in vivo. The monolayer method was compared with the embryoid body and five stage method for its efficiency in generating GABAergic neurons from mESCs. All three methods yielded a similar percentage of GABAergic neurons from mESCs. Monolayer method-derived GABAergic neurons expressed the MSN marker dopamine- and cyclic AMP-regulated phosphoprotein (DARPP32). The pluripotent stem cell population could be eliminated in vitro by treating cells with puromycin and retinoic acid. Using patch-clamp recordings, the functional properties of GABAergic neurons derived from mESCs were compared to GABAergic neurons derived from primary lateral ganglionic eminence. Both types of neurons showed active membrane properties (voltage-gated Na(+) and K(+) currents, Na(+)-dependent action potentials, and spontaneous postsynaptic currents) and possessed functional glutamatergic receptors and transporters. mESC-derived neural progenitors were transplanted into a mouse model of HD. Grafted cells differentiated to mature neurons expressing glutamate decarboxylase, dopamine type 1 receptors, and DARPP32. Also, neural precursors and dividing populations were found in the grafts. In summary, mESCs are able to differentiate efficiently into functional GABAergic neurons using defined in vitro conditions, and these survive and differentiate following grafting to a mouse model of HD.

DMH1, a highly selective small molecule BMP inhibitor promotes neurogenesis of hiPSCs: comparison of PAX6 and SOX1 expression during neural induction

Recent successes in deriving human-induced pluripotent stem cells (hiPSCs) allow for the possibility of studying human neurons derived from patients with neurological diseases. Concomitant inhibition of the BMP and TGF-β1 branches of the TGF-β signaling pathways by the endogenous antagonist, Noggin, and the small molecule SB431542, respectively, induces efficient neuralization of hiPSCs, a method known as dual-SMAD inhibition. The use of small molecule inhibitors instead of their endogenous counterparts has several advantages including lower cost, consistent activity, and the maintenance of xeno-free culture conditions. We tested the efficacy of DMH1, a highly selective small molecule BMP-inhibitor for its potential to replace Noggin in the neuralization of hiPSCs. We compare Noggin and DMH1-induced neuralization of hiPSCs by measuring protein and mRNA levels of pluripotency and neural precursor markers over a period of seven days. The regulation of five of the six markers assessed was indistinguishable in the presence of concentrations of Noggin or DMH1 that have been shown to effectively inhibit BMP signaling in other systems. We observed that by varying the DMH1 or Noggin concentration, we could selectively modulate the number of SOX1 expressing cells, whereas PAX6, another neural precursor marker, remained the same. The level and timing of SOX1 expression have been shown to affect neural induction as well as neural lineage. Our observations, therefore, suggest that BMP-inhibitor concentrations need to be carefully monitored to ensure appropriate expression levels of all transcription factors necessary for the induction of a particular neuronal lineage. We further demonstrate that DMH1-induced neural progenitors can be differentiated into β3-tubulin expressing neurons, a subset of which also express tyrosine hydroxylase. Thus, the combined use of DMH1, a highly specific BMP-pathway inhibitor, and SB431542, a TGF-β1-pathway specific inhibitor, provides us with the tools to independently regulate these two pathways through the exclusive use of small molecule inhibitors.

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

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

Electrophysiological properties of embryonic stem cell-derived neurons

In vitro generation of functional neurons from embryonic stem (ES) cells and induced pluripotent stem cells offers exciting opportunities for dissecting gene function, disease modelling, and therapeutic drug screening. To realize the potential of stem cells in these biomedical applications, a complete understanding of the cell models of interest is required. While rapid advances have been made in developing the technologies for directed induction of defined neuronal subtypes, most published works focus on the molecular characterization of the derived neural cultures. To characterize the functional properties of these neural cultures, we utilized an ES cell model that gave rise to neurons expressing the green fluorescent protein (GFP) and conducted targeted whole-cell electrophysiological recordings from ES cell-derived neurons. Current-clamp recordings revealed that most neurons could fire single overshooting action potentials; in some cases multiple action potentials could be evoked by depolarization, or occurred spontaneously. Voltage-clamp recordings revealed that neurons exhibited neuronal-like currents, including an outward current typical of a delayed rectifier potassium conductance and a fast-activating, fast-inactivating inward current, typical of a sodium conductance. Taken together, these results indicate that ES cell-derived GFP(+) neurons in culture display functional neuronal properties even at early stages of differentiation.

A targeted NKX2.1 human embryonic stem cell reporter line enables identification of human basal forebrain derivatives

We have used homologous recombination in human embryonic stem cells (hESCs) to insert sequences encoding green fluorescent protein (GFP) into the NKX2.1 locus, a gene required for normal development of the basal forebrain. Generation of NKX2.1-GFP(+) cells was dependent on the concentration, timing, and duration of retinoic acid treatment during differentiation. NKX2.1-GFP(+) progenitors expressed genes characteristic of the basal forebrain, including SHH, DLX1, LHX6, and OLIG2. Time course analysis revealed that NKX2.1-GFP(+) cells could upregulate FOXG1 expression, implying the existence of a novel pathway for the generation of telencephalic neural derivatives. Further maturation of NKX2.1-GFP(+) cells gave rise to γ-aminobutyric acid-, tyrosine hydroxylase-, and somatostatin-expressing neurons as well as to platelet-derived growth factor receptor α-positive oligodendrocyte precursors. These studies highlight the diversity of cell types that can be generated from human NKX2.1(+) progenitors and demonstrate the utility of NKX2.1(GFP/w) hESCs for investigating human forebrain development and neuronal differentiation.

Neuropharmacological properties of neurons derived from human stem cells

Human pluripotent stem cells have enormous potential value in neuropharmacology and drug discovery yet there is little data on the major classes and properties of receptors and ion channels expressed by neurons derived from these stem cells. Recent studies in this lab have therefore used conventional patch-clamp electrophysiology to investigate the pharmacological properties of the ligand and voltage-gated ion channels in neurons derived and maintained in vitro from the human stem cell (hSC) line, TERA2.cl.SP12. TERA2.cl.SP12 stem cells were differentiated with retinoic acid and used in electrophysiological experiments 28-50 days after beginning differentiation. HSC-derived neurons generated large whole cell currents with depolarizing voltage steps (-80 to 30 mV) comprised of an inward, rapidly inactivating component and a delayed, slowly deactivating outward component. The fast inward current was blocked by the sodium channel blocker tetrodotoxin (0.1 μM) and the outward currents were significantly reduced by tetraethylammonium ions (TEA, 5 mM) consistent with the presence of functional Na and K ion channels. Application of the inhibitory neurotransmitters, GABA (0.1-1000 μM) or glycine (0.1-1000 μM) evoked concentration dependent currents. The GABA currents were inhibited by the convulsants, picrotoxin (10 μM) and bicuculline (3 μM), potentiated by the NSAID mefenamic acid (10-100 μM), the general anaesthetic pentobarbital (100 μM), the neurosteroid allopregnanolone and the anxiolytics chlordiazepoxide (10 μM) and diazepam (10 μM) all consistent with the expression of GABA(A) receptors. Responses to glycine were reversibly blocked by strychnine (10 μM) consistent with glycine-gated chloride channels. The excitatory agonists, glutamate (1-1000 μM) and NMDA (1-1000 μM) activated concentration-dependent responses from hSC-derived neurons. Glutamate currents were inhibited by kynurenic acid (1 mM) and NMDA responses were blocked by MgCl(2) (2 mM) in a highly voltage-dependent manner. Together, these findings show that neurons derived from human stem cells develop an array of functional receptors and ion channels with a pharmacological profile in keeping with that described for native neurons. This study therefore provides support for the hypothesis that stem cells may provide a powerful source of human neurons for future neuropharmacological studies.

Primary cells and stem cells in drug discovery: emerging tools for high-throughput screening

Many drug discovery screening programs employ immortalized cells, recombinantly engineered to express a defined molecular target. Several technologies are now emerging that render it feasible to employ more physiologically, and clinically relevant, cell phenotypes. Consequently, numerous approaches use primary cells, which retain many functions seen in vivo, as well as endogenously expressing the target of interest. Furthermore, stem cells, of either embryonic or adult origin, as well as those derived from differentiated cells, are now finding a place in drug discovery. Collectively, these cells are expanding the utility of authentic human cells, either as screening tools or as therapeutics, as well as providing cells derived directly from patients. Nonetheless, the growing use of phenotypically relevant cells (including primary cells or stem cells) is not without technical difficulties, particularly when their envisioned use lies in high-throughput screening (HTS) protocols. In particular, the limited availability of homogeneous primary or stem cell populations for HTS mandates that novel technologies be developed to accelerate their adoption. These technologies include detection of responses with very few cells as well as protocols to generate cell lines in abundant, homogeneous populations. In parallel, the growing use of changes in cell phenotype as the assay readout is driving greater use of high-throughput imaging techniques in screening. Taken together, the greater availability of novel primary and stem cell phenotypes as well as new detection technologies is heralding a new era of cellular screening. This convergence offers unique opportunities to identify drug candidates for disorders at which few therapeutics are presently available.

P2X2, P2X4 and P2Y1 receptors elevate intracellular Ca2+ in mouse embryonic stem cell-derived GABAergic neurons

BACKGROUND AND PURPOSE

Neurons derived from mouse embryonic stem cells (mESCs) are a valuable resource for basic pharmacological research. With the exception of cardiomyocytes, there is relatively little understanding of the pharmacology of stem cell-derived differentiated cells. In this study we investigate P2 receptor agonist effects on GABAergic neurons derived from mESCs.

EXPERIMENTAL APPROACH

mESCs were differentiated into GABAergic neurons in the presence of N2B27 culture medium. At day 24 of differentiation GABAergic neuronal responsiveness to purinergic agonists was investigated using calcium imaging and [3H]-GABA release studies.

KEY RESULTS

Sub-populations of GABAergic neurons responded to some or all of the adenine and uracil nucleotides ATP, ADP, UTP and UDP (all 100 microM) with elevations of intracellular Ca2+ ([Ca2+]i). The number of neurons responding to ATP was reduced by suramin (100 microM), PPADS (10 microM) and MRS2179 (10 microM), but not by NF023 (10 microM). The response to ATP was modulated by extracellular Zn2+ and pH. Neurons also responded to ATP (100 microM) with the release of [3H]-GABA, an effect completely inhibited by tetrodotoxin (100 nM). Ap4A and 2-methylthioATP both elicited significant [3H]-GABA release. Reverse transcriptase PCR showed the presence of P2X1,2,3,4,5,6 and P2X7, and P2Y1,2 and P2Y6 receptors. mESCs expressed P2X2,5 and P2X7 and P2Y1,2 and P2Y6 receptors.

CONCLUSIONS AND IMPLICATIONS

GABAergic neurons derived from stem cells elevate [Ca2+]i predominantly via the activation of P2X2, P2X4 and P2Y1 receptors. This study shows that mESCs generate good models of neuronal function for in vitro pharmacological investigation.

High-throughput screening in embryonic stem cell-derived neurons identifies potentiators of alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate-type glutamate receptors

Stem cell biology offers advantages to investigators seeking to identify new therapeutic molecules. Specifically, stem cells are genetically stable, scalable for molecular screening, and function in cellular assays for drug efficacy and safety. A key hurdle for drug discoverers of central nervous system disease is a lack of high quality neuronal cells. In the central nervous system, alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate (AMPA) subtype glutamate receptors mediate the vast majority of excitatory neurotransmissions. Embryonic stem (ES) cell protocols were developed to differentiate into neuronal subtypes that express AMPA receptors and were pharmacologically responsive to standard compounds for AMPA potentiation. Therefore, we hypothesized that stem cell-derived neurons should be predictive in high-throughput screens (HTSs). Here, we describe a murine ES cell-based HTS of a 2.4 x 10(6) compound library, the identification of novel chemical "hits" for AMPA potentiation, structure function relationship of compounds and receptors, and validation of chemical leads in secondary assays using human ES cell-derived neurons. This reporting of murine ES cell derivatives being formatted to deliver HTS of greater than 10(6) compounds for a specific drug target conclusively demonstrates a new application for stem cells in drug discovery. In the future new molecular entities may be screened directly in human ES or induced pluripotent stem cell derivatives.

Niche-dependent development of functional neuronal networks from embryonic stem cell-derived neural populations

BACKGROUND

The present work was performed to investigate the ability of two different embryonic stem (ES) cell-derived neural precursor populations to generate functional neuronal networks in vitro. The first ES cell-derived neural precursor population was cultivated as free-floating neural aggregates which are known to form a developmental niche comprising different types of neural cells, including neural precursor cells (NPCs), progenitor cells and even further matured cells. This niche provides by itself a variety of different growth factors and extracellular matrix proteins that influence the proliferation and differentiation of neural precursor and progenitor cells. The second population was cultivated adherently in monolayer cultures to control most stringently the extracellular environment. This population comprises highly homogeneous NPCs which are supposed to represent an attractive way to provide well-defined neuronal progeny. However, the ability of these different ES cell-derived immature neural cell populations to generate functional neuronal networks has not been assessed so far.

RESULTS

While both precursor populations were shown to differentiate into sufficient quantities of mature NeuN+ neurons that also express GABA or vesicular-glutamate-transporter-2 (vGlut2), only aggregate-derived neuronal populations exhibited a synchronously oscillating network activity 24 weeks after initiating the differentiation as detected by the microelectrode array technology. Neurons derived from homogeneous NPCs within monolayer cultures did merely show uncorrelated spiking activity even when differentiated for up to 12 weeks. We demonstrated that these neurons exhibited sparsely ramified neurites and an embryonic vGlut2 distribution suggesting an inhibited terminal neuronal maturation. In comparison, neurons derived from heterogeneous populations within neural aggregates appeared as fully mature with a dense neurite network and punctuated vGlut2 expression within presynaptic vesicles. Also those NPCs that had migrated away from adherent neural aggregates maintained their ability to generate a synchronously oscillating neuronal network, even if they were separated from adherent aggregates, dissociated and re-plated.

CONCLUSION

These findings suggest that the complex environment within niches and aggregates of heterogeneous neural cell populations support the generation of fully mature neurons and functional neuronal networks from ES cell-derived neural cells. In contrast, homogeneous ES cell-derived NPCs within monolayer cultures exhibited an impaired functional neuronal maturation.

Propagation of embryonic stem cells in stirred suspension without serum

Embryonic stem cells (ESCs) with their unlimited capacity for self-renewal and ability to differentiate along multiple cell lineages are a superb starting material for biotechnology applications and cellular therapies. However, realization of the potential of ESCs requires the development of scalable systems for their production in large quantities and in a regulated manner. Here, we describe a methodology for the expansion of mouse ESCs (mESCs) as pluripotent aggregates in a stirred suspension bioreactor and in medium without serum. Initially, the culture of feeder cell-independent mESCs in dishes was adapted to serum-free conditions. Also, we explored whether spinner flasks equipped with a triangle-shaped impeller and baffles support the culture of mESC aggregates. Serum-free culture in these vessels resulted in an almost 20-fold increase in the live mESC concentration over 4 days without significant loss of cell viability. Even after consecutive passages, mESCs retained high expression of pluripotency markers Oct3/4, Rex1 and SSEA-1. More importantly, when differentiation was induced these cells adopted fates of all three germ layers namely neuroectoderm, cardiac mesoderm and definitive endoderm. These findings demonstrate that stem cells can be propagated under serum-free conditions in a scalable stirred-suspension culture without loss of their pluripotency.

Derivation of homogeneous GABAergic neurons from mouse embryonic stem cells

Embryonic stem cells (ESCs) promise an unlimited source of defined cells for cell transplantation therapy, while protocols for derivation of homogeneous populations of desirable cell types are yet to be developed and/or refined. Gamma aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system, and disturbed GABAergic signaling is associated with a host of neurological conditions. We developed a simple ES cell differentiation protocol which led to the production of uniform GABAergic neurons in approximately 2 weeks. The differentiation protocol involved treatment of embryoid bodies (EBs) with high concentrations (10(-5)-10(-)(4) M) of all-trans-retinoic acid (RA) for 3 days. After plating these EBs on attached dishes in neural supportive medium, 93-96% of the cells became GABA-positive neurons in 7-11 days. These cells also expressed immature neuronal markers with voltage-gated delayed rectifier potassium currents, suggesting that they were immature GABAergic neurons. The technology may have implications for modeling and treatment of GABAergic signaling-related diseases and injuries.

Endothelium-induced proliferation and electrophysiological differentiation of human embryonic stem cell-derived neuronal precursors

Neurogenesis occurs in a stem cell niche in which vascular elements, including endothelial cells (ECs), are thought to play an important role. Using co-culture experiments, we investigated the effect of ECs on proliferation and functional neuronal differentiation of human embryonic stem (ES) cellderived neuronal precursor cells (NPCs). NPCs were cultured for 5 days in medium containing fibroblast growth factor-2 (FGF-2), with or without ECs. FGF-2 and ECs were then removed, and NPCs were maintained in culture for additional periods. Compared to control NPC cultures, EC-treated NPC cultures showed increased cell proliferation at short intervals (5 days) after withdrawal of FGF-2 and larger tetrodotoxin-sensitive inward membrane currents at longer intervals (10-14 days), but a similar pattern of development of neuronal differentiation markers. The effects of ECs appeared to result from the release of soluble factors rather than from cell contact, because they were observed despite the physical separation of NPCs from ECs by a cell-impermeable membrane. These findings indicate that ECs can regulate the proliferation and electrophysiological neuronal differentiation of human NPCs.

Embryonic stem cells as a source of models for drug discovery

Embryonic stem cells (ESCs) will become a source of models for a wide range of adult differentiated cells, providing that reliable protocols for directed differentiation can be established. Stem-cell technology has the potential to revolutionize drug discovery, making models available for primary screens, secondary pharmacology, safety pharmacology, metabolic profiling and toxicity evaluation. Models of differentiated cells that are derived from mouse ESCs are already in use in drug discovery, and are beginning to find uses in high-throughput screens. Before analogous human models can be obtained in adequate numbers, reliable methods for the expansion of human ESC cultures will be needed. For applications in drug discovery, involving either species, protocols for directed differentiation will need to be robust and affordable. Here, we explore current challenges and future opportunities in relation to the use of stem-cell technology in drug discovery, and address the use of both mouse and human models.

Heterogeneous population of dopaminergic neurons derived from mouse embryonic stem cells: preliminary phenotyping based on receptor expression and function

The possibility exists that directed differentiation of mouse embryonic stem (mES) cells is capable of yielding enriched populations of dopaminergic neurons, but at present there is little understanding of the pharmacological properties of these cells; or whether such cells represent a pharmacologically, phenotypically similar population. In this study we used a simple culture protocol to generate dopaminergic neurons and offer a preliminary pharmacological investigation of these cells using Ca2+ imaging and [3H]-dopamine release studies. In fluo-4 AM loaded cells, 13-17 days postplating, and after the addition of tetrodotoxin some of the population of mouse embryonic stem cell-derived neurons responded to adenosine triphosphate (ATP), noradrenaline (NA), acetylcholine (ACh) and L-glutamate (L-glut) with elevations of Ca2+ influx. Within the microtubule-associated protein and tyrosine hydroxylase (TH)-positive cell population adenosine triphosphate, noradrenaline, acetylcholine and L-glutamate elicited positive elevations of Ca2+ in 74, 66, 58 and 67% of the population; cells could be further subdivided into three major pharmacologically distinct populations based on the combinations of agonist they responded to. Acetylcholine (30 microM) and noradrenaline (30 microM) were the only agonists to elicit significant tritium overflow from [3H]-dopamine loaded cells. The acetylcholine effect was blocked by atropine (1 microM) and tetrodotoxin (1 microM) and elevated by haloperidol (100 nM). The noradrenaline effects were reduced by cocaine (10 microM), but not by tetrodotoxin (100 nM). These data indicate that the dopaminergic neurons derived from mouse embryonic stem cells represent a heterogeneous population possessing combinations of purinergic, adrenergic, cholinergic and glutamatergic receptors located on the cell soma.

Embryonic stem cells as a cellular model for neuroectodermal commitment and skin formation

Embryonic stem (ES) cells can be differentiated into many cell types in vitro, thus providing a potential unlimited supply of cells for cognitive in vitro studies and cell-based therapy. We recently reported the efficient derivation of ectodermal and epidermal cells from murine ES cells. These differentiated ES cells were able to form, in culture, a multilayered epidermis coupled with an underlying dermal compartment, similar to native skin. We clarified the function of BMP-4 in the binary neuroectodermal choice by stimulating sox-1(+) neural precursors to undergo specific apoptosis while inducing epidermal differentiation through DeltaNp63 gene activation. We further demonstrated that DeltaNp63 enhances ES-derived ectodermal cell proliferation and is necessary for epidermal commitment. This unique cellular model further provides a powerful tool for identifying the molecular mechanisms controlling normal skin development and for investigating p63-ectodermal dysplasia human congenital pathologies.

Identification and selection of cardiomyocytes during human embryonic stem cell differentiation

Human embryonic stem cells (hESC) are pluripotent lines that can differentiate in vitro into cell derivatives of all three germ layers, including cardiomyocytes. Successful application of these unique cells in the areas of cardiovascular research and regenerative medicine has been hampered by difficulties in identifying and selecting specific cardiac progenitor cells from the mixed population of differentiating cells. We report the generation of stable transgenic hESC lines, using lentiviral vectors, and single-cell clones that express a reporter gene (eGFP) under the transcriptional control of a cardiac-specific promoter (the human myosin light chain-2V promoter). Our results demonstrate the appearance of eGFP-expressing cells during the differentiation of the hESC as embryoid bodies (EBs) that can be identified and sorted using FACS (purity>95%, viability>85%). The eGFP-expressing cells were stained positively for cardiac-specific proteins (>93%), expressed cardiac-specific genes, displayed cardiac-specific action-potentials, and could form stable myocardial cell grafts following in vivo cell transplantation. The generation of these transgenic hESC lines may be used to identify and study early cardiac precursors for developmental studies, to robustly quantify the extent of cardiomyocyte differentiation, to label the cells for in vivo grafting, and to allow derivation of purified cell populations of cardiomyocytes for future myocardial cell therapy strategies.

Functional neural development from human embryonic stem cells: accelerated synaptic activity via astrocyte coculture

How a naive human neuroepithelial cell becomes an electrophysiologically active neuron remains unknown. Here, we describe the early physiological development of neurons differentiating from naive human embryonic stem (hES) cells. We found that differentiating neuronal cells progressively decrease their resting membrane potential, gain characteristic Na+ and K+ currents, and fire mature action potentials by 7 weeks of differentiation. This is similar to the maturation pattern observed in animals, albeit on a greatly expanded time scale. An additional 3 weeks of differentiation resulted in neurons that could fire repetitive trains of action potentials in response to depolarizing current pulses. The onset of spontaneous synaptic activity also occurred after 7 weeks of differentiation, in association with the differentiation of astrocytes within the culture. Cocultures of hES cell-derived neuroepithelial cells with exogenous astrocytes significantly accelerated the onset of synaptic currents but did not alter action potential generation. These findings suggest that the development of membrane characteristics and action potentials depend on the intrinsic maturation of Na+ and K+ currents, whereas synaptic transmission is enhanced by astrocytes, which may be achieved independently of the maturation of action potentials. Furthermore, we found that although astrocyte-conditioned medium accelerated synaptic protein localization, it did not increase synaptic activity, suggesting a contact-dependent mechanism by which astrocytes augment synaptic activity. These results lay the foundation for future studies examining the functional development of human neurons and provide support for the potential application of human cells in restorative neuronal therapies.

Genetic selection of sox1GFP-expressing neural precursors removes residual tumorigenic pluripotent stem cells and attenuates tumor formation after transplantation

Because of their ability to proliferate and to differentiate into diverse cell types, embryonic stem (ES) cells are a potential source of cells for transplantation therapy of various diseases, including Parkinson's disease. A critical issue for this potential therapy is the elimination of undifferentiated cells that, even in low numbers, could result in teratoma formation in the host brain. We hypothesize that an efficient solution would consist of purifying the desired cell types, such as neural precursors, prior to transplantation. To test this hypothesis, we differentiated sox1-green fluorescent protein (GFP) knock-in ES cells in vitro, purified neural precursor cells by fluorescence-activated cell sorting (FACS), and characterized the purified cells in vitro as well as in vivo. Immunocytofluorescence and RT-PCR analyses showed that this genetic purification procedure efficiently removed undifferentiated pluripotent stem cells. Furthermore, when differentiated into mature neurons in vitro, the purified GFP+ cell population generated enriched neuronal populations, whereas the GFP- population generated much fewer neurons. When treated with dopaminergic inducing signals such as sonic hedgehog (SHH) and fibroblast growth factor-8 (FGF8), FACS-purified neural precursor cells responded to these molecules and generated dopaminergic neurons as well as other neural subtypes. When transplanted, the GFP+ cell population generated well contained grafts containing dopaminergic neurons, whereas the GFP- population generated significantly larger grafts (about 20-fold) and frequent tumor-related deaths in the transplanted animals. Taken together, our results demonstrate that genetic purification of neural precursor cells using FACS isolation can effectively remove unwanted proliferating cell types and avoid tumor formation after transplantation.