Coordination of sonic hedgehog and Wnt signaling determines ventral and dorsal telencephalic neuron types from human embryonic stem cells

Endogenous WNT signaling regulates hPSC-derived neural progenitor cell heterogeneity and specifies their regional identity

Neural progenitor cells (NPCs) derived from human pluripotent stem cells (hPSCs) are a multipotent cell population that is capable of nearly indefinite expansion and subsequent differentiation into the various neuronal and supporting cell types that comprise the CNS. However, current protocols for differentiating NPCs toward neuronal lineages result in a mixture of neurons from various regions of the CNS. In this study, we determined that endogenous WNT signaling is a primary contributor to the heterogeneity observed in NPC cultures and neuronal differentiation. Furthermore, exogenous manipulation of WNT signaling during neural differentiation, through either activation or inhibition, reduces this heterogeneity in NPC cultures, thereby promoting the formation of regionally homogeneous NPC and neuronal cultures. The ability to manipulate WNT signaling to generate regionally specific NPCs and neurons will be useful for studying human neural development and will greatly enhance the translational potential of hPSCs for neural-related therapies.

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Heterogeneous endogenous WNT signaling regulates hPSC-derived neuronal diversity

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Endogenous WNT signaling specifies the regional identity of hPSC-derived neurons

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Exogenous WNT signaling leads to uniform neuronal cultures from hPSCs

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Effects of WNT signaling on neurogenesis are recapitulated in an hPSC-based system

An in vitro model of human neocortical development using pluripotent stem cells: cocaine-induced cytoarchitectural alterations

Neocortical development involves ordered specification of forebrain cortical progenitors to various neuronal subtypes, ultimately forming the layered cortical structure. Modeling of this process using human pluripotent stem cells (hPSCs) would enable mechanistic studies of human neocortical development, while providing new avenues for exploration of developmental neocortical abnormalities. Here, we show that preserving hPSCs aggregates - allowing embryoid body formation - while adding basic fibroblast growth factor (bFGF) during neuroepithelial development generates neural rosettes showing dorsal forebrain identity, including Mash1(+) dorsal telencephalic GABAergic progenitors. Structures that mirrored the organization of the cerebral cortex formed after rosettes were seeded and cultured for 3 weeks in the presence of FGF18, BDNF and NT3. Neurons migrated along radial glia scaffolding, with deep-layer CTIP2(+) cortical neurons appearing after 1 week and upper-layer SATB2(+) cortical neurons forming during the second and third weeks. At the end of differentiation, these structures contained both glutamatergic and GABAergic neurons, with glutamatergic neurons being most abundant. Thus, this differentiation protocol generated an hPSC-based model that exhibits temporal patterning and a neuronal subtype ratio similar to that of the developing human neocortex. This model was used to examine the effects of cocaine during neocorticogenesis. Cocaine caused premature neuronal differentiation and enhanced neurogenesis of various cortical neuronal subtypes. These cocaine-induced changes were inhibited by the cytochrome P450 inhibitor cimetidine. This in vitro model enables mechanistic studies of neocorticogenesis, and can be used to examine the mechanisms through which cocaine alters the development of the human neocortex.

Directed differentiation of embryonic stem cells using a bead-based combinatorial screening method

We have developed a rapid, bead-based combinatorial screening method to determine optimal combinations of variables that direct stem cell differentiation to produce known or novel cell types having pre-determined characteristics. Here we describe three experiments comprising stepwise exposure of mouse or human embryonic cells to 10,000 combinations of serum-free differentiation media, through which we discovered multiple novel, efficient and robust protocols to generate a number of specific hematopoietic and neural lineages. We further demonstrate that the technology can be used to optimize existing protocols in order to substitute costly growth factors with bioactive small molecules and/or increase cell yield, and to identify in vitro conditions for the production of rare developmental intermediates such as an embryonic lymphoid progenitor cell that has not previously been reported.

Loss of spastin function results in disease-specific axonal defects in human pluripotent stem cell-based models of hereditary spastic paraplegia

Human neuronal models of hereditary spastic paraplegias (HSP) that recapitulate disease-specific axonal pathology hold the key to understanding why certain axons degenerate in patients and to developing therapies. SPG4, the most common form of HSP, is caused by autosomal dominant mutations in the SPAST gene, which encodes the microtubule-severing ATPase spastin. Here, we have generated a human neuronal model of SPG4 by establishing induced pluripotent stem cells (iPSCs) from an SPG4 patient and differentiating these cells into telencephalic glutamatergic neurons. The SPG4 neurons displayed a significant increase in axonal swellings, which stained strongly for mitochondria and tau, indicating the accumulation of axonal transport cargoes. In addition, mitochondrial transport was decreased in SPG4 neurons, revealing that these patient iPSC-derived neurons recapitulate disease-specific axonal phenotypes. Interestingly, spastin protein levels were significantly decreased in SPG4 neurons, supporting a haploinsufficiency mechanism. Furthermore, cortical neurons derived from spastin-knockdown human embryonic stem cells (hESCs) exhibited similar axonal swellings, confirming that the axonal defects can be caused by loss of spastin function. These spastin-knockdown hESCs serve as an additional model for studying HSP. Finally, levels of stabilized acetylated-tubulin were significantly increased in SPG4 neurons. Vinblastine, a microtubule-destabilizing drug, rescued this axonal swelling phenotype in neurons derived from both SPG4 iPSCs and spastin-knockdown hESCs. Thus, this study demonstrates the successful establishment of human pluripotent stem cell-based neuronal models of SPG4, which will be valuable for dissecting the pathogenic cellular mechanisms and screening compounds to rescue the axonal degeneration in HSP.

Comparison and optimization of hiPSC forebrain cortical differentiation protocols

Several protocols have been developed for human induced pluripotent stem cell neuronal differentiation. We compare several methods for forebrain cortical neuronal differentiation by assessing cell morphology, immunostaining and gene expression. We evaluate embryoid aggregate vs. monolayer with dual SMAD inhibition differentiation protocols, manual vs. AggreWell aggregate formation, plating substrates, neural progenitor cell (NPC) isolation methods, NPC maintenance and expansion, and astrocyte co-culture. The embryoid aggregate protocol, using a Matrigel substrate, consistently generates a high yield and purity of neurons. NPC isolation by manual selection, enzymatic rosette selection, or FACS all are efficient, but exhibit some differences in resulting cell populations. Expansion of NPCs as neural aggregates yields higher cell purity than expansion in a monolayer. Finally, co-culture of iPSC-derived neurons with astrocytes increases neuronal maturity by day 40. This study directly compares commonly employed methods for neuronal differentiation of iPSCs, and can be used as a resource for choosing between various differentiation protocols.

Survival and Integration of Neurons Derived from Human Embryonic Stem Cells in MPTP-Lesioned Primates

A human embryonic stem cell (HESC) line, H1, was studied after differentiation to a dopaminergic phenotype in vitro in order to carry out in vivo studies in Parkinsonian monkeys. To identify morphological characteristics of transplanted donor cells, HESCs were transfected with a GFP lentiviral vector. Gene expression studies were performed at each step of a neural rosette-based dopaminergic differentiation protocol by RT-PCR. In vitro immunofluorescence revealed that >90% of the differentiated cells exhibited a neuronal phenotype by β-III-tubulin immunocytochemistry, with 17% of the cells coexpressing tyrosine hydroxylase prior to implantation. Biochemical analyses demonstrated dopamine release in culture in response to potassium chloride-induced membrane depolarization, suggesting that the cells synthesized and released dopamine. These characterized, HESC-derived neurons were then implanted into the striatum and midbrain of MPTP (1-methyl-4- phenyl-1,2,3,6-tetrahydropyridine)-exposed monkeys that were triple immunosuppressed. Here we demonstrate robust survival of transplanted HESC-derived neurons after 6 weeks, as well as morphological features consistent with polarization, organization, and extension of processes that integrated into the host striatum. Expression of the dopaminergic marker tyrosine hydroxylase was not maintained in HESC-derived neural grafts in either the striatum or substantia nigra, despite a neuronal morphology and expression of β-III-tubulin. These results suggest that dopamine neuronal cells derived from neuroectoderm in vitro will not maintain the correct midbrain phenotype in vivo in nonhuman primates, contrasted with recent studies showing dopamine neuronal survival using an alternative floorplate method.

The double inhibition of endogenously produced BMP and Wnt factors synergistically triggers dorsal telencephalic differentiation of mouse ES cells

Embryonic stem (ES) cells are becoming a popular model of in vitro neurogenesis, as they display intrinsic capability to generate neural progenitors that undergo the known steps of in vivo neural development. These include the acquisition of distinct regional fates, which depend on growth factors and signals that are present in the culture medium. The control of the intracellular signaling that is active at different steps of ES cell neuralization, even when cells are cultured in chemically defined medium, is complicated by the endogenous production of growth factors. However, this endogenous production has been poorly investigated so far. To address this point, we performed a high-throughput analysis of the expression of morphogens during mouse ES cell neuralization in minimal medium. We found that during their neuralization, ES cells increased the expression of members of Wnt, Fibroblast Growth Factor (FGF), and BMP families. Conversely, the expression of Activin/Nodal and Shh ligands was low in early steps of neuralization. In this experimental condition, neural progenitors and neurons generated by ES cells expressed a gene expression profile that was consistent with a midbrain identity. We found that endogenous BMP and Wnt signaling, but not FGF signaling, synergistically affected ES cell neural patterning, by turning off a profile of dorsal/telencephalic gene expression. Double BMP and Wnt inhibition allowed neuralized ES cells to sequentially activate key genes of cortical differentiation. Our findings are consistent with a novel synergistic effect of Wnt and BMP endogenous signaling of ES cells in inhibiting a cortical differentiation program.

Regulation of Human PAX6 Expression by miR-7

The paired box gene 6 (PAX6) is a powerful mediator of eye and brain organogenesis whose spatiotemporal expression is exquisitely controlled by multiple mechanisms, including post-transcriptional regulation by microRNAs (miRNAs). In the present study, we use bioinformatic predictions to identify three candidate microRNA-7 (miR-7) target sites in the human PAX6 3′ untranslated region (3′-UTR) and demonstrate that two of them are functionally active in a human cell line. Furthermore, transient transfection of cells with synthetic miR-7 inhibits PAX6 protein expression but does not alter levels of PAX6 mRNA, suggesting that miR-7 induces translational repression of PAX6. Finally, a comparison of PAX6 3′-UTRs across species reveals that one of the functional miR-7 target sites is conserved, whereas the second functional target site is found only in primates. Thus, the interaction between PAX6 and miR-7 appears to be highly conserved; however, the precise number of sites through which this interaction occurs may have expanded throughout evolution.

Pharmacologic rescue of axon growth defects in a human iPSC model of hereditary spastic paraplegia SPG3A

Hereditary spastic paraplegias are a large, diverse group of neurological disorders (SPG1-71) with the unifying feature of prominent lower extremity spasticity, owing to a length-dependent axonopathy of corticospinal motor neurons. The most common early-onset form of pure, autosomal dominant hereditary spastic paraplegia is caused by mutation in the ATL1 gene encoding the atlastin-1 GTPase, which mediates homotypic fusion of ER tubules to form the polygonal ER network. We have identified a p.Pro342Ser mutation in a young girl with pure SPG3A. This residue is in a critical hinge region of atlastin-1 between its GTPase and assembly domains, and it is conserved in all known eukaryotic atlastin orthologs. We produced induced pluripotent stem cells from skin fibroblasts and differentiated these into forebrain neurons to generate a human neuronal model for SPG3A. Axons of these SPG3A neurons showed impaired growth, recapitulating axonal defects in atlastin-1-depleted rat cortical neurons and impaired root hair growth in loss-of-function mutants of the ATL1 ortholog rhd3 in the plant Arabidopsis. Both the microtubule cytoskeleton and tubular ER are important for mitochondrial distribution and function within cells, and SPG3A neurons showed alterations in mitochondrial motility. Even so, it is not clear whether this change is involved in disease pathogenesis. The SPG3A axon growth defects could be rescued with microtubule-binding agents, emphasizing the importance of tubular ER interactions with the microtubule cytoskeleton in hereditary spastic paraplegia pathogenesis. The prominent alterations in axon growth in SPG3A neurons may represent a particularly attractive target for suppression in screens for novel pharmacologic agents.

Slice Culture Method for Studying Migration of Neuronal Progenitor Cells Derived from Human Embryonic Stem Cells (hESC)

In this unit we describe an overlay brain slice culture assay for studying migration of transgenic neurospheres derived from human embryonic stem cells (hESC). Neuronal progenitor cells were generated from hESC by derivation of embryoid bodies and rosettes. Rosettes were transfected using the PiggyBac transposon system with either control plasmids (GFP) or plasmid encoding a gene important for migration of neuronal progenitor cells, Doublecortin (DCX). Transfected cells were subsequently grown in low-adhesion plates to generate transgenic human neurospheres (t-hNS). Organotypic slice cultures were prepared from postnatal rat forebrain and maintained using the interface method, before transfected t-hNS were overlaid below the cortex of each hemisphere. After 1 to 5 days, forebrain slices were fixed and processed for immunofluorescence. The distance at which cells migrated from the center of neurospheres to the host forebrain tissue was measured using Image J software. This protocol provides details for using the slice culture method for studying migration and integration of human neuronal cells into the host brain tissue.

Stem cell therapy and cellular engineering for treatment of neuronal dysfunction in Huntington's disease

Huntington's disease (HD) is a fatal inherited neurodegenerative disorder characterized by progressive loss of neurons in the striatum, a sub-cortical region of the forebrain. The sub-cortical region of the forebrain is associated with the control of movement and behavior, thus HD initially presents with coordination difficulty and cognitive decline. Recent reprogramming technologies, including induced pluripotent stem cells (iPSCs) and induced neural stem cells (iNSCs), have created opportunities to understand the pathological cascades that underlie HD and to develop new treatments for this currently incurable neurological disease. The ultimate objectives of stem cell-based therapies for HD are to replace lost neurons and to prevent neuronal dysfunction and death. In this review, we examine the current understanding of the molecular and pathological mechanisms involved in HD. We discuss disease modeling with HD-iPSCs derived from the somatic cells of patients, which could provide an invaluable platform for understanding HD pathogenesis. We speculate about the benefits and drawbacks of using iNSCs as an alternative stem cell source for HD treatment. Finally, we discuss cell culture and engineering systems that promote the directed differentiation of pluripotent stem cell-derived NSCs into a striatal DARPP32(+) GABAergic MSN phenotype for HD. In conclusion, this review summarizes the potentials of cell reprogramming and engineering technologies relevant to the development of cell-based therapies for HD.

Self-organization of neural tissue architectures from pluripotent stem cells

Despite being a subject of intensive research, the mechanisms underlying the formation of neural tissue architectures during development of the central nervous system remain largely enigmatic. So far, studies into neural pattern formation have been restricted mainly to animal experiments. With the advent of pluripotent stem cells it has become possible to explore early steps of nervous system development in vitro. These studies have unraveled a remarkable propensity of primitive neural cells to self-organize into primitive patterns such as neural tube-like rosettes in vitro. Data from more advanced 3D culture systems indicate that this intrinsic propensity for self-organization can even extend to the formation of complex architectures such as a multilayered cortical neuroepithelium or an entire optic cup. These novel experimental paradigms not only demonstrate the enormous self-organization capacity of neural stem cells, they also provide exciting prospects for studying the earliest steps of human neural tissue development and the pathogenesis of brain malformations in reductionist in vitro paradigms.

In vitro neurogenesis: development and functional implications of iPSC technology

Neurogenesis is the developmental process regulating cell proliferation of neural stem cells, determining their differentiation into glial and neuronal cells, and orchestrating their organization into finely regulated functional networks. Can this complex process be recapitulated in vitro using induced pluripotent stem cell (iPSC) technology? Can neurodevelopmental and neurodegenerative diseases be modeled using iPSCs? What is the potential of iPSC technology in neurobiology? What are the recent advances in the field of neurological diseases? Since the applications of iPSCs in neurobiology are based on the capacity to regulate in vitro differentiation of human iPSCs into different neuronal subtypes and glial cells, and the possibility of obtaining iPSC-derived neurons and glial cells is based on and hindered by our poor understanding of human embryonic development, we reviewed current knowledge on in vitro neural differentiation from a developmental and cellular biology perspective. We highlight the importance to further advance our understanding on the mechanisms controlling in vivo neurogenesis in order to efficiently guide neurogenesis in vitro for cell modeling and therapeutical applications of iPSCs technology.

Interneurons from embryonic development to cell-based therapy

Many neurologic and psychiatric disorders are marked by imbalances between neural excitation and inhibition. In the cerebral cortex, inhibition is mediated largely by GABAergic (γ-aminobutyric acid-secreting) interneurons, a cell type that originates in the embryonic ventral telencephalon and populates the cortex through long-distance tangential migration. Remarkably, when transplanted from embryos or in vitro culture preparations, immature interneurons disperse and integrate into host brain circuits, both in the cerebral cortex and in other regions of the central nervous system. These features make interneuron transplantation a powerful tool for the study of neurodevelopmental processes such as cell specification, cell death, and cortical plasticity. Moreover, interneuron transplantation provides a novel strategy for modifying neural circuits in rodent models of epilepsy, Parkinson's disease, mood disorders, and chronic pain.

Cortical neurogenesis from pluripotent stem cells: complexity emerging from simplicity

The cerebral cortex contains dozens of neuronal subtypes grouped in specific layers and areas. Recent studies have revealed how embryonic and induced pluripotent stem cells (PSC) can differentiate into a wide diversity of cortical neurons in vitro, while recapitulating many of the temporal and spatial features that characterize corticogenesis. PSC-derived neurons can integrate into the brain following in vivo transplantation and display patterns of morphology and connectivity specific of cortical neurons. PSC-corticogenesis thus emerges as a robust model that provides new ways to link cortical development, evolution, and disease.

Thinking out of the dish: what to learn about cortical development using pluripotent stem cells

The development of the cerebral cortex requires the tightly coordinated generation of dozens of neuronal subtypes that will populate specific layers and areas. Recent studies have revealed how pluripotent stem cells (PSC), whether of mouse or human origin, can differentiate into a wide range of cortical neurons in vitro, which can integrate appropriately into the brain following in vivo transplantation. These models are largely artificial but recapitulate a substantial fraction of the complex temporal and regional patterning events that occur during in vivo corticogenesis. Here, we review these findings with emphasis on the new perspectives that they have brought for understanding of cortical development, evolution, and diseases.

Optimizing neuronal differentiation from induced pluripotent stem cells to model ASD

Autism spectrum disorder (ASD) is an early-onset neurodevelopmental disorder characterized by deficits in social communication, and restricted and repetitive patterns of behavior. Despite its high prevalence, discovery of pathophysiological mechanisms underlying ASD has lagged due to a lack of appropriate model systems. Recent advances in induced pluripotent stem cell (iPSC) technology and neural differentiation techniques allow for detailed functional analyses of neurons generated from living individuals with ASD. Refinement of cortical neuron differentiation methods from iPSCs will enable mechanistic studies of specific neuronal subpopulations that may be preferentially impaired in ASD. In this review, we summarize recent accomplishments in differentiation of cortical neurons from human pluripotent stems cells and efforts to establish in vitro model systems to study ASD using personalized neurons.

From pluripotency to forebrain patterning: an in vitro journey astride embryonic stem cells

Embryonic stem cells (ESCs) have been used extensively as in vitro models of neural development and disease, with special efforts towards their conversion into forebrain progenitors and neurons. The forebrain is the most complex brain region, giving rise to several fundamental structures, such as the cerebral cortex, the hypothalamus, and the retina. Due to the multiplicity of signaling pathways playing different roles at distinct times of embryonic development, the specification and patterning of forebrain has been difficult to study in vivo. Research performed on ESCs in vitro has provided a large body of evidence to complement work in model organisms, but these studies have often been focused more on cell type production than on cell fate regulation. In this review, we systematically reassess the current literature in the field of forebrain development in mouse and human ESCs with a focus on the molecular mechanisms of early cell fate decisions, taking into consideration the specific culture conditions, exogenous and endogenous molecular cues as described in the original studies. The resulting model of early forebrain induction and patterning provides a useful framework for further studies aimed at reconstructing forebrain development in vitro for basic research or therapy.

Stem cells on the brain: modeling neurodevelopmental and neurodegenerative diseases using human induced pluripotent stem cells

Seven years have passed since the initial report of the generation of induced pluripotent stem cells (iPSCs) from adult human somatic cells, and in the intervening time the field of neuroscience has developed numerous disease models using this technology. Here, we review progress in the field and describe both the advantages and potential pitfalls of modeling neurodegenerative and neurodevelopmental diseases using this technology. We include tables with information on neural differentiation protocols and studies that developed human iPSC lines to model neurological diseases. We also discuss how one can: investigate effects of genetic mutations with iPSCs, examine cell fate-specific phenotypes, best determine the specificity of a phenotype, and bring in vivo relevance to this in vitro technique.

Functional maturation of hPSC-derived forebrain interneurons requires an extended timeline and mimics human neural development

Directed differentiation from human pluripotent stem cells (hPSCs) has seen significant progress in recent years. However, most differentiated populations exhibit immature properties of an early embryonic stage, raising concerns about their ability to model and treat disease. Here, we report the directed differentiation of hPSCs into medial ganglionic eminence (MGE)-like progenitors and their maturation into forebrain type interneurons. We find that early-stage progenitors progress via a radial glial-like stem cell enriched in the human fetal brain. Both in vitro and posttransplantation into the rodent cortex, the MGE-like cells develop into GABAergic interneuron subtypes with mature physiological properties along a prolonged intrinsic timeline of up to 7 months, mimicking endogenous human neural development. MGE-derived cortical interneuron deficiencies are implicated in a broad range of neurodevelopmental and degenerative disorders, highlighting the importance of these results for modeling human neural development and disease.

Physiological normoxia and absence of EGF is required for the long-term propagation of anterior neural precursors from human pluripotent cells

Widespread use of human pluripotent stem cells (hPSCs) to study neuronal physiology and function is hindered by the ongoing need for specialist expertise in converting hPSCs to neural precursor cells (NPCs). Here, we describe a new methodology to generate cryo-preservable hPSC-derived NPCs that retain an anterior identity and are propagatable long-term prior to terminal differentiation, thus abrogating regular de novo neuralization. Key to achieving passagable NPCs without loss of identity is the combination of both absence of EGF and propagation in physiological levels (3%) of O₂. NPCs generated in this way display a stable long-term anterior forebrain identity and importantly retain developmental competence to patterning signals. Moreover, compared to NPCs maintained at ambient O₂ (21%), they exhibit enhanced uniformity and speed of functional maturation, yielding both deep and upper layer cortical excitatory neurons. These neurons display multiple attributes including the capability to form functional synapses and undergo activity-dependent gene regulation. The platform described achieves long-term maintenance of anterior neural precursors that can give rise to forebrain neurones in abundance, enabling standardised functional studies of neural stem cell maintenance, lineage choice and neuronal functional maturation for neurodevelopmental research and disease-modelling.

Directed Differentiation of Human Embryonic Stem Cells into Neural Progenitors

A variety of protocols have been used to produce neural progenitors from human embryonic stem cells. We have focused on a monolayer culture approach that generates neural rosettes. To initiate differentiation, cells are plated in a serum-free nutrient-poor medium in the presence of a BMP inhibitor. Depending on the cell line used, additional growth factor inhibitors may be required to promote neural differentiation. Long-term culture and addition of the Notch inhibitor DAPT can promote terminal neuronal differentiation. Extent of differentiation is monitored using immunocytochemistry for cell type-specific markers.

Shifts in the vascular endothelial growth factor isoforms result in transcriptome changes correlated with early neural stem cell proliferation and differentiation in mouse forebrain

Regulation of neural stem cell (NSC) fate decisions is critical during the transition from a multicellular mammalian forebrain neuroepithelium to the multilayered neocortex. Forebrain development requires coordinated vascular investment alongside NSC differentiation. Vascular endothelial growth factor A (Vegf) has proven to be a pleiotrophic gene whose multiple protein isoforms regulate a broad range of effects in neurovascular systems. To test the hypothesis that the Vegf isoforms (120, 164, and 188) are required for normal forebrain development, we analyzed the forebrain transcriptome of mice expressing specific Vegf isoforms, Vegf120, VegfF188, or a combination of Vegf120/188. Transcriptome analysis identified differentially expressed genes in embryonic day (E) 9.5 forebrain, a time point preceding dramatic neuroepithelial expansion and vascular investment in the telencephalon. Meta-analysis identified gene pathways linked to chromosome-level modifications, cell fate regulation, and neurogenesis that were altered in Vegf isoform mice. Based on these gene network shifts, we predicted that NSC populations would be affected in later stages of forebrain development. In the E11.5 telencephalon, we quantified mitotic cells [Phospho-Histone H3 (pHH3)-positive] and intermediate progenitor cells (Tbr2/Eomes-positive), observing quantitative and qualitative shifts in these populations. We observed qualitative shifts in cortical layering at P0, particularly with Ctip2-positive cells in layer V. The results identify a suite of genes and functional gene networks that can be used to further dissect the role of Vegf in regulating NSC differentiation and downstream consequences for NSC fate decisions.

Stepwise, non-adherent differentiation of human pluripotent stem cells to generate basal forebrain cholinergic neurons via hedgehog signaling

Basal forebrain cholinergic neurons (bfCNs) which provide innervation to the hippocampus and cortex, are required for memory and learning, and are primarily affected in Alzheimer's Disease (AD), resulting in related cognitive decline. Therefore generation of a source of bfCNs from human pluripotent stem cells (hPSCs) is crucial for in vitro disease modeling and development of novel AD therapies. In addition, for the advancement of regenerative approaches there is a requirement for an accurate developmental model to study the neurogenesis and survival of this population. Here we demonstrate the efficient production of bfCNs, using a novel embryoid body (EB) based non-adherent differentiation (NAdD) protocol. We establish a specific basal forebrain neural stem cell (NSC) phenotype via expression of the basal forebrain transcription factors NKX2.1 and LHX8, as well as the general forebrain marker FOXG1. We present evidence that this lineage is achieved via recapitulation of embryonic events, with induction of intrinsic hedgehog signaling, through the use of a 3D non-adherent differentiation system. This is the first example of hPSC-derived basal forebrain-like NSCs, which are scalable via self-renewal in prolonged culture. Furthermore upon terminal differentiation these basal forebrain-like NSCs generate high numbers of cholinergic neurons expressing the specific markers ChAT, VACht and ISL1. These hPSC-derived bfCNs possess characteristics that are crucial in a model to study AD related cholinergic neuronal loss in the basal forebrain. Examples are expression of the therapeutic target p75(NTR), the release of acetylcholine, and demonstration of a mature, and functional electrophysiological profile. In conclusion, this work provides a renewable source of human functional bfCNs applicable for studying AD specifically in the cholinergic system, and also provides a model of the key embryonic events in human bfCN development.

High yields of oligodendrocyte lineage cells from human embryonic stem cells at physiological oxygen tensions for evaluation of translational biology

We have established and efficient system to specify NG2/PDGF-Rα/OLIG2+ oligodendrocyte precursor cells (OPCs) from human embryonic stem cells (hESCs) at low, physiological (3%) oxygen levels. This was achieved via both forebrain and spinal cord origins, with up to 98% of cells expressing NG2. Developmental insights reveal a critical role for fibroblast growth factor 2 (FGF-2) in OLIG2 induction via ventral forebrain pathways. The OPCs mature in vitro to express O4 (46%) and subsequently become galactocerebroside (GALC), O1, and myelin basic protein-positive (MBP+) multibranching oligodendrocytes. These were cultured alongside hESC-derived neurons. The electrophysiological properties of human OPCs are similar to those of rat OPCs, with large voltage-gated sodium currents and the ability to fire action potentials. Exposure to a selective retinoid X receptor agonist increased the proportion of O4+ oligodendrocytes that express MBP from 5% to 30%. Thus, we have established a developmentally engineered system to investigate the biological properties of human OPCs and test the effects of putative remyelinating agents prior to clinical application.

Human induced pluripotent stem cell-derived cortical neurons integrate in stroke-injured cortex and improve functional recovery

Stem cell-based approaches to restore function after stroke through replacement of dead neurons require the generation of specific neuronal subtypes. Loss of neurons in the cerebral cortex is a major cause of stroke-induced neurological deficits in adult humans. Reprogramming of adult human somatic cells to induced pluripotent stem cells is a novel approach to produce patient-specific cells for autologous transplantation. Whether such cells can be converted to functional cortical neurons that survive and give rise to behavioural recovery after transplantation in the stroke-injured cerebral cortex is not known. We have generated progenitors in vitro, expressing specific cortical markers and giving rise to functional neurons, from long-term self-renewing neuroepithelial-like stem cells, produced from adult human fibroblast-derived induced pluripotent stem cells. At 2 months after transplantation into the stroke-damaged rat cortex, the cortically fated cells showed less proliferation and more efficient conversion to mature neurons with morphological and immunohistochemical characteristics of a cortical phenotype and higher axonal projection density as compared with non-fated cells. Pyramidal morphology and localization of the cells expressing the cortex-specific marker TBR1 in a certain layered pattern provided further evidence supporting the cortical phenotype of the fated, grafted cells, and electrophysiological recordings demonstrated their functionality. Both fated and non-fated cell-transplanted groups showed bilateral recovery of the impaired function in the stepping test compared with vehicle-injected animals. The behavioural improvement at this early time point was most likely not due to neuronal replacement and reconstruction of circuitry. At 5 months after stroke in immunocompromised rats, there was no tumour formation and the grafted cells exhibited electrophysiological properties of mature neurons with evidence of integration in host circuitry. Our findings show, for the first time, that human skin-derived induced pluripotent stem cells can be differentiated to cortical neuronal progenitors, which survive, differentiate to functional neurons and improve neurological outcome after intracortical implantation in a rat stroke model.

Efficient derivation of cortical glutamatergic neurons from human pluripotent stem cells: a model system to study neurotoxicity in Alzheimer's disease

Alzheimer's disease (AD) is among the most prevalent forms of dementia affecting the aging population, and pharmacological therapies to date have not been successful in preventing disease progression. Future therapeutic efforts may benefit from the development of models that enable basic investigation of early disease pathology. In particular, disease-relevant models based on human pluripotent stem cells (hPSCs) may be promising approaches to assess the impact of neurotoxic agents in AD on specific neuronal populations and thereby facilitate the development of novel interventions to avert early disease mechanisms. We implemented an efficient paradigm to convert hPSCs into enriched populations of cortical glutamatergic neurons emerging from dorsal forebrain neural progenitors, aided by modulating Sonic hedgehog (Shh) signaling. Since AD is generally known to be toxic to glutamatergic circuits, we exposed glutamatergic neurons derived from hESCs to an oligomeric pre-fibrillar forms of Aβ known as "globulomers", which have shown strong correlation with the level of cognitive deficits in AD. Administration of such Aβ oligomers yielded signs of the disease, including cell culture age-dependent binding of Aβ and cell death in the glutamatergic populations. Furthermore, consistent with previous findings in postmortem human AD brain, Aβ-induced toxicity was selective for glutamatergic rather than GABAeric neurons present in our cultures. This in vitro model of cortical glutamatergic neurons thus offers a system for future mechanistic investigation and therapeutic development for AD pathology using human cell types specifically affected by this disease.

Pluripotent stem cells as a model to study non-coding RNAs function in human neurogenesis

As fine regulators of gene expression, non-coding RNAs, and more particularly micro-RNAs (miRNAs), have emerged as key players in the development of the nervous system. In vivo experiments manipulating miRNAs expression as neurogenesis proceeds are very challenging in the mammalian embryo and totally impossible in the human. Human pluripotent stem cells (hPSCs), from embryonic origin (hESCs) or induced from adult somatic cells (iPSCs), represent an opportunity to study the role of miRNAs in the earliest steps of human neurogenesis in both physiological and pathological contexts. Robust protocols are now available to convert pluripotent stem cells into several sub-types of fully functional neurons, recapitulating key developmental milestones along differentiation. This provides a convenient cellular system for dissecting the role of miRNAs in phenotypic transitions critical to brain development and plasticity that may be impaired in neurological diseases with onset during development. The aim of this review is to illustrate how hPSCs can be used to recapitulate early steps of human neurogenesis and summarize recent reports of their contribution to the study of the role of miRNA in regulating development of the nervous system.

Brief report: self-organizing neuroepithelium from human pluripotent stem cells facilitates derivation of photoreceptors

Retinitis pigmentosa, other inherited retinal diseases, and age-related macular degeneration lead to untreatable blindness because of the loss of photoreceptors. We have recently shown that transplantation of mouse photoreceptors can result in improved vision. It is therefore timely to develop protocols for efficient derivation of photoreceptors from human pluripotent stem (hPS) cells. Current methods for photoreceptor derivation from hPS cells require long periods of culture and are rather inefficient. Here, we report that formation of a transient self-organized neuroepithelium from human embryonic stem cells cultured together with extracellular matrix is sufficient to induce a rapid conversion into retinal progenitors in 5 days. These retinal progenitors have the ability to differentiate very efficiently into Crx(+) photoreceptor precursors after only 10 days and subsequently acquire rod photoreceptor identity within 4 weeks. Directed differentiation into photoreceptors using this protocol is also possible with human-induced pluripotent stem (hiPS) cells, facilitating the use of patient-specific hiPS cell lines for regenerative medicine and disease modeling.

Directed differentiation of human embryonic stem cells into corticofugal neurons uncovers heterogeneous Fezf2-expressing subpopulations

Understanding how neuronal diversity is achieved within the cerebral cortex remains a major challenge in neuroscience. The advent of human embryonic stem cells (hESCs) as a model system provides a unique opportunity to study human corticogenesis in vitro and to identify the mechanisms that promote neuronal differentiation to achieve neuronal diversity in human brain. The transcription factor Fezf2 is necessary and sufficient for the specification of subcerebral projection neurons in mouse. However, its function during human corticogenesis is poorly understood. This study reports the differentiation of a hFezf2-YFP hESC reporter line into corticofugal projection neurons capable of extending axons toward the spinal cord upon transplantation into neonatal mouse brains. Additionally, we show that triple inhibition of the TGFß/BMP/Wnt-Shh pathway promotes the generation of hFezf2-expressing cells in vitro. Finally, this study unveils the isolation of two novel and distinct populations of hFezf2-YFP expressing cells reminiscent of the distinct Fezf2-expressing neuronal subtypes in the developing mouse brain. Overall our data suggest that the directed differentiation of hESCs into corticofugal neurons provides a useful model to identify the molecular mechanisms regulating human corticofugal differentiation and survival.

Deficits in human trisomy 21 iPSCs and neurons

Down syndrome (trisomy 21) is the most common genetic cause of intellectual disability, but the precise molecular mechanisms underlying impaired cognition remain unclear. Elucidation of these mechanisms has been hindered by the lack of a model system that contains full trisomy of chromosome 21 (Ts21) in a human genome that enables normal gene regulation. To overcome this limitation, we created Ts21-induced pluripotent stem cells (iPSCs) from two sets of Ts21 human fibroblasts. One of the fibroblast lines had low level mosaicism for Ts21 and yielded Ts21 iPSCs and an isogenic control that is disomic for human chromosome 21 (HSA21). Differentiation of all Ts21 iPSCs yielded similar numbers of neurons expressing markers characteristic of dorsal forebrain neurons that were functionally similar to controls. Expression profiling of Ts21 iPSCs and their neuronal derivatives revealed changes in HSA21 genes consistent with the presence of 50% more genetic material as well as changes in non-HSA21 genes that suggested compensatory responses to oxidative stress. Ts21 neurons displayed reduced synaptic activity, affecting excitatory and inhibitory synapses equally. Thus, Ts21 iPSCs and neurons display unique developmental defects that are consistent with cognitive deficits in individuals with Down syndrome and may enable discovery of the underlying causes of and treatments for this disorder.

Derivation and isolation of NKX2.1-positive basal forebrain progenitors from human embryonic stem cells

Gamma aminobutyric acid (GABA)-expressing interneurons are the major inhibitory cells of the cerebral cortex and hippocampus. These interneurons originate in the medial ganglionic eminence (MGE) and lateral ganglionic eminence of the ventral forebrain during embryonic development and show reduced survival and function in a variety of neurological disorders, including temporal lobe epilepsy. We and others have proposed that embryonic stem cell (ESC)-derived ventral forebrain progenitors might provide a source of new GABAergic interneurons for cell-based therapies. While human ESCs (hESCs) are readily differentiated in vitro into dorsal telencephalic neural progenitors, standard protocols for generating ventral subtypes of telencephalic progenitors are less effective. We now report efficient derivation of GABAergic progenitors using an established hESC reporter line that expresses green fluorescent protein (GFP) under the control of an endogenous NKX2.1 promoter. GABAergic progenitors were derived from this hESC line by a modified monolayer neural differentiation protocol. Consistent with sonic hedgehog (SHH)-dependent specification of NKX2.1-positive progenitors in the embryonic MGE, we show a dose-dependent increase in the generation of NKX2.1:GFP-positive progenitors after SHH treatment in vitro. Characterization of NKX2.1:GFP-positive cells confirms their identity as MGE-like neural progenitors, based on gene expression profiles and their ability to differentiate into GABAergic interneurons. We are also able to generate highly enriched populations of NKX2.1:GFP-positive progenitors, including cells with telencephalic identity, by fluorescence-activated cell sorting. These hESC-derived ventral forebrain progenitors are suitable candidates for cell-based therapies that aim at replacing dysfunctional or damaged cortical or hippocampal GABAergic interneurons.

Medial ganglionic eminence-like cells derived from human embryonic stem cells correct learning and memory deficits

Dysfunction of basal forebrain cholinergic neurons (BFCNs) and γ-aminobutyric acid (GABA) interneurons, derived from medial ganglionic eminence (MGE), is implicated in disorders of learning and memory. Here we present a method for differentiating human embryonic stem cells (hESCs) to a nearly uniform population of NKX2.1(+) MGE-like progenitor cells. After transplantation into the hippocampus of mice in which BFCNs and some GABA neurons in the medial septum had been destroyed by mu P75-saporin, human MGE-like progenitors, but not ventral spinal progenitors, produced BFCNs that synaptically connected with endogenous neurons, whereas both progenitors generated similar populations of GABA neurons. Mice transplanted with MGE-like but not spinal progenitors showed improvements in learning and memory deficits. These results suggest that progeny of the MGE-like progenitors, particularly BFCNs, contributed to learning and memory. Our findings support the prospect of using human stem cell-derived MGE-like progenitors in developing therapies for neurological disorders of learning and memory.

The specification of telencephalic glutamatergic neurons from human pluripotent stem cells

Here, a stepwise procedure for efficiently generating telencephalic glutamatergic neurons from human pluripotent stem cells (PSCs) has been described. The differentiation process is initiated by breaking the human PSCs into clumps which round up to form aggregates when the cells are placed in a suspension culture. The aggregates are then grown in hESC medium from days 1-4 to allow for spontaneous differentiation. During this time, the cells have the capacity to become any of the three germ layers. From days 5-8, the cells are placed in a neural induction medium to push them into the neural lineage. Around day 8, the cells are allowed to attach onto 6 well plates and differentiate during which time the neuroepithelial cells form. These neuroepithelial cells can be isolated at day 17. The cells can then be kept as neurospheres until they are ready to be plated onto coverslips. Using a basic medium without any caudalizing factors, neuroepithelial cells are specified into telencephalic precursors, which can then be further differentiated into dorsal telencephalic progenitors and glutamatergic neurons efficiently. Overall, our system provides a tool to generate human glutamatergic neurons for researchers to study the development of these neurons and the diseases which affect them.

Pyramidal neurons derived from human pluripotent stem cells integrate efficiently into mouse brain circuits in vivo

The study of human cortical development has major implications for brain evolution and diseases but has remained elusive due to paucity of experimental models. Here we found that human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), cultured without added morphogens, recapitulate corticogenesis leading to the sequential generation of functional pyramidal neurons of all six layer identities. After transplantation into mouse neonatal brain, human ESC-derived cortical neurons integrated robustly and established specific axonal projections and dendritic patterns corresponding to native cortical neurons. The differentiation and connectivity of the transplanted human cortical neurons complexified progressively over several months in vivo, culminating in the establishment of functional synapses with the host circuitry. Our data demonstrate that human cortical neurons generated in vitro from ESC/iPSC can develop complex hodological properties characteristic of the cerebral cortex in vivo, thereby offering unprecedented opportunities for the modeling of human cortex diseases and brain repair.

In vitro human corticogenesis

Whether neurons generated in vitro from human embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) have in vivo-like properties is unknown. In this issue of Neuron, Espuny-Camacho et al. (2013) show that ESC-/iPSC-derived cortical neurons make specific projections and functional synapses when transplanted into a neonatal mouse brain.

Neurogenic potential of hESC-derived human radial glia is amplified by human fetal cells

The efficient production of human neocortical neurons from human embryonic stem cells (hESC) is the primary requirement for studying early stages of human cortical development. We used hESC to obtain radial glial cells (hESC-RG) and then compared them with RG cells isolated from human fetal forebrain. Fate of hESC-RG cells critically depends on intrinsic and extrinsic factors. The expression of Pax6 (intrinsic factor) has a similar neurogenic effect on hESC-RG differentiation as reported for human fetal RG cells. Factors from the microenvironment also play a significant role in determining hESC-RG cell fate. In contrast to control cultures, wherein hESC-RG generate mainly astroglia and far fewer neurons, in co-cultures with human fetal forebrain cells, the reverse was found to be true. This neurogenic effect was partly due to soluble factors from human fetal brain cultures. The detected shift towards neurogenesis has significance for developing future efficient neuro-differentiation protocols. Importantly, we established that hESC-RG cells are similar in many respects to human fetal RG cells, including their proliferative capacity, neurogenic potential, and ability to generate various cortical neuronal sub-types. Unlike fetal RG cells, the hESC-RG cells are readily available and can be standardized, features that have considerable practical advantages in research and clinics.

Glycogen synthase kinase 3β and activin/nodal inhibition in human embryonic stem cells induces a pre-neuroepithelial state that is required for specification to a floor plate cell lineage

The floor plate is one of the major organizers of the developing nervous system through its secretion of sonic hedgehog (Shh). Although the floor plate is located within the neural tube, the derivation of the floor plate during development is still debatable and some studies suggest that floor plate cells are specified by Shh in a temporarily restricted window different to neuroepithelial cells. Using human embryonic stem cells (hESC) as a model of neurogenesis, we sought to determine how floor plate cells may be temporarily specified by SHH signaling during human embryogenesis. We found that inhibition of both GSK3β and activin/nodal pathways in hESC induces a cellular state of SOX2+/PAX6− expression, we describe as “pre-neuroepithelial.” Exposure of SHH during this pre-neuroepithelial period causes the expression of GLI transcription factors to function as activators and consequently upregulate expression of the floor plate marker, FOXA2, while also supressing PAX6 expression to inhibit neuroepithelial fate. FOXA2+ cells were able to efficiently generate mesencephalic dopaminergic neurons, a floor plate derivative. Overall, this study demonstrates a highly efficient system for generating floor plate cells from hESC and, most importantly, reveals that specification of floor plate cells is temporally dependent, whereby it occurs prior to the onset of PAX6 expression, within a pre-neuroepithelial stage. Stem Cells2012;30:2400–2411

Cortical interneurons from human pluripotent stem cells: prospects for neurological and psychiatric disease

Cortical interneurons represent 20% of the cells in the cortex. These cells are local inhibitory neurons whose function is to modulate the firing activities of the excitatory projection neurons. Cortical interneuron dysfunction is believed to lead to runaway excitation underlying (or implicated in) seizure-based diseases, such as epilepsy, autism, and schizophrenia. The complex development of this cell type and the intricacies involved in defining the relative subtypes are being increasingly well defined. This has led to exciting experimental cell therapy in model organisms, whereby fetal-derived interneuron precursors can reverse seizure severity and reduce mortality in adult epileptic rodents. These proof-of-principle studies raise hope for potential interneuron-based transplantation therapies for treating epilepsy. On the other hand, cortical neurons generated from patient iPSCs serve as a valuable tool to explore genetic influences of interneuron development and function. This is a fundamental step in enhancing our understanding of the molecular basis of neuropsychiatric illnesses and the development of targeted treatments. Protocols are currently being developed for inducing cortical interneuron subtypes from mouse and human pluripotent stem cells. This review sets out to summarize the progress made in cortical interneuron development, fetal tissue transplantation and the recent advance in stem cell differentiation toward interneurons.

Modeling Huntington's disease with induced pluripotent stem cells

Huntington's disease (HD) causes severe motor dysfunction, behavioral abnormalities, cognitive impairment and death. Investigations into its molecular pathology have primarily relied on murine tissues; however, the recent discovery of induced pluripotent stem cells (iPSCs) has opened new possibilities to model neurodegenerative disease using cells derived directly from patients, and therefore may provide a human-cell-based platform for unique insights into the pathogenesis of HD. Here, we will examine the practical implementation of iPSCs to study HD, such as approaches to differentiate embryonic stem cells (ESCs) or iPSCs into medium spiny neurons, the cell type most susceptible in HD. We will explore the HD-related phenotypes identified in iPSCs and ESCs and review how brain development and neurogenesis may actually be altered early, before the onset of HD symptoms, which could inform the search for drugs that delay disease onset. Finally, we will speculate on the exciting possibility that ESCs or iPSCs might be used as therapeutics to restore or replace dying neurons in HD brains.

Developmentally coordinated extrinsic signals drive human pluripotent stem cell differentiation toward authentic DARPP-32+ medium-sized spiny neurons

Medium-sized spiny neurons (MSNs) are the only neostriatum projection neurons, and their degeneration underlies some of the clinical features of Huntington's disease. Using knowledge of human developmental biology and exposure to key neurodevelopmental molecules, human pluripotent stem (hPS) cells were induced to differentiate into MSNs. In a feeder-free adherent culture, ventral telencephalic specification is induced by BMP/TGFβ inhibition and subsequent SHH/DKK1 treatment. The emerging FOXG1(+)/GSX2(+) telencephalic progenitors are then terminally differentiated, resulting in the systematic line-independent generation of FOXP1(+)/FOXP2(+)/CTIP2(+)/calbindin(+)/DARPP-32(+) MSNs. Similar to mature MSNs, these neurons carry dopamine and A2a receptors, elicit a typical firing pattern and show inhibitory postsynaptic currents, as well as dopamine neuromodulation and synaptic integration ability in vivo. When transplanted into the striatum of quinolinic acid-lesioned rats, hPS-derived neurons survive and differentiate into DARPP-32(+) neurons, leading to a restoration of apomorphine-induced rotation behavior. In summary, hPS cells can be efficiently driven to acquire a functional striatal fate using an ontogeny-recapitulating stepwise method that represents a platform for in vitro human developmental neurobiology studies and drug screening approaches.

Increasing doublecortin expression promotes migration of human embryonic stem cell-derived neurons

Human embryonic stem cell-derived neuronal progenitors (hNPs) provide a potential source for cellular replacement following neurodegenerative diseases. One of the greatest challenges for future neuron replacement therapies will be to control extensive cell proliferation and stimulate cell migration of transplanted cells. The doublecortin (DCX) gene encodes the protein DCX, a microtubule-associated protein essential for the migration of neurons in the human brain. In this study, we tested whether increasing the expression of DCX in hNPs would favorably alter their proliferation and migration. Migration and proliferation of hNPs was compared between hNPs expressing a bicistronic DCX/IRES-GFP transgene and those expressing a green fluorescent protein (GFP) transgene introduced by piggyBac-mediated transposition. The DCX-transfected hNPs showed a significant decrease in their proliferation and migrated significantly further on two different substrates, Matrigel and brain slices. Additionally, a dense network of nestin-positive (+) and vimentin+ fibers were found to extend from neurospheres transplanted onto brain slices, and this fiber growth was increased from neurospheres containing DCX-transfected hNPs. In summary, our results show that increased DCX expression inhibits proliferation and promotes migration of hNPs.

Robust formation and maintenance of continuous stratified cortical neuroepithelium by laminin-containing matrix in mouse ES cell culture

In the mammalian cortex, the dorsal telencephalon exhibits a characteristic stratified structure. We previously reported that three-dimensional (3D) culture of mouse ES cells (mESCs) can efficiently generate cortical neuroepithelium (NE) and layer-specific cortical neurons. However, the cortical NE generated in this mESC culture was structurally unstable and broke into small neural rosettes by culture day 7, suggesting that some factors for reinforcing the structural integrity were missing. Here we report substantial supporting effects of the extracellular matrix (ECM) protein laminin on the continuous formation of properly polarized cortical NE in floating aggregate culture of mESCs. The addition of purified laminin and entactin (a laminin-associated protein), even at low concentrations, stabilized the formation of continuous cortical NE as well as the maintenance of basement membrane and prevented rosette formation. Treatment with the neutralizing ß1-integrin antibody impaired the continuous NE formation. The stabilized cortical NE exhibited typical interkinetic nuclear migration of cortical progenitors, as seen in the embryonic cortex. The laminin-treated cortical NE maintained a continuous structure even on culture days 12 and 15, and contained ventricular, basal-progenitor, cortical-plate and Cajal-Retzius cell layers. The cortical NE in this culture was flanked by cortical hem-like tissue. Furthermore, when Shh was added, ventral telencephalic structures such as lateral ganglionic eminence–like tissue formed in the region adjacent to the cortical NE. Thus, our results indicate that laminin-entactin ECM promotes the formation of structurally stable telencephalic tissues in 3D ESC culture, and supports the morphogenetic recapitulation of cortical development.

Recapitulation of spinal motor neuron-specific disease phenotypes in a human cell model of spinal muscular atrophy

Establishing human cell models of spinal muscular atrophy (SMA) to mimic motor neuron-specific phenotypes holds the key to understanding the pathogenesis of this devastating disease. Here, we developed a closely representative cell model of SMA by knocking down the disease-determining gene, survival motor neuron (SMN), in human embryonic stem cells (hESCs). Our study with this cell model demonstrated that knocking down of SMN does not interfere with neural induction or the initial specification of spinal motor neurons. Notably, the axonal outgrowth of spinal motor neurons was significantly impaired and these disease-mimicking neurons subsequently degenerated. Furthermore, these disease phenotypes were caused by SMN-full length (SMN-FL) but not SMN-Δ7 (lacking exon 7) knockdown, and were specific to spinal motor neurons. Restoring the expression of SMN-FL completely ameliorated all of the disease phenotypes, including specific axonal defects and motor neuron loss. Finally, knockdown of SMN-FL led to excessive mitochondrial oxidative stress in human motor neuron progenitors. The involvement of oxidative stress in the degeneration of spinal motor neurons in the SMA cell model was further confirmed by the administration of N-acetylcysteine, a potent antioxidant, which prevented disease-related apoptosis and subsequent motor neuron death. Thus, we report here the successful establishment of an hESC-based SMA model, which exhibits disease gene isoform specificity, cell type specificity, and phenotype reversibility. Our model provides a unique paradigm for studying how motor neurons specifically degenerate and highlights the potential importance of antioxidants for the treatment of SMA.

Experimental and therapeutic opportunities for stem cells in multiple sclerosis

Multiple Sclerosis (MS) is an inflammatory demyelinating neurodegenerative disorder of the brain and spinal cord that causes significant disability in young adults. Although the precise aetiopathogenesis of MS remains unresolved, its pathological hallmarks include inflammation, demyelination, axonal injury (acute and chronic), astrogliosis and variable remyelination. Despite major recent advances in therapeutics for the early stage of the disease there are currently no disease modifying treatments for the progressive stage of disease, whose pathological substrate is axonal degeneration. This represents the great and unmet clinical need in MS. Against this background, human stem cells offer promise both to improve understanding of disease mechanism(s) through in-vitro modeling as well as potentially direct use to supplement and promote remyelination, an endogenous reparative process where entire myelin sheaths are restored to demyelinated axons. Conceptually, stem cells can act directly to myelinate axons or indirectly through different mechanisms to promote endogenous repair; importantly these two mechanisms of action are not mutually exclusive. We propose that discovery of novel methods to invoke or enhance remyelination in MS may be the most effective therapeutic strategy to limit axonal damage and instigate restoration of structure and function in this debilitating condition. Human stem cell derived neurons and glia, including patient specific cells derived through reprogramming, provide an unprecedented experimental system to model MS “in a dish” as well as enable high-throughput drug discovery. Finally, we speculate upon the potential role for stem cell based therapies in MS.