A high concentration of epidermal growth factor increases the growth and survival of neurogenic radial glial cells within human neurosphere cultures

Cell-Based Therapies: Strategies for Regeneration

The neural retina of mammals, like most of the rest of the central nervous system, does not regenerate new neurons after they are lost through damage or disease. The ability of nonmammalian vertebrates, like fish and amphibians, is remarkable, and lessons learned over the last 20 years have revealed some of the mechanisms underlying this potential. This knowledge has recently been applied to mammals to develop methods that can stimulate regeneration in mice. In this review, we highlight the progress in this area, and propose a "wish list" of how the clinical implementation of regenerative strategies could be applicable to various human retinal diseases.

Decoding the molecular crosstalk between grafted stem cells and the stroke-injured brain

Stem cell therapy shows promise for multiple disorders; however, the molecular crosstalk between grafted cells and host tissue is largely unknown. Here, we take a step toward addressing this question. Using translating ribosome affinity purification (TRAP) with sequencing tools, we simultaneously decode the transcriptomes of graft and host for human neural stem cells (hNSCs) transplanted into the stroke-injured rat brain. Employing pathway analysis tools, we investigate the interactions between the two transcriptomes to predict molecular pathways linking host and graft genes; as proof of concept, we predict host-secreted factors that signal to the graft and the downstream molecular cascades they trigger in the graft. We identify a potential host-graft crosstalk pathway where BMP6 from the stroke-injured brain induces graft secretion of noggin, a known brain repair factor. Decoding the molecular interplay between graft and host is a critical step toward deciphering the molecular mechanisms of stem cell action.

Cell Surface Proteins for Enrichment and In Vitro Characterization of Human Pluripotent Stem Cell-Derived Myogenic Progenitors

Human myogenic progenitors can be derived from pluripotent stem cells (PSCs) for use in modeling natural and pathological myogenesis, as well as treating muscle diseases. Transgene-free methods of deriving myogenic progenitors from different PSC lines often produce mixed populations that are heterogeneous in myogenic differentiation potential, yet detailed and accurate characterization of human PSC-derived myogenic progenitors remains elusive in the field. The isolation and purification of human PSC-derived myogenic progenitors is thus an important methodological consideration when we investigate the properties and behaviors of these cells in culture. We previously reported a transgene-free, serum-free floating sphere culture method for the derivation of myogenic progenitors from human PSCs. In this study, we first performed comprehensive cell surface protein profiling of the sphere culture cells through the screening of 255 antibodies. Next, we used magnetic activated cell sorting and enriched the cells according to the expression of specific surface markers. The ability of muscle differentiation in the resulting cells was characterized by immunofluorescent labeling and quantification of positively stained cells. Our results revealed that myotube-forming cells resided in the differentiated cultures of CD29+, CD56+, CD271+, and CD15– fractions, while thick and multinucleated myotubes were identified in the differentiated cultures from CD9+ and CD146+ fractions. We found that PAX7 localization to the nucleus correlates with myotube-forming ability in these sorted populations. We also demonstrated that cells in unsorted, CD271+, and CD15– fractions responded differently to cryopreservation and prolonged culture expansion. Lastly, we showed that CD271 expression is essential for terminal differentiation of human PSC-derived myogenic progenitors. Taken together, these cell surface proteins are not only useful markers to identify unique cellular populations in human PSC-derived myogenic progenitors but also functionally important molecules that can provide valuable insight into human myogenesis.

APP Binds to the EGFR Ligands HB-EGF and EGF, Acting Synergistically with EGF to Promote ERK Signaling and Neuritogenesis

The amyloid precursor protein (APP) is a transmembrane glycoprotein central to Alzheimer's disease (AD) with functions in brain development and plasticity, including in neurogenesis and neurite outgrowth. Epidermal growth factor (EGF) and heparin-binding EGF-like growth factor (HB-EGF) are well-described neurotrophic and neuromodulator EGFR ligands, both implicated in neurological disorders, including AD. Pro-HB-EGF arose as a putative novel APP interactor in a human brain cDNA library yeast two-hybrid screen. Based on their structural and functional similarities, we first aimed to verify if APP could bind to (HB-)EGF proforms. Here, we show that APP interacts with these two EGFR ligands, and further characterized the effects of APP-EGF interaction in ERK activation and neuritogenesis. Yeast co-transformation and co-immunoprecipitation assays confirmed APP interaction with HB-EGF. Co-immunoprecipitation also revealed that APP binds to cellular pro-EGF. Overexpression of HB-EGF in HeLa cells, or exposure of SH-SY5Y cells to EGF, both resulted in increased APP protein levels. EGF and APP were observed to synergistically activate the ERK pathway, crucial for neuronal differentiation. Immunofluorescence analysis of cellular neuritogenesis in APP overexpression and EGF exposure conditions confirmed a synergistic effect in promoting the number and the mean length of neurite-like processes. Synergistic ERK activation and neuritogenic effects were completely blocked by the EGFR inhibitor PD 168393, implying APP/EGF-induced activation of EGFR as part of the mechanism. This work shows novel APP protein interactors and provides a major insight into the APP/EGF-driven mechanisms underlying neurite outgrowth and neuronal differentiation, with potential relevance for AD and for adult neuroregeneration.

Epidermal Growth Factor in the CNS: A Beguiling Journey from Integrated Cell Biology to Multiple Sclerosis. An Extensive Translational Overview

This article reviews the wealth of papers dealing with the different effects of epidermal growth factor (EGF) on oligodendrocytes, astrocytes, neurons, and neural stem cells (NSCs). EGF induces the in vitro and in vivo proliferation of NSCs, their migration, and their differentiation towards the neuroglial cell line. It interacts with extracellular matrix components. NSCs are distributed in different CNS areas, serve as a reservoir of multipotent cells, and may be increased during CNS demyelinating diseases. EGF has pleiotropic differentiative and proliferative effects on the main CNS cell types, particularly oligodendrocytes and their precursors, and astrocytes. EGF mediates the in vivo myelinotrophic effect of cobalamin on the CNS, and modulates the synthesis and levels of CNS normal prions (PrP^Cs), both of which are indispensable for myelinogenesis and myelin maintenance. EGF levels are significantly lower in the cerebrospinal fluid and spinal cord of patients with multiple sclerosis (MS), which probably explains remyelination failure, also because of the EGF marginal role in immunology. When repeatedly administered, EGF protects mouse spinal cord from demyelination in various experimental models of autoimmune encephalomyelitis. It would be worth further investigating the role of EGF in the pathogenesis of MS because of its multifarious effects.

Extracellular Control of Radial Glia Proliferation and Scaffolding During Cortical Development and Pathology

During the development of the cortex, newly generated neurons migrate long-distances in the expanding tissue to reach their final positions. Pyramidal neurons are produced from dorsal progenitors, e.g., radial glia (RGs) in the ventricular zone, and then migrate along RG processes basally toward the cortex. These neurons are hence dependent upon RG extensions to support their migration from apical to basal regions. Several studies have investigated how intracellular determinants are required for RG polarity and subsequent formation and maintenance of their processes. Fewer studies have identified the influence of the extracellular environment on this architecture. This review will focus on extracellular factors which influence RG morphology and pyramidal neuronal migration during normal development and their perturbations in pathology. During cortical development, RGs are present in different strategic positions: apical RGs (aRGs) have their cell bodies located in the ventricular zone with an apical process contacting the ventricle, while they also have a basal process extending radially to reach the pial surface of the cortex. This particular conformation allows aRGs to be exposed to long range and short range signaling cues, whereas basal RGs (bRGs, also known as outer RGs, oRGs) have their cell bodies located throughout the cortical wall, limiting their access to ventricular factors. Long range signals impacting aRGs include secreted molecules present in the embryonic cerebrospinal fluid (e.g., Neuregulin, EGF, FGF, Wnt, BMP). Secreted molecules also contribute to the extracellular matrix (fibronectin, laminin, reelin). Classical short range factors include cell to cell signaling, adhesion molecules and mechano-transduction mechanisms (e.g., TAG1, Notch, cadherins, mechanical tension). Changes in one or several of these components influencing the RG extracellular environment can disrupt the development or maintenance of RG architecture on which neuronal migration relies, leading to a range of cortical malformations. First, we will detail the known long range signaling cues impacting RG. Then, we will review how short range cell contacts are also important to instruct the RG framework. Understanding how RG processes are structured by their environment to maintain and support radial migration is a critical part of the investigation of neurodevelopmental disorders.

AP-1 controls the p11-dependent antidepressant response

Selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed drugs for mood disorders. While the mechanism of SSRI action is still unknown, SSRIs are thought to exert therapeutic effects by elevating extracellular serotonin levels in the brain, and remodel the structural and functional alterations dysregulated during depression. To determine their precise mode of action, we tested whether such neuroadaptive processes are modulated by regulation of specific gene expression programs. Here we identify a transcriptional program regulated by activator protein-1 (AP-1) complex, formed by c-Fos and c-Jun that is selectively activated prior to the onset of the chronic SSRI response. The AP-1 transcriptional program modulates the expression of key neuronal remodeling genes, including S100a10 (p11), linking neuronal plasticity to the antidepressant response. We find that AP-1 function is required for the antidepressant effect in vivo. Furthermore, we demonstrate how neurochemical pathways of BDNF and FGF2, through the MAPK, PI3K, and JNK cascades, regulate AP-1 function to mediate the beneficial effects of the antidepressant response. Here we put forth a sequential molecular network to track the antidepressant response and provide a new avenue that could be used to accelerate or potentiate antidepressant responses by triggering neuroplasticity.

Huntington's Disease Patient-Derived Astrocytes Display Electrophysiological Impairments and Reduced Neuronal Support

In Huntington’s disease (HD), while the ubiquitously expressed mutant Huntingtin (mtHTT) protein primarily compromises striatal and cortical neurons, glia also undergo disease-contributing alterations. Existing HD models using human induced pluripotent stem cells (iPSCs) have not extensively characterized the role of mtHTT in patient-derived astrocytes. Here physiologically mature astrocytes are generated from HD patient iPSCs. These human astrocytes exhibit hallmark HD phenotypes that occur in mouse models, including impaired inward rectifying K⁺ currents, lengthened spontaneous Ca²⁺ waves and reduced cell membrane capacitance. HD astrocytes in co-culture provided reduced support for the maturation of iPSC-derived neurons. In addition, neurons exposed to chronic glutamate stimulation are not protected by HD astrocytes. This iPSC-based HD model demonstrates the critical effects of mtHTT on human astrocytes, which not only broadens the understanding of disease susceptibility beyond cortical and striatal neurons but also increases potential drug targets.

Rapid and efficient generation of neural progenitors from adult bone marrow stromal cells by hypoxic preconditioning

Background

Bone marrow stromal cells (BMSCs) are attractive as a source of neural progenitors for ex vivo generation of neurons and glia. Limited numbers of this subpopulation, however, hinder translation into autologous cell-based therapy. Here, we demonstrate rapid and efficient conditioning with hypoxia to enrich for these neural progenitor cells prior to further expansion in neurosphere culture.

Method

Adherent cultures of BMSCs (rat/human) were subjected to 1 % oxygen for 24 h and then subcultured as neurospheres with epidermal growth factor (EGF) and basic fibroblast growth factor supplementation. Neurospheres and cell progeny were monitored immunocytochemically for marker expression. To generate Schwann cell-like cells, neurospheres were plated out and exposed to gliogenic medium. The resulting cells were co-cultured with purified dorsal root ganglia (rat) neurons and then tested for commitment to the Schwann cell fate. Fate-committed Schwann cells were subjected to in vitro myelination assay.

Results

Transient hypoxic treatment increased the size and number of neurospheres generated from both rat and human BMSCs. This effect was EGF-dependent and attenuated with the EGF receptor inhibitor erlotinib. Hypoxia did not affect the capacity of neurospheres to generate neuron- or glia-like precursors. Human Schwann cell-like cells generated from hypoxia-treated BMSCs demonstrated expression of S100β /p75 and capacity for myelination in vitro.

Conclusion

Enhancing the yield of neural progenitor cells with hypoxic preconditioning of BMSCs in vitro but without inherent risks of genetic manipulation provides a platform for upscaling production of neural cell derivatives for clinical application in cell-based therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0409-x) contains supplementary material, which is available to authorized users.

A new technique for modeling neuronal connectivity using human pluripotent stem cells

Purpose: We describe a technique for independently differentiating neocortical and mesencephalic dopaminergic (mDA) neurons from a single human pluripotent stem cell (hPSC) line, and subsequently allowing the two cell types to interact and form connections.

Methods: Dopaminergic and neocortical progenitors were differentiated in separate vessels, then separately seeded into the inner and outer compartments of specialized cell culture vessels designed for in vitro studies of wound healing. Cells were further differentiated using dopamine-specific and neocortex-specific trophic factors, respectively. The barrier was then removed, and differentiation was continued for three weeks in the presence of BDNF.

Results: After three weeks of differentiation, neocortical and mDA cell bodies largely remained in the areas into which they had been seeded, and the gap between the mDA and neocortical neuron populations could still be discerned. Abundant tyrosine hydroxylase (TH)-positive projections had extended from the area of the inner chamber to the outer chamber neocortical area.

Conclusions: We have developed a hPSC-based system for producing connections between neurons from two brain regions, neocortex and midbrain. Future experiments could employ modifications of this method to examine connections between any two brain regions or neuronal subtypes that can be produced from hPSCs in vitro.

Analysis of Neural Stem Cells from Human Cortical Brain Structures In Vitro

Comparative immunohistochemical analysis of the neocortex from human fetuses showed that neural stem and progenitor cells are present in the brain throughout the gestation period, at least from week 8 through 26. At the same time, neural stem cells from the first and second trimester fetuses differed by the distribution, morphology, growth, and quantity. Immunocytochemical analysis of neural stem cells derived from fetuses at different gestation terms and cultured under different conditions showed their differentiation capacity. Detailed analysis of neural stem cell populations derived from fetuses on gestation weeks 8-9, 18-20, and 26 expressing Lex/SSEA1 was performed.

Pluripotent stem cell-derived radial glia-like cells as stable intermediate for efficient generation of human oligodendrocytes

Neural precursor cells (NPCs) derived from human pluripotent stem cells (hPSCs) represent an attractive tool for the in vitro generation of various neural cell types. However, the developmentally early NPCs emerging during hPSC differentiation typically show a strong propensity for neuronal differentiation, with more limited potential for generating astrocytes and, in particular, for generating oligodendrocytes. This phenomenon corresponds well to the consecutive and protracted generation of neurons and GLIA during normal human development. To obtain a more gliogenic NPC type, we combined growth factor-mediated expansion with pre-exposure to the differentiation-inducing agent retinoic acid and subsequent immunoisolation of CD133-positive cells. This protocol yields an adherent and self-renewing population of hindbrain/spinal cord radial glia (RG)-like neural precursor cells (RGL-NPCs) expressing typical neural stem cell markers such as nestin, ASCL1, SOX2, and PAX6 as well as RG markers BLBP, GLAST, vimentin, and GFAP. While RGL-NPCs maintain the ability for tripotential differentiation into neurons, astrocytes, and oligodendrocytes, they exhibit greatly enhanced propensity for oligodendrocyte generation. Under defined differentiation conditions promoting the expression of the major oligodendrocyte fate-determinants OLIG1/2, NKX6.2, NKX2.2, and SOX10, RGL-NPCs efficiently convert into NG2-positive oligodendroglial progenitor cells (OPCs) and are subsequently capable of in vivo myelination. Representing a stable intermediate between PSCs and OPCs, RGL-NPCs expedite the generation of PSC-derived oligodendrocytes with O4-, 4860-, and myelin basic protein (MBP)-positive cells that already appear within 7 weeks following growth factor withdrawal-induced differentiation. Thus, RGL-NPCs may serve as robust tool for time-efficient generation of human oligodendrocytes from embryonic and induced pluripotent stem cells.

Derivation of myogenic progenitors directly from human pluripotent stem cells using a sphere-based culture

Using stem cells to replace degenerating muscle cells and restore lost skeletal muscle function is an attractive therapeutic strategy for treating neuromuscular diseases. Myogenic progenitors are a valuable cell type for cell-based therapy and also provide a platform for studying normal muscle development and disease mechanisms in vitro. Human pluripotent stem cells represent a valuable source of tissue for generating myogenic progenitors. Here, we present a novel protocol for deriving myogenic progenitors from human embryonic stem (hES) and induced pluripotent stem (iPS) cells using free-floating spherical culture (EZ spheres) in a defined culture medium. hES cell colonies and human iPS cell colonies were expanded in medium supplemented with high concentrations (100 ng/ml) of fibroblast growth factor-2 (FGF-2) and epidermal growth factor in which they formed EZ spheres and were passaged using a mechanical chopping method. We found myogenic progenitors in the spheres after 6 weeks of culture and multinucleated myotubes following sphere dissociation and 2 weeks of terminal differentiation. A high concentration of FGF-2 plays a critical role for myogenic differentiation and is necessary for generating myogenic progenitors from pluripotent cells cultured as EZ spheres. Importantly, EZ sphere culture produced myogenic progenitors from human iPS cells generated from both healthy donors and patients with neuromuscular disorders (including Becker's muscular dystrophy, spinal muscular atrophy, and familial amyotrophic lateral sclerosis). Taken together, this study demonstrates a simple method for generating myogenic cells from pluripotent sources under defined conditions for potential use in disease modeling or cell-based therapies targeting skeletal muscle.

Epidermal growth factor, from gene organization to bedside

In 1962, epidermal growth factor (EGF) was discovered by Dr. Stanley Cohen while studying nerve growth factor (NGF). It was soon recognized that EGF is the prototypical member of a family of peptide growth factors that activate the EGF receptors, and that the EGF/EGF receptor signaling pathway plays important roles in proliferation, differentiation and migration of a variety of cell types, especially in epithelial cells. After the basic characterization of EGF function in the first decade or so after its discovery, the studies related to EGF and its signaling pathway have extended to a broad range of investigations concerning its biological and pathophysiological roles in development and in human diseases. In this review, we briefly describe the gene organization and tissue distribution of EGF, with emphasis on its biological and pathological roles in human diseases.

Single-cell enzyme-free dissociation of neurospheres using a microfluidic chip

Obtaining single dissociated cells from neurospheres is difficult using nonenzymatic methods. In this paper we report the development of a microfluidic-chip-based approach that utilizes flow and microstructures to dissociate neurospheres. We show that this microfluidic-chip-based neurosphere-dissociation method can generate high yields of single cells from dissociated neurospheres of mouse KT98 and DC115 cell models (passage number, 3-8; diameter range, 40-250 μm): 90% and 95%, respectively. The microfluidic-chip-dissociated cells had high viabilities (80-85%) and the ability to regrow into neurospheres, demonstrating the applicability of this device to neurosphere assay applications. In addition, the dissociated cells retained their normal differentiation potentials, as shown by their capabilities to differentiate into three neural lineages (neurons, astroglia, and oligodendrocytes) when cultured in differentiation culture conditions. Since this microfluidic-chip-based method does not require the use of enzymatic reagents, the risk of contamination from exogenous substances could be reduced, making it an attractive tool for a wide range of applications where neurosphere dissociation is needed.

Therapeutic effect of oncolytic adenovirus expressing relaxin in radioresistant oral squamous cell carcinoma

Radioresistance is one of the main determinants of treatment outcome in oral squamous cell carcinoma (OSCC), and treatment of radioresistant OSCC is difficult due to cross resistance to other conventional treatments. We aimed to identify whether genetically modified oncolytic adenovirus expressing relaxin (RLX), which affects collagen metabolism, can effectively inhibit growth of the radioresistant OSCC. Therapeutic effect of oncolytic adenovirus was compared between radiosensitive and radioresistant OSCC cell lines in vitro and in vivo, and spread of adenovirus throughout the tumor mass was verified by immunohistochemistry (IHC). Oncolytic adenovirus effectively killed cancer cells and there was no significant difference in the cytotoxic effect between radiosensitive and radioresistant OSCC cell lines. In animal experiments, the adenovirus significantly reduced the size of tumor, and there was no significant difference between radiosensitive and radioresistant OSCC. In IHC, RLX expressing adenovirus showed better proliferation and eliminated collagens more effectively compared to RLX nonexpressing adenovirus. These findings suggested that genetically modified oncolytic adenovirus can effectively inhibit growth of the radioresistant OSCC and might be a new therapeutic option in radioresistant OSCC.

EZ spheres: a stable and expandable culture system for the generation of pre-rosette multipotent stem cells from human ESCs and iPSCs

We have developed a simple method to generate and expand multipotent, self-renewing pre-rosette neural stem cells from both human embryonic stem cells (hESCs) and human induced pluripotent stem cells (iPSCs) without utilizing embryoid body formation, manual selection techniques, or complex combinations of small molecules. Human ESC and iPSC colonies were lifted and placed in a neural stem cell medium containing high concentrations of EGF and FGF-2. Cell aggregates (termed EZ spheres) could be expanded for long periods using a chopping method that maintained cell-cell contact. Early passage EZ spheres rapidly down-regulated OCT4 and up-regulated SOX2 and nestin expression. They retained the potential to form neural rosettes and consistently differentiated into a range of central and peripheral neural lineages. Thus, they represent a very early neural stem cell with greater differentiation flexibility than other previously described methods. As such, they will be useful for the rapidly expanding field of neurological development and disease modeling, high-content screening, and regenerative therapies based on pluripotent stem cell technology.

Identifying genes related to radiation resistance in oral squamous cell carcinoma cell lines

Radioresistance is one of the main determinants of treatment outcome in oral cancer, but the prediction of radioresistance is difficult. The authors aimed to establish radioresistant oral squamous cell carcinoma (OSCC) cell lines to identify genes with altered expression in response to radioresistance. To induce radioresistant cell lines, the authors treated OSCC cell lines with an accumulated dosage of 60Gy over 30 cycles of radiotherapy. They compared the results from cDNA arrays and proteomics between non-radiated and radioresistant cell lines in order to identify changes in gene expression. Western blot analysis was used to validate the results. The cDNA array revealed 265 commonly up-regulated genes and 268 commonly down-regulated genes in radioresistant cell lines, 30 of which were cancer-related genes. Proteomics identified 51 proteins with commonly altered expression in radioresistant cell lines, 18 of which were cancer-related proteins. Both the cDNA array and proteomics indicated that NM23-H1 and PA2G4 were over-expressed. Western blot analysis showed increased expression of NM23-H1, but not PA2G4, in radioresistant cell lines. The authors concluded that NM23-H1 may be a radioresistance-related gene and over-expression of NM23-H1 could serve as a biomarker to predict radioresistance in OSCC.

Male-specific differences in proliferation, neurogenesis, and sensitivity to oxidative stress in neural progenitor cells derived from a rat model of ALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive motor dysfunction and the loss of large motor neurons in the spinal cord and brain stem. A clear genetic link to point mutations in the superoxide dismutase 1 (SOD1) gene has been shown in a small group of familial ALS patients. The exact etiology of ALS is still uncertain, but males have consistently been shown to be at a higher risk for the disease than females. Here we present male-specific effects of the mutant SOD1 transgene on proliferation, neurogenesis, and sensitivity to oxidative stress in rat neural progenitor cells (rNPCs). E14 pups were bred using SOD1(G93A) transgenic male rats and wild-type female rats. The spinal cord and cortex tissues were collected, genotyped by PCR using primers for the SOD1(G93A) transgene or the male-specific Sry gene, and cultured as neurospheres. The number of dividing cells was higher in male rNPCs compared to female rNPCs. However, SOD1(G93A) over-expression significantly reduced cell proliferation in male cells but not female cells. Similarly, male rNPCs produced more neurons compared to female rNPCs, but SOD1(G93A) over-expression significantly reduced the number of neurons produced in male cells. Finally we asked whether sex and SOD1(G93A) transgenes affected sensitivity to oxidative stress. There was no sex-based difference in cell viability after treatment with hydrogen peroxide or 3-morpholinosydnonimine, a free radical-generating agent. However, increased cytotoxicity by SOD1(G93A) over-expression occurred, especially in male rNPCs. These results provide essential information on how the mutant SOD1 gene and sexual dimorphism are involved in ALS disease progression.

Ensheathing cell-conditioned medium directs the differentiation of human umbilical cord blood cells into aldynoglial phenotype cells

Despite their similarities to bone marrow precursor cells (PC), human umbilical cord blood (HUCB) PCs are more immature and, thus, they exhibit greater plasticity. This plasticity is evident by their ability to proliferate and spontaneously differentiate into almost any cell type, depending on their environment. Moreover, HUCB-PCs yield an accessible cell population that can be grown in culture and differentiated into glial, neuronal and other cell phenotypes. HUCB-PCs offer many potential therapeutic benefits, particularly in the area of neural replacement. We sought to induce the differentiation of HUCB-PCs into glial cells, known as aldynoglia. These cells can promote neuronal regeneration after lesion and they can be transplanted into areas affected by several pathologies, which represents an important therapeutic strategy to treat central nervous system damage. To induce differentiation to the aldynoglia phenotype, HUCB-PCs were exposed to different culture media. Mononuclear cells from HUCB were isolated and purified by identification of CD34 and CD133 antigens, and after 12 days in culture, differentiation of CD34+ HUCB-PCs to an aldynoglia phenotypic, but not that of CD133+ cells, was induced in ensheathing cell (EC)-conditioned medium. Thus, we demonstrate that the differentiation of HUCB-PCs into aldynoglia cells in EC-conditioned medium can provide a new source of aldynoglial cells for use in transplants to treat injuries or neurodegenerative diseases.

Isolation of radial glia-like neural stem cells from fetal and adult mouse forebrain via selective adhesion to a novel adhesive peptide-conjugate

Preferential adhesion of neural stem cells to surfaces covered with a novel synthetic adhesive polypeptide (AK-cyclo[RGDfC]) provided a unique, rapid procedure for isolating radial glia-like cells from both fetal and adult rodent brain. Radial glia-like (RGl) neural stem/progenitor cells grew readily on the peptide-covered surfaces under serum-free culture conditions in the presence of EGF as the only growth factor supplement. Proliferating cells derived either from fetal (E 14.5) forebrain or from different regions of the adult brain maintained several radial glia-specific features including nestin, RC2 immunoreactivity and Pax6, Sox2, Blbp, Glast gene expression. Proliferating RGl cells were obtained also from non-neurogenic zones including the parenchyma of the adult cerebral cortex and dorsal midbrain. Continuous proliferation allowed isolating one-cell derived clones of radial glia-like cells. All clones generated neurons, astrocytes and oligodendrocytes under appropriate inducing conditions. Electrophysiological characterization indicated that passive conductance with large delayed rectifying potassium current might be a uniform feature of non-induced radial glia-like cells. Upon induction, all clones gave rise to GABAergic neurons. Significant differences were found, however, among the clones in the generation of glutamatergic and cathecolamine-synthesizing neurons and in the production of oligodendrocytes.

Valproic acid induces apoptosis in differentiating hippocampal neurons by the release of tumor necrosis factor-α from activated astrocytes

Human studies of neurodevelopment suggest that children exposed in utero to certain antiepileptic drugs (AEDs) suffer a variety of brain-behavior sequelae, such as neural tube defects, developmental delays, cognitive deficits, etc. Valproic acid (VPA), a commonly used AED, has greater risk for these side effects compared with other AEDs. However, the detailed molecular mechanisms underlying this developmental neurotoxicity of VPA is unclear despite previous research demonstrating that VPA could induce widespread apoptotic neurodegeneration in developing brains of animal models. This study characterizes the role of astrocytes in VPA-induced neurodegeneration. In developing brains, we evaluated the developmental neurotoxicity of VPA on differentiating neurons and astrocytes from neural progenitor cells cultured from the hippocampus of human fetuses. Exposure of a neuron-enriched culture to VPA at 250μM or 500μM did not cause neuronal apoptosis, but at 1mM and 7 days exposure, a slight increase in the percentage of apoptotic cells was observed. In contrast, VPA at 250μM to 1mM, selectively induced neuronal apoptosis in a neuron-astrocyte mixed cell culture model. The VPA-treated astrocytes showed morphological changes, and the level of tumor necrosis factor-α (TNF-α) was elevated in the supernatant. Both neuronal apoptosis and TNF-α release from astrocytes increased with concentration and exposure time to VPA, suggesting a synergism between the two cell types. Treatment of the neuron-astrocyte mixed culture exposed to VPA with TNF-α antibody partly prevented neuronal apoptosis, while the addition of exogenous TNF-α induced apoptosis in both cultures. Moreover, this pro-apoptotic effect was specific to VPA, as another AED, valpromide, failed to mimic this pro-apoptotic effect, nor did an inhibitor of histone deacetylase (iHDAC), sodium butyrate (NaB). We report a novel finding that astrocytes participate in VPA induced neurodegeneration by releasing TNF-α.

In vitro regulation of neural differentiation and axon growth by growth factors and bioactive nanofibers

Human embryonic stem cell (ESC)-derived neural cells are a potential cell source for neural tissue regeneration. Understanding the biochemical and biophysical regulation of neural differentiation and axon growth will help us develop cell therapies and bioactive scaffolds. We demonstrated that basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) had different effects on human ESC differentiation into neural cells. EGF was more effective in inducing expression of neuron and glial markers and cell extensions. In addition to biochemical cues, poly(l-lactic acid) scaffolds with aligned nanofibers increased axon growth from ESC-derived neural cells, demonstrating the significant effects of biophysical guidance at nanoscale. To combine the biochemical and biophysical cues, bFGF and EGF were either adsorbed or bound to heparin on nanofibrous scaffolds. EGF, but not bFGF, was effectively adsorbed onto nanofibers. However, adsorbed EGF and bFGF did not effectively enhance axon growth. In contrast, immobilization of bFGF or EGF onto nanofibers using heparin as the adapter molecule significantly promoted axon growth. This study elucidated the effect of bFGF and EGF in neural differentiation and axon growth, and demonstrated a method to immobilize active bFGF and EGF onto aligned nanofibers to promote neural tissue regeneration.

PI3K mediated electrotaxis of embryonic and adult neural progenitor cells in the presence of growth factors

Correct guidance of the migration of neural progenitor cells (NPCs) is essential for the development and repair of the central nervous system (CNS). Electric field (EF)-guided migration, electrotaxis, has been observed in many cell types. We report here that, in applied EFs of physiological magnitude, embryonic and adult NPCs show marked electrotaxis, which is dependent on the PI3K/Akt pathway. The electrotaxis was also evidenced by ex vivo investigation that transplanted NPCs migrated directionally towards cathode in organotypic spinal cord slice model when treated with EFs. Genetic disruption or pharmacological inhibition of phosphoinositide 3-kinase (PI3K) impaired electrotaxis, whereas EF exposure increased Akt phosphorylation in a growth factor-dependent manner and increased phosphatidylinositol-3,4,5-trisphosphate (PIP3) levels. EF treatments also induced asymmetric redistribution of PIP3, growth factor receptors, and actin cytoskeleton. Electrotaxis in both embryonic and adult NPCs requires epidermal growth factor (EGF) and fibroblast growth factor (FGF). Our results demonstrate the importance of the PI3K/Akt pathway in directed migration of NPCs driven by EFs and growth factors and highlight the potential of EFs to enhance the guidance of various NPC populations in CNS repair therapies.

Neuronal vs. glial fate of embryonic stem cell-derived neural progenitors (ES-NPs) is determined by FGF2/EGF during proliferation

Fate-specific differentiation of neural progenitors attracts keen interest in modern medicine due to its application in cell replacement therapy. Though various signaling pathways are involved in maintenance and differentiation of neural progenitors, the mechanism of development of lineage-restricted progenitors from embryonic stem (ES) cells is not clearly understood. Here, we have demonstrated that neuronal vs. glial differentiation potential of ES cell-derived neural progenitors (ES-NPs) are governed by the growth factors, exposed during their proliferation/expansion phase and cannot be significantly altered during differentiation phase. Exposure of ES-NPs to fibroblast growth factor-2 (FGF2) during proliferation triggered the expression of pro-neural genes that are required for neuronal lineage commitment, and upon differentiation, predominantly generated neurons. On the other hand, epidermal growth factor (EGF)-exposed ES-NPs are not committed to neuronal fate due to decreased expression of pro-neural genes. These ES-NPs further generate more glial cells due to expression of glial-restricted factors. Exposure of ES-NPs to the same growth factors during proliferation/expansion and differentiation phase augments the robust differentiation of neurons or glial subtypes. We also demonstrate that, during differentiation, exposure to growth factors other than that in which the ES-NPs were expanded does not significantly alter the fate of ES-NPs. Thus, we conclude that FGF2 and EGF determine the neural vs. glial fate of ES-NPs during proliferation and augment it during differentiation. Further modification of these protocols would help in generating fate-specified neurons for various regenerative therapies.

Neural stem cell systems: physiological players or in vitro entities?

Neural stem cells (NSCs) can be experimentally derived or induced from different sources, and the NSC systems generated so far are promising tools for basic research and biomedical applications. However, no direct and thorough comparison of their biological and molecular properties or of their physiological relevance and possible relationship to endogenous NSCs has yet been carried out. Here we review the available information on different NSC systems and compare their properties. A better understanding of these systems will be crucial to control NSC fate and functional integration following transplantation and to make NSCs suitable for regenerative efforts following injury or disease.

Chromosome 7 and 19 trisomy in cultured human neural progenitor cells

Background

Stem cell expansion and differentiation is the foundation of emerging cell therapy technologies. The potential applications of human neural progenitor cells (hNPCs) are wide ranging, but a normal cytogenetic profile is important to avoid the risk of tumor formation in clinical trials. FDA approved clinical trials are being planned and conducted for hNPC transplantation into the brain or spinal cord for various neurodegenerative disorders. Although human embryonic stem cells (hESCs) are known to show recurrent chromosomal abnormalities involving 12 and 17, no studies have revealed chromosomal abnormalities in cultured hNPCs. Therefore, we investigated frequently occurring chromosomal abnormalities in 21 independent fetal-derived hNPC lines and the possible mechanisms triggering such aberrations.

Methods and Findings

While most hNPC lines were karyotypically normal, G-band karyotyping and fluorescent in situ hybridization (FISH) analyses revealed the emergence of trisomy 7 (hNPC⁺⁷) and trisomy 19 (hNPC⁺¹⁹), in 24% and 5% of the lines, respectively. Once detected, subsequent passaging revealed emerging dominance of trisomy hNPCs. DNA microarray and immunoblotting analyses demonstrate epidermal growth factor receptor (EGFR) overexpression in hNPC⁺⁷ and hNPC⁺¹⁹ cells. We observed greater levels of telomerase (hTERT), increased proliferation (Ki67), survival (TUNEL), and neurogenesis (β_III-tubulin) in hNPC⁺⁷ and hNPC⁺¹⁹, using respective immunocytochemical markers. However, the trisomy lines underwent replicative senescence after 50–60 population doublings and never showed neoplastic changes. Although hNPC⁺⁷ and hNPC⁺¹⁹ survived better after xenotransplantation into the rat striatum, they did not form malignant tumors. Finally, EGF deprivation triggered a selection of trisomy 7 cells in a diploid hNPC line.

Conclusions

We report that hNPCs are susceptible to accumulation of chromosome 7 and 19 trisomy in long-term cell culture. These results suggest that micro-environmental cues are powerful factors in the selection of specific hNPC aneuploidies, with trisomy of chromosome 7 being the most common. Given that a number of stem cell based clinical trials are being conducted or planned in USA and a recent report in PLoS Medicine showing the dangers of grafting an inordinate number of cells, these data substantiate the need for careful cytogenetic evaluation of hNPCs (fetal or hESC-derived) before their use in clinical or basic science applications.

Regionally specified human neural progenitor cells derived from the mesencephalon and forebrain undergo increased neurogenesis following overexpression of ASCL1

Human neural progenitor cells (hNPC) derived from the developing brain can be expanded in culture and subsequently differentiated into neurons and glia. They provide an interesting source of tissue for both modeling brain development and developing future cellular replacement therapies. It is becoming clear that hNPC are regionally and temporally specified depending on which brain region they were isolated from and its developmental stage. We show here that hNPC derived from the developing cortex (hNPC(CTX)) and ventral midbrain (hNPC(VM)) have similar morphological characteristics and express the progenitor cell marker nestin. However, hNPC(CTX) cultures were highly proliferative and produced large numbers of neurons, whereas hNPC(VM) divided slowly and produced fewer neurons but more astrocytes. Microarray analysis revealed a similar expression pattern for some stemness markers between the two growing cultures, overlaid with a regionally specific profile that identified some important differentially expressed neurogenic transcription factors. By overexpressing one of these, the transcription factor ASCL1, we were able to regain neurogenesis from hNPC(VM) cultures, which produced larger neurons with more neurites than hNPC(CTX) but no fully mature dopamine neurons. Thus, hNPC are regionally specified and can be induced to undergo neurogenesis following genetic manipulation. Although this restores neuronal production with a region-specific phenotype, it does not restore full neurochemical maturation, which may require additional factors.