Basic and clinical neuroscience applications of embryonic stem cells

The Emerging Roles for Telomerase in the Central Nervous System

Telomerase, a specialized ribonucleoprotein enzyme complex, maintains telomere length at the 3′ end of chromosomes, and functions importantly in stem cells, cancer and aging. Telomerase exists in neural stem cells (NSCs) and neural progenitor cells (NPCs), at a high level in the developing and adult brains of humans and rodents. Increasing studies have demonstrated that telomerase in NSCs/NPCs plays important roles in cell proliferation, neuronal differentiation, neuronal survival and neuritogenesis. In addition, recent works have shown that telomerase reverse transcriptase (TERT) can protect newborn neurons from apoptosis and excitotoxicity. However, to date, the link between telomerase and diseases in the central nervous system (CNS) is not well reviewed. Here, we analyze the evidence and summarize the important roles of telomerase in the CNS. Understanding the roles of telomerase in the nervous system is not only important to gain further insight into the process of the neural cell life cycle but would also provide novel therapeutic applications in CNS diseases such as neurodegenerative condition, mood disorders, aging and other ailments.

The science and ethics of cell-based therapies for Parkinson's disease

Parkinson's Disease (PD) is an age-related, disabling neurodegenerative disorder. Although sufferers usually respond to dopamine agonists for extended periods, the disease remains progressive and adverse drug effects can compromise effective long term treatment. Cell-based therapies have been the subject of much hype and optimism with regard to PD. Proof of principle was provided in the 1980s with fetal tissue transplantation trials demonstrating successful graft survival. Embryonic stem cells and reprogrammed or transdifferentiated somatic cells may provide alternative sources of tissue with the potential to overcome the material shortages and technical difficulties that have hindered fetal neural transplants. This article will review the state of the science for cell based therapies and examine the ethical issues that societies must negotiate regarding their clinical use.

Embryo Form Project: An original technique for the three-dimensional reconstruction of human embryo morphology

Our current knowledge on the developmental stages of human embryogenesis has derived from limited numbers of classical studies. Computer technology now permits accurate 3D reconstruction of embryo morphology from serial histological sections. We present a successful technique that uses either fresh or preserved serial histological sections to generate highly detailed 3D image reconstructions of very small human embryos. We present the data we obtained from the reconstruction in virtual space of previously sectioned 15 and 22.5mm embryos. Their morphologies were studied using a DICOM viewer which permitted the analysis of any specific structure in any required orientation. To our knowledge, this is the first time human embryos have been reconstructed in this way. We believe that this reconstruction technique could improve our knowledge on embryo morphogenesis, especially if coupled to the study of genes involved in embryonic development. It may also prove to be a useful pedagogical tool.

Pluripotent stem cell-derived neural stem cells: From basic research to applications

Basic research on pluripotent stem cells is designed to enhance understanding of embryogenesis, whereas applied research is designed to develop novel therapies and prevent diseases. Attainment of these goals has been enhanced by the establishment of embryonic stem cell lines, the technological development of genomic reprogramming to generate induced-pluripotent stem cells, and improvements in vitro techniques to manipulate stem cells. This review summarizes the techniques required to generate neural cells from pluripotent stem cells. In particular, this review describes current research applications of a simple neural differentiation method, the neural stem sphere method, which we developed.

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

Surgical repair of severe peripheral nerve injuries represents not only a pressing medical need, but also a great clinical challenge. Autologous nerve grafting remains a golden standard for bridging an extended gap in transected nerves. The formidable limitations related to this approach, however, have evoked the development of tissue engineered nerve grafts as a promising alternative to autologous nerve grafts. A tissue engineered nerve graft is typically constructed through a combination of a neural scaffold and a variety of cellular and molecular components. The initial and basic structure of the neural scaffold that serves to provide mechanical guidance and optimal environment for nerve regeneration was a single hollow nerve guidance conduit. Later there have been several improvements to the basic structure, especially introduction of physical fillers into the lumen of a hollow nerve guidance conduit. Up to now, a diverse array of biomaterials, either of natural or of synthetic origin, together with well-defined fabrication techniques, has been employed to prepare neural scaffolds with different structures and properties. Meanwhile different types of support cells and/or growth factors have been incorporated into the neural scaffold, producing unique biochemical effects on nerve regeneration and function restoration. This review attempts to summarize different nerve grafts used for peripheral nerve repair, to highlight various basic components of tissue engineered nerve grafts in terms of their structures, features, and nerve regeneration-promoting actions, and finally to discuss current clinical applications and future perspectives of tissue engineered nerve grafts.

REST and CoREST modulate neuronal subtype specification, maturation and maintenance

Background

The repressor element-1 silencing transcription factor/neuron-restrictive silencer factor (REST/NRSF) is a master regulator of neuronal gene expression. REST functions as a modular scaffold for dynamic recruitment of epigenetic regulatory factors including its primary cofactor, the corepressor for element-1-silencing transcription factor (CoREST), to genomic loci that contain the repressor element-1 (RE1) binding motif. While REST was initially believed to silence RE1 containing neuronal genes in neural stem cells (NSCs) and non-neuronal cells, emerging evidence shows an increasingly complex cell type- and developmental stage-specific repertoire of REST target genes and functions that include regulation of neuronal lineage maturation and plasticity.

Methodology/Principal Findings

In this study, we utilized chromatin immunoprecipitation on chip (ChIP-chip) analysis to examine REST and CoREST functions during NSC-mediated specification of cholinergic neurons (CHOLNs), GABAergic neurons (GABANs), glutamatergic neurons (GLUTNs), and medium spiny projection neurons (MSNs). We identified largely distinct but overlapping profiles of REST and CoREST target genes during neuronal subtype specification including a disproportionately high percentage that are exclusive to each neuronal subtype.

Conclusions/Significance

Our findings demonstrate that the differential deployment of REST and CoREST is an important regulatory mechanism that mediates neuronal subtype specification by modulating specific gene networks responsible for inducing and maintaining neuronal subtype identity. Our observations also implicate a broad array of factors in the generation of neuronal diversity including but not limited to those that mediate homeostasis, cell cycle dynamics, cell viability, stress responses and epigenetic regulation.

Transdifferentiation of bone marrow stromal cells into Schwann cell phenotype using progesterone as inducer

Bone marrow stromal cells (BMSCs) were reported to transdifferentiate into Schwann cells by a two-stage protocol, using beta-mercaptoethanol and retinoic acid (BME-RA) as preinducers (preinduction stage: PS) and platelet derived growth factor (PDGF), basic fibroblast growth factor (bFGF), forskolin (FSK) and heregulin (HRG) as inducers (induction stage: IS). In this study, six groups were used, group one was used as control (PS: BME-RA; IS: PDGF, bFGF, FSK and HRG). In group 2, the preinducer was similar to group 1, and in the induction stage, progesterone replaced HRG. In groups 3 and 4, the preinducer was progesterone; and at the induction stage, the inducer was similar to groups 1 and 2. Accordingly, in groups 5 and 6, the preinducer was FSK. The immunohistochemical differentiation markers were S-100 and P0, and RT-PCR markers were OCT-4 and P0 at the preinduction stage, while at the induction stage P0 and NeuroD were used. The results of the study showed that S-100 was expressed in the groups after the induction stage, however, P0 was not expressed in any group. There was not any significant difference between the percentage of S100 positive cells in the 1st and 2nd groups. P0 was expressed at the mRNA level in the undifferentiated BMSCs and in the 3rd and 4th groups after the preinduction and the induction stages. The conclusion of this study is that progesterone can induce BMSCs into Schwann cell phenotype.

Glutathione induces neuronal differentiation in rat bone marrow stromal cells

It has been reported that rat bone marrow stromal cells (BMSCs) are differentiated into neuronal cells by administration of 2-mercaptoethanol [Woodbury et al (2000) J Neurosci Res 61:364-370]. In this study, we examined the effects of various sulfhydryl (SH) compounds on the differentiation of BMSCs obtained from rat femurs. Neuronal differentiation was detected morphologically and immunocytochemically. It was found that the cells treated with reduced glutathione (GSH) apparently differentiated into neurons, showing extensive processes, and expressing neuron-specific enolase and microtubule-associated protein 2. Glutathione monoethyl ester (GEE), which increased the cellular GSH content, showed no effect on the expression of neuronal markers. It is concluded that the neural differentiation of BMSCs occurs by the administration of GSH. It was suggested that extracellular and not intracellular GSH have effects on the induction of the neuronal differentiation of BMSCs.

Embryonic stem cell—derived astrocytes expressing drug-inducible transgenes: differentiation and transplantion into the mouse brain

OBJECT

Embryonic stem cell (ESC)-derived astrocytes have many theoretical and practical advantages as vectors for delivery of gene therapy to the central nervous system (CNS). The aim of this study was to generate highly pure populations of ESC-derived astrocytes expressing drug-inducible transgenes, while minimizing contamination by undifferentiated ESCs

METHODS

Embryonic stem cells carrying a doxycycline-inducible green fluorescent protein (GFP) transgene were induced to differentiate into astrocytes by using feeder cell-free conditions that are completely defined. More than 95% of these cells expressed the astrocyte markers glial fibrillary acidic protein and GLT-1 glutamate transporter, and the morphological characteristics of these cells were typical of astrocytes. The expression of additional astrocyte markers was detected using reverse transcription-polymerase chain reaction. Undifferentiated ESCs comprised fewer than 0.1% of the cells after 10 days in this culture. Positive and negative selection techniques based on fluorescence-activated cell sorting were successfully used to decrease further the numbers of undifferentiated ESCs. Fully differentiated astrocytes expressed a GFP transgene under the tight control of a doxycycline-responsive promoter, and maintained their astrocytic phenotype 24 hours after transplantation into the mouse brain.

CONCLUSIONS

This study shows that transgenic ESCs can be induced to differentiate into highly pure populations of astrocytes. The astrocytes continue to express the transgene under the tight control of a drug-inducible promoter and are suitable for transplantation into the mouse brain. The number of potentially hazardous ESCs can be minimized using cell-sorting techniques. This strategy may be used to generate cellular vectors for delivering gene therapy to the CNS.

Culture method for the induction of neurospheres from mouse embryonic stem cells by coculture with PA6 stromal cells

Embryonic stem (ES) cells proliferate and maintain their pluripotency for over 1 year in vitro and may therefore provide a sufficient source for cell therapies. However, most of the previously reported methods for obtaining a source for cell therapies have not been simple. We describe here a novel method for induction of neurospheres from mouse ES cells by coculturing on PA6 cells instead of the formation of embryoid bodies. The ES cells cocultured with the PA6 stromal cell line for at least 3 days were capable of differentiating into spheres. The cells in the spheres were all green fluorescent protein (GFP) positive, showing that they were derived from GFP-expressing D3-ES cells. The spheres contained nestin-positive cells. The number of spheres increased when they were cocultured with PA6 for a longer period. Sphere formation was observed even after 10 mechanical dissociations and subculturings, showing its self-renewal ability. The cells differentiated into microtubule-associated protein-2 (MAP2)-positive neuronal cells and glial fibrillary acidic protein (GFAP)-positive glial cells. gamma-Aminobutyric acid-positive cells and tyrosine hydroxylase-positive cells were also observed in the spheres. The percentages of the MAP2- or GFAP-positive cells in the sphere changed according to the period of coculture on PA6 cells. At an early stage of coculture, more neurons were generated and, at a later period, more glial cells were generated. These results suggested that neurosphere could be generated from ES cells by coculturing with PA6, and that these cells resembled neural stem cells derived from mouse fetal brain tissue.

Efficient production of neural stem cells and neurons from embryonic stem cells

We have developed a simple method to efficiently produce a large number of neural stem cells and neurons from mouse embryonic stem (ES) cells. When cultured in astrocyte-conditioned medium (ACM) with mitogens (FGF-2 and EGF) under free-floating conditions, colonies of undifferentiated ES cells give rise to neural stem spheres (NSSs), composed of plentiful neural stem cells. Subsequent culture of the NSSs on an adhesive substrate with mitogens results in the migration of neural stem cells onto the substrate. These cells can be expanded, preserved by freezing, and differentiated into functional neurons. Neural stem cells and neurons provided by this NSS method may be valuable as potential donor cells for neuronal transplantation and also as convenient alternatives to tissue-derived neural cells.

Astrocyte-derived factors instruct differentiation of embryonic stem cells into neurons

Pluripotent embryonic stem (ES) cells may differentiate into neurons in vitro. This is valuable in the study of neurogenesis and in the generation of donor cells for neuronal transplantation. Here we show that astrocyte-derived factors instruct mouse and primate ES cells to differentiate into neurons. Cultured in astrocyte-conditioned medium (ACM) under free-floating conditions, within 4 days, colonies of undifferentiated mouse ES cells give rise to floating spheres of concentric stratiform structure with a periphery of neural stem cells, which are termed Neural Stem Spheres. Culturing the spheres on an adhesive substrate in ACM promotes neurogenesis, and cells in the spheres differentiate into neurons within 5 days, including dopaminergic neurons. In contrast, neither astrocytes nor oligodendrocytes are formed. The procedure developed for mouse ES cells can be applied to monkey ES cells. This neurogenesis pathway provides a new insight into mechanisms of specification of cell fates in early development and also provides a simple procedure for fast and efficient generation of a vast number of neural stem cells and neurons.

In vitro differentiation of size-sieved stem cells into electrically active neural cells

Size-sieved stem (SS) cells isolated from human bone marrow and propagated in vitro are a population of cells with consistent marker typing, and can form bone, fat, and cartilage. In this experiment, we demonstrated that SS cells could be induced to differentiate into neural cells under experimental cell culture conditions. Five hours after exposure to antioxidant agents (beta-mercaptoethanol +/- retinoic acid) in serum-free conditions, SS cells expressed the protein for nestin, neuron-specific enolase (NSE), neuron-specific nuclear protein (NeuN), and neuron-specific tubulin-1 (TuJ-1), and the mRNA for NSE and Tau. Immunofluorescence showed that almost all the cells (>98%) expressed NeuN and TuJ-1. After 5 days of beta-mercaptoethanol treatment, the SS cells expressed neurofilament high protein but not mitogen-activated protein-2, glial filament acidic protein, and galactocerebroside. For such long-term-treated cells, voltage-sensitive ionic current could be detected by electrophysiological recording, and the intracellular calcium ion, Ca(2+), concentration can be elevated by high potassium (K(+)) buffer and glutamate. These findings suggest that SS cells may be an alternative source of undifferentiated cells for cell therapy and gene therapy in neural dysfunction.

Postnatal histogenesis in the peripheral nervous system

The issue of postnatal neurogenesis has gained great importance over the last few years and the recent amazing scientific advancements, changing our viewpoint on the long-lasting "no new neurons" dogma, have opened promising new perspectives on the treatment of the damaged nervous system. While most of the researchers have focused on the central nervous system, the peripheral nervous system has received little attention so far with respect to postnatal histogenesis. To attract scientific attention on this issue, the present article was written with the aim of reviewing the body of literature on postnatal histogenesis in the various districts of the peripheral nervous system, from the historical roots to the most recent reports.

Modification of brain aging and neurodegenerative disorders by genes, diet, and behavior

Multiple molecular, cellular, structural, and functional changes occur in the brain during aging. Neural cells may respond to these changes adaptively, or they may succumb to neurodegenerative cascades that result in disorders such as Alzheimer's and Parkinson's diseases. Multiple mechanisms are employed to maintain the integrity of nerve cell circuits and to facilitate responses to environmental demands and promote recovery of function after injury. The mechanisms include production of neurotrophic factors and cytokines, expression of various cell survival-promoting proteins (e.g., protein chaperones, antioxidant enzymes, Bcl-2 and inhibitor of apoptosis proteins), preservation of genomic integrity by telomerase and DNA repair proteins, and mobilization of neural stem cells to replace damaged neurons and glia. The aging process challenges such neuroprotective and neurorestorative mechanisms. Genetic and environmental factors superimposed upon the aging process can determine whether brain aging is successful or unsuccessful. Mutations in genes that cause inherited forms of Alzheimer's disease (amyloid precursor protein and presenilins), Parkinson's disease (alpha-synuclein and Parkin), and trinucleotide repeat disorders (huntingtin, androgen receptor, ataxin, and others) overwhelm endogenous neuroprotective mechanisms; other genes, such as those encoding apolipoprotein E(4), have more subtle effects on brain aging. On the other hand, neuroprotective mechanisms can be bolstered by dietary (caloric restriction and folate and antioxidant supplementation) and behavioral (intellectual and physical activities) modifications. At the cellular and molecular levels, successful brain aging can be facilitated by activating a hormesis response in which neurons increase production of neurotrophic factors and stress proteins. Neural stem cells that reside in the adult brain are also responsive to environmental demands and appear capable of replacing lost or dysfunctional neurons and glial cells, perhaps even in the aging brain. The recent application of modern methods of molecular and cellular biology to the problem of brain aging is revealing a remarkable capacity within brain cells for adaptation to aging and resistance to disease.

Directed differentiation of embryonic stem cells: genetic and epigenetic methods

Embryonic stem cells are derived from the inner cell mass of the pre-implantation blastocyst, and can both self-renew and differentiate into all the cells and tissues of the body. The embryonic stem cell is an unsurpassed starting material to begin to understand a critical, largely inaccessible, period of development, as well as an important source of cells for transplantation and gene therapy. Despite their potential, attempts to obtain specific cell types from embryonic stem cells have been only partially successful because many of the growth factor combinations and developmental control genes involved in cell type restricted differentiation are unknown. This article summarizes some of the recent advances in promoting lineage restricted differentiation of embryonic stem cells, focusing on growth factor manipulation, or genetically altering embryonic stem cells to produce a desired phenotype. The two approaches epitomize current scientific concerns regarding the therapeutic use of these cells; genetic alterations will produce more pure cells with the risk of increasing the likelihood of malignant transformation; epigenetic methods for the manipulation of stem cell phenotype are often incomplete and remaining pluripotent cells are likely to form teratomas. As more is known about lineage specification during development, it will be possible to more precisely control cell type specification.

Adult stem cells and neurogenesis: historical roots and state of the art

Over the last few years, an impressive number of papers have addressed the stem cell issue. However, as often occurs when a scientific subject undergoes a period of fast growth, some confusion is generated. To help reduce the existing uncertainty, this paper focuses on the concept of adult stem cells in relation to the classification of cell populations on the basis their proliferative behavior. Particular attention is dedicated to adult neural stem cells, an issue that has recently seen the most amazing advances. Finally, the concept of adult stem cells is differentiated from that of developmental stem cells in relation to the employment of stem cells for transplantation therapies.