Increased survival of rat EGF-generated CNS precursor cells using B27 supplemented medium

Growth Hormone (GH) Enhances Endogenous Mechanisms of Neuroprotection and Neuroplasticity after Oxygen and Glucose Deprivation Injury (OGD) and Reoxygenation (OGD/R) in Chicken Hippocampal Cell Cultures

As a classical growth promoter and metabolic regulator, growth hormone (GH) is involved in development of the central nervous system (CNS). This hormone might also act as a neurotrophin, since GH is able to induce neuroprotection, neurite growth, and synaptogenesis during the repair process that occurs in response to neural injury. After an ischemic insult, the neural tissue activates endogenous neuroprotective mechanisms regulated by local neurotrophins that promote tissue recovery. In this work, we investigated the neuroprotective effects of GH in cultured hippocampal neurons exposed to hypoxia-ischemia injury and further reoxygenation. Hippocampal cell cultures obtained from chick embryos were incubated under oxygen-glucose deprivation (OGD, <5% O₂, 1 g/L glucose) conditions for 24 h and simultaneously treated with GH. Then, cells were either collected for analysis or submitted to reoxygenation and normal glucose incubation conditions (OGD/R) for another 24 h, in the presence of GH. Results showed that OGD injury significantly reduced cell survival, the number of cells, dendritic length, and number of neurites, whereas OGD/R stage restored most of those adverse effects. Also, OGD/R increased the mRNA expression of several synaptogenic markers (i.e., NRXN1, NRXN3, NLG1, and GAP43), as well as the growth hormone receptor (GHR). The expression of BDNF, IGF-1, and BMP4 mRNAs was augmented in response to OGD injury, and exposure to OGD/R returned it to normoxic control levels, while the expression of NT-3 increased in both conditions. The addition of GH (10 nM) to hippocampal cultures during OGD reduced apoptosis and induced a significant increase in cell survival, number of cells, and doublecortin immunoreactivity (DCX-IR), above that observed in the OGD/R stage. GH treatment also protected dendrites and neurites during OGD, inducing plastic changes reflected in an increase and complexity of their outgrowths during OGD/R. Furthermore, GH increased the expression of NRXN1, NRXN3, NLG1, and GAP43 after OGD injury. GH also increased the BDNF expression after OGD, but reduced it after OGD/R. Conversely, BMP4 was upregulated by GH after OGD/R. Overall, these results indicate that GH protective actions in the neural tissue may be explained by a synergic combination between its own effect and that of other local neurotrophins regulated by autocrine/paracrine mechanisms, which together accelerate the recovery of tissue damaged by hypoxia-ischemia.

Establishment of a Simple Method for Inducing Neuronal Differentiation of P19 EC Cells without Embryoid Body Formation and Analysis of the Role of Histone Deacetylase 8 Activity in This Differentiation

P19 pluripotent embryonic carcinoma (EC) stem cells are derived from pluripotent germ cell tumours and can differentiate into three germ layers. Treatment of these cells in suspension culture with retinoic acid induces their differentiation into neurons and glial cells. Hence, these cells are an excellent in vitro model to study the transition from the upper blastoderm to the neuroectoderm. However, because of the complex nature of the techniques involved, the results are highly dependent on the skills of the experimenter. Herein, we developed a simple method to induce neuronal differentiation of adherent P19 EC cells in TaKaRa NDiff^® 227 serum-free medium (originally N2B27 medium). This medium markedly induced neuronal differentiation of P19 EC cells. The addition of retinoic acid to the NDiff^® 227 medium further enhanced differentiation. Furthermore, cells differentiated by the conventional method, as well as the new method, showed identical expression of the mature neuronal marker, neuronal nuclei. To determine whether our approach could be applied for neuronal studies, we measured histone deacetylase 8 (HDAC8) activity using an HDAC8 inhibitor and HDAC8-knockout P19 EC cells. Inhibition of HDAC8 activity suppressed neuronal maturation. Additionally, HDAC8-knockout cell lines showed immature differentiation compared to the wild-type cell line. These results indicate that HDAC8 directly regulates the neuronal differentiation of P19 EC cells. Thus, our method involving P19 EC cells can be used as an experimental system to study the nervous system. Moreover, this method is suitable for screening drugs that affect the nervous system and cell differentiation.

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.

The necessity for standardization of glioma stem cell culture: a systematic review

BACKGROUND

The cancer stem cell hypothesis is an old idea which has been revived in recent years for many cancers, including gliomas. However, this concept has become controversial due to a series of studies with conflicting results.

METHODS

A systematic literature search was conducted in PubMed and the Web of Science database to analyze studies using serum-free medium and its components in glioma stem cells, glioma stem-like cells, glioma-initiating cells, or glioma neurosphere cultures. All the studies reviewed were published between 1970 and 2019. We found that no standardized culture method was used, and the data were incomparable due to differing culture conditions and the use of media with different components.

CONCLUSIONS

Here, we review the most commonly used serum-free media and added components for glioma stem cell culture while highlighting the function of each component used in the media. We emphasize the necessity for standardization of glioma stem cell culture and propose a standard culture medium to prevent bias in glioma stem cell research.

Strategies for retinal cell generation from human pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are specialized self-renewing cells that are generated by exogenously expressing pluripotency-associated transcription factors in somatic cells such as fibroblasts, peripheral blood mononuclear cells, or lymphoblastoid cell lines (LCLs). iPSCs are functionally similar to naturally pluripotent embryonic stem cells (ESCs) in their capacity to propagate indefinitely and potential to differentiate into all human cell types, and are devoid of the associated ethical complications of origin. iPSCs are useful for studying embryonic development, disease modeling, and drug screening. Additionally, iPSCs provide a personalized approach for pathological studies, particularly for diseases that lack appropriate animal models. Retinal cell differentiations using iPSCs have been successful in this regard. Several protocols to generate various retinal cells have been developed to maximize a specific cell type or, most recently, to mimic in vivo retinal structure and cellular environment. As differentiation protocols continue to improve we are likely to see an increase in our basic understanding of various retinal degenerative diseases and the utilization of iPSCs in clinical trials.

Muscle Reinnervation with Delayed or Immediate Transplant of Embryonic Ventral Spinal Cord Cells into Adult Rat Peripheral Nerve

Muscle denervation is common in various neuromuscular diseases and after trauma. It induces skeletal muscle atrophy. Only muscle reinnervation leads to functional recovery. In previous studies, denervated adult rat muscles were rescued by transplantation of embryonic day 14–15 (E14–15) ventral spinal cord cells into a nearby peripheral nerve. In the present study, changes were made in the environment into which the cells were placed to test whether reinnervation was improved by: 1) prior nerve degeneration, induced by sciatic nerve transection 1 week before cell transplantation; 2) transplantation of 1 million versus 5 million cells; 3) addition of nerve growth factor (NGF) to the transplant. Ten weeks after cell transplantation, axons had grown from all of the transplants. The numbers of myelinated axons that regenerated into the tibial, medial (MG), and lateral gastrocnemius-soleus (LGS) nerves were similar across treatments. The mean diameters of large LGS axons (>6 μm) were significantly larger with nerve degeneration before transplantation. The mean diameters of MG and LGS axons were significantly larger with transplantation of 1 million versus 5 million cells. Silver-stained experimental and control lateral gastronemius (LG) muscles showed axons that terminated at motor end plates. Nodal and terminal sprouts were more common in reinnervated muscles (45–63% of all end plates) than in control muscles (10%). Electrical stimulation of the transplants induced weak contractions in 39 of 47 MG muscles (83%) and 33 of 46 LG muscles (72%) but at higher voltages than needed to excite control muscles. The threshold for MG contraction was lower with transplantation of 1 million cells, while LG thresholds were lower without NGF. The cross-sectional area of whole LG muscles was significantly larger with cell transplantation (immediate or delayed) than with media alone, but all of these muscle areas were reduced significantly compared with control muscle areas. These data suggest that delayed transplantation of fewer cells without NGF assists regeneration of larger diameter axons and prevents some muscle atrophy.

Differentiation of human olfactory bulb-derived neural stem cells toward oligodendrocyte

In the central nervous system (CNS), oligodendrocytes are the glial element in charge of myelin formation. Obtaining an overall presence of oligodendrocyte precursor cells/oligodendrocytes (OPCs/OLs) in culture from different sources of NSCs is an important research area, because OPCs/OLs may provide a promising therapeutic strategy for diseases affecting myelination of axons. The present study was designed to differentiate human olfactory bulb NSCs (OBNSCs) into OPCs/OLs and using expression profiling (RT-qPCR) gene, immunocytochemistry, and specific protein expression to highlight molecular mechanism(s) underlying differentiation of human OBNSCs into OPCs/OLs. The differentiation of OBNSCs was characterized by a simultaneous appearance of neurons and glial cells. The differentiation medium, containing cAMP, PDGFA, T3, and all-trans-retinoic acid (ATRA), promotes OBNSCs to generate mostly oligodendrocytes (OLs) displaying morphological changes, and appearance of long cytoplasmic processes. OBNSCs showed, after 5 days in OLs differentiation medium, a considerable decrease in the number of nestin positive cells, which was associated with a concomitant increase of NG2 immunoreactive cells and few O4(+)-OPCs. In addition, a significant up regulation in gene and protein expression profile of stage specific cell markers for OPCs/OLs (CNPase, Galc, NG2, MOG, OLIG1, OLIG2, MBP), neurons, and astrocytes (MAP2, β-TubulinIII, GFAP) and concomitant decrease of OBNSCs pluripotency markers (Oct4, Sox2, Nestin), was demonstrated following induction of OBNSCs differentiation. Taken together, the present study demonstrate the marked ability of a cocktail of factors containing PDGFA, T3, cAMP, and ATRA, to induce OBNSCs differentiation into OPCs/OLs and shed light on the key genes and pathological pathways involved in this process.

Neuronal Progenitor Cells of the Neonatal Subventricular Zone Differentiate and Disperse following Transplantation into the Adult Rat Striatum

We have investigated the suitability of a recently identified and characterized population of neuronal progenitor cells for their potential use in the replacement of degenerating or damaged neurons in the mammalian brain. The unique population of neuronal progenitor cells is situated in a well-delineated region of the anterior part of the neonatal subventricular zone (referred to as SVZa). This region can be separated from the remaining proliferative, gliogenic, subventricular zone encircling the lateral ventricles of the forebrain. Because the neurons arising from the highly enriched neurogenic progenitor cell population of the SVZa ordinarily migrate considerable distances and ultimately express the neurotransmitters GABA and dopamine, we have examined whether they could serve as an alternative source of tissue for neural transplantation. SVZa cells from postnatal day 0-2 rats, prelabeled by intraperitoneal injections of the cell proliferation marker BrdU, were implanted into the striatum of adult rats approximately 1 mo after unilateral denervation by 6-OHDA. To examine the spatio-temporal distribution and phenotype of the transplanted SVZa cells, the experimental recipients were perfused at short (less than 1 wk), intermediate (2-3 wk) and long (5 mo) postimplantation times. The host brains were sectioned and stained with an antibody to BrdU and one of several cell-type specific markers to determine the phenotypic characteristics of the transplanted SVZa cells. To identify neurons we used the neuron-specific antibody TuJ1, or antimembrane-associated protein 2 (MAP-2), and anti-GFAP was used to identify astrocytic glia. At all studied intervals the majority of the surviving SVZa cells exhibited a neuronal phenotype. Moreover, morphologically they could be distinguished from the cells of the host striatum because they resembled the intrinsic granule cells of the olfactory bulb, their usual fate. At longer times, a greater number of the transplanted SVZa cells had migrated from their site of implantation, often towards an outlying blood vessel, and the density of cells within the core of the transplant was reduced. Furthermore, there were rarely signs of transplant rejection or a glial scar surrounding the transplant. In the core of the transplant there were low numbers of GFAP-positive cells, indicating that the transplanted SVZa cells, predominantly TuJ1-positive/MAP2-positive, express a neuronal phenotype. Collectively, the propensity of the SVZa cells to express a neuronal phenotype and to survive and integrate in the striatal environment suggest that they may be useful in the reconstruction of the brain following CNS injury or disease.

Poly(ADP-ribose) polymerase inhibitors activate the p53 signaling pathway in neural stem/progenitor cells

Background

Poly(ADP-ribose) polymerase 1 (PARP-1), which catalyzes poly(ADP-ribosyl)ation of proteins by using NAD⁺ as a substrate, plays a key role in several nuclear events, including DNA repair, replication, and transcription. Recently, PARP-1 was reported to participate in the somatic cell reprogramming process. Previously, we revealed a role for PARP-1 in the induction of neural apoptosis in a cellular model of cerebral ischemia and suggested the possible use of PARP inhibitors as a new therapeutic intervention. In the present study, we examined the effects of PARP inhibitors on neural stem/progenitor cells (NSPCs) of the mouse brain.

Results

PARP-1 was more abundant and demonstrated higher activity in NSPCs than in mouse embryonic fibroblasts. Treatment with PARP inhibitors suppressed the formation of neurospheres by NSPCs through the suppression of cell cycle progression and the induction of apoptosis. In order to identify the genes responsible for these effects, we investigated gene expression profiles by microarray analyses and found that several genes in the p53 signaling pathway were upregulated, including Cdkn1a, which is critical for cell cycle control, and Fas, Pidd, Pmaip1, and Bbc3, which are principal factors in the apoptosis pathway. Inhibition of poly(ADP-ribosyl)ation increased the levels of p53 protein, but not p53 mRNA, and enhanced the phosphorylation of p53 at Ser18. Experiments with specific inhibitors and also shRNA demonstrated that PARP-1, but not PARP-2, has a role in the regulation of p53. The effects of PARP inhibitors on NSPCs were not observed in Trp53^−/− NSPCs, suggesting a key role for p53 in these events.

Conclusions

On the basis of the finding that PARP inhibitors facilitated the p53 signaling pathway, we propose that poly(ADP-ribosyl)ation contributes to the proliferation and self-renewal of NSPCs through the suppression of p53 activation.

Comparison of mammosphere formation from breast cancer cell lines and primary breast tumors

BACKGROUND

Breast cancer stem cells (BCSCs) can be enriched by culturing of cells in non-adherent non-differentiating conditions. However, culturing mammospheres from primary breast tumors are costly and difficult to control. In order to overcome problems associated with using primary human tissues, continuous breast cancer cell lines have been developed from various sources.

METHODS

In this study, a luminal subtype breast cancer cell line MCF-7 and a basal subtype cell line MDA-MB-231 were chosen. We explored the optimal culturing system for BCSCs from the two cell lines and primary breast tumors. Then, mammosphere formation efficiency (MFE), CD44(+)/CD24(-/low)ESA(+)Lin(-) cell proportion in mammospheres, and tumorigenecity of mammospheres generated from the two breast cancer cell lines and primary breast tumors were compared.

RESULTS

Enzymatic digestion of 60 mins and the addition of B27 to the culture medium were optimal for mammosphere culturing. Mammospheres could be formed in all the three cells, in which MCF-7 had the highest MFE. After 3 weeks culture, CD44(+)/CD24(-/low)ESA(+)Lin(-) cell proportion in mammospheres from MCF-7, MDA-MB-231 cells and primary breast tumors was 95.0%±2.5%, 82%±22% and 21.5%±1.0%, respectively. A total of 1,000 cells from MCF-7, MDA-MB-231 mammospheres but not primary mammospheres were tumorigenic.

CONCLUSIONS

This study validates the use of breast cancer cell lines as models to elucidate the nature of BCSCs.

A cGMP-applicable expansion method for aggregates of human neural stem and progenitor cells derived from pluripotent stem cells or fetal brain tissue

A cell expansion technique to amass large numbers of cells from a single specimen for research experiments and clinical trials would greatly benefit the stem cell community. Many current expansion methods are laborious and costly, and those involving complete dissociation may cause several stem and progenitor cell types to undergo differentiation or early senescence. To overcome these problems, we have developed an automated mechanical passaging method referred to as "chopping" that is simple and inexpensive. This technique avoids chemical or enzymatic dissociation into single cells and instead allows for the large-scale expansion of suspended, spheroid cultures that maintain constant cell/cell contact. The chopping method has primarily been used for fetal brain-derived neural progenitor cells or neurospheres, and has recently been published for use with neural stem cells derived from embryonic and induced pluripotent stem cells. The procedure involves seeding neurospheres onto a tissue culture Petri dish and subsequently passing a sharp, sterile blade through the cells effectively automating the tedious process of manually mechanically dissociating each sphere. Suspending cells in culture provides a favorable surface area-to-volume ratio; as over 500,000 cells can be grown within a single neurosphere of less than 0.5 mm in diameter. In one T175 flask, over 50 million cells can grow in suspension cultures compared to only 15 million in adherent cultures. Importantly, the chopping procedure has been used under current good manufacturing practice (cGMP), permitting mass quantity production of clinical-grade cell products.

A new and safe method for stereotactically harvesting neural stem/progenitor cells from the adult rat subventricular zone

BACKGROUND

Adult neural stem/progenitor cells (NS/PCs) are one of the outstanding cell sources for therapeutic purposes in the central nervous system diseases. Autologous transplantation of NS/PCs still is a matter of controversy due to the safety issue as well as efficiency of harvesting these cells from the live mammalian brain subventricular zone (SVZ).

NEW METHOD

In this new and safe method, a 16-guage semi-automatic biopsy needle was used stereotactically to remove a piece of SVZ. Then, the proliferation and differentiation capacity of obtained cells were assessed. In addition, the safety of the biopsy procedure was analyzed employing the Morris water maze, modified neurologic severity score, passive avoidance and open field tests.

RESULTS

Despite being very small in size, the SVZ specimen could generate a large number of progeny with the ability to differentiate into neuronal and glial cells. The biopsy procedure introduced in this study did not have any impact on the behavioral and neurological processes.

COMPARISON WITH EXISTING METHOD(S)

existing SVZ biopsy methods were uncontrollable techniques which harvested brain tissue by aspiration using a syringe not a semi-automatic biopsy needle. Also, previous methods were not evaluated in terms of behavior and cognition.

CONCLUSIONS

This study revealed a considerable safety and efficacy for the stereotactical removal of the adult rat SVZ to harvest NS/PCs for autologous transplantation.

Mimicking the neurotrophic factor profile of embryonic spinal cord controls the differentiation potential of spinal progenitors into neuronal cells

Recent studies have indicated that the choice of lineage of neural progenitor cells is determined, at least in part, by environmental factors, such as neurotrophic factors. Despite extensive studies using exogenous neurotrophic factors, the effect of endogenous neurotrophic factors on the differentiation of progenitor cells remains obscure. Here we show that embryonic spinal cord derived-progenitor cells express both ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) mRNA before differentiation. BDNF gene expression significantly decreases with their differentiation into the specific lineage, whereas CNTF gene expression significantly increases. The temporal pattern of neurotrophic factor gene expression in progenitor cells is similar to that of the spinal cord during postnatal development. Approximately 50% of spinal progenitor cells differentiated into astrocytes. To determine the effect of endogenous CNTF on their differentiation, we neutralized endogenous CNTF by administration of its polyclonal antibody. Neutralization of endogenous CNTF inhibited the differentiation of progenitor cells into astrocytes, but did not affect the numbers of neurons or oligodendrocytes. Furthermore, to mimic the profile of neurotrophic factors in the spinal cord during embryonic development, we applied BDNF or neurotrophin (NT)-3 exogenously in combination with the anti-CNTF antibody. The exogenous application of BDNF or NT-3 promoted the differentiation of these cells into neurons or oligodendrocytes, respectively. These findings suggest that endogenous CNTF and exogenous BDNF and NT-3 play roles in the differentiation of embryonic spinal cord derived progenitor cells into astrocytes, neurons and oligodendrocytes, respectively.

Delayed functional maturation of human neuronal progenitor cells in vitro

INTRODUCTION

Differentiation of neuronal progenitor cells (NPCs) in vitro into functional neurons is dependent on a complex cascade of molecular signaling pathways, many of which remain unknown. More specifically, in human NPCs the relationship between the expression of typical neuronal marker proteins and functional properties, such as firing action potential and synaptic transmission, is not well understood. In the present report, the immunocytochemical, morphological and electrophysiological changes that human NPCs undergo during neuronal differentiation in vitro were investigated.

METHODS

Human NPCs were differentiated toward a neuronal phenotype. The time course of the expression of neuronal markers and morphological cell changes was mapped and passive and active electrophysiological membrane properties assessed, throughout the neuronal maturation process.

RESULTS

The acquisition of neuronal markers preceded functional physiological maturation by several weeks. Cell input resistance decreased in the first 2 weeks as cells became less sensitive to input current, while cell capacitance progressively increased with continued neuronal process growth. Functional maturation was observed only by the fifth/sixth week, preceded by a marked increase in Na+ and K+ currents. In contrast, electrophysiological maturation of rodent precursor cells was observed at the end of the first week in vitro. Functionally, human neuronal cells became capable of firing action potentials and forming active synaptic contacts. Many features of the firing pattern however remained immature.

CONCLUSIONS

The results showed that human NPCs develop remarkably slowly and retain immature neuronal features for a prolonged period. The importance of Na-dependent activity for proper neuronal maturation is emphasized.

Dose-dependent effect of EGF on migration and differentiation of adult subventricular zone astrocytes

Adult neural stem cells (NSCs) are located in the subventricular zone (SVZ), a specialized brain niche located on the walls of the lateral ventricle. Under physiological conditions, NSCs generate a large number of young neurons and some oligodendrocytes, however the mechanisms controlling cell proliferation and migration are unclear. In vitro, epidermal growth factor (EGF) signaling has been shown to be an important mediator of cell proliferation and migration in the adult brain; however, the primary SVZ progenitors that respond to EGF are not well known. In this study, we isolated SVZ type-B astrocytes and cultured them under different EGF concentrations. We found a dose-dependent effect of EGF on proliferation rates and migration of SVZ type-B astrocytes. We found that GFAP+ type-B astrocytes gave rise to highly migratory and proliferating cells that expressed Olig2 and NG2. After EGF withdrawal, a significant number of EGF-stimulated cells differentiated into S100beta+/O4+ oligodendrocytes. This study provides new insights about the production of oligodendrocytes derived from the astrocyte NSCs residing in the adult SVZ. To be able to manipulate the endogenous adult progenitors, it is crucial to identify and isolate the responding primary precursors and determine the extracellular signals that regulate their cell division, migration, and fate.

BDNF and extracellular matrix regulate differentiation of mice neurosphere-derived cells into a GABAergic neuronal phenotype

Differentiation of neurosphere-derived cells is regulated by extracellular cues, namely, growth factors and proteins of the extracellular matrix (ECM). In this study we analyzed the influence of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), retinoic acid plus potassium chloride (RA-KCl), and the nonsynthetic ECMs laminin (LN) and fibronectin (FN) versus the synthetic adhesion substrate poly-L-lysine (PLL) in the in vitro differentiation of postnatal neurosphere cells. BDNF increased the number of differentiated neurons and decreased the number of neuronal precursors (nestin-positive cells) compared with NGF or RA-KCl. Moreover, cells treated with BDNF plus B27 supplement acquired a gamma-aminobutyric acid (GABA)-ergic phenotype and showed increased survival. No significant differences were found in the number of differentiated neurons in the presence of the ECMs alone. Nevertheless, FN or PLL in combination with BDNF promoted the acquisition of a GABAergic phenotype. The results obtained in this study highlight the importance of growth factors and ECM proteins for the potential of neurosphere cells to differentiate into neurons.

Long-term multilayer adherent network (MAN) expansion, maintenance, and characterization, chemical and genetic manipulation, and transplantation of human fetal forebrain neural stem cells

Human neural stem/precursor cells (hNSC/hNPC) have been targeted for application in a variety of research models and as prospective candidates for cell-based therapeutic modalities in central nervous system (CNS) disorders. To this end, the successful derivation, expansion, and sustained maintenance of undifferentiated hNSC/hNPC in vitro, as artificial expandable neurogenic micro-niches, promises a diversity of applications as well as future potential for a variety of experimental paradigms modeling early human neurogenesis, neuronal migration, and neurogenetic disorders, and could also serve as a platform for small-molecule drug screening in the CNS. Furthermore, hNPC transplants provide an alternative substrate for cellular regeneration and restoration of damaged tissue in neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Human somatic neural stem/progenitor cells (NSC/NPC) have been derived from a variety of cadaveric sources and proven engraftable in a cytoarchitecturally appropriate manner into the developing and adult rodent and monkey brain while maintaining both functional and migratory capabilities in pathological models of disease. In the following unit, we describe a new procedure that we have successfully employed to maintain operationally defined human somatic NSC/NPC from developing fetal, pre-term post-natal, and adult cadaveric forebrain. Specifically, we outline the detailed methodology for in vitro expansion, long-term maintenance, manipulation, and transplantation of these multipotent precursors.

Isolating, expanding, and infecting human and rodent fetal neural progenitor cells

Neural progenitor cells have tremendous utility for understanding basic developmental processes, disease modeling, and therapeutic intervention. The protocols described in this unit provide detailed information to isolate and expand human and rodent neural progenitor cells in culture for several months as floating aggregates (termed neurospheres) or plated cultures. Detailed protocols for cryopreservation, neural differentiation, exogenous gene expression using lentivirus, and transplantation into the rodent nervous system are also described.

Behavior of hippocampal stem/progenitor cells following grafting into the injured aged hippocampus

Multipotent neural stem/progenitor cells (NSCs) from the embryonic hippocampus are potentially useful as donor cells to repopulate the degenerated regions of the aged hippocampus after stroke, epilepsy, or Alzheimer's disease. However, the efficacy of the NSC grafting strategy for repairing the injured aged hippocampus is unknown. To address this issue, we expanded FGF-2-responsive NSCs from the hippocampus of embryonic day 14 green fluorescent protein-expressing transgenic mice as neurospheres in vitro and grafted them into the hippocampus of 24-month-old F344 rats 4 days after CA3 region injury. Engraftment, migration, and neuronal/glial differentiation of cells derived from NSCs were analyzed 1 month after grafting. Differentiation of neurospheres in culture dishes or after placement on organotypic hippocampal slice cultures demonstrated that these cells had the ability to generate considerable numbers of neurons, astrocytes, and oligodendrocytes. Following grafting into the injured aged hippocampus, cells derived from neurospheres survived and dispersed, but exhibited no directed migration into degenerated or intact hippocampal cell layers. Phenotypic analyses of graft-derived cells revealed neuronal differentiation in 3%-5% of cells, astrocytic differentiation in 28% of cells, and oligodendrocytic differentiation in 6%-10% cells. The results demonstrate for the first time that NSCs derived from the fetal hippocampus survive and give rise to all three CNS phenotypes following transplantation into the injured aged hippocampus. However, grafted NSCs do not exhibit directed migration into lesioned areas or widespread neuronal differentiation, suggesting that direct grafting of primitive NSCs is not adequate for repair of the injured aged brain without priming the microenvironment.

Effect of low-level laser irradiation and epidermal growth factor on adult human adipose-derived stem cells

The study investigated the effects of low-level laser radiation and epidermal growth factor (EGF) on adult adipose-derived stem cells (ADSCs) isolated from human adipose tissue. Isolated cells were cultured to semi-confluence, and the monolayers of ADSCs were exposed to low-level laser at 5 J/cm(2) using 636 nm diode laser. Cell viability and proliferation were monitored using adenosine triphosphate (ATP) luminescence and optical density at 0 h, 24 h and 48 h after irradiation. Application of low-level laser irradiation at 5 J/cm(2) on human ADSCs cultured with EGF increased the viability and proliferation of these cells. The results indicate that low-level laser irradiation in combination with EGF enhances the proliferation and maintenance of ADSCs in vitro.

Laminin enhances the growth of human neural stem cells in defined culture media

Background

Human neural stem cells (hNSC) have the potential to provide novel cell-based therapies for neurodegenerative conditions such as multiple sclerosis and Parkinson's disease. In order to realise this goal, protocols need to be developed that allow for large quantities of hNSC to be cultured efficiently. As such, it is important to identify factors which enhance the growth of hNSC. In vivo, stem cells reside in distinct microenvironments or niches that are responsible for the maintenance of stem cell populations. A common feature of niches is the presence of the extracellular matrix molecule, laminin. Therefore, this study investigated the effect of exogenous laminin on hNSC growth.

Results

To measure hNSC growth, we established culture conditions using B27-supplemented medium that enable neurospheres to grow from human neural cells plated at clonal densities. Limiting dilution assays confirmed that neurospheres were derived from single cells at these densities. Laminin was found to increase hNSC numbers as measured by this neurosphere formation. The effect of laminin was to augment the proliferation/survival of the hNSC, rather than promoting the undifferentiated state. In agreement, apoptosis was reduced in dissociated neurospheres by laminin in an integrin β1-dependent manner.

Conclusion

The addition of laminin to the culture medium enhances the growth of hNSC, and may therefore aid their large-scale production.

Rapid And Efficient in Vitro Generation of Pancreatic Islet Progenitor Cells from Nonendocrine Epithelial Cells in The Adult Human Pancreas

The absence of efficient and directed methods for the differentiation of adult pancreatic progenitor cell populations to pancreatic islet cells has raised doubts concerning the regeneration potential inherent in the adult pancreas. Relatively low levels of islet cell differentiation have been reported using adult pancreatic cells in vivo and in vitro. In the present study, we initially enriched for a nonendocrine epithelial component of the adult human pancreas and defined conditions that are permissive to islet cell differentiation in vitro. Sequential progression of cell differentiation in the permissive conditions allowed for incremental evaluation of changes occurring in the cell population. Optimization of the differentiation process, for the efficient production of islet endocrine cells, was accomplished by identifying specific factors and culture conditions that increased islet progenitor production 250-fold. Ultimately, 85% percent of the nonendocrine epithelial cells isolated from human pancreatic tissue and cultured in the optimized conditions for 8 days, readily re-expressed pancreatic duodenal homeobox-1 (Pdx1). Sixty-five percent of these Pdx1-expressing cells were capable of additional islet endocrine cell differentiation. This represents a significant advancement in the differentiation of an adult pancreatic progenitor cell population in vitro and suggests that the nonendocrine compartment of the human pancreas remains an important cell resource for the generation of transplantable islets to treat diabetes.

Gene expression changes in long term expanded human neural progenitor cells passaged by chopping lead to loss of neurogenic potential in vivo

Numerous cell culture protocols have been described for the proliferation of multipotent human neural progenitor cells (HNPCs). The mitogen combinations used to expand HNPCs vary, and it is not clear to what extent this may affect the subsequent differentiation of these cells. In this study human foetal cortical tissue was cultured in the presence of either EGF, or FGF-2, or a combination of both using a unique chopping method in which cell to cell contact is maintained. The differentiation potential of neurospheres following mitogen withdrawal was assessed at early (8 weeks) and late (20 weeks) times of expansion, both in vitro and in vivo. In addition, changes in gene expression with time were analysed by microarray experiments. Results show that the presence of FGF-2 was highly predictive of neuronal differentiation after short term culture both in vitro and in vivo. In addition, time in culture had a significant effect on transplant size and neural constituents suggesting that cells have a limited life span and restricted lineage potential. Array analysis confirms that following extensive time in culture cells are entering growth arrest with fundamental expression changes in genes associated with cell cycle regulation, apoptosis and immune functions.

Lysophosphatidic acid stimulates neuronal differentiation of cortical neuroblasts through the LPA1–Gi/o pathway

Lysophosphatidic acid (LPA) is an extracellular lipid mediator that regulates cortical development. Here we examined how LPA influences the cell fate of cortical neuroblasts using a neurosphere culture system. We generated neurospheres in the presence of basic fibroblast growth factor (bFGF). Treatment with LPA throughout the culture period significantly reduced the number of cells in the neurospheres. When dissociated single cells derived from neurospheres were induced to differentiate by adherence on coverslips, the proportion of MAP2-positive neurons was higher in LPA-treated neurospheres than in those treated with bFGF alone, and the proportion of myelin basic protein-positive oligodendrocytes was lower. Consistent with this finding, LPA raised the ratio of beta-tubulin type III-positive young neurons and reduced the ratio of CD140a-positive oligodendrocyte precursors in neurospheres. These effects of LPA were inhibited by pretreatment of neurospheres with pertussis toxin or an LPA(1)-preferring antagonist, Ki16425. Moreover, LPA-induced enhancement of neuronal differentiation was not observed in neurospheres derived from lpa(1)-null mice. These results suggest that LPA promotes the commitment of neuroblasts to the neural lineage through the LPA(1)-G(i/o) pathway.

Autocrine/Paracrine Platelet-Derived Growth Factor Regulates Proliferation of Neural Progenitor Cells

Growth factors play an important role in regulating neural stem cell proliferation and differentiation. This study shows that platelet-derived growth factor (PDGF) induces a partial differentiation of neural stem/progenitor cells (NSPCs) in the absence of other mitogens in vitro. NSPCs thus acquire an immature morphology and display markers for both neurons and glia. In addition, these cells do not readily mature in the absence of further stimuli. When NSPC cultures treated with PDGF were exposed to additional differentiation factors, however, the differentiation proceeded into neurons, astrocytes, and oligodendrocytes. We find that NSPC cultures are endowed with an endogenous PDGF-BB production. The PDGF-BB expression peaks during early differentiation and is present both in cell lysates and in conditioned medium, allowing for autocrine as well as paracrine signaling. When the NSPC-derived PDGF was inhibited, progenitor cell numbers decreased, showing that PDGF is involved in NSPC expansion. Addition of a PDGF receptor (PDGFR) inhibitor resulted in a more rapid differentiation. Neurons and oligodendrocytes appeared earlier and had more elaborate processes than in control cultures where endogenous PDGFR signaling was not blocked. Our observations point to PDGF as an inducer of partial differentiation of NSPC that also sustains progenitor cell division. Such an intermediate stage in stem cell differentiation is of relevance for the understanding of brain tumor development because autocrine PDGF stimulation is believed to drive malignant conversion of central nervous system progenitor cells.

Notch, epidermal growth factor receptor, and beta1-integrin pathways are coordinated in neural stem cells

Notch1 and beta1-integrins are cell surface receptors involved in the recognition of the niche that surrounds stem cells through cell-cell and cell-extracellular matrix interactions, respectively. Notch1 is also involved in the control of cell fate choices in the developing central nervous system (Lewis, J. (1998) Semin. Cell Dev. Biol. 9, 583-589). Here we report that Notch and beta1-integrins are co-expressed and that these proteins cooperate with the epidermal growth factor receptor in neural progenitors. We describe data that suggests that beta1-integrins may affect Notch signaling through 1) physical interaction (sequestration) of the Notch intracellular domain fragment by the cytoplasmic tail of the beta1-integrin and 2) affecting trafficking of the Notch intracellular domain via caveolin-mediated mechanisms. Our findings suggest that caveolin 1-containing lipid rafts play a role in the coordination and coupling of beta1-integrin, Notch1, and tyrosine kinase receptor signaling pathways. We speculate that this will require the presence of the adequate beta1-activating extracellular matrix or growth factors in restricted regions of the central nervous system and namely in neurogenic niches.

EGF and FGF-2 responsiveness of rat and mouse neural precursors derived from the embryonic CNS

EGF and FGF-2 induce the proliferation of embryonic neural precursors (ENPs) in vitro from a number of different species. In this study, we demonstrate that embryonic age is a crucial determinant of the number and differentiation potential of rat embryonic neural precursor cells responding to either EGF and/or FGF-2, in that (i) there is a differential response to the two growth factors (both alone and in combination) according to the gestational age of isolation and (ii) when allowed to differentiate, there are temporal changes in the ability of these cells to produce neurons. Furthermore, for cultures of all gestational ages, there is a defined pattern of senescence, with cultures expanding longest when cells are isolated earlier in gestation. The suggestion is that rat ENPs in this study consist predominantly of neural progenitor cells with limited division potential rather than self-renewing multipotential neural stem cells. In contrast, mouse ENPs appeared to expand indefinitely and thus allow for longer studies to be carried out looking at the effects of growth factor concentrations. The effect of varying the concentration of EGF was assessed using mouse ENPs.

Factors involved in the determination of the neurotransmitter phenotype of developing neurons of the CNS: Applications in cell replacement treatment for Parkinson's disease

The developmental stages involved in the conversion of stem cells to fully functional neurons of specific neurotransmitter phenotype are complex and not fully understood. Over the past decade many studies have been published that demonstrate that in vitro manipulation of the epigenetic environment of the stem cells allows experimental control of final neuronal phenotypic choice. This review presents the evidence for the involvement of a number of endogenous neurobiochemicals, which have been reported to potently influence DAergic (and other neurotransmitter) phenotype expression in vitro. They act at different stages on the pathway to neurotransmitter phenotype determination, and in different ways. Many are better known for their involvement in other aspects of development, and in other biochemical roles. Their proper place, and precise roles, in neurotransmitter phenotype determination in vivo will no doubt be determined in the future. Meanwhile, considerable medical benefits are offered from producing large, long-term, viable cryostores of self-regenerating multipotential neural precursor cells (i.e., brain stem cells), which can be used for cell replacement therapies in the treatment of degenerative brain diseases, such as Parkinson's disease.

Regulation of neural progenitor proliferation and survival by beta1 integrins

Neural stem cells give rise to undifferentiated nestin-positive progenitors that undergo extensive cell division before differentiating into neuronal and glial cells. The precise control of this process is likely to be, at least in part, controlled by instructive cues originating from the extracellular environment. Some of these cues are interpreted by the integrin family of extracellular matrix receptors. Using neurosphere cell cultures as a model system, we show that beta1-integrin signalling plays a crucial role in the regulation of progenitor cell proliferation, survival and migration. Following conditional genetic ablation of the beta1-integrin allele, and consequent loss of beta1-integrin cell surface protein, mutant nestin-positive progenitor cells proliferate less and die in higher numbers than their wild-type counterparts. Mutant progenitor cell migration on different ECM substrates is also impaired. These effects can be partially compensated by the addition of exogenous growth factors. Thus, beta1-integrin signalling and growth factor signalling tightly interact to control the number and migratory capacity of nestin-positive progenitor cells.

Requirement for neurogenesis to proceed through the division of neuronal progenitors following differentiation of epidermal growth factor and fibroblast growth factor-2-responsive human neural stem cells

Epidermal growth factor (EGF)- and fibroblast growth factor-2 (FGF-2)-responsive human neural stem cells may provide insight into mechanisms of neural development and have applications in cell-based therapeutics for neurological disease. However, their biology after expansion in vitro is currently poorly understood. Cells grown in either EGF or FGF-2 or a combination of both mitogens displayed characteristically similar levels of transcriptional activation and comparable proliferative profiles with linear cell-cycle kinetics and possessed similar neuronal differentiation capabilities. These data support the view that human neurospheres at later stages of expansion (>10 weeks) are comprised overwhelmingly of a single type of stem cell responsive to both EGF and FGF-2. After mitogen withdrawal and neurosphere plating, bromodeoxyuridine pulse-chase experiments revealed that the stem cells did not undergo differentiation directly into neurons. Instead, most immature neurons arose via the division of emerging progenitor cells in the absence of exogenous EGF or FGF-2. Neurogenesis was abolished by application of high concentrations of either EGF/FGF-2 or the mitotic inhibitor cytosine-b-arabinofuranoside, suggesting that there is an obligatory requirement for at least one round of cell division in the absence of mitogens as a prelude to terminal neuronal differentiation. The differentiation of human neurospheres provides a useful model of human neurogenesis, and the data presented indicate that it proceeds through the division of committed neuronal progenitor cells rather than directly from the neural stem cell.

Embryonic neural progenitor cells: the effects of species, region, and culture conditions on long-term proliferation and neuronal differentiation

One of the major obstacles to the use of neural stem/progenitor cells in neuronal replacement therapy is the limited ability of these cells to generate sufficient numbers of specific neuronal phenotypes either in the culture dish or after transplantation in animal models of neurodegenerative disease. It is not yet fully understood whether embryonic neural stem and progenitor cells show species-specific or regional identities, or if current culture paradigms select for a particular subset of stem cells/progenitors with similar proliferation and differentiation capacities. To investigate this issue, we isolated embryonic neural progenitors derived from the developing rat and mouse central nervous system for in vitro culture to assess the regional, species-specific, and temporal effects on both cell proliferation and generation of neurons. Neurosphere cultures were derived from E13-15 mouse or rat developing striatum (medial, lateral, or whole ganglionic eminence), ventral mesencephalon, and cortex. We compared basic fibroblast growth factor and epidermal growth factor for their influence on cell proliferation and neuronal differentiation under defined differentiation paradigms. Seeding density and conditioned media were also tested for their effects on maintenance of cell proliferation over protracted time periods. Results showed that embryonic neural stem/progenitor cells maintained defined patterns of proliferation and neuronal differentiation, with both declining with time in vitro. Proliferation rate was more dependent on species and region than the neurotrophins or conditions used for culture. These results suggest that the appropriate selection of embryonic neural stem cells and culture conditions may be crucial for the optimization of their neurogenic potential.

Beta1 integrins activate a MAPK signalling pathway in neural stem cells that contributes to their maintenance

The emerging evidence that stem cells develop in specialised niches highlights the potential role of environmental factors in their regulation. Here we examine the role of beta1 integrin/extracellular matrix interactions in neural stem cells. We find high levels of beta1 integrin expression in the stem-cell containing regions of the embryonic CNS, with associated expression of the laminin alpha2 chain. Expression levels of laminin alpha2 are reduced in the postnatal CNS, but a population of cells expressing high levels of beta1 remains. Using neurospheres - aggregate cultures, derived from single stem cells, that have a three-dimensional architecture that results in the localisation of the stem cell population around the edge of the sphere - we show directly that beta1 integrins are expressed at high levels on neural stem cells and can be used for their selection. MAPK, but not PI3K, signalling is required for neural stem cell maintenance, as assessed by neurosphere formation, and inhibition or genetic ablation of beta1 integrin using cre/lox technology reduces the level of MAPK activity. We conclude that integrins are therefore an important part of the signalling mechanisms that control neural stem cell behaviour in specific areas of the CNS.

Alternative culture conditions for isolation and expansion of retinal progenitor cells

PURPOSE

To investigate different in vitro model systems for retinal progenitor cell (RPC) isolation and expansion.

METHODS

RPCs were isolated from embryonic day (E) 17 Long Evans rat retinas. Three different culture media: (1) modified serum free defined media (2) serum-containing media and (3) embryonic stem cell (ES)-conditioned media were used for RPC isolation and long term expansion. Expression of various cellular markers and cell morphologies were compared among the three culture systems at different passages by immunostaining and confocal microscopy.

RESULTS

All three culture systems could maintain RPCs as nestin-positive cells (78-87%) after long-term in vitro expansion. However, RPCs appeared to proliferate faster in the serum-free culture system. The ES-conditioned media provided the best RPC survival. Cells appeared smaller at early passages compared with later passages. This morphology change occurred at P9-P10 in the serum-free medium, and at P5-P6 in the other two culture systems.

CONCLUSIONS

The serum-free medium may be superior for preventing RPC differentiation during expansion.

Is there a future for neural transplantation?

Traditionally neural transplantation has had as its central tenet the replacement of missing neurons that have been lost because of neurodegenerative processes, as exemplified by diseases such as Parkinson disease (PD). However, the effectiveness and widespread application of this approach clinically has been limited, primarily because of the poor donor supply of human fetal neural tissue and the incomplete neurobiological understanding of the circuit reconstruction required to normalize function in these diseases. So, in PD the progress from promising neural transplantation in animal models to proof-of-principle, open-labeled clinical transplants, to randomized, placebo-controlled studies of neural transplantation has not been straightforward. The emergence of previously undescribed adverse effects and lack of significant functional advantage in recent clinical studies has been disappointing and has served to cast a new, and perhaps more realistic, perspective on this treatment approach. In fact, there have been calls by some involved in neural transplantation to return to the drawing board before pressing on with further clinical trials, and the return to basic experimentation. This therefore precipitates the question - is there a future for neural transplantation? It is important to remember that there are a number of possible explanations for the disappointing results from the recent clinical trials in PD, ranging from the mode of transplantation to patient selection. Nevertheless, almost irrespective of these reasons for the current trial results, there have always been significant practical and ethical problems with using human fetal tissue, and so a number of alternative cell sources have been investigated. These alternative sources include stem cells, which are attractive for cell-based therapies because of their potential ease of isolation, propagation and manipulation, and their ability in some cases to migrate to areas of pathology and differentiate into specific and appropriate cell types. Furthermore, the availability of stem cells derived from non-embryonic sources (e.g. adult stem cells derived from the sub-ventricular zone) has removed some of the ethical limitations associated with the use of embryonic human tissue. These potentially beneficial aspects of stem cells means that there is a future for neural transplantation as a means of treating patients with a range of neurological disorders, although whether this will ever translate into a truly effective, widely available therapy remains unknown.

Gene therapy of rat malignant gliomas using neural stem cells expressing IL-12

Primary malignant brain tumors have a poor prognosis. This report investigates the potential for gene therapy of experimental brain tumors using neural stem cells (NSCs) expressing IL-12. In this study NSCs were isolated from the hippocampi of 3-5-month human embryos and used for lipofectamine mediated transfer of the IL-12 gene. Positive clones of anti-G418 were obtained and were proliferated in culture and expression of IL-12 was demonstrated by RT-PCR. For the in vivo studies three groups of rats were used and stereotactic injections were made into the striatum. In the first group C6 tumor cells were injected, in the second C6 cells and hNSCs. IL-12, and in the third C6 cells on Day 0 followed by hNSCs.IL-12 on day 5. The growth of the resulting tumors was monitored by magnetic resonance imaging (MRI) and after sacrifice by immunohistochemistry. Rats injected with C6 cells and hNSCs.IL-12 had a significantly prolonged survival. Injections of hNSCs.IL-12 were also made into established gliomas. The survival time was also significantly prolonged compared to controls. MR imaging demonstrated that there was initial growth of tumor followed by shrinkage and then disappearance. After sacrifice, tumor areas were studied by histochemistry. NSCs were often seen intermingled with tumor cells, particularly when they had been injected into established tumors; they were also present at the boundaries of the tumor mass. The immunohistochemical analysis showed that these infiltrates were mostly constituted by CD4(+) and CD8(+) T-lymphocytes, the CD8(+) being more numerous than the CD4(+). These findings indicated that NSCs engineered to release IL-12 could have a strong antitumor effect. Neural stem/precursor cells could be useful vectors in genetic approaches to brain tumors.

Heparin stabilizes FGF-2 and modulates striatal precursor cell behavior in response to EGF

Fibroblast and epidermal growth factors (FGF-2 and EGF) are powerful mitogens for neural precursor cells isolated from the developing striatum and grown as neurospheres. However, questions remain as to the exact role of each of these molecules, and how the proteoglycan heparin may modify their behavior. Here, we show that FGF-2 is remarkably unstable in culture media, but that heparin could completely prevent its degradation, which led to faster cell growth rates. In addition, heparin significantly increased the number of cells within the E14 striatum responding to a brief pulse of FGF-2. In contrast, EGF was unable to stimulate the growth of E14 striatal precursors. However, EGF could induce the division of E18 striatal precursors as neurospheres and acted synergistically with FGF-2. FGF-2/heparin neurospheres generated significantly more neurons than EGF neurospheres. Interestingly, the addition of heparin to EGF neurospheres, which had no effects on EGF stability or growth rates, increased the numbers of neurons generated to that seen for FGF-2/heparin neurospheres. EGF neurospheres were found to produce FGF-2, but addition of heparin did not affect its concentration within cells or in the medium suggesting this released FGF-2 may already be bound to a proteoglycan. In addition, expanding cells with EGF plus heparin in the presence of an FGF-2 blocker did not have a significant effect on the number of neurons generated confirming that the increase in neuronal number is through a mechanism which is independent of FGF-2.

Characterization of long-term mouse brain aggregating cultures: Evidence for maintenance of neural precursor cells

An extensive characterization of fetal mouse brain cell aggregates has been performed using immunohistochemical and stereological methods. Single cell suspensions from mechanically dissociated cortex and hippocampus were cultured in serum-free, B27-supplemented medium under constant gyratory agitation for up to 56 days. Three-dimensional aggregates started to form immediately after seeding and reached a final average size of 500 microm in diameter. Among the cell types identified, neurons were the most abundant cells in the aggregates, followed by astrocytes, microglia, and oligodendrocytes. Western blotting for synaptophysin and immunostaining for neurotransmitter-related molecules indicated the presence of well-defined phenotypic characteristics of the neurons in this culture system, suggesting functionality. Proliferating cells, many with neural precursor cell properties, were seen throughout the culture period and could be isolated from the aggregates even after 2 months in culture. Neural precursor cells were isolated from the aggregates after more than 1 month in culture; these cells were successfully differentiated into neurons, astrocytes, and oligodendrocytes. The aggregate culture system may provide a versatile tool for molecular dissection of processes identified in mouse models, including transgenic animals and manipulation of neural precursor cells.

Adult human olfactory neural progenitors cultured in defined medium

Neurosphere-forming cells (NSFCs) derived from primary cultures of adult human olfactory epithelium were established in minimum essential medium (MEM) with Hanks balanced salts and 10% heat-inactivated fetal bovine serum (FBS). A totally defined medium (DM) was employed to examine their proliferation, lineage restriction and differentiation. DMEM/F12 (DF) was found to support NSFCs and served as the base medium for this study. NSFCs were adapted to the DM through serial serum reductions at successive feedings. NSFCs in DF supplemented with N2, B27 or insulin attained saturation density and formed extensive processes. Immunolocalization of lineage specific markers [i.e., nestin, beta-tubulin III, peripherin, neural cell adhesion molecule, A2B5, O4, microtubule-associated-protein-2 (MAP2) and glial fibrillary acidic protein], as well as 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide and ornithine decarboxylase assays were employed to characterize the NSFCs. The effects of trophic factors including epidermal growth factor (EGF), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), neurotrophic factors (NT-3), and basic fibroblast growth factor (bFGF) were evaluated. With the reduction of serum and the addition N2, B27, and other nutrients, there was a change in lineage restriction including an increase the expression of A2B5 and other glial markers as well as the expression of mature neuronal markers with a simultaneous reduction of nestin reactivity. NSFCs proliferated and maintained their pluripotency for over a year in the DM. Further studies will determine the utility of NSFCs for cell replacement therapy.

Progenitor cells from the CA3 region of the embryonic day 19 rat hippocampus generate region-specific neuronal phenotypes in vitro

Progenitor cells that endure in different regions of the CNS after the initial neurogenesis can be expanded in culture and used as a source of donor tissue for grafting in neurodegenerative diseases. However, the proliferation and differentiation characteristics of residual neural progenitor cells from distinct regions of the CNS are mostly unknown. This study elucidated the characteristics of progenitor cells that endure in the CA3 region of the hippocampus after neurogenesis, by in vitro analyses of cells that are responsive to epidermal growth factor (EGF) or fibroblast growth factor-2 (FGF-2) in the embryonic day 19 (E19) rat hippocampus. Isolated cells from the E19 CA3 region formed neurospheres in the presence of either EGF or FGF-2, but the yield of neurospheres was greater with FGF-2 exposure, Differentiation cultures revealed a greater yield of neurons from FGF-2 neurospheres (60%) than from EGF neurospheres (35%). Exposure to brain-derived neurotrophic factor (BDNF) enhanced the yield of neurons from EGF neurospheres but had no consequence on FGF-2 neurospheres. A large number of neurons from EGF/FGF-2 neurospheres demonstrated clearly palpable morphological features of CA3 pyramidal neurons and lacked gamma-aminobutyric acid (GABA) expression. However, a fraction of neurons (17-20%) from EGF/FGF-2 neurospheres expressed GABA, and exposure to BDNF increased the number of GABAergic neurons (30%) from EGF neurospheres. Neurons from EGF/FGF-2 neurospheres also contained smaller populations of calbindin- and calretinin-positive interneuron-like cells. Thus, progenitor cells responsive to FGF-2 are prevalent in the CA3 region of the E19 rat hippocampus and give rise to a greater number of neurons than progenitor cells responsive to EGF. However, both FGF-2- and EGF-responsive progenitor cells from E19 CA3 region are capable of giving rise to CA3 field-specific phenotypic neurons. These results imply that progenitor cells that persist in the hippocampus after neurogenesis remain regionally restricted and hence retain their ability to give rise to region-specific phenotypic neurons even after isolation and expansion in vitro.

The in vivo positional identity gene expression code is not preserved in neural stem cells grown in culture

Neural stem cell specification depends on antero-posterior (AP) and dorso-ventral (DV) information provided during development. In the present study we identified similar neural stem cell (NSC) populations along the AP axis of the mouse central nervous system: the 'early' NSCs responsive to fibroblast growth factor-2 and the 'late' NSCs responsive to epidermal growth factor (EGF). Gene expression analysis shows that AP and DV transcription factor code is not preserved in NSCs in culture. Neurospheres generated with EGF from different regions showed Emx2, En2 and Krox20 expression beyond their corresponding AP restricted areas (telencephalon, mesencephalon and rhomboencephalon, respectively). Hox genes were rarely expressed. DV markers such as Pax7 and Dbx1 were not expressed in neurosphere cells, whereas Pax6 and Nkx2.1 were highly expressed independently of the NSC source region. In general, this pattern was found under different culture conditions. We propose that signals surrounding NSCs determine their positional identity gene expression code, which may be relevant to establish their definitive fate.

Mechanism of stem cells in the central nervous system

Injury to the central nervous system (CNS) can result in severe functional impairment. The brain and spinal cord, which constitute the CNS, have been viewed for decades as having a very limited capacity for regeneration. However, over the last several years, the body of evidence supporting the concept of regeneration and continuous renewal of neurons in specific regions of the CNS has increased. This evidence has significantly altered our perception of the CNS and has offered new hope for possible cell therapy strategies to repair lost function. Transplantation of stem cells or the recruitment of endogenous stem cells to repair specific regions of the brain or spinal cord is the next exciting research challenge. However, our understanding of the existing stem cell pool in the adult CNS remains limited. This review will discuss the identification and characterization of CNS stem cells in the adult brain and spinal cord.

Long-term cultivation of multipotential neural stem cells from adult rat subependyma

Cultivation of adult rat neural stem cells (RNSCs) from the ventricular subependyma has been reported to be more difficult than growth of mouse neural stem cells. This is unfortunate, because rats provide useful models of brain function and disease, and implantation of RNSCs in these models could provide critical information on allograft behavior. Growing the cells in an appropriate medium (NS-A+B27 supplement), plating at sufficient densities (>5 cells per mm(2)), and minimizing opportunities for detachment from the substratum made it possible to isolate and cultivate these cells for over 6 months for >50 passages with no apparent change in phenotype. Single clones could be expanded indefinitely and differentiated to form astrocytes, oligodendrocytes, and neurons, demonstrating that the cultures did indeed contain neural stem cells. The cells had a much shorter cell cycle time ( approximately 13 h) than doubling time ( approximately 35 h), suggesting that these cells produce post-mitotic cells in approximately two of three divisions, thus making expansion difficult. The optimization of methods to grow adult RNSCs and identification of characteristics that limit their growth should prove useful in increasing the use of RNSCs for studies of their potential role in brain health and disease.