Epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), and basic fibroblast growth factor (bFGF) differentially influence neural precursor cells of mouse embryonic mesencephalon

Peptides derived from growth factors: Exploring their diverse impact from antimicrobial properties to neuroprotection

Growth factor-derived peptides are bioactive molecules that play a crucial role in various physiological processes within the human body. Over the years, extensive research has revealed their diverse applications, ranging from antimicrobial properties to their potential in neuroprotection and treating various diseases. These peptides exhibit innate immune responses and have been found to possess potent antimicrobial properties against a wide range of pathogens. Growth factor-derived peptides have demonstrated the ability to promote neuronal survival, prevent cell death, and stimulate neural regeneration. As a result, they hold immense promise in the treatment of various neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis, as well as in the management of traumatic brain injuries. Moreover, growth factor-derived peptides have shown potential for supporting tissue repair and wound healing processes. By enhancing cell proliferation and migration, these peptides contribute to the regeneration of damaged tissues and promote a more efficient healing response. The applications of growth factor-derived peptides extend beyond their therapeutic potential in health; they also have a role in various disease conditions. For example, researchers have explored their influence on cancer cells, where some peptides have demonstrated anti-cancer properties, inhibiting tumor growth and promoting apoptosis in cancer cells. Additionally, their immunomodulatory properties have been investigated for potential applications in autoimmune disorders. Despite the immense promise shown by growth factor-derived peptides, some challenges need to be addressed. Nevertheless, ongoing research and advancements in biotechnology offer promising avenues to overcome these obstacles. The review summarizes the foundational biology of growth factors and the intricate signaling pathways in various physiological processes as well as diseases such as cancer, neurodegenerative disorders, cardiovascular ailments, and metabolic syndromes.

Newly Identified Deficiencies in the Multiple Sclerosis Central Nervous System and Their Impact on the Remyelination Failure

The pathogenesis of multiple sclerosis (MS) remains enigmatic and controversial. Myelin sheaths in the central nervous system (CNS) insulate axons and allow saltatory nerve conduction. MS brings about the destruction of myelin sheaths and the myelin-producing oligodendrocytes (ODCs). The conundrum of remyelination failure is, therefore, crucial in MS. In this review, the roles of epidermal growth factor (EGF), normal prions, and cobalamin in CNS myelinogenesis are briefly summarized. Thereafter, some findings of other authors and ourselves on MS and MS-like models are recapitulated, because they have shown that: (a) EGF is significantly decreased in the CNS of living or deceased MS patients; (b) its repeated administration to mice in various MS-models prevents demyelination and inflammatory reaction; (c) as was the case for EGF, normal prion levels are decreased in the MS CNS, with a strong correspondence between liquid and tissue levels; and (d) MS cobalamin levels are increased in the cerebrospinal fluid, but decreased in the spinal cord. In fact, no remyelination can occur in MS if these molecules (essential for any form of CNS myelination) are lacking. Lastly, other non-immunological MS abnormalities are reviewed. Together, these results have led to a critical reassessment of MS pathogenesis, partly because EGF has little or no role in immunology.

Human Keratinocytes Adopt Neuronal Fates After In Utero Transplantation in the Developing Rat Brain

Human skin contains keratinocytes in the epidermis. Such cells share their ectodermal origin with the central nervous system (CNS). Recent studies have demonstrated that terminally differentiated somatic cells can adopt a pluripotent state, or can directly convert its phenotype to neurons, after ectopic expression of transcription factors. In this article we tested the hypothesis that human keratinocytes can adopt neural fates after culturing them in suspension with a neural medium. Initially, keratinocytes expressed Keratins and Vimentin. After neural induction, transcriptional upregulation of NESTIN, SOX2, VIMENTIN, SOX1, and MUSASHI1 was observed, concomitant with significant increases in NESTIN detected by immunostaining. However, in vitro differentiation did not yield the expression of neuronal or astrocytic markers. We tested the differentiation potential of control and neural-induced keratinocytes by grafting them in the developing CNS of rats, through ultrasound-guided injection. For this purpose, keratinocytes were transduced with lentivirus that contained the coding sequence of green fluorescent protein. Cell sorting was employed to select cells with high fluorescence. Unexpectedly, 4 days after grafting these cells in the ventricles, both control and neural-induced cells expressed green fluorescent protein together with the neuronal proteins βIII-Tubulin and Microtubule-Associated Protein 2. These results support the notion that in vivo environment provides appropriate signals to evaluate the neuronal differentiation potential of keratinocytes or other non-neural cell populations.

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.

TGFα preserves oligodendrocyte lineage cells and improves white matter integrity after cerebral ischemia

Transforming growth factor α (TGF-α) has been reported to play important roles in neurogenesis and angiogenesis in the injured brain. The present study characterizes a novel role for TGFα in oligodendrocyte lineage cell survival and white matter integrity after ischemic stroke. Three days after transient (60 min) middle cerebral artery occlusion (tMCAO), TGFα expression was significantly increased in microglia/macrophages and neurons. Expression of the receptor of TGFα-epidermal growth factor receptor (EGFR)-was increased in glial cells after ischemia, including in oligodendrocyte lineage cells. TGFα knockout enlarged brain infarct volumes and exacerbated cell death in oligodendrocyte precursor cells (OPCs) and oligodendrocytes three days after tMCAO. TGFα-deficient mice displayed long-term exacerbation of sensorimotor deficits after tMCAO, and these functional impairments were accompanied by loss of white matter integrity and impaired oligodendrocyte replacement. In vitro studies confirmed that 5 or 10 ng/mL TGFα directly protected OPCs and oligodendrocytes against oxygen and glucose deprivation (OGD)-induced cell death, but exerted no effects on OPC differentiation. Further studies identified STAT3 as a key transcription factor mediating the effects of TGFα on OPCs and oligodendrocytes. In conclusion, TGFα provides potent oligodendrocyte protection against cerebral ischemia, thereby maintaining white matter integrity and improving neurological recovery after stroke.

Derivation of Neural Stem Cells from the Developing and Adult Human Brain

Neural stem cells isolated from the developing and adult brain are an ideal source of cells for use in clinical applications such as cell replacement therapy. The clear advantage of these cells over the more commonly utilised embryonic and pluripotent stem cells is that they are already neurally committed. Of particular importance is the fact that these cells don't require the same level of in vitro culture that can be cost and labour intensive. Foetal neural stem cells can be readily derived from the foetal brain and expand in culture over time. Similarly, adult stem cells have been explored for their potential in vitro and in vivo animal models. In this chapter we identify the progress made in developing these cells as well as the advantages of taking them forward for clinical use.

An Overview of Protocols for the Neural Induction of Dental and Oral Stem Cells In Vitro

To date, various adult stem cells have been identified within the oral cavity, including dental pulp stem cells, dental follicle stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, and mesenchymal stem cells from the gingiva. All of these possess neurogenic potential due to their common developmental origin from the embryonic neural crest. Besides the relative ease of isolation of these adult stem cells from readily available biological waste routinely produced during dental treatment, these cells also possess the advantage of immune compatibility in autologous transplantation. In recent years, much interest has been focused on the derivation of neural lineages from these adult stem cells for therapeutic applications in the brain, spinal cord, and peripheral nerve regeneration. In addition, there are also promising nontherapeutic applications of stem cell-derived neurons in pharmacological and toxicological screening of neuroactive drugs, and for in vitro modeling of neurodevelopmental and neurodegenerative diseases. Hence, this review will critically examine the diverse array of in vitro neural induction protocols that have been devised for dental and oral-derived stem cells. These protocols are defined not only by the culture milieu comprising the basal medium plus growth factors, small molecules, and other culture supplements but also by the substrata/surface coatings utilized, the presence of multiple culture stages, the total culture duration, the initial seeding density, and whether the spheroid/neurosphere formation is being utilized to recapitulate the three-dimensional neural differentiation microenvironment that is naturally present physiologically in vivo.

Stem cell research in Latin America: update, challenges and opportunities in a priority research area

Stem cell research is attracting wide attention as a promising and fast-growing field in Latin America, as it is worldwide. Many countries in the region have defined Regenerative Medicine as a research priority and a focus of investment. This field generates not only opportunities but also regulatory, technical and operative challenges. In this review, scientists from Uruguay, Mexico, Chile, Brazil and Argentina provide their view on stem cell research in each of their countries. Despite country-specific characteristics, all countries share several issues such as regulatory challenges. Key initiatives of each country to promote stem cell research are also discussed. As a conclusion, it is clear that regional integration should be more emphasized and international collaboration, promoted.

Tl(I) and Tl(III) alter the expression of EGF-dependent signals and cyclins required for pheochromocytoma (PC12) cell-cycle resumption and progression

The effects of thallium [Tl(I) and Tl(III)] on the PC12 cell cycle were evaluated without (EGF(-)) or with (EGF(+)) media supplementation with epidermal growth factor (EGF). The following markers of cell-cycle phases were analyzed: cyclin D1 (G1 ); E2F-1, cyclin E and cytosolic p21 (G1 →S transition); nuclear PCNA and cyclin A (S); and cyclin B1 (G2). The amount of cells in each phase and the activation of the signaling cascade triggered by EGF were also analyzed. Tl(I) and Tl(III) (5-100 μM) caused dissimilar effects on PC12 cell proliferation. In EGF(-) cells, Tl(I) increased the expression of G1 →S transition markers and nuclear PCNA, without affecting cyclin A or cyclin B1. In addition to those, cyclin B1 was also increased in EGF(+) cells. In EGF(-) cells, Tl(III) increased the expression of cyclin D1, all the G1→S and S phase markers and cyclin B1. In EGF(+) cells, Tl(III) increased cyclin D1 expression and decreased all the markers of G1 →S transition and the S phase. Even when these cations did not induce the activation of EGF receptor (EGFR) in EGF(-) cells, they promoted the phosphorylation of ERK1/2 and Akt. In the presence of EGF, the cations anticipated EGFR phosphorylation without affecting the kinetics of EGF-dependent ERK1/2 and Akt phosphorylation. Altogether, results indicate that Tl(I) promoted cell proliferation in both EGF(-) and EGF(+) cells. In contrast, Tl(III) promoted the proliferation of EGF(-) cells but delayed it in EGF(+) cells, which may be related to the toxic effects of this cation in PC12 cells.

Study of transforming growth factor alpha for the maintenance of human embryonic stem cells

Human embryonic stem cells (hESCs) have great potential for regenerative medicine as they have self-regenerative and pluripotent properties. Feeder cells or their conditioned medium are required for the maintenance of hESC in the undifferentiated state. Feeder cells have been postulated to produce growth factors and extracellular molecules for maintaining hESC in culture. The present study has aimed at identifying these molecules. The gene expression of supportive feeder cells, namely human foreskin fibroblast (hFF-1) and non-supportive human lung fibroblast (WI-38) was analyzed by microarray and 445 genes were found to be differentially expressed. Gene ontology analysis showed that 20.9% and 15.5% of the products of these genes belonged to the extracellular region and regulation of transcription activity, respectively. After validation of selected differentially expressed genes in both human and mouse feeder cells, transforming growth factor α (TGFα) was chosen for functional study. The results demonstrated that knockdown or protein neutralization of TGFα in hFF-1 led to increased expression of early differentiation markers and lower attachment rates of hESC. More importantly, TGFα maintained pluripotent gene expression levels, attachment rates and pluripotency by the in vitro differentiation of H9 under non-supportive conditions. TGFα treatment activated the p44/42 MAPK pathway but not the PI3K/Akt pathway. In addition, TGFα treatment increased the expression of pluripotent markers, NANOG and SSEA-3 but had no effects on the proliferation of hESCs. This study of the functional role of TGFα provides insights for the development of clinical grade hESCs for therapeutic applications.

Glial commitment of mesencephalic neural precursor cells expanded as neurospheres precludes their engagement in niche-dependent dopaminergic neurogenesis

Neural precursor cells (NPCs) with high proliferative potential are commonly expanded in vitro as neurospheres. As a population, neurosphere cells show long-term self-renewal capacity and multipotentiality in vitro. These features have led to the assumption that neurosphere cells represent an expansion of the endogenous NPCs residing within the embryonic and adult brain. If this is the case, in principle, bona-fide expansion of endogenous NPCs should not significantly affect their capacity to respond to their original niche of differentiation. To address this issue, we generated primary neurospheres from the dopaminergic niche of the ventral mesencephalon and then transplanted these cells to their original niche within mesencephalic explant cultures. Primary neurosphere cells showed poor capacity to generate dopaminergic neurons in the mesencephalic niche of dopaminergic neurogenesis. Instead, most primary neurosphere cells showed glial commitment as they differentiated into astrocytes in an exclusively neurogenic niche. Subculture of primary cells demonstrated that the neurosphere assay does not amplify niche-responsive dopaminergic progenitors. Further, neurospheres cells were largely unable to acquire the endogenous positional identity within the Nkx6.1(+), Nkx2.2(+), and Pax7(+) domains of mesencephalic explants. Finally, we demonstrate that our observations are not specific for embryonic mesencephalic cells, as NPCs in the adult subventricular zone also showed an intrinsic fate switch from neuronal to glial potential upon neurosphere amplification. Our data suggest that neurosphere formation does not expand the endogenous neurogenic NPCs but rather promotes amplification of gliogenic precursors that do not respond to niche-derived signals of cellular specification and differentiation.

[Instability of cell phenotype and tumor initiating cells in gliomas]

Gliomas, the most frequent primitive CNS tumors, have been suggested to originate from astrocytes or from neural progenitors/stem cells. However, the precise identity of the cells at the origin of gliomas remains a matter of debate because no pre-neoplastic state has been yet identified. TGFα, an EGF family member, is frequently over-expressed in the early stages of glioma progression. We questioned whether prolonged TGFα exposure affects the stability of the normal mature astrocyte phenotype and, eventually, their propensity to cancerous transformation. Using mouse astrocyte cultures devoid of residual neural stem cells or progenitors, we demonstrate that several days of TGFα-treatment result in the functional conversion of a population of mature astrocytes into radial glial cells, a population of neural progenitors, without any accompanying sign of cancerous transformation. In contrast, when astrocytes de-differentiated with TGFα were submitted to oncogenic stress using gamma irradiation, they acquired cancerous properties, forming high-grade glioma-like tumors after brain grafting. Gamma irradiation was without effect on astrocytes which were not treated with TGFα. These results suggested that most gliomas should contain tumor cells with stem-like properties (TSCs). Our study of 55 pediatric brain tumors show that tumor cells with stem cell-like or progenitor-like properties can be isolated from a majority of gliomas. Survival analysis showed an association between isolation of TSCs with extended self-renewal capabilities and a patient's higher mortality rate.

The FGF-2/FGFRs neurotrophic system promotes neurogenesis in the adult brain

Neurogenesis occurs in two regions of the adult brain, namely, the subventricular zone (SVZ) throughout the wall of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus (DG) in hippocampal formation. Adult neurogenesis requires several neurotrophic factors to sustain and regulate the proliferation and differentiation of the adult stem cell population. In the present review, we examine the cellular and functional aspects of a trophic system mediated by fibroblast growth factor-2 (FGF-2) and its receptors (FGFRs) related to neurogenesis in the SVZ and SGZ of the adult rat brain. In the SVZ, FGF-2 is expressed in GFAP-positive cells of SVZ but is not present in proliferating precursor cells, which instead express FGFR-1 and FGFR-2, but not FGFR-3 mRNA, although expressed in the SVZ, and FGFR-4. Therefore, it seems that in the SVZ FGF-2 may be released by GFAP-positive cells, different from the precursor cell lineage, and via volume transmission it reaches the proliferating precursor cells. FGFR-1 mRNA is also expressed in the SGZ and is localized in BrdU-labeled precursor cells, whereas FGFR-2 and FGFR-3 mRNA, although expressed in the SGZ, are not located within proliferating precursor cells. An aged-related decline of proliferating precursor cells in the SVZ and DG of old rats has been well documented, and there is the suggestion that in part it could be the consequence of alterations in growth factor expression levels. Thus, the old precursors may respond to growth factors, suggesting that during aging the basic components for neuronal precursor cell proliferation are retained and the capacity to increase neurogenesis after appropriate stimulation is still preserved. In conclusion, the trophic system mediated by FGF-2 and its receptors contributes to create an important micro-environmental niche that promotes neurogenesis in the adult and aged brain.

TGF-alpha increases astrocyte invasion and promotes axonal growth into the lesion following spinal cord injury in mice

Astrocytes respond to environmental cues and play a multifaceted role in the response to trauma in the central nervous system. As the most prevalent contributors to the glial scar, astrocytes are targeted as barriers to regeneration. However, there is also strong evidence that astrocytes are vital for neuroprotection and metabolic support after injury. In addition, consistent with their role during development, astrocytes may be capable of supporting the growth of injured axons. Therefore, we hypothesized that with appropriate stimulation, the reparative functions of endogenous astrocytes could be harnessed to promote axon growth and recovery after spinal cord injury. Transforming growth factor-alpha (TGF-alpha) is a mitogenic growth factor that is active on astrocytes and is poised to contribute to such a strategy. Recombinant TGF-alpha was administered intrathecally to adult C57BL/6 mice for two weeks following a moderate mid-thoracic spinal cord contusion. By three weeks post-injury, TGF-alpha infusion had not affected locomotor recovery, but promoted extensive axon growth and altered the composition of the lesion site. The center of the lesion in the treated mice contained greater numbers of new cells and increased astrocyte invasion. Despite the expression of inhibitory proteoglycans, there was a marked increase in axons expressing neurofilament and GAP-43 immunoreactivity, and the new axons were closely associated with increased laminin expression within and beyond the astrocyte matrix. The results demonstrate that astrocytes are dynamic players in the response to spinal cord injury, and the growth-supportive role of these cells can be enhanced by TGF-alpha infusion.

In vitro neural injury model for optimization of tissue-engineered constructs

Stem cell transplantation is a promising approach for the treatment of traumatic brain injury, although the therapeutic benefits are limited by a high degree of donor cell death. Tissue engineering is a strategy to improve donor cell survival by providing structural and adhesive support. However, optimization prior to clinical implementation requires expensive and time-consuming in vivo studies. Accordingly, we have developed a three-dimensional (3-D) in vitro model of the injured host-transplant interface that can be used as a test bed for high-throughput evaluation of tissue-engineered strategies. The neuronal-astrocytic cocultures in 3-D were subjected to mechanical loading (inducing cell death and specific astrogliotic alterations) or to treatment with transforming growth factor-beta1 (TGF-beta1), inducing astrogliosis without affecting viability. Neural stem cells (NSCs) were then delivered to the cocultures. A sharp increase in the number of TUNEL(+) donor cells was observed in the injured cocultures compared to that in the TGF-beta1-treated and control cocultures, suggesting that factors related to mechanical injury, but not strictly astrogliosis, were detrimental to donor cell survival. We then utilized the mechanically injured cocultures to evaluate a methylcellulose-laminin (MC-LN) scaffold designed to reduce apoptosis. When NSCs were co-delivered with MC alone or MC-LN to the injured cocultures, the number of caspase(+) donor cells significantly decreased compared to that with vehicle delivery (medium). Collectively, these results demonstrate the utility of an in vitro model as a pre-animal test bed and support further investigation of a tissue-engineering approach for chaperoned NSC delivery targeted to improve donor cell survival in neural transplantation.

Nicotine-induced fibroblast growth factor-2 restores the age-related decline of precursor cell proliferation in the subventricular zone of rat brain

Precursor cell proliferation is present in the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus of the hippocampus of adult rat and persists during aging although at reduced levels. Previous studies have shown that acute intermittent nicotine treatment significantly increases fibroblast growth factor-2 (FGF-2) expression in several brain regions of aged rats. The aim of the present investigation was to test the hypothesis that nicotine-induced expression of FGF-2 may restore the age-related decline of precursor cell proliferation. It was first demonstrated that nicotine treatment increases both mRNA and protein FGF-2 in the SVZ of aged male rats (18 months old). The effect of nicotine on precursor cell proliferation in the SVZ was studied by i.p. injection of 5-bromo-2'-deoxyuridine (BrdU) 40 mg/kg to label dividing cells. The nicotine treatment was found to significantly enhance precursor cell proliferation in the SVZ. This increase was sufficiently large to restore the age-related decline of proliferating precursor cells observed in aged rats to that found in young adult rats (3 months old). FGF-2 was expressed in GFAP-positive cells and may act via its receptor FGFR1 that was found expressed in nestin-positive cells of the SVZ. The data obtained demonstrated that the age-related decline of precursor cell proliferation may be counteracted by activating a trophic mechanism mediated by FGF-2.

Waved-1 mutant mice are hypersensitive to the locomotor actions of cocaine

Transforming growth factor-alpha (TGFalpha) is a well-known regulator of many developmental processes, and is expressed heavily in basal forebrain and striatal regions. When TGFalpha is reduced in Waved-1 (Wa-1) mutant mice, brain anatomy, biogenic amines, stress response, and behavior are normal prior to, but altered following puberty. As an initial screen for possible alterations in nigrostriatal and mesolimbic dopamine (DA) systems, we tested adult Wa-1 mutant mice in an open field, following acute injection with cocaine (15 mg/kg). Wa-1 mice exhibited significantly greater ambulatory distance, number of ambulatory episodes, and cocaine-induced motor stereotypies than do controls. These data indicate that adult Wa-1 mice are hypersensitive to the locomotor effects of cocaine and provide a new potential link between neurodevelopmental processes and adult psychostimulant responsiveness.

Acute intermittent nicotine treatment induces fibroblast growth factor-2 in the subventricular zone of the adult rat brain and enhances neuronal precursor cell proliferation

Over the past years, evidence has accumulated that stem cells are present in the adult brain, and generate neurons and/or glia from two active germinal zones: the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus of the hippocampus. This study shows that acute intermittent nicotine treatment significantly enhances neuronal precursor cell proliferation in the SVZ of adult rat brain, but not in the SGZ of the hippocampus, and pre-treatment with mecamylamine, a nonselective nAChR antagonist, blocks the enhanced precursor proliferation by nicotine. This effect is supported by up-regulation of fibroblast growth factor-2 (FGF-2) mRNA in the SVZ and the expression of its receptor FGFR-1 in cells of SVZ showing precursor cells profile. It is also demonstrated that the nicotine effect on neuronal precursor proliferation is mediated by FGF-2 via fibroblast growth factor receptor 1 (FGFR-1) activation by showing that i.c.v. pre-treatment with anti-FGF-2 antibodies or with FGFR-1 inhibitor 3-[(3-(2-carboxyethyl)-4-methylpyrrol-2-yl)methylene]-2-indolinone (SU5402) blocks nicotine-induced precursor cell proliferation. This nicotine enhancement of neuronal precursor cell proliferation was not accompanied by an increase in the number of apoptotic cells. Taken together the present findings revealed the existence in the SVZ of the adult rat brain of a trophic mechanism mediated by FGF-2 and its receptor and regulated by nAchR activation. This possibility of in vivo regulation of neurogenesis in the adult brain by exogenous factors may aid to develop treatments stimulating neurogenesis with potential therapeutic implications.

Rapid and efficient differentiation of dopaminergic neurons from mouse embryonic stem cells

We have developed a fast and effective method for the differentiation of dopaminergic neurons from mouse embryonic stem cells. Neuronal precursors are obtained by formation of embryonic bodies or neural stem spheres via free-floating culture in the presence of the mitogens basic fibroblast growth factor and epidermal growth factor together with L-ascorbic acid. Subsequent culturing of the precursor cells in medium containing epidermal growth factor, FGF8b, SHH and ascorbic acid induces cell proliferation, following withdrawal of the growth factors leads differentiation into predominantly dopaminergic neurons. Mature neurons are obtained within 10 days of replacing the proliferation to differentiation medium. Embryonic stem-derived dopaminergic neurons are purified by cell sorting and may serve as a convenient source for the study of molecular, genetic and cellular properties of dopaminergic neurons.

Transforming growth factor-α induces sex-specific neurochemical imbalance in the stress- and memory-associated brain structures

Transforming growth factor-alpha (TGFalpha) is a well-known regulator of many developmental processes. However, its role in adult nervous system is yet unclear. Studies have shown that TGFalpha can regulate stress and memory behavior in adult mice. When TGFalpha is reduced in Waved-1 (Wa-1) mutant mice, the stress response and memory are impaired predominantly in males and only after puberty. To determine the neurochemical changes resulting from the reduced TGFalpha levels that could explain the reported behavioral outcomes, biogenic amine and amino acid levels were determined in the brain regions associated with stress and memory. Interestingly, sex-specific alterations in neurochemical levels were detected, including elevated noradrenaline and reduced glutamate levels in striatum of Wa-1 males, increased noradrenaline and reduced serotonin metabolite levels in hippocampus of Wa-1 females, reduced serotonin metabolite levels in cortex and amygdala of Wa-1 females, and reduced noradrenaline, dopamine, serotonin, glutamate and glycine levels in hypothalamus of Wa-1 females compared to their respective controls. Increased dopamine turnover in cortex and reduced dopamine and serotonin turnover in amygdala were observed in both male and female Wa-1 mice. The data indicate sex-specific alterations of specific neurochemicals as a result of reduced TGFalpha expression, which may underlie sex-dependent stress response and memory impairment in Wa-1 mice.

Murine embryonic EGF-responsive ventral mesencephalic neurospheres display distinct regional specification and promote survival of dopaminergic neurons

Similar to embryonic forebrain, the embryonic mesencephalon contains Fibroblast Growth Factor 2 (FGF2)- and Epidermal Growth Factor (EGF)-responsive progenitors that can be isolated as neurospheres. Developmentally, the FGF2-responsive population appears first and is thought to give rise to EGF-responsive neural stem cells. It is not known whether following this developmental switch of growth factor responsiveness ventral mesencephalic (VM)-derived neural stem cells display distinct region-specific properties. We found that murine VM- and dorsal mesencephalic (DM)-derived primary neurospheres isolated with EGF at embryonic day 14.5 differed with respect to neurosphere formation efficacy and size. VM- but not DM-derived spheres expressed En1, the molecular marker of isthmic organizer, and contained transcripts of BDNF, FGF2, IGF-I and NT-3. Both VM and DM primary neurospheres were self-renewing and gave rise to astroglial cells, but 20% of VM spheres also generated neurons. According to in vitro properties, DM- and majority of VM-derived EGF-responsive progenitors represent glial precursors. VM- but not DM-derived primary neurospheres enriched their respective conditioned medium with factors that promoted the survival of dopaminergic neurons in vitro, suggesting that ventral mesencephalic EGF-responsive progenitors are endowed with the potential to provide trophic support to nearby nascent dopaminergic neurons. These data may have implications in the treatment of Parkinson's disease.

Characterizing the Mitogenic Effect of Basic Fibroblast Growth Factor in the Adult Rat Striatum

The limited regenerative capacity of the adult central nervous system (CNS) renders it unable to fully recover from injury or disease. Although stem and progenitor cells have been shown to reside throughout the brain, in most regions they exist as quiescent cell populations and do not divide sufficiently to replace damaged or destroyed cells. In an effort to stimulate the proliferative capacity of these multipotent cells, we sought to determine the in vivo response of the adult CNS to an exogenous application of basic fibroblast growth factor (bFGF), a known mitogen to stem and progenitor cells. Specifically, we administered bFGF to the striatum of adult rats at varying concentrations (1, 10, 100, 1,000, or 10,000 ng/mL in saline) so as to establish a dose response curve for bFGF-induced cell proliferation. Forty-eight hours following bFGF administration, animals were injected with 5-bromodeoxyuridine to label dividing cells. Of the doses assessed, we found that 1,000 ng/mL bFGF generated the greatest proliferative response over that observed in animals given a control saline injection. Further, the proliferative response of the striatum to bFGF administration could be enhanced twofold by supplementing this growth factor with heparin sulfate, a factor that facilitates the binding of bFGF to its receptors. By determining the maturational fate of the proliferating cell population, we found that a significant proportion of newly generated cells resulting from bFGF administration differentiated into astrocytes. Collectively, these studies demonstrate the potential of bFGF to promote proliferation in the adult brain, which can be exploited to facilitate cell replacement therapies.

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.

New therapeutic approaches to Parkinson's disease including neural transplants

Parkinson's disease (PD) is a common neurodegenerative disorder of the brain and typically presents with a disorder of movement. The core pathological event underlying the condition is the loss of the dopaminergic nigrostriatal pathway with the formation of alpha-synuclein positive Lewy bodies. As a result, drugs that target the degenerating dopaminergic network within the brain work well at least in the early stages of the disease. Unfortunately, with time these therapies fail and produce their own unique side-effect profile, and this, coupled with the more diffuse pathological and clinical findings in advancing disease, has led to a search for more effective therapies. In this review, the authors will briefly discuss the emerging new drug therapies in PD before concentrating on a more detailed discussion on the state of cell therapies to cure PD.

Combination of hTERT and bmi-1, E6, or E7 induces prolongation of the life span of bone marrow stromal cells from an elderly donor without affecting their neurogenic potential

Murine bone marrow stromal cells differentiate not only into mesodermal derivatives, such as osteocytes, chondrocytes, adipocytes, skeletal myocytes, and cardiomyocytes, but also into neuroectodermal cells in vitro. Human bone marrow stromal cells are easy to isolate but difficult to study because of their limited life span. To overcome this problem, we attempted to prolong the life span of bone marrow stromal cells and investigated whether bone marrow stromal cells modified with bmi-1, hTERT, E6, and E7 retained their differentiated capability, or multipotency. In this study, we demonstrated that the life span of bone marrow stromal cells derived from a 91-year-old donor could be extended and that the stromal cells with an extended life span differentiated into neuronal cells in vitro. We examined the neuronally differentiated cells morphologically, physiologically, and biologically and compared the gene profiles of undifferentiated and differentiated cells. The neuronally differentiated cells exhibited characteristics similar to those of midbrain neuronal progenitors. Thus, the results of this study support the possible use of autologous-cell graft systems to treat central nervous system diseases in geriatric patients.

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.

NT3 inhibits FGF2-induced neural progenitor cell proliferation via the PI3K/GSK3 pathway

Neurotrophin 3 (NT3), a member of the neurotrophin family, antagonizes the proliferative effect of fibroblast growth factor 2 (FGF2) on cortical precursors. However, the mechanism by which NT3 inhibits FGF2-induced neural progenitor (NP) cell proliferation is unclear. Here, using an FGF2-dependent rat neurosphere culture system, we found that NT3 inhibits both FGF2-induced neurosphere growth and bromodeoxyuridine (BrdU) incorporation in a dose-dependent manner. U0126, a mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor, and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, both inhibited FGF2-induced BrdU incorporation, suggesting that the extracellular signal-regulated kinase1/2 (ERK1/2) and PI3K pathways are required for FGF2-induced NP cell proliferation. NT3 significantly inhibited FGF2-induced phosphorylation of Akt and glycogen synthase kinase 3beta (GSK3beta), a downstream kinase of Akt, whereas phosphorylation of ERK1/2 was unaffected. The inhibitory effect of NT3 on FGF2-induced NP cell proliferation was abolished by LY294002, and treatment with SB216763, a specific GSK3 inhibitor, antagonized the NT3 effect, rescuing both neurosphere growth and BrdU incorporation. Moreover, experiments with anti-NT3 antibody revealed that endogenous NT3 also plays a role in inhibiting FGF2-induced NP cell proliferation, and that anti-NT3 antibody enhanced phospho-Akt and phospho-GSK3beta levels in the presence of FGF2. These findings indicate that FGF2-induced NP cell proliferation is inhibited by NT3 via the PI3K/GSK3 pathway.

Sex differences in expression of transforming growth factor-α and epidermal growth factor receptor mRNA in waved-1 and C57Bl6 mice

A reduction of transforming growth factor-alpha (TGFalpha) expression in the spontaneous Waved-1 (Wa-1) mutant mouse causes specific behavioral and anatomical changes, including reduced fear learning and stress response and enlarged lateral ventricles. These alterations are observed predominantly in male Wa-1 mice after puberty. We hypothesized that regional differences in the expression of TGFalpha and its receptor, epidermal growth factor receptor (EGFR), may regulate the sexual dimorphism of the brain structures and functions during postnatal development. In general, fear learning-associated structures, including hippocampus and amygdala, showed maximum expression before puberty, regardless of genotype. In contrast, an overall temporal delay in the rise of both transcript levels, which peaked around or after puberty onset, was observed for the major stress regulatory hypothalamo-pituitary-adrenal axis. This pattern of expression was reversed for amygdala EGFR and hypothalamus TGFalpha and EGFR transcripts in males. When regional TGFalpha expression was compared between control and Wa-1 mice, far more complex patterns than expected were observed that revealed sex- and structure-dependent differences. In fact, the amygdala, hypothalamus, and pituitary TGFalpha expression pattern in Wa-1 exhibited a clear sex dependency across various age groups. Surprisingly, there was no compensatory up-regulation of the EGFR transcript in Wa-1 mice. The observed expression patterns of the TGFalpha signaling system during normal development and in the Wa-1 mutant mouse suggest complex sex- and age-dependent transcription regulatory mechanisms.

The effects of various concentrations of FGF-2 on the proliferation and neuronal yield of murine embryonic neural precursor cells in vitro

Embryonic neural precursors (ENPs), also termed neural stem cells or "neurospheres," are an attractive potential source of tissue for neural transplantation, because of their capacity to expand in number in vitro while retaining the ability to develop into the major phenotypes of the CNS. ENPs are isolated from the developing brain and proliferate in the presence of mitogens such as FGF-2 and EGF. Subsequent withdrawal of these mitogens and exposure to a suitable substrate results in differentiation into the major cell types of the CNS. As well as its role in precursor cell expansion, FGF-2 also plays a key role in the division of astrocytes, and in neuronal differentiation. Thus, it is important to establish the optimal concentrations of this factor for expansion and differentiation of neuronal phenotypes. Here we explore the effect of FGF-2 concentrations ranging from 1 to 20 ng/ml on the expansion and differentiation capacity of ENPs isolated from the cortex and striatum of E14 mice. ENP expansion was seen under all conditions, but was greatest at 10 and 20 ng/ml and least at 1 ng/ml. The numbers of neurons (as a proportion of total cell number) differentiating from these ENP populations appeared to be greatest at 1 ng/ml. However, once adjustments were made for the amount of expansion at each dose, final neuronal yield was maximum at the highest concentration of FGF-2 used (20 ng/ml).

Neural stem cells in development and regenerative medicine

In the last 10 years, enormous interest in neural stem cells has arisen from both basic and medical points of view. The discovery of neurogenesis in the adult brain has opened our imagination to consider novel strategies for the treatment of neurodegenerative diseases. Characterization of neurogenesis during development plays a fundamental role for the rational design of therapeutic procedures. In the present review, we describe recent progress in the characterization of embryo and adult neural stem cells (NSCs). We emphasize studies directed to determine the in vivo and in vitro differentiation potential of different NSC populations and the influence of the surrounding environment on NSC-specific differentiation. From a different perspective, the fact that NSCs and progenitors continuously proliferate and differentiate in some areas of the adult brain force us to ask how this process can be affected in neurodegenerative diseases. We propose that both abnormal cell death activation and decreased natural neuronal regeneration can contribute to the neuronal loss associated with aging, and perhaps even with that occurring in some neurodegenerative diseases. Furthermore, although NSC activation can be useful to treat neurodegenerative diseases, uncontrolled NSC proliferation, survival, and/or differentiation could cause tumorigenesis in the brain. NSC-mediated therapeutic procedures must take into account this latter possibility.

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.

Epidermal growth factor receptor expression is related to post-mitotic events in cerebellar development: regulation by thyroid hormone

It has been established that thyroid hormone and neurotrophic factors both orchestrate developmental events in the brain. However, it is not clear how these two influences are related. In this study, we investigated the effects of thyroid hormone on cerebellar development and the coincident expression of transforming growth factor-alpha (TGF-alpha), a ligand in the epidermal growth factor (EGF) family, and the epidermal growth factor receptor (EGFR). Profiles of thyroid hormone expression were measured in postnatal animals and were found to peak at postnatal day 15 (P15). These levels dropped below detectable levels when mice were made hypothyroid with propylthiouracil (PTU). TGF-alpha and EGFR expression, as determined by RNAse protection assay, was maximal at P6 in normal animals, but remained low in hypothyroid animals, suggesting that thyroid hormone was responsible for their induction. In situ hybridization and immunohistochemical analysis of EGFR expression revealed that this receptor was present on granule cells within the inner zone of the external granule cell layer (EGL), suggesting that EGFR-ligands were not inducing granule cell proliferation. The persistence of EGFR expression on migrating granule cells and subsequent down-regulation of expression in the internal granule cell layer (IGL) implicates a role for EGFR-ligands in differentiation and/or migration. In hypothyroid animals, we observed a delayed progression of granule cell migration, consistent with the persistence of EGFR labeling in the EGL, and in the 'pile-up' of labeled cells at the interface between the molecular layer and the Purkinje cell layer. Taken together, these results implicate thyroid hormone in the coordinated expression of TGF-alpha and EGFR, which are positioned to play a role in post-mitotic developmental events in the cerebellum.

Properties of a fetal multipotent neural stem cell (NEP cell)

Multipotent neural stem cells (NSCs) present in the developing neural tube (E10.5, neuroepithelial cells; NEP) were examined for the expression of candidate stem cell markers, and the expression of these markers was compared with later appearing precursor cells (E14.5) that can be distinguished by the expression of embryonic neural cell adhesion molecule (E-NCAM) and A2B5. NEP cells possess gap junctions, express connexins, and appear to lack long cilia. Most candidate markers, including Nestin, Presenilin, Notch, and Numb, were expressed by both NEP cells as well as other cell populations. Fibroblast growth factor receptor 4 (FGFR4), Frizzled 9 (Fz9), and SRY box-containing gene 2 (Sox2) as assessed by immunocytochemistry and in situ hybridization are markers that appear to distinguish NSCs from other precursor cells. Neither Hoechst 33342 nor rhodamine-123 staining, telomerase (Tert) expression, telomerase activity, or breakpoint cluster region protein 1 (Bcrp1) transporter expression could be used to distinguish NEP stem cells from other dividing cells. NEP cells, however, lacked expression of several lineage markers that are expressed by later appearing cells. These included absence of expression of CD44, E-NCAM, A2B5, epidermal growth factor receptor (EGFR), and platelet-derived growth factor receptor-alpha (PDGFR alpha), suggesting that negative selection using cell surface epitopes could be used to isolate stem cell populations from mixed cultures of cells. Using mixed cultures of cells isolated from E14.5 stage embryos, we show that NEP cells can be enriched by depleting differentiating cells that express E-NCAM or A2B5 immunoreactivity. Overall, our results show that a spectrum of markers used in combination can reliably distinguish multipotent NSCs from other precursor cells as well as differentiated cells present in the CNS.

Growth factor treatment promotes mobilization of young but not aged adult subventricular zone precursors in response to demyelination

Precursor cells of the adult mouse subventricular zone (SVZ) are mobilized and recruited by a lysolecithin (LPC)-induced demyelination of the corpus callosum. Because age decreases the proliferation of the SVZ neural precursors as well as the potential for myelin repair of the adult central nervous system, we have compared the ability of young and aged adult neural precursors to respond to LPC-induced demyelination. With age, the SVZ cells lost their capacity to proliferate and to be recruited by the lesion. Whereas a single injection of fibroblast growth factor-2 or transforming growth factor-alpha stimulated the proliferation of SVZ and rostral migratory stream precursors in both groups of animals after demyelination, they favored recruitment at the lesion in young mice but not in aged ones. In vitro experiments using neurospheres derived from young and aged animals indicated that both populations have the same migratory performances. Our in vivo data thus suggest that aged neural precursors may loose their intrinsic capacities to respond to demyelination-induced signals. Alternatively, their function may be altered by modification of the aged extracellular environment.

Mechanisms of muscle stem cell expansion with cytokines

Stem cell expansion and proliferation are important for cell transplantation and stem cell-mediated applications. While we have demonstrated that muscle stem cells can be obtained from adult skeletal muscle tissue, these cells represent only a small percentage of the muscle-derived cells and require in vitro expansion for successful stem cell-mediated therapies. In this study, we have examined the potential of several cytokines to stimulate stem cell growth by combining a non-exponential mathematical model with a unique cell culture system. The growth kinetics of two populations of muscle stem cells were characterized in culture medium supplemented with epidermal growth factor (EGF), fibroblast growth factor-2 (FGF-2), insulin-like growth factor-1 (IGF-1), FLT-3 ligand, hepatocyte growth factor, or stem cell factor (SCF). The division time (DT) and fraction of mitotically active cells were investigated as key parameters to further understand the mechanism of the expansion of the stem cell populations. Our results show that expansion of the freshly isolated, muscle-derived stem cells (MDSC) occurred by recruiting cells into the cell cycle in the presence of EGF, IGF-1, and SCF. However, expansion of the cultured stem cell clone, MC13, is attributed to a reduction of the length of the cell cycle in the presence of FGF-2, EGF, IGF-1, and SCF. Both MDSC and MC13 growth were inhibited in the presence of FLT-3 ligand by increasing the length of the cell cycle. Our results suggest that EGF, IGF-1, FGF-2, and SCF are important cytokines for stimulating the proliferation of MDSC. In addition, this study illustrates that expansion of stem cells occurs through different mechanisms, which consequently demonstrates the importance of monitoring several parameters of cell growth, such as DT and dividing fraction, following stimulation with growth factors.

Differentiation of embryonic stem cell-derived dopaminergic neurons is enhanced by survival-promoting factors

Here, we describe the generation of viable and dopamine-producing neurons derived from pluripotent mouse embryonic stem cells. Neurotrophic factors in combination with survival-promoting factors, such as interleukin-1beta, glial cell line-derived neurotrophic factor, neurturin, transforming growth factor-beta(3) and dibutyryl-cyclic AMP, significantly enhanced Nurr1 and tyrosine hydroxylase (TH) mRNA levels, whereas En-1, mash-1 and dopamine-2-receptor mRNA levels were not upregulated. In parallel, mRNA levels of the anti-apoptotic gene bcl-2 were found to be upregulated at terminal stages. Double immunofluorescence analysis revealed increased numbers of TH- and dopamine transporter-, but not gamma-aminobutyric acid- and serotonin-positive neurons in relation to synaptophysin-labeled cells by survival-promoting factors. Moreover, high-performance liquid chromatography analysis showed detectable levels of intracellular dopamine. We conclude that survival-promoting factors enhance differentiation, survival and maintenance of dopaminergic neurons derived from embryonic stem cells.

What role(s) for TGFalpha in the central nervous system?

Transforming growth factor alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR or erbB1). Identified since 1985 in the central nervous system (CNS), its functions in this organ have started to be determined during the past decade although numerous questions remain unanswered. TGFalpha is widely distributed in the nervous system, both glial and neuronal cells contributing to its synthesis. Although astrocytes appear as its main targets, mediating in part TGFalpha effects on different neuronal populations, results from different studies have raised the possibility for a direct action of this growth factor on neurons. A large array of experimental data have thus pointed to TGFalpha as a multifunctional factor in the CNS. This review is an attempt to present, in a comprehensive manner, the very diverse works performed in vitro and in vivo which have provided evidences for (i) an intervention of TGFalpha in the control of developmental events such as neural progenitors proliferation/cell fate choice, neuronal survival/differentiation, and neuronal control of female puberty onset, (ii) its role as a potent regulator of astroglial metabolism including astrocytic reactivity, (iii) its neuroprotective potential, and (iv) its participation to neuropathological processes as exemplified by astroglial neoplasia. In addition, informations regarding the complex modes of TGFalpha action at the molecular level are provided, and its place within the large EGF family is precised with regard to the potential interactions and substitutions which may take place between TGFalpha and its kindred.

Characterization of neurosphere cell phenotypes by flow cytometry

BACKGROUND

Neural stem cell research regularly utilizes neurosphere cultures as a continuous source of primitive neural cells. Results from current progenitor cell assays show that these cultures contain a low number of neural progenitors. Our goal is to characterize neurosphere cultures and define subpopulations in order to purify neural progenitor cells.

METHODS

Cells from embryonic mouse neurosphere cultures were stained with Hoechst 33342 and analyzed by flow cytometry. Subpopulations were sorted based on their relative fluorescence intensity in the blue and red regions of the spectrum. Individual sorted subpopulations were reanalyzed after 7 days in culture.

RESULTS

Neurosphere cultures contain a relatively high number of cells that stain weakly with Hoechst 33342. This subpopulation is present when cultured as an entire batch in the presence of epidermal growth factor (EGF). When cultured separately, this subpopulation gives rise to a neurosphere population with essentially the same characteristics as freshly isolated embryonic mouse brain cells but contains substantially fewer weakly Hoechst-stained cells.

CONCLUSIONS

Similar to hemopoietic systems, neurosphere cultures contain a subpopulation that can be characterized by a low emission of Hoechst fluorescence. When cultured separately, this subpopulation gives rise to a phenotype similar to freshly isolated, uncultured neural cells.

Three to four-year-old nonpassaged EGF-responsive neural progenitor cells: proliferation, apoptosis, and DNA repair

Epidermal growth factor responsive (EGFr) neural progenitor (NP) cells have been shown to be a potential alternative tissue source for neural transplantation and for developmental study. We have shown that nonpassaged EGFr NP cells can self-renew for 2 years in neurospheres and can robustly differentiate into glia and a number of neuronal cell types. We are now attempting to investigate if the EGFr NP cells will die or continue to live beyond the life span of the donor. In addition, we and other investigators have also found that EGFr NP cells, after transplant, retain only a small number of cells in the transplant site. In this study, we investigate the plasticity and fate of the EGFr NP cells. Using the nonpassaged method, we found EGFr NP cells live in the EGF supplement medium for over 4 years-the longest-lived EGFr NP cells ever reported. The 4-year-old striatal or cortical EGFr neurospheres, when subplated with substrate coating, migrate out of neurospheres and have robust growth with many processes. Furthermore, when nucleotide marker bromodeoxyuridine (BrdU) was added 3 days prior to the subplating, the EGFr NP cells were labeled positively with BrdU in the nucleus, indicating active proliferation activity. Meanwhile two other events were also found in the long-term EGFr NP cells. In the midst of the proliferation, apoptosis occurred. A subpopulation of EGFr NP cells are undergoing programmed cell death as indicated by the cell morphology and the TUNEL staining for DNA strand breaks. The TUNEL fluorescein-staining indicates that over 50% of EGFr NP cells are positive in the nuclei. On the other hand, we have also found that the major base excision repair enzyme, APE/ref-1, which is responsible for recognizing and repairing baseless sites in DNA, was present in the progenitor cells. However, in those cells undergoing apoptosis, APE/ref-1 levels were dramatically reduced or missing, and only a small percentage of cells were TUNEL and APE/ref-1 positive. These observations indicate that EGFr neural progenitor cells can live beyond the life span of the donor animal. The longevity of these cells in culture may be enhanced due to decreased apoptosis and the retention of normal DNA repair capacity.

Implantation of bioactive growth factor-secreting rods enhances fetal dopaminergic graft survival, outgrowth density, and functional recovery in a rat model of Parkinson's disease

One of the drawbacks with fetal ventral mesencephalic (VM) grafts in Parkinson's disease is the limited outgrowth into the host striatum. In order to enhance graft outgrowth, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) were administered by implantation of bioactive rods to the lateral part of the striatum to support grafted fetal VM implanted to the medial portion of the striatum. The polymer-based bioactive rods allow for a local secretion of neurotrophic factors over a time period of approximately 2 weeks. Moreover, glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta1 (TGFbeta1) were administered using the same technique. Concomitant administration of GDNF and TGFbeta1 was achieved by insertion of one GDNF and one TGFbeta1 rod. This was performed to investigate possible additive effects between GDNF and TGFbeta1. Rotational behavior, outgrowth from and nerve fiber density within the VM graft, and the number of TH-positive cells were studied. Functional compensation by reduction of rotational behavior was significantly enhanced in animals carrying bFGF and GDNF rods in comparison with animals carrying only VM graft. EGF and bFGF significantly increased the innervation density. Moreover, the nerve fiber density within the grafts was significantly enhanced by bFGF. Cell counts showed that a significantly higher number of TH-positive neurons was found in grafts treated with bFGF than that found in GDNF-treated grafts. An additive effect of TGFbeta1 and GDNF was not detectable. These results suggest that bioactive rods is a useful tool to deliver neurotrophic factors into the brain, and since bFGF was a potent factor concerning both functional, immunohistochemical and cell survival results, it might be of interest to use bFGF-secreting rods for enhancing the overall outcome of VM grafts into patients suffering from Parkinson's disease.

Roles of transforming growth factor-alpha and related molecules in the nervous system

The epidermal growth factor (EGF) family of polypeptides is regulators for tissue development and repair, and is characterized by the fact that their mature forms are proteolytically derived from their integral membrane precursors. This article reviews roles of the prominent members of the EGF family (EGF, transforming growth factor-alpha [TGF-alpha] and heparin-binding EGF [HB-EGF]) and the related neuregulin family in the nerve system. These polypeptides, produced by neurons and glial cells, play an important role in the development of the nervous system, stimulating proliferation, migration, and differentiation of neuronal, glial, and Schwann precursor cells. These peptides are also neurotrophic, enhancing survival and inhibiting apoptosis of post-mitotic neurons, probably acting directly through receptors on neurons, or indirectly via stimulating glial proliferation and glial synthesis of other molecules such as neurotrophic factors. TGF-alpha, EGF, and neuregulins are involved in mediating glial-neuronal and axonal-glial interactions, regulating nerve injury responses, and participating in injury-associated astrocytic gliosis, brain tumors, and other disorders of the nerve system. Although the collective roles of the EGF family (as well as those of the neuregulins) are shown to be essential for the nervous system, redundancy may exist among members of the EGF family.

Lineage-restricted neural precursors can be isolated from both the mouse neural tube and cultured ES cells

We have previously identified multipotent neuroepithelial (NEP) stem cells and lineage-restricted, self-renewing precursor cells termed NRPs (neuron-restricted precursors) and GRPs (glial-restricted precursors) present in the developing rat spinal cord (A. Kalyani, K. Hobson, and M. S. Rao, 1997, Dev. Biol. 186, 202-223; M. S. Rao and M. Mayer-Proschel, 1997, Dev. Biol. 188, 48-63; M. Mayer-Proschel, A. J. Kalyani, T. Mujtaba, and M. S. Rao, 1997, Neuron 19, 773-785). We now show that cells identical to rat NEPs, NRPs, and GRPs are present in mouse neural tubes and that immunoselection against cell surface markers E-NCAM and A2B5 can be used to isolate NRPs and GRPs, respectively. Restricted precursors similar to NRPs and GRPs can also be isolated from mouse embryonic stem cells (ES cells). ES cell-derived NRPs are E-NCAM immunoreactive, undergo self-renewal in defined medium, and differentiate into multiple neuronal phenotypes in mass culture. ES cells also generate A2B5-immunoreactive cells that are similar to E9 NEP-cell-derived GRPs and can differentiate into oligodendrocytes and astrocytes. Thus, lineage restricted precursors can be generated in vitro from cultured ES cells and these restricted precursors resemble those derived from mouse neural tubes. These results demonstrate the utility of using ES cells as a source of late embryonic precursor cells.

Multipotent and restricted precursors in the central nervous system

Acquisition of cell type-specific properties in the nervous system is likely a process of sequential restriction in developmental potential. At least two classes of pluripotent stem cells, neuroepithelial (NEP) stem cells and EGF-dependent neurosphere stem cells, have been identified in distinct spatial and temporal domains. Pluripotent stem cells likely generate central nervous system (CNS) and peripheral nervous system (PNS) derivatives via the generation of intermediate lineage-restricted precursors that differ from each other and from multipotent stem cells. Neuronal precursors termed neuronal-restricted precursors (NRPs), multiple classes of glial precursors termed glial-restricted precursors (GRPs), oligodendrocyte-type 2 astrocytes (O2As), astrocyte precursor cells (APCs), and PNS precursors termed neural crest stem cells (NCSCs) have been identified. Multipotent stem cells and restricted precursor cells can be isolated from embryonic stem (ES) cell cultures providing a non-fetal source of such cells. Analysis in multiple species illustrates similarities between rat, mouse, and human cell differentiation raising the possibility that similar factors and markers may be used to isolate precursor cells from human tissue or ES cells. Anat Rec (New Anat): 257:137-143, 1999.

Cell lineage in the developing neural tube

Acquisition of cell type specific properties in the spinal cord is a process of sequential restriction in developmental potential. A multipotent stem cell of the nervous system, the neuroepithelial cell, generates central nervous system and peripheral nervous system derivatives via the generation of intermediate lineage restricted precursors that differ from each other and from neuroepithelial cells. Intermediate lineage restricted neuronal and glial precursors termed neuronal restricted precursors and glial restricted precursors, respectively, have been identified. Differentiation is influenced by extrinsic environmental signals that are stage and cell type specific. Analysis in multiple species illustrates similarities between chick, rat, mouse, and human cell differentiation. The utility of obtaining these precursor cell types for gene discovery, drug screening, and therapeutic applications is discussed.Key words: stem cells, oligodendrocytes, astrocytes, neurons, spinal cord.