Co-expression of MAP-2 and GFAP in cells developing from rat EGF responsive precursor cells

Ghrelin peptide improves glial conditioned medium effects on neuronal differentiation of human adipose mesenchymal stem cells

The influences of ghrelin on neural differentiation of adipose-derived mesenchymal stem cells (ASCs) were investigated in this study. The expression of typical neuronal markers, such as protein gene product 9.5 (PGP9.5) and Microtubule Associated Protein 2 (MAP2), as well as glial Fibrillary Acid Protein (GFAP) as a glial marker was evaluated in ASCs in different conditions. In particular, 2 µM ghrelin was added to control ASCs and to ASCs undergoing neural differentiation. For this purpose, ASCs were cultured in Conditioned Media obtained from Olfactory Ensheathing cells (OEC-CM) or from Schwann cells (SC-CM). Data on marker expression were gathered after 1 and 7 days of culture by fluorescence immunocytochemistry and flow cytometry. Results show that only weak effects were induced by the addition of only ghrelin. Instead, dynamic ghrelin-induced modifications were detected on the increased marker expression elicited by glial conditioned media. In fact, the combination of ghrelin and conditioned media consistently induced a further increase of PGP9.5 and MAP2 expression, especially after 7 days of treatment. The combination of ghrelin with SC-CM produced the most evident effects. Weak or no modifications were found on conditioned medium-induced GFAP increases. Observations on the ghrelin receptor indicate that its expression in control ASCs, virtually unchanged by the addition of only ghrelin, was considerably increased by CM treatment. These increases were enhanced by combining ghrelin and CM treatment, especially at 7 days. Overall, it can be assumed that ghrelin favors a neuronal rather than a glial ASC differentiation.

Tunable Substrate Functionalities Direct Stem Cell Fate toward Electrophysiologically Distinguishable Neuron-like and Glial-like Cells

Engineering cellular microenvironment on a functional platform using various biophysical cues to modulate stem cell fate has been the central theme in regenerative engineering. Among the various biophysical cues to direct stem cell differentiation, the critical role of physiologically relevant electric field (EF) stimulation was established in the recent past. The present study is the first to report the strategy to switch EF-mediated differentiation of human mesenchymal stem cells (hMSCs) between neuronal and glial pathways, using tailored functional properties of the biomaterial substrate. We have examined the combinatorial effect of substrate functionalities (conductivity, electroactivity, and topography) on the EF-mediated stem cell differentiation on polyvinylidene-difluoride (PVDF) nanocomposites in vitro, without any biochemical inducers. The functionalities of PVDF have been tailored using conducting nanofiller (multiwall-carbon nanotube, MWNT) and piezoceramic (BaTiO₃, BT) by an optimized processing approach (melt mixing-compression molding-rolling). The DC conductivity of PVDF nanocomposites was tuned from ∼10^-11 to ∼10^-4 S/cm and the dielectric constant from ∼10 to ∼300. The phenotypical changes and genotypical expression of hMSCs revealed the signatures of early differentiation toward neuronal pathway on rolled-PVDF/MWNT and late differentiation toward glial lineage on rolled-PVDF/BT/MWNT. Moreover, we were able to distinguish the physiological properties of differentiated neuron-like and glial-like cells using membrane depolarization and mechanical stimulation. The excitability of the EF-stimulated hMSCs was also determined using whole-cell patch-clamp recordings. Mechanistically, the roles of intracellular reactive oxygen species (ROS), Ca²⁺ oscillations, and synaptic and gap junction proteins in directing the cellular fate have been established. Therefore, the present work critically unveils complex yet synergistic interaction of substrate functional properties to direct EF-mediated differentiation toward neuron-like and glial-like cells, with distinguishable electrophysiological responses.

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.

SOX2 and SOX2-MYC Reprogramming Process of Fibroblasts to the Neural Stem Cells Compromised by Senescence

Tumorigenic potential of induced pluripotent stem cells (iPSCs) infiltrating population of induced neural stem cells (iNSCs) generated from iPSCs may limit their medical applications. To overcome such a difficulty, direct reprogramming of adult somatic cells into iNSCs was proposed. The aim of this study was the systematic comparison of induced neural cells (iNc) obtained with different methods—direct reprogramming of human adult fibroblasts with either SOX2 (SiNSc-like) or SOX2 and c-MYC (SMiNSc-like) and induced pluripotent stem cells differentiation to ebiNSc—in terms of gene expression profile, differentiation potential as well as proliferation properties. Immunocytochemistry and real-time PCR analyses were used to evaluate gene expression profile and differentiation potential of various iNc types. Bromodeoxyuridine (BrdU) incorporation and senescence-associated beta-galactosidase (SA-β-gal) assays were used to estimate proliferation potential. All three types of iNc were capable of neuronal differentiation; however, astrocytic differentiation was possible only in case of ebiNSc. Contrary to ebiNSc generation, the direct reprogramming was rarely a propitious process, despite 100% transduction efficiency. The potency of direct iNSCs-like cells generation was lower as compared to iNSCs obtained by iPSCs differentiation, and only slightly improved when c-MYC was added. Directly reprogrammed iNSCs-like cells were lacking the ability to differentiate into astrocytic cells and characterized by poor efficiency of neuronal cells formation. Such features indicated that these cells could not be fully reprogrammed, as confirmed mainly with senescence detection. Importantly, SiNSc-like and SMiNSc-like cells were unable to achieve the long-term survival and became senescent, which limits their possible therapeutic applicability. Our results suggest that iNSCs-like cells, generated in the direct reprogramming attempts, were either not fully reprogrammed or reprogrammed only into neuronal progenitors, mainly because of the inaccuracies of currently available protocols.

Kuwanon V inhibits proliferation, promotes cell survival and increases neurogenesis of neural stem cells

Neural stem cells (NSCs) have the ability to proliferate and differentiate into neurons and glia. Regulation of NSC fate by small molecules is important for the generation of a certain type of cell. The identification of small molecules that can induce new neurons from NSCs could facilitate regenerative medicine and drug development for neurodegenerative diseases. In this study, we screened natural compounds to identify molecules that are effective on NSC cell fate determination. We found that Kuwanon V (KWV), which was isolated from the mulberry tree (Morus bombycis) root, increased neurogenesis in rat NSCs. In addition, during NSC differentiation, KWV increased cell survival and inhibited cell proliferation as shown by 5-bromo-2-deoxyuridine pulse experiments, Ki67 immunostaining and neurosphere forming assays. Interestingly, KWV enhanced neuronal differentiation and decreased NSC proliferation even in the presence of mitogens such as epidermal growth factor and fibroblast growth factor 2. KWV treatment of NSCs reduced the phosphorylation of extracellular signal-regulated kinase 1/2, increased mRNA expression levels of the cyclin-dependent kinase inhibitor p21, down-regulated Notch/Hairy expression levels and up-regulated microRNA miR-9, miR-29a and miR-181a. Taken together, our data suggest that KWV modulates NSC fate to induce neurogenesis, and it may be considered as a new drug candidate that can regenerate or protect neurons in neurodegenerative diseases.

Novel Insights into NeuN: from Neuronal Marker to Splicing Regulator

Neuronal nuclei (NeuN) is a well-recognized "marker" that is detected exclusively in post-mitotic neurons and was initially identified through an immunological screen to produce neuron-specific antibodies. Immunostaining evidence indicates that NeuN is distributed in the nuclei of mature neurons in nearly all parts of the vertebrate nervous system. NeuN is highly conserved among species and is stably expressed during specific stages of development. Therefore, NeuN has been considered to be a reliable marker of mature neurons for the past two decades. However, this role has been challenged by recent studies indicating that NeuN staining is variable and even absent during certain diseases and specific physiological states. More importantly, despite the widespread use of the anti-NeuN antibody, the natural identity of the NeuN protein remained elusive for 17 years. NeuN was recently eventually identified as an epitope of Rbfox3, which is a novel member of the Rbfox1 family of splicing factors. This identification might provide a novel perspective on NeuN expression during both physiological and pathological conditions. This review summarizes the current progress on the biochemical identity and biological significance of NeuN and recommends caution when applying NeuN immunoreactivity as a definitive marker of mature neurons in certain diseases and specific physiological states.

Human muscle-derived stem/progenitor cells promote functional murine peripheral nerve regeneration

Peripheral nerve injuries and neuropathies lead to profound functional deficits. Here, we have demonstrated that muscle-derived stem/progenitor cells (MDSPCs) isolated from adult human skeletal muscle (hMDSPCs) can adopt neuronal and glial phenotypes in vitro and ameliorate a critical-sized sciatic nerve injury and its associated defects in a murine model. Transplanted hMDSPCs surrounded the axonal growth cone, while hMDSPCs infiltrating the regenerating nerve differentiated into myelinating Schwann cells. Engraftment of hMDSPCs into the area of the damaged nerve promoted axonal regeneration, which led to functional recovery as measured by sustained gait improvement. Furthermore, no adverse effects were observed in these animals up to 18 months after transplantation. Following hMDSPC therapy, gastrocnemius muscles from mice exhibited substantially less muscle atrophy, an increase in muscle mass after denervation, and reorganization of motor endplates at the postsynaptic sites compared with those from PBS-treated mice. Evaluation of nerve defects in animals transplanted with vehicle-only or myoblast-like cells did not reveal histological or functional recovery. These data demonstrate the efficacy of hMDSPC-based therapy for peripheral nerve injury and suggest that hMDSPC transplantation has potential to be translated for use in human neuropathies.

The microenvironment-specific transformation of adult stem cells models malignant triton tumors

Here, we demonstrated the differentiation potential of murine muscle-derived stem/progenitor cells (MDSPCs) toward myogenic, neuronal, and glial lineages. MDSPCs, following transplantation into a critical-sized sciatic nerve defect in mice, showed full regeneration with complete functional recovery of the injured peripheral nerve at 6 weeks post-implantation. However, several weeks after regeneration of the sciatic nerve, neoplastic growths were observed. The resulting tumors were malignant peripheral nerve sheath tumors (MPNSTs) with rhabdomyoblastic differentiation, expressing myogenic, neurogenic, and glial markers, common markers of human malignant triton tumors (MTTs). No signs of tumorigenesis were observed 17 weeks post-implantation of MDSPCs into the gastrocnemius muscles of dystrophic/mdx mice, or 1 year following subcutaneous or intravenous injection. While MDSPCs were not oncogenic in nature, the neoplasias were composed almost entirely of donor cells. Furthermore, cells isolated from the tumors were serially transplantable, generating tumors when reimplanted into mice. However, this transformation could be abrogated by differentiation of the cells toward the neurogenic lineage prior to implantation. These results establish that MDSPCs participated in the regeneration of the injured peripheral nerve but transformed in a microenvironment- and time-dependent manner, when they likely received concomitant neurogenic and myogenic differentiation signals. This microenvironment-specific transformation provides a useful mouse model for human MTTs and potentially some insight into the origins of this disease.

In vivo intermittent hypoxia elicits enhanced expansion and neuronal differentiation in cultured neural progenitors

In vitro exposure of neural progenitor cell (NPC) populations to reduced O(2) (e.g. 3% versus 20%) can increase their proliferation, survival and neuronal differentiation. Our objective was to determine if an acute (<1hr), in vivo exposure to intermittent hypoxia (AIH) alters expansion and/or differentiation of subsequent in vitro cultures of NPC from the subventricular zone (SVZ). Neonatal C57BL/6 mice (postnatal day 4) were exposed to an AIH paradigm (20×1 minute; alternating 21% and 10% O(2)). Immediately after AIH, SVZ tissue was isolated and NPC populations were cultured and assayed either as neurospheres (NS) or as adherent monolayer cells (MASC). AIH markedly increased the capacity for expansion of cultured NS and MASC, and this was accompanied by increases in a proliferation maker (Ki67), MTT activity and hypoxia-inducible factor-1α (HIF-1α) signaling in NS cultures. Peptide blockade experiments confirmed that proteins downstream of HIF-1α are important for both proliferation and morphological changes associated with terminal differentiation in NS cultures. Finally, immunocytochemistry and Western blotting experiments demonstrated that AIH increased expression of the neuronal fate determination transcription factor Pax6 in SVZ tissue, and this was associated with increased neuronal differentiation in cultured NS and MASC. We conclude that in vivo AIH exposure can enhance the viability of subsequent in vitro SVZ-derived NPC cultures. AIH protocols may therefore provide a means to "prime" NPC prior to transplantation into the injured central nervous system.

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.

Characterization of neural stem/progenitor cells expressing VEGF and its receptors in the subventricular zone of newborn piglet brain

Neural stem/progenitor cell (NSP) biology and neurogenesis in adult central nervous system (CNS) are important both towards potential future therapeutic applications for CNS repair, and for the fundamental function of the CNS. In the present study, we report the characterization of NSP population from subventricular zone (SVZ) of neonatal piglet brain using in vivo and in vitro systems. We show that the nestin and vimentin-positive neural progenitor cells are present in the SVZ of the lateral ventricles of neonatal piglet brain. In vitro, piglet NSPs proliferated as neurospheres, expressed the typical protein of neural progenitors, nestin and a range of well-established neurodevelopmental markers. Upon dissociation and subculture, piglet NSPs differentiated into neurons and glial cells. Clonal analysis demonstrates that piglet NSPs are multipotent and retain the capacity to generate both glia and neurons. These cells expressed VEGF, VEGFR1, VEGFR2 and Neuropilin-1 and -2 mRNAs. Real time PCR revealed that SVZ NSPs from newborn piglet expressed total VEGF and all VEGF splice variants. These findings show that piglet NSPs may be helpful to more effectively design growth factor based strategies to enhance endogenous precursor cells for cell transplantation studies potentially leading to the application of this strategy in the nervous system disease and injury.

Leukemia inhibitory factor favours neurogenic differentiation of long-term propagated human midbrain precursor cells

There is a lot of excitement about the potential use of multipotent neural stem cells for the treatment of neurodegenerative diseases. However, the strategy is compromised by the general loss of multipotency and ability to generate neurons after long-term in vitro propagation. In the present study, human embryonic (5 weeks post-conception) ventral mesencephalic (VM) precursor cells were propagated as neural tissue-spheres (NTS) in epidermal growth factor (EGF; 20 ng/ml) and fibroblast growth factor 2 (FGF2; 20 ng/ml). After more than 325 days, the NTS were transferred to media containing either EGF+FGF2, EGF+FGF2+heparin or leukemia inhibitory factor (LIF; 10 ng/ml)+FGF2+heparin. Cultures were subsequently propagated for more than 180 days with NTS analyzed at various time-points. Our data show for the first time that human VM neural precursor cells can be long-term propagated as NTS in the presence of EGF and FGF2. A positive effect of heparin was found only after 150 days of treatment. After switching into different media, only NTS exposed to LIF contained numerous cells positive for markers of newly formed neurons. Besides of demonstrating the ability of human VM NTS to be long-term propagated, our study also suggests that LIF favours neurogenic differentiation of human VM precursor cells.

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.

Class III beta-tubulin is constitutively coexpressed with glial fibrillary acidic protein and nestin in midgestational human fetal astrocytes: implications for phenotypic identity

Class III beta-tubulin isotype (betaIII-tubulin) is widely regarded as a neuronal marker in developmental neurobiology and stem cell research. To test the specificity of this marker protein, we determined its expression and distribution in primary cultures of glial fibrillary acidic protein (GFAP)-expressing astrocytes isolated from the cerebral hemispheres of 2 human fetuses at 18 to 20 weeks of gestation. Cells were maintained as monolayer cultures for 1 to 21 days without differentiation induction. By immunofluorescence microscopy, coexpression of betaIII-tubulin and GFAP was detected in cells at all time points but in spatially distinct patterns. The numbers of GFAP+ cells gradually decreased from Days 1 to 21 in vitro, whereas betaIII-tubulin immunoreactivity was present in 100% of cells at all time points. beta-III-tubulin mRNA and protein expression were demonstrated in cultured cells by reverse-transcriptase-polymerase chain reaction and immunoblotting, respectively. Glial fibrillary acidic protein+/beta-III-tubulin-positive cells coexpressed nestin and vimentin but lacked neurofilament proteins, CD133, and glutamate-aspartate transporter. Weak cytoplasmic staining was detected with antibodies against microtubule-associated protein 2 isoforms. Confocal microscopy, performed on autopsy brain samples of human fetuses at 16 to 20 gestational weeks, revealed widespread colocalization of GFAP and betaIII-tubulin in cells of the ventricular/subventricular zones and the cortical plate. Our results indicate that in the midgestational human brain, betaIII-tubulin is not neuron specific because it is constitutively expressed in GFAP+/nestin+ presumptive fetal astrocytes.

Revisiting nestin expression in retinal progenitor cells in vitro and after transplantation in vivo

The purpose of this study is to characterize the co-expression of nestin--a neuroectodermal stem cell and a reactive glial marker-with various mature retinal cell markers in retinal progenitor cells (RPCs) expanded in vitro, followed either by in vitro induction or subretinal transplantation. Rat RPCs derived from embryonic day (E) 17 rat retina were expanded in serum free defined culture, and induced to differentiate by all-trans retinoic acid (RA). Following induction, cells were stained for nestin in combination with retinal neuronal and glial markers. Cultured cells were collected for quantitative RT-PCR gene expression analysis prior to and after induction. In a second series, passage 2 RPCs were transplanted into the subretinal space of S334ter-3 retinal degeneration rats at postnatal day 28. After 1-4 weeks, sections through the transplant were double immunostained for nestin and various retinal specific neuronal markers. The cultured RPCs treated with RA exhibited nestin co-expression with various retinal specific markers, including protein kinase C alpha (PKC), neurofilament 200 (NF200), cellular retinaldehyde binding protein (CRALBP), and rhodopsin. Following RA induction, quantitative RT-PCR analysis demonstrated downregulation of nestin, PAX-6, thy1.1, and PKCalpha, and upregulation of rhodopsin, glial fibrillary acidic protein (GFAP), and CrX. No nestin coexpression was observed with any of the retinal specific neuronal markers in RPC transplants in vivo except for some nestin-immunoreactivity overlapping with GFAP positive cells in the host retina. The role of nestin as a unique neural stem/progenitor cell marker should be reconsidered. Nestin expression during RPC maturation appears to be different in vitro versus in vivo.

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.

Neuronal differentiation of human umbilical cord blood neural stem-like cell line

The expanding population of neural stem/progenitor cells can be selected from human cord blood nonhematopoietic (CD34-negative) mononuclear fraction. Due to repeated expansion and selection of these cells we have established the first clonogenic, nonimmortalized human umbilical cord blood neural stem-like cell (HUCB-NSC) line. This line can be maintained at different stages of neural progenitor development by the presence of trophic factors, mitogens and neuromorphogens in culture media. Neurogenic potential of HUCB-NSC was established for serum-free and low-serum cultured cells. Commitment of HUCB-NSC by serum was shown to be important for the optimal response to the signals provided by surrounding environment in vitro. Enhanced neuronal differentiation induced by dBcAMP treatment was accompanied by expression of several functional proteins including glutamatergic, GABAergic, dopamine, serotonin and acetylcholine receptors, which was shown by microarray, immunocytochemistry and electrophysiology. Electrophysiological studies, whole-cell patch-clamp recordings, revealed in differentiated HUCB-NSC two types of voltage-sensitive and several ligand-gated currents typical for neuronal cells. The above HUCB-NSC characteristic conceivably implicates that cord blood-derived progenitors could be effectively differentiated into functional neuron-like cells in vitro.

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.

Alterations in cellular phenotypes differentiating from embryonic rat brain neurosphere cultures by immunoselection of neuronal progenitors

The neurosphere culture system is widely used to expand neural stem/progenitor cells in vitro and to provide a source of cells for transplantation approaches to CNS disorders. This study describes the populations of neurones, astrocytes and oligodendrocytes which differentiated from embryonic day (E) 14 rat cortical and striatal tissue grown as neurosphere cultures over three passages. The percentages of cells that adopted neuronal phenotypes decreased with passage, astrocytic percentages increased and oligodendrocytic percentages remained constant. In the second part of this study, immunomagnetic separation was used to positively select neuronal progenitor cells from E14 rat cortical and striatal tissue using an antibody, 2F7, which recognises an epitope on the cell surface of pre- and post-mitotic neurones. These immunomagnetically selected cells were grown as neurosphere cultures over three passages and gave rise to significantly different percentages of neurones, astrocytes and oligodendrocytes than those found in the baseline study. In particular, the percentage of neurones arising from the second and third passages was significantly higher following immunoselection. This indicates that neuronal progenitor cells can be isolated using immunomagnetic separation and then expanded using the neurosphere culture system, to generate enriched populations of neurones that can be used in CNS repair.

Aberrant neuronal-glial differentiation in Taylor-type focal cortical dysplasia (type IIA/B)

Focal cortical dysplasia (FCD) type IIA/B (Taylor type) is a malformation of cortical development characterized by laminar disorganization and dysplastic neurons. FCD IIA and FCD IIB denote subtypes in which balloon cells are absent or present, respectively. The etiology of FCD IIA/B is unknown, but previous studies suggest that its pathogenesis may involve aberrant, mixed neuronal-glial differentiation. To investigate whether aberrant differentiation is a consistent phenotype in FCD IIA/B, we studied a panel of neuronal and glial marker antigens in a series of 15 FCD IIB cases, and 2 FCD IIA cases. Double-labeling immunofluorescence and confocal imaging revealed that different combinations of neuronal and glial antigens were co-expressed by individual cells in all cases of FCD IIA/B, but not in control cases of epilepsy due to other causes. Co-expression of neuronal and glial markers was most common in balloon cells, but was also observed in dysplastic neurons. The relative expression of neuronal and glial antigens varied over a broad range. Microtubule-associated protein 1B, an immature neuronal marker, was more frequently co-expressed with glial antigens than were mature neuronal markers, such as neuronal nuclear antigen. Our results indicate that aberrant neuronal-glial differentiation is a consistent and robust phenotype in FCD IIA/B, and support the hypothesis that developmental defects of neuronal and glial fate specification play an important role in its pathogenesis.

bFGF and EGF modulate trauma-induced proliferation and neurogenesis in juvenile organotypic hippocampal slice cultures

Since postnatal and adult mammalian brains have been shown to retain an ability to generate neurons from endogenous stem cells throughout life, these cells could play a central role in regeneration after neuronal loss. Therefore, we studied cell proliferation, glio- and neurogenesis respectively after brain injury in organotypic hippocampal slice cultures using a focal trauma by transecting Schaffer collaterals in the cornu ammonis (CA) 2 region mechanically. After determination of cell death using propidium iodide, neuroregenerative processes were quantitatively analyzed by various immunohistochemical techniques at different time points post injury. As this endogenous insult-induced neurogenesis is rather inefficient, we investigated if it can be enhanced by application of exogenous growth factors. Exogenous basic fibroblast growth factor (bFGF) enhanced neurogenesis significantly in the dentate gyrus (DG) region. A neutralizing antibody against endogenous bFGF revealed a significant decrease of basal and trauma-induced proliferation. Reverse transcription polymerase chain reaction (RT-PCR) studies exhibited a downregulation of FGF messenger ribonucleic acid (mRNA) transcription after the antibody treatment. In contrast, epidermal growth factor (EGF) increased proliferation, but not neurogenesis. A combination of bFGF and EGF displayed an EGF-like effect on proliferation and no effect on neurogenesis. These results demonstrate, that in our model bFGF but not EGF sustains neurogenesis, whereas together the two growth factors permit an increased proliferation but not neurogenesis in organic hippocampal slice cultures.

The human NTERA2 neural cell line generates neurons on growth under neural stem cell conditions and exhibits characteristics of radial glial cells

NTERA2 cells are a human neural cell line generating neurons after exposure to retinoic acid and, as such, are widely used as a model of neurogenesis. We report that these cells form spheres when grown in serum-free medium supplemented with basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). These spheres were found to express markers of radial glial cells such as, Pax6, glutamate transporter (GLAST), tenascin C, brain lipid-binding protein (BLBP), and the 3CB2 antigen. On plating on an adhesive substrate, NTERA2 spheres generate a large percentage of immature neurons (30-50%) together with a minority of cells of the oligodendrocyte lineage. Thus NTERA2 cells share properties with neural stem cells. However, at variance with the latter, we found that they produce their own bFGF implicated in an autocrine or paracrine proliferative loop and that they do not generate astrocytes after differentiation. These results provide an interesting model to study radial glial cells and their role in human neurogenesis.

Emergence of muscle and neural hematopoiesis in humans

During human development, hematopoiesis is thought to be compartmentalized to the fetal circulation, liver, and bone marrow. Here, we show that combinations of cytokines together with bone morphogenetic protein-4 and erythropoietin could induce multiple blood lineages from human skeletal muscle or neural tissue. Under defined serum-free conditions, the growth factors requirements, proliferation, and differentiation capacity of muscle and neural hematopoiesis were distinct to that derived from committed hematopoietic sites and were uniquely restricted to CD45(-)CD34(-) cells expressing the prominin AC133. Our study defines epigenetic factors required for the emergence of hematopoiesis from unexpected tissue origins and illustrates that embyronically specified microenvironments do not limit cell fate in humans.

Neuronal differentiation of stem cells isolated from adult muscle

Lineage uncommitted pluripotent stem cells reside in the connective tissue of skeletal muscle. The present study was carried out with pluripotent stem cells (PPSCs) isolated from 6-month old rat muscle. Before differentiation, these cells were vimentin+, CD90+, CD45-, and varied in their expression of CD34. The PPSCs were expanded as non-adherent aggregates under similar conditions to those used to generate neurospheres from embryonic or neural stem cells. The PPSC-derived neurospheres were positive for nestin, an early marker present in neuronal precursors, and expressed the two alternative mRNA forms of the neuroectodermal marker Pax-6, as well as mRNA for Oct-4, a gene related to the pluripotentiality of stem cells. To confirm their neural potential, PPSC-derived neurospheres were plated on coated coverslips under varying conditions: Neurobasal medium with N2 or B27, and either NT3 or BDNF. After 4-6 days the cells expressed neuronal (Tuj1+, NF68), astrocytic (GFAP) and oligodendrocytic (MOSP+, MBP+) markers, both by immunocytochemistry and RT-PCR. In addition, PPSCs were cultured as monolayers under adherent conditions, exposed to growth factors and defined differentiating conditions for 5 hr, and subsequently kept for 2 days in a maturation medium. At this point they gave rise to a mixed population of early neural progenitors (Nestin+ or NG2+), immature and mature neurons (Tuj1+ and NF145+) and myelin producing oligodendrocytes (CNPase + and MOSP+). Our study shows that PPSCs present in adult muscle can overcome germ lineage restrictions and express the molecular characteristics of brain cells. Therefore, PPSCs isolated from adult muscle could provide a novel source for autologous cell replacement in neurodegenerative and demyelinating diseases.

Human cord blood-derived cells attain neuronal and glial features in vitro

Neural stem cells are clonogenic, self-renewing cells with the potential to differentiate into brain-specific cell lines. Our study demonstrates that a neural-stem-cell-like subpopulation can be selected and expanded in vitro by the use of human umbilical cord blood cells, which are a relatively easily available starting material. Through a combination of antigen-driven magnetic cell sorting and subfractionation according to cell surface adhesive properties, we have isolated a clonogenic fraction devoid of hematopoietic or angiogenetic properties but with relatively high self-renewal potency. The resulting clones express nestin, a neurofilament protein that is one of the most specific markers of multipotent neural stem cells. In the presence of selected growth factors or in the rat brain co-culture system, the progeny of these cells can be oriented towards the three main neural phenotypes: neurons,astroglia and oligodendroglia. The cells show high commitment (about 30% and 40% of the population) to neuronal and astrocytic fate, respectively. Interestingly, upon differentiation, the neural-type precursor cells of cord blood origin also give rise to a relatively high proportion of oligodendrocytes — 11% of the total population of differentiating cells.

Microtubule-associated protein 2 (MAP-2) is expressed in low and high grade diffuse astrocytomas

The expression of neuronal antigens in diffuse astrocytomas has not been thoroughly evaluated. We have investigated the expression of microtubule associated protein 2 (MAP-2), synaptophysin and non-phosphorylated epitopes of neurofilament protein (NFP) by immunohistochemistry in 15 low grade diffuse astrocytomas and 15 glioblastomas. MAP-2 was strongly expressed in 97% of cases, using an antibody to both low and high molecular weight isoforms. An antibody specific to high molecular weight isoforms of MAP-2 (hmw-MAP-2) revealed weaker, focal staining in 60% of cases with greater expression in the glioblastomas (P=0.027). NFP was expressed in 50% of cases, but was generally weak and focal. There was little evidence of synaptophysin expression. We conclude that MAP-2 expression in astrocytomas is due predominantly to low molecular weight isoforms, which may be expressed in astrocytes as well as neurons. Focal expression of hmw-MAP-2 and NFP, however, suggest that neuronal antigens may be expressed, particularly in high grade astrocytomas. Immunopositivity for these antigens should not preclude the diagnosis of diffuse astrocytoma.

Isolation of multipotent neural precursors residing in the cortex of the adult human brain

Multipotent precursors able to generate neurons, astrocytes, and oligodendrocytes have previously been isolated from human brain embryos and recently from neurogenic regions of the adult human brains. The isolation of multipotent neural precursors from adult human should open new perspectives to study adult neurogenesis and for brain repair. The present study describes the in vitro isolation from adult human brains of a progenitor responsive to both epidermal and basic fibroblast growth factors that forms spheres as it proliferates. Single spheres derived from various regions of the brain generate in vitro neurons, astrocytes, and oligodendrocytes. The clonal origin of the spheres was revealed by genomic viral insertion using lentiviral vector. Interestingly, this vector appears to be a potent tool for gene transfer into human neural progeny. Ninety-six percent of the spheres investigated were multipotent. Multipotent precursors were isolated from all brain regions studied, including the temporal and the frontal cortex, the amygdala, the hippocampus, and the ventricular zone. This study is the first evidence that primitive precursors such as multipotent precursors exist in the adult human cortex and can reside far from the ventricles. Neurogenesis derived from adult human progenitors differ to murine neurogenesis by the requirement of laminin for oligodendrocyte generation and by the action of basic-fibroblast growth factor and platelet derived growth factor that prevented the formation of oligodendrocytes and neurons. Moreover, the differentiation of human adult precursors seems to differ from fetal ones: adult precursors do not necessitate the removal of mitogen for differentiation. These results indicate that the study of adult multipotent precursors is a new platform to study adult human neurogenesis, potentially generate neural cells for transplantation, and design protocols for in vivo stimulation.

The subventricular zone: source of neuronal precursors for brain repair

The subventricular zone (SVZ) is a major germinal zone which persists in the adult brain. The SVZ contains cells that self renew and continuously produce new neurons and glia. In this chapter we discuss the development, architecture and function of the adult SVZ, as well as the fate of SVZ cells after transplantation. We focus on identification of neural stem cells, factors which regulate neurogenesis and mechanisms for neuronal migration through the adult brain. Detailed understanding of these processes is necessary to utilize the SVZ as a source of neuronal and glial precursors for genetic manipulation, transplantation or brain self repair.

Neurogenesis in the adult brain: death of a dogma

For over 100 years a central assumption in the field of neuroscience has been that new neurons are not added to the adult mammalian brain. This perspective examines the origins of this dogma, its perseverance in the face of contradictory evidence, and its final collapse. The acceptance of adult neurogenesis may be part of a contemporary paradigm shift in our view of the plasticity and stability of the adult brain.

Cortical neurogenesis in adult rats after reversible photothrombotic stroke

Neurogenesis occurs throughout life in the dentate gyrus of hippocampus and subventricular zone, but this phenomenon has rarely been observed in other brain regions of adult mammals. The aim of the current study was to investigate the cell proliferation process in the ischemically challenged region-at-risk after focal cerebral ischemia in the adult rat brain. A reversible photothrombotic ring stroke model was used, which features sustained hypoperfusion followed by late spontaneous reperfusion and a remarkable morphologic tissue recovery in the anatomically well defined somatosensory cortical region-at-risk. Twelve-week-old male Wistar rats received repeated intraperitoneal injections of the cell proliferation specific marker 5-bromodeoxyuridine (BrdU) after stroke induction. Immunocytochemistry of coronal brain sections revealed that the majority of BrdU-positive cells were of glial, macrophage, and endothelial origin, whereas 3% to 6% of the BrdU-positive cells were double-labeled by BrdU and the neuronspecific marker Map-2 at 7 and 100 days after stroke onset in the region-at-risk. They were distributed randomly in cortical layers II-VI. Three-dimensional confocal analyses of BrdU and the neuronal-specific marker Neu N by double immunofluorescence confirmed their colocalization within the same cells at 72 hours and 30 days after stroke induction. This study suggests that, as a potential pathway for brain repair, new neurons can be generated in the cerebral cortex of adult rats after sublethal focal cerebral ischemia.

The morphological development of neurons derived from EGF- and FGF-2-driven human CNS precursors depends on their site of integration in the neonatal rat brain

Neural precursor cells derived from the developing human brain were expanded in vitro under the influence of fibroblast growth factor-2 (FGF-2) and epidermal growth hormone (EGF), and were then transplanted into different regions of the neonatal rat brain. Four weeks later neurons were seen to have developed from human embryonic precursors, using a human-specific antibody to tau (htau). There were morphological differences between implanted neurons developing in the hippocampus, striatum and neocortex, which were confirmed by cell volume measurements, although no specific neurochemical phenotypes were identified. Htau-positive fibres were seen to project extensively along fibre pathways appropriate for the site of neuronal integration. This study demonstrates that, following cell division in vitro, neurons differentiating from human precursor cell populations retain the ability to respond appropriately to regional determinants present in the neonatal rat brain. This is important for the application of such cells in CNS repair strategies, in particular neural transplantation.

Characterisation of stem cell expression using two-dimensional electrophoresis

Stem cells were isolated from foetal human brain tissue and induced to proliferate using the mitogens epidermal growth factor (EFG) and fibroblast growth factor (FGF). Under these conditions the dividing cells formed spheres which could be maintained in an undifferentiated state for extended periods of time. Following removal of the mitogen and addition of serum, the human stem cells rapidly began to differentiate. Samples from differentiated and undifferentiated cultures were lysed and analysed using two-dimensional (2-D) electrophoresis, a powerful technique for the separation and characterisation of proteins in complex mixtures. After 1 h post-differentiation, marked differences in protein expression could be observed between undifferentiated and differentiated stem cell samples.

Heparin, but not other proteoglycans potentiates the mitogenic effects of FGF-2 on mesencephalic precursor cells

There is increasing evidence that the proteoglycan heparin plays a critical role in the regulation of the activity of FGF-2 by either interacting with its receptor or modifying its stability and functioning. In this study precursor cells were isolated from the rat E14 ventral mesencephalon and cultured as free floating spheres in FGF-2 alone or in combination with heparin or other related proteoglycans, including chondroitin sulfate, keratin sulfate, dermatan sulfate, or hyaluronic acid. Our results show the mitogenic effects of FGF-2 could be potentiated by heparin but not the other four proteoglycans. Sodium chlorate, which blocks the cells ability to sulfate its proteoglycans, was shown to reduce the mitogenic effects of FGF-2 alone to below that of control levels, suggesting that endogenous sulfated molecules are required for the FGF-2 effects on mesencephalic precursors. Cells expanded for 7 days with either FGF-2 or FGF-2 + heparin were plated onto a substrate and allowed to differentiate for a further 7 days in the absence of growth factors. Approximately 6% of the precursors developed into neurons whether grown with or without heparin and none were positive for TH, a marker for dopamine neurons. However, there was a significant decrease in the number of astrocytes developing from cultures grown in FGF-2 + heparin when compared to FGF-2 alone. Interestingly we could not find an EGF responsive cell in the mesencephalon at this embryonic age in the absence or presence of heparin. However, there was a synergistic effect of combining EGF + FGF-2, which could be potentiated by heparin. We conclude that heparin, but not other closely related proteoglycans, is vital for the growth of FGF-2-responsive mesencephalic neural precursors.

In vitro survival and differentiation of neurons derived from epidermal growth factor-responsive postnatal hippocampal stem cells: inducing effects of brain-derived neurotrophic factor

Neural stem cells proliferate in vitro and form neurospheres in the presence of epidermal growth factor (EGF), and are capable of differentiating into both neurons and glia when exposed to a substrate. We hypothesize that specific neurotrophic factors induce differentiation of stem cells from different central nervous system (CNS) regions into particular fates. We investigated differentiation of stem cells from the postnatal mouse hippocampus in culture using the following trophic factors (20 ng/mL): brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and glial-derived neurotrophic factor (GDNF). Without trophic factors, 32% of stem cells differentiated into neurons by 4 days in vitro (DIV), decreasing to 10% by 14 DIV. Addition of BDNF (starting at either day 0 or day 3) significantly increased neuron survival (31-43% by 14 DIV) and differentiation. Morphologically, many well-differentiated neurons resembled hippocampal pyramidal neurons. 5'-Bromodeoxyuridine labeling demonstrated that the pyramidal-like neurons originated from stem cells which had proliferated in EGF-containing cultures. However, similar application of NT-3 and GDNF did not exert such a differentiating effect. Addition of BDNF to stem cells from the postnatal cerebellum, midbrain, and striatum did not induce these neuronal phenotypes, though similar application to cortical stem cells yielded pyramidal-like neurons. Thus, BDNF supports survival of hippocampal stem cell-derived neurons and also can induce differentiation of these cells into pyramidal-like neurons. The presence of pyramidal neurons in BDNF-treated hippocampal and cortical stem cell cultures, but not in striatal, cerebellar, and midbrain stem cell cultures, suggests that stem cells from different CNS regions differentiate into region-specific phenotypic neurons when stimulated with an appropriate neurotrophic factor.

Incorporation and glial differentiation of mouse EGF-responsive neural progenitor cells after transplantation into the embryonic rat brain

In vitro, epidermal growth factor (EGF)-responsive neural progenitor cells exhibit multipotent properties and can differentiate into both neurons and glia. Using an in utero xenotransplantation approach we examined the developmental potential of EGF-responsive cells derived from E14 mouse ganglionic eminences, cortical primordium, and ventral mesencephalon, after injection into the E15 rat forebrain ventricle. Cell cultures were established from control mice or from mice carrying the lacZ transgene under control of the promoters for nestin, glial fibrillary acidic protein (GFAP), or myelin basic protein (MBP). The grafted cells, visualized with mouse-specific markers or staining for the reporter gene product, displayed widespread incorporation into distinct forebrain and midbrain structures and differentiated predominantly into glial cells. The patterns of incorporation of cells from all three regions were very similar without preference for the homotopic brain areas. These results suggest that EGF-responsive progenitor cells can respond to host derived environmental cues, differentiate into cells with glial-like features, and become integrated in the developing recipient brain.