EGF-responsive rat neural stem cells: molecular follow-up of neuron and astrocyte differentiation in vitro

Heparin-mediated electrostatic immobilization of bFGF via functional polymer films for enhanced self-renewal of human neural stem cells

Preserving the self-renewal capability of undifferentiated human neural stem cells (hNSCs) is one of the crucial prerequisites for efficient hNSC-based regenerative medicine. Considering that basic fibroblast growth factor (bFGF) is one of the key contributing factors in maintaining the self-renewal property of hNSCs, the bioactivity and stability of bFGF in the hNSC culture should be regulated carefully. In this study, we developed a functional polymer film of poly(glycidyl methacrylate (GMA)-co-N,N-dimethylaminoethyl methacrylate (DMAEMA)) (coGD, or p(GMA-co-DMAEMA)) via initiated chemical vapor deposition (iCVD), which facilitated a stable, electrostatic adsorption of heparin and subsequent immobilization of bFGF. The bFGF-immobilized coGD surface substantially enhanced the proliferation rate and neurosphere forming ability of hNSCs compared to tissue culture plate (TCP). The expression of the stemness markers of hNSCs such as NESTIN and SOX-2 was also upregulated prominently on the coGD surface. Also, the hNSCs cultured on the coGD surface showed enhanced neurogenesis upon spontaneous differentiation. The immobilized bFGF on the coGD surface stimulated the expression of bFGF receptors and subsequently activated the mitogen-activated protein kinase (MAPK) pathway, attributed to the increase in self-renewal property of hNSCs. Our results indicate that the coGD surface allowed in situ heparin-mediated bFGF immobilization, which served as a robust platform to generate hNSC neurospheres with enhanced self-renewal and differentiation capabilities and thereby will prompt an advance in the field of therapeutics of neurodegenerative diseases.

The epidermal growth factor receptor variant type III mutation frequently found in gliomas induces astrogenesis in human cerebral organoids

Objectives

The epidermal growth factor receptor variant type III (EGFRvIII) is the most common mutation of EGFR in glioblastoma multiforme (GBM) and is found in approximately 25% of all GBMs. Intriguingly, EGFRvIII is mostly found in GFAP⁺ astrocytic tumour cells in the brain, suggesting connection of EGFRvIII to astrogenesis. In this study, we explored whether EGFRvIII mutation facilitates astrogenesis in human development setting.

Materials and methods

Using CRISPR‐Cas9, we generated EGFRvIII mutations in H9‐hESCs. Wild type (wt) H9‐hESCs were used as an isogenic control. Next, we generated cerebral organoids using the wt and EGFRvIII‐hESCs and examined the astrogenic differentiation of the brain organoids.

Results

EGFRvIII‐organoids showed abundant astrocytes (GFAP⁺, S100β⁺), while no astrocytes were detected in wt hESC‐derived organoids at day 49. On the contrary, TUJ1⁺ neurons were more abundant in the wt‐organoids than the EGFRvIII‐organoids. This result suggested that constitutively active EGFRvIII promoted astrogenesis at the expense of neurogenesis. In addition, the EGFRvIII‐organoids were larger in size and retained more Ki67⁺ cells than wt‐organoids, indicating enhanced cell proliferation by the mutation. The EGFRvIII‐organoids displayed massive apoptotic cell death after treatment with temozolomide and hence, could be used for evaluation of anti‐GBM drugs.

Conclusions

EGFRvIII mutation‐induced astrogenesis and massive cell proliferation in a human brain development model. These results provide us new insights into the mechanisms relating EGFRvIII mutation‐mediated gliogenesis and gliomagenesis.

Astragaloside VI Promotes Neural Stem Cell Proliferation and Enhances Neurological Function Recovery in Transient Cerebral Ischemic Injury via Activating EGFR/MAPK Signaling Cascades

Radix Astragali (AR) is a commonly used medicinal herb for post-stroke disability in Traditional Chinese Medicine but its active compounds for promoting neurogenic effects are largely unknown. In the present study, we tested the hypothesis that Astragaloside VI could be a promising active compound from AR for adult neurogenesis and brain repair via targeting epidermal growth factor (EGF)-mediated MAPK signaling pathway in post-stroke treatment. By using cultured neural stem cells (NSCs) and experimental stroke rat model, we investigated the effects of Astragaloside VI on inducing NSCs proliferation and self-renewal in vitro, and enhancing neurogenesis for the recovery of the neurological functions in post-ischemic brains in vivo. For animal experiments, rats were undergone 1.5 h middle cerebral artery occlusion (MCAO) plus 7 days reperfusion. Astragaloside VI (2 μg/kg) was daily administrated by intravenous injection (i.v.) for 7 days. Astragaloside VI treatment promoted neurogenesis and astrogenic formation in dentate gyrus zone, subventricular zone, and cortex of the transient ischemic rat brains in vivo. Astragaloside VI treatment enhanced NSCs self-renewal and proliferation in the cultured NSCs in vitro without affecting NSCs differentiation. Western blot analysis showed that Astragaloside VI up-regulated the expression of nestin, p-EGFR and p-MAPK, and increased neurosphere sizes, whose effects were abolished by the co-treatment of EGF receptor inhibitor gefitinib and ERK inhibitor PD98059. Behavior tests revealed that Astragaloside VI promoted the spatial learning and memory and improved the impaired motor function in transient cerebral ischemic rats. Taken together, Astragaloside VI could effectively activate EGFR/MAPK signaling cascades, promote NSCs proliferation and neurogenesis in transient cerebral ischemic brains, and improve the repair of neurological functions in post-ischemic stroke rats. Astragaloside VI could be a new therapeutic drug candidate for post-stroke treatment.

In vitro investigation of the mechanism underlying the effect of ginsenoside on the proliferation and differentiation of neural stem cells subjected to oxygen-glucose deprivation/reperfusion

The present study comprised a series of experiments to investigate the mechanism underlying the effect of ginsenoside on the self-renewal, proliferation and differentiation of neural stem cells (NSCs) undergoing oxygen-glucose deprivation/reperfusion (OGD/R) in vitro. The NSCs, which were isolated from the hippocampus of embryonic day 17 embryo rats, were subjected to OGD/R to establish an in vitro model of brain ischemia-reperfusion, following which different doses of ginsenoside were administered to the model. The proliferation of the NSCs was determined using MTT colorimetry and nestin/bromodeoxyuridine (BrdU) immunofluorescent double-labeling. The NSCs were identified by measuring the expression of nestin, and the differentiation of NSCs was assessed through the immunofluorescent double-labeling of nestin/vimentin and nestin/neuron-specific class III β-tubulin (tuj-1). The protein levels of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) were detected to investigate the function and mechanism of ginsenoside on ischemic stroke using an enzyme-linked immunosorbent assay. Marked increases in the optical density, area density and numbers of nestin/BrdU-, nestin/vimentin- and nestin/tuj-1-positive cells were found in the ginsenoside-treated group. Compared with the control group, enhanced expression levels of BrdU, tuj-1 and vimentin were found in the ginsenoside-treated group, suggesting that ginsenoside may significantly promote the proliferation and differentiation of NSCs. The results of the present study also showed that ginsenoside significantly increased the protein level of HIF-1α (P<0.05) in the NSCs exposed to OGD/R. These results indicated that ginsenoside may maintain NSC replication, promote NSC proliferation and promote NSC differentiation into neurons and astrocytes. Ginsenoside may initiate the expression of downstream VEGF, which is involved in promoting the survival, self-renewal and differentiation of NSCs.

Efficient generation of functional hepatocyte-like cells from mouse liver progenitor cells via indirect co-culture with immortalized human hepatic stellate cells

BACKGROUND

Differentiation of liver progenitor cells (LPCs) to functional hepatocytes holds great potential to develop new strategies for hepatocyte transplantation and the screening of drug-induced cytotoxicity. However, reports on the efficient and convenient hepatic differentiation of LPCs to hepatocytes are few. The present study aims to investigate the possibility of generating functional hepatocytes from LPCs in an indirect co-culture system.

METHODS

Mouse LPCs were co-cultured in Transwell plates with an immortalized human hepatic stellate cell line (HSC-Li) we previously established. The morphology, expression of hepatic markers, and functions of mouse LPC-derived cells were monitored and compared with those of conventionally cultured LPCs.

RESULTS

Co-culturing with HSC-Li cells induced differentiation of mouse LPCs into functional hepatocyte-like cells. The differentiated cells were morphologically transformed into hepatocyte-like cells 3 days after co-culture initiation. In addition, the differentiated cells expressed liver-specific genes and possessed hepatic functions, including glycogen storage, low-density lipoprotein uptake, albumin secretion, urea synthesis, and cytochrome P450 1A2 enzymatic activity.

CONCLUSIONS

Our method, which employs indirect co-culture with HSC-Li cells, can efficiently induce the differentiation of LPCs into functional hepatocytes. This finding suggests that this co-culture system can be a useful method for the efficient generation of functional hepatocytes from LPCs.

Elevation of Brain Magnesium Potentiates Neural Stem Cell Proliferation in the Hippocampus of Young and Aged Mice

In the adult brain, neural stem cells (NSCs) can self-renew and generate all neural lineage types, and they persist in the sub-granular zone (SGZ) of the hippocampus and the sub-ventricular zone (SVZ) of the cortex. Here, we show that dietary-supplemented - magnesium-L-threonate (MgT), a novel magnesium compound designed to elevate brain magnesium regulates the NSC pool in the adult hippocampus. We found that administration of both short- and long-term regimens of MgT, increased the number of hippocampal NSCs. We demonstrated that in young mice, dietary supplementation with MgT significantly enhanced NSC proliferation in the SGZ. Importantly, in aged mice that underwent long-term (12-month) supplementation with MgT, MgT did not deplete the hippocampal NSC reservoir but rather curtailed the age-associated decline in NSC proliferation. We further established an association between extracellular magnesium concentrations and NSC self-renewal in vitro by demonstrating that elevated Mg(2+) concentrations can maintain or increase the number of cultured hippocampal NSCs. Our study also suggests that key signaling pathways for cell growth and proliferation may be candidate targets for Mg(2+) 's effects on NSC self-renewal. J. Cell. Physiol. 231: 1903-1912, 2016. © 2016 Wiley Periodicals, Inc.

Biomimetic niche for neural stem cell differentiation using poly-L-lysine/hyaluronic acid multilayer films

Polyelectrolyte multilayer films have been suggested as tunable substrates with flexible surface properties that can modulate cell behavior. However, these films’ biological effects on neural stem/progenitor cells have rarely been studied. Herein, biomimetic multilayer films composed of hyaluronic acid and poly-L-lysine were chosen to mimic the native extracellular matrix niche of brain tissue and were evaluated for their inductive effects, without the addition of chemical factors. Because neural stem/progenitor cells are sensitive to substrate properties, it is important that this system provides control over the surface charge, and slight stiffness variations are also possible. Both of these factors affect neural stem/progenitor cell differentiation. The results showed that neural stem/progenitor cells were induced to differentiate on the poly-L-lysine/hyaluronic acid multilayer films with 0.5–4 alternating layers. In addition, the neurite outgrowth length was regulated by the surface charge of the terminal layer but did not increase with the layer number. In contrast, the quantity of differentiated neurons was enhanced slightly as the number of layers increased but was not affected by the surface charge of the terminal layer. In sum, material pairs in the form of native poly-L-lysine/hyaluronic acid films achieved important targets for neural regenerative medicine, including enhancement of the neurite outgrowth length, regulation of neuron differentiation, and the formation of a network. These extracellular matrix–mimetic poly-L-lysine/hyaluronic acid multilayer films may provide a versatile platform that could be useful for surface modification for applications in neural engineering.

Differentiation of neural stem/progenitor cells using low-intensity ultrasound

Herein, we report the evaluation of apoptosis, cell differentiation, neurite outgrowth and differentiation of neural stem/progenitor cells (NSPCs) in response to low-intensity ultrasound (LIUS) exposure. NSPCs were cultured under different conditions, with and without LIUS exposure, to evaluate the single and complex effects of LIUS. A lactic dehydrogenase assay revealed that the cell viability of NSPCs was maintained with LIUS exposure at an intensity range from 100 to 500 mW/cm(2). Additionally, in comparison with no LIUS exposure, the cell survival rate was improved with the combination of medium supplemented with nerve growth factor and LIUS exposure. Our results indicate that LIUS exposure promoted NSPC attachment and differentiation on a glass substrate. Neurite outgrowth assays revealed the generation of longer, thicker neurites after LIUS exposure. Furthermore, LIUS stimulation substantially increased the percentage of differentiating neural cells in NSPCs treated with nerve growth factor in comparison with the unstimulated group. The high percentage of differentiated neural cells indicated that LIUS induced neuronal networks denser than those observed in the unstimulated groups. Furthermore, the release of nitric oxide, an important small-molecule neurotransmitter, was significantly upregulated after LIUS exposure. It is therefore reasonable to suggest that LIUS promotes the differentiation of NSPCs into neural cells, induces neurite outgrowth and regulates nitric oxide production; thus, LIUS may be a potential candidate for NSPC induction and neural cell therapy.

ADAM-17/tumor necrosis factor-α-converting enzyme inhibits neurogenesis and promotes gliogenesis from neural stem cells

Neural precursor cells (NPCs) are activated in central nervous system injury. However, despite being multipotential, their progeny differentiates into astrocytes rather than neurons in situ. We have investigated the role of epidermal growth factor receptor (EGFR) in the generation of non-neurogenic conditions. Cultured mouse subventricular zone NPCs exposed to differentiating conditions for 4 days generated approximately 50% astrocytes and 30% neuroblasts. Inhibition of EGFR with 4-(3-chloroanilino)-6,7-dimethoxyquinazoline significantly increased the number of neuroblasts and decreased that of astrocytes. The same effects were observed upon treatment with the metalloprotease inhibitor galardin, N-[(2R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl]-L-tryptophan methylamide (GM 6001), which prevented endogenous transforming growth factor-α (TGF-α) release. These results suggested that metalloprotease-dependent EGFR-ligand shedding maintained EGFR activation and favored gliogenesis over neurogenesis. Using a disintegrin and metalloprotease 17 (ADAM-17) small interference RNAs transfection of NPCs, ADAM-17 was identified as the metalloprotease involved in cell differentiation in these cultures. In vivo experiments revealed a significant upregulation of ADAM-17 mRNA and de novo expression of ADAM-17 protein in areas of cortical injury in adult mice. Local NPCs, identified by nestin staining, expressed high levels of ADAM-17, as well as TGF-α and EGFR, the three molecules necessary to prevent neurogenesis and promote glial differentiation in vitro. Chronic local infusions of GM6001 resulted in a notable increase in the number of neuroblasts around the lesion. These results indicate that, in vivo, the activation of a metalloprotease, most probably ADAM-17, initiates EGFR-ligand shedding and EGFR activation in an autocrine manner, preventing the generation of new neurons from NPCs. Inhibition of ADAM-17, the limiting step in this sequence, may contribute to the generation of neurogenic niches in areas of brain damage.

A protein interaction network for the analysis of the neuronal differentiation of neural stem cells in response to titanium dioxide nanoparticles

The effects of titanium dioxide (TiO(2)) nanoparticles (NPs) on the differentiation of neural stem cells are reported. Our findings indicate that TiO(2) NPs lead to a differentiational tendency towards neurons from neural stem cells, suggesting TiO(2) NPs might be a beneficial inducer for neuronal differentiation. To insight into the possible molecular mechanism of the neuronal differentiation, we conducted a protein-protein interaction network (PIN) analysis. To this end, a global mapping of target proteins induced by TiO(2) NPs was first made by a 2-dimensional electrophoresis analysis. Results showed that 9 proteins were significantly changed and then they were subjected to the mass spectrometric assay. All 9 identified proteins are involved in signal, molecular chaperones, cytoskeleton, and nucleoprotein. Further, based on our experimental data and DIP, IntAct-EBI, GRID database, a protein-protein interaction network was constructed, which provides highly integrated information exhibiting the protein-protein interaction. By analysis of the gene expression, the signal pathway involving Cx43 phosphorylation, which is negatively regulated by the protein kinase C epsilon (PKCepsilon), is demonstrated. It is inferred that PKCepsilon plays a pivotal negative role in the neuronal differentiation of stem neural cells in response to the TiO(2) NPs exposure.

Production, characterization, and efficient transfection of highly pure oligodendrocyte precursor cultures from mouse embryonic neural progenitors

Much current knowledge of oligodendrocyte biology, the myelin-forming cells in the central nervous system, comes from cell culture studies mainly from postnatal rat tissue but mouse cells have been much more difficult to produce in large quantities. We have developed a high yield protocol for production of oligodendrocyte precursor cells from mouse embryonic neural progenitors grown as neurospheres. Neurospheres can be maintained and expanded for long periods in culture in the presence of epidermal growth factor (EGF). When floating neurospheres were plated on substrate-coated dishes in media supplemented with platelet derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), the spheres attached and generated migrating cells that were predominantly oligodendrocyte-lineage cells. Furthermore, cells in spheres could be shifted to the oligodendrocyte phenotype prior to plating on substrate, by incubation in suspension with PDGF/bFGF. Single cell suspensions plated after dissociation of either EGF-treated neurospheres or PDGF/bFGF-treated oligospheres had the bipolar, elongated morphology characteristic of oligodendrocyte precursor cells. mRNA and protein expression analysis of the cells generated by this method confirmed their oligodendrocyte lineage. Oligodendrocyte precursors generated by this method matured in response to ciliary neurotrophic factor treatment, producing cells with multiple processes and myelin-like membranes. The most important aspect of this protocol is the ability to generate very high numbers of relatively pure mouse oligodendrocyte progenitor cells, which can be easily transfected. These studies open up many kinds of investigations on transgenic and mutant mouse oligodendrocytes, thereby providing a valuable tool to study oligodendrocyte biology and development.

Characterization and transformation potential of "Synthetic" astrocytes differentiated from murine embryonic stem cells

Our objective was to determine if murine embryonic stem (ES) cells, which are readily available from repositories, could be developed as a model of gliomagenesis, recognizing the difficulty in obtaining and transforming somatic astrocytes. Using a stringently controlled sequential differentiation procedure on wild type (wt) and p53+/- ES cells, we established GFAP+A2B5-synthetic astrocytes with high efficiency (>90%). The synthetic astrocytes stably express several differentiated astrocyte associated structural proteins and biochemical markers, but lacked expression of differentiated neurons and oligodendrocytes. However, in contrast to somatic differentiated astrocytes, the synthetic astrocytes expressed stem cell markers, with a transcriptome profile similar to astrocytes differentiated from neural stem cells (NSC) and somatic astrocyte cultures established from E13.5-Cortex and P4-hippocampus. In addition, the synthetic astrocytes demonstrated plasticity, with ability to dedifferentiate into neuronal and oligodendrocyte lineages. Intracranial injection of postnatal differentiated somatic astrocytes or synthetic astrocytes of either wt or p53+/- background did not grow tumors, unlike corresponding ES cells that develop teratomas. In contrast, retroviral transduction of either wt or p53+/- synthetic astrocytes and not the postnatal somatic astrocytes, with relevant oncogenes found in human malignant astrocytomas (MDM2, myr-AKT, V12H-RAS), led to intracranial high-grade undifferentiated gliomas. This study demonstrates utilization of readily available ES cells of varying genetic backgrounds to model and further our understanding of gliomagenesis. Large numbers of replenishable derivative synthetic glial lineage cells retain genetic and phenotypic characteristics of progenitor cells and thereby are more amenable to transformation by genetic aberrations involved in gliomagenesis.

Gliomagenesis and neural stem cells: Key role of hypoxia and concept of tumor “neo-niche”

Gliomas represent the most common primary brain tumors and the most devastating pathology of the central nervous system. Despite progress in conventional treatments, the prognosis remains dismal. Recent studies have suggested that a glioma brain tumor may arise from a "cancer stem cell". To understand this theory we summarize studies of the concepts of neural stem cell, and its specialized microenvironment, namely the niche which can regulate balanced self-renewal, differentiation and stem cell quiescence. We summarize the molecular mechanism known or postulated to be involved in the disregulation of normal stem cells features allowing them to undergo neoplasic transformation. We seek data pointing out the key role of hypoxia in normal homeostasis of stem cells and in the initiation, development and aggressiveness of gliomas. We develop the concept of tumor special microenvironment and we propose the new concept of neo-niche, surrounding the glioma, in which hypoxia could be a key factor to recruit and deregulate different stem cells for gliogenesis process. Substantial advances in treatment would come from obtaining better knowledge of molecular impairs of this disease.

RB and RB2/P130 genes cooperate with extrinsic signals to promote differentiation of rat neural stem cells

Mechanisms governing commitment and differentiation of the cells of the nervous system begin to be elucidated: how extrinsic and intrinsic components are related remains poorly understood. To investigate this issue, we overexpressed genes of the retinoblastoma (Rb) family RB and RB2/p130, which play an important role during nerve cell maturation, in rat neural stem cells (NSCs). Immunostaining of neurons, astrocytes and oligodendrocytes in cultures overexpressing pRb or pRb2/p130 revealed that these genes affect lineage specification of differentiating NSCs. We observed modifications in percentage of differentiated cells indicating a shift towards the phenotype induced by culture conditions. Results were confirmed by detection of the expression levels of differentiation markers by RT-PCR. Analysis of BrdU incorporation and detection of an early marker of apoptosis suggest that the effect of pRb and pRb2/p130 overexpression is not dependent on the inhibition of cell proliferation, nor does it rely on the regulation of cell survival. Our findings suggest that Rb family genes are involved in fate determination of the cells of the nervous system. However, their role seems subsidiary to that of the extrinsic signals that promote lineage specification and appear to be mediated by a direct effect on the acquisition of a specific phenotype.

Auditory hair cell explant co-cultures promote the differentiation of stem cells into bipolar neurons

Auditory neurons, the target neurons of the cochlear implant, degenerate following a sensorineural hearing loss. The goal of this research is to direct the differentiation of embryonic stem cells (SCs) into bipolar auditory neurons that can be used to replace degenerating neurons in the deafened mammalian cochlea. Successful replacement of auditory neurons is likely to result in improved clinical outcomes for cochlear implant recipients. We examined two post-natal auditory co-culture models with and without neurotrophic support, for their potential to direct the differentiation of mouse embryonic SCs into characteristic, bipolar, auditory neurons. The differentiation of SCs into neuron-like cells was facilitated by co-culture with auditory neurons or hair cell explants, isolated from post-natal day five rats. The most successful combination was the co-culture of hair cell explants with whole embryoid bodies, which resulted in significantly greater numbers of neurofilament-positive, neuron-like cells. While further characterization of these differentiated cells will be essential before transplantation studies commence, these data illustrate the effectiveness of post-natal hair cell explant co-culture, at providing valuable molecular cues for directed differentiation of SCs towards an auditory neuron lineage.

The neurobiology of neurooncology

The histological classification of brain tumors currently is based on the morphological appearance and protein expression patterns that reflect specific cell types within the central nervous system. Recent studies have suggested that the cells of origin for brain tumors may persist in the fully formed tumors, and that these "cancer stem cells" might represent the relevant cellular targets for anticancer therapy. In this regard, insights into the developmental neurobiology of brain tumors has significant impact on our understanding of the molecular and cellular pathogenesis of these devastating cancers, as well as the development of new strategies for treating brain tumors.

Loss of p53 induces changes in the behavior of subventricular zone cells: implication for the genesis of glial tumors

The role of multipotential progenitors and neural stem cells in the adult subventricular zone (SVZ) as cell-of-origin of glioblastoma has been suggested by studies on human tumors and transgenic mice. However, it is still unknown whether glial tumors are generated by all of the heterogeneous SVZ cell types or only by specific subpopulations of cells. It has been proposed that transformation could result from lack of apoptosis and increased self-renewal, but the definition of the properties leading to neoplastic transformation of SVZ cells are still elusive. This study addresses these questions in mice carrying the deletion of p53, a tumor-suppressor gene expressed in the SVZ. We show here that, although loss of p53 by itself is not sufficient for tumor formation, it provides a proliferative advantage to the slow- and fast-proliferating subventricular zone (SVZ) populations associated with their rapid differentiation. This results in areas of increased cell density that are distributed along the walls of the lateral ventricles and often associated with increased p53-independent apoptosis. Transformation occurs when loss of p53 is associated with a mutagenic stimulus and is characterized by dramatic changes in the properties of the quiescent adult SVZ cells, including enhanced self-renewal, recruitment to the fast-proliferating compartment, and impaired differentiation. Together, these findings provide a cellular mechanism for how the slow-proliferating SVZ cells can give rise to glial tumors in the adult brain.

You can't go home again: transcriptionally driven alteration of cell signaling by NGF

Here we review findings indicating that neurotrophins such as NGF promote changes in gene transcription that in turn influence the ways that cells subsequently respond to trophic factors. As a result, initial responses of "naïve" cells to NGF and other trophic agents differ from those of cells with prior NGF exposure. We discuss specific examples based on reports in the literature as well as on data derived from a serial analysis of gene expression (SAGE) study of NGF-promoted transcriptional changes in PC12 pheochromocytoma cells.

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.

The role of p38 MAP kinase and c-Jun N-terminal protein kinase signaling in the differentiation and apoptosis of immortalized neural stem cells

The two distinct members of the mitogen-activated protein (MAP) kinase family c-Jun N-terminal protein kinase (JNK) and p38 MAP kinase, play an important role in central nervous system (CNS) development and differentiation. However, their role and functions are not completely understood in CNS. To facilitate in vitro study, we have established an immortal stem cell line using SV40 from fetal rat embryonic day 17. In these cells, MAP kinase inhibitors (SP600125, SB202190, and PD98059) were treated for 1, 24, 48, and 72 h to examine the roles of protein kinases. Early inhibition of JNK did not alter phenotypic or morphological changes of immortalized cells, however overexpression of Bax and decrease of phosphorylated AKT was observed. The prolonged inhibition of JNK induced polyploidization of immortalized cells, and resulted in differentiation and inhibition of cell proliferation. Moreover, JNK and p38 MAP kinase but not ERK1/2 was activated, and p21, p53, and Bax were overexpressed by prolonged inhibition of JNK. These results indicate that JNK and p38 MAP kinase could play dual roles on cell survival and apoptosis. Furthermore, this established cell line could facilitate study of the role of JNK and p38 MAP kinase on CNS development or differentiation/apoptosis.

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.

RB and RB2/p130 genes demonstrate both specific and overlapping functions during the early steps of in vitro neural differentiation of marrow stromal stem cells

Marrow stromal stem cells (MSCs) are stem-like cells that are currently being tested for their potential use in cell therapy for a number of human diseases. MSCs can differentiate into both mesenchymal and nonmesenchymal lineages. In fact, in addition to bone, cartilage and fat, it has been demonstrated that MSCs are capable of differentiating into neurons and astrocytes. RB and RB2/p130 genes are involved in the differentiation of several systems. For this reason, we evaluated the role of RB and RB2/p130 in the differentiation and apoptosis of MSCs under experimental conditions that allow for MSC differentiation toward the neuron-like phenotype. To this end, we ectopically expressed either RB or RB2/p130 and monitored proliferation, differentiation and apoptosis in rat primary MSC cultures induced to differentiate toward the neuron-like phenotype. Both RB and RB2/P130 decreased cell proliferation rate. In pRb-overexpressing cells, the arrest of cell growth was also observed in the presence of the HDAC-inhibitor TSA, suggesting that its antiproliferative activity does not rely upon the HDAC pathway, while the addition of TSA to pRb2/p130-overexpressing cells relieved growth inhibition. TUNEL reactions and studies on the expression of genes belonging to the Bcl-2 family showed that while RB protected differentiating MSCs from apoptosis, RB2/p130 induced an increase of apoptosis compared to controls. The effects of both RB and RB2/p130 on programmed cell death appeared to be HDAC- independent. Molecular analysis of neural differentiation markers and immunocytochemistry revealed that RB2/p130 contributes mainly to the induction of generic neural properties and RB triggers cholinergic differentiation. Moreover, the differentiation potentials of RB2/p130 and RB appear to rely, at least in part, on the activity of HDACs.

Expression profile of an operationally-defined neural stem cell clone

Neural stem cells (NSCs) are the most primordial and least committed cells of the nervous system, the cells that exist before regional specification develops. Because immunocytochemically-detectable markers that are sufficiently specific and sensitive to define an NSC have not yet been fully defined, we have taken the strong view that, to be termed a "stem cell" in the nervous system--in contrast to a "progenitor" or "precursor" (whose lineage commitment is further restricted)--a single neuroectodermally-derived cell must fulfill an operational definition that is essentially similar to that used in hematopoiesis. In other words, it must possess the following functional properties: (1) "Multipotency", i.e., the ability to yield mature cells in all three fundamental neural lineages throughout the nervous system--neurons (of all subtypes), astrocytes (of all types), oligodendrocytes--in multiple regional and developmental contexts and in a region and developmental stage-appropriate manner. (2) The ability to populate a developing region and/or repopulate an ablated or degenerated region of the nervous system with appropriate cell types. (3) The ability to be serially transplanted. (4) "Self-renewal", i.e., the ability to produce daughter cells (including new NSCs) with identical properties and potential. Having identified a murine neural cell clone that fulfills this strict operational definition--in contrast to other studies that used less rigorous or non-operational criteria for defining an NSC (e.g., the "neurosphere" assay)--we then examined, by comparing gene expression profiles, the relationship such a cell might have to (a) a multipotent somatic stem cell from another organ system (the hematopoietic stem cell [HSC]); (b) a pluripotent stem cell derived from the inner cell mass and hence without organ assignment (an embryonic stem cell); (c) neural cells isolated and maintained primarily as neurospheres but without having been subjected to the above mentioned operational screen ("CNS-derived neurospheres"). ESCs, HSCs, and operationally-defined NSCs--all of which have been identified not only by markers but by functional assays in their respective systems and whose state of differentiation could be synchronized--shared a large number of genes. Although, as expected, the most stem-like genes were expressed by ESCs, NSCs and HSCs shared a number of genes. CNS-derived neurospheres, on the other hand, expressed fewer "stem-like" genes held in common by the other operationally-defined stem cell populations. Rather they displayed a profile more consistent with differentiated neural cells. (Genes of neural identity were shared with the NSC clone.) Interestingly, when the operationally-defined NSC clone was cultured as a neurosphere (rather than in monolayer), its expression pattern shifted from a "stem-like" pattern towards a more "differentiated" one, suggesting that the neurosphere, without functional validation, may be a poor model for predicting stem cell attributes because it consists of heterogeneous populations of cells, only a small proportion of which are truly "stem-like". Furthermore, when operational definitions are employed, a common set of stem-like genes does emerge across both embryonic and somatic stem cells of various organ systems, including the nervous system.

Ischemia-stimulated neurogenesis is regulated by proliferation, migration, differentiation and caspase activation of hippocampal precursor cells

A brief ischemic injury to the gerbil forebrain that caused selective damage in the CA1 region of the hippocampus also enhanced the production of new cells in the hippocampal neurogenic area. When evaluated 1 week after bromodeoxyuridine (BrdU) injection, approximately ten times more labeled cells were detected in the hippocampal dentate gyrus in ischemic animals than controls, indicating a stimulation of mitotic activity. To assess the temporal course of the survival and fate of these newborn cells, we monitored BrdU labeling and cell marker expression up to 60 days after ischemia (DAI). Loss of BrdU-positive cells was observed from both control and ischemic animals, but at 30 DAI and afterward, the ischemic group maintained more than 3 times as many BrdU-positive cells as the control group. In addition, ischemic injury also fostered the neuronal differentiation of these cells beyond the capacity observed in control animals and facilitated the migration of developing neurons to a neuronal cellular layer. The establishment of a temporal correlation between differentiation and migration provides evidence of the functional maturation of these cells. Surprisingly, we found that ischemic injury induced activation of caspase-3, not only in the CA1 region as expected, but also in the dentate subgranular zone (SGZ). Active caspase-3 immunoreactivity in the subgranular layer was co-localized with an early neuronal marker, suggesting that caspase-mediated apoptosis could mediate the loss of neurogenic cells in the SGZ. Inhibiting caspase-3 in the context of ischemia-induced neurogenesis might provide an opportunity for functional repair and a therapeutic outcome in the wake of ischemic injury.

Lack of response to epidermal growth factor in adult neural progenitor cells

Neural progenitor/stem cells reside in the subventricular zone and dentate gyrus of the adult rat brain, which proliferate in response to several growth factors. Here we show that the neurospheres generated from the adult dentate gyrus and subventricular zone proliferate in vitro in response to fibroblast growth factor-2, but not epidermal growth factor. Likewise, extracellular signal-regulated kinase phosphorylation was stimulated by fibroblast growth factor-2, but not epidermal growth factor. Immunoblotting demonstrated negligible epidermal growth factor receptor content in these neurospheres, indicating that neural progenitor cells isolated from the adult rat brain are not responsive to epidermal growth factor in vitro, because of the lack of epidermal growth factor receptors and/or their signaling. However, the lack of response by epidermal growth factor in our study could be because of the culture conditions, and may not reflect the physiological condition.

Role of gap junctional intercellular communication (GJIC) through p38 and ERK1/2 pathway in the differentiation of rat neuronal stem cells

Gap junctional intercellular communications (GJIC) contributes to neural function in development and differentiation of CNS. In this study, we have investigated the expression of GJIC during the differentiation of neuronal stem cells and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced neuronal stem cell-derived cells from rat brain. During neuronal stem cell differentiation, expressions of Cx43 and 32 were increased for the duration of 72 hr, however the effect were decreased on the 7d. In the neuronal stem cell-derived cells, pretreatments with p38 MAP kinase inhibitor, SB203580, and MEK inhibitor, PD98059, could protect GJIC against TPA-induced inhibition of GJIC. Our data suggest that GJIC plays an important role during neuronal stem cell differentiation, and ERK1/2 and p38 MAP kinase signaling pathway may be closely related functionally to regulate gap junction in rat neuronal stem cell-derived cells.

In vitro differentiated neural stem cells express functional glial glutamate transporters

The possibility to isolate stem cells from the adult central nervous system and to maintain and propagate these cells in vitro has raised a general interest with regards to their use in cell replacement therapy for degenerative brain diseases. Considering the critical role played by astrocytes in the control of glutamate homeostasis, we have characterised the expression of functional glutamate transporters in neural stem cells exposed to selected culture conditions favouring their differentiation into astrocytes. Commonly, neural stem cells proliferate in suspension as neurospheres in serum-free medium. The addition of serum or a supplement of growth factors (G5) to the culture medium was found to trigger cell adhesion on coated surfaces and to favour their differentiation. Indeed, after 7 days in these conditions, the vast majority of the cells adopted markedly distinct morphologies corresponding to protoplasmic (with serum) or fibrous (with G5 supplement) astrocytes and approximately 35-40% acquired the expression of the glial fibrillary acidic protein (GFAP). Immunocytochemical analysis also revealed that the treatments with serum or with the G5 supplement triggered the expression of the glial glutamate transporters GLT-1 (35 and 21%, respectively) and GLAST (29 and 69%, respectively). This effect was correlated with a robust increase in the Na+ -dependent [3H]-d-aspartate uptake, which was partially inhibited by dihydrokainate, a selective blocker of GLT-1. Together, these results indicate that in vitro differentiation of cultured neural stem cells can give rise to distinct populations of astrocytes expressing functional glutamate transporters.

Role of RB and RB2/P130 genes in marrow stromal stem cells plasticity

Marrow stromal cells (MSCs) are stem-like cells having a striking somatic plasticity. In fact, besides differentiating into mesenchymal lineages (bone, cartilage, and fat), they are capable of differentiating into neurons and astrocytes in vitro and in vivo. The RB and RB2/P130 genes, belonging to the retinoblastoma gene family, play a key role in neurogenesis, and for this reason, we investigated their role in neural commitment and differentiation of MSCs. In MSCs that were either uncommitted or committed toward neural differentiation, we ectopically expressed RB and RB2/P130 genes and analyzed their role in regulating the cell cycle, apoptosis and differentiation. In uncommitted MSCs, the activity of RB and RB2/P130 appeared limited to negatively regulating cell cycle progression, having no role in apoptosis and differentiation (toward either mesenchymal or neural lineages). On the other hand, in MSCs committed toward the neural phenotype, both RB and RB2/P130 reduced cell proliferation rate and affected the apoptotic process. RB protected differentiating cells from programmed cell death. On the contrary, RB2/P130 increased the percentage of cells in apoptosis. All of these activities were accomplished mainly in an HDAC-independent way. The retinoblastoma genes also influenced differentiation in neural committed MSCs. RB2/P130 contributes mainly to the induction of generic neural properties, while RB triggers cholinergic differentiation. These differentiating activities are HDAC-dependent. Our research shows that there is a critical temporal requirement for the RB genes during neuronal differentiation of MSCs: they are not required for cell commitment but play a role in the maturation process. For the above reasons, RB and RB2/P130 may have a role in neural differentiation but not in neural determination.

FDG PET can replace bone scintigraphy in primary staging of malignant lymphoma

Recent studies indicated that 18F-fluorodeoxyglucose (FDG) PET may be more accurate than CT in staging nodal and extranodal malignant lymphoma. The objective of this study was to compare conventional bone scintigraphy as an established skeletal staging procedure with PET using FDG in the detection of osseous involvement in malignant lymphoma.

METHODS

Whole-body PET-based staging studies of 56 consecutive patients with proven Hodgkin's disease (n = 34) or non-Hodgkin's lymphoma (n = 22) were compared with the results of bone scintigraphy. Positive PET or bone scintigraphic findings were confirmed, if possible, by biopsy, MRI, CT or radiographic investigations.

RESULTS

Of the 56 patients studied, 12 were found to have skeletal involvement on both studies (PET, 30 regions; bone scintigraphy, 20 regions). Findings were confirmed in all 12 patients. FDG PET detected an additional 12 involved regions in 5 patients. This was subsequently verified in 3 patients, although the other 2 cases remained unresolved. Conversely, bone scintigraphy revealed five abnormalities compatible with lymphoma in 5 patients. Three of these lesions were found to be erroneous; final evaluation of the remaining two findings was not possible.

CONCLUSION

FDG PET is suitable for identifying osseous involvement in malignant lymphoma with a high positive predictive value and is thereby more sensitive and specific than bone scintigraphy.