Human neural stem cells in vitro. A focus on their isolation and perpetuation

Effects of cytomegalovirus infection in human neural precursor cells depend on their differentiation state

Cytomegalovirus (CMV) is the most common cause of congenital infection in developed countries and a major cause of neurological disability in children. Although CMV can affect multiple organs, the most important sequelae of intrauterine infection are related to lesions of the central nervous system. However, little is known about the pathogenesis and the cellular events responsible for neuronal damage in infants with congenital infection. Some studies have demonstrated that neural precursor cells (NPCs) show the greatest susceptibility to CMV infection in the developing brain. We sought to establish an in vitro model of CMV infection of the developing brain in order to analyze the cellular events associated with invasion by this virus. To this end, we employed two cell lines as a permanent source of NPC, avoiding the continuous use of human fetal tissue, the human SK-N-MC neuroblastoma cell line, and an immortalized cell line of human fetal neural origin, hNS-1. We also investigated the effect of the differentiation stage in relation to the susceptibility of these cell lines by comparing the neuroblastoma cell line with the multipotent cell line hNS-1. We found that the effects of the virus were more severe in the neuroblastoma cell line. Additionally, we induced hNS-1 to differentiate and evaluated the effect of CMV in these differentiated cells. Like SK-N-MC cells, hNS-1-differentiated cells were also susceptible to infection. Viability of differentiated hNS-1 cells decreased after CMV infection in contrast to undifferentiated cells. In addition, differentiated hNS-1 cells showed an extensive cytopathic effect whereas the effect was scarce in undifferentiated cells. We describe some of the effects of CMV in neural stem cells, and our observations suggest that the degree of differentiation is important in the acquisition of susceptibility.

V-myc immortalizes human neural stem cells in the absence of pluripotency-associated traits

A better understanding of the molecular mechanisms governing stem cell self-renewal will foster the use of different types of stem cells in disease modeling and cell therapy strategies. Immortalization, understood as the capacity for indefinite expansion, is needed for the generation of any cell line. In the case of v-myc immortalized multipotent human Neural Stem Cells (hNSCs), we hypothesized that v-myc immortalization could induce a more de-differentiated state in v-myc hNSC lines. To test this, we investigated the expression of surface, biochemical and genetic markers of stemness and pluripotency in v-myc immortalized and control hNSCs (primary precursors, that is, neurospheres) and compared these two cell types to human Embryonic Stem Cells (hESCs) and fibroblasts. Using a Hierarchical Clustering method and a Principal Component Analysis (PCA), the v-myc hNSCs associated with their counterparts hNSCs (in the absence of v-myc) and displayed a differential expression pattern when compared to hESCs. Moreover, the expression analysis of pluripotency markers suggested no evidence supporting a reprogramming-like process despite the increment in telomerase expression. In conclusion, v-myc expression in hNSC lines ensures self-renewal through the activation of some genes involved in the maintenance of stem cell properties in multipotent cells but does not alter the expression of key pluripotency-associated genes.

Human olfactory bulb neural stem cells expressing hNGF restore cognitive deficit in Alzheimer's disease rat model

In this study, we aim to demonstrate the fate of allogenic adult human olfactory bulb neural stem/progenitor cells (OBNSC/NPCs) transplanted into the rat hippocampus treated with ibotenic acid (IBO), a neurotoxicant specific to hippocampal cholinergic neurons that are lost in Alzheimer's disease. We assessed their possible ability to survive, integrate, proliferate, and differentiate into different neuronal and glial elements: we also evaluate their possible therapeutic potential, and the mechanism(s) relevant to neuroprotection following their engraftment into the CNS milieu. OBNSC/NPCs were isolated from adult human olfactory bulb patients, genetically engineered to express GFP and human nerve growth factor (hNGF) by lentivirus-mediated infection, and stereotaxically transplanted into the hippocampus of IBO-treated animals and controls. Stereological analysis of engrafted OBNSCs eight weeks post transplantation revealed a 1.89 fold increase with respect to the initial cell population, indicating a marked ability for survival and proliferation. In addition, 54.71 ± 11.38%, 30.18 ± 6.00%, and 15.09 ± 5.38% of engrafted OBNSCs were identified by morphological criteria suggestive of mature neurons, oligodendrocytes and astrocytes respectively. Taken together, this work demonstrated that human OBNSCs expressing NGF ameliorate the cognitive deficiencies associated with IBO-induced lesions in AD model rats, and the improvement can probably be attributed primarily to neuronal and glial cell replacement as well as the trophic influence exerted by the secreted NGF.

Cells isolated from human glioblastoma multiforme express progesterone-induced blocking factor (PIBF)

Glioblastoma multiforme (GBM) is the most common and malignant tumor in the central nervous system. One of the contemporary hypotheses postulates that its pathogenesis is associated with the cancer stem cells (CSCs) which originate from mutations in the normal neural stem cells residing in their specific "niches." Simultaneously with its aggressive development the tumor suppresses the local immune system by different secreted and/or cell expressed factors. Progesterone-induced blocking factor (PIBF) is an immunomodulatory protein with known role in the regulation of the immune response in the reproductive system. Expression of PIBF has been described in some tumors as one of the factors suppressing the anti-tumor immunity. The aim of the present study was to check for the expression of PIBF from cells isolated from six GBMs. To characterize the cultured cells and to study the PIBF expression confocal microscopy, flow cytometry, ELISA, and real-time PCR were used. The results obtained showed expression of markers typical for cancer CSCs and secretion of interleukin 6 by the GBM-derived cultured cells. The results convincingly prove that PIBF is intracellularly expressed by the cultured cells from the all six GBM samples, and this fact is confirmed by three different methods-flow cytometry, confocal microscopy, and real-time PCR. This paper reports for the first time the expression of PIBF by GBM-derived cells cultured in vitro and reveals a new aspect of the immunosuppressive mechanism used by GBM in escaping the immune control.

Transcription factors expressed in embryonic and adult olfactory bulb neural stem cells reveal distinct proliferation, differentiation and epigenetic control

TF genomic markers associated with neurogenesis, proliferation, differentiation, and epigenetic control in human embryonic neural stem cells (hENSC(, and adult human olfactory bulb neural stem cells (OBNSC) were studied by immunohistochemistry (IHC) and DNA microarray. The biological impact of TF gene changes in the examined cell types was estimated using DAVID to specify a different GO class and signaling pathway based on KEGG database. Eleven, and twenty eight TF genes were up-regulated (fold change≤2-39) in OBNSC, and hENSC respectively. KEGG pathway analysis for the up-regulated TF genes revealed significant enrichments for the basal transcription factor pathway, and Notch signaling pathway in OBNSCs, and hENSCs, respectively. Immunofluorescence analysis revealed a significantly greater number of β-tubulin III (TUBB3), MAP, glial fibrillary acidic protein (GFAP), and O4 in hENSC when compared to those in OBNSC. Furthermore, the expression of epigenetic-related TF-genes SMARCC1, TAF12, and UHRF1 increased significantly in OBNSC when compared with hENSC.

Gene expression profile of adult human olfactory bulb and embryonic neural stem cell suggests distinct signaling pathways and epigenetic control

Global gene expression profiling was performed using RNA from human embryonic neural stem cells (hENSC), and adult human olfactory bulb-derived neural stem cells (OBNSCs), to define a gene expression pattern and signaling pathways that are specific for each cell lineage. We have demonstrated large differences in the gene expression profile of human embryonic NSC, and adult human OBNSCs, but less variability between parallel cultures. Transcripts of genes involved in neural tube development and patterning (ALDH1A2, FOXA2), progenitor marker genes (LMX1a, ALDH1A1, SOX10), proliferation of neural progenitors (WNT1 and WNT3a), neuroplastin (NPTN), POU3F1 (OCT6), neuroligin (NLGN4X), MEIS2, and NPAS1 were up-regulated in both cell populations. By Gene Ontology, 325 out of 3875 investigated gene sets were scientifically different. 41 out of the 307 investigated Cellular Component (CC) categories, 45 out of the 620 investigated Molecular Function (MF) categories, and 239 out of the 2948 investigated Biological Process (BP) categories were significant. KEGG Pathway Class Comparison had revealed that 75 out of 171 investigated gene sets passed the 0.005 significance threshold. Levels of gene expression were explored in three signaling pathways, Notch, Wnt, and mTOR that are known to be involved in NS cell fates determination. The transcriptional signature also deciphers the role of genes involved in epigenetic modifications. SWI/SNF DNA chromatin remodeling complex family, including SMARCC1 and SMARCE1, were found specifically up-regulated in our OBNSC but not in hENSC. Differences in gene expression profile of transcripts controlling epigenetic modifications, and signaling pathways might indicate differences in the therapeutic potential of our examined two cell populations in relation to in cell survival, proliferation, migration, and differentiation following engraftments in different CNS insults.

Neural tissue-spheres: A microexplant culture method for propagation of precursor cells from the rat forebrain subventricular zone

By combining new and established protocols we have developed a procedure for isolation and propagation of neural precursor cells from the forebrain subventricular zone (SVZ) of newborn rats. Small tissue blocks of the SVZ were dissected and propagated en bloc as free-floating neural tissue-spheres (NTS) in EGF and FGF2 containing medium. The spheres were cut into quarters when passaged every 10-15th day, avoiding mechanical or enzymatic dissociation in order to minimize cellular trauma and preserve intercellular contacts. For analysis of regional differences within the forebrain SVZ, NTS were derived from three rostro-caudal levels of the lateral ventricles (anterior, intermediate and posterior) and propagated separately. Explants from all three levels produced proliferating NTS, but "anterior" NTS in general grew to smaller sizes than "intermediate" and "posterior" NTS. Posterior NTS moreover maintained their neurogenic potential throughout 77 days of propagation, while the ability of anterior NTS to generate neurons severely declined from day 40. The present procedure describes isolation and long-term expansion of forebrain SVZ tissue with potential preservation of the endogenous cellular content, thus allowing experimental studies of neural precursor cells and their niche.

Cell Sorting Technique Based on Thermoresponsive Differential Cell Adhesiveness

Cell sorting of specific target cells from a mixture of different cell types is a prerequisite for development of functional engineered tissues based on stem-cell and tissue engineering. This paper presents a new method of cell sorting that uses a mixture of thermoresponsive cell-adhesive and non-cell-adhesive substances. The former substance is poly(N-isopropylacrylamide)-grafted gelatin (PNIPAM-gelatin) and the latter is PNIPAM. Graded cell adhesion, produced by mixed coating of these thermoresponsive substances at an appropriate mixing ratio, clearly differentiated the adhesive potentials of two bovine vascular cell types (endothelial cell and smooth muscle cell). The sequential procedures of detachment at room temperature and subsequent replating at 37 degrees C on dishes coated with a mixed coating with the same composition as that employed previously yielded remarkably pure target cells, as determined using confocal laser scanning fluorescence microscopy. This method, leading to harvesting of target cells, is characteristic of simple manipulation with no cell damage. Such advantages are expected to facilitate stem-cell and tissue engineering.

A novel, immortal, and multipotent human neural stem cell line generating functional neurons and oligodendrocytes

The discovery and study of neural stem cells have revolutionized our understanding of the neurogenetic process, and their inherent ability to adopt expansive growth behavior in vitro is of paramount importance for the development of novel therapeutics based on neural cell replacement. Recent advances in high-throughput assays for drug development and gene discovery dictate the need for rapid, reproducible, long-term expansion of human neural stem cells (hNSCs). In this view, the complement of wild-type cell lines currently available is insufficient. Here we report the establishment of a stable human neural stem cell line (immortalized human NSCs [IhNSCs]) by v-myc-mediated immortalization of previously derived wild-type hNSCs. These cells demonstrate three- to fourfold faster proliferation than wild-type cells in response to growth factors but retain rather similar properties, including multipotentiality. By molecular biology, biochemistry, immunocytochemistry, fluorescence microscopy, and electrophysiology, we show that upon growth factor removal, IhNSCs completely downregulate v-myc expression, cease proliferation, and differentiate terminally into three major neural lineages: astrocytes, oligodendrocytes, and neurons. The latter are functional, mature cells displaying clear-cut morphological and physiological features of terminally differentiated neurons, encompassing mostly the GABAergic, glutamatergic, and cholinergic phenotypes. Finally, IhNSCs produce bona fide oligodendrocytes in fractions up to 20% of total cell number. This is in contrast to the negligible propensity of hNSCs to generate oligodendroglia reported so far. Thus, we describe an immortalized hNSC line endowed with the properties of normal hNSCs and suitable for developing the novel, reliable assays and reproducible high-throughput gene and drug screening that are essential in both diagnostics and cell therapy studies.

Human stem cells isolated from adult skeletal muscle differentiate into neural phenotypes

Multipotent neural stem cells have been isolated from the adult [Kirschenbaum B, Nedergaard M, Preuss A, Barami K, Fraser RA, Goldman SA. In vitro neuronal production and differentiation by precursor cells derived from the adult human forebrain. Cereb Cortex 1994;4(6):576-89; Laywell ED, Kukekov VG, Steindler DA. Multipotent neurospheres can be derived from forebrain subependymal zone and spinal cord of adult mice after protracted postmortem intervals. Exp Neurol 1999;156:430-3; Pluchino S, Quattrini A, Brambilla E, Gritti A, Salani G, Dina G, et al. Injection of adult neurospheres induces recovery in a chronic model of multiple sclerosis. Nature 2003;422:688-94] and embryonic [Vescovi AL, Parati EA, Gritti A, Poulin P, Ferrario M, Wanke E, et al. Isolation and cloning of multipotential stem cells from the embryonic human CNS and establishment of transplantable human neural stem cell lines by epigenetic stimulation. Exp Neurol 1999;156:71-83] central nervous system (CNS). In addition, neural cells can be obtained from sources other than the CNS by differentiating stem cells from a non-neural source down a neural lineage. This has previously been performed with pluripotent embryonic stem cells and adult stem cells derived from rat bone marrow [Woodbury D, Schwarz EJ, Prockop DJ, Black IB. Adult rat and human bone marrow stromal cells differentiate into neurons. J Neurosci Res 2000;61:364-70; Woodbury D, Reynolds K, Black IB. Adult bone marrow stromal stem cells express germline, ectodermal, endodermal, and mesodermal genes prior to neurogenesis. J Neurosci 2002;69(6):908-17] and skeletal muscle [Romero-Ramos M, Vourc'h P, Young HE, Lucas PA, Wu Y, Chivatakarn O, et al. Neuronal differentiation of stem cells isolated from adult muscle. J Neurosci Res 2002;69:894-907]. Previously, we have isolated adult stem cells from human skeletal muscle with the potential to differentiate into mesoderm, ectoderm, and endoderm. The following in vitro experiments were designed to determine whether human adult stem cells behaved similarly to rat adult stem cells when both were isolated from skeletal muscle by the same procedure [Romero-Ramos M, Vourc'h P, Young HE, Lucas PA, Wu Y, Chivatakarn O, et al. Neuronal differentiation of stem cells isolated from adult muscle. J Neurosci Res 2002;69:894-907] and subjected to the same protocols to induce neurogenesis. The neural phenotypes that were created through the neurococktail or neurosphere protocol were analyzed for neural characteristics through morphology and immunohistochemistry antibody labeling for proteins to neurons (RT-97, beta-tubulin III, NF-160, NF-200, and synapsin), oligodendrocytes (CNPase and RIP), and astrocytes (GFAP). A calcium uptake assay also showed response to the neuronal excitotoxic agent glutamic acid. In conclusion, the neural differentiated stem cells derived from adult skeletal muscle may be a less invasive alternative for the treatment of CNS disorders over CNS derived neural stem cells.

Long-term expansion of human neural progenitor cells by epigenetic stimulation in vitro

Human neural progenitor cells (hNPCs) are currently believed to have important potential for clinical application and basic neuroscience research. In the present study, we have developed a new technique for expansion of human neural progenitor cells in vitro. We showed that the cultures of hNPCs in monolayer could keep the same features with that growing in neurospheres. These cells expressed the typical protein of neural progenitors, nestin, and could form neurons and astrocytes upon differentiation. Using this method, we achieved an exponential increase in cells number over a period of 240 days in vitro. We also confirmed these cells expressed the orphan nuclear receptor-related factor 1 (Nurr1). Furthermore, we acquired the GFP-expressing human neural progenitor cells using retroviral-mediated transgenic system. The results of present study indicate the feasibility of long-term in vitro expansion of human neural progenitor cells using the monolayer culture technique, which may be of value as vehicles for ex vivo gene transfer to the CNS and as a potential source for basic research of dopaminergic (DA) neurons development.

Long-term molecular and cellular stability of human neural stem cell lines

Human Neural Stem Cells (hNSCs) are excellent candidates for in vitro and in vivo molecular, cellular, and developmental research, and also for ex-vivo gene transfer and cell therapy in the nervous system. However, hNSCs are mortal somatic cells, and thus invariably enter an irreversible growth arrest after a finite number of cell divisions in culture. It has been proposed that this is due to telomere shortening. Here, we show that long-term cultured (up to 4 years) v-myc perpetuated hNSC lines do preserve short but stable and homogeneous telomeres (TRF and Q-FISH determinations). hNSC lines (but not strains) express high levels of telomerase activity, which is activated by v-myc, as demonstrated here. Telomerase activity is not constitutive, becoming non-detectable after differentiation (in parallel to v-myc down-regulation). hNSC lines also maintain a stable cell cycle length, mitotic potential, differentiation and neuron generation capacity, and do not express senescence-associated beta-galactosidase over years, as studied here. These data, collectively, help to explain the immortal nature of v-myc-perpetuated hNSC lines, and to establish them as excellent research tools for basic and applied neurobiological and translational studies.

Genetic perpetuation of in vitro expanded human neural stem cells: cellular properties and therapeutic potential

Long-term propagated human neural stem cells (self-renewing and multipotent) allow for the unlimited and predictable generation of different types of human neural cells in vitro. In addition, these cell lines may be of help for the elucidation of basic neuro-developmental issues, and also for the development of innovative therapeutic strategies for nervous system disorders (through cell replacement and/or gene transfer-based therapies). In this article we summarize our current knowledge about these long-term cultured cells, particularly that of immortalized cells, with the aim of critically addressing their usefulness and potential for therapeutic use. Perpetuation methods and in vitro properties of immortalized cells are analyzed. Although reports on in vivo studies are scarce, present data on survival, integration, migration, and differentiation of the cells indicate that they may be useful for the development of cellular and genetic therapies, in various models of neurodegeneration. A great deal of basic and applied research remains to be done in order to fully explore, understand, and exploit the therapeutic potential of human neural precursor cells.

Evaluation of progenitor cell cultures from human embryos for neurotransplantation

Human neural stem cells (HNSCs) are used in studies of neural development and differentiation, and are regarded as an alternative source of tissue for neural transplantation in degenerative diseases. Selection and standardization of HNSC samples is an important task in research and clinical approaches. We evaluated embryonal brain matter obtained from human 8-12-week-old fetuses by means of flow cytometry on a panel including: nestin; vimentin; NeuN; GFAP; beta-tubulin III; CD56; N-Cad; OB-Cad; HLA-ABC; HLA-DR; CD34, and annexin. Samples from embryos of even the same gestation differ dramatically regarding neural cell development, their phenotype and viability. The samples containing the highest proportion of stem cells and multipotent progenitors of neural types, and the least of definitive cells and antigens of histocompatibility, were selected for further expansion in serum-free medium. Secondary phenotyping 14 days later revealed again a marked heterogeneity of the cultures. For the final culturing for 24 h in a serum-containing medium we selected only samples having following phenotype: nestin+, and vimentin+ no less than 25%; HLA-DR+ and CD34+ no more than 5%; GFAP+ no more than 10%; beta-tubulin+ no more than 20%; CD56+, N-Cad+, OB-Cad+, HLA-A,B,C+, and annexin+ no more than 15%; cell viability no less than 60%. Immunocytochemical study of selected samples proved that numerous neural stem cells, and neuro- and glioblasts necessary for transplantation were present. Our results demonstrate that the flow cytometry phenotyping allows the screening and standardization of HNSC samples for further expansion and transplantation.

Alpha Gal is widely expressed in embryonic porcine stem cells and neural tissue

Fetal porcine neural xenografts are an alternative to human fetal tissue for cell based treatments of a number of neurodegenerative conditions but are currently limited by host immunological rejection. The expression of a major immunological epitope, Galalpha1-3Galbeta1-4GlcNAcbeta-R (alphaGal) was determined on stem cells and primary cells derived from E26 porcine fetal brains. alphaGal was detected on the majority of neural stem cells and cells from primary cell suspensions. The expression of this epitope paralleled the binding of human IgG and IgM to the cells, a binding that was significantly reduced with anti-alphaGal depleted human serum. This study demonstrates that alphaGal expression is extensive in embryonic porcine neural cells and will be of relevance to any clinical trials using this tissue.