Human neural stem cells express extra-neural markers

The angiopoietin-Tie2 pathway regulates Purkinje cell dendritic morphogenesis in a cell-autonomous manner

Neuro-vascular communication is essential to synchronize central nervous system development. Here, we identify angiopoietin/Tie2 as a neuro-vascular signaling axis involved in regulating dendritic morphogenesis of Purkinje cells (PCs). We show that in the developing cerebellum Tie2 expression is not restricted to blood vessels, but it is also present in PCs. Its ligands angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) are expressed in neural cells and endothelial cells (ECs), respectively. PC-specific deletion of Tie2 results in reduced dendritic arborization, which is recapitulated in neural-specific Ang1-knockout and Ang2 full-knockout mice. Mechanistically, RNA sequencing reveals that Tie2-deficient PCs present alterations in gene expression of multiple genes involved in cytoskeleton organization, dendritic formation, growth, and branching. Functionally, mice with deletion of Tie2 in PCs present alterations in PC network functionality. Altogether, our data propose Ang/Tie2 signaling as a mediator of intercellular communication between neural cells, ECs, and PCs, required for proper PC dendritic morphogenesis and function.

Endothelial Progenitor Cells in Moyamoya Disease: Current Situation and Controversial Issues

Due to the lack of animal models and difficulty in obtaining specimens, the study of pathogenesis of moyamoya disease (MMD) almost stagnated. In recent years, endothelial progenitor cells (EPCs) have attracted more and more attention in vascular diseases due to their important role in neovascularization. With the aid of paradigms and methods in cardiovascular diseases research, people began to explore the role of EPCs in the processing of MMD. In the past decade, studies have shown that abnormalities in cell amounts and functions of EPCs were closely related to the vascular pathological changes in MMD. However, the lack of consistent criteria, such as isolation, cultivation, and identification standards, is also blocking the way forward. The goal of this review is to provide an overview of the current situation and controversial issues relevant to studies about EPCs in the pathogenesis and etiology of MMD.

Insights into Endothelial Progenitor Cells: Origin, Classification, Potentials, and Prospects

With the discovery of endothelial progenitor cells (EPCs) in the late 1990s, a paradigm shift in the concept of neoangiogenesis occurred. The identification of circulating EPCs in peripheral blood marked the beginning of a new era with enormous potential in the rapidly transforming regenerative field. Overwhelmed with the revelation, researchers across the globe focused on isolating, defining, and interpreting the role of EPCs in various physiological and pathological conditions. Consequently, controversies emerged regarding the isolation techniques and classification of EPCs. Nevertheless, the potential of using EPCs in tissue engineering as an angiogenic source has been extensively explored. Concomitantly, the impact of EPCs on various diseases, such as diabetes, cancer, and cardiovascular diseases, has been studied. Within the limitations of the current knowledge, this review attempts to delineate the concept of EPCs in a sequential manner from the speculative history to a definitive presence (origin, sources of EPCs, isolation, and identification) and significance of these EPCs. Additionally, this review is aimed at serving as a guide for investigators, identifying potential research gaps, and summarizing our current and future prospects regarding EPCs.

Subependymal Zone: Immunohistochemically Distinct Compartment in the Adult Mammalian Forebrain

The subependymal zone (SEZ) lining lateral walls of the lateral cerebral ventricles represents the site of active neurogenesis in the brain of adult mammals. Peroxidase immunohistochemistry performed in paraffin-embedded sections reveals that structural organization of the SEZ differs from other regions in the brain. The SEZ is devoid of synapses that are abundant in the adjacent striatal neuropil. Therefore immunostaining of synaptophysin detects sharp borders of the SEZ. Using immunophenotypization, we identified cell types constituting the SEZ in the intact rat forebrain. The presence of neural progenitor/stem cells was confirmed by finding of nestin-immunopositive cells. Detection of the astroglial marker GFAP confirmed that astrocytes represented major supporting elements responsible for creating a unique microenvironment of the SEZ. One type of the astroglia participated in covering surfaces of the blood vessels and boundaries of the SEZ. The second astroglial cell type formed branched elongated tubes that enwrapped other SEZ cell types with their cytoplasmic extensions. The interior of astrocytic channels was occupied with small densely aggregated NCAM-immunoreactive neuroblasts. Bipolar morphology indicated that these cells probably underwent migration. Immunodetection of other neuronal markers like β-III tubulin, MAP-2 and Pan neurofilaments identified positive cells in the neighbouring brain parenchyma but not in the SEZ. The rostral migratory stream (RMS) linked with the anterior SEZ had a similar structural arrangement. It contained a large amount of nestin+and vimentin+cells. The RMS consisted of GFAP+astrocytic tubes ensheathing NCAM+neuroblasts. On the contrary to the SEZ, the RMS neuroblasts expressed β-III tubulin. However, markers of postmitotic neurons MAP-2, Pan neurofilaments and synaptophysin were not expressed in the RMS. Our study describes a complex histological structure of the rat SEZ, identifies its individual cell types and demonstrates a usefulness of immunohistochemical detection of cell-specific markers in a study of microenvironment forming neurogenic zones in the mammalian brain.

Ang1/Tie2 induces cell proliferation and migration in human papillary thyroid carcinoma via the PI3K/AKT pathway

The angiopoietin 1 (Ang1)/angiopoietin receptor (Tie2) signaling pathway may have a notable role in the pathogenesis of inflammatory diseases. The abnormal expression of angiopoietin 1 and Tie2 has also been reported in various malignant tumors, including papillary thyroid carcinoma (PTC). However, the role and mechanism of the Ang1/Tie2 pathway in the progression of PTC remains unclear. Therefore, the aims of the present study were to clarify this. Significantly high expression levels of Ang1 and Tie2 were observed in PTC tissues and cell lines. Furthermore, MTT and wound-healing assays revealed that the Ang1-mediated stimulation of human PTC cells resulted in increased proliferation and migration. Conversely, the downregulation of Tie2 levels using short hairpin RNA targeted at Tie2 abrogated the Ang1-mediated effect on cell proliferation and migration. In studying the expression of phosphoinositide-3 kinase (PI3K)/RAC serine/threonine-protein kinase (Akt) pathway, the upregulation of Ang1/Tie2 was found to be associated with the activation of the PI3K/Akt pathway in PTC. In conclusion, the data from the present study indicated that the Ang1/Tie2 induces PTC oncogenesis via the PI3K/Akt pathway, providing novel insights into human PTC therapy.

Vascular Transdifferentiation in the CNS: A Focus on Neural and Glioblastoma Stem-Like Cells

Glioblastomas are devastating and extensively vascularized brain tumors from which glioblastoma stem-like cells (GSCs) have been isolated by many groups. These cells have a high tumorigenic potential and the capacity to generate heterogeneous phenotypes. There is growing evidence to support the possibility that these cells are derived from the accumulation of mutations in adult neural stem cells (NSCs) as well as in oligodendrocyte progenitors. It was recently reported that GSCs could transdifferentiate into endothelial-like and pericyte-like cells both in vitro and in vivo, notably under the influence of Notch and TGFβ signaling pathways. Vascular cells derived from GBM cells were also observed directly in patient samples. These results could lead to new directions for designing original therapeutic approaches against GBM neovascularization but this specific reprogramming requires further molecular investigations. Transdifferentiation of nontumoral neural stem cells into vascular cells has also been described and conversely vascular cells may generate neural stem cells. In this review, we present and discuss these recent data. As some of them appear controversial, further validation will be needed using new technical approaches such as high throughput profiling and functional analyses to avoid experimental pitfalls and misinterpretations.

Three-dimensional self-organizing neural architectures: a neural stem cells reservoir and a system for neurodevelopmental studies

Complex microenvironmental stimuli influence neural cell properties. To study this, we developed a three-dimensional (3-D) neural culture system, composed of different populations including neurons, astrocytes, and neural stem cells (NSCs). In particular, these last-mentioned cells represent a source potentially exploitable to test drugs, to study neurodevelopment and cell-therapies for neuroregenerations. On seeding on matrigel in a medium supplemented with serum and mitogens, cells obtained from human fetal brain tissue formed 3-D self-organizing neural architectures. Immunocytochemical analysis demonstrated the presence of undifferentiated nestin+ and CD133+ cells, surrounded by β-tub-III+ and GFAP+ cells, suggesting the formation of niches containing potential human NSCs (hNSCs). The presence of hNSCs was confirmed by both neurosphere assay and RT-PCR, and their multipotentiality was demonstrated by both immunofluorescent staining and RT-PCR. Flow cytometry analysis revealed that neurosphere forming cells originating from at least two different subsets expressing, respectively, CD133 and CD146 markers were endowed with different proliferative and differentiation potential. Our data implicate that the complexity of environment within niches and aggregates of heterogeneous neural cell subsets may represent an innovative platform for neurobiological and neurodevelopmental investigations and a reservoir for a rapid expansion of hNSCs.

Growing tumor vessels: more than one way to skin a cat - implications for angiogenesis targeted cancer therapies

The establishment of a functional, integrated vascular system is instrumental for tissue growth and homeostasis. Without blood vessels no adequate nutrition and oxygen would be provided to cells, nor could the undesired waste products be efficiently removed. Blood vessels constitute therefore one of the largest and most complex body network whose assembly depends on the precise balance of growth factors acting in a complementary and coordinated manner with cells of several identities. However, the vessels that are crucial for life can also foster death, given their involvement in cancer progression towards malignancy and metastasis. Targeting tumor vasculature has thus arisen as an appealing anti-cancer therapeutic approach. Since the milestone achievements that vascular endothelial growth factor (VEGF) blockade suppressed angiogenesis and tumor growth in mice and prolonged the survival of cancer patients when administered in combination with chemotherapy, the clinical development of anti-VEGF(R) drugs has accelerated remarkably. FDA has approved the use of bevacizumab - a humanized monoclonal antibody against VEGF - in colorectal, lung and metastatic breast cancers in combination with standard chemotherapy. Additional broad-spectrum VEGF receptor tyrosine kinase inhibitors, such as sunitinib and sorafenib, are used in monotherapy for metastatic renal carcinoma, while sunitinib is also approved for imatinib resistant gastrointestinal stromal tumors and sorafenib for advanced stage hepatocellular carcinoma. Nevertheless, the survival benefit offered by VEGF(R) blockers, either as single agents or in combination with chemotherapy, is calculated merely in the order of months. Posterior studies in preclinical models have reported that despite reducing primary tumor growth, the inhibition of VEGF increased tumor invasiveness and metastasis. The clinical implications of these findings urge the need to reconcile these conflicting results. Anti-angiogenic therapy represents a significant step forth in cancer therapy and in our understanding of cancer biology, but it is also clear that we need to learn how to use it. What is the biological consequence of VEGF-blockade? Does VEGF inhibition starve the tumor to death - as initially postulated - or does it rather foster malignancy? Can anti-VEGF(R) therapy favor tumor vessel formation by VEGF-independent means? Tumors are very diverse and plastic entities, able to adapt to the harshest conditions; this is also reflected by the tumor vasculature. Lessons from the bench to the bedside and vice versa have taught us that the diversity of signals underlying tumor vessel growth will likely be responsive (or resistant) to distinct therapeutic approaches. In this review, we propose a reflection of the different strategies tumors use to grow blood vessels and how these can have impact on the (un)success of current anti-angiogenic therapies.

The angiogenic factor angiopoietin-1 is a proneurogenic peptide on subventricular zone stem/progenitor cells

In the adult mammalian brain, the subventricular zone (SVZ) hosts stem cells constantly generating new neurons. Angiopoietin-1 (Ang-1) is an endothelial growth factor with a critical role in division, survival, and adhesion of endothelial cells via Tie-2 receptor activity. Expression of Tie-2 in nonendothelial cells, especially neurons and stem cells, suggests that Ang-1 may be involved in neurogenesis. In the present work, we investigated the putative role of Ang-1 on SVZ neurogenesis. Immature cells from SVZ-derived neurospheres express Ang-1 and Tie-2 mRNA, suggesting a role for the Ang-1/Tie-2 system in the neurogenic niche. Moreover, we also found that Tie-2 protein expression is retained on differentiation in neurons and glial cells. Ang-1 triggered proliferation via activation of the ERK1/2 (extracellular signal-regulated kinase 1/2) mitogen-activated protein kinase (MAPK) kinase pathway but did not induce cell death. Accordingly, coincubation with an anti-Tie-2 neutralizing antibody prevented the pro-proliferative effect of Ang-1. Furthermore, Ang-1 increased the number of NeuN (neuronal nuclear protein)-positive neurons in cultures treated for 7 d, as well as the number of functional neurons, as assessed by monitoring [Ca(2+)](i) rises after application of specific stimuli for neurons and immature cells. The proneurogenic effect of Ang-1 is mediated by Tie-2 activation and subsequent mTOR (mammalian target of rapamycin kinase) mobilization. In agreement, neuronal differentiation significantly decreased after exposure to an anti-Tie-2 neutralizing antibody and to rapamycin. Moreover, Ang-1 elicited the activation of the SAPK (stress-activated protein kinase)/JNK (c-Jun N-terminal kinase) MAPK, involved in axonogenesis. Our work shows a proneurogenic effect of Ang-1, highlighting the relevance of blood vessel/stem cell cross talk in health and disease.

An Ang1-Tie2-PI3K axis in neural progenitor cells initiates survival responses against oxygen and glucose deprivation

Neural progenitor cells (NPCs) have the potential to survive brain ischemia and participate in neurogenesis after stroke. However, it is not clear how survival responses are initiated in NPCs. Using embryonic mouse NPCs and the in vitro oxygen and glucose deprivation (OGD) model, we found that angiopoietin-1 (Ang1) could prevent NPCs from OGD-induced apoptosis, as evidenced by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and annexin V labeling. Ang1 significantly elevated tunica intima endothelial kinase 2 (Tie2) autophosphorylation level, suggesting the existence of functional Tie2 receptors on NPCs. NPCs under OGD conditions exhibited reduction of Akt phosphorylation, decrease of the Bcl-2/Bax ratio, activation of caspase-3, cleavage of PARP, and downregulation of beta-catenin and nestin. Ang1 reversed the above changes concomitantly with significant rising of survival rates of NPCs under OGD, but all these effects of Ang1 could be blocked by either soluble extracellular domain of Tie2 Fc fusion protein (sTie2Fc) or the phosphoinositide 3-kinase (PI3K) inhibitor 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one (LY294002). Our findings suggest the existence of an Ang1-Tie2-PI3K signaling axis that is essential in initiation of survival responses in NPCs against cerebral ischemia and hypoxia.

Allorecognition of human neural stem cells by peripheral blood lymphocytes despite low expression of MHC molecules: role of TGF-beta in modulating proliferation

Neural stem cells (NSCs) transplantation has been proposed as a means of restoring damaged brain tissue, a possibility rendered more likely by reports of low NSCs immunogenicity in various experimental models because of low expression of MHC class I and II as well as co-stimulatory molecules. We investigated the immunogenicity of a human NSC line grown in normal culture conditions and in the presence of pro-inflammatory cytokines IFN-gamma and tumor necrosis factor alpha by one-way mixed lymphocyte reaction (MLR) experiments with peripheral blood lymphocytes from eight HLA-incompatible donors. NSCs stimulated lymphocyte proliferation in almost all donors tested, with stimulation indices in the range of the low-end distribution curve of MLR between donors. The healthy subject that gave negative MLR results was the best compatible donor with respect to NSC haplotype. Since we observed low MLR responses overall, we studied if NSCs might exert any immunomodulatory activity. We detected transcription and release of the immunomodulatory molecule transforming growth factor beta (TGF-beta)-1; moreover, the addition of TGF-beta1 in MLR experiments down-regulated proliferative responses. To further confirm the immunological potential of human NSCs, we studied xenogeneic recognition of NSCs by immunocompetent cells derived from C57BL/6 mice, showing that NSCs can elicit an allo(xeno) response ex vivo. Our data indicate that NSCs have low but not negligible immunogenic potential that is sufficient to activate peripheral lymphocytes. Secretion of TGF-beta1 might balance the immunogenicity of NSCs. Nevertheless, the possibility that allo-NSCs grafting might induce in the long term an immune activation, thus vanishing their therapeutical effect, should not be overlooked and deserves further investigation.

Human fetal aorta contains vascular progenitor cells capable of inducing vasculogenesis, angiogenesis, and myogenesis in vitro and in a murine model of peripheral ischemia

Vasculogenesis, the formation of blood vessels in embryonic or fetal tissue mediated by immature vascular cells (ie, angioblasts), is poorly understood. We report the identification of a population of vascular progenitor cells (hVPCs) in the human fetal aorta composed of undifferentiated mesenchymal cells that coexpress endothelial and myogenic markers. Under culture conditions that promoted cell differentiation, hVPCs gave rise to a mixed population of mature endothelial and mural cells when progenitor cells were stimulated with vascular endothelial growth factor-A or platelet-derived growth factor-betabeta. hVPCs grew as nonadherent cells and, when embedded in a three-dimensional collagen gel, reorganized into cohesive cellular cords that resembled mature vascular structures. hVPC-conditioned medium contained angiogenic substances (vascular endothelial growth factor-A and angiopoietin-2) and strongly stimulated the proliferation of endothelial cells. We also demonstrate the therapeutic efficacy of a small number of hVPCs transplanted into ischemic limb muscle of immunodeficient mice. hVPCs markedly improved neovascularization and inhibited the loss of endogenous endothelial cells and myocytes, thus ameliorating the clinical outcome from ischemia. We conclude that fetal aorta represents an important source for the investigation of the phenotypic and functional features of human vascular progenitor cells.

Different networks, common growth factors: shared growth factors and receptors of the vascular and the nervous system

Growth factors and their respective receptors are key regulators during development and for homeostasis of the nervous system. In addition, changes in growth factor function, availability or downstream signaling is involved in many neuropathological disorders like Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke and brain tumours. Research of the recent years revealed that some growth factors, initially discovered as neural growth factors are also affecting blood vessels [e.g. nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF)]. Likewise, vascular growth factors, such as vascular endothelial growth factor (VEGF), which was previously described as an endothelial cell specific mitogen, also affect neural cells. The discovery of shared growth factors affecting the vascular and the nervous system is of relevance for potential therapies of vascular and neurological diseases. This review aims to give an overview about the growing field of common growth factors and receptors within the two different networks.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Expression of the receptor tyrosine kinase Tie2 in neoplastic glial cells is associated with integrin beta1-dependent adhesion to the extracellular matrix

The abnormal function of tyrosine kinase receptors is a hallmark of malignant gliomas. Tie2 receptor tyrosine kinase is a specific endothelial cell receptor whose function is positively regulated by angiopoietin 1 (Ang1). Recently, Tie2 has also been found in the nonvascular compartment of several tumors, including leukemia as well as breast, gastric, and thyroid cancers. There is, however, little information on the function of the Ang1/Tie2 pathway in the non-stromal cells within human tumors. We found that surgical glioblastoma specimens contained a subpopulation of Tie2+/CD31- and Tie2+/GFAP+ cells, suggesting that Tie2 is indeed expressed outside the vascular compartment of gliomas. Furthermore, analysis of a tissue array consisting of 116 human glioma samples showed that Tie2 expression in the neoplastic glial cells was significantly associated with progression from a lower to higher grade. Importantly, Ang1 stimulation of Tie2+ glioma cells resulted in increased adherence of the cells to collagen I and IV, suggesting that Tie2 regulates glioma cell adhesion to the extracellular matrix. Conversely, the down-regulation of Tie2 levels by small interference RNA or the addition of soluble Tie2 abrogated the Ang1-mediated effect on cell adhesion. In studying the expression of cell adhesion molecules, we found that Tie2 activation was related to the up-regulation of integrin beta1 levels and the formation of focal adhesions. These results, together with the reported fact that malignant gliomas express high levels of Ang1, suggest the existence of an autocrine loop in malignant gliomas and that a Tie2-dependent pathway modulates cell-to-extracellular matrix adhesion, providing new insights into the highly infiltrative phenotype of human gliomas.

CD133+ renal progenitor cells contribute to tumor angiogenesis

In the present study, we tested the hypothesis that resident progenitor cells may contribute to tumor vascularization and growth. CD133+ cells were isolated from 30 human renal carcinomas and characterized as renal resident progenitor cells on the basis of the expression of renal embryonic and mesenchymal stem cell markers. CD133+ progenitors differentiated into endothelial and epithelial cells as the normal CD133+ counterpart present in renal tissue. In the presence of tumor-derived growth factors, these cells were committed to differentiate into endothelial cells able to form vessels in vivo in SCID mice. Undifferentiated CD133+ progenitors were unable to form tumors when transplanted alone in SCID mice. When co-transplanted with renal carcinoma cells, CD133+ progenitors significantly enhanced tumor development and growth. This effect was not attributable to the tumorigenic nature of CD133+ progenitor cells because the same results were obtained with CD133+ cells from normal kidney. CD133+ progenitors contributed to tumor vascularization as the majority of neoformed vessels present within the transplanted tumors were of human origin and derived from the co-transplanted CD133+ progenitors. In conclusion, these results indicate the presence of a renal progenitor cell population in renal carcinomas that may differentiate in endothelial cells and favor vascularization and tumor growth.

Glioblastoma-derived tumorospheres identify a population of tumor stem-like cells with angiogenic potential and enhanced multidrug resistance phenotype

We investigated in vitro the properties of selected populations of cancer stem-like cells defined as tumorospheres that were obtained from human glioblastoma. We also assessed their potential and capability of differentiating into mature cells of the central nervous system. In vivo, their tumorigenicity was confirmed after transplantation into the brain of non-obese diabetic/severe combined immunodeficient (NOD-SCID) mice. The angiogenic potential of tumorospheres and glioblastoma-derived cells grown as adherent cells was revealed by evaluating the release of angiogenic factors such as vascular endothelial growth factor and CXCL12 by ELISA, as well as by rat aortic ring assay. The proliferative response of tumorospheres in the presence of CXCL12 was observed for the first time. Multidrug resistance-associated proteins 1 and 3 as well as other molecules conferring multidrug resistance were higher when compared with primary adherent cells derived from the same tumor. Finally, we obtained cells from the tumor developing after grafting that clearly expressed the putative neural stem cell marker CD133 as shown by FACS analysis and also nestin and CXCR4. The cells' positivity for glial fibrillary acidic protein was very low. Moreover these cells preserved their angiogenic potential. We conclude that human glioblastoma could contain tumor cell subsets with angiogenic and chemoresistance properties and that this chemoresistance potential is highly preserved by immature cells whereas the angiogenic potential is, to a higher extent, a property of mature cells. A better understanding of the features of these cell subsets may favor the development of more specifically targeted therapies.

Human central nervous system tissue culture: a historical review and examination of recent advances

Tissue culture has been and continues to be widely used in medical research. Since the beginning of central nervous system (CNS) tissue culture nearly 100 years ago, the scientific community has contributed innumerable protocols and materials leading to the current wide variety of culture systems. While nonhuman cultures have traditionally been more widely used, interest in human CNS tissue culture techniques has accelerated since the middle of the last century. This has been fueled largely by the desire to model human physiology and disease in vitro with human cells. We review the history of human CNS tissue culture summarizing advances that have led to the current breadth of options available. The review addresses tissue sources, culture initiation, formats, culture ware, media, supplements and substrates, and maintenance. All of these variables have been influential in the development of culturing options and the optimization of culture survival and propagation.

Parallel analysis of multiple surface markers expressed on rat neural stem cells using antibody microarrays

Neural stem cells are the attractive cell source for functional regeneration of damaged central nervous tissues by means of cell transplantation or in situ induction of differentiated neural cells. Such stem cell therapies require the prospective identification and isolation of neural stem cells. However they are difficult due to limited information on surface markers. This study aimed at developing an antibody microarray that permits parallel analysis of multiple surface antigens expressed on neural stem cells present in a neurosphere-forming cell population. A microarray was prepared by micro-spotting antibodies directed to surface antigens and ligands for membrane-associated receptors onto the patterned monolayer of alkanethiols self-assembled on a gold-evaporated glass plate. Neurosphere-forming cells were subjected to a cell-binding assay on the microarray followed by immunofluorescent staining of nestin, an intracellular marker of neural stem cells. It was demonstrated that such a cell based assay facilitated to examine the specificity of surface antigens for nestin-positive neural stem cells. Furthermore, the microarray could also be used to assess proliferation capability of cells bound to individual spots. These results suggest that the microarray-based strategy will provide a useful tool for the parallel analysis of surface markers expressed on a specific cell type in a heterogeneous population.

Human neural stem/progenitor cells, expanded in long-term neurosphere culture, promote functional recovery after focal ischemia in Mongolian gerbils

Transplantation of human neural stem cells (NSCs) is a promising potential therapy for neurologic dysfunctions after the hyperacute stage of stroke in humans, but large amounts of human NSCs must be expanded in long-term culture for such therapy. To determine their possible therapeutic potential for human stroke, human fetal neural stem/progenitor cells (NSPCs) (i.e., neurosphere-forming cells) were isolated originally from forebrain tissues of one human fetus, and expanded in long-term neurosphere culture (exceeding 24 weeks), then xenografted into the lesioned areas in the brains of Mongolian gerbils 4 days after focal ischemia. Sensorimotor and cognitive functions were evaluated during the 4 weeks after transplantation. The total infarction volume in the NSPC-grafted animals was significantly lower than that in controls. Approximately 8% of the grafted NSPCs survived, mainly in areas of selective neuronal death, and were costained with antibodies against neuronal nuclei antibody (NeuN), microtubule associated protein (MAP-2), glial fibrillary acidic protein (GFAP), and anti-2'3' cyclic nucleotide 3'-phosphodiesterase (CNPase). Synaptic structures between NSPCs-derived neurons and host neurons were observed. Furthermore, gradual improvement of neurologic functions was observed clearly in the NSPC-grafted animals, compared to that in controls. Human NSPCs, even from long-term culture, remarkably improved neurologic functions after focal ischemia in the Mongolian gerbil, and maintained their abilities to migrate around the infarction, differentiate into mature neurons, and form synapses with host neuronal circuits. These results indicate that in vitro-expanded human neurosphere cells are a potential source for transplantable material for treatment of stroke.

Neuronal differentiation of murine bone marrow Thy-1- and Sca-1-positive cells

Recent evidence suggests that cells from bone marrow can acquire neuroectodermal phenotypes in cell culture or after transplantation in animal models and in the human brain. However, isolation of the bone marrow cell subpopulation with neuronal differentiation potential remains a challenge. To isolate and expand neural progenitors from whole murine bone marrow, bone marrow was obtained from hind limb bone of C57BL6 mice and plated in culture with neuronal medium with basic fibroblast growth factor and epidermal growth factor. After 5-7 days in culture, cellular spheres similar to brain neurospheres appeared either floating or attached to culture dishes. These spheres were collected, dissociated, and expanded. The bone marrow-derived spheres were positive for nestin as assessed by immunocytochemistry and by reverse transcriptase polymerase chain reaction. Thy-1- and Sca-1-positive bone marrow cells selected by magnetic cell sorting resulted in a higher yield of nestin-positive spheres. After exposure to neuronal differentiative medium retinoic acid with and without Sonic hedgehog, cells positive for neuronal markers tubulin III (TuJ-1) and neurofilament (NF) were detected. The mRNA profile of these cells included the expression of TuJ-1, neuronal-specific enolase (NSE), and NF-light chain. To evaluate the in vivo behavior of these cells, spheres derived from bone marrow-derived cells of transgenic green fluorescent protein (GFP) mice were transplanted into newborn mouse brain. Two months later, the mouse neural cortex contained a minor proportion of GFP(+) cells co-expressing neuronal markers (TuJ-1, NF, MAP-2, NeuN). Although cell fusion phenomena with the host cells could not be ruled out, bone marrow-derived neurosphere transplantation could be a strategy for cellular mediated gene therapy.

Genetically Engineered Stem Cell Therapy for Tissue Regeneration

Therapeutic angiogenesis/vasculogenesis represents a new approach to treat patients with ischemic disease not curable with conventional treatment. This review focuses on the rationale and preliminary results of combining stem cell and gene therapy for regenerative medicine. Under disease conditions, impaired neovascularization results from diminished vascular growth factor production and primary dysfunction of endothelial cells and their progenitors. Advances in our ability to genetically manipulate cells ex vivo has provided the technological platform to implement stem cell biology and circumvent the potential hazard of direct gene transfer. Ex vivo engineered endothelial progenitor cells have been used for the treatment of peripheral limb ischemia. The approach eliminates the drawback of immune response against viral vectors and makes feasible repeating the therapeutic procedure in case of injury recurrence. The strategy of using stem cells as vectors for curative agents proved to be of value for the treatment of pulmonary hypertension and thrombosis. Transplantation of neural stem cells genetically modified to secrete nerve growth factor was able to ameliorate the death of striatal projection neurons caused by transient focal ischemia in the adult rat. By a similar approach, engineered neural stem cells might be used for treating neurodegenerative disorders. Therefore, genetic manipulation of stem cells opens new avenues for regenerative medicine.

Neuronal and glial differentiation following culture of the human embryonic cortical stem cells

OBJECTIVE

To set up long-term in vitro culture system of the human neural stem cells (hNSC) and to study their biological properties.

METHODS

Human fetuses aged about 20 weeks following spontaneous abortion were adopted. A serum-free medium containing basic fibroblast growth factor and epidermal growth factor was used to make the hNSCs divide continuously in the culture. The growth curve of continually passaged cells was examined. The effects of long-term culture on the cell cycle, cell differentiation were analyzed. The cell cycles of these cells were analyzed using flow cytometry.

RESULTS

The cells from the human embryonic cortical tissue could be maintained and propagated in the presence of growth factors. Neurospheres were generated continually. Only one month after the primary culture, the precursors could be effectively discarded. The cells could be cultured for ten months. The cells had an exponential, consistent growth. The cell cycle analysis indicated that the hNSCs maintained remarkable proliferation. Upon differentiation, the hNSCs gave rise to mature cells. The multi-lineage potential of differentiation after different passages remained unchanged.

CONCLUSION

The hNSCs isolated from the human embryonic tissues retained their biological features after long-term culture in vitro.

Neurosphere and neurosphere-forming cells: morphological and ultrastructural characterization

Despite recent advances in our understanding of neural stem cell (NSC) biology, the free-floating structures generated by these cells in vitro, the "neurospheres", have not been fully characterized. To fill this gap, we examined neurospheres and neurosphere-derived NSCs by confocal microscopy, electron microscopy (EM) and cytofluorimetry. Here, we show that neurospheres and neurosphere-forming cells are morphologically and functionally heterogeneous. Confocal microscopy reveals differences in cell size, viability, cytoplasmic content and in the presence and distribution of active mitochondria. By electron microscopy, neurospheres appear as complex structures in which biological events such as mitosis, apoptosis and even phagocytosis are influenced by NSCs localization within the architecture of the neurosphere. NSCs derived from neurospheres are not synchronized and are represented in all phases of the cell cycle. Cytofluorimetric studies demonstrate NSCs' heterogeneity in cell size by forward scatter (FSC) analysis, and in cytoplasmic granularity by side scatter (SSC) profiling. These findings may contribute to our understanding of the morphogenesis of the neurospheres, particularly as this process relates to the high environmental adaptability of the NSCs and the reported existence of different subpopulations of neural stem cells.

Angiogenesis In Vitro: Vascular Tube Formation From the Differentiation of Neural Stem Cells

Neural stem cells (NSCs) were isolated from the mouse cortex on embryonic day 12.5 and cultured by neurosphere formation in serum-free medium in the presence of basic fibroblast growth factor (bFGF). When NSCs were inoculated in collagen gels with 10% fetal bovine serum (FBS) and bFGF and incubated for 10 days, vessel-like tube structures consisting of PECAM-1- or VE-cadherin-immunoreactive cells were formed in the gels. Moreover, the formation of vascular tube-like structures with a massive investment of alpha-smooth muscle actin-immunoreactive or GFAP-immunoreactive cells was occasionally observed, indicating angiogenesis identical to cerebral vascular development in vivo. To examine whether NSCs are capable of producing endothelial cells, differentiation was induced by the addition of 10% FBS after bFGF withdrawal. Most of the cells displayed a cobblestone-like morphology. Immunological analyses and RT-PCR indicated that NSCs expressed endothelial cell-specific marker proteins such as PECAM-1, VE-cadherin, and Flk-1; and these expressions were maintained or up-regulated during differentiation. Similar tube structures were also observed when the differentiated cells were inoculated in collagen gels and incubated for 5 days. These results suggested that NSCs give rise to two types of vascular cells, endothelial cells and mural cells in vitro, which have the ability to form vascular tubes.

Paracrine control of vascularization and neurogenesis by neurotrophins

The neuronal system plays a fundamental role in the maturation of primitive embryonic vascular network by providing a paracrine template for blood vessel branching and arterial differentiation. Furthermore, postnatal vascular and neural regeneration cooperate in the healing of damaged tissue. Neurogenesis continues in adulthood although confined to specific brain regions. Following ischaemic insult, neural staminal cells contribute towards the healing process through the stimulation of neurogenesis and vasculogenesis. Evidence indicates that nerves and blood vessels exert a reciprocal control of their own growth by paracrine mechanisms. For instance, guidance factors, including vascular endothelial growth factor A (VEGF-A) and semaphorins, which share the ability of binding neuropilin receptors, play a pivotal role in the tridimensional growth pattern of arterial vessels and nerves. Animal models and clinical studies have demonstrated a role of VEGF-A in the pathogenesis of ischaemic and diabetic neuropathies. Further, supplementation with VEGF-A ameliorates neuronal recovery by exerting protective effects on nerves and stimulating reparative neovascularization. Human tissue kallikrein, a recently discovered angiogenic and arteriogenic factor, accelerates neuronal recovery by stimulating the growth of vasa nervorum. Conversely, the neurotrophin nerve growth factor, known to regulate neuronal survival and differentiation, is now regarded as a stimulator of angiogenesis and arteriogenesis. These results indicate that angiogenesis and neurogenesis are paracrinally regulated by growth factors released by endothelial cells and neurons. Supplementation of these growth factors, alone or in combination, could benefit the treatment of ischaemic diseases and neuropathies.