Unique astrocyte ribbon in adult human brain contains neural stem cells but lacks chain migration

Fibroblast growth factor-2 increases the expression of neurogenic genes and promotes the migration and differentiation of neurons derived from transplanted neural stem/progenitor cells

The capacity of neural stem cells (NSC) to generate different types of neurons and glia depends on the action of intrinsic determinants and extracellular signals. Here, we isolated adult olfactory bulb stem cells (aOBSC) that express nestin, RC2 and Sox2, and that have the capacity to generate neurons possessing mature features in culture and in vivo. The differentiation of aOBSC into neurons and glia, as well as their genetic profile, was compared to that of embryonic OBSC (eOBSC) and ganglionic eminence stem cells (GESC). While these eOBSC express neurogenin (Ngn) 1 and 2, two telencephalic dorsal markers, GESC only express Ngn2. Adult OBSC express either little or no detectable Ngn1 and 2, and they produced significantly fewer neurons in culture than eOBSC. By contrast, Dlx2 transcripts (a telencephalic ventral marker) were only clearly detected in GESC. When transplanted into the early postnatal P5-P7 OB, each of the three populations gave rise to cells with a distinct pattern of neuronal migration and/or dendritic arborization. Overall, these findings suggest that cultured NSC partially maintain their regional and temporal specification. Notably, significant neuronal migration and differentiation were only observed in vivo when the NSC were briefly exposed to fibroblast growth factor-2 (FGF-2) before grafting, a treatment that enhanced the neurogenin expression. Hence, the migration and maturation of neurons derived from transplanted NSC can be promoted by upregulating neurogenic gene expression with FGF-2.

Regenerative capacity of neural precursors in the adult mammalian brain is under the control of p53

The question of whether or not stem cell loss drives aging in the brain has not been fully resolved. Here, we used mice over-expressing the short isoform of p53 (DeltaNp53 or p44) as a model of aging to gain insight into the cellular mechanisms underlying age-related functional deficits in the brain. By BrdU labeling, we observed an accelerated decline in the number of subventricular zone proliferating cells with age in p44Tg mice compared to mice with normal p53 expression. A 2-3-fold reduction in the number of slowly dividing stem cells was evident in the subventricular zone of 9-12-month-old p44Tg mice, but not in younger p44Tg mice or in normal mice. Consequently, the supply of new olfactory bulb neurons was also reduced. The number and size of neurospheres generated from subventricular zone cells from p44Tg mice was significantly reduced, and cells derived from these neurospheres had limited self-renewal and amplification capacities. At the cellular level, p44 lengthened the cell cycle and affected cell cycle reentry properties, evident by an increased proportion of cells in G0. At the functional level, p44 expression resulted in impaired olfactory discrimination in 15-16-month-old mice. This phenotype is driven by constitutive activation of p53 and constitutive expression of p21(Cip1/waf1) in neural stem cells. Our results demonstrate that p53 plays a crucial role in the maintenance of the regenerative capacity of the brain by regulating the proliferation of stem and progenitor cells.

Changes in adult olfactory bulb neurogenesis in mice expressing the A30P mutant form of alpha-synuclein

In familial and sporadic forms of Parkinson's disease (PD), alpha-synuclein pathology is present in the brain stem nuclei and olfactory bulb (OB) long before Lewy bodies are detected in the substantia nigra. The OB is an active region of adult neurogenesis, where newly generated neurons physiologically integrate. While accumulation of wild-type alpha-synuclein is one of the pathogenic hallmarks of non-genetic forms of PD, the A30P alpha-synuclein mutation results in an earlier disease onset and a severe clinical phenotype. Here, we study the regulation of adult neurogenesis in the subventricular zone (SVZ)/OB system in a tetracycline-suppressive (tet-off) transgenic model of synucleinopathies, expressing human mutant A30P alpha-synuclein under the control of the calcium/calmodulin-dependent protein kinase II alpha (CaMK) promoter. In A30P transgenic mice alpha-synuclein was abundant at the site of integration in the glomerular cell layer of the OB. Without changes in proliferation in the SVZ, significantly fewer newly generated neurons were observed in the OB granule cell and glomerular layers of A30P transgenic mice than in controls, most probably due to increased cell death. By tetracycline-dependent abrogation of A30P alpha-synuclein expression, OB neurogenesis and programmed cell death was restored to control levels. Our results indicate that, using A30P conditional (tet-off) mice, A30P alpha-synuclein has a negative impact on olfactory neurogenesis and suppression of A30P alpha-synuclein enhances survival of newly generated neurons. This finding suggests that interfering with alpha-synuclein pathology can rescue newly generated neurons, possibly leading to new targets for therapeutic interventions in synucleinopathies.

Adult neural stem cells and their role in brain pathology

Stem cells are multipotent cells that can give rise to a differentiated progeny as well as self-renew. The balanced coordination of these two stem cell fates is essential for embryonic development and tissue homeostasis in the adult. Perturbed stem cell function contributes significantly to a variety of pathological conditions, eg impaired self-renewal capacity due to cellular senescence contributes to ageing, and degenerative diseases or impaired stem cell differentiation by oncogenic mutations contribute to cancer formation. This review focuses on the molecular mechanisms involved in regulating the normal function of neural stem cells in the adult mammalian brain and on the involvement of these cells in brain pathology.

Attributes of adult stem cells

While cultured embryonic stem (ES) cells can be harvested in abundance and appear to be the most versatile of cells for regenerative medicine, adult stem cells also hold promise, but the identity and subsequent isolation of these comparatively rare cells remains problematic in most tissues, perhaps with the notable exception of the bone marrow. The ability to continuously self-renew and produce the differentiated progeny of the tissue of their location are their defining properties. Identifying surface molecules (markers) that would aid in stem cell isolation is a major goal. Considerable overlap exists between different putative organ-specific stem cells in their repertoire of gene expression, often related to self-renewal, cell survival and cell adhesion. More robust tests of 'stemness' are now being employed, using lineage-specific genetic marking and tracking to show production of long-lived clones and multipotentiality in vivo. Moreover, the characterization of normal stem cells in specific tissues may provide a dividend for the treatment of cancer. The successful treatment of neoplastic disease may well require the specific targeting of neoplastic stem cells, cells that may well have many of the characteristics of their normal counterparts.

Ultrastructural and antigenic properties of neural stem cells and their progeny in adult rat subventricular zone

Neural stem cells (NSCs) in the subventricular zone (SVZ) continuously generate olfactory bulb interneurons in the adult rodent brain. Based on their ultrastructural and antigenic properties, NSCs, transient amplifying precursor cells, and neuroblasts (B, C, and A cells, respectively) have been distinguished in mouse SVZ. Here, we aimed to identify these cell types in rat SVZ ultrastructurally and at the light microscopy level, and to determine the antigenic properties of each cell type using gold and fluorescence immunolabeling. We found astrocytes with single cilia (NSCs, correspond to B cells) and neuroblasts (A cells). We also observed mitotic cells, ependymal cells, displaced ependymal cells, and mature astrocytes. In contrast, transient amplifying precursor cells (C cells) were not detected. The NSCs and neuroblasts had epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor alpha (PDGFRalpha) expressed on the ciliary apparatus and were the only cell types incorporating the proliferation marker BrdU. Throughout mitosis, EGFR and PDGFRalpha were associated with the microtubule of the mitotic spindle. Ependymal and displaced ependymal cells also expressed EGFR and PDGFRalpha on their cilia but did not incorporate BrdU. Our findings indicate that the NSCs in adult rat SVZ give rise directly to neuroblasts. During mitosis, the NSCs disassemble the primary cilium and symmetrically distribute EGFR and PDGFRalpha among their progeny.

A comparison between stem cells from the adult human brain and from brain tumors

OBJECTIVE

To directly compare stem cells from the normal adult human brain (adult human neural stem cells [AHNSC]), Grade II astrocytomas (AC II), and glioblastoma multiforme (GBM), with respect to proliferative and tumor-forming capacity and differentiation potential.

METHODS

Cells were isolated from tissue obtained during epilepsy surgery (AHNSCs) or tumor surgery (glioma stem cells [GSC]). They were cultured and investigated in vitro or after transplantation in immunodeficient mice.

RESULTS

Under identical experimental conditions, the following were found: 1) GBM stem cells formed tumors after orthotopic transplantation; AHNSCs showed no sign of tumor formation; 2) GSCs showed a significantly higher growth rate and self-renewal capacity; 3) both the growth rate and telomerase expression were high in GSCs and correlated with malignancy grade (GBM higher than AC II); AHNSCs had low telomerase expression; 4) GSCs invaded normal neurospheres, not vice versa; 5) both AHNSCs and stem cells from AC II and GBM responded to differentiation cues with a dramatic decrease in the proliferation index (Ki-67); 6) GSCs differentiated faster than AHNSCs; 7) upon differentiation, AHNSCs produced normal glia and neurons; GSCs produced morphologically aberrant cells often expressing both glial and neuronal antigens; and 8) differentiation of AHNSCs resulted in 2 typical functional phenotypes: neurons (high electrical membrane resistance, ability to generate action potentials) and glial cells (low membrane resistance, no action potentials). In contrast, GSCs resulted in only 1 functional phenotype: cells with high electrical resistance and active membrane properties capable of generating action potentials.

CONCLUSION

AHNSCs and stem cells from AC II and GBM differ with respect to proliferation, tumor-forming capacity, and rate and pattern of differentiation.

Targeted therapy in the treatment of malignant gliomas

Malignant gliomas are invasive tumors with the potential to progress through current available therapies. These tumors are characterized by a number of abnormalities in molecular signaling that play roles in tumorigenesis, spread, and survival. These pathways are being actively investigated in both the pre-clinical and clinical settings as potential targets in the treatment of malignant gliomas. We will review many of the therapies that target the cancer cell, including the epidermal growth factor receptor, mammalian target of rapamycin, histone deacetylase, and farnesyl transferase. In addition, we will discuss strategies that target the extracellular matrix in which these cells reside as well as angiogenesis, a process emerging as central to tumor development and growth. Finally, we will briefly touch on the role of neural stem cells as both potential targets as well as delivery vectors for other therapies. Interdependence between these varied pathways, both in maintaining health and in causing disease, is clear. Thus, attempts to easily classify some targeted therapies are problematic.

Foetal Alcohol Spectrum Disorders and alterations in brain and behaviour

The term 'Foetal Alcohol Spectrum Disorders (FASD)' refers to the range of disabilities that may result from prenatal alcohol exposure. This article reviews the effects of ethanol on the developing brain and its long-term structural and neurobehavioural consequences. Brain imaging, neurobehavioural and experimental studies demonstrate the devastating consequences of prenatal alcohol exposure on the developing central nervous system (CNS), identifying specific brain regions affected, the range of severity of effects and mechanisms involved. In particular, neuroimaging studies have demonstrated overall and regional volumetric and surface area reductions, abnormalities in the shape of particular brain regions, and reduced and increased densities for white and grey matter, respectively. Neurobehaviourally, FASD consists of a continuum of long-lasting deficits affecting multiple aspects of cognition and behaviour. Experimental studies have also provided evidence of the vulnerability of the CNS to the teratogenic effects of ethanol and have provided new insight on the influence of risk factors in the type and severity of observed brain abnormalities. Finally, the potential molecular mechanisms that underlie the neuroteratological effects of alcohol are discussed, with particular emphasis on the role of glial cells in long-term neurodevelopmental liabilities.

Gene and cell delivery to the degenerated striatum: status of preclinical efforts in primate models

Significant progress has been achieved in developing restorative neurosurgical strategies for movement disorders on the basis of preclinical gene and cell therapy experiments in primates. Because of the unique similarities between human and primate anatomy and physiology, experiments in primate models are the critical step in translating these innovative neurosurgical treatment concepts into successful human applications. To clarify progress toward this goal, we have examined recent preclinical data regarding the delivery of gene and cell therapy to the lesioned primate striatum. Improved behavioral outcomes after in vivo gene transduction, achieved by brain delivery of adeno-associated vectors, have resulted in the initiation of ongoing clinical trials. Cell transplantation experiments are transitioning from the grafting of fetal tissue, which has met with mixed clinical success, to the grafting of expanded neural stem cells, for which preliminary results in primates are encouraging. Careful attention to the surgical delivery parameters for these agents in primate studies, along with the ability to realistically model imaging and behavioral outcomes in these animals, is essential for optimizing the restoration of function for patients. The authors review data obtained from primate models that form the basis for ongoing clinical trials to consider how new preclinical models should be developed to answer questions that arise from experimental clinical data.

Malignant astrocytomas originate from neural stem/progenitor cells in a somatic tumor suppressor mouse model

Malignant astrocytomas are infiltrative and incurable brain tumors. Despite profound therapeutic implications, the identity of the cell (or cells) of origin has not been rigorously determined. We previously reported mouse models based on conditional inactivation of the human astrocytoma-relevant tumor suppressors p53, Nf1, and Pten, wherein through somatic loss of heterozygosity, mutant mice develop tumors with 100% penetrance. In the present study, we show that tumor suppressor inactivation in neural stem/progenitor cells is both necessary and sufficient to induce astrocytoma formation. We demonstrate in vivo that transformed cells and their progeny undergo infiltration and multilineage differentiation during tumorigenesis. Tumor suppressor heterozygous neural stem/progenitor cultures from presymptomatic mice show aberrant growth advantage and altered differentiation, thus identifying a pretumorigenic cell population.

Transplanted human embryonic neural stem cells survive, migrate, differentiate and increase endogenous nestin expression in adult rat cortical peri-infarction zone

Transplantation of stem cells is a potential therapeutic strategy for stroke damage. The survival, migration, and differentiation of transplanted human embryonic neural stem cells in the acute post-ischemic environment were characterized and endogenous nestin expression after transplantation was investigated. Human embryonic neural stem cells obtained from the temporal lobe cortex were cultured and labeled with fluorescent 1,1'-dioctadecy-6,6'-di (4-sulfopheyl)-3,3,3',3'-tetramethylindocarbocyanin (DiI) in vitro. Labeled cells were transplanted into cortical peri-infarction zones of adult rats 24 h after permanent middle cerebral artery occlusion. Survival, migration, and differentiation of grafted cells were quantified in immunofluorescence-stained sections from rats sacrificed at 7, 14, and 28 days after transplantation. Endogenous nestin-positive cells in the cortical peri-infarction zone were counted at serial time points. The cells transplanted into the cortical peri-infarction zone displayed the morphology of living cells and became widely located around the ischemic area. Moreover, some of the transplanted cells expressed nestin, GFAP, or NeuN in the peri-infarction zone. Furthermore, compared with the control group, endogenous nestin-positive cells in the peri-infarction zone had increased significantly 7 days after cell transplantation. These results confirm the survival, migration, and differentiation of transplanted cells in the acute post-ischemic environment and enhanced endogenous nestin expression within a brief time window. These findings indicate that transplantation of neural stem cells into the peri-infarction zone may be performed as early as 24 h after ischemia.

Brain tumor stem cells

The dogma that solid tumors are composed of tumor cells that all share the same ability to produce proliferating daughter cells has been challenged in recent years. There is growing evidence that many adult tissues contain a set of tissue stem cells, which might undergo malignant transformation while retaining their stem cell characteristics. These include the ability of indefinite self-renewal and the capability to differentiate into daughter cells of tissue-specific lineages. Brain tumors such as medulloblastomas or glioblastomas often contain areas of divergent differentiation, which raises the intriguing question of whether these tumors could derive from neural stem cells (NSCs).This chapter reviews the current knowledge of NSCs and relates them to brain tumor pathology. Current therapy protocols for malignant brain tumors are targeted toward the reduction of bulk tumor mass. The concept of brain-tumor stem cells could provide new insights for future therapies, if the capacity for self-renewal of tumor cells and growth of the tumor mass would reside within a small subset of cancer cells.

The glial nature of embryonic and adult neural stem cells

Glial cells were long considered end products of neural differentiation, specialized supportive cells with an origin very different from that of neurons. New studies have shown that some glial cells--radial glia (RG) in development and specific subpopulations of astrocytes in adult mammals--function as primary progenitors or neural stem cells (NSCs). This is a fundamental departure from classical views separating neuronal and glial lineages early in development. Direct visualization of the behavior of NSCs and lineage-tracing studies reveal how neuronal lineages emerge. In development and in the adult brain, many neurons and glial cells are not the direct progeny of NSCs, but instead originate from transit amplifying, or intermediate, progenitor cells (IPCs). Within NSCs and IPCs, genetic programs unfold for generating the extraordinary diversity of cell types in the central nervous system. The timing in development and location of NSCs, a property tightly linked to their neuroepithelial origin, appear to be the key determinants of the types of neurons generated. Identification of NSCs and IPCs is critical to understand brain development and adult neurogenesis and to develop new strategies for brain repair.

Preclinical assessment of stem cell therapies for neurological diseases

Stem cells, as subjects of study for use in treating neurological diseases, are envisioned as a replacement for lost neurons and glia, a means of trophic support, a therapeutic vehicle, and, more recently, a tool for in vitro modeling to understand disease and to screen and personalize treatments. In this review we analyze the requirements of stem cell-based therapy for clinical translation, advances in stem cell research toward clinical application for neurological disorders, and different animal models used for analysis of these potential therapies. We focus on Parkinson's disease (typically defined by the progressive loss of dopaminergic nigral neurons), stroke (neurodegeneration associated with decreased blood perfusion in the brain), and multiple sclerosis (an autoimmune disorder that generates demyelination, axonal damage, astrocytic scarring, and neurodegeneration in the brain and spinal cord). We chose these disorders for their diversity and the number of people affected by them. An additional important consideration was the availability of multiple animal models in which to test stem cell applications for these diseases. We also discuss the relationship between the limited number of systematic stem cell studies performed in animals, in particular nonhuman primates and the delayed progress in advancing stem cell therapies to clinical success.

Neurogenesis in substantia nigra of parkinsonian brains?

The clinical motor dysfunction in Parkinson's disease is primarily the consequence of a progressive degeneration of dopaminergic neurons in the substantia nigra of the nigrostriatal pathway. The degeneration of this tract provokes a depletion of dopamine in the striatum, where it is required as a permissive factor for normal motor function. Despite intense investigations, no effective therapy is available to prevent the onset or to halt the progression of the neuronal cell loss. Therefore, recent years have seen research into the mechanisms of endogenous repair processes occurring in the adult brain, particularly in the substantia nigra. Neurogenesis occurs in the adult brain in a constitutive manner under physiological circumstances within two regions: the dentate gyrus of the hippocampus and the subventricular zone of the lateral ventricles. In contrast to these two so-called neurogenic areas, the remainder of the brain is considered to be primarily nonneurogenic in nature, implying that no new neurons are produced there under normal conditions. The occurrence of adult neurogenesis in the substantia nigra under the pathological conditions of Parkinson's disease, however, remains controversial. Here, we review the published evidence of whether adult neurogenesis exists or not within the substantia nigra, where dopaminergic neurons are lost in Parkinson's disease.

Cells of adult brain germinal zone have properties akin to hair cells and can be used to replace inner ear sensory cells after damage

Auditory hair cell defect is a major cause of hearing impairment, often leading to spiral ganglia neuron (SGN) degeneration. The cell loss that follows is irreversible in mammals, because inner ear hair cells (HCs) have a limited capacity to regenerate. Here, we report that in the adult brain of both rodents and humans, the ependymal layer of the lateral ventricle contains cells with proliferative potential, which share morphological and functional characteristics with HCs. In addition, putative neural stem cells (NSCs) from the subventricular zone of the lateral ventricle can differentiate into functional SGNs. Also important, the NSCs can incorporate into the sensory epithelia, demonstrating their therapeutic potential. We assert that NSCs and edendymal cells can undergo an epigenetic functional switch to assume functional characteristics of HCs and SGNs. This study suggests that the functional plasticity of renewable cells and conditions that promote functional reprogramming can be used for cell therapy in the auditory setting.

Relationship of gliomas to the ventricular walls

The role of neural stem cells in gliomagenesis remains controversial. The aim of this study was to determine the anatomic relationship of human gliomas to the lining of the ventricular walls, known as the subventricular zone, an area replete with neural stem cells. We performed a retrospective radiographic analysis of 100 consecutive patients with gliomas and sought to determine the relationship of the lesions to the ventricular walls as seen on their MRI scans. Our results indicated that in 93% of cases the lesions contacted at least one region of the lateral ventricular wall. Contact with the ventricular wall was independent of the glioma size or mass effect. These findings were correlated to cytoarchitectural studies of the human subventricular zone. Our findings lend further support that there is an intimate association between gliomas and the subventricular zone.

Glioma formation, cancer stem cells, and akt signaling

Several recent reports have provided evidence that cancer is initiated by a rare fraction of cells called "cancer stem cells" which are multipotent, self-renewing subset of the tumor. However, several issues regarding the biology and techniques of isolating these cells from solid tumors remain to be clarified. In addition, experimental data supports two possibilities for glioma cell of origin. First, that stem cells or early progenitors are transformed and show variable differentiation of their progeny during tumor development. Second, that more differentiated glia are transformed by genetic events that lead to a loss of differentiation maintenance. In human gliomas, these two theories are not mutually exclusive. In this review we will summarize both theories, and highlight outstanding issues that remain to be resolved.

Adult neurogenesis and its alteration under pathological conditions

Even in the adult brain, neural stem cells in the dentate gyrus and subventricular zone continue to produce neuronal precursors, which migrate and differentiate into functional mature neurons. This physiological neurogenesis is thought to be involved in neuronal plasticity. Moreover, recent studies indicate that adult neurogenesis can change in response to various brain insults, including psychiatric diseases, stroke, and neurodegenerative disorders. Although increased neurogenesis in these pathological conditions could contribute to the restoration and regeneration of the damaged brain, an inadequate and/or excessive supply of new neurons, or suppressed neurogenesis, could contribute to their pathophysiology. To develop successful regenerative treatments for the injured brain, we need to understand more precisely and comprehensively the mechanisms regulating adult neurogenesis under both physiological and pathological conditions.

The astrocyte odyssey

Neurons have long held the spotlight as the central players of the nervous system, but we must remember that we have equal numbers of astrocytes and neurons in the brain. Are these cells only filling up the space and passively nurturing the neurons, or do they also contribute to information transfer and processing? After several years of intense research since the pioneer discovery of astrocytic calcium waves and glutamate release onto neurons in vitro, the neuronal-glial studies have answered many questions thanks to technological advances. However, the definitive in vivo role of astrocytes remains to be addressed. In addition, it is becoming clear that diverse populations of astrocytes coexist with different molecular identities and specialized functions adjusted to their microenvironment, but do they all belong to the umbrella family of astrocytes? One population of astrocytes takes on a new function by displaying both support cell and stem cell characteristics in the neurogenic niches. Here, we define characteristics that classify a cell as an astrocyte under physiological conditions. We will also discuss the well-established and emerging functions of astrocytes with an emphasis on their roles on neuronal activity and as neural stem cells in adult neurogenic zones.

Neurogliogenesis in the mature olfactory system: a possible protective role against infection and toxic dust

The outpost position of the olfactory bulb (OB) between the direct inputs from sensory neurons of the nasal epithelium and other parts of the brain suggests its highest vulnerability among all brain structures to penetration of exogenous agents. A number of neurotropic viruses have been found to invade the brain through the OB. There is growing evidence that microscopic particles of toxic dusts can propagate from the nasal epithelium to the OB and further into the brain. These harmful agents impair cellular elements of the brain. Apparently, cells in the OB are the most affected, as they are the first to encounter viral infections and toxic particles. It is well known that neuronal and glial progenitors are continuously generated from neuronal stem cells in the subventricular zone of the adult brain and then migrate predominantly into the OB. Therefore, it is feasible to suggest that substitution of injured or dead cells in the OB by new-born neurons, differentiating from progenitors, plays a role in protecting the OB neuronal microcircuits from destruction. Furthermore, some cytokines and chemokines released in response to infection and/or intoxication can modulate different stages of neurogenesis (proliferation, migration, and differentiation). We hypothesize that continuous neurogenesis in the olfactory system throughout adulthood evolved as a protective mechanism to prevent impairment of the most ancient but vitally important sensory system. In addition, differentiation of a substantial portion of progenitors to glial cells, including macrophages and microglia, may create an additional barrier to exogenous agents on their way deep to the brain.

Ventral mesencephalon astrocytes are more efficient than those of other regions in inducing dopaminergic neurons through higher expression level of TGF-beta3

Being supportive cells for neurons in the central nervous system, astrocytes have recently found to be associated with neurogenesis. Ventral mesencephalon (VM) astrocytes were also detected being instructive for VM dopaminergic (DA) neurogenesis, but the underling mechanisms are still unclear. This research is to figure out whether VM astrocytes are more efficient than those from other brain regions in inducing VM DA neurons from their precursors and whether transforming growth factor-betas (TGF-betas) are the underlying molecules. We found that, compared with astrocytes preparations from striatum and hippocampus, VM astrocytes preparations displayed markedly higher efficacy in inducing DA neurogenesis. Besides, they also expressed higher level of TGF-beta3 than those of two other regions. When TGF-beta3 gene expression in astrocytes preparations was inhibited by its antisense oligonucleotide, the induction of DA neurons decreased to a similar level among these three astrocytes preparations. Thus, our experiment indicates that VM astrocytes preparations which contained highly purified astrocytes are more efficient in inducing DA neurogenesis than those from other regions. Furthermore, it also suggests that the regional differences are regulated by different expression levels of TGF-beta3 in those astrocytes preparations from different derivations.

Disease-responsive neural precursor cells are present in multiple sclerosis lesions

AIMS

Spontaneous tissue repair occurs in multiple sclerosis (MS), but the origin of remyelinating cells remains obscure. Here we explore the hypothesis that endogenous neural precursors are involved in MS disease processes.

MATERIALS & METHODS

We studied postmortem brain and spinal cord samples from MS patients using immunocytochemical techniques.

RESULTS

We show that cells co-positive for nestin and musashi-1 are not merely present in lesions, but found in markedly increased numbers (up to fivefold). Small numbers of nestin-positive cells show direct evidence of proliferation, co-staining for Ki67; some also coexpress glial fibrillary acidic protein or oligodendrocyte progenitor markers (NG-2 or PDGF-alpha receptor), or the early neuronal marker doublecortin, consistent with transition from neural precursors.

CONCLUSIONS

These findings suggest that endogenous neural precursors react to disease processes in MS.

Functional organization of the transcriptome in human brain

The enormous complexity of the human brain ultimately derives from a finite set of molecular instructions encoded in the human genome. These instructions can be directly studied by exploring the organization of the brain's transcriptome through systematic analysis of gene coexpression relationships. We analyzed gene coexpression relationships in microarray data generated from specific human brain regions and identified modules of coexpressed genes that correspond to neurons, oligodendrocytes, astrocytes and microglia. These modules provide an initial description of the transcriptional programs that distinguish the major cell classes of the human brain and indicate that cell type-specific information can be obtained from whole brain tissue without isolating homogeneous populations of cells. Other modules corresponded to additional cell types, organelles, synaptic function, gender differences and the subventricular neurogenic niche. We found that subventricular zone astrocytes, which are thought to function as neural stem cells in adults, have a distinct gene expression pattern relative to protoplasmic astrocytes. Our findings provide a new foundation for neurogenetic inquiries by revealing a robust and previously unrecognized organization to the human brain transcriptome.

A specialized vascular niche for adult neural stem cells

Stem cells reside in specialized niches that regulate their self-renewal and differentiation. The vasculature is emerging as an important component of stem cell niches. Here, we show that the adult subventricular zone (SVZ) neural stem cell niche contains an extensive planar vascular plexus that has specialized properties. Dividing stem cells and their transit-amplifying progeny are tightly apposed to SVZ blood vessels both during homeostasis and regeneration. They frequently contact the vasculature at sites that lack astrocyte endfeet and pericyte coverage, a modification of the blood-brain barrier unique to the SVZ. Moreover, regeneration often occurs at these sites. Finally, we find that circulating small molecules in the blood enter the SVZ. Thus, the vasculature is a key component of the adult SVZ neural stem cell niche, with SVZ stem cells and transit-amplifying cells uniquely poised to receive spatial cues and regulatory signals from diverse elements of the vascular system.

Adult neurogenesis and neuronal regeneration in the brain of teleost fish

Whereas adult neurogenesis appears to be a universal phenomenon in the vertebrate brain, enormous differences exist in neurogenic potential between "lower" and "higher" vertebrates. Studies in the gymnotiform fish Apteronotus leptorhynchus and in zebrafish have indicated that the relative number of new cells, as well as the number of neurogenic sites, are at least one, if not two, orders of magnitude larger in teleosts than in mammals. In teleosts, these neurogenic sites include brain regions homologous to the mammalian hippocampus and olfactory bulb, both of which have consistently exhibited neurogenesis in all species examined thus far. The source of the new cells in the teleostean brain are intrinsic stem cells that give rise to both glial cells and neurons. In several brain regions, the young cells migrate, guided by radial glial fibers, to specific target areas where they integrate into existing neural networks. Approximately half of the new cells survive for the rest of the fish's life, whereas the other half are eliminated through apoptotic cell death. A potential mechanism regulating development of the new cells is provided by somatic genomic alterations. The generation of new cells, together with elimination of damaged cells through apoptosis, also enables teleost fish rapid and efficient neuronal regeneration after brain injuries. Proteome analysis has identified a number of proteins potentially involved in the individual regenerative processes. Comparative analysis has suggested that differences between teleosts and mammals in the growth of muscles and sensory organs are key to explain the differences in adult neurogenesis that evolved during phylogenetic development of the two taxa.

Neural precursor cells as a novel target for interferon-beta

The immunomodulating agent interferon-beta (IFNbeta) is administered therapeutically in several autoimmune diseases and endogenously released by immune cells during diverse infections. As in recent years a variety of pro- and anti-inflammatory substances were shown to influence significantly neural precursor cells that are implicated in a variety of regenerative mechanisms but also in tumor growth, we studied a possible effect of IFNbeta on neural precursor cells derived from murine embryonic day 14 neurospheres. First, we demonstrated that interferon type-I receptors are expressed on neural precursor cells and that these cells respond to IFNbeta treatment by up-regulating IFNbeta inducible genes including Myxovirus 1 and viperin. Furthermore, we could show for the first time that IFNbeta treatment significantly inhibited the proliferation of neural precursor cells possibly through induction of p21, a cyclin-dependent kinase inhibitor. IFNbeta did not exert cytotoxic or neuroprotective effects and we could not see effects on the differentiation of neural precursor cells into total amounts of neurons, astrocytes or oligodendrocytes. However, we found that IFNbeta markedly diminished neurite outgrowth and neuronal maturation of neural precursor-derived neurons.

Radial glia cells in the developing human brain

Human radial glia (RG) share many of the features described in rodents, but also have a number of characteristics unique to the human brain. Results obtained from different mammalian species including human and non-human primates reveal differences in the involvement of RG in neurogenesis and oligodendrogenesis and in the timing of the initial expression of typical RG immunomarkers. A common problem in studying the human brain is that experimental procedures using modern molecular and genetic methods, such as in vivo transduction with retroviruses or creation of knockout or transgenic mutants, are not possible. Nevertheless, abundant and valuable information about the development of the human brain has been revealed using postmortem human material. Additionally, a combination and spectrum of in vitro techniques are used to gain knowledge about normal developmental processes in the human brain, including better understanding of RG as progenitor cells. Molecular and functional characterization of multipotent progenitors, such as RG, is important for future cell replacement therapies in neurological and psychiatric disorders, which are often resistant to conventional treatments. The protracted time of development and larger size of the human brain could provide insight into processes that may go unnoticed in the much smaller rodent cortex, which develops over a much shorter period. With that in mind, we summarize results on the role of RG in the human fetal brain.

Neural stem cells confer unique pinwheel architecture to the ventricular surface in neurogenic regions of the adult brain

Neural stem cells (NSCs, B1 cells) are retained in the walls of the adult lateral ventricles but, unlike embryonic NSCs, are displaced from the ventricular zone (VZ) into the subventricular zone (SVZ) by ependymal cells. Apical and basal compartments, which in embryonic NSCs play essential roles in self-renewal and differentiation, are not evident in adult NSCs. Here we show that SVZ B1 cells in adult mice extend a minute apical ending to directly contact the ventricle and a long basal process ending on blood vessels. A closer look at the ventricular surface reveals a striking pinwheel organization specific to regions of adult neurogenesis. The pinwheel's core contains the apical endings of B1 cells and in its periphery two types of ependymal cells: multiciliated (E1) and a type (E2) characterized by only two cilia and extraordinarily complex basal bodies. These results reveal that adult NSCs retain fundamental epithelial properties, including apical and basal compartmentalization, significantly reshaping our understanding of this adult neurogenic niche.

Neural stem cells: involvement in adult neurogenesis and CNS repair

Recent advances in stem cell research, including the selective expansion of neural stem cells (NSCs) in vitro, the induction of particular neural cells from embryonic stem cells in vitro, the identification of NSCs or NSC-like cells in the adult brain and the detection of neurogenesis in the adult brain (adult neurogenesis), have laid the groundwork for the development of novel therapies aimed at inducing regeneration in the damaged central nervous system (CNS). There are two major strategies for inducing regeneration in the damaged CNS: (i) activation of the endogenous regenerative capacity and (ii) cell transplantation therapy. In this review, we summarize the recent findings from our group and others on NSCs, with respect to their role in insult-induced neurogenesis (activation of adult NSCs, proliferation of transit-amplifying cells, migration of neuroblasts and survival and maturation of the newborn neurons), and implications for therapeutic interventions, together with tactics for using cell transplantation therapy to treat the damaged CNS.

Cancer stem cells: markers or biomarkers?

INTRODUCTION

The lineages assumed by stem cells during hematopoiesis can be identified by the pattern of protein markers present on the surface of cells at different stages of differentiation. Specific antibodies directed at these markers have facilitated the isolation of hematopoietic stem cells by flow cytometry.

DISCUSSION

Similarly, stem cells in solid organs also can be identified using cell surface markers. In addition, solid tumors have recently been found to contain small proportions of cells that are capable of proliferation, self-renewal, and differentiation into the various cell types seen in the bulk tumor. Of particular concern, these tumor-initiating cells (termed cancer stem cells when multipotency and self-renewal have been demonstrated) often display characteristics of treatment resistance, particularly to ionizing radiation. Thus, it is important to be able to identify these cells in order to better understand the mechanisms of resistance, and to be able to predict outcome and response to treatment. This depends, of course, on identifying markers that can be used to identify the cells, and for some solid tumors, a specific pattern of cell surface markers is emerging. In breast cancer, for example, the tumor-initiating cells have a characteristic Lin(-)CD44(+)CD24(-/lo) ESA(+) antigenic pattern. In cells derived from some high-grade gliomas, expression of CD133 on the cell surface appears to select for a population of tumor-initiating, treatment resistant cells.

CONCLUSION

Because multiple markers, typically examined on single cells using flow cytometry, are used routinely to identify the subpopulation of tumor-initiating cells, and because the number of these cells is small, the challenge remains to detect them in clinical samples and to determine their ability to predict outcome and/or response to treatment, the hallmarks of established biomarkers.

Everything that glitters isn't gold: a critical review of postnatal neural precursor analyses

Adult neurogenesis research has made enormous strides in the last decade but has been complicated by several failures to replicate promising findings. Prevalent use of highly sensitive methods with inherent sources of error has led to extraordinary conclusions without adequate crossvalidation. Perhaps the biggest culprit is the reliance on molecules involved in DNA synthesis and genetic markers to indicate neuronal neogenesis. In this Protocol Review, we present an overview of common methodological issues in the field and suggest alternative approaches, including viral vectors, siRNA, and inducible transgenic/knockout mice. A multipronged approach will enhance the overall rigor of research on stem cell biology and related fields by allowing increased replication of findings between groups and across systems.

Neurogenesis in the chronic lesions of multiple sclerosis

Subcortical white matter in the adult human brain contains a population of interneurons that helps regulate cerebral blood flow. We investigated the fate of these neurons following subcortical white matter demyelination. Immunohistochemistry was used to examine neurons in normal-appearing subcortical white matter and seven acute and 59 chronic demyelinated lesions in brains from nine patients with multiple sclerosis and four controls. Seven acute and 44 of 59 chronic multiple sclerosis lesions had marked neuronal loss. Compared to surrounding normal-appearing white matter, the remaining 15 chronic multiple sclerosis lesions contained a 72% increase in mature interneuron density, increased synaptic densities and cells with phenotypic characteristics of immature neurons. Lesion areas with increased neuron densities contained a morphologically distinct population of activated microglia. Subventricular zones contiguous with demyelinated lesions also contained an increase in cells with phenotypes of neuronal precursors. These results support neurogenesis in a subpopulation of demyelinated subcortical white matter lesions in multiple sclerosis brains.

Improved technique for stereotactic placement of nerve grafts between two locations inside the rat brain

Peripheral nerve grafts have shown the ability to facilitate central axonal growth and regenerate the adult central nervous system. However, the detailed description of a technique for atraumatic graft placement within the brain is lacking. We present a stereotactic procedure to implant a peripheral nerve graft within a rat's brain with minimal brain tissue damage. The procedure permits a correct graft placement joining two chosen points, and the survival and integration of the graft in the host tissue with a light glial reaction, with evidence of central axonal growth inside the graft, at least up to 8 weeks after its implantation.

Neurologic phenotype of Schimke immuno-osseous dysplasia and neurodevelopmental expression of SMARCAL1

Schimke immuno-osseous dysplasia (OMIM 242900) is an uncommon autosomal-recessive multisystem disease caused by mutations in SMARCAL1 (swi/snf-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1), a gene encoding a putative chromatin remodeling protein. Neurologic manifestations identified to date relate to enhanced atherosclerosis and cerebrovascular disease. Based on a clinical survey, we determined that half of Schimke immuno-osseous dysplasia patients have a small head circumference, and 15% have social, language, motor, or cognitive abnormalities. Postmortem examination of 2 Schimke immuno-osseous dysplasia patients showed low brain weights and subtle brain histologic abnormalities suggestive of perturbed neuron-glial migration such as heterotopia, irregular cortical thickness, incomplete gyral formation, and poor definition of cortical layers. We found that SMARCAL1 is highly expressed in the developing and adult mouse and human brain, including neural precursors and neuronal lineage cells. These observations suggest that SMARCAL1 deficiency may influence brain development and function in addition to its previously recognized effect on cerebral circulation.

Cancer stem cells and glioma

Despite continued advances in surgical and medical therapies, the outcomes for patients diagnosed with glioblastoma multiforme remain dismal. Recent data suggest that progression of these brain tumors is driven by a small subpopulation of tumor cells, which are termed cancer stem cells (CSCs) because of their capability to self-renew, proliferate and give rise to progeny of multiple neuroepithelial lineages. According to the CSC hypothesis, current therapies that are extremely cytotoxic to the bulk of highly proliferative tumor cells fail to obliterate the relatively quiescent and resistant CSC compartment, thereby allowing these cells to survive and drive tumor recurrence. This Review summarizes current knowledge regarding neural stem cells in the normal adult brain and CSCs in glial tumors and discusses the implications of the CSC hypothesis for the development of future therapies for brain tumors.

The new challenge of stem cell: brain tumour therapy

The surprising similarity of much brain tumour behavior to the intrinsic properties of the neural stem/progenitor cell has triggered a recent interest in both arming stem cells to track and help eradicate tumours and in viewing stem cell biology as somehow integral to the emergence and/or production of the neoplasm itself. Moreover, based on the unique capacity of neural stem cells (NSCs) to migrate throughout the brain and to target invading tumour cells, the transplantation of NSCs offers a new potential therapeutic approach as a cell-based delivery system for gene therapy in brain tumours. On the one hand, both stem cells and cancer cells are thought to be capable of unlimited proliferation. While on the other, many tumours and cancer cell lines express stem cell markers, suggesting either that cancer cells resemble stem cells or that cancers contain stem-like cells. In this review we highlight the close relationship between normal neural stem cells and brain tumour stem cells and also suggest the possible clinical implications that these similarities could offer.

Principles of glomerular organization in the human olfactory bulb--implications for odor processing

Olfactory sensory neurons (OSN) in mice express only 1 of a possible 1,100 odor receptors (OR) and axons from OSNs expressing the same odor receptor converge into ∼2 of the 1,800 glomeruli in each olfactory bulb (OB) in mice; this yields a convergence ratio that approximates 2∶1, 2 glomeruli/OR. Because humans express only 350 intact ORs, we examined human OBs to determine if the glomerular convergence ratio of 2∶1 established in mice was applicable to humans. Unexpectedly, the average number of human OB glomeruli is >5,500 yielding a convergence ratio of ∼16∶1. The data suggest that the initial coding of odor information in the human OB may differ from the models developed for rodents and that recruitment of additional glomeruli for subpopulations of ORs may contribute to more robust odor representation.

CD133 identifies perivascular niches in grade II-IV astrocytomas

The aim of the present study was to investigate the localization and distribution of the putative brain tumour stem cell marker CD133 in formalin fixed paraffin embedded astrocytomas. A retrospective analysis of 114 grade II, III and IV astrocytomas was undertaken. The immunohistochemical expression of CD133 in paraffin sections was analysed using morphometry. In all grades, CD133 was expressed on tumour and endothelial cells. Tumour cells were found in perivascular niches, as dispersed single cells and in pseudopalisade formations around necrosis. There was no correlation between the mean volume fraction of CD133(+) niches and all CD133(+) tumour cells and tumour grade. However, the volume fraction of CD133(+) blood vessels increased significantly from 0.4% in diffuse astrocytomas to 2.2% in glioblastomas. Neither of them was related to patient survival. Double immunofluorescence stainings showed that the CD133(+) niches both contained CD133(+) cells with and without co-expression of the intermediate filament protein marker nestin, and only few CD133(+)/MIB-1(+) proliferating cells were found. In conclusion, a CD133(+) perivascular stem cell-like entity exists in astrocytomas. CD133(+) tumour vessels may play an important role in a brain tumour stem cell context, while CD133 alone does not appear to be a specific tumour stem cell marker related to patient survival.

Adult stem cell maintenance and tissue regeneration in the ageing context: the role for A-type lamins as intrinsic modulators of ageing in adult stem cells and their niches

Adult stem cells have been identified in most mammalian tissues of the adult body and are known to support the continuous repair and regeneration of tissues. A generalized decline in tissue regenerative responses associated with age is believed to result from a depletion and/or a loss of function of adult stem cells, which itself may be a driving cause of many age-related disease pathologies. Here we review the striking similarities between tissue phenotypes seen in many degenerative conditions associated with old age and those reported in age-related nuclear envelope disorders caused by mutations in the LMNA gene. The concept is beginning to emerge that nuclear filament proteins, A-type lamins, may act as signalling receptors in the nucleus required for receiving and/or transducing upstream cytosolic signals in a number of pathways central to adult stem cell maintenance as well as adaptive responses to stress. We propose that during ageing and in diseases caused by lamin A mutations, dysfunction of the A-type lamin stress-resistant signalling network in adult stem cells, their progenitors and/or stem cell niches leads to a loss of protection against growth-related stress. This in turn triggers an inappropriate activation or a complete failure of self-renewal pathways with the consequent initiation of stress-induced senescence. As such, A-type lamins should be regarded as intrinsic modulators of ageing within adult stem cells and their niches that are essential for survival to old age.