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

Human umbilical cord blood stem cells show PDGF-D-dependent glioma cell tropism in vitro and in vivo

Despite advances in clinical therapies and technologies, the prognosis for patients with malignant glioma is poor. Neural stem cells (NSCs) have a chemotactic tropism toward glioma cells. The use of NSCs as carriers of therapeutic agents for gliomas is currently being explored. Here, we demonstrate that cells isolated from the umbilical cord blood show mesenchymal characteristics and can differentiate to adipocytes, osteocytes, and neural cells and show tropism toward cancer cells. We also show that these stem cells derived from the human umbilical cord blood (hUCB) induce apoptosis-like cell death in the glioma cell line SNB19 via Fas-mediated caspase-8 activation. From our glioma tropism studies, we have observed that hUCB cells show tropism toward glioma cells in vitro, in vivo, and ex vivo. We determined that this migration is partially dependent on the expression levels of platelet-derived growth factor (PDGF)-D from glioma cells and have observed that local concentration gradient of PDGF-D is sufficient to cause migration of hUCB cells toward the gradient as seen from our brain slice cultures. In our animal experiment studies, we observed that intracranially implanted SNB19 green fluorescent protein cells induced tropism of the hUCB cells toward themselves. In addition, the ability of these hUCBs to inhibit established intracranial tumors was also observed. We also determined that the migration of stem cells toward glioma cells was partially dependent on PDGF secreted by glioma cells and that the presence of PDGF-receptor (PDGFR) on hUCB is required for migration. Our results demonstrate that hUCB are capable of inducing apoptosis in human glioma cells and also show that glioma tropism and hUCB tropism toward glioma cells are partially dependent on the PDGF/PGGFR system.

Proliferation of human glioblastoma stem cells occurs independently of exogenous mitogens

Primary glial tumors of the central nervous system, most commonly glioblastoma multiforme (GBM), are aggressive lesions with a dismal prognosis. Despite identification and isolation of human brain tumor stem cells (BTSCs), characteristics that distinguish BTSCs from neural stem cells remain to be elucidated. We cultured cells isolated from gliomas, using the neurosphere culture system, to understand their growth requirements. Both CD133(+) and CD133(-) adult GBM BTSCs proliferated in the absence of exogenous mitogenic stimulation and gave rise to multipotent GBM spheres that were capable of self-renewal. Epidermal growth factor (EGF) and fibroblast growth factor-2 enhanced GBM BTSC survival, proliferation, and subsequent sphere size. Blockade of EGF receptor (EGFR) signaling reduced exogenous mitogen-independent GBM sphere growth. Implantation of as few as 10 exogenous mitogen-independent GBM BTSCs led to the formation of highly invasive intracranial tumors, which closely resembled human GBMs, in immunocompromised mice. These results demonstrate that exogenous mitogen independence, mediated in part through EGFR signaling, is one characteristic that distinguishes CD133(+) and CD133(-) GBM BTSCs from neural stem cells. This novel experimental system will permit the elucidation of additional constitutively activated mechanisms that promote GBM BTSC survival, self-renewal, and proliferation.

GFAPdelta in radial glia and subventricular zone progenitors in the developing human cortex

A subpopulation of glial fibrillary acidic protein (GFAP)-expressing cells located along the length of the lateral ventricles in the subventricular zone (SVZ) have been identified as the multipotent neural stem cells of the adult mammalian brain. We have previously found that, in the adult human brain, a splice variant of GFAP, termed GFAPdelta, was expressed specifically in these cells. To investigate whether GFAPdelta is also present in the precursors of SVZ astrocytes during development and whether GFAPdelta could play a role in the developmental process, we analyzed GFAPdelta expression in the normal developing human cortex and in the cortex of foetuses with the migration disorder lissencephaly type II. We demonstrated for the first time that GFAPdelta is specifically expressed in radial glia and SVZ neural progenitors during human brain development. Expression of GFAPdelta in radial glia starts at around 13 weeks of pregnancy and disappears before birth. GFAPdelta is continuously expressed in the SVZ progenitors at later gestational ages and in the postnatal brain. Co-localization with Ki67 proved that these GFAPdelta-expressing cells are able to proliferate. Furthermore, we showed that the expression pattern of GFAPdelta was disturbed in lissencephaly type II. Overall, these results suggest that the adult SVZ is indeed a remnant of the foetal SVZ, which develops from radial glia. Furthermore, we provide evidence that GFAPdelta can distinguish resting astrocytes from proliferating SVZ progenitors.

Chemotherapy associated central nervous system damage

Chemotherapy is commonly associated with harmful effects to multiple organ systems, including the central nervous system (CNS). Neurotoxicity may manifest as both acute and delayed complications, which is particularly a concern for long-term survivors. Patients may experience a wide range of neurotoxic syndromes, ranging from neuro-vascular complications and focal neurological deficits to generalized neurological decline with cognitive impairment, cortical atrophy and white matter abnormalities. Along with the use of more aggressive and combined treatment modalities and prolonged survival of cancer patients, neurological complications have been observed with increasing frequency. The mechanisms by which cancer therapy, including chemotherapy and radiation, result in neurological complications, have been poorly understood. Recent studies have now started to unravel the cell-biological basis for commonly seen neurotoxic syndromes and have provided compelling explanations for delayed neurological complications, such as cognitive decline, progressive myelin disruption and brain atrophy.

Fate and manipulations of endogenous neural stem cells following brain ischemia

Stem cells have been proposed as a new form of cell-based therapy in a variety of disorders, including acute and degenerative brain diseases. Endogenous neural stem cells (eNSCs) have been identified in the central nervous system where they reside largely in the subventricular zone and in the subgranular zone of the hippocampus. eNSCs are capable of self-renewal and differentiation into functional glia and neurons throughout life. However, spontaneous brain regeneration does not suffice to induce significant behavioral improvement in acute or chronic brain injury. Nevertheless, eNSCs responses can be considerably increased by tweaking the pathways governing cell proliferation, migration and differentiation. Contemporary evidence now suggests that such perturbations may lead to better functional outcome after brain injury.

Mouse models for cancer stem cell research

The cancer stem cell concept assumes that cancers are mainly sustained by a small pool of neoplastic cells, known as cancer stem cells or tumor initiating cells, which are able to reproduce themselves and produce phenotypically heterogeneous cells with lesser tumorigenic potential. Cancer stem cells represent an appealing target for development of more selective and efficient therapies. However, direct testing of the cancer stem cell concept and assessment of its therapeutic implications in human cancers have been complicated by the use of immunocompromised mice. Genetically defined immunocompetent autochthonous mouse models of human cancer provide a valuable tool to address this problem. Furthermore, they allow for a better understanding of the relevance of mechanisms controlling normal stem cell compartment to carcinogenesis. Advantages and disadvantages of some of the existing mouse models are reviewed, and future challenges in cancer stem cell research are outlined.

Grafting neural precursor cells promotes functional recovery in an SCA1 mouse model

The B05 transgenic SCA1 mice, expressing human ataxin-1 with an expanded polyglutamine tract in cerebellar Purkinje cells (PCs), recapitulate many pathological and behavioral characteristics of the neurodegenerative disease spinocerebellar ataxia type 1 (SCA1), including progressive ataxia and PC loss. We transplanted neural precursor cells (NPCs) derived from the subventricular zone of GFP-expressing adult mice into the cerebellar white matter of SCA1 mice when they showed absent (5 weeks), initial (13 weeks), and significant (24 weeks) PC loss. Only in mice with significant cell loss, grafted NPCs migrated into the cerebellar cortex. These animals showed improved motor skills compared with sham-treated controls. No grafted cell adopted the morphological and immunohistochemical characteristics of PCs, but the cerebellar cortex in NPC-grafted SCA1 mice had a significantly thicker molecular layer and more surviving PCs. Perforated patch-clamp recordings revealed a normalization of the PC basal membrane potential, which was abnormally depolarized in sham-treated animals. No significant increase in levels of several neurotrophic factors was observed, suggesting, along with morphological observation, that the neuroprotective effect of grafted NPCs was mediated by direct contact with the host PCs. We postulate that a similar neuroprotective effect of NPCs may be applicable to other cerebellar degenerative diseases.

Neuroprotection of host cells by human central nervous system stem cells in a mouse model of infantile neuronal ceroid lipofuscinosis

Infantile neuronal ceroid lipofuscinosis (INCL) is a fatal neurodegenerative disease caused by a deficiency in the lysosomal enzyme palmitoyl protein thioesterase-1 (PPT1). Ppt1 knockout mice display hallmarks of INCL and mimic the human pathology: accumulation of lipofuscin, degeneration of CNS neurons, and a shortened life span. Purified non-genetically modified human CNS stem cells, grown as neurospheres (hCNS-SCns), were transplanted into the brains of immunodeficient Ppt1(-/)(-) mice where they engrafted robustly, migrated extensively, and produced sufficient levels of PPT1 to alter host neuropathology. Grafted mice displayed reduced autofluorescent lipofuscin, significant neuroprotection of host hippocampal and cortical neurons, and delayed loss of motor coordination. Early intervention with cellular transplants of hCNS-SCns into the brains of INCL patients may supply a continuous and long-lasting source of the missing PPT1 and provide some therapeutic benefit through protection of endogenous neurons. These data provide the experimental basis for human clinical trials with these banked hCNS-SCns.

Brain cancer propagating cells: biology, genetics and targeted therapies

Cancer propagating cells (CPCs) within primary central nervous system (CNS) tumors (glioblastoma multiforme (GBM), medulloblastoma (MB) and ependymoma) might be integral to tumor development and perpetuation. These cells, also known as brain cancer propagating cells (BCPCs), have the ability to self-renew and proliferate. BCPCs can initiate new tumors in mice with high efficiency and these exhibit many features that are characteristic of patient's brain tumors. Accumulating evidence suggests that BCPCs might originate from the transformation of neural stem cells (NSCs) and their progenitors. Furthermore, recent studies have shown that NSC surface markers also define BCPCs. Ultimately, treatments that include specific targeting of BCPCs might potentially be more effective at treating the entire tumor mass, translating to improved patient survival and quality of life.

Activated EGFR signaling increases proliferation, survival, and migration and blocks neuronal differentiation in post-natal neural stem cells

Recent evidence supports the notion that transformation of undifferentiated neural stem cell (NSC) precursors may contribute to the development of glioblastoma multiforme (GBM). The over-expression and mutation of the epidermal growth factor receptor (EGFR), along with other cellular pathway mutations, plays a significant role in GBM maintenance progression. Though EGFR signaling is important in determining neural cell fate and conferring astrocyte differentiation, there is a limited understanding of its role in NSC and tumor stem cell (TSC) biology. We hypothesized that EGFR expression and mutation in post-natal NSCs may contribute to cellular aggressiveness including enhanced cellular proliferation, survival and migration. Stable subclones of C17.2 murine NSCs were transfected to over-express either the wild-type EGFR (wtEGFR) or its most common mutated variant EGFRvIII. Activated EGFR signaling in these cells induced behaviors characteristic of GBM TSCs, including enhanced proliferation, survival and migration, even in the absence of EGF ligand. wtEGFR activation was also found to block neuronal differentiation and was associated with a dramatic increase in chemotaxis in the presence of EGF. EGFRvIII expression lead to an increase in NSC proliferation and survival, while it simultaneously blocked neuronal differentiation and promoted glial fate. Our findings suggest that activated EGFR signaling enhances the aggressiveness of NSCs. Understanding the regulatory mechanisms of NSCs may lend insight into deregulated mechanisms of GBM TSC invasion, proliferation, survival and resistance to current treatment modalities.

The neurovascular link in health and disease: an update

Although the nervous and vascular systems are functionally different, they show a high degree of anatomic parallelism and cross-talk. They also share similar mechanisms and molecular cues that regulate their development and maintenance. Malfunctioning of this cross-talk can cause or influence several vascular and neuronal disorders. In this review, we first provide a brief overview of the molecular and cellular mechanisms that govern the neurovascular link. Second, we focus on two neurodegenerative diseases, Alzheimer's disease and amyotrophic lateral sclerosis, to illustrate how a defective neurovascular link might contribute to their pathogenesis. Finally, we briefly discuss some therapeutic implications of the neurovascular link for designing strategies to treat these diseases.

Adult neurogenesis and the olfactory system

Though initially described in the early 1960s, it is only within the past decade that the concept of continuing adult neurogenesis has gained widespread acceptance. Neuroblasts from the subventricular zone (SVZ) migrate along the rostral migratory stream (RMS) into the olfactory bulb, where they differentiate into interneurons. Neuroblasts from the subgranular zone (SGZ) of the hippocampal formation show relatively little migratory behavior, and differentiate into dentate gyrus granule cells. In sharp contrast to embryonic and perinatal development, these newly differentiated neurons must integrate into a fully functional circuit, without disrupting ongoing performance. Here, after a brief historical overview and introduction to olfactory circuitry, we review recent advances in the biology of neural stem cells, mechanisms of migration in the RMS and olfactory bulb, differentiation and survival of new neurons, and finally mechanisms of synaptic integration. Our primary focus is on the olfactory system, but we also contrast the events occurring there with those in the hippocampal formation. Although both SVZ and SGZ neurogenesis are involved in some types of learning, their full functional significance remains unclear. Since both systems offer models of integration of new neuroblasts, there is immense interest in using neural stem cells to replace neurons lost in injury or disease. Though many questions remain unanswered, new insights appear daily about adult neurogenesis, regulatory mechanisms, and the fates of the progeny. We discuss here some of the central features of these advances, as well as speculate on future research directions.

Involvement of Notch1 signaling in neurogenesis in the subventricular zone of normal and ischemic rat brain in vivo

The Notch1 signaling pathway is regarded as one of the main regulators of neural stem cell behavior during development, but its role in the adult brain is less well understood. We found that Notch1 was mainly expressed in doublecortin (DCX)-positive cells corresponding to newborn neurons, whereas the Notch1 ligand, Jagged1, was predominantly expressed in glial fibrillary acidic protein (GFAP)-positive astrocytic cells in the subventricular zone (SVZ) of the normal adult brain. These findings were confirmed by conditional depletion of DCX-positive cells in transgenic mice carrying herpes simplex virus thymidine kinase (HSV-TK) under the control of the DCX promoter. In addition, the activated form of Notch1 (Notch intracellular domain, NICD) and its downstream transcriptional targets, Hes1 and sonic hedgehog (Shh), were also expressed in SVZ cells. Increased activation of Notch1 signaling increased SVZ cell proliferation, whereas inhibiting Notch1 signaling resulted in a reduction of proliferating cells in the SVZ. Levels of NICD, Hes1, and Shh were increased in the SVZ at 4 and 24 h after focal cerebral ischemia. Finally, ischemia-induced cell proliferation in the SVZ was blocked by inhibition of the Notch1 signaling pathway, suggesting that Notch1 signaling may have a key role in normal adult and ischemia-induced neurogenesis.

Strategies to promote differentiation of newborn neurons into mature functional cells in Alzheimer brain

Adult neurogenesis occurs in the subgranular zone (SGZ) and subventricular zone (SVZ). New SGZ neurons migrate into the granule cell layer of the dentate gyrus (DG). New SVZ neurons seem to enter the association neocortex and entorhinal cortex besides the olfactory bulb. Alzheimer disease (AD) is characterized by neuron loss in the hippocampus (DG and CA1 field), entorhinal cortex, and association neocortex, which underlies the learning and memory deficits. We hypothesized that, if the AD brain can support neurogenesis, strategies to stimulate the neurogenesis process could have therapeutic value in AD. We reviewed the literature on: (a) the functional significance of adult-born neurons; (b) the occurrence of endogenous neurogenesis in AD; and (c) strategies to stimulate the adult neurogenesis process. We found that: (a) new neurons in the adult DG contribute to memory function; (b) new neurons are generated in the SGZ and SVZ of AD brains, but they fail to differentiate into mature neurons in the target regions; and (c) numerous strategies (Lithium, Glatiramer Acetate, nerve growth factor, environmental enrichment) can enhance adult neurogenesis and promote maturation of newly generated neurons. Such strategies might help to compensate for the loss of neurons and improve the memory function in AD.

Cell-based therapies for Parkinson's disease: past, present, and future

Parkinson's disease (PD) researchers have pioneered the use of cell-based therapies (CBTs) in the central nervous system. CBTs for PD were originally envisioned as a way to replace the dopaminergic nigral neurons lost with the disease. Several sources of catecholaminergic cells, including autografts of adrenal medulla and allografts or xenografts of mesencephalic fetal tissue, were successfully assessed in animal models, but their clinical translation has yielded poor results and much controversy. Recent breakthroughs on cell biology are helping to develop novel cell lines that could be used for regenerative medicine. Their future successful clinical application depends on identifying and solving the problems encountered in previous CBTs trials. In this review, we critically analyze past CBTs' clinical translation, the impact of the host in graft survival, and the role of preclinical studies and emerging new cell lines. We propose that the prediction of clinical results from preclinical studies requires experimental designs that allow blind data acquisition and statistical analysis, assessment of the therapy in models that parallel clinical conditions, looking for sources of complications or side effects, and limiting optimism bias when reporting outcomes.

Interactions between environmental changes and brain plasticity in birds

Neurogenesis and neuronal recruitment occur in many vertebrates, including humans. Most of the new neurons die before reaching their destination. Those which survive migrate to various brain regions, replace older ones and connect to existing circuits. Evidence suggests that this replacement is related to acquisition of new information. Therefore, neuronal replacement can be seen as a form of brain plasticity that enables organisms to adjust to environmental changes. However, direct evidence of a causal link between replacement and learning remains elusive. Our hypothesis is that increased neuronal recruitment is associated with increase in memory load. Moreover, since neuronal recruitment is part of a turnover process, we assume that the same conditions that favor survival of some neurons induce the death of others. I present studies that investigated the effect of various behaviors and environmental conditions (food-hoarding, social change, reproductive cycle) on neuronal recruitment and survival in adult avian brains, and discuss how these phenomena relate to the life of animals. I offer a frame and rationale for comparing neuronal replacement in the adult brain, in order to uncover the pressures, rules, and mechanisms that govern its constant rejuvenation. The review emphasizes the importance of using various approaches (behavioral, anatomical, cellular and hormonal) in neuroethological research, and the need to study natural populations, in order to fully understand how neurogenesis and neuronal replacement contribute to life of animals. Finally, the review indicates to future directions and ends with the hope that a better understanding of adult neuronal replacement will lead to medical applications.

The SCHER Report on Non-human Primate Research —Biased and Deeply Flawed

The European Commission's Scientific Committee on Health and Environmental Risks (SCHER) recently issued an Opinion on the need for non-human primate (NHP) use in biomedical research, and the possibilities of replacing NHP use with alternatives, as part of the Directive 86/609/EEC revision process. Here, we summarise our recent complaint to the European Ombudsman about SCHER's Opinion and the entire consultation process. It is our opinion that the Working Group almost entirely failed to address its remit, and that the Group was unbalanced and contained insufficient expertise. The Opinion presumed the validity of NHP research with inadequate supporting evidence, and ignored substantial evidence against the need for NHP research and examples of valid alternatives that could replace the use of NHPs. Because the European Commission and others might base their approach to NHP research directly on the inquiry's findings during the revision of Directive 86/609/EEC, the implications of a flawed analysis of the efficacy of NHP research are extremely serious, both for animal welfare and for human health and safety. The conduct of the SCHER inquiry, and its published Opinion, should therefore be of major and widespread concern, and should not be given any political, scientific or legislative credibility.

Neural progenitors of the postnatal and adult mouse forebrain retain the ability to self-replicate, form neurospheres, and undergo multipotent differentiation in vivo

Somatic stem cells are reservoirs to replace lost cells or damaged tissue. Cells with neural stem cell (NSC) characteristics can be isolated from the postnatal mammalian brain into adulthood and expanded as neurospheres. We addressed the ability of these in vitro expanded putative NSCs to retain progenitor characteristics in vivo, in analogy to hematopoietic stem cells. When transplanted in utero, both postnatal and adult neural progenitors colonize host brains and contribute neurons and glia. In stark contrast to what has been reported when transplanted in postnatal hosts, epidermal growth factor-expanded cells also remain self-replicating and multipotent in vivo over many months and can be serially transplanted into multiple hosts. Surprisingly, embryonically transplanted NSCs remain in the neurogenic regions in adult hosts, where they express progenitor cell markers and continue to proliferate even after 6 months without tumor formation. These data indicate that spherogenic cells of the postnatal and adult mammalian brain retain their potential in vitro and in vivo throughout the life of the organism and beyond transplantation, which has important implications for cell replacement strategies.

Neural stem cells and new neurons in the cerebral cortex of stroke-prone spontaneously hypertensive rats after stroke

Stroke-prone spontaneously hypertensive rats (SHRSP) are the only animal model that suffers from spontaneous cerebral stroke. In this study, we investigated the appearance of neural stem cells (NSCs) and new neurons in the penumbra and the subventricular zone (SVZ) after cerebral stroke in SHRSP. SHRSP before cerebral stroke were intraperitoneally injected with 5-bromo-2'-deoxyuridine (BrdU). SHRSP were divided into acute and chronic phase groups after cerebral stroke. Brain sections from both groups were studied with cell-specific markers such as BrdU, a cell division and proliferation marker, sex-determining region Y-box 2, a marker of NSCs, nestin, an NSC and immature astrocyte marker, doublecortin, an immature new neuron marker, and neuron-specific nuclear protein, a marker of mature neurons. NSCs and new neurons appeared in the penumbra in the early stages after cerebral stroke, and these cells differentiated into mature neurons in the chronic phase. Furthermore, soon after being affected by a cerebral stroke, there were many new neurons and immature cells, which appear to be NSCs, in the ipsilateral SVZ. Immature cells and new neurons from the ipsilateral SVZ might migrate into the penumbra after cerebral stroke, and this is the first report of their observation after a spontaneous cerebral stroke.

Review of Alexander disease: beyond the classical concept of leukodystrophy

Alexander disease is classified as one of the leukodystrophies, which are degenerative diseases primarily affecting the cerebral white matter. Formal diagnosis is achieved by showing diffuse accumulation of Rosenthal fibers in the brain by biopsy or autopsy. Showing a heterozygous mutation in the glial fibrillary acidic protein (GFAP) gene is currently sufficient for diagnosis. The mechanisms of Rosenthal fiber formation remain unclear. However, both the quality and quantity of GFAP are important. GFAP-epsilon (rodent homologous GFAP-delta), one of the alternatively spliced GFAP isoforms, may also play a modulating role in aggregate formation. The current ease of diagnosis has accelerated the accumulation of a wide variety of patients with Alexander disease along with the widespread use of MRI. In contrast to the classical infantile type, patients with juvenile and adult types mainly complain of bulbar symptoms and usually show progressive atrophy of the lower brainstem and cervical spinal cord with mild or minimal leukodystrophic changes. Among the many MRI findings of Alexander disease, periventricular linear lesions with various names depending on the thickness and shape seem to represent the unique pathophysiology, because the subventricular zone of the adult human brain includes special astrocytes that behave as multipotent progenitor cells and specifically produce GFAP-epsilon. Except for a few mutations, no clear phenotype-genotype correlation has been established for Alexander disease, although male preponderance in the infantile type suggests that phenotypes may be partly affected by gender.

Age-dependent depletion of human skin-derived progenitor cells

A major unanswered question in autologous cell therapy is the appropriate timing for cell isolation. Many of the putative target diseases arise with old age and previous evidence, mainly from animal models, suggests that the stem/progenitor cell pool decreases steadily with age. Studies with human cells have been generally hampered to date by poor sample availability. In recent years, several laboratories have reported on the existence, both in rodents and humans, of skin-derived precursor (SKP) cells with the capacity to generate neural and mesodermal progenies. This easily obtainable multipotent cell population has raised expectations for their potential use in cell therapy of neurodegeneration. However, we still lack a clear understanding of the spatiotemporal abundance and phenotype of human SKPs. Here we show an analysis of human SKP abundance and in vitro differentiation potential, by using SKPs isolated from four distinct anatomic sites (abdomen, breast, foreskin, and scalp) from 102 healthy subjects aged 8 months to 85 years. Human SKP abundance and differentiation potential decrease sharply with age, being extremely difficult to isolate, expand, and differentiate when obtained from the elderly. Our data suggest preserving human SKP cell banks early in life would be desirable for use in clinical protocols in the aging population.

Subventricular zone neural progenitors from rapid brain autopsies of elderly subjects with and without neurodegenerative disease

In mice and in young adult humans, the subventricular zone (SVZ) contains multipotent, dividing astrocytes, some of which, when cultured, produce neurospheres that differentiate into neurons and glia. It is unknown whether the SVZ of very old humans has this capacity. Here, we report that neural stem/progenitor cells can also be cultured from rapid autopsy samples of SVZ from elderly human subjects, including patients with age-related neurologic disorders. Histological sections of SVZ from these cases showed a glial fibrillary acidic protein (GFAP)-positive ribbon of astrocytes similar to the astrocyte ribbon in human periventricular white matter biopsies that is reported to be a rich source of neural progenitors. Cultures of the SVZ contained 1) neurospheres with a core of Musashi-1-, nestin-, and nucleostemin-immunopositive cells as well as more differentiated GFAP-positive astrocytes; 2) SMI-311-, MAP2a/b-, and beta-tubulin(III)-positive neurons; and 3) galactocerebroside-positive oligodendrocytes. Neurospheres continued to generate differentiated progeny for months after primary culturing, in some cases nearly 2 years postinitial plating. Patch clamp studies of differentiated SVZ cells expressing neuron-specific antigens revealed voltage-dependent, tetrodotoxin-sensitive, inward Na+ currents and voltage-dependent, delayed, slowly inactivating K+ currents, electrophysiologic characteristics of neurons. A subpopulation of these cells also exhibited responses consistent with the kinetics and pharmacology of the h-current. However, although these cells displayed some aspects of neuronal function, they remained immature, insofar as they did not fire action potentials. These studies suggest that human neural progenitor activity may remain viable throughout much of the life span, even in the face of severe neurodegenerative disease.

Dopamine receptor activation promotes adult neurogenesis in an acute Parkinson model

Cell proliferation of neural progenitors in the subventricular zone (SVZ) of Parkinson disease (PD) patients and animal models is decreased. It was previously demonstrated that the neurotransmitter dopamine modulates cell proliferation in the embryonic brain. The aim of the present study was to analyze whether oral treatment with the dopamine receptor agonist pramipexole (PPX) modulates adult neurogenesis in the SVZ/olfactory bulb system in a dopaminergic lesion model. 6-Hydroxydopamine (6-OHDA) lesioned adult rats received either PPX (1.0 mg/kg) or PBS orally twice daily and bromodeoxyuridine (BrdU, a cell proliferation marker) for 10 days and were perfused immediately after treatment or 4 weeks after PPX withdrawal. Stereological analysis revealed a significant augmentation in SVZ proliferation by PPX. Consecutively, enhanced neuronal differentiation and more new neurons were present in the olfactory bulb 4 weeks after PPX withdrawal. In addition, dopaminergic neurogenesis was increased in the olfactory bulb after PPX treatment. Motor activity as assessed by using an open field paradigm was permanently increased even after long term PPX withdrawal. In addition, we demonstrate that D2 and D3 receptors are present on adult rat SVZ-derived neural progenitors in vitro, and PPX specifically increased mRNA levels of epidermal growth factor receptor (EGF-R) and paired box gene 6 (Pax6). Oral PPX treatment selectively increases adult neurogenesis in the SVZ-olfactory bulb system by increasing proliferation and cell survival of newly generated neurons. Analyzing the neurogenic fate decisions mediated by D2/D3 signaling pathways may lead to new avenues to induce neural repair in the adult brain.

The role of oxygen in regulating neural stem cells in development and disease

Oxygen (O2) is a substrate for energy production in the cell and is a rapid regulator of cellular metabolism. Recent studies have also implicated O2 and its signal transduction pathways in controlling cell proliferation, fate, and morphogenesis during the development of many tissues, including the nervous system. O2 tensions in the intact brain are much lower than in room air, and there is evidence that dynamic control of O2 availability may be a component of the in vivo neural stem cell (NSC) niche. At lower O2 tensions, hypoxia-inducible factor 1alpha (HIF1alpha) facilitates signal transduction pathways that promote self-renewal (e.g., Notch) and inhibits pathways that promote NSC differentiation or apoptosis (e.g., bone morphogenetic proteins). Increasing O2 tension degrades HIF1alpha, thus promoting differentiation or apoptosis of NSCs and progenitors. These dynamic changes in O2 tension can be mimicked to optimize ex vivo production methods for cell replacement therapies. Conversely, disrupted O2 availability may play a critical role in disease states such as stroke or brain tumor progression. Hypoxia during stroke activates precursor proliferation in vivo, while glioblastoma stem cells proliferate maximally in a more hypoxic environment than normal stem cells, which may make them resistant to certain anti-neoplastic therapies. These findings suggest that O2 response is central to the normal architecture and dynamics of NSC regulation and in the etiology and treatment of brain diseases.

Novel treatment strategies for malignant gliomas using neural stem cells

Recent studies in stem cell biology have refined our understanding of the origin and progression of cancer. Identification and characterization of endogenous neural stem cells (NSCs), especially those in the adult human brain, have inspired new ideas for selectively targeting and destroying malignant gliomas. Gliomas consist of a heterogeneous population of cells, and some of these cells have characteristics of cancer stem cells. These brain tumor stem cells (BTSCs) share certain characteristics with normal NSCs. It is still unclear, however, whether malignant gliomas in human patients originate from these aberrant BTSCs. Nonetheless, the cellular and molecular similarities between BTSCs and normal NSCs suggest a common research landscape underlying both normal and cancer stem cell biology, wherein findings of one field are relevant to the other. Furthermore, the natural tropism of NSCs to gliomas has generated the idea that modified NSCs can deliver modified genes to selectively destroy malignant brain tumor cells, and even BTSCs, while leaving healthy surrounding neurons intact. These studies and others on the basic biology of both BTSCs and NSCs will be crucial to expanding our treatment strategies for malignant gliomas.

Long-term multilayer adherent network (MAN) expansion, maintenance, and characterization, chemical and genetic manipulation, and transplantation of human fetal forebrain neural stem cells

Human neural stem/precursor cells (hNSC/hNPC) have been targeted for application in a variety of research models and as prospective candidates for cell-based therapeutic modalities in central nervous system (CNS) disorders. To this end, the successful derivation, expansion, and sustained maintenance of undifferentiated hNSC/hNPC in vitro, as artificial expandable neurogenic micro-niches, promises a diversity of applications as well as future potential for a variety of experimental paradigms modeling early human neurogenesis, neuronal migration, and neurogenetic disorders, and could also serve as a platform for small-molecule drug screening in the CNS. Furthermore, hNPC transplants provide an alternative substrate for cellular regeneration and restoration of damaged tissue in neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Human somatic neural stem/progenitor cells (NSC/NPC) have been derived from a variety of cadaveric sources and proven engraftable in a cytoarchitecturally appropriate manner into the developing and adult rodent and monkey brain while maintaining both functional and migratory capabilities in pathological models of disease. In the following unit, we describe a new procedure that we have successfully employed to maintain operationally defined human somatic NSC/NPC from developing fetal, pre-term post-natal, and adult cadaveric forebrain. Specifically, we outline the detailed methodology for in vitro expansion, long-term maintenance, manipulation, and transplantation of these multipotent precursors.

Glioma stem cell lines expanded in adherent culture have tumor-specific phenotypes and are suitable for chemical and genetic screens

Human brain tumors appear to have a hierarchical cellular organization suggestive of a stem cell foundation. In vitro expansion of the putative cancer stem cells as stable cell lines would provide a powerful model system to study their biology. Here, we demonstrate routine and efficient derivation of adherent cell lines from malignant glioma that display stem cell properties and initiate high-grade gliomas following xenotransplantation. Significantly, glioma neural stem (GNS) cell lines from different tumors exhibit divergent gene expression signatures and differentiation behavior that correlate with specific neural progenitor subtypes. The diversity of gliomas may, therefore, reflect distinct cancer stem cell phenotypes. The purity and stability of adherent GNS cell lines offer significant advantages compared to "sphere" cultures, enabling refined studies of cancer stem cell behavior. A proof-of-principle live cell imaging-based chemical screen (450 FDA-approved drugs) identifies both differential sensitivities of GNS cells and a common susceptibility to perturbation of serotonin signaling.

Tuberous sclerosis complex: everything old is new again

Tuberous Sclerosis Complex (TSC) is a multiorgan genetic disease caused by loss of function of either the TSC1 (encodes hamartin) or TSC2 (encodes tuberin) genes. Patients with TSC have benign tumors (hamartomas) in multiple organs though brain involvement is typically the most disabling aspect of the disease as very high rates of neurodevelopmental disorders are seen. While first described well over 120 years ago, recent advances have transformed TSC into a prototypical disorder that exemplifies the methods and potential of molecular medicine. This review will detail historical aspects of TSC and its strong associations with neurodevelopmental disorders focusing on epilepsy and autism. Finally, promising new approaches for the treatment of epilepsy and autism in patients with TSC as well as those in the general population will be discussed.

Oligodendrocyte development and the onset of myelination in the human fetal brain

Oligodendrocytes are cells that myelinate axons, providing saltatory conduction of action potentials and proper function of the central nervous system. Myelination begins prenatally in the human, and the sequence of oligodendrocyte development and the onset of myelination are not thoroughly investigated. This knowledge is important to better understand human diseases, such as periventricular leukomalacia, one of the leading causes of motor deficit in premature babies, and demyelinating disorders such as multiple sclerosis (MS). In this review we discuss the spatial and temporal progression of oligodendrocyte lineage characterized by the expression of specific markers and transcription factors in the human fetal brain from the early embryonic period (5 gestational weeks, gw) until midgestation (24 gw). Our in vitro evidence indicated that a subpopulation of human oligodendrocytes may have dorsal origin, from cortical radial glia cells, in addition to their ventral telencephalic origin. Furthermore, we demonstrated that the regulation of myelination in the human fetal brain includes positive and negative regulators. Chemokines, such as CXCL1, abundant in proliferative zones during brain development and in regions of remyelination in adult, are discussed in the view of their potential roles in stimulating oligodendrocyte development. Other signals are inhibitory and may include, but are not limited to, polysialic acid modification of the neural cell adhesion molecule on axons. Overall, important differences in temporal and spatial distribution and regulatory signals for oligodendrocyte differentiation exist between human and rodent brains. Those differences may underlie the unique susceptibility of humans to demyelinating diseases, such as MS.

Intra-operatively obtained human tissue: protocols and techniques for the study of neural stem cells

The discoveries of neural (NSCs) and brain tumor stem cells (BTSCs) in the adult human brain and in brain tumors, respectively, have led to a new era in neuroscience research. These cells represent novel approaches to studying normal phenomena such as memory and learning, as well as pathological conditions such as Parkinson's disease, stroke, and brain tumors. This new paradigm stresses the importance of understanding how these cells behave in vitro and in vivo. It also stresses the need to use human-derived tissue to study human disease because animal models may not necessarily accurately replicate the processes that occur in humans. An important, but often underused, source of human tissue and, consequently, both NSCs and BTSCs, is the operating room. This study describes in detail both current and newly developed laboratory techniques, which in our experience are used to process and study human NSCs and BTSCs from tissue obtained directly from the operating room.

NG2+/Olig2+ cells are the major cycle-related cell population of the adult human normal brain

A persistent cycling cell population in the normal adult human brain is well established. Neural stem cells or neural progenitors have been identified in the subventricular zone and the dentate gyrus subgranular layer (SGL), two areas of persistent neurogenesis. Cycling cells in other human normal brain areas, however, remains to be established. Here, we determined the distribution and identity of these cells in the cortex, the white matter and the hippocampal formation of adult patients with and without chronic temporal lobe epilepsy using immunohistochemistry for the cell cycle markers Ki-67 (Mib-1) and minichromosome maintenance protein 2. Rare proliferative neuronal precursors expressing the neuronal antigen neuronal nuclei were restricted to the SGL. In contrast, the oligodendrocyte progenitor cell markers Olig2 and the surface antigen NG2 were expressed by the vast majority of cycling cells scattered throughout the cortex and white matter of both control and epileptic patients. Most of these cycling cells were in early G1 phase, and were significantly more numerous in epileptic than in non-epileptic patients. These results provide evidence for a persistent gliogenesis in the human cortex and white matter that is enhanced in an epileptic environment.

Targeting novel integrative nuclear FGFR1 signaling by nanoparticle-mediated gene transfer stimulates neurogenesis in the adult brain

Neurogenesis, the process of differentiation of neuronal stem/progenitor cells (NS/PC) into mature neurons, holds the key to the treatment of various neurodegenerative disorders, which are a major health issue for the world's aging population. We report that targeting the novel integrative nuclear FGF Receptor 1 signaling (INFS) pathway enhances the latent potential of NS/PCs to undergo neuronal differentiation, thus promoting neurogenesis in the adult brain. Employing organically modified silica (ORMOSIL)-DNA nanoplexes to efficiently transfect recombinant nuclear forms of FGFR1 and its FGF-2 ligand into the brain subventricular zone, we find that INFS stimulates the NS/PC to withdraw from the cell cycle, differentiate into doublecortin expressing migratory neuroblasts and neurons that migrate to the olfactory bulb, subcortical brain regions and in the brain cortex. Thus, nanoparticle-mediated non-viral gene transfer may be used to induce selective differentiation of NS/PCs, providing a potentially significant impact on the treatment of a broad range of neurological disorders.

Neurorestorative therapies for stroke: underlying mechanisms and translation to the clinic

Restorative cell-based and pharmacological therapies for experimental stroke substantially improve functional outcome. These therapies target several types of parenchymal cells (including neural stem cells, cerebral endothelial cells, astrocytes, oligodendrocytes, and neurons), leading to enhancement of endogenous neurogenesis, angiogenesis, axonal sprouting, and synaptogenesis in the ischaemic brain. Interaction between these restorative events probably underpins the improvement in functional outcome. This Review provides examples of cell-based and pharmacological restorative treatments for stroke that stimulate brain plasticity and functional recovery. The molecular pathways activated by these therapies, which induce remodelling of the injured brain via angiogenesis, neurogenesis, and axonal and dendritic plasticity, are discussed. The ease of treating intact brain tissue to stimulate functional benefit in restorative therapy compared with treating injured brain tissue in neuroprotective therapy might more readily help with translation of restorative therapy from the laboratory to the clinic.

Applications of neural and mesenchymal stem cells in the treatment of gliomas

In addition to stem cells providing a better understanding about the biology and origins of gliomas, new therapeutic approaches have been developed based on the use of stem cells as delivery vehicles. The unique ability of stem cells to track down tumor cells makes them a very appealing therapeutic modality. This review introduces neural and mesenchymal stem cells, discusses the advances that have been made in the utilization of these stem cells as therapies and in diagnostic imaging (to track the advancement of the stem cells towards the tumor cells), and concludes by addressing various challenges and concerns regarding these therapies.

Cell migration in the normal and pathological postnatal mammalian brain

In the developing brain, cell migration is a crucial process for structural organization, and is therefore highly regulated to allow the correct formation of complex networks, wiring neurons, and glia. In the early postnatal brain, late developmental processes such as the production and migration of astrocyte and oligodendrocyte progenitors still occur. Although the brain is completely formed and structured few weeks after birth, it maintains a degree of plasticity throughout life, including axonal remodeling, synaptogenesis, but also neural cell birth, migration and integration. The subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus are the two main neurogenic niches in the adult brain. Neural stem cells reside in these structures and produce progenitors that migrate toward their ultimate location: the olfactory bulb and granular cell layer of the DG respectively. The aim of this review is to synthesize the increasing information concerning the organization, regulation and function of cell migration in a mature brain. In a normal brain, proteins involved in cell-cell or cell-matrix interactions together with secreted proteins acting as chemoattractant or chemorepellant play key roles in the regulation of neural progenitor cell migration. In addition, recent data suggest that gliomas arise from the transformation of neural stem cells or progenitor cells and that glioma cell infiltration recapitulates key aspects of glial progenitor migration. Thus, we will consider glioma migration in the context of progenitor migration. Finally, many observations show that brain lesions and neurological diseases trigger neural stem/progenitor cell activation and migration toward altered structures. The factors involved in such cell migration/recruitment are just beginning to be understood. Inflammation which has long been considered as thoroughly disastrous for brain repair is now known to produce some positive effects on stem/progenitor cell recruitment via the regulation of growth factor signaling and the secretion of a number of chemoattractant cytokines. This knowledge is crucial for the development of new therapeutic strategies. One of these strategies could consist in increasing the mobilization of endogenous progenitor cells that could replace lost cells and improve functional recovery.

Endogenous Wnt signaling maintains neural progenitor cell potency

Wnt signaling regulates neural stem cell (NSC) function and development throughout an individual's lifetime. Intriguingly, adult hippocampal progenitors (AHPs) produce several Wnts, and the intracellular machinery necessary to respond to them, creating the potential for an active autocrine-signaling loop within this stem cell niche. However, the standard luciferase-based Wnt assay failed to detect this signaling loop. This assay is inherently less temporally sensitive to activity among a population of unsynchronized proliferating cells because it relies on the rapidly degrading reporter luciferase. We circumvented this limitation using a promoter assay that employs green fluorescent protein (GFP), as a relatively long-lived reporter of canonical Wnt activity. We found that at baseline, AHPs secreted functional Wnt that self-stimulates low-level canonical Wnt signaling. Elimination baseline Wnt activity, via application of an extracellular Wnt antagonist promoted neurogenesis, based on a combination of unbiased gene expression analysis and cell-fate analysis. A detailed clonal analysis of progenitors transduced with specific intracellular antagonists of canonical signaling, either Axin or truncated cadherin (beta-catenin sequestering), revealed that loss of baseline signaling depletes the population of multipotent precursors, thereby driving an increasing fraction to assume a committed cell fate (i.e., unipotent progenitors). Similarly, baseline Wnt signaling repressed differentiation of human NSCs. Although the specific Wnts produced by neural precursors vary with age and between species, their effects remain remarkably consistent. In sum, this study establishes that autonomous Wnt signaling is a conserved feature of the neurogenic niche that preserves the delicate balance between NSC maintenance and differentiation.

Sera from children with autism alter proliferation of human neuronal progenitor cells exposed to oxidation

Altered brain development during embryogenesis and early postnatal life has been hypothesized to be responsible for the abnormal behaviors of people with autism. The specific genetic background that alters vulnerability to some environmental insults has been suggested in the etiology of autism; however, the specific pathomechanisms have not been identified. Recently, we showed that sera from children with autism alter the maturation of human neuronal progenitor cells (NPCs) in culture. Results suggest that pre-programmed neurogenesis, i.e., neuronal proliferation, migration, differentiation, growth, and circuit organization, can be affected differently by factors present in autistic sera. In this report, we tested the effect of autistic sera on the vulnerability of NPCs to oxidative stress-a recognized risk factor of autism. We found that mild oxidative stress reduced proliferation of differentiating NPCs but not immature NPCs. This decrease of proliferation was less prominent in cultures treated with sera from children with autism than from age-matched controls. These results suggest that altered response of NPCs to oxidative stress may play a role in the etiology of autism.

Emerging antiangiogenic treatments for gliomas - efficacy and safety issues

PURPOSE OF REVIEW

To review the rationale and recent experience of angiogenesis inhibitors in malignant gliomas and to highlight both the promise and potential complications of these agents.

RECENT FINDINGS

Several new agents targeting angiogenesis in malignant gliomas have become available and have been increasingly used to complement conventional chemotherapy. Specifically, bevacizumab, often in combination with irinotecan, has demonstrated favorable results in achieving significant radiographic responses and in prolonging progression-free survival in patients with recurrent malignant glioma.

SUMMARY

Antiangiogenic drugs have been shown to have promising activity in recurrent malignant gliomas. Investigation of novel antiangiogenic compounds and future clinical trials will determine whether these drugs have a role in first-line therapy. This article reviews the rationale for targeting angiogenesis in malignant brain tumors and summarizes the results of recent clinical trials. In addition, this review will outline potential toxicities associated with angiogenesis inhibition in an attempt to provide practical guidance to physicians treating patients with malignant gliomas.

An efficient method for derivation and propagation of glioblastoma cell lines that conserves the molecular profile of their original tumours

A growing body of evidence suggests that glioma stem-like cells are more representative of their parent tumours when cultured under defined serum-free conditions with the mitogens epidermal growth factor (EGF) and fibroblast growth factor (FGF). However, culturing these cells as free-floating spheroids can result in difficulty in efficiently deriving and propagating cell lines. We have combined neurosphere and monolayer culture techniques to improve the efficiency with which cells can be derived from clinical tumour samples under defined serum-free conditions. We have applied our protocol to consecutive samples of glioblastoma to show that they can form experimental tumours that recapitulate many of the histological features of the parent tumour. We go on to show that the tumour initiating cells also retain the cytogenetic abnormalities of the parent tumour. Finally we examined the cell lines for expression of markers associated with neural stem cells. Our results confirm the expression of transcription factors associated with neural patterning and specification including Sox2, Olig2, Pax6 and Nkx2.2. We went on to establish that these factors were also expressed in the parent tumour indicating that their expression was not a function of our culture conditions. The Cambridge Protocol is an efficient method of deriving stem-like tumour initiating cells from glioblastoma. Improving the efficiency of derivation will facilitate the improvement of in vitro and in vivo model systems to study disease mechanisms, screen drugs and develop novel therapeutic approaches in the future.

Tumor initiating cells in malignant gliomas: biology and implications for therapy

A rare subpopulation of cells within malignant gliomas, which shares canonical properties with neural stem cells (NSCs), may be integral to glial tumor development and perpetuation. These cells, also known as tumor initiating cells (TICs), have the ability to self-renew, develop into any cell in the overall tumor population (multipotency), and proliferate. A defining property of TICs is their ability to initiate new tumors in immunocompromised mice with high efficiency. Mounting evidence suggests that TICs originate from the transformation of NSCs and their progenitors. New findings show that TICs may be more resistant to chemotherapy and radiation than the bulk of tumor cells, thereby permitting recurrent tumor formation and accounting for the failure of conventional therapies. The development of new therapeutic strategies selectively targeting TICs while sparing NSCs may provide for more effective treatment of malignant gliomas.

Simultaneous prospective purification of adult subventricular zone neural stem cells and their progeny

The ability to prospectively isolate adult neural stem cells and their progeny is crucial to study their biology and therapeutic potential. Stem cells in adult mammalian neurogenic niches are a subset of astrocytes. A major limitation in the field has been the inability to distinguish stem cell astrocytes from niche astrocytes. Here, we show that epidermal growth factor receptor (EGFR)-positive subventricular-zone (SVZ) astrocytes are activated stem cells that are eliminated by antimitotic treatment. We developed a simple strategy to simultaneously purify cells at different stages of the adult SVZ stem cell lineage by using FACS. This method combines the use of fluorescent EGF ligand, CD24, and GFP expression in GFAP::GFP transgenic mice and allows the simultaneous purification of activated stem cell astrocytes (GFP(+)EGFR(+)CD24(-)), niche astrocytes (GFP(+)EGFR(-)CD24(-)), transit amplifying cells (GFP(-)EGFR(+)CD24(-)), and neuroblasts (GFP(-)EGFR(-)CD24(low)). One in three EGFR(+) astrocytes gives rise to neurospheres in vitro, a 20-fold enrichment over unsorted cells. Importantly, these cells constitute the neurosphere-forming population among SVZ astrocytes. This approach will be of great utility for future functional and molecular studies of the SVZ stem cell lineage.

Cancer stem cells in brain tumor biology

Tumors are aberrant organ systems containing a complex interplay between the neoplastic compartment and recruited vascular, inflammatory, and stromal elements. Furthermore, most cancers display a hierarchy of differentiation states within the tumor cell population. Molecular signals that drive tumor formation and maintenance commonly overlap with those involved in normal development and wound responses--two processes in which normal stem cells function. It is therefore not surprising that cancers invoke stem cell programs that promote tumor malignancy. Stem-cell-like cancer cells (or cancer stem cells) need not be derived from normal stem cells but may be subjected to evolutionary pressures that select for the capacity to self-renew extensively or differentiate depending on conditions. Current cancer model systems may not fully recapitulate the cellular complexity of cancers, perhaps partially explaining the lack of power of these models in predicting clinical outcomes. New methods are enabling researchers to identify and characterize cancer stem cells. Our laboratory focuses on the roles of brain tumor stem cells in clinically relevant tumor biology, including therapeutic resistance, angiogenesis, and invasion/metastasis. We hope that these studies will translate into improved diagnostic, prognostic, and therapeutic approaches for these lethal cancers.