Multipotent stem/progenitor cells with similar properties arise from two neurogenic regions of adult human brain

Isolation of human multipotent neural progenitors from adult filum terminale

Stem cells have been isolated from several CNS regions, including the spinal cord. However, the terminal end of the spinal cord, filum terminale, has been referred to as a fibrovascular tag without neurogenic potential and of no clinical significance. Recently, we were fortunate to acquire some samples of this tissue. We show for the first time that progenitor cells exhibiting the hallmarks of stem cells can be isolated from adult human filum terminale (FTNPs). More specifically, FTNPs self-renew and proliferate to form neurospheres, and exhibit tripotent differentiation into neurons, astrocytes, and oligodendrocytes. Equally important, FTNPs develop the electrophysiological profile of neurons and glia. Whole-cell patch-clamp recordings show beta-III-tubulin(+) neurons exhibiting overshooting action potentials, displaying both the fast inactivating TTX-sensitive sodium current as well as 4-AP and TEA sensitive potassium currents. To assess potency in vivo, FTNPs were transplanted into the posterior periventricular region of control or ischemic rat brains. Despite a vigorous immune response against the xenograft, FTNPs survived and were found not only in the graft area but had also migrated to the lesioned CA1 region. Notwithstanding the immune response, FTNPs differentiated into astrocytes, but no neuronal differentiation was observed in the transplant milieu tested. However, neuronal differentiation in vivo cannot be ruled out and assessment of the conditions necessary to promote neurogenesis in vivo requires more research. Significantly, no tumor formation or aberrant cell morphology was seen in or adjacent to the graft area. Thus, filum terminale provides a novel source of adult human neural progenitor cells that develop into functional neurons with possible clinical applications.

Beta4 tubulin identifies a primitive cell source for oligodendrocytes in the mammalian brain

We have identified a novel population of cells in the subventricular zone (SVZ) of the mammalian brain that expresses beta4 tubulin (betaT4) and has properties of primitive neuroectodermal cells. betaT4 cells are scattered throughout the SVZ of the lateral ventricles in adult human brain and are significantly increased in the SVZs bordering demyelinated white matter in multiple sclerosis brains. In human fetal brain, betaT4 cell densities peak during the latter stages of gliogenesis, which occurs in the SVZ of the lateral ventricles. betaT4 cells represent <2% of the cells present in neurospheres generated from postnatal rat brain but >95% of cells in neurospheres treated with the anti-mitotic agent Ara C. betaT4 cells produce oligodendrocytes, neurons, and astrocytes in vitro. We compared the myelinating potential of betaT4-positive cells with A2B5-positive oligodendrocyte progenitor cells after transplantation (25,000 cells) into postnatal day 3 (P3) myelin-deficient rat brains. At P20, the progeny of betaT4 cells myelinated up to 4 mm of the external capsule, which significantly exceeded that of transplanted A2B5-positive progenitor cells. Such extensive and rapid mature CNS cell generation by a relatively small number of transplanted cells provides in vivo support for the therapeutic potential of betaT4 cells. We propose that betaT4 cells are an endogenous cell source that can be recruited to promote neural repair in the adult telencephalon.

Stem cells for enhancing recovery after stroke: a review

The potential application for stem cell therapy is vast, and development for use in ischaemic stroke is still in its infancy. Access to stem cells for research is contentious; however, stem cells are obtainable from both animal and human. Despite a limited understanding of their mechanisms of action, clinical trials assessing stem cells in human stroke have been performed. Trials are also underway evaluating haematopoietic precursors mobilised with granulocyte-colony stimulating factor, an approach offering an autologous means of administrating stem cells for therapeutic purposes. This review summarises current knowledge in regard to stem cells and their potential for helping improve recovery after stroke.

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.

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.

Origins and clinical implications of the brain tumor stem cell hypothesis

With the advent of the cancer stem cell hypothesis, the field of cancer research has experienced a revolution in how we think of and approach cancer. The discovery of "brain tumor stem cells" has offered an explanation for several long-standing conundrums on why brain tumors behave the way they do to treatment. Despite the great amount of research that has been done in order to understand the molecular aspects of malignant gliomas, the prognosis of brain tumors remains dismal. The slow progress in extending the survival of patients with malignant CNS neoplasms is very likely due to poor understanding of the cell of origin in these tumors. This review article discusses the progress in our understanding of brain tumor stem cells as the cell of origin in brain cancers. We review the different proposed mechanisms of how brain tumor stem cells may originate, the intracellular pathways disrupted in the pathogenesis of BTSCs, the molecular markers used to identify BTSCs, the molecular mechanisms of cancer initiation and progression, and finally the clinical implications of this research.

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.

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.

Paving the axonal highway: from stem cells to myelin repair

Multiple sclerosis (MS), a demyelinating disorder of the central nervous system (CNS), remains among the most prominent and devastating diseases in contemporary neurology. Despite remarkable advances in anti-inflammatory therapies, the inefficiency or failure of myelin-forming oligodendrocytes to remyelinate axons and preserve axonal integrity remains a major impediment for the repair of MS lesions. To this end, the enhancement of remyelination through endogenous and exogenous repair mechanisms and the prevention of axonal degeneration are critical objectives for myelin repair therapies. Thus, recent advances in uncovering myelinating cell sources and the intrinsic and extrinsic factors that govern neural progenitor differentiation and myelination may pave a way to novel strategies for myelin regeneration. The scope of this review is to discuss the potential sources of stem/progenitor cells for CNS remyelination and the molecular mechanisms underlying oligodendrocyte myelination.

Neurogenesis in the human hippocampus and its relevance to temporal lobe epilepsies

Ample evidence points to the dentate gyrus as anatomical region for persistent neurogenesis in the adult mammalian brain. This has been confirmed in a variety of animal models under physiological as well as pathophysiological conditions. Notwithstanding, similar experiments are difficult to perform in humans. Postmortem studies demonstrated persisting neurogenesis in the elderly human brain. In addition, neural precursor cells can be isolated from surgical specimens obtained from patients with intractable temporal lobe epilepsy (TLE) and propagated or differentiated into neuronal and glial lineages. It remains a controversial issue, whether epileptic seizures have an effect on or even increase hippocampal neurogenesis in humans. Recent data support the notion that seizures induce neurogenesis in young patients, whereas the capacity of neuronal recruitment and proliferation decreases with age. Animal models of TLE further indicate that these newly generated neurons integrate into epileptogenic networks and contribute to increased seizure susceptibility. However, pathomorphological disturbances within the epileptic hippocampus, such as granule cell dispersion (GCD), may not directly result from compromised neurogenesis. Still, the majority of adult TLE patients present with significant dentate granule cell loss at an end stage of the disease, which relates to severe memory and learning disabilities. In conclusion, surgical specimens obtained from TLE patients represent an important tool to study mechanisms of stem cell recruitment, proliferation and differentiation in the human brain. In addition, increasing availability of surgical specimens opens new avenues to systematically explore disease pathomechanisms in chronic epilepsies.

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.

Stem and progenitor cell therapies: recent progress for spinal cord injury repair

Mechanical trauma to the spinal cord is often accompanied by irreversible tissue damage, limited endogenous repair and permanent loss of motor, sensory and autonomic function. The implantation of exogenous cells or the stimulation of endogenous cells, to repopulate and replace or to provide a conducive environment for repair, offers a promising therapeutic direction for overcoming the multitude of obstacles facing successful recovery from spinal cord injury. Although relatively new to the scene of cell based therapies for reparative medicine, stem cells and their progenitors have been labeled as the 'cell of the future' for revolutionizing the treatment of CNS injury and neurodegenerative disorders. The following review examines the different types of stem cells and their progenitors, their utility in experimental models of spinal cord injury and explores the outstanding issues that still need to be addressed before they move towards clinical implementation.

Neurogenesis in adult CNS: from denial to opportunities and challenges for therapy

The discovery of neurogenesis and neural stem cells (NSC) in the adult CNS has overturned a long-standing and deep-routed "dogma" in neuroscience, established at the beginning of the 20(th) century. This dogma lasted for almost 90 years and died hard when NSC were finally isolated from the adult mouse brain. The scepticism in accepting adult neurogenesis has now turned into a rush to find applications to alleviate or cure the devastating diseases that affect the CNS. Here we highlight a number of methodological, technical and conceptual drawbacks responsible for the historical denial of adult neurogenesis. Furthermore, we discuss old and new issues that need to be faced before NSC or endogenous neurogenesis can safely enter into the doctor's bag for therapies.

Neural stem cells in the mammalian brain

New fundamental results on stem cell biology have been obtained in the past 15 years. These results allow us to reinterpret the functioning of the cerebral tissue in health and disease. Proliferating stem cells have been found in the adult brain, which can be involved in postinjury repair and can replace dead cells under specific conditions. Numerous genomic mechanisms controlling stem cell proliferation and differentiation have been identified. The involvement of stem cells in the genesis of malignant tumors has been demonstrated. Neural stem cell tropism toward tumors has been shown. These findings suggest new lines of research on brain functioning and development. Stem cells can be used to develop radically new treatments of neurodegenerative and cancer diseases of the brain.

Myelin repair: the role of stem and precursor cells in multiple sclerosis

Multiple sclerosis is the most common potential cause of neurological disability in young adults. The disease has two distinct clinical phases, each reflecting a dominant role for separate pathological processes: inflammation drives activity during the relapsing-remitting stage and axon degeneration represents the principal substrate of progressive disability. Recent advances in disease-modifying treatments target only the inflammatory process. They are ineffective in the progressive stage, leaving the science of disease progression unsolved. Here, the requirement is for strategies that promote remyelination and prevent axonal loss. Pathological and experimental studies suggest that these processes are tightly linked, and that remyelination or myelin repair will both restore structure and protect axons. This review considers the basic and clinical biology of remyelination and the potential contribution of stem and precursor cells to enhance and supplement spontaneous remyelination.

Adult mammalian neurogenesis and the New Zealand white rabbit

Although the central nervous system is unable to undergo spontaneous repair and is hostile to the integration of exogenously delivered cells, various examples of adult structural plasticity have been shown to occur. It is now widely accepted that endogenous proliferative activity leading to the production of new neurons exists, at least within two restricted brain sites: the hippocampal dentate gyrus and the forebrain subventricular zone. A substantial insight into spontaneous neurogenesis within these allocortical regions in rodents has been obtained, but less is known regarding its occurrence in other mammalian brain regions. In this review, differences in the structural and temporal characteristics of protracted neurogenesis in mammals will be considered. Attention will be focused on the rabbit cerebrum and cerebellum, where unexpected features of structural plasticity have been found to occur despite the relative closeness of the Orders Lagomorpha and Rodentia.

Neurogenesis in the aging brain

Neurogenesis, or the birth of new neural cells, was thought to occur only in the developing nervous system and a fixed neuronal population in the adult brain was believed to be necessary to maintain the functional stability of adult brain circuitry. However, recent studies have demonstrated that neurogenesis does indeed continue into and throughout adult life in discrete regions of the central nervous systems (CNS) of all mammals, including humans. Although neurogenesis may contribute to the ability of the adult brain to function normally and be induced in response to cerebral diseases for self-repair, this nevertheless declines with advancing age. Understanding the basic biology of neural stem cells and the molecular and cellular regulation mechanisms of neurogenesis in young and aged brain will allow us to modulate cell replacement processes in the adult brain for the maintenance of healthy brain tissues and for repair of disease states in the elderly.

Mature astrocytes in the adult human neocortex express the early neuronal marker doublecortin

Doublecortin (DCX) is a microtubule-associated protein expressed by migrating neuroblasts and is considered to be a reliable marker of neurogenesis. DCX has been used to study the relation between neurogenesis in adult human brain and neurological and neurodegenerative disease processes in the search for putative therapeutic strategies. Using autopsy and surgically resected tissue from a total of 60 patients, we present evidence that DCX is present in several cellular compartments of differentiated astrocytes in the adult human neocortex. One of these compartments consisted of peripheral processes forming punctate envelopes around mature neuronal cell bodies. Markers of glial activation, such as GFAP and HLA, were not associated with DCX immunoreactivity, however, the presence of cytoarchitectural alterations tended to correlate with reduced DCX staining of astrocytic somata. Interestingly, local Alzheimer pathology that showed no relation with cytoarchitectural abnormalities appeared to correlate negatively with the expression of DCX in the astrocytic somata. In combination with the literature our data support the view that DCX in the adult human neocortex may have a function in glia-to-neuron communication. Furthermore, our results indicate that in the adult human neocortex DCX is neither a reliable nor a selective marker of neurogenesis.

Routes of stem cell administration in the adult rodent

Stem cell transplantation to replace damaged tissue or correct metabolic disease holds the promise of helping a myriad of human afflictions. Although a great deal of attention has focused on pluripotent stem cells derived from embryos, adult stem cells have been described in a variety of tissues, and they likely will prove to be as beneficial as embryonic stem cells in cell replacement therapy and control of inbred errors of metabolism. We describe methods by which stem cells can be introduced into the nervous system, although the techniques are applicable to any portion of the body to be targeted or any cell that may be used for cell therapy. The first and most straight-forward method is introduction of stem cells directly into the brain parenchyma. The second, which in our hands has proven to be superior in some instances, is introduction of the stem cells into the circulatory system.

Production of neurospheres from CNS tissue

The relatively recent discovery of persistent adult neurogenesis has led to the experimental isolation and characterization of central nervous system neural stem cell populations. Protocols for in vitro analysis and expansion of neural stem cells are crucial for understanding their properties and defining characteristics. The methods described here allow for cell and molecular analysis of individual clones of cells--neurospheres--derived from neural stem/progenitor cells. Neurospheres can be cultivated from a variety of normal, genetically altered, or pathological tissue specimens, even with protracted postmortem intervals, for studies of mechanisms underlying neurogenesis, cell fate decisions, and cell differentiation. Neurosphere-forming cells hold great promise for the development of cell and molecular therapeutics for a variety of neurological diseases.

Comparison of the therapeutic potential of adult and embryonic neural precursor cells in a rat model of Parkinson disease

Object

The therapeutic effects of adult and embryonic neural precursor cells (NPCs) were evaluated and their therapeutic potential compared in a rat model of Parkinson disease.

Methods

Adult NPCs were obtained from the subventricular zone and embryonic NPCs were taken from the ganglionic eminence of 14-day-old embryos. Each NPC type was cultured with epidermal growth factor. The in vitro neuronal differentiation rate of adult NPCs was approximately equivalent to that of embryonic NPCs after two passages. Next, the NPCs were transfected with either green fluorescent protein or glial cell line–derived neurotrophic factor (GDNF) by adenoviral infection and transplanted into the striata in a rat model of Parkinson disease (PD) induced by unilateral intrastriatal injection of 6-hydroxydopamine. An amphetamine-induced rotation test was used to evaluate rat behavioral improvement, and immunohistochemical analysis was performed to compare grafted cell survival, differentiation, and host tissue changes.

Results

The rats with GDNF-transfected NPCs had significantly fewer amphetamine-induced rotations and less histological damage. Except for the proportion of surviving grafted cells, there were no significant differences between adult and embryonic NPCs.

Conclusions

Adult and embryonic NPCs have a comparable therapeutic potential in a rat model of PD.

Fibroblast growth factor-20 increases the yield of midbrain dopaminergic neurons derived from human embryonic stem cells

In the central nervous system, fibroblast growth factor (FGF)-20 has been reported to act preferentially on midbrain dopaminergic neurons. It also promotes the dopaminergic differentiation of stem cells. We have analyzed the effects of FGF-20 on human embryonic stem cells (hESCs) differentiation into dopaminergic neurons. We induced neuronal differentiation of hESCs by co-culturing those with PA6 mouse stromal cells for 3 weeks. When we supplemented the culture medium with FGF-20, the number of tyrosine hydroxylase (TH)-expressing neurons increased fivefold, from 3% to 15% of the hESC-derived cells. The cultured cells also expressed other midbrain dopaminergic markers (PITX3, En1, Msx1, and Aldh1), suggesting that some had differentiated into midbrain dopaminergic neurons. We observed no effect of FGF-20 on the size of the soma area or neurite length of the TH-immunopositive neurons. Regardless of whether FGF-20 had been added or not, 17% of the hESC-derived cells expressed the pan-neuronal marker b-III-Tubulin. The proportion of proliferating cells positive for Ki-67 was also not affected by FGF-20 (7% of the hESC-derived cells). By contrast, after 3 weeks in culture FGF-20 significantly reduced the proportion of cells undergoing cell death, as revealed by immunoreactivity for cleaved caspase-8, Bcl-2 associated X protein (BAX) and cleaved caspase-3 (2.5% to 1.2% of cleaved caspase-3-positive cells out of the hESC-derived cells). Taken together, our results indicate that FGF-20 specifically increases the yield of dopaminergic neurons from hESCs grown on PA6 feeder cells and at least part of this effect is due to a reduction in cell death.

The biology of cancer stem cells

Cancers originally develop from normal cells that gain the ability to proliferate aberrantly and eventually turn malignant. These cancerous cells then grow clonally into tumors and eventually have the potential to metastasize. A central question in cancer biology is, which cells can be transformed to form tumors? Recent studies elucidated the presence of cancer stem cells that have the exclusive ability to regenerate tumors. These cancer stem cells share many characteristics with normal stem cells, including self-renewal and differentiation. With the growing evidence that cancer stem cells exist in a wide array of tumors, it is becoming increasingly important to understand the molecular mechanisms that regulate self-renewal and differentiation because corruption of genes involved in these pathways likely participates in tumor growth. This new paradigm of oncogenesis has been validated in a growing list of tumors. Studies of normal and cancer stem cells from the same tissue have shed light on the ontogeny of tumors. That signaling pathways such as Bmi1 and Wnt have similar effects in normal and cancer stem cell self-renewal suggests that common molecular pathways regulate both populations. Understanding the biology of cancer stem cells will contribute to the identification of molecular targets important for future therapies.

A putative link of PUFA, GPR40 and adult-born hippocampal neurons for memory

Long chain polyunsaturated fatty acids (PUFA) such as docosahexaenoic and arachidonic acids, which are enriched in the brain, are important for multiple aspects of neuronal development and function including neurite outgrowth, signal transduction and membrane fluidity. Recent studies show that PUFA are capable of improving hippocampal long-term potentiation, learning ability of aged rats, and cognitive function of humans with memory deficits, although the underlying mechanisms are unknown. There have been several reports studying physiological roles of G-protein coupled receptor 40 (GPR40) in the pancreas, but no studies have focused on the function of GPR40 in the brain. As GPR40 was recently identified in neurons throughout the brain, it is probable that certain PUFA may act, as endogenous ligands, on GPR40 at their cell surface. However, the effects of PUFA upon neuronal functions are still not clearly understood. Here, although circumferential, a combination of in vitro and in vivo data is introduced to consider the effects of docosahexaenoic and arachidonic acids on brain functions. GPR40 was found in the newborn neurons of the normal and postischemic hippocampi of adult macaque monkeys, while the positive effects of PUFA upon Ca(2+) mobilization and cognitive functions were demonstrated in both GPR40 gene-transfected PC12 cells and human subjects with memory deficits. The purpose of this review is to propose a putative link among PUFA, GPR40, and hippocampal newborn neurons by discussing whether PUFA can improve memory functions through GPR40 activation of adult-born neurons. At present, little is known about PUFA requirements that make possible neurogenesis in the adult hippocampus. However, the idea that 'PUFA-GPR40 interaction might be crucial for adult neurogenesis and/or memory' should be examined in detail using various experimental paradigms.

Causality of stem cell based neurogenesis and depression--to be or not to be, is that the question?

Mood disorders compose a considerable portion of the worldwide prevailing diseases with high suicide rates and urgent demand for novel therapeutic interventions as efficacious treatment is still lacking. Depression is thought to feature distinct morphological correlatives in the brain and has recently been linked to adult neurogenesis (NG) in the hippocampal formation. Numerous findings give rise to the hypothesis that depression and declining NG in the hippocampus may be causally connected. This implies that depressive symptoms could originate from impairments in NG and, vice versa, that improved NG could mediate antidepressant action and alleviate symptoms. Thus, great hopes rest on the question whether the observed increase in NG following antidepression treatment may have the potential to become a novel drug target and specific mechanism in the development of the next generation of antidepressants that specifically involves targeting of neuropoetic factors in addition to their "traditional" effects as modulators of synaptic transmission. Along the still hypothetical association of depression and NG, however, several controversies and unresolved questions exist with respect to the presently available data and interpretation. This article highlights and summarizes some of the most pressing issues and identifies the crucial ones that await urgent clarification and resolving. Without their reliable answering, the fascinating notion of a neurogenic basis for depression will remain to be greatly speculative.

Neurogenesis in the postnatal human epileptic brain

OBJECT

The normal adult human telencephalon does not reveal evidence of spontaneous neuronal migration and differentiation despite the robust germinal capacity of the subventricular zone (SVZ) astrocyte ribbon that contains neural stem cells. This might be because it is averse to accepting new neurons into an established neuronal network, probably representing an evolutionary acquisition to prevent the formation of anomalous neuronal circuits. Some forms of epilepsy, such as malformations of cortical development, are thought to be due to abnormal corticogenesis during the embryonic and early postnatal periods. The role of postnatal architectural reorganization and possibly postnatal neurogenesis in some forms of epilepsy in humans remains unknown. In this study the authors used resected specimens of epileptic brain to determine whether neurogenesis could occur in the diseased tissue.

METHODS

The authors studied freshly resected brain tissue obtained in 47 patients who underwent neurosurgical procedures and four autopsies. Forty-four samples were harvested in patients who underwent resection for the treatment of pharmacoresistant epilepsy.

RESULTS

Using organotypic brain slice preparations cultured with 5-bromodeoxyuridine (a marker for cell proliferation), immunohistochemistry, and cell trackers, the authors demonstrate the presence of spontaneous cell proliferation, migration, and neuronal differentiation in the adult human telencephalon that starts in the SVZ and progresses to the adjacent white matter and neocortex in human neocortical pathological structures associated with epilepsy. No cell migration or neuronal differentiation was found in the control group.

CONCLUSIONS

The presence of spontaneous neurogenesis associated with some forms of human neocortical epilepsy may represent an erroneous and maladaptive mechanism for neuronal circuitry repair, or it may be an intrinsic part of the pathogenic process.

Altered development of neuronal progenitor cells after stimulation with autistic blood sera

Changes of brain structure and functions in people with autism may result from altered neuronal development, however, no adequate cellular or animal models are available to study neurogenesis in autism. Neuronal development can be modeled in culture of neuronal progenitor cells (NPCs) stimulated with serum to differentiate into neurons. Because sera from people with autism and age-matched controls contain different levels of numerous biologically active factors, we hypothesized that development of human NPCs induced to differentiate into neurons with sera from children with autism reflects the altered early neuronal development that leads to autism. The control and autistic sera were collected from siblings aged below 6 years that lived in the same environment. The effect of sera on differentiation of NPC neurospheres into neuronal colonies was tested in 72-h-long cultures by morphometry, immunocytochemistry and immunoblotting. We found that sera from children with autism significantly reduced NPCs' proliferation, but stimulated cell migration, development of small neurons with processes, length of processes and synaptogenesis. These results suggest that development of network of processes and synaptogenesis--the specific events in the brain during postnatal ontogenesis--are altered in autism. Further studies in this cell culture model may explain some of the cellular alterations described in autistic patients.

Alternative splicing events identified in human embryonic stem cells and neural progenitors

Human embryonic stem cells (hESCs) and neural progenitor (NP) cells are excellent models for recapitulating early neuronal development in vitro, and are key to establishing strategies for the treatment of degenerative disorders. While much effort had been undertaken to analyze transcriptional and epigenetic differences during the transition of hESC to NP, very little work has been performed to understand post-transcriptional changes during neuronal differentiation. Alternative RNA splicing (AS), a major form of post-transcriptional gene regulation, is important in mammalian development and neuronal function. Human ESC, hESC-derived NP, and human central nervous system stem cells were compared using Affymetrix exon arrays. We introduced an outlier detection approach, REAP (Regression-based Exon Array Protocol), to identify 1,737 internal exons that are predicted to undergo AS in NP compared to hESC. Experimental validation of REAP-predicted AS events indicated a threshold-dependent sensitivity ranging from 56% to 69%, at a specificity of 77% to 96%. REAP predictions significantly overlapped sets of alternative events identified using expressed sequence tags and evolutionarily conserved AS events. Our results also reveal that focusing on differentially expressed genes between hESC and NP will overlook 14% of potential AS genes. In addition, we found that REAP predictions are enriched in genes encoding serine/threonine kinase and helicase activities. An example is a REAP-predicted alternative exon in the SLK (serine/threonine kinase 2) gene that is differentially included in hESC, but skipped in NP as well as in other differentiated tissues. Lastly, comparative sequence analysis revealed conserved intronic cis-regulatory elements such as the FOX1/2 binding site GCAUG as being proximal to candidate AS exons, suggesting that FOX1/2 may participate in the regulation of AS in NP and hESC. In summary, a new methodology for exon array analysis was introduced, leading to new insights into the complexity of AS in human embryonic stem cells and their transition to neural stem cells.

Activation of subventricular zone stem cells after neuronal injury

The mammalian subventricular zone (SVZ) has garnered a tremendous amount of attention as a potential source of replacement cells for neuronal injury. This zone is highly neurogenic, harbours stem cells and supports long-distance migration. The general pattern of activation includes increased proliferation, neurogenesis and emigration towards the injury. Intrinsic transcription factors and environmental signalling molecules are rapidly being discovered that may facilitate the induction of these cells to mount appropriate therapeutic responses. The extent of SVZ neurogenesis in humans is controversial. However, tantalizing new data suggest that humans are capable of generating increased numbers of neurons after a variety of diseases.

Abnormalities in Neural Progenitor Cells in a Dog Model of Lysosomal Storage Disease

Lysosomal storage disorders constitute a large group of genetic diseases, many of which are characterized by mental retardation and other neurologic symptoms. The mechanisms of neural dysfunction remain poorly understood. Because neural progenitor cells (NPCs) are fundamentally important to normal brain development and function, we investigated NPC properties in a canine model of mucopolysaccharidosis VII (MPS VII). MPS VII is a lysosomal storage disorder characterized by defects in the catabolism of glycosaminoglycans. NPCs were isolated from the olfactory bulb, cerebellum, and striatal subventricular zone of normal and MPS VII (beta-glucuronidase-deficient) postnatal dog brains. Canine NPCs (cNPCs) from normal and MPS VII brains had similar growth curves, but cerebellar-derived cNPCs grew significantly slower than those derived from other regions. In differentiation assays, MPS VII cNPCs from the striatal subventricular zone and cerebellum generated fewer mature neuronal and/or glial cells than normal, and MPS VII olfactory bulb-derived cNPCs retained significantly more phenotypically immature cells. These differences were only present at the earliest time point after isolation; at later passages, there were no differences attributable to genotype. The data suggest that MPS VII cNPCs respond differently to developmental cues in vivo, probably because of the diseased neural microenvironment rather than intrinsic cellular deficits.

Transplantation of stem cells from the adult human brain to the adult rat brain

OBJECTIVE

To investigate the migration, proliferation, and differentiation of stem cells and neural progenitor cells (NPCs) from the adult human brain after transplantation into adult rodent brains.

METHODS

Adult human NPCs were obtained from temporal lobe specimens removed because of medical intractable epilepsy. The cells were transplanted into the posterior periventricular region above the hippocampus in the brains of either healthy adult rats (control) or rats with selective injury of the hippocampal CA1 region (global ischemia).

RESULTS

In the control animals, grafted cells were mainly distributed from the site of transplantation toward the midline along white matter tracts. The density of transplanted cells elsewhere, including the hippocampus, was low and apparently random. In animals with CA1 damage, NPCs showed targeted migration into the injured area. Cell survival at 10 weeks was 4.7 +/- 0.3% (control, n = 3) and 3.7 +/- 1.1% (ischemia, n = 3); at 16 weeks, cell survival was 3.4 +/- 0.6% (control, n = 2) and 7.2 +/- 1.5% (ischemia, n = 2), i.e., comparable to what has been observed earlier when transplanting embryonic tissue into the human brain or progenitor cells between inbred rats. The number of dividing cells decreased with time. Sixteen weeks after transplantation, 4 +/- 1% (n = 4) of the cells showed proliferative activity. We did not observe signs of tumor formation or aberrant cell morphology. Neuronal differentiation was much slower than what has been observed earlier in vitro or after transplantation to the developing nervous system, and 16 weeks after transplantation many surviving cells were still in maturation.

CONCLUSION

The present study shows that adult human NPCs survive, show targeted migration, proliferate, and differentiate after grafting into the adult rat brain.

Multipotent stem and progenitor cells of the olfactory epithelium

In recent decades, a wide spectrum of fetal and embryonic stem and progenitor cells were used for cell therapy of diseases of the central nervous system, but the olfactory glial ensheathing cells exhibited certain advantages due to their biological properties and capacity to stimulate regeneratory processes in spinal injury. The therapeutic effect of a heterogeneous complex of olfactory epithelial cells is more pronounced; apart from glial ensheathing cells, this complex includes fibroblasts, Schwann cells, stem and progenitor cells of this structure. The use of minimally invasive methods for isolation of human olfactory epithelial tissue is important for clinical practice, because they provide cells for autologous transplantation and rule out graft rejection immune reaction and the risk of transmission viral infection and transfer of genetic defects, which can be associated with allotransplantation.

Long-term culture and neuronal survival after intraspinal transplantation of human spinal cord-derived neurospheres

There is heterogeneity in neural stem and progenitor cell characteristics depending on their species and regional origin. In search for potent in vitro-expanded human neural precursor cells and cell therapy methods to repair the injured human spinal cord, the possible influence exerted by intrinsic cellular heterogeneity has to be considered. Data available on in vitro-expanded human spinal cord-derived cells are sparse and it has previously been difficult to establish long-term neurosphere cultures showing multipotentiality. In the present paper, human spinal cord-derived neurospheres were cultured in the presence of EGF, bFGF and CNTF for up to 25 passages (>350 days) in vitro. In contrast to the human first trimester subcortical forebrain, spinal cord tissue>9.5 weeks of gestation could not serve as a source for long-term neurosphere cultures under the present conditions. After withdrawal of mitogens, cultured neurospheres (at 18 passages) gave rise to cells with neuronal, astrocytic and oligodendrocytic phenotypes in vitro. After transplantation of human spinal cord-derived neurospheres to the lesioned spinal cord of immuno-deficient adult rats, large numbers of cells survived at least up to 6 weeks, expressing neuronal and astrocytic phenotypes. These results demonstrate that it is possible to expand and maintain multipotent human spinal cord-derived neurospheres in vitro for extended time-periods and that they have promising in vivo potential after engraftment to the injured spinal cord.

Most C6 Cells Are Cancer Stem Cells: Evidence from Clonal and Population Analyses

Cancer stem cells have been isolated from human gliomas and many other parenchymal tumors. It was previously assumed that many established malignant cell lines also contain a rare subpopulation of stem cells. This study was designed to investigate the fraction of cancer stem cells in the C6 glioma cell line using clonal and population analyses, rather than isolating methods, which are based on specific markers. Interestingly, in the serum-containing medium, each of the 67 single C6 cells plated per miniwell was able to generate a clone and subclones, which subsequently gave rise to a xenograft glioma in the BALB/C-nude mouse. The CD133- C6 cells also possessed clonogenic, self-renewal, and tumorigenic capacities. Moreover, our findings indicated that brief exposure to Hoechst 33342 was harmful to the clonogenicity and proliferation of individual C6 cells. Therefore, the non-side-population cells may be deprived of their stem cell features in the process of Hoechst 33342 staining as a step in isolating a Hoechst-negative side population with flow cytometry. Thus, we concluded that the C6 line was mainly composed of cancer stem cells, although many of them were neither CD133+ nor side population.

Adult neurogenesis and cellular brain repair with neural progenitors, precursors and stem cells

Recent work in neuroscience has shown that the adult central nervous system (CNS) contains neural progenitors, precursors and stem cells that are capable of generating new neurons, astrocytes and oligodendrocytes. While challenging the previous dogma that no new neurons are born in the adult mammalian CNS, these findings bring with them the future possibilities for development of novel neural repair strategies. The purpose of this review is to present the current knowledge about constitutively occurring adult mammalian neurogenesis, highlight the critical differences between 'neurogenic' and 'non-neurogenic' regions in the adult brain, and describe the cardinal features of two well-described neurogenic regions-the subventricular zone/olfactory bulb system and the dentate gyrus of the hippocampus. We also provide an overview of presently used models for studying neural precursors in vitro, mention some precursor transplantation models and emphasize that, in this rapidly growing field of neuroscience, one must be cautious with respect to a variety of methodological considerations for studying neural precursor cells both in vitro and in vivo. The possibility of repairing neural circuitry by manipulating neurogenesis is an intriguing one, and, therefore, we also review recent efforts to understand the conditions under which neurogenesis can be induced in non-neurogenic regions of the adult CNS. This work aims towards molecular and cellular manipulation of endogenous neural precursors in situ, without transplantation. We conclude this review with a discussion of what might be the function of newly generated neurons in the adult brain, and provide a summary of present thinking about the consequences of disturbed adult neurogenesis and the reaction of neurogenic regions to disease.

Comparative analysis of in vitro conditions for rat adult neural progenitor cells

Various protocols have been published for in vitro expansion and maintenance of adult neural progenitor cells (ANPC). However, there are only few data comparing these protocols regarding their influence on proliferation, migration and differentiation. Freshly isolated ANPC from olfactory bulb (BO) and dentate gyrus (DG) of adult rat brains forming neurospheres and expressing the neural stem cell markers nestin and Sox-2 were used in a comparative analysis of five different medium combinations. Medium containing N2 and fetal calf serum (FCS), but no additional cytokines was unsuitable for an effective long-term expansion of ANPC due to a significantly reduced proliferation rate. Media containing BIT, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), platelet-derived growth factor AB (PDGF-AB) and leukemia inhibitory factor (LIF) or B27, bFGF and EGF are recommendable for the cultivation of DG-derived ANPC as neurospheres only. Unlike, culture media containing BIT, bFGF, EGF and PDGF-AB or N2, bFGF and EGF were suitable for all applications tested as they responded similarly regarding proliferation, migration and expression of differentiation markers. The results of the present study might help to improve the effective in vitro expansion of ANPC derived from rare human tissue samples.

The human subventricular zone: a source of new cells and a potential source of brain tumors

The mammalian brain has been perceived as a quiescent organ incapable of postnatal neurogenesis for many years. Most recently, several studies have demonstrated that the adult mammalian brain is indeed capable of neurogenesis and that the process is primarily confined to the subventricular zone (SVZ) of the forebrain and the subgranular zone (SGZ) of the hippocampus. Of these regions, the SVZ is the largest niche of neurogenesis in the adult mammalian brain. Within this niche resides a subpopulation of astrocytes with stem cell-like features of self-renewal and multipotentiality. Interestingly, there is also a subpopulation of cells within brain tumors that possess these same characteristics. Based on these findings, the emerging hypothesis is that brain tumor stem cells may be derived from neural stem cells and that both of these populations may originate from the SVZ. This possible connection stresses the importance of studying and understanding the role that the human SVZ plays in not only harboring neural and brain tumor stem cells, but how this microenvironment may support both neurogenesis and tumorigenesis. Furthermore, the obvious differences in the SVZ between humans and other animals make it important to understand the human model when studying human disease. Such an understanding may lead to novel therapeutic strategies for both neurodegenerative diseases and currently intractable brain tumors.

Activation of the subventricular zone in multiple sclerosis: evidence for early glial progenitors

In multiple sclerosis (MS), oligodendrocyte and myelin destruction lead to demyelination with subsequent axonal loss. Experimental demyelination in rodents has highlighted the activation of the subventricular zone (SVZ) and the involvement of progenitor cells expressing the polysialylated form of neural cell adhesion molecule (PSA-NCAM) in the repair process. In this article, we studied the distribution of early PSA-NCAM(+) progenitors in the SVZ and MS lesions in human postmortem brains. Compared with controls, MS SVZ showed a 2- to 3-fold increase in cell density and proliferation, which correlated with enhanced numbers of PSA-NCAM(+) and glial fibrillary acidic protein-positive (GFAP(+)) cells. PSA-NCAM(+) progenitors mainly were Sox9(+), and a few expressed Sox10 and Olig2, markers of oligodendroglial specification. PSA-NCAM(+) progenitors expressing Sox10 and Olig2 also were detected in demyelinated MS lesions. In active and chronic active lesions, the number of PSA-NCAM(+) progenitors was 8-fold higher compared with chronic silent lesions, shadow plaques, and normal-appearing white matter. In active and chronic active lesions, PSA-NCAM(+) progenitors were more frequent in periventricular lesions (30-50%) than in lesions remote from the ventricular wall. These data indicate that, as in rodents, activation of gliogenesis in the SVZ occurs in MS and suggest the mobilization of SVZ-derived early glial progenitors to periventricular lesions, where they could give rise to oligodendrocyte precursors. These early glial progenitors could be a potential target for therapeutic strategies designed to promote myelin repair in MS.

Strategies for achieving and monitoring myelin repair

A number of factors more or less unique to multiple sclerosis have suggested that this disease may be particularly amenable to cell-based reparative therapies. The relatively focussed damage to oligodendrocytes and myelin at least in early disease implies that only a single population of cells need be replaced-and that the daunting problem of re-establishing connectivity does not apply. The presence of significant though partial spontaneous myelin repair in multiple sclerosis proves there to be no insurmountable barrier to remyelination intrinsic to the CNS: the therapeutic challenge becomes that of supplementing this spontaneous process, rather than creating repair de novo. Finally, the large body of available knowledge concerning the biology of oligodendrocytes, and the success of experimental myelin repair, have allowed cautious optimism that future prospects for such therapies are not unrealistic. Nonetheless, particular and significant problems are not hard to list: the occurrence of innumerable lesions scattered throughout the CNS, axon loss, astrocytosis, and a continuing inflammatory process, to name but a few. Here we review the progress and the areas where difficulties have yet to be resolved in efforts to develop remyelinating therapies for multiple sclerosis.

Transcription profiling of adult and fetal human neuroprogenitors identifies divergent paths to maintain the neuroprogenitor cell state

Global gene expression profiling was performed using RNA from adult human hippocampus-derived neuroprogenitor cells (NPCs) and multipotent frontal cortical fetal NPCs compared with adult human mesenchymal stem cells (hMSCs) as a multipotent adult stem cell control, and adult human hippocampal tissue, to define a gene expression pattern that is specific for human NPCs. The results were compared with data from various databases. Hierarchical cluster analysis of all neuroectodermal cell/tissue types revealed a strong relationship of adult hippocampal NPCs with various white matter tissues, whereas fetal NPCs strongly correlate with fetal brain tissue. However, adult and fetal NPCs share the expression of a variety of genes known to be related to signal transduction, cell metabolism and neuroectodermal tissue. In contrast, adult NPCs and hMSCs overlap in the expression of genes mainly involved in extracellular matrix biology. We present for the first time a detailed transcriptome analysis of human adult NPCs suggesting a relationship between hippocampal NPCs and white matter-derived precursor cells. We further provide a framework for standardized comparative gene expression analysis of human brain-derived NPCs with other stem cell populations or differentiated tissues. Disclosure of potential conflicts of interest is found at the end of this article.

Inflammation and depression: is there a causal connection with dementia?

Epidemiological studies show that there is a correlation between chronic depression and the likelihood of dementia in later life. There is evidence that inflammatory changes in the brain are pathological features of both depression and dementia. This suggests that an increase in inflammation-induced apoptosis, together with a reduction in the synthesis of neurotrophic factors caused by a rise in brain glucocorticoids, may play a role in the pathology of these disorders. A reduction in the neuroprotective components of the kynurenine pathway, such as kynurenic acid, and an increase in the neurodegenerative components, 3- hydroxykynurenine and quinolinic acid, contribute to the pathological changes. Such changes are postulated to cause neuronal damage and thereby predispose chronically depressed patients to dementia.

Stem Cells, Regenerative Medicine, and Animal Models of Disease

The field of stem cell biology and regenerative medicine is rapidly moving toward translation to clinical practice, and in doing so has become even more dependent on animal donors and hosts for generating cellular reagents and assaying their potential therapeutic efficacy in models of human disease. Advances in cell culture technologies have revealed a remarkable plasticity of stem cells from embryonic and adult tissues, and transplantation models are now needed to test the ability of these cells to protect at-risk cells and replace cells lost to injury or disease. With such a mandate, issues related to acceptable sources and controversial (e.g., chimeric) models have challenged the field to provide justification of their potential efficacy before the passage of new restrictions that may curb anticipated breakthroughs. Progress from the use of both in vitro and in vivo regenerative medicine models already offers hope both for the facilitation of stem cell phenotyping in recursive gene expression profile models and for the use of stem cells as powerful new therapeutic reagents for cancer, stroke, Parkinson's, and other challenging human diseases that result in movement disorders. This article describes research in support of the following three objectives: (1) To discover the best stem or progenitor cell in vitro protocols for isolating, expanding, and priming these cells to facilitate their massive propagation into just the right type of neuronal precursor cell for protection or replacement protocols for brain injury or disease, including those that affect movement such as Parkinson's disease and stroke; (2) To discover biogenic factors--compounds that affect stem/progenitor cells (e.g., from high-throughput screening and other bioassay approaches)--that will encourage reactive cell genesis, survival, selected differentiation, and restoration of connectivity in central nervous system movement and other disorders; and (3) To establish the best animal models of human disease and injury, using both small and large animals, for testing new regenerative medicine therapeutics.

The Human Brain Subventricular Zone: Stem Cells in This Niche and Its Organization

The human brain harbors stem cells in the subventricular zone (SVZ). The authors have collected postmortem and intraoperative tissue from adult human patients and found that it contains a unique ribbon of astrocytes that proliferate in vivo and can function as neural stem cells in vitro. Furthermore, they have conducted an anatomic, cytoarchitectural, and ultrastructural study in complete postmortem brains to define the precise organization of the lateral walls of the human lateral ventricles. With immunohistochemistry, the authors mapped a proliferative glial fibrillary acidic protein (GFAP)--positive ribbon of astrocytic cells in the human SVZ. In this article, the authors report on four main types of SVZ walls in the human brain. Types A through C line the striatum from dorsal (type A), to middle (type B), to ventral (type C) regions along the lateral wall of the lateral ventricle. Type D wall lines the floor of the temporal horn over the hippocampus. Understanding the organization of the adult human SVZ represents a necessary first step in understanding cellular proliferation, precursor migration, and the neurogenic niche of the largest known germinal region in the adult human brain.

Microglia instruct subventricular zone neurogenesis

Microglia are increasingly implicated as a source of non-neural regulation of postnatal neurogenesis and neuronal development. To evaluate better the contributions of microglia to neural stem cells (NSCs) of the subventricular neuraxis, we employed an adherent culture system that models the continuing proliferation and differentiation of the dissociated neuropoietic subventricular tissues. In this model, neuropoietic cells retain the ability to self-renew and form multipotent neurospheres, but progressively lose the ability to generate committed neuroblasts with continued culture. Neurogenesis in highly expanded NSCs can be rescued by coculture with microglial cells or microglia-conditioned medium, indicating that microglia provide secreted factor(s) essential for neurogenesis, but not NSC maintenance, self-renewal, or propagation. Our findings suggest an instructive role for microglial cells in contributing to postnatal neurogenesis in the largest neurogenic niche of the mammalian brain.