Neuronal Progenitor Cells of the Neonatal Subventricular Zone Differentiate and Disperse following Transplantation into the Adult Rat Striatum

Adult Neural Stem Cells from Midbrain Periventricular Regions Show Limited Neurogenic Potential after Transplantation into the Hippocampal Neurogenic Niche

The regulation of adult neural stem or progenitor cell (aNSC) proliferation and differentiation as an interplay of cell-intrinsic and local environmental cues remains in part unclear, impeding their role in putative regenerative therapies. aNSCs with all major properties of NSCs in vitro have been identified in a variety of brain regions beyond the classic neurogenic niches, including the caudal periventricular regions (PVRs) of the midbrain, though active neurogenesis is either limited or merely absent in these regions. To elucidate cell-intrinsic properties of aNSCs from various PVRs, we here examined the proliferation and early differentiation capacity of murine aNSCs from non-neurogenic midbrain PVRs (PVRMB) compared to aNSCs from the neurogenic ventricular-subventricular zone (PVRV-SVZ) 7 days after transplantation into the permissive pro-neurogenic niche of the dentate gyrus (DG) of the hippocampus in mice. An initial in vitro characterization of the transplants displayed very similar characteristics of both aNSC grafts after in vitro expansion with equal capacities of terminal differentiation into astrocytes and Tuj1+ neurons. Upon the allogenic transplantation of the respective aNSCs into the DG, PVRMB grafts showed a significantly lower graft survival and proliferative capacity compared to PVRV-SVZ transplants, whereby the latter are exclusively capable of generating new neurons. Although these differences might be-in part-related to the transplantation procedure and the short-term study design, our data strongly imply important cell-intrinsic differences between aNSCs from neurogenic compared to non-neurogenic PVRs with respect to their neurogenic potential and/or their sensitivity to neurogenic cues.

Histological Studies of the Ventricular-Subventricular Zone as Neural Stem Cell and Glioma Stem Cell Niche

The neural stem cell niche of the ventricular-subventricular zone supports the persistence of stem and progenitor cells in the mature brain. This niche has many notable cytoarchitectural features that affect the activity of stem cells and may also support the survival and growth of invading tumor cells. Histochemical studies of the niche have revealed many proteins that, in combination, can help to reveal stem-like cells in the normal or cancer context, although many caveats persist in the quest to consistently identify these cells in the human brain. Here, we explore the complex relationship between the persistent proliferative capacity of the neural stem cell niche and the malignant proliferation of brain tumors, with a special focus on histochemical identification of stem cells and stem-like tumor cells and an eye toward the potential application of high-dimensional imaging approaches to the field.

Human Umbilical Cord Blood Cells Express Neural Antigens after Transplantation into the Developing Rat Brain

Recently, our laboratory began to characterize the mononuclear cells from human umbilical cord blood (HUCB) both in vitro and in vivo. These cryopreserved human cells are available in unlimited quantities and it is believed that they may represent a source of cells with possible therapeutic and practical value. Our previous molecular and immunocytochemical studies on cultured HUCB cells revealed their ability to respond to nerve growth factor (NGF) by increased expression of neural markers typical for nervous system-derived stem cells. In addition, the DNA microarray detected downregulation of several genes associated with development of blood cell lines. To further explore the survival and phenotypic properties of HUCB cells we transplanted them into the developing rat brain, which is known to provide a conducive environment for development of neural phenotypes. Prior to transplantation, HUCB cells were either cultured with DMEM and fetal bovine serum or were exposed to retinoic acid (RA) and nerve growth factor (NGF). Neonatal pups (1 day old) received unilateral injection of cell suspension into the anterior part of subventricular zone. One month after transplantation animals were perfused, their brains cryosectioned, and immunocytochemistry was performed for identification of neural phenotypes. Our results clearly demonstrated that approximately 20% of transplanted HUCB survived (without immunosuppression) within the neonatal brain. Additionally, double-labeling with cell-type-specific markers revealed that some HUCB-derived cells (recognized by anti-human nuclei labeling) were immunopositive for glial fibrillary acidic protein (GFAP) and few donor cells expressed the neuronal marker TuJ1 (class III β-tubulin). These findings suggest that at least some of the transplanted HUCB cells differentiated into cells with distinct glial or neuronal phenotypes after being exposed to instructive signals from the developing brain.

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.

Glial cell loss, proliferation and replacement in the contused murine spinal cord

Studies in the rat have shown that contusive spinal cord injury (SCI) results in devastating pathology, including significant loss of mature oligodendrocytes and astrocytes even in spared white matter. Subsequently, there is increased proliferation of endogenous NG2(+) cells, postulated to contribute to replacement of mature glia chronically, which is important for functional recovery. Studies of mechanisms that stimulate endogenous progenitor cells would be facilitated by using mouse models with naturally occurring and genetically engineered mutations. To determine whether the murine response is similar to that in the rat, we performed contusive SCI on adult female C57Bl/6 mice at the T8-9 level. Animals received bromodeoxyuridine injections in the first week following injury and were killed at 1, 3, 4, 7 or 28 days postinjury (DPI). The overall loss of macroglia and the temporal-spatial response of NG2(+) cells after SCI in the (C57Bl/6) mouse was very similar to that in the (Sprague-Dawley) rat. By 24 h after SCI nearly half of the macroglia in spared ventral white matter had been lost. Cell proliferation was increased at 1-7 DPI, peaking at 3-4 DPI. Dividing cells included NG2(+) cells and Cd11b(+) macrophages and microglia. Furthermore, cells dividing in the first week expressed markers of mature glia at 28 DPI. The similarities in endogenous progenitor cell response to SCI in the mouse and rat suggest that this is a fundamental injury response, and that transgenic mouse models may be used to further probe how this cellular response to SCI might be enhanced to improve recovery after SCI.

Transplantation of motoneurons derived from MASH1-transfected mouse ES cells reconstitutes neural networks and improves motor function in hemiplegic mice

Mouse embryonic stem (ES) cells were transfected with a MASH1 expression vector and G418-resistant cells were selected. The MASH1-transfected cells became neuron-like appearance and expressed betaIIItubulin and panNCAM. Glial fibrillary acidic protein (GFAP) and galactocerebroside (GalC)-expressing cells were rarely detected. Half of the neural cells differentiated into the Islet1+ motoneuron lineage. Thus, we obtained motoneuron lineage-enriched neuronal cells by transfection of ES cells with MASH1. A hemiplegic model of mice was developed by cryogenic injury of the motor cortex, and motoneuron lineage-enriched neuronal cells were transplanted underneath the injured motor cortex neighboring the periventricular region. The motor function of the recipients was assessed by a beam walking and rotarod tests, whereby the results gradually improved, but little improvement was observed in vehicle injected control mice. We found that the grafted cells not only remained close to the implantation site, but also exhibited substantial migration, penetrating into the damaged lesion in a directed manner up to the cortical region. Grafted neuronal cells that had migrated into the cortex were elongated axon-positive for neurofilament middle chain (NFM). Synaptophysin immunostaining showed a positive staining pattern around the graft, suggesting that the transplanted neurons interacted with the recipient neurons to form a neural network. Our study suggests that the motoneuron lineage can be induced from ES cells, and grafted cells adapt to the host environment and can reconstitute a neural network to improve motor function of a paralyzed limb.

Anatomical and functional recovery by embryonic stem cell-derived neural tissue of a mouse model of brain damage

We have treated undifferentiated mouse embryonic stem (ES) cells with all-trans retinoic acid (RA) to induce differentiation in vitro into neuron-like cells with good cell viability for use as a graft. Furthermore, we asked whether the RA-induced neuron-like cells restored neurological dysfunction. To this end, the cells were transplanted into right hemiplegia model of mice, developed by a cryogenic injury of motor cortex. Motor function of the recipients was gradually improved, whereas little improvement was observed in control mice. The lesion showed clustering of mature and almost mature neuron-like cells in mice transplanted with the RA-treated cells. The grafted cells had synaptic vesicles. This finding may suggest their maturation and synaptic connection in the recipient brain. Even though further study is necessary to elucidate molecular and cellular mechanisms responsible for the functional recovery, we consider that the ES cells may have advantage for use as a donor source in various neurological disorders including motor dysfunction.

Polysialic acid regulates cell contact-dependent neuronal differentiation of progenitor cells from the subventricular zone

Expression of polysialic acid (PSA) promotes migration of progenitor cells from the subventricular zone (SVZ) to the olfactory bulb, where they differentiate into interneurons. This differentiation has been found to coincide with a loss of PSA. Moreover, specific removal of PSA from the mouse SVZ by endoneuraminidase-N was found to cause premature differentiation, as evidenced by neurite outgrowth and tyrosine hydroxylase synthesis in vivo and by expression of neurofilament-L and beta III-tubulin in SVZ explant cultures. This differentiation involved activation of mitogen-activated protein kinase through p59fyn and was blocked by its inhibition. The effects of PSA removal were found to be cell contact-dependent and to be reduced by anti-neural cell adhesion molecule antibodies. These findings indicate that PSA expression regulates the fate of SVZ precursors by two contact-dependent mechanisms, the previously reported reduction in cell-cell adhesion that allows cell translocation, and the postponement of cell differentiation that otherwise would be induced by signals generated through surface molecule-mediated cell-cell interactions.

Transplantation of motoneuron-enriched neural cells derived from mouse embryonic stem cells improves motor function of hemiplegic mice

Embryonic stem (ES) cells are expected to be a potential donor source for neural transplantation. We have obtained motoneuron-enriched neural progenitor cells by culturing mouse ES cells with retinoic acid (RA). The cells also expressed mRNA of a neurotrophic factor, neurotrophin-3 (NT-3). The left motor cortex area of mice was damaged by cryogenic brain injury, and the neural cells were transplanted underneath the injured motor cortex, neighboring to the paraventricular region. We found that the cells expressing neuronal phenotypes not only remained close to the implantation site, but also exhibited substantial migration penetrating into the damaged lesion, in a seemingly directed manner up to cortical region. We found that some of the neural cells differentiated into Islet1-positive motoneurons. It seems likely that the ability of the ES cell-derived neural progenitor cells to respond in vivo to guidance cues and signals that can direct their migration and differentiation may contribute to functional recovery of the recipient mice. We found that an "island of the mature neuronal cells" of recipient origin emerged in the damaged motor cortex. This may be associated with the neuroprotective effects of the ES cell-derived neural cells. The ES cells differentiated into CD31+ vasculoendothelial cells with the RA treatment in vitro. Furthermore, the grafted cells may provide sufficient neurotrophic factors such as NT-3 for neuroprotection and regeneration. The grafted neural cells that migrated into residual cortex and differentiated into neurons had purposefully elongated axons that were stained with anti-neurofilament middle chain (NFM) antibody. Our study suggests that motoneurons can be induced from ES cells, and ES cells become virtually an unlimited source of cells for experimental and clinical neural cell transplantation.

Transfer of the von Hippel-Lindau gene to neuronal progenitor cells in treatment for Parkinson's disease

Neuronal progenitor cells (NPCs) may provide dopaminergic neurons for the treatment of Parkinson's disease (PD). However, transplantation of NPCs into the striatum by current methods has had limited success. It is possible to reverse the symptoms of PD in model rats but difficult to reverse them in humans because the number of dopaminergic neurons generated from NPCs is low. We transduced the von Hippel-Lindau (VHL) gene into NPCs isolated from embryonic rat brain. The NPCs with the transduced VHL gene efficiently differentiated into tyrosine hydroxylase-positive neurons in vitro. NPCs with the transduced VHL gene, which were labeled in advance with bromodeoxyuridine, were transplanted into the striatum of a rat model of PD. Numerous bromodeoxyuridine-tyrosine hydroxylase double-labeled cells were seen close to the transplant site, showing that the transplanted cells efficiently generated new dopaminergic neurons within the host striatum. Moreover, all of the animals with NPCs with VHL showed a remarkable decrease in apomorphine-induced rotations. These findings show that NPCs with the VHL gene can efficiently generate dopaminergic neurons and that a sufficient number of dopaminergic neurons can develop from them to reverse the symptoms of PD in humans. VHL gene transduction provides a new therapeutic approach for treatment of PD.

GABA depolarizes neuronal progenitors of the postnatal subventricular zone via GABAA receptor activation

Previous studies have reported the presence of migrating and dividing neuronal progenitors in the subventricular zone (SVZ) and rostral migratory stream (RMS) of the postnatal mammalian brain. Although the behaviour of these progenitors is thought to be influenced by local signals, the nature and mode of action of the local signals are largely unknown. One of the signalling molecules known to affect the behaviour of embryonic neurons is the neurotransmitter GABA. In order to determine whether GABA affects neuronal progenitors via the activation of specific receptors, we performed cell-attached, whole-cell and gramicidin perforated patch-clamp recordings of progenitors in postnatal mouse brain slices containing either the SVZ or the RMS. Recorded cells displayed a morphology typical of migrating neuronal progenitors had depolarized zero-current resting potentials, and lacked action potentials. A subset of progenitors contained GABA and stained positive for glutamic acid decarboxylase 67 (GAD-67) as shown by immunohistochemistry. In addition, every neuronal progenitor responded to GABA via picrotoxin-sensitive GABAA receptor (GABAAR) activation. GABAARs displayed an ATP-dependent rundown and a low sensitivity to Zn2+. GABA responses were sensitive to benzodiazepine agonists, an inverse agonist, as well as a barbiturate agonist. While GABA was hyperpolarizing at the zero-current resting potentials, it was depolarizing at the cell resting potentials estimated from the reversal potential of K+ currents through a cell-attached patch. Thus, our study demonstrates that neuronal progenitors of the SVZ/RMS contain GABA and are depolarized by GABA, which may constitute the basis for a paracrine signal among neuronal progenitors to dynamically regulate their proliferation and/or migration.

Magnetic resonance imaging and neurosphere therapy of stroke in rat

We intracisternally transplanted subventricular zone (SVZ) cells labeled by ferromagnetic particles into stroked rats. Migration of transplanted cells was non-invasively tracked using magnetic resonance imaging (MRI). We found that transplanted cells selectively migrated towards the ischemic parenchyma at a mean speed of 65 +/- 14.6 microm/hr in living rats. Migration of transplanted cells in the brain was also measured histopathologically. Rats transplanted with SVZ cells exhibited significant improvement of neurological function. Our data suggest that intracisternal transplantation of SVZ cells provides an avenue for cell therapy of stroke and that MRI can be used to track grafted cells in the brain.

Stem cell repair of central nervous system injury

Neural stem cells (NSCs) have great potential as a therapeutic tool for the repair of a number of CNS disorders. NSCs can either be isolated from embryonic and adult brain tissue or be induced from both mouse and human ES cells. These cells proliferate in vitro through many passages without losing their multipotentiality. Following engraftment into the adult CNS, NSCs differentiate mainly into glia, except in neurogenic areas. After engraftment into the injured and diseased CNS, their differentiation is further retarded. In vitro manipulation of NSC fate prior to transplantation and/or modification of the host environment may be necessary to control the terminal lineage of the transplanted cells to obtain functionally significant numbers of neurons. NSCs and a few types of glial precursors have shown the capability to differentiate into oligodendrocytes and to remyeliate the demyelinated axons in the CNS, but the functional extent of remyelination achieved by these transplants is limited. Manipulation of endogenous neural precursors may be an alternative therapy or a complimentary therapy to stem cell transplantation for neurodegenerative disease and CNS injury. However, this at present is challenging and so far has been unsuccessful. Understanding mechanisms of NSC differentiation in the context of the injured CNS will be critical to achieving these therapeutic strategies.

Opinion: neural stem cell therapy for neurological diseases: dreams and reality

There is a pressing need for treatments for neurodegenerative diseases. Hopes have been raised by the prospect of neural stem cell therapy; however, despite intense research activities and media attention, stem cell therapy for neurological disorders is still a distant goal. Effective strategies must be developed to isolate, enrich and propagate homogeneous populations of neural stem cells, and to identify the molecules and mechanisms that are required for their proper integration into the injured brain. This article examines these requirements, discusses the results obtained so far, and considers the steps that need to be taken to provide instruction to donor cells and to elucidate the neurogenic potential of the adult central nervous system environment.

Region-specific differentiation of neural tube-derived neuronal restricted progenitor cells after heterotopic transplantation

Spinal cord neuronal restricted progenitor (NRP) cells, when transplanted into the neonatal anterior forebrain subventricular zone, migrate to distinct regions throughout the forebrain including the olfactory bulb, frontal cortex, and occipital cortex but not to the hippocampus. Their migration pattern and differentiation potential is distinct from anterior forebrain subventricular zone NRPs. Irrespective of their final destination, NRP cells do not differentiate into glia. Rather they synthesize neurotransmitters, acquire region-specific phenotypes, and receive synapses from host neurons after transplantation. Spinal cord NRPs express choline acetyl transferase even in regions where host neurons do not express this marker. The restricted distribution of transplanted spinal cord NRP cells and their acquisition of varied region-specific phenotypes suggest that their ultimate fate and phenotype is dictated by a combination of intrinsic properties and extrinsic cues from the host.

The X-gal caution in neural transplantation studies

Cell transplantation into host brain requires a reliable cell marker to trace lineage and location of grafted cells in host tissue. The lacZ gene encodes the bacterial (E. coli) enzyme beta-galactosidase (beta-gal) and is commonly visualized as a blue intracellular precipitate following its incubation with a substrate, "X gal," in an oxidation reaction. LacZ is the "reporter gene" most commonly employed to follow gene expression in neural tissue or to track the fate of transplanted exogenous cells. If the reaction is not performed carefully-with adequate optimization and individualization of various parameters (e.g.. pH, concentration of reagents, addition of chelators, composition of fixatives) and the establishment of various controls--then misleading nonspecific background X-gal positivity can result, leading to the misidentification of cells. Some of this background results from endogenous nonbacterial beta-gal activity in discrete populations of neurons in the mammalian brain; some results from an excessive oxidation reaction. Surprisingly, few articles have empha sized how to recognize and to eliminate these potential confounding artifacts in order to maximize the utility and credibility of this histochemical technique as a cell marker. We briefly review the phenomenon in general, discuss a specific case that illustrates how an insufficiently scrutinized X-gal positivity can be a pitfall in cell transplantation studies, and then provide recommendations for optimizing the specificity and reliability of this histochemical reaction for discerning E. coli beta-gal activity.

Cortical neurogenesis in adult rats after reversible photothrombotic stroke

Neurogenesis occurs throughout life in the dentate gyrus of hippocampus and subventricular zone, but this phenomenon has rarely been observed in other brain regions of adult mammals. The aim of the current study was to investigate the cell proliferation process in the ischemically challenged region-at-risk after focal cerebral ischemia in the adult rat brain. A reversible photothrombotic ring stroke model was used, which features sustained hypoperfusion followed by late spontaneous reperfusion and a remarkable morphologic tissue recovery in the anatomically well defined somatosensory cortical region-at-risk. Twelve-week-old male Wistar rats received repeated intraperitoneal injections of the cell proliferation specific marker 5-bromodeoxyuridine (BrdU) after stroke induction. Immunocytochemistry of coronal brain sections revealed that the majority of BrdU-positive cells were of glial, macrophage, and endothelial origin, whereas 3% to 6% of the BrdU-positive cells were double-labeled by BrdU and the neuronspecific marker Map-2 at 7 and 100 days after stroke onset in the region-at-risk. They were distributed randomly in cortical layers II-VI. Three-dimensional confocal analyses of BrdU and the neuronal-specific marker Neu N by double immunofluorescence confirmed their colocalization within the same cells at 72 hours and 30 days after stroke induction. This study suggests that, as a potential pathway for brain repair, new neurons can be generated in the cerebral cortex of adult rats after sublethal focal cerebral ischemia.

Endogenous IGF-1 regulates the neuronal differentiation of adult stem cells

Stem cells from the adult forebrain of mice were stimulated to form clones in vitro using fibroblast growth factor-2 (FGF-2). At concentrations above 10 ng/ml of FGF-2, very few clones gave rise to neurons; however, if FGF-2 was removed after 5 days, 20-30% of clones subsequently gave rise to neurons. The number of neuron-containing clones and the number of neurons per clone was significantly enhanced, if insulin-like growth factor (IGF)-1 or heparin were added subsequent to FGF-2 removal. The spontaneous production of neurons after FGF-2 removal was shown to be due to endogenous IGF-1, since antibodies to IGF-1 and an IGF-1 binding protein totally inhibited neuronal production. Similarly, these reagents also abrogated the neuron-promoting effects of heparin. Thus, it appears that endogenous IGF-1 may be a major regulator of stem cell differentiation into neurons. Furthermore, it was found that high levels of IGF-1 or insulin promoted the maturation and affected the neurotransmitter phenotype of the neurons generated.

Adult-derived neural precursors transplanted into multiple regions in the adult brain

Neural stem cells persist in the adult brain subventricular zone (SVZ). These cells generate a large number of new neurons that migrate to the olfactory bulb, where they complete their differentiation. Here, we transplanted cells carrying beta-galactosidase under the control of neuron-specific enolase promoter (NSE::LacZ) from the SVZ of adult mice into the striatum cortex and olfactory bulb, with or without an excitotoxin lesion. Between 2 and 8 weeks after transplantation, grafted cells were present in the recipient regions, but extensive migration and differentiation into mature neurons of grafted cells were only observed in the olfactory bulb. Clusters of graft-derived neuroblasts forming chain-like structures were observed within or close to the grated sites in the cortex and striatum; electron microscopy confirmed that graft-derived cells in the olfactory bulb and a small number in the striatum were neurons. Surprisingly, most of the cells expressing NSE::LacZ outside the olfactory bulb were astrocytes. We conclude that primary precursors from the SVZ migrate and differentiate effectively only within the environment of the olfactory bulb. Only limited survival and differentiation were observed in other brain regions studied.

Young neurons from medial ganglionic eminence disperse in adult and embryonic brain

In this study, we identified neuronal precursors that can disperse through adult mammalian brain tissue. Transplanted neuronal precursors from embryonic medial ganglionic eminence (MGE), but not from lateral ganglionic eminence (LGE) or neocortex, dispersed and differentiated into neurons in multiple adult brain regions. In contrast, only LGE cells were able to migrate efficiently from the adult subventricular zone to the olfactory bulb. In embryonic brain slices, MGE cells migrated extensively toward cortex. Our results demonstrate that cells in different germinal regions have unique migratory potentials, and that adult mammalian brain can support widespread dispersion of specific populations of neuronal precursors. These findings could be useful in repair of diffuse brain damage.