Growth and fate of PSA-NCAM+ precursors of the postnatal brain

Lineage tracing reveals the origin of Nestin-positive cells are heterogeneous and rarely from ependymal cells after spinal cord injury

Nestin is expressed extensively in neural stem/progenitor cells during neural development, but its expression is mainly restricted to the ependymal cells in the adult spinal cord. After spinal cord injury (SCI), Nestin expression is reactivated and Nestin-positive (Nestin⁺) cells aggregate at the injury site. However, the derivation of Nestin⁺ cells is not clearly defined. Here, we found that Nestin expression was substantially increased in the lesion edge and lesion core after SCI. Using a tamoxifen inducible CreER(T2)-loxP system, we verified that ependymal cells contribute few Nestin⁺ cells either to the lesion core or the lesion edge after SCI. In the lesion edge, GFAP⁺ astrocytes were the main cell type that expressed Nestin; they then formed an astrocyte scar. In the lesion core, Nestin⁺ cells expressed αSMA or Desmin, indicating that they might be derived from pericytes. Our results reveal that Nestin⁺ cells in the lesion core and edge came from various cell types and rarely from ependymal cells after complete transected SCI, which may provide new insights into SCI repair.

Hormonal Regulation of Oligodendrogenesis I: Effects across the Lifespan

The brain’s capacity to respond to changing environments via hormonal signaling is critical to fine-tuned function. An emerging body of literature highlights a role for myelin plasticity as a prominent type of experience-dependent plasticity in the adult brain. Myelin plasticity is driven by oligodendrocytes (OLs) and their precursor cells (OPCs). OPC differentiation regulates the trajectory of myelin production throughout development, and importantly, OPCs maintain the ability to proliferate and generate new OLs throughout adulthood. The process of oligodendrogenesis, the creation of new OLs, can be dramatically influenced during early development and in adulthood by internal and environmental conditions such as hormones. Here, we review the current literature describing hormonal regulation of oligodendrogenesis within physiological conditions, focusing on several classes of hormones: steroid, peptide, and thyroid hormones. We discuss hormonal regulation at each stage of oligodendrogenesis and describe mechanisms of action, where known. Overall, the majority of hormones enhance oligodendrogenesis, increasing OPC differentiation and inducing maturation and myelin production in OLs. The mechanisms underlying these processes vary for each hormone but may ultimately converge upon common signaling pathways, mediated by specific receptors expressed across the OL lineage. However, not all of the mechanisms have been fully elucidated, and here, we note the remaining gaps in the literature, including the complex interactions between hormonal systems and with the immune system. In the companion manuscript in this issue, we discuss the implications of hormonal regulation of oligodendrogenesis for neurological and psychiatric disorders characterized by white matter loss. Ultimately, a better understanding of the fundamental mechanisms of hormonal regulation of oligodendrogenesis across the entire lifespan, especially in vivo, will progress both basic and translational research.

Camel regulates development of the brain ventricular system

Development of the brain ventricular system of vertebrates and the molecular mechanisms involved are not fully understood. The developmental genes expressed in the elements of the brain ventricular system such as the ependyma and circumventricular organs act as molecular determinants of cell adhesion critical for the formation of brain ventricular system. They control brain development and function, including the flow of cerebrospinal fluid. Here, we describe the novel distantly related member of the zebrafish L1-CAM family of genes-camel. Whereas its maternal transcripts distributed uniformly, the zygotic transcripts demonstrate clearly defined expression patterns, in particular in the axial structures: floor plate, hypochord, and roof plate. camel expresses in several other cell lineages with access to the brain ventricular system, including the midbrain roof plate, subcommissural organ, organum vasculosum lamina terminalis, median eminence, paraventricular organ, flexural organ, and inter-rhombomeric boundaries. This expression pattern suggests a role of Camel in neural development. Several isoforms of Camel generated by differential splicing of exons encoding the sixth fibronectin type III domain enhance cell adhesion differentially. The antisense oligomer morpholino-mediated loss-of-function of Camel affects cell adhesion and causes hydrocephalus and scoliosis manifested via the tail curled down phenotype. The subcommissural organ's derivative-the Reissner fiber-participates in the flow of cerebrospinal fluid. The Reissner fiber fails to form upon morpholino-mediated Camel loss-of-function. The Camel mRNA-mediated gain-of-function causes the Reissner fiber misdirection. This study revealed a link between Chl1a/Camel and Reissner fiber formation, and this supports the idea that CHL1 is one of the scoliosis factors.

Primary hypothyroidism and autoimmune thyroiditis alter the transcriptional activity of genes regulating neurogenesis in the blood of patients

Objective. Thyroid hormones play an important role in the development and maturation of the central nervous symptom and their failure in the prenatal period leading to an irreversible brain damage. Their effect on the brain of adult, however, has not been fully studied. With the discovery of neurogenesis in the adult brain, many recent studies have been focused on the understanding the basic mechanisms controlling this process. Many neurogenesis regulatory genes are not only transcribed but also translated into the blood cells. The goal of our study was to analyze the transcriptional activity of neurogenesis regulatory genes in peripheral blood cells in patients with thyroid pathology.Methods. The pathway-specific PCR array (Neurotrophins and Receptors RT2 Profiler PCR Array, QIAGEN, Germany) was used to identify and validate the neurogenesis regulatory genes expression in patients with thyroid pathology and control group.Results. The results showed that GFRA3, NGFR, NRG1, NTF3, NTRK1, and NTRK2 significantly decreased their expression in patients with autoimmune thyroiditis with rising serum of autoantibodies. The patients with primary hypothyroidism, as a result of autoimmune thyroiditis and postoperative hypothyroidism, had significantly lower expression of FGF2, NGFR, NRG1, and NTF3. The mRNA level of CNTFR was markedly decreased in the group of patients with postoperative hypothyroidism. No change in the ARTN, PSPN, TFG, MT3, and NELL1 expression was observed in any group of patients.Conclusion. The finding indicates that a decrease in thyroid hormones and a high level of autoantibodies, such as anti-thyroglobulin antibody and anti-thyroid peroxidase antibody, affect the expression of mRNA neurogenesis-regulated genes in patients with thyroid pathology.

Promoting remyelination through cell transplantation therapies in a model of viral-induced neurodegenerative disease

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Several United States Food and Drug Administration-approved therapies exist that impede activated lymphocytes from entering the CNS thereby limiting new lesion formation in patients with relapse-remitting forms of MS. However, a significant challenge within the field of MS research is to develop effective and sustained therapies that allow for axonal protection and remyelination. In recent years, there has been increasing evidence that some kinds of stem cells and their derivatives seem to be able to mute neuroinflammation as well as promote remyelination and axonal integrity. Intracranial infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in immune-mediated demyelination and axonopathy, making this an excellent model to interrogate the therapeutic potential of stem cell derivatives in evoking remyelination. This review provides a succinct overview of our recent findings using intraspinal injection of mouse CNS neural progenitor cells and human neural precursors into JHMV-infected mice. JHMV-infected mice receiving these cells display extensive remyelination associated with axonal sparing. In addition, we discuss possible mechanisms associated with sustained clinical recovery. Developmental Dynamics 248:43-52, 2019. © 2018 Wiley Periodicals, Inc.

Brain Region-Dependent Rejection of Neural Precursor Cell Transplants

The concept of CNS as an immune-privileged site has been challenged by the occurrence of immune surveillance and allogeneic graft rejection in the brain. Here we examined whether the immune response to allogeneic neural grafts is determined by the site of implantation in the CNS. Dramatic regional differences were observed between immune responses to allogeneic neural precursor/stem cell (NPC) grafts in the striatum vs. the hippocampus. Striatal grafts were heavily infiltrated with IBA-1+ microglia/macrophages and CD3+ T cells and completely rejected. In contrast, hippocampal grafts exhibited milder IBA-1+ cell infiltration, were not penetrated efficiently by CD3+ cells, and survived efficiently for at least 2 months. To evaluate whether the hippocampal protective effect is universal, astrocytes were then transplanted. Allogeneic astrocyte grafts elicited a vigorous rejection process from the hippocampus. CD200, a major immune-inhibitory signal, plays an important role in protecting grafts from rejection. Indeed, CD200 knock out NPC grafts were rejected more efficiently than wild type NPCs from the striatum. However, lack of CD200 expression did not elicit NPC graft rejection from the hippocampus. In conclusion, the hippocampus has partial immune-privilege properties that are restricted to NPCs and are CD200-independent. The unique hippocampal milieu may be protective for allogeneic NPC grafts, through host-graft interactions enabling sustained immune-regulatory properties of transplanted NPCs. These findings have implications for providing adequate immunosuppression in clinical translation of cell therapy.

Neural precursor cells derived from induced pluripotent stem cells exhibit reduced susceptibility to infection with a neurotropic coronavirus

The present study examines the susceptibility of mouse induced pluripotent stem cell-derived neural precursor cells (iPSC-NPCs) to infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Similar to NPCs derived from striatum of day 1 postnatal GFP-transgenic mice (GFP-NPCs), iPSC-derived NPCs (iPSC-NPCs) are able to differentiate into terminal neural cell types and express MHC class I and II in response to IFN-γ treatment. However, in contrast to postnatally-derived NPCs, iPSC-NPCs express low levels of carcinoembryonic antigen-cell adhesion molecule 1a (CEACAM1a), the surface receptor for JHMV, and are less susceptible to infection and virus-induced cytopathic effects. The relevance of this in terms of therapeutic application of NPCs resistant to viral infection is discussed.

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The neurotropic virus JHMV infects and kills mouse post-natal neural progenitor cells (NPCs).

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This study examines if JHMV infects mouse inducible pluripotent stem cell-derived NPCs.

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iPSC-NPCs are less susceptible to infection with JHMV and subsequent lytic effects.

Highly Efficient Neural Conversion of Human Pluripotent Stem Cells in Adherent and Animal-Free Conditions

Neural differentiation of human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) can produce a valuable and robust source of human neural cell subtypes, holding great promise for the study of neurogenesis and development, and for treating neurological diseases. However, current hESCs and hiPSCs neural differentiation protocols require either animal factors or embryoid body formation, which decreases efficiency and yield, and strongly limits medical applications. Here we develop a simple, animal-free protocol for neural conversion of both hESCs and hiPSCs in adherent culture conditions. A simple medium formula including insulin induces the direct conversion of >98% of hESCs and hiPSCs into expandable, transplantable, and functional neural progenitors with neural rosette characteristics. Further differentiation of neural progenitors into dopaminergic and spinal motoneurons as well as astrocytes and oligodendrocytes indicates that these neural progenitors retain responsiveness to instructive cues revealing the robust applicability of the protocol in the treatment of different neurodegenerative diseases. The fact that this protocol includes animal-free medium and human extracellular matrix components avoiding embryoid bodies makes this protocol suitable for the use in clinic. Stem Cells Translational Medicine 2017;6:1217-1226.

Glial Cells Generate Neurons—Master Control within CNS Regions: Developmental Perspectives on Neural Stem Cells

A common problem in neural stem cell research is the poor generation of neuronal or oligodendroglial descendants. The author takes a developmental perspective to propose solutions to this problem. After a general overview of the recent progress in developmental neurobiology, she highlights the necessity of the sequential and hierarchical specification of CNS precursors toward the generation of specific cell types, for example, neurons. In the developing as well as the adult CNS, multipotent stem cells do not directly generate neurons but give rise to precursors that are specified and restricted toward the generation of neurons. Some molecular determinants of this fate restriction have been identified during recent years and reveal that progression via this fate-restricted state is a necessary step of neurogenesis. These discoveries also demonstrate that neuronal fate specification is inseparably linked at the molecular level to regionalization of the developing CNS. These fate determinants and their specific action in distinct region-specific con-texts are essential to direct the progeny of stem cells more efficiently toward the generation of the desired cell types. Recent data are discussed that demonstrate the common identity of precursors and stem cells in the developing and adult nervous system as radial glia, astroglia, or non-myelinating glia. A novel line-age model is proposed that incorporates these new views and explains why the default pathway of stem cells is astroglia. These new insights into the cellular and molecular mechanisms of neurogenesis help to design novel approaches for reconstitutive therapy of neurodegenerative diseases.

Sphingosine-1-phosphate receptor antagonism enhances proliferation and migration of engrafted neural progenitor cells in a model of viral-induced demyelination

The oral drug FTY720 affects sphingosine-1-phosphate (S1P) signaling on targeted cells that bear the S1P receptors S1P1, S1P3, S1P4, and S1P5. We examined the effect of FTY720 treatment on the biology of mouse neural progenitor cells (NPCs) after transplantation in a viral model of demyelination. Intracerebral infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) resulted in an acute encephalomyelitis, followed by demyelination similar in pathology to the human demyelinating disease, multiple sclerosis. We have previously reported that intraspinal transplantation of mouse NPCs into JHMV-infected animals resulted in selective colonization of demyelinated lesions, preferential differentiation into oligodendroglia accompanied by axonal preservation, and increased remyelination. Cultured NPCs expressed transcripts for S1P receptors S1P1, S1P2, S1P3, S1P4, and S1P5. FTY720 treatment of cultured NPCs resulted in increased mitogen-activated protein kinase phosphorylation and migration after exposure to the chemokine CXCL12. Administration of FTY720 to JHMV-infected mice resulted in enhanced migration and increased proliferation of transplanted NPCs after spinal cord engraftment. FTY720 treatment did not improve clinical disease, diminish neuroinflammation or the severity of demyelination, nor increase remyelination. These findings argue that FTY720 treatment selectively increases NPC proliferation and migration but does not either improve clinical outcome or enhance remyelination after transplantation into animals in which immune-mediated demyelination is initiated by the viral infection of the central nervous system.

Characterization and isolation of immature neurons of the adult mouse piriform cortex

Physiological studies indicate that the piriform or primary olfactory cortex of adult mammals exhibits a high degree of synaptic plasticity. Interestingly, a subpopulation of cells in the layer II of the adult piriform cortex expresses neurodevelopmental markers, such as the polysialylated form of neural cell adhesion molecule (PSA-NCAM) or doublecortin (DCX). This study analyzes the nature, origin, and potential function of these poorly understood cells in mice. As previously described in rats, most of the PSA-NCAM expressing cells in layer II could be morphologically classified as tangled cells and only a small proportion of larger cells could be considered semilunar-pyramidal transitional neurons. Most were also immunoreactive for DCX, confirming their immature nature. In agreement with this, detection of PSA-NCAM combined with that of different cell lineage-specific antigens revealed that most PSA-NCAM positive cells did not co-express markers of glial cells or mature neurons. Their time of origin was evaluated by birthdating experiments with halogenated nucleosides performed at different developmental stages and in adulthood. We found that virtually all cells in this paleocortical region, including PSA-NCAM-positive cells, are born during fetal development. In addition, proliferation analyses in adult mice revealed that very few cells were cycling in layer II of the piriform cortex and that none of them was PSA-NCAM-positive. Moreover, we have established conditions to isolate and culture these immature neurons in the adult piriform cortex layer II. We find that although they can survive under certain conditions, they do not proliferate in vitro either. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 748-763, 2016.

Magnetic-activated cell sorting (MACS) can be used as a large-scale method for establishing zebrafish neuronal cell cultures

Neuronal cell cultures offer a crucial tool to mechanistically analyse regeneration in the nervous system. Despite the increasing importance of zebrafish (Danio rerio) as an in vivo model in neurobiological and biomedical research, in vitro approaches to the nervous system are lagging far behind and no method is currently available for establishing enriched neuronal cell cultures. Here we show that magnetic-activated cell sorting (MACS) can be used for the large-scale generation of neuronal-restricted progenitor (NRP) cultures from embryonic zebrafish. Our findings provide a simple and semi-automated method that is likely to boost the use of neuronal cell cultures as a tool for the mechanistic dissection of key processes in neuronal regeneration and development.

Two-photon imaging of remyelination of spinal cord axons by engrafted neural precursor cells in a viral model of multiple sclerosis

Neural precursor cells (NPCs) offer a promising approach for treating demyelinating diseases. However, the cellular dynamics that underlie transplanted NPC-mediated remyelination have not been described. Using two-photon imaging of a newly developed ventral spinal cord preparation and a viral model of demyelination, we describe the motility and intercellular interactions of transplanted mouse NPCs expressing green fluorescent protein (GFP) with damaged axons expressing yellow fluorescent protein (YFP). Our findings reveal focal axonal degeneration that occurs in the ventral side of the spinal cord within 1 wk following intracranial instillation with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Axonal damage precedes extensive demyelination and is characterized by swelling along the length of the axon, loss of YFP signal, and transected appearance. NPCs engrafted into spinal cords of JHMV-infected mice exhibited diminished migration velocities and increased proliferation compared with transplanted cells in noninfected mice. NPCs preferentially accumulated within areas of axonal damage, initiated direct contact with axons, and subsequently expressed the myelin proteolipid protein gene, initiating remyelination. These findings indicate that NPCs transplanted into an inflammatory demyelinating microenvironment participate directly in therapeutic outcome through the wrapping of myelin around damaged neurons.

PDGF-responsive progenitors persist in the subventricular zone across the lifespan

The SVZ (subventricular zone) contains neural stem cells and progenitors of various potentialities. Although initially parsed into A, B, and C cells, this germinal zone is comprised of a significantly more diverse population of cells. Here, we characterized a subset of postnatal PRPs (PDGF-AA-responsive precursors) that express functional PDGFα and β receptors from birth to adulthood. When grown in PDGF-AA, dissociated neonatal rat SVZ cells divided to produce non-adherent clusters of progeny. Unlike the self-renewing EGF/FGF-2-responsive precursors that produce neurospheres, these PRPs failed to self-renew after three passages; therefore, we refer to the colonies they produce as spheroids. Upon differentiation these spheroids could produce neurons, type 1 astrocytes and oligodendrocytes. When maintained in medium supplemented with BMP-4 they also produced type 2 astrocytes. Using lineage tracing methods, it became evident that there were multiple types of PRPs, including a subset that could produce neurons, oligodendrocytes, and type 1 and type 2 astrocytes; thus some of these PRPs represent a unique population of precursors that are quatropotential. Spheroids also could be generated from the newborn neocortex and they had the same potentiality as those from the SVZ. By contrast, the adult neocortex produced less than 20% of the numbers of spheroids than the adult SVZ and spheroids from the adult neocortex only differentiated into glial cells. Interestingly, SVZ spheroid producing capacity diminished only slightly from birth to adulthood. Altogether these data demonstrate that there are PRPs that persist in the SVZ that includes a unique population of quatropotential PRPs.

The genetically modified polysialylated form of neural cell adhesion molecule-positive cells for potential treatment of X-linked adrenoleukodystrophy

PURPOSE

Cell transplantation of myelin-producing exogenous cells is being extensively explored as a means of remyelinating axons in X-linked adrenoleukodystrophy. We determined whether 3,3',5-Triiodo-L-thyronine (T3) overexpresses the ABCD2 gene in the polysialylated (PSA) form of neural cell adhesion molecule (NCAM)-positive cells and promotes cell proliferation and favors oligodendrocyte lineage differentiation.

MATERIALS AND METHODS

PSA-NCAM+ cells from newborn Sprague-Dawley rats were grown for five days on uncoated dishes in defined medium with or without supplementation of basic fibroblast growth factor (bFGF) and/or T3. Then, PSA-NCAM+ spheres were prepared in single cells and transferred to polyornithine/fibronectin-coated glass coverslips for five days to determine the fate of the cells according to the supplementation of these molecules. T3 responsiveness of ABCD2 was analyzed using real-time quantitative polymerase chain reaction, the growth and fate of cells were determined using 5-bromo-2-deoxyuridine incorporation and immunocytochemistry, respectively.

RESULTS

Results demonstrated that T3 induces overexpression of the ABCD2 gene in PSA-NCAM+ cells, and can enhance PSA-NCAM+ cell growth in the presence of bFGF, favoring an oligodendrocyte fate.

CONCLUSION

These results may provide new insights into investigation of PSA-NCAM+ cells for therapeutic application to X-linked adrenoleukodystrophy.

Efficient neuronal in vitro and in vivo differentiation after immunomagnetic purification of mESC derived neuronal precursors

The cellular heterogeneity that is generated during the differentiation of pluripotent stem cells into specific neural subpopulations represents a major obstacle for experimental and clinical progress. To address this problem we developed an optimized strategy for magnetic isolation of PSA-NCAM positive neuronal precursors from embryonic stem cells (ESCs) derived neuronal cultures. PSA-NCAM enrichment at an early step of the in vitro differentiation process increased the number of ES cell derived neurons and reduced cellular diversity. Gene expression analysis revealed that mainly genes involved in neuronal activity were over-represented after purification. In vitro derived PSA-NCAM(+) enriched precursors were characterized in vivo through grafting into the forebrain of adult mice. While unsorted control cells 40 days post graft gave rise to a mixed population composed of immature precursors, early postmitotic neurons and glial cells, PSA-NCAM(+) enriched cells differentiated predominantly into NeuN positive cells. Furthermore, PSA-NCAM enriched population showed efficient migration towards the olfactory bulb after transplantation into the rostral migratory stream of the forebrain neurogenic system. Thus, enrichment of neuronal precursors based on PSA-NCAM expression represents a general and straightforward approach to narrow cellular heterogeneity during neuronal differentiation of pluripotent cells.

Time associated decline in neurotrophic properties of neural stem cell grafts render them dependent on brain region-specific environmental support

Fetal neural stem/precursor cells (NPCs) possess powerful neurotrophic properties by which they can facilitate self repair processes in the adult central nervous system. The therapeutic value of NPC therapy in neurodegenerative diseases is critically dependent on their long term survival and enduring functional properties. An important aspect of NPC neurotrophic properties is their ability to support their own survival independent of any exogenous growth factor. Here, we examined whether NPCs survive and maintain their properties for extended periods of time, or become dependent on environmental support. Two months following transplantation to naïve brains, large grafts were detected in the ventricles and hippocampus, but only little survival was evident in the striatum. To point at possible regional characteristics which underlie the differential survival of NPC grafts we performed several manipulations of the brain environment. Acute neurotoxic injury with 6-hydroxydopamine induced a 3-fold increase in striatal graft survival, associated with induction of nestin, CD31, β1-integrin, GFAP and cycling cells. Disruption of the extracellular matrix structure of this reactive niche by continuous blockage of host striatum β1-integrin caused 73% reduction in graft survival. In the hippocampus, NPC graft survival did not correspond to β1-integrin and CD31 expression. This suggests that hippocampal environmental support to graft survival rely on different mechanisms than in the reactive striatum. In correlation with in vivo findings, long term cultured neural precursors exhibited an increase in apoptotic cells and dramatic decline in neurotrophic effects, as indicated by two in vitro functional assays. We conclude that long-term changes in transplanted NPC properties render them dependent on region specific environmental support. The major extracellular matrix protein β1-integrin is essential for providing tissue support for graft survival in the striatum. The neurotrophic properties of transplanted neural stem cells are limited in time, representing a shortcoming which should be taken into consideration when developing clinical transplantation protocols for chronic neurological disorders.

Novel Cell and Tissue Acquisition System (CTAS): microdissection of live and frozen brain tissues

We developed a novel, highly accurate, capillary based vacuum-assisted microdissection device CTAS - Cell and Tissue Acquisition System, for efficient isolation of enriched cell populations from live and freshly frozen tissues, which can be successfully used in a variety of molecular studies, including genomics and proteomics. Specific diameter of the disposable capillary unit (DCU) and precisely regulated short vacuum impulse ensure collection of the desired tissue regions and even individual cells. We demonstrated that CTAS is capable of dissecting specific regions of live and frozen mouse and rat brain tissues at the cellular resolution with high accuracy. CTAS based microdissection avoids potentially harmful physical treatment of tissues such as chemical treatment, laser irradiation, excessive heat or mechanical cell damage, thus preserving primary functions and activities of the dissected cells and tissues. High quality DNA, RNA, and protein can be isolated from CTAS-dissected samples, which are suitable for sequencing, microarray, 2D gel-based proteomic analyses, and Western blotting. We also demonstrated that CTAS can be used to isolate cells from native living tissues for subsequent recultivation of primary cultures without affecting cellular viability, making it a simple and cost-effective alternative for laser-assisted microdissection.

Olig1 function is required for remyelination potential of transplanted neural progenitor cells in a model of viral-induced demyelination

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) resulting in cumulative neurologic deficits associated with progressive myelin loss. We have previously shown that transplantation of neural progenitor cells (NPCs) into mice persistently infected with the JHM strain of mouse hepatitis virus (JHMV) results in enhanced differentiation into oligodendrocyte progenitor cells (OPCs) that is associated with remyelination and axonal sparing. The current study examines the contributions of the transcription factor Olig1 on NPC differentiation and remyelination. Under defined conditions, NPCs preferentially differentiate into oligodendroglia whereas NPCs isolated from Olig1-deficient (Olig1-/-) mice exhibit enhanced differentiation into astrocytes. Transplantation of Olig1-/- and Olig1+/+ NPCs into JHMV-infected mice resulted in similar cell survival, proliferation, and selective migration to areas of demyelination. However, only recipients of wild type NPCs exhibited extensive remyelination compared to mice receiving Olig1-/- NPCs. In vivo characterization of NPCs revealed that Olig1+/+ NPCs preferentially differentiated into NG2-positive OPCs and formed processes expressing myelin basic protein that encircled axons. In contrast, the majority of transplanted Olig1-/- NPCs differentiated into GFAP-positive cells consistent with the astrocyte lineage. These results indicate that exogenous NPCs contribute to improved clinical and histological outcome and this is associated with remyelination by this donor population. Further, these findings reveal that Olig1function is required for the remyelination potential of NPCs after transplant, through specification and/or maintenance of oligodendroglial identity.

Cell therapy for multiple sclerosis

The spontaneous recovery observed in the early stages of multiple sclerosis (MS) is substituted with a later progressive course and failure of endogenous processes of repair and remyelination. Although this is the basic rationale for cell therapy, it is not clear yet to what degree the MS brain is amenable for repair and whether cell therapy has an advantage in comparison to other strategies to enhance endogenous remyelination. Central to the promise of stem cell therapy is the therapeutic plasticity, by which neural precursors can replace damaged oligodendrocytes and myelin, and also effectively attenuate the autoimmune process in a local, nonsystemic manner to protect brain cells from further injury, as well as facilitate the intrinsic capacity of the brain for recovery. These fundamental immunomodulatory and neurotrophic properties are shared by stem cells of different sources. By using different routes of delivery, cells may target both affected white matter tracts and the perivascular niche where the trafficking of immune cells occur. It is unclear yet whether the therapeutic properties of transplanted cells are maintained with the duration of time. The application of neural stem cell therapy (derived from fetal brain or from human embryonic stem cells) will be realized once their purification, mass generation, and safety are guaranteed. However, previous clinical experience with bone marrow stromal (mesenchymal) stem cells and the relative easy expansion of autologous cells have opened the way to their experimental application in MS. An initial clinical trial has established the probable safety of their intravenous and intrathecal delivery. Short-term follow-up observed immunomodulatory effects and clinical benefit justifying further clinical trials.

Immunohistological markers for proliferative events, gliogenesis, and neurogenesis within the adult hippocampus

Biologists long believed that, once development is completed, no new neurons are produced in the forebrain. However, as is now firmly established, new neurons can be produced at least in two specific forebrain areas: the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampal formation. Neurogenesis within the adult DG occurs constitutively throughout postnatal life, and the rate of neurogenesis within the DG can be altered under various physiological and pathophysiological conditions. The process of adult neurogenesis within the DG is a multi-step process (proliferation, differentiation, migration, targeting, and synaptic integration) that ends with the formation of a post-mitotic functionally integrated new neuron. Various markers are expressed during specific stages of adult neurogenesis. The availability of such markers allows the time-course and fate of newly born cells to be followed within the DG in a detailed and precise fashion. Several of the available markers (e.g., PCNA, Ki-67, PH3, MCM2) are markers for proliferative events, whereas others are more specific for early phases of neurogenesis and gliogenesis within the adult DG (e.g., nestin, GFAP, Sox2, Pax6). In addition, markers are available allowing events to be distinguished that are related to later steps of gliogenesis (e.g., vimentin, BLBP, S100beta) or neurogenesis (e.g., NeuroD, PSA-NCAM, DCX).

Reversal of chlorpyrifos neurobehavioral teratogenicity in mice by allographic transplantation of adult subventricular zone-derived neural stem cells

Neurobehavioral teratogenicity can be reversed with transplantation of neural stem cells. However, the usefulness of this therapy would be greatly enhanced by employing adult stem cells. In pursuit of this this goal, we developed a model that uses subventricular zone (SVZ) cells. HS/Ibg mice were exposed prenatally to chlorpyrifos on gestational days 9-18 (3 mg/kg/day, SC) in order to induce deficits in their performance in the Morris water maze test. Both the control and the exposed offspring were transplanted with SVZ cells (or vehicle) on postnatal day 35; this actually represents an allogenic transplantation, because the HS/Ibg strain is a heterogeneous stock. The transplanted cells were later observed in the host brain by DiI tracing, and their initial differentiation to cholinergic neurons and astrocytes was ascertained. On postnatal day 80, animals that had been exposed prenatally to chlorpyrifos displayed impaired Morris water maze performance, requiring more time to reach the platform. Transplantation of adult SVZ-derived neural stem cells (NSC) reversed the deficits. Applying autologous transplantation provides an important demonstration that the methodological obstacles of immunological rejection and the ethical concerns related to using embryonic stem cells may be successfully bypassed in developing stem cell therapies for neurodevelopmental disorders.

Cell surface N-glycans-mediated isolation of mouse neural stem cells

The isolation of neural stem cells (NSCs) has been hampered by the lack of valid cell-surface antigens on NSCs, and novel valuable markers have been proposed. Glycan (oligosaccharide chain) is a potential candidate as a marker to isolate NSCs, because the species and the combination order of saccharides in glycan generate remarkable structural diversity and specificity. At present, the expression of hundreds of glycoconjugates with glycans have been found in the NSCs; however, just a few glycan-epitopes have been identified as valuable cell-surface markers. This review focused on the isolation of NSC using glycoprotein, especially complex type N-glycans. The cell-surface N-glycan-mediated isolation of NSCs is therefore expected to provide a comprehensive understanding of the biologic characteristics of NSCs in the brain, and thereby help to develop novel strategies in the field of regenerative medicine.

CXCR2 signaling protects oligodendrocytes and restricts demyelination in a mouse model of viral-induced demyelination

BACKGROUND

The functional role of ELR-positive CXC chemokines during viral-induced demyelination was assessed. Inoculation of the neuroattenuated JHM strain of mouse hepatitis virus (JHMV) into the CNS of susceptible mice results in an acute encephalomyelitis that evolves into a chronic demyelinating disease, modeling white matter pathology observed in the human demyelinating disease Multiple Sclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

JHMV infection induced the rapid and sustained expression of transcripts specific for the ELR+ chemokine ligands CXCL1 and CXCL2, as well as their binding receptor CXCR2, which was enriched within the spinal cord during chronic infection. Inhibiting CXCR2 signaling with neutralizing antiserum significantly (p<0.03) delayed clinical recovery. Moreover, CXCR2 neutralization was associated with an increase in the severity of demyelination that was independent of viral recrudescence or modulation of neuroinflammation. Rather, blocking CXCR2 was associated with increased numbers of apoptotic cells primarily within white matter tracts, suggesting that oligodendrocytes were affected. JHMV infection of enriched oligodendrocyte progenitor cell (OPC) cultures revealed that apoptosis was associated with elevated expression of cleaved caspase 3 and muted Bcl-2 expression. Inclusion of CXCL1 within JHMV infected cultures restricted caspase 3 cleavage and increased Bcl-2 expression that was associated with a significant (p<0.001) decrease in apoptosis. CXCR2 deficient oligodendrocytes were refractory to CXCL1 mediated protection from JHMV-induced apoptosis, readily activating caspase 3 and down regulating Bcl-2.

CONCLUSION/SIGNIFICANCE

These findings highlight a previously unappreciated role for CXCR2 signaling in protecting oligodendrocyte lineage cells from apoptosis during inflammatory demyelination initiated by viral infection of the CNS.

Conserved fate and function of ferumoxides-labeled neural precursor cells in vitro and in vivo

Recent progress in cell therapy research for brain diseases has raised the need for non-invasive monitoring of transplanted cells. For therapeutic application in multiple sclerosis, transplanted cells need to be tracked both spatially and temporally, in order to assess their migration and survival in the host tissue. Magnetic resonance imaging (MRI) of superparamagnetic iron oxide-(SPIO)-labeled cells has been widely used for high resolution monitoring of the biodistribution of cells after transplantation into the central nervous system (CNS). Here we labeled mouse glial-committed neural precursor cells (NPCs) with the clinically approved SPIO contrast agent ferumoxides and examined their survival and differentiation in vitro, as well as their functional response to environmental signals present within the inflamed brain of experimental autoimmune encephalomyelitis (EAE) mice in vivo. We show that ferumoxides labeling does not affect NPC survival and pluripotency in vitro. Following intracerebroventricular (ICV) transplantation in EAE mice, ferumoxides-labeled NPCs responded to inflammatory cues in a similar fashion as unlabeled cells. Ferumoxides-labeled NPCs migrated over comparable distances in white matter tracts and differentiated equally into the glial lineages. Furthermore, ferumoxides-labeled NPCs inhibited lymph node cell proliferation in vitro, similarly to non-labeled cells, suggesting a preserved immunomodulatory function. These results demonstrate that ferumoxides-based MRI cell tracking is well suited for non-invasive monitoring of NPC transplantation.

Cell replacement therapies to promote remyelination in a viral model of demyelination

Persistent infection of the central nervous system (CNS) of mice with the neuroadapted JHM strain of mouse hepatitis (MHV) is characterized by ongoing demyelination mediated by inflammatory T cells and macrophages that is similar both clinically and histologically with the human demyelinating disease multiple sclerosis (MS). Although extensive demyelination occurs in mice persistently infected with MHV there is only limited remyelination. Therefore, the MHV model of demyelination is a relevant model for studying disease and evaluating therapeutic approaches to protect cells of the oligodendrocyte lineage and promote remyelination. This concept is further highlighted as the etiology of MS remains enigmatic, but viruses have long been considered as potential triggering agents in initiating and/or maintaining MS symptoms. As such, understanding mechanisms associated with promoting repair within the CNS in the context of a persistent viral infection is critical given the possible viral etiology of MS. This review focuses on recent studies using either mouse neural stem cells (NSCs) or human oligodendrocyte progenitor cells (OPCs) derived from human embryonic stem cell (hESC) to promote remyelination in mice persistently infected with MHV. In addition, the potential role for chemokines in positional migration of transplanted cells is addressed.

An avian model for the reversal of neurobehavioral teratogenicity with neural stem cells

A fast and simple model which uses lower animals on the evolutionary scale is beneficial for developing procedures for the reversal of neurobehavioral teratogenicity with neural stem cells. Here, we established a procedure for the derivation of chick neural stem cells, establishing embryonic day (E) 10 as optimal for progression to neuronal phenotypes. Cells were obtained from the embryonic cerebral hemispheres and incubated for 5-7 days in enriched medium containing epidermal growth factor (EGF) and basic fibroblast growth factor (FGF2) according to a procedure originally developed for mice. A small percentage of the cells survived, proliferated and formed nestin-positive neurospheres. After removal of the growth factors to allow differentiation (5 days), 74% of the cells differentiated into all major lineages of the nervous system, including neurons (Beta III tubulin-positive, 54% of the total number of differentiated cells), astrocytes (GFAP-positive, 26%), and oligodendrocytes (O4-positive, 20%). These findings demonstrate that the cells were indeed neural stem cells. Next, the cells were transplanted in two allograft chick models; (1) direct cerebral transplantation to 24-h-old chicks, followed by post-transplantation cell tracking at 24 h, 6 days and 14 days, and (2) intravenous transplantation to chick embryos on E13, followed by cell tracking on E19. With both methods, transplanted cells were found in the brain. The chick embryo provides a convenient, precisely-timed and unlimited supply of neural progenitors for therapy by transplantation, as well as constituting a fast and simple model in which to evaluate the ability of neural stem cell transplantation to repair neural damage, steps that are critical for progress toward therapeutic applications.

Distribution of EFHC1 or Myoclonin 1 in mouse neural structures

EFHC1, a gene mutated in juvenile myoclonic epilepsy, encodes EFHC1, a protein with three DM10 domains and one EF-hand motif. We recently demonstrated that this molecule is a microtubule-associated protein (MAP) implicated in neuronal migration. Because some controversies persist about the precise localization in the CNS, we studied the neuroanatomical distribution of EFHC1 in mature and developing mouse brain. In the adult, low mRNA expression was detected in several brain structures such as cortex, striatum, hippocampus and cerebellum. At E16, EFHC1 mRNA was shown to be expressed in cortex and not only in cells lining ventricles. Using a purified polyclonal antibody, EFHC1 staining was observed in all cortical layers, in piriform cortex, in hippocampus and in Purkinje cells of cerebellum. In the cortex, the majority of EFHC1 positive cells correspond to neurons, however some glial cells were also stained. In agreement with a previous study, we demonstrated strong EFHC1 expression in cilia of ependymal cells lining cerebral ventricles. Moreover, at E16, the protein was observed at the borders of brain ventricles, in choroid plexus, but also, although to a lesser extent, in piriform and neocortex. In these latter structures, the pattern of expression seems to correspond to the extensions of the radial glia fibers as demonstrated by BLBP immunostaining. Finally, we confirmed that EFHC1 was also expressed and co-localized with the mitotic spindle of neural stem cells. These results confirm that EFHC1 is a protein with a likely low expression level in mouse brain but detectable both in adult and embryonic brain supporting our previous data and hypothesis that EFHC1 could play an important role during brain development. As discussed, this opens the door to a new conceptual approach viewing some idiopathic generalized epilepsies as developmental diseases instead of classical channelopathies.

Analysis of stem cell lineage progression in the neonatal subventricular zone identifies EGFR+/NG2- cells as transit-amplifying precursors

In the adult subventricular zone (SVZ), astroglial stem cells generate transit-amplifying precursors (TAPs). Both stem cells and TAPs form clones in response to epidermal growth factor (EGF). However, in vivo, in the absence of sustained EGF receptor (EGFR) activation, TAPs divide a few times before differentiating into neuroblasts. The lack of suitable markers has hampered the analysis of stem cell lineage progression and associated functional changes in the neonatal germinal epithelium. Here we purified neuroblasts and clone-forming precursors from the neonatal SVZ using expression levels of EGFR and polysialylated neural cell adhesion molecule (PSANCAM). As in the adult SVZ, most neonatal clone-forming precursors did not express the neuroglia proteoglycan 2 (NG2) but displayed characteristics of TAPs, and only a subset exhibited antigenic characteristics of astroglial stem cells. Both precursors and neuroblasts were PSANCAM(+); however, neuroblasts also expressed doublecortin and functional voltage-dependent Ca(2+) channels. Neuroblasts and precursors had distinct outwardly rectifying K(+) current densities and passive membrane properties, particularly in precursors contacting each other, because of the contribution of gap junction coupling. Confirming the hypothesis that most are TAPs, cell tracing in brain slices revealed that within 2 days the majority of EGFR(+) cells had exited the cell cycle and differentiated into a progenitor displaying intermediate antigenic and functional properties between TAPs and neuroblasts. Thus, distinct functional and antigenic properties mark stem cell lineage progression in the neonatal SVZ.

Prospects of cell therapy for disorders of myelin

Recent advances in stem cell biology have raised expectations that both diseases of, and injuries to, the central nervous system may be ameliorated by cell transplantation. In particular, cell therapy has been studied for inducing efficient remyelination in disorders of myelin, including both the largely pediatric disorders of myelin formation and maintenance and the acquired demyelinations of both children and adults. Potential cell-based treatments of two major groups of disorders include both delivery of myelinogenic replacements and mobilization of residual oligodendrocyte progenitor cells as a means of stimulating endogenous repair; the choice of modality is then predicated upon the disease target. In this review we consider the potential application of cell-based therapeutic strategies to disorders of myelin, highlighting the promises as well as the problems and potential perils of this treatment approach.

IFN-gamma-mediated suppression of coronavirus replication in glial-committed progenitor cells

The neurotropic JHM strain of mouse hepatitis virus (JHMV) replicates primarily within glial cells following intracranial inoculation of susceptible mice, with relative sparing of neurons. This study demonstrates that glial cells derived from neural progenitor cells are susceptible to JHMV infection and that treatment of infected cells with IFN-γ inhibits viral replication in a dose-dependent manner. Although type I IFN production is muted in JHMV-infected glial cultures, IFN-β is produced following IFN-γ-treatment of JHMV-infected cells. Also, direct treatment of infected glial cultures with recombinant mouse IFN-α or IFN-β inhibits viral replication. IFN-γ-mediated control of JHMV replication is dampened in glial cultures derived from the neural progenitor cells of type I receptor knock-out mice. These data indicate that JHMV is capable of infecting glial cells generated from neural progenitor cells and that IFN-γ-mediated control of viral replication is dependent, in part, on type I IFN secretion.

Intrahippocampal transplantation of transgenic neural precursor cells overexpressing interleukin-1 receptor antagonist blocks chronic isolation-induced impairment in memory and neurogenesis

The proinflammatory cytokine interleukin-1 (IL-1) within the brain is critically involved in mediating the memory impairment induced by acute inflammatory challenges and psychological stress. However, the role of IL-1 in memory impairment and suppressed neurogenesis induced by chronic stress exposure has not been investigated before now. We report here that mice that were isolated for 4 weeks displayed a significant elevation in hippocampal IL-1beta levels concomitantly with body weight loss, specific impairment in hippocampal-dependent memory, and decreased hippocampal neurogenesis. To examine the causal role of IL-1 in these effects, we developed a novel approach for long-term delivery of IL-1 receptor antagonist (IL-1ra) into the brain, using transplantation of neural precursor cells (NPCs), obtained from neonatal mice with transgenic overexpression of IL-1ra (IL-1raTG) under the glial fibrillary acidic protein promoter. Four weeks following intrahippocampal transplantation of IL-1raTG NPCs labeled with PKH-26, the transplanted cells were incorporated within the dentate gyrus and expressed mainly astrocytic markers. IL-1ra levels were markedly elevated in the hippocampus, but not in other brain regions, by 10 days and for at least 4 weeks post-transplantation. Transplantation of IL-1raTG NPCs completely rescued the chronic isolation-induced body weight loss, memory impairment, and suppressed hippocampal neurogenesis, compared with isolated mice transplanted with WT cells or sham operated. The transplantation had no effect in group-housed mice. These findings elucidate the role of IL-1 in the pathophysiology of chronic isolation and suggest that transplantation of IL-1raTG NPCs may provide a useful therapeutic procedure for IL-1-mediated memory disturbances in chronic inflammatory and neurological conditions.

Activation of inflammatory response by a combination of growth factors in cuprizone-induced demyelinated brain leads to myelin repair

In vivo remyelination promoted by a combination of four oligodendrocyte specific growth factors (GFs) in cuprizone-induced demyelinated mice brains was described recently by our group. Here we report activation of inflammatory response in mice brain following cuprizone-induced demyelination and its further enhancement immediately after injection of growth factors in vivo, while no significant inflammatory response was evident in GFs-injected normal brains. Cuprizone-induced demyelination was accompanied by increased expression of inflammatory cytokines, TNFalpha and IL-1beta, anti-inflammatory cytokines TGFbeta, IL-10 and increased levels of chemokines, CCL2, CCL5, and CXCL10, produced by resident microglia and astrocytes. During demyelination, involvement of oxidative stress was evident by disruption of mitochondrial structure and temporal decline in reduced glutathione levels, later returning to normal. Increase in the cytokines and chemokines was further enhanced within 2 days post injection (dpi) of GFs, coinciding with signal for repair via activation of pAkt and NFkappaB transcription factor reported earlier. Upregulation of mRNA and protein level of antioxidant genes, metallothionein (MT) I/II and activity of a cytosolic oxidoreductase enzyme, glycerolphosphate-3 dehydrogenase (cGPDH) occurred, resulting in a metabolic shuttle with an increase in glycerol in mice brains during period of demyelination and early GF-mediated repair.

Glial precursor cell transplantation therapy for neurotrauma and multiple sclerosis

Traumatic injury to the brain or spinal cord and multiple sclerosis (MS) share a common pathophysiology with regard to axonal demyelination. Despite advances in central nervous system (CNS) repair in experimental animal models, adequate functional recovery has yet to be achieved in patients in response to any of the current strategies. Functional recovery is dependent, in large part, upon remyelination of spared or regenerating axons. The mammalian CNS maintains an endogenous reservoir of glial precursor cells (GPCs), capable of generating new oligodendrocytes and astrocytes. These GPCs are upregulated following traumatic or demyelinating lesions, followed by their differentiation into oligodendrocytes. However, this innate response does not adequately promote remyelination. As a result, researchers have been focusing their efforts on harvesting, culturing, characterizing, and transplanting GPCs into injured regions of the adult mammalian CNS in a variety of animal models of CNS trauma or demyelinating disease. The technical and logistic considerations for transplanting GPCs are extensive and crucial for optimizing and maintaining cell survival before and after transplantation, promoting myelination, and tracking the fate of transplanted cells. This is especially true in trials of GPC transplantation in combination with other strategies such as neutralization of inhibitors to axonal regeneration or remyelination. Overall, such studies improve our understanding and approach to developing clinically relevant therapies for axonal remyelination following traumatic brain injury (TBI) or spinal cord injury (SCI) and demyelinating diseases such as MS.

Thyroid hormones promote differentiation of oligodendrocyte progenitor cells and improve remyelination after cuprizone-induced demyelination

In the present work we analyzed the capacity of thyroid hormones (THs) to improve remyelination using a rat model of cuprizone-induced demyelination previously described in our laboratories. Twenty one days old Wistar rats were fed a diet containing 0.6% cuprizone for two weeks to induce demyelination. After cuprizone withdrawal, rats were injected with triiodothyronine (T3). Histological studies carried out in these animals revealed that remyelination in the corpus callosum (CC) of T3-treated rats improved markedly when compared to saline treated animals. The cellular events occurring in the CC and in the subventricular zone (SVZ) during the first week of remyelination were analyzed using specific oligodendroglial cell (OLGc) markers. In the CC of saline treated demyelinated animals, mature OLGcs decreased and oligodendroglial precursor cells (OPCs) increased after one week of spontaneous remyelination. Furthermore, the SVZ of these animals showed an increase in early progenitor cell numbers, dispersion of OPCs and inhibition of Olig and Shh expression compared to non-demyelinated animals. The changes triggered by demyelination were reverted after T3 administration, suggesting that THs could be regulating the emergence of remyelinating oligodendrocytes from the pool of proliferating cells residing in the SVZ. Our results also suggest that THs receptor beta mediates T3 effects on remyelination. These results support a potential role for THs in the remyelination process that could be used to develop new therapeutic approaches for demyelinating diseases.

A population of prenatally generated cells in the rat paleocortex maintains an immature neuronal phenotype into adulthood

New neurons in the adult brain transiently express molecules related to neuronal development, such as the polysialylated form of neural cell adhesion molecule, or doublecortin (DCX). These molecules are also expressed by a cell population in the rat paleocortex layer II, whose origin, phenotype, and function are not clearly understood. We have classified most of these cells as a new cell type termed tangled cell. Some cells with the morphology of semilunar-pyramidal transitional neurons were also found among this population, as well as some scarce cells resembling semilunar, pyramidal. and fusiform neurons. We have found that none of these cells in layer II express markers of glial cells, mature, inhibitory, or principal neurons. They appear to be in a prolonged immature state, confirmed by the coexpression of DCX, TOAD/Ulip/CRMP-4, A3 subunit of the cyclic nucleotide-gated channel, or phosphorylated cyclic adenosine monophosphate response element-binding protein. Moreover, most of them lack synaptic contacts, are covered by astroglial lamellae, and fail to express cellular activity markers, such as c-Fos or Arc, and N-methyl-d-aspartate or glucocorticoid receptors. We have found that none of these cells appear to be generated during adulthood or early youth and that most of them have been generated during embryonic development, mainly in E15.5.

Prospects for neural stem cell-based therapies for neurological diseases

Neural stem and progenitor cells have great potential for the treatment of neurological disorders. However, many obstacles remain to translate this field to the patient's bedside, including rationales for using neural stem cells in individual neurological disorders; the challenges of neural stem cell biology; and the caveats of current strategies of isolation and culturing neural precursors. Addressing these challenges is critical for the translation of neural stem cell biology to the clinic. Recent work using neural stem cells has yielded novel biologic concepts such as the importance of the reciprocal interaction between neural stem cells and the neurodegenerative environment. The prospect of using transplants of neural stem cells and progenitors to treat neurological diseases requires a better understanding of the molecular mechanisms of both neural stem cell behavior in experimental models and the intrinsic repair capacity of the injured brain.

Complex interactions between thyroid hormone and fibroblast growth factor signalling

PURPOSE OF REVIEW

Thyroid hormone and fibroblast growth factors are critically important for normal development. Recent evidence points to complex interactions between thyroid hormone and fibroblast growth factors that regulate cell proliferation and differentiation. We discuss mechanisms of thyroid hormone and fibroblast growth factor action, and identify downstream signalling responses that offer opportunities for regulatory crosstalk.

RECENT FINDINGS

Thyroid hormone action is mediated by nuclear receptors that regulate gene expression in response to thyroid hormone. Recent studies have shown thyroid hormone also acts at the cell membrane via the alpha(V)beta(3) integrin receptor and these actions also communicate with nuclear responses to thyroid hormone. Fibroblast growth factors act via receptor tyrosine kinases to stimulate second messenger pathways that also communicate with nuclear events. Several common pathways, including mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and signal transducer and activator of transcription signalling, are activated by thyroid hormone and fibroblast growth factor, and may act as points of convergence for interaction in tissues, such as bone, central nervous system and heart, as well as in the extra-cellular matrix and during angiogenesis.

SUMMARY

Although there is convincing evidence that thyroid hormone and fibroblast growth factors interact widely, little is known about molecular mechanisms that determine this interplay. Future research in this expanding field may result in identification of new pharmacological targets for manipulation of cell proliferation and differentiation.

Neural cell adhesion molecule polysialylation enhances the sensitivity of embryonic stem cell-derived neural precursors to migration guidance cues

The development of stem cell-based neural repair strategies requires detailed knowledge on the interaction of migrating donor cells with the host brain environment. Here we report that overexpression of polysialic acid (PSA), a carbohydrate polymer attached to the neural cell adhesion molecule (NCAM), in embryonic stem (ES) cell-derived glial precursors (ESGPs) strikingly modifies their migration behavior in response to guidance cues. ESGPs transduced with a retrovirus encoding the polysialyltransferase STX exhibit enhanced migration in monolayer cultures and an increased penetration of organotypic slice cultures. Chemotaxis assays show that overexpression of PSA results in an enhanced chemotactic migration toward gradients of a variety of chemoattractants, including fibroblast growth factor 2 (FGF2), platelet-derived growth factor, and brain-derived neurotrophic factor (BDNF), and that this effect is mediated via the phosphatidylinositol 3'-kinase (PI3K) pathway. Moreover, PSA-overexpressing ESGPs also exhibit an enhanced chemotactic response to tissue explants derived from different brain regions. The effect of polysialylation on directional migration is preserved in vivo. Upon transplantation into the adult striatum, PSA-overexpressing but not control cells display a targeted migration toward the subventricular zone. On the basis of these data, we propose that PSA plays a crucial role in modulating the ability of migrating precursor cells to respond to regional guidance cues within the brain tissue. Disclosure of potential conflicts of interest is found at the end of this article.

Expression of the cell surface markers mAb 2F7 and PSA-NCAM in the embryonic rat brain

Cell surface markers of neuronal precursor cells are of interest since they allow the isolation of these cells from mixed populations of cells. The monoclonal antibody (mAb) 2F7, a cell surface marker, has been shown to label neuronal precursors and post-mitotic neurones in the embryonic rat spinal cord and cortex. Little is known about the expression of the epitope recognised by mAb 2F7 in other regions of the developing brain. The present study found expression of this epitope in the embryonic rat cortex, ventral mesencephalon (VM) and striatum at times at which neurogenesis is known to occur in these regions. The expression profile of mAb 2F7 was similar to that of the polysialylated form of the neural adhesion molecule (PSA-NCAM), a commonly used marker of neuronal precursor cells. The percentage of mAb 2F7-positive cells incorporating bromodeoxyuridine (BrdU) was found to be comparable to that of PSA-NCAM-positive cells in primary cell cultures of embryonic rat cortex, VM and striatum. These data demonstrate that mAb 2F7 can be used as a cell surface marker for neuronal precursor cells in several regions of the embryonic rat brain.