FGF-2 is sufficient to isolate progenitors found in the adult mammalian spinal cord

Origin of new glial cells in intact and injured adult spinal cord

Several distinct cell types in the adult central nervous system have been suggested to act as stem or progenitor cells generating new cells under physiological or pathological conditions. We have assessed the origin of new cells in the adult mouse spinal cord by genetic fate mapping. Oligodendrocyte progenitors self-renew, give rise to new mature oligodendrocytes, and constitute the dominating proliferating cell population in the intact adult spinal cord. In contrast, astrocytes and ependymal cells, which are restricted to limited self-duplication in the intact spinal cord, generate the largest number of cells after spinal cord injury. Only ependymal cells generate progeny of multiple fates, and neural stem cell activity in the intact and injured adult spinal cord is confined to this cell population. We provide an integrated view of how several distinct cell types contribute in complementary ways to cell maintenance and the reaction to injury.

Nestin-GFP transgene reveals neural precursor cells in adult skeletal muscle

BACKGROUND

Therapy for neural lesions or degenerative diseases relies mainly on finding transplantable active precursor cells. Identifying them in peripheral tissues accessible for biopsy, outside the central nervous system, would circumvent the serious immunological and ethical concerns impeding cell therapy.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we isolated neural progenitor cells in cultured adult skeletal muscle from transgenic mice in which nestin regulatory elements control GFP expression. These cells also expressed the early neural marker Tuj1 and light and heavy neurofilament but not S100β, indicating that they express typical neural but not Schwann cell markers. GFP+/Tuj1+ cells were also negative for the endothelial and pericyte markers CD31 and α-smooth muscle actin, respectively. We established their a) functional response to glutamate in patch-clamp recordings; b) interstitial mesenchymal origin; c) replicative capacity; and d) the environment necessary for their survival after fluorescence-activated cell sorting.

CONCLUSIONS/SIGNIFICANCE

We propose that the decline in nestin-GFP expression in muscle progenitor cells and its persistence in neural precursor cells in muscle cultures provide an invaluable tool for isolating a population of predifferentiated neural cells with therapeutic potential.

Isolation and characterization of neural stem cells from the neonatal rat cochlear nucleus

Neural stem cells have been identified in multiple parts of the postnatal mammalian brain, as well as in the inner ear. No investigation of potential neural stem cells in the cochlear nucleus has yet been performed. The aim of this study was to investigate potential neural stem cells from the cochlear nucleus by neurosphere assay and in histological sections to prove their capacity for self-renewal and for differentiation into progenitor cells and cells of the neuronal lineage. For this purpose, cells of the cochlear nucleus of postnatal day 6 rats were isolated and cultured for generation of primary neurospheres. Spheres were dissociated and cells analyzed for capacity for mitosis and differentiation. Cell division was detected by cell-counting assay and BrdU incorporation. Differentiated neural progenitor cells showed distinct labeling for Nestin and for Atoh1. Positive staining of ß-III Tubulin, glial fibrillary acid protein (GFAP) and myelin basic protein (MBP) showed differentiation into neurons, astrocytes and oligodendrocytes. Furthermore, Nestin- and BrdU-labeled cells could also be detected in histological sections. In conclusion, the isolated cells from the cochlear nucleus presented all the features of neural stem cells: cell division, presence of progenitor cells and differentiation into different cells of the neuronal lineage. The existence of neural stem cells may add to the understanding of developmental features in the cochlear nucleus.

Fgf-2 in astroglial cells during vertebrate spinal cord recovery

Fibroblast growth factor-2 is a pleiotrophic cytokine with neurotrophic and gliogenic properties. It is known to regulate CNS injury responses, which include transformation of reactive astrocytes, neurogenesis, and promotion of neurotrophic activities. In the brain, it is localized in astrocytes and discrete neuronal populations. Following both central and peripheral nervous system injury, astrocytes become reactive. These activated cells undergo hypertrophy. A key indicator of astrocyte activation is the increased accumulation of intermediate filaments composed of glial fibrillary acidic protein (GFAP). Following physical insult of brain or spinal cord, reactive astrocytes show increased FGF-2 immunoreactivity. Thus, FGF-2 appears to participate in astrocytic differentiation and proliferation and a good candidate for astrocytic function regulation in healthy, injured, or diseased CNS. To further investigate the cellular mechanisms underlying FGF-2 restorative actions and to analyze the changes within astroglial cells, we studied the localization of GFAP and FGF-2 in adult intact and injured Pleurodeles CNS. Our results show that spinal cord injury triggers a significant increase in FGF-2 immunoreactivity in reactive astrocytes at sites of insult. In addition, these results were time-dependent. Increase in FGF-2 immunoreactivity along the CNS axis, starting 1-week post-injury, was long-lasting extending to 6 weeks. This increase was accompanied by an increase in GFAP immunoreactivity in the same spatial pattern except in SC3 where its level was almost similar to sham-operated animals. Therefore, we suggest that FGF-2 may be involved in cell proliferation and/or astroglial cells differentiation after body spinal cord transection, and could thus play an important role in locomotion recovery.

Influence of FGF2 and PEG hydrogel matrix properties on hMSC viability and spreading

In this study, three-dimensional (3-D) poly(ethylene glycol) (PEG) hydrogel arrays were used to screen for the effects of fibroblast growth factor-2 (FGF2), combined with multiple hydrogel matrix parameters, on human mesenchymal stem cell (hMSC) viability and spreading. In particular, we examined the effects of FGF2 while co-varying hydrogel matrix degradability, cell adhesion ligand type, and cell adhesion ligand density. FGF2 significantly improved viability of hMSCs in a dose-dependent manner in both nondegrading and degrading PEG hydrogels in the absence of extracellular matrix-derived cell adhesion ligands. The presence of a small molecule that inhibits autophosphorylation of the FGF2 receptor blocked the effects of FGF2 on hMSC viability in PEG hydrogels, both in the presence and absence of the Arg-Gly-Asp-Ser-Pro (RGDSP) ligand. FGF2 effects on hMSC viability were less pronounced when FGF2 was presented in combination with the RGDSP cell adhesion ligand or the IKVAV cell adhesion ligand in nondegrading PEG hydrogels. Importantly, spread hMSC morphologies were observed and quantified in a select subset of hydrogel networks, which were degradable and included both FGF2 and RGDSP. These results indicate that the hydrogel arrays described here can be used to efficiently study the influence of soluble and insoluble hydrogel matrix parameters on stem cell behavior, and to identify synthetic, 3-D environments that promote specific hMSC behaviors.

Insights into neurogenesis and aging: potential therapy for degenerative disease?

Neurogenesis is the process by which new neural cells are generated from a small population of multipotent stem cells in the adult CNS. This natural generation of new cells is limited in its regenerative capabilities and also declines with age. The use of stem cells in the treatment of neurodegenerative disease may hold great potential; however, the age-related incidence of many CNS diseases coincides with reduced neurogenesis. This review concisely summarizes current knowledge related to adult neurogenesis and its alteration with aging and examines the feasibility of using stem cell and gene therapies to combat diseases of the CNS with advancing age.

Interaction of NG2(+) glial progenitors and microglia/macrophages from the injured spinal cord

Spinal cord contusion produces a central lesion surrounded by a peripheral rim of residual white matter. Despite stimulation of NG2(+) progenitor cell proliferation, the lesion remains devoid of normal glia chronically after spinal cord injury (SCI). To investigate potential cell-cell interactions of the predominant cells in the lesion at 3 days after injury, we used magnetic activated cell sorting to purify NG2(+) progenitors and OX42(+) microglia/macrophages from contused rat spinal cord. Purified NG2(+) cells from the injured cord grew into spherical masses when cultured in defined medium with FGF2 plus GGF2. The purified OX42(+) cells did not form spheroids and significantly reduced sphere growth by NG2(+) cells in co-cultures. Conditioned medium from these OX42(+) cells, unlike that from normal peritoneal macrophages or astrocytes also inhibited growth of NG2(+) cells, suggesting inhibition by secreted factors. Expression analysis of freshly purified OX42(+) cells for a panel of six genes for secreted factors showed expression of several that could contribute to inhibition of NG2(+) cells. Further, the pattern of expression of four of these, TNFalpha, TSP1, TIMP1, MMP9, in sequential coronal tissue segments from a 2 cm length of cord centered on the injury epicenter correlated with the expression of Iba1, a marker gene for OX42(+) cells, strongly suggesting a potential regional influence by activated microglia/macrophages on NG2(+) cells in vivo after SCI. Thus, the nonreplacement of lost glial cells in the central lesion zone may involve, at least in part, inhibitory factors produced by microglia/macrophages that are concentrated within the lesion.

A mesenchymal-like ZEB1(+) niche harbors dorsal radial glial fibrillary acidic protein-positive stem cells in the spinal cord

In humans and rodents the adult spinal cord harbors neural stem cells located around the central canal. Their identity, precise location, and specific signaling are still ill-defined and controversial. We report here on a detailed analysis of this niche. Using microdissection and glial fibrillary acidic protein (GFAP)-green fluorescent protein (GFP) transgenic mice, we demonstrate that neural stem cells are mostly dorsally located GFAP(+) cells lying ependymally and subependymally that extend radial processes toward the pial surface. The niche also harbors doublecortin protein (Dcx)(+) Nkx6.1(+) neurons sending processes into the lumen. Cervical and lumbar spinal cord neural stem cells maintain expression of specific rostro-caudal Hox gene combinations and the niche shows high levels of signaling proteins (CD15, Jagged1, Hes1, differential screening-selected gene aberrative in neuroblastoma [DAN]). More surprisingly, the niche displays mesenchymal traits such as expression of epithelial-mesenchymal-transition zinc finger E-box-binding protein 1 (ZEB1) transcription factor and smooth muscle actin. We found ZEB1 to be essential for neural stem cell survival in vitro. Proliferation within the niche progressively ceases around 13 weeks when the spinal cord reaches its final size, suggesting an active role in postnatal development. In addition to hippocampus and subventricular zone niches, adult spinal cord constitutes a third central nervous system stem cell niche with specific signaling, cellular, and structural characteristics that could possibly be manipulated to alleviate spinal cord traumatic and degenerative diseases.

Unconditioned adult-derived neurosphere cells mainly differentiate towards astrocytes upon transplantation in sclerotic rat hippocampus

PURPOSE

Cell transplantation is being investigated as an alternative treatment for medically refractory temporal lobe epilepsy (TLE). In this study the fate of adult-derived neurosphere cells was evaluated after transplantation in the lesioned hippocampus of the intrahippocampal kainic acid (KA) model for TLE.

METHODS

Neurosphere-forming cells were derived from the subventricular zone (SVZ) of transgenic green fluorescent protein (GFP) reporter mice and expanded in culture. After 10 passages in vitro neurosphere-derived cells were transplanted in the hippocampus three days (KA3d group) and three weeks (KA3w group) after intrahippocampal KA injection. Survival and differentiation of neurosphere cells were evaluated three and six weeks after transplantation.

RESULTS

A fraction (about 1%) of GFP-expressing neurosphere cells survived for at least six weeks after transplantation with a higher and more robust survival rate in the KA3d compared to the KA3w group. Although a small fraction of the cells expressed the neuronal marker NeuN, neurosphere cells mainly differentiated towards astrocytes.

DISCUSSION

Our results indicate that adult-derived neurosphere cells are able to survive upon transplantation in the sclerotic hippocampus. The transplanted cells do not or hardly contribute to neuronal replacement and mainly adopt an astrogliotic fate.

Peripheral glial cell differentiation from neurospheres derived from adipose mesenchymal stem cells

Mesenchymal stem cells derived from bone marrow and adipose tissue are being considered for use in neural repair because they can differentiate after appropriate induction in culture into neurons and glia. The question we asked was if neurospheres could be harvested from adipose-derived stem cells and if they then could differentiate in culture to peripheral glial-like cells. Here, we demonstrate that adipose-derived mesenchymal stem cells can form nestin-positive non-adherent neurosphere cellular aggregates when cultured with basic fibroblast growth factor and epidermal growth factor. Dissociation of these neurospheres and removal of mitogens results in expression of the characteristic Schwann cell markers S100 and p75 nerve growth factor receptor and GFAP. The simultaneous expression of these glia markers are characteristic features of Schwann cells and olfactory ensheathing cells which have unique properties regarding remyelination and enhancement of axonal regeneration. When co-cultured with dorsal root ganglion neurons, the peripheral glial-like cells derived from adipose mesenchymal stem cells aligned with neuritis and stimulated neuritic outgrowth. These results indicate that neurospheres can be generated from adipose-derived mesenchymal stem cells, and upon mitogen withdrawal can differentiate into peripheral glial cells with neurotrophic effects.

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.

Region-specific differentiation potential of adult rat spinal cord neural stem/precursors and their plasticity in response to in vitro manipulation

This study characterized the differentiation of neural stem/precursor cells (NSPCs) isolated from different levels of the spinal cord (cervical vs lumbar cord) and different regions along the neuraxis (brain vs cervical spinal cord) of adult male Wistar enhanced green fluorescent protein rats. The differentiation of cervical spinal cord NSPCs was further examined after variation of time in culture, addition of growth factors, and changes in cell matrix and serum concentration. Brain NSPCs did not differ from cervical cord NSPCs in the percentages of neurons, astrocytes, or oligodendrocytes but produced 26.9% less radial glia. Lumbar cord NSPCs produced 30.8% fewer radial glia and 6.9% more neurons compared with cervical cord NSPCs. Spinal cord NSPC differentiation was amenable to manipulation by growth factors and changes in in vitro conditions. This is the first study to directly compare the effect of growth factors, culturing time, serum concentration, and cell matrix on rat spinal cord NSPCs isolated, propagated, and differentiated under identical conditions.

Cell lineage and regional identity of cultured spinal cord neural stem cells and comparison to brain-derived neural stem cells

Neural stem cells (NSCs) can be isolated from different regions of the central nervous system. There has been controversy whether regional differences amongst stem and progenitor cells are cell intrinsic and whether these differences are maintained during expansion in culture. The identification of inherent regional differences has important implications for the use of these cells in neural repair. Here, we compared NSCs derived from the spinal cord and embryonic cortex. We found that while cultured cortical and spinal cord derived NSCs respond similarly to mitogens and are equally neuronogenic, they retain and maintain through multiple passages gene expression patterns indicative of the region from which they were isolated (e.g Emx2 and HoxD10). Further microarray analysis identified 229 genes that were differentially expressed between cortical and spinal cord derived neurospheres, including many Hox genes, Nuclear receptors, Irx3, Pace4, Lhx2, Emx2 and Ntrk2. NSCs in the cortex express LeX. However, in the embryonic spinal cord there are two lineally related populations of NSCs: one that expresses LeX and one that does not. The LeX negative population contains few markers of regional identity but is able to generate LeX expressing NSCs that express markers of regional identity. LeX positive cells do not give rise to LeX-negative NSCs. These results demonstrate that while both embryonic cortical and spinal cord NSCs have similar self-renewal properties and multipotency, they retain aspects of regional identity, even when passaged long-term in vitro. Furthermore, there is a population of a LeX negative NSC that is present in neurospheres derived from the embryonic spinal cord but not the cortex.

Endogenous neural progenitor cells as therapeutic target after spinal cord injury

Growing knowledge about the role of neural progenitor cells supports the hope that stem cell-based therapeutic approaches aimed at restoring function in the lesioned central nervous system can be established. Possible therapies for promoting recovery after spinal cord injury include stimulating the formation of neurons and glial cells by endogenous progenitor cells. This article reviews the current knowledge about the nature of adult progenitor cells in the intact and injured spinal cord and summarizes possibilities and limitations of cellular replacement strategies based on manipulations of endogenous spinal cord progenitor cells and their environment.

Characterization of human skin-derived mesenchymal stem cell proliferation rate in different growth conditions

This study investigated conditions for optimal in vitro propagation of human skin-derived mesenchymal stem cells (S-MSC). Forty primary skin-derived precursor cell (SKP) cultures were established from both male and female donors (age 29-65 years) and eight of them were randomly selected for in-depth characterization. Effects of basic fibroblast growth factor (FGF-2), epidermal growth factor (EGF), leukemia inhibiting factor (LIF) and dibutyryl-cyclic adenosine monophosphate (db-cAMP) on S-MSC proliferation were investigated. Primary SKP cultures were >95% homogenous for CD90, CD73, and CD105 marker expression enabling to classify these cells as S-MSC. FGF-2 dose-dependent stimulation was observed in low serum medium only, whereas EGF neither stimulated S-MSC proliferation nor potentates the effect of FGF-2. Pronounced donor to donor differences among S-MSC cultures were observed in 3-day proliferation assay. This study demonstrates that homogenous S-MSC populations can be reproducibly isolated from individual donors of different age. Optimal cell culture conditions for in vitro propagation of S-MSC are B27 supplemented or low serum media with FGF-2 (4 ng/ml). EGF and LIF as well as db-cAMP are dispensable for S-MSC proliferation.

Spinal cord injury reveals multilineage differentiation of ependymal cells

Spinal cord injury often results in permanent functional impairment. Neural stem cells present in the adult spinal cord can be expanded in vitro and improve recovery when transplanted to the injured spinal cord, demonstrating the presence of cells that can promote regeneration but that normally fail to do so efficiently. Using genetic fate mapping, we show that close to all in vitro neural stem cell potential in the adult spinal cord resides within the population of ependymal cells lining the central canal. These cells are recruited by spinal cord injury and produce not only scar-forming glial cells, but also, to a lesser degree, oligodendrocytes. Modulating the fate of ependymal progeny after spinal cord injury may offer an alternative to cell transplantation for cell replacement therapies in spinal cord injury.

Stem cells for spinal cord repair

Spinal cord injury typically results in permanent disability. Many studies have indicated that transplantation of several different types of stem cells promotes functional recovery in animal models of spinal cord injury. A conceptually different approach to utilize stem cells for regenerative therapies may be recruitment of endogenous neural stem cells resident in the adult spinal cord. We discuss the possibilities, risks, and mechanisms for stem cells in spinal cord repair.

Current status of experimental cell replacement approaches to spinal cord injury

Despite advances in medical and surgical care, the current clinical therapies for spinal cord injury (SCI) are largely ineffective. During the last 2 decades, the search for new therapies has been revolutionized by the discovery of stem cells, which has inspired scientists and clinicians to search for a stem cell-based reparative approaches to many diseases, including neurotrauma. In the present study, the authors briefly summarize current knowledge related to the pathophysiology of SCI, including the concepts of primary and secondary injury and the importance of posttraumatic demyelination. Key inhibitory obstacles that impede axonal regeneration include the glial scar and a number of myelin inhibitory molecules including Nogo. Recent advancements in cell replacement therapy as a therapeutic strategy for SCI are summarized. The strategies include the use of pluripotent human stem cells, embryonic stem cells, and a number of adult-derived stem and progenitor cells such as mesenchymal stem cells, Schwann cells, olfactory ensheathing cells, and adult-derived neural precursor cells. Although current strategies to repair the subacutely injured cord appear promising, many obstacles continue to render the treatment of chronic injuries challenging. Nonetheless, the future for stem cell-based reparative strategies for treating SCI appears bright.

Adult rodent spinal cord-derived neural stem cells: isolation and characterization

Self-renewing multipotent stem/progenitor cells have been isolated from various areas of the adult central nervous system, both neurogenic and non-neurogenic, in vitro by using a variety of mitogens and culture conditions. Mitogenic growth factors stimulate the proliferation of multipotent stem/progenitor cells from embryonic and adult rodent, primates, and human. Neural stem cells were isolated from the adult rat spinal cord as follows: Adult rat spinal cords were dissected, and tissue was mechanically and enzymatically dissociated. The cell suspension was filtered and further purified from debris and enriched for progenitors by using a Percoll density gradient. The dissociated cells were grown on polyornithine- and laminin-coated plates in N2 medium containing fibroblast growth factor-2. The cells grew as attached layers. Cultures were passaged by trypsinization, and rapidly proliferating cells that could be passaged, frozen, and thawed were isolated. Clonal cultures derived from single founder cells identified by marker genes generate neurons, astrocytes, and oligodendrocytes, confirming the multipotent nature of the parent cell. Subcloning analysis showed that after serial passaging, recloning, and expansion, these cells retained multipotentiality, indicating that they are self-renewing.

Olfactory ensheathing cells promote proliferation and inhibit neuronal differentiation of neural progenitor cells through activation of Notch signaling

A population of neural progenitor cells (NPCs) has been known to exist in adult spinal cord and migrate toward the lesion regions during spinal cord injury (SCI). Although there are some positive effects of the transplanted olfactory ensheathing cells (OECs) on axonal regeneration in SCI, little is known about the effects and the underlying mechanism of these grafted OECs on NPCs. In this study, we have investigated how soluble factors derived from rat OECs regulate the proliferation and differentiation of rat NPCs. The conditioned medium from cultured OECs showed its ability to promote proliferation and inhibit neuronal differentiation of NPCs. Notch signaling was apparently involved in this process. With the addition of DAPT, which inhibited Notch signaling, the effects of OEC-conditioned medium on NPCs were blocked. We thus conclude that diffusible factors released from OECs activate the Notch signaling pathway to stimulate the proliferation and suppress neuronal differentiation of NPCs. These findings reveal the likely limitation of using OECs transplantation for SCI repair.

Time-dependent neurosphere-forming ability of adult rat spinal cord after irradiation

To determine whether there was evidence for long-term time-dependent changes in neurosphere-forming ability of rat spinal cord after irradiation, a 15-mm length of spinal cord (C2-T2) of 10-week-old female rats was irradiated with a single dose of 2, 5, 10 or 19 Gy. Cells were isolated from the central 10-mm segment of the irradiated spinal cord immediately or at 0.5, 1, 2 or 5 months to form neurospheres. The number and sizes of neurospheres were determined at day 10, 12, 14 and 16 in vitro. The multipotential properties of neurosphere cells were assessed by immunocytochemistry using lineage-specific markers for neurons and glia. In nonirradiated controls, the number and size of the neurospheres decreased with increasing age of the animals. Regardless of the time after irradiation, there was a dose-dependent decrease in the number and size of neurospheres obtained from the irradiated cord compared to age-matched controls. Using three-way ANOVA, the number of neurospheres was dependent on radiation dose (P < 0.0001), time after irradiation (P < 0.0001), and day of counting in vitro (P < 0.0001). Compared to cells cultured immediately after irradiation, there was an increase in the relative plating efficiency of neurospheres cultured 1 month after irradiation. However, no further increase was apparent up to 5 months after irradiation. The multipotential properties of neurosphere cells in vitro remained unchanged with increasing time after irradiation. These results may suggest a time-dependent recovery of radiation damage using neurosphere-forming ability as the end point and agree with data that show time-dependent recovery of radiation damage in spinal cord using histological or functional end points.

Creating a neurogenic environment: The role of BDNF and FGF2

Regional environmental cues present in the adult brain determine the fate of adult neural progenitor cells. To determine whether the growth factors BDNF or FGF2 can create a neurogenic environment outside the SVZ, we used AAV(1/2)-mediated gene transfer to produce ectopic BDNF or FGF2 expression in the normal adult rat striatum and transplanted SVZ-derived progenitor cells into this region. We observed that ectopic expression of BDNF in the striatum promoted neuronal differentiation of transplanted adult neural progenitor cells, while FGF2 expression supported the survival and proliferation of transplanted progenitor cells in the adult striatum. However, region-specific neuronal differentiation of transplanted progenitor cells was not observed in the adult striatum, suggesting ectopic BDNF or FGF2 expression was insufficient for the generation of mature neuronal phenotypes. This study provides direct in vivo evidence that ectopic striatal expression of either BDNF or FGF2 can induce neurogenesis in non-neurogenic regions of the adult brain.

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.

Cell therapy in models for temporal lobe epilepsy

For patients with refractory epilepsy it is important to search for alternative treatments. One of these potential treatments could be introducing new cells or modulating endogenous neurogenesis to reconstruct damaged epileptic circuits or to bring neurotransmitter function back into balance. In this review the scientific basis of these cell therapy strategies is discussed and the results are critically evaluated. Research on cell transplantation strategies has mainly been performed in animal models for temporal lobe epilepsy, in which seizure foci or seizure propagation pathways are targeted. Promising results have been obtained, although there remains a lot of debate about the relevance of the animal models, the appropriate target for transplantation, the suitable cell source and the proper time point for transplantation. From the presented studies it should be evident that transplanted cells can survive and sometimes even integrate in an epileptic brain and in a brain that is subjected to epileptogenic interventions. There is evidence that transplanted cells can partially restore damaged structures and/or release substances that modulate existent or induced hyperexcitability. Even though several studies show encouraging results, more studies need to be done in animal models with spontaneous seizures in order to have a better comparison to the human situation.

Differential development of neuronal physiological responsiveness in two human neural stem cell lines

BACKGROUND

Neural stem cells (NSCs) are powerful research tools for the design and discovery of new approaches to neurodegenerative disease. Overexpression of the myc family transcription factors in human primary cells from developing cortex and mesencephalon has produced two stable multipotential NSC lines (ReNcell VM and CX) that can be continuously expanded in monolayer culture.

RESULTS

In the undifferentiated state, both ReNcell VM and CX are nestin positive and have resting membrane potentials of around -60 mV but do not display any voltage-activated conductances. As initially hypothesized, using standard methods (stdD) for differentiation, both cell lines can form neurons, astrocytes and oligodendrocytes according to immunohistological characteristics. However it became clear that this was not true for electrophysiological features which designate neurons, such as the firing of action potentials. We have thus developed a new differentiation protocol, designated 'pre-aggregation differentiation' (preD) which appears to favor development of electrophysiologically functional neurons and to lead to an increase in dopaminergic neurons in the ReNcell VM line. In contrast, the protocol used had little effect on the differentiation of ReNcell CX in which dopaminergic differentiation was not observed. Moreover, after a week of differentiation with the preD protocol, 100% of ReNcell VM featured TTX-sensitive Na+-channels and fired action potentials, compared to 25% after stdD. Currents via other voltage-gated channels did not appear to depend on the differentiation protocol. ReNcell CX did not display the same electrophysiological properties as the VM line, generating voltage-dependant K+ currents but no Na+ currents or action potentials under either stdD or preD differentiation.

CONCLUSION

These data demonstrate that overexpression of myc in NSCs can be used to generate electrophysiologically active neurons in culture. Development of a functional neuronal phenotype may be dependent on parameters of isolation and differentiation of the cell lines, indicating that not all human NSCs are functionally equivalent.

Neural stem cells LewisX+ CXCR4+ modify disease progression in an amyotrophic lateral sclerosis model

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease characterized by the degeneration of the motor neurons. We tested whether treatment of superoxide dismutase (SOD1)-G93A transgenic mouse, a model of ALS, with a neural stem cell subpopulation double positive for Lewis X and the chemokine receptor CXCR4 (LeX+CXCR4+) can modify the disease's progression. In vitro, after exposure to morphogenetic stimuli, LeX+CXCR4+ cells generate cholinergic motor neuron-like cells upon differentiation. LeX+CXCR4+ cells deriving from mice expressing Green Fluorescent Protein in all tissues or only in motor neurons, after a period of priming in vitro, were grafted into spinal cord of SOD1-G93A mice. Transplanted transgenic mice exhibited a delayed disease onset and progression, and survived significantly longer than non-treated animals by 23 days. Examination of the spinal cord revealed integration of donor-derived cells that differentiated mostly in neurons and in a lower proportion in motor neuron-like cells. Quantification of motor neurons of the spinal cord suggests a significant neuroprotection by LeX+CXCR4+ cells. Both VEGF- and IGF1-dependent pathways were significantly modulated in transplanted animals compared to controls, suggesting a role of these neurotrophins in MN protection. Our results support the therapeutic potential of neural stem cell fractions through both neurogenesis and growth factors release in motor neuron disorders.

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

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

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Neurotrophin-directed differentiation of human adult marrow stromal cells to dopaminergic-like neurons

Marrow-isolated adult multilineage inducible (MIAMI) cells were differentiated in vitro to neuronal cells in a neurotrophin-dependent fashion. After induction, the cells revealed electrophysiological features similar to those observed in mature neurons. Primary early passage human MIAMI cells without any type of co-cultures with other cell types were used. The developmental program involved a multi-step process requiring the concerted action of brain-derived neurotrophic factor, nerve growth factor and depended on neurotrophin-3, after basic fibroblast growth factor withdrawal. MIAMI-derived neuron-like cells sequentially expressed the neuronal markers, developed a complex neurite outgrowth and arborization, and acquired electrophysiological characteristics similar to those observed in mature neurons. The young and old MIAMI-derived neuronal cells developed both inward and outward currents upon depolarization, similar to those observed in normal neurons. These results represent the earliest evidence that neurotrophin-3 can direct the differentiation of non-neural stem cells from human adult bone marrow stroma to neuron-like cells in vitro. Supplementing the aforementioned multi-step process with sonic hedgehog, fibroblast growth factor 8, and retinoic acid increased the expression of molecules involved in dopaminergic differentiation and of tyrosine hydroxylase, the rate limiting enzyme of dopamine synthesis. MIAMI cells from young and old individuals represent autologous human cell populations for the treatment of disorders of the skeletal and nervous systems and for applications in cell therapy and reparative medicine approaches.

Fibroblast growth factors as regulators of stem cell self-renewal and aging

Organ and tissue dysfunction which is readily observable during aging results from a loss of cellular homeostasis and reduced stem cell self-renewal. Over the past 10 years, studies have been aimed at delineating growth factors that will sustain and promote the self-renewal potential of stem cells and support the expansion of primitive stem cells in vitro and in vivo. Recently, strong evidence is emerging indicating that fibroblast growth factors (FGFs) play a crucial role in stem cell maintenance. FGFs belong to a family of polypeptide growth factors that are involved in multiple functions including cell proliferation, differentiation, survival and motility. In this review, we discuss the regulatory role of FGFs on hematopoietic stem cells (HSCs), neural stem cells (NSCs) and embryonic stem (ES) cells in maintaining stem cell self-renewal. These findings are useful and important to further our knowledge in stem cell biology and for therapeutic approaches.

Differentiation of adult mouse olfactory precursor cells into hair cells in vitro

Many forms of deafness result from degeneration of the sensory cells for hearing, the hair cells in the cochlea. Stem cells offer a potential cell-based therapy for the treatment of deafness. Here, we investigate whether adult olfactory precursor cells can differentiate into hair cells in culture. Precursor cells were isolated from mouse olfactory neuroepithelium, were sphere-forming, showed proliferative capacity, and contained cells expressing neuronal and non-neuronal proteins. To induce differentiation, precursor cells were cocultured with cochlear cells and/or cochlear supernatant. Differentiated precursor cells were immunopositive for specific hair cell markers, including myosin VIIa, FM1-43, calretinin, phalloidin, and espin, and resembled hair cells anatomically and immunocytochemically in culture. The results demonstrate for the first time that adult olfactory precursor cells can differentiate into hair cell-like cells, thus providing a potential autotransplantation therapy for hearing loss.

Concise review: therapeutic strategies for Parkinson disease based on the modulation of adult neurogenesis

Parkinson disease (PD) is a progressive neurodegenerative disorder affecting millions of people worldwide. To date, treatment strategies are mainly symptomatic and aimed at increasing dopamine levels in the degenerating nigrostriatal system. Hope rests upon the development of effective neurorestorative or neuroregenerative therapies based on gene and stem cell therapy or a combination of both. The results of experimental therapies based on transplanting exogenous dopamine-rich fetal cells or glial cell line-derived neurotrophic factor overexpression into the brain of Parkinson disease patients encourage future cell- and gene-based strategies. The endogenous neural stem cells of the adult brain provide an alternative and attractive cell source for neuroregeneration. Prior to designing endogenous stem cell therapies, the possible impact of PD on adult neuronal stem cell pools and their neurogenic potential must be investigated. We review the experimental data obtained in animal models or based on analysis of patients' brains prior to describing different treatment strategies. Strategies aimed at enhancing neuronal stem cell proliferation and/or differentiation in the striatum or the substantia nigra will have to be compared in animal models and selected prior to clinical studies.

Physical activity-mediated functional recovery after spinal cord injury: potential roles of neural stem cells

As data elucidating the complexity of spinal cord injury pathophysiology emerge, it is increasingly being recognized that successful repair will probably require a multifaceted approach that combines tactics from various biomedical disciplines, including pharmacology, cell transplantation, gene therapy and material sciences. Recently, new evidence highlighting the benefit of physical activity and rehabilitation interventions during the post-injury phase has provided novel possibilities in realizing effective repair after spinal cord injury. However, before a comprehensive therapeutic strategy that optimally utilizes the benefits of each of these disciplines can be designed, the basic mechanisms by which these various interventions act must be thoroughly explored and important synergistic and antagonistic interactions identified. In examining the mechanisms by which physical activity-based functional recovery after spinal cord injury is effected, endogenous neural stem cells, in our opinion, engender a potentially key role. Multipotent neural stem cells possess many faculties that abet recovery, including the ability to assess the local microenvironment and deliver biofactors that promote neuroplasticity and regeneration, as well as the potential to replenish damaged or eradicated cellular elements. Encouragingly, the functional recovery owing to physical activity-based therapies appears relatively robust, even when therapy is initiated in the chronic stage of spinal cord injury. In this article, we review experimental outcomes related to our hypothesis that endogenous neural stem cells mediate the functional recovery noted in spinal cord injury following physical activity-based treatments. Overall, the data advocates the incorporation of increased physical activity as a component of the multidimensional treatment of spinal cord injury and underscores the critical need to employ research-based mechanistic approaches for developing future advances in the rehabilitation of neurological injury and disorders.

Fate of endogenous stem/progenitor cells following spinal cord injury

The adult mammalian spinal cord contains neural stem and/or progenitor cells that slowly multiply throughout life and differentiate exclusively into glia. The contribution of adult progenitors to repair has been highlighted in recent studies, demonstrating extensive cell proliferation and gliogenesis following central nervous system (CNS) trauma. The present experiments aimed to determine the relative roles of endogenously dividing progenitor cells versus quiescent progenitor cells in posttraumatic gliogenesis. Using the mitotic indicator bromodeoxyuridine (BrdU) and a retroviral vector, we found that, in the adult female Fisher 344 rat, endogenously dividing neural progenitors are acutely vulnerable in response to T8 dorsal hemisection spinal cord injury. We then studied the population of cells that divide postinjury in the injury epicenter by delivering BrdU or retrovirus at 24 hours after spinal cord injury. Animals were euthanized at five timepoints postinjury, ranging from 6 hours to 9 weeks after BrdU delivery. At all timepoints, we observed extensive proliferation of ependymal and periependymal cells that immunohistochemically resembled stem/progenitor cells. BrdU+ incorporation was noted to be prominent in NG2-immunoreactive progenitors that matured into oligodendrocytes, and in a transient population of microglia. Using a green fluorescence protein (GFP) hematopoietic chimeric mouse, we determined that 90% of the dividing cells in this early proliferation event originate from the spinal cord, whereas only 10% originate from the bone marrow. Our results suggest that dividing, NG2-expressing progenitor cells are vulnerable to injury, but a separate, immature population of neural stem and/or progenitor cells is activated by injury and rapidly divides to replace this vulnerable population.

Loss of arginase I results in increased proliferation of neural stem cells

Loss of arginase I (AI) results in a metabolic disorder characterized by growth retardation, increased mental impairment and spasticity, and potentially fatal hyperammonemia. This syndrome plus a growing body of evidence supports a role for arginase and arginine metabolites in normal neuronal development and function. Here we report our initial observations of the effects of AI loss on proliferation and differentiation of neural stem cells (NSCs) isolated from the germinal zones of embryonic and newborn AI knockout (KO) mice compared with heterozygous (HET) and wild-type (WT) control animals. By using both short and long-term proliferation assays (3 and 10 days, respectively), we found a 1.5-2-fold increase in the number of KO cells compared with WT. FACS analysis showed an increase in KO cells in the synthesis phase of the cell cycle vs. WT cells. After NSC differentiation, AI-deficient cells expressed beta-tubulin, SMI81 (SNAP25), glial fibrillary acidic protein, and CNPase, which are markers consistent with neurons, astrocytes, and oligodendrocytes. Many KO cells exhibited a more mature morphology and expressed mature neuronal markers that were decreased or not present in HET or WT cells. Limited, comparative expression array and quantitative RT-PCR analysis identified differences in the levels of several mRNAs encoding structural, signaling, and arginine metabolism proteins between KO and WT cells. The consequence of these changes may contribute to the differential phenotypes of KO vs. WT cells. It appears that AI may play an important and unanticipated role in growth and development of NSCs.

The realized niche of adult neural stem cells

This review gives an overview of current issues concerning the application of the concept of the stem cell niche to the adult mammalian brain. It describes how the niche manifests itself at different structural levels as well as the main applications that are influenced by this concept. Finally, special regard is given to what is known for the adult human brain and how far the findings from lower animals can be applied in harnessing the regenerative potential of stem cells for therapy.

Transplanted adult neural progenitor cells survive, differentiate and reduce motor function impairment in a rodent model of Huntington's disease

The present study investigated the ability for adult rat neural progenitor cells to survive transplantation, structurally repopulate the striatum and improve motor function in the quinolinic acid (QA) lesion rat model of Huntington's disease. Neural progenitor cells were isolated from the subventricular zone of adult Wistar rats, propagated in culture and labeled with BrdU (50 microM). Fourteen days following QA lesioning, one group of rats (n = 12) received a unilateral injection of adult neural progenitor cells ( approximately 180,000 cells total) in the lesioned striatum, while a second group of rats (n = 10) received a unilateral injection of vehicle only (sham transplant). At the time of transplantation adult neural progenitor cells were phenotypically immature, as demonstrated by SOX2 immunocytochemistry. Eight weeks following transplantation, approximately 12% of BrdU-labeled cells had survived and migrated extensively throughout the lesioned striatum. Double-label immunocytochemical analysis demonstrated that transplanted BrdU-labeled progenitor cells differentiated into either astrocytes, as visualized by GFAP immunocytochemistry, or mature neurons, demonstrated with NeuN. A proportion of BrdU-labeled cells also expressed DARPP-32 and GAD67, specific markers for striatal medium spiny projection neurons and interneurons. Rats transplanted with adult neural progenitor cells also demonstrated a significant reduction in motor function impairment as determined by apomorphine-induced rotational asymmetry and spontaneous exploratory forelimb use when compared to sham transplanted animals. These results demonstrate that adult neural progenitor cells survive transplantation, undergo neuronal differentiation with a proportion of newly generated cells expressing markers characteristic of striatal neurons and reduce functional impairment in the QA lesion model of Huntington's disease.

Differential properties of adult rat and mouse brain-derived neural stem/progenitor cells

Adult neurogenesis from neural stem/progenitor cells occurs in discrete regions of the central nervous system of all mammals, but the mechanisms regulating endogenous neurogenesis are poorly understood. Advances in understanding the neurogenesis depend on knowing their intrinsic properties and responses to environmental signals that control their behavior. Before these issues can be addressed, it is necessary to know whether there are significant species-specific differences in the properties of the stem/progenitor cells derived from CNS of two commonly studied model systems, mouse and rat. We found major differences between rat and mouse stem/progenitor cell proliferation in response to various substrates, mitogenic growth factors and heparin and to the influence of differentiation factors on generation of neurons and glia. Thus, extrapolation of cell properties from one species to another based on studies of these cells should be made with caution.

Increase in bFGF-responsive neural progenitor population following contusion injury of the adult rodent spinal cord

The number of neural progenitor cells, especially nestin+ cells or BrdU-uptake cells is sparse in the normal adult rodent spinal cord. However, in the present study, we show that after spinal cord injury (SCI), many ordinarily quiescent cells were activated to become nestin+ and undergo mitosis (BrdU+) in the ependymal layer as well as in the parenchyma of the spinal cord. Nestin+ cells and BrdU+ cells were in most cases immunohistochemically GFAP+, some of which displayed radial glial cell morphology and partly participated in the border formation of the lesion. The culturing of injured rat spinal cord tissues generated more neurospheres earlier than did the culturing of intact tissues, and these neurosphere cells were multipotent and bFGF-responsive. Immunohistochemical analysis showed that there existed many bFGF+ cells after SCI, the number of which were almost 15 times greater than that in an intact spinal cord. Increased bFGF production after SCI might activate quiescent progenitor cells, and thus initiate their cell proliferation. Finally, SCI to the nestin-promoter green fluorescent protein (GFP) transgenic mice showed broad proliferation of progenitor cells that were induced in the injured spinal cord. The culturing of injured spinal cord tissues from these transgenic mice provides direct evidence that neurospheres can be generated by SCI-activated nestin+ cells. Thus, the activation of bFGF-responsive progenitor cells and the concomitant increase in the population of bFGF+ cells following SCI might be beneficial for spinal cord repair if these progenitor cells are properly manipulated.

Region-specific growth properties and trophic requirements of brain- and spinal cord-derived rat embryonic neural precursor cells

To determine whether neural precursor cells have region-specific growth properties, we compared the proliferation, mitogenicity, and differentiation of these cells isolated from the embryonic day 16 rat forebrain and spinal cord. Neural precursor cells isolated from both regions were cultured in growth medium supplemented with epidermal growth factor, basic fibroblast growth factor, or epidermal growth factor+basic fibroblast growth factor. Under all three conditions, both neural precursor cell populations proliferated for multiple passages. While spinal cord-derived neural precursor cells proliferated moderately faster in epidermal growth factor-enriched growth medium, brain-derived cells proliferated much faster in basic fibroblast growth factor-enriched growth medium. When exposed to both epidermal growth factor and basic fibroblast growth factor, the two neural precursor cell populations expanded and proliferated more rapidly than when exposed to a single factor, with brain-derived neural precursor cells expanding significantly faster than spinal cord-derived ones (P<0.0001). Differentiation studies showed that both neural precursor cell populations were multi-potent giving rise to neurons, astrocytes, and oligodendrocytes. However, neuronal differentiation from brain-derived neural precursor cells was greater than spinal cord-derived ones (11.95+/-5.00% vs 1.92+/-1.13%; passage 2). Further, the two neural precursor cell populations differentiated into a similar percentage of oligodendrocytes (brain: 8.66+/-5.85%; spinal cord: 7.69+/-3.91%; passage 2). Immunofluorescence and Western blot studies showed that neural precursor cells derived from both regions expressed receptors for basic fibroblast growth factor and epidermal growth factor. However, brain-derived neural precursor cells expressed higher levels of the two receptors than spinal cord-derived ones in growth medium containing epidermal growth factor+basic fibroblast growth factor. Thus, our results showed that neural precursor cells isolated from the two regions of the CNS have distinct properties and growth requirements. Identifying phenotypic differences between these neural precursor cell populations and their growth requirements should provide new insights into the development of cell therapies for region-specific neurological degenerative diseases.

Transplanted ALDHhiSSClo neural stem cells generate motor neurons and delay disease progression of nmd mice, an animal model of SMARD1

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is an infantile autosomal-recessive motor neuron disease caused by mutations in the immunoglobulin micro-binding protein 2. We investigated the potential of a spinal cord neural stem cell population isolated on the basis of aldehyde dehydrogenase (ALDH) activity to modify disease progression of nmd mice, an animal model of SMARD1. ALDH(hi)SSC(lo) stem cells are self-renewing and multipotent and when intrathecally transplanted in nmd mice generate motor neurons properly localized in the spinal cord ventral horns. Transplanted nmd animals presented delayed disease progression, sparing of motor neurons and ventral root axons and increased lifespan. To further investigate the molecular events responsible for these differences, microarray and real-time reverse transcription-polymerase chain reaction analyses of wild-type, mutated and transplanted nmd spinal cord were undertaken. We demonstrated a down-regulation of genes involved in excitatory amino acid toxicity and oxidative stress handling, as well as an up-regulation of genes related to the chromatin organization in nmd compared with wild-type mice, suggesting that they may play a role in SMARD1 pathogenesis. Spinal cord of nmd-transplanted mice expressed high transcript levels for genes related to neurogenesis such as doublecortin (DCX), LIS1 and drebrin. The presence of DCX-expressing cells in adult nmd spinal cord suggests that both exogenous and endogenous neurogeneses may contribute to the observed nmd phenotype amelioration.

Increased growth factor expression and cell proliferation after contusive spinal cord injury

The damage caused by traumatic central nervous system (CNS) injury can be divided into two phases: primary and secondary. The initial injury destroys many of the local neurons and glia and triggers secondary mechanisms that result in further cell loss. Approximately 50% of the astrocytes and oligodendrocytes in the spared white matter of the epicenter die by 24 h after spinal cord injury (SCI), but their densities return to normal levels by 6 weeks. This repopulation is largely due to the proliferation of local progenitors that divide in response of CNS injury. Previous studies indicate that the secondary events that cause cell death after SCI also increase the local levels of several growth factors that stimulate the proliferation of these endogenous progenitors. We compared the spatial pattern of the post-injury up-regulation of the pro-mitotic growth factors with that of 5-bromodeoxyuridine (BrdU) incorporation to determine if each could play a role in proliferation. Three days after a standard contusive SCI or laminectomy, animals received intraperitoneal BrdU injections to label dividing cells and were perfused 2 h after the last injection. Immunohistochemistry for BrdU and basic fibroblast growth factor (FGF2) and in situ hybridization for ciliary neurotrophic factor (CNTF) and glial growth factor (GGF2) mRNA were used to compare the number of dividing cells with growth factor levels in sections 2 and 4 mm from the epicenter. All three growth factors are significantly up-regulated 3 days after SCI, when cell proliferation is maximal. The increase in GGF2 and FGF2 levels is highest in sections 2 mm rostral to the epicenter, mimicking BrdU incorporation. Addition of rhGGF2 to cultured cells isolated from the spinal cord 3 days after SCI increased the number of NG2+ glial progenitors. These data suggest that FGF2 and GGF2 may contribute to the spontaneous recovery observed after SCI by stimulating the proliferation of local progenitors that help repopulate the injured cord.

The repair of complex neuronal circuitry by transplanted and endogenous precursors

During the past three decades, research exploring potential neuronal replacement therapies has focused on replacing lost neurons by transplanting cells or grafting tissue into diseased regions of the brain. However, in the last decade, the development of novel approaches has resulted in an explosion of new research showing that neurogenesis, the birth of new neurons, normally occurs in two limited and specific regions of the adult mammalian brain, and that there are significant numbers of multipotent neural precursors in many parts of the adult mammalian brain. Recent advances in our understanding of related events of neural development and plasticity, including the role of radial glia in developmental neurogenesis, and the ability of endogenous precursors present in the adult brain to be induced to produce neurons and partially repopulate brain regions affected by neurodegenerative processes, have led to fundamental changes in the views about how the brain develops, as well as to approaches by which transplanted or endogenous precursors might be used to repair the adult brain. For example, recruitment of new neurons can be induced in a region-specific, layer-specific, and neuronal type-specific manner, and, in some cases, newly recruited neurons can form long-distance connections to appropriate targets. Elucidation of the relevant molecular controls may both allow control over transplanted precursor cells and potentially allow for the development of neuronal replacement therapies for neurodegenerative disease and other CNS injuries that might not require transplantation of exogenous cells.

Adult neurogenesis and repair of the adult CNS with neural progenitors, precursors, and stem cells

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