Transplantation of CG4 oligodendrocyte progenitor cells in the myelin-deficient rat brain results in myelination of axons and enhanced oligodendroglial markers

Modulation of Stem Cells as Therapeutics for Severe Mental Disorders and Cognitive Impairments

Severe mental illnesses (SMI) such as schizophrenia and bipolar disorder affect 2-4% of the world population. Current medications and diagnostic methods for mental illnesses are not satisfying. In animal studies, stem cell therapy is promising for some neuropsychiatric disorders and cognitive/social deficits, not only treating during development (targeting modulation and balancing) but also following neurodegeneration (cell replacement and regenerating support). We believe that novel interventions such as modulation of particular cell populations to develop cell-based treatment can improve cognitive and social functions in SMI. With pathological synaptic/myelin damage, oligodendrocytes seem to play a role. In this review, we have summarized oligodendrogenesis mechanisms and some related calcium signals in neural cells and stem/progenitor cells. The related benefits from endogenous stem/progenitor cells within the brain and exogenous stem cells, including multipotent mesenchymal-derived stromal cells (MSC), fetal neural stem cells (NSC), pluripotent stem cells (PSC), and differentiated progenitors, are discussed. These also include stimulating mechanisms of oligodendrocyte proliferation, maturation, and myelination, responsive to the regenerative effects by both endogenous stem cells and transplanted cells. Among the mechanisms, calcium signaling regulates the neuronal/glial progenitor cell (NPC/GPC)/oligodendrocyte precursor cell (OPC) proliferation, migration, and differentiation, dendrite development, and synaptic plasticity, which are involved in many neuropsychiatric diseases in human. On the basis of numerous protein annotation and protein-protein interaction databases, a total of 119 calcium-dependent/activated proteins that are related to neuropsychiatry in human are summarized in this investigation. One of the advanced methods, the calcium/cation-channel-optogenetics-based stimulation of stem cells and transplanted cells, can take advantage of calcium signaling regulations. Intranasal-to-brain delivery of drugs and stem cells or local delivery with the guidance of brain imaging techniques may provide a unique new approach for treating psychiatric disorders. It is also expected that preconditioning stem cell therapy following precise brain imaging as pathological confirmation has high potential if translated to cell clinic use. Generally, modulable cell transplantation followed by stimulations should provide paracrine protection, synaptic modulation, and myelin repair for the brain in SMI.

Trophic factors are essential for the survival of grafted oligodendrocyte progenitors and for neuroprotection after perinatal excitotoxicity

The consequences of neonatal white matter injury are devastating and represent a major societal problem as currently there is no cure. Prematurity, low weight birth and maternal pre-natal infection are the most frequent causes of acquired myelin deficiency in the human neonate leading to cerebral palsy and cognitive impairment. In the developing brain, oligodendrocyte (OL) maturation occurs perinatally, and immature OLs are particularly vulnerable. Cell replacement therapy is often considered a viable option to replace progenitors that die due to glutamate excitotoxicity. We previously reported directed specification and mobilization of endogenous committed and uncommitted neural progenitors by the combination of transferrin and insulin growth factor 1 (TSC1). Here, considering cell replacement and integration as therapeutic goals, we examined if OL progenitors (OLPs) grafted into the brain parenchyma of mice that were subjected to an excitotoxic insult could rescue white matter injury. For that purpose, we used a well-established model of glutamate excitotoxic injury. Four-day-old mice received a single intraparenchymal injection of the glutamate receptor agonist N-methyl-D-aspartate alone or in conjunction with TSC1 in the presence or absence of OLPs grafted into the brain parenchyma. Energetics and expression of stress proteins and OL developmental specific markers were examined. A comparison of the proteomic profile per treatment was also ascertained. We found that OLPs did not survive in the excitotoxic environment when grafted alone. In contrast, when combined with TSC1, survival and integration of grafted OLPs was observed. Further, energy metabolism in OLPs was significantly increased by N-methyl-D-aspartate and modulated by TSC1. The proteomic profile after the various treatments showed elevated ubiquitination and stress/heat shock protein 90 in response to N-methyl-D-aspartate. These changes were reversed in the presence of TSC1 and ubiquitination was decreased. The results obtained in this pre-clinical study indicate that the use of a combinatorial intervention including both trophic support and healthy OLPs constitutes a promising approach for long-term survival and successful graft integration. We established optimal conditioning of the host brain environment to promote long-term survival and integration of grafted OLPs into an inflamed neonate host brain. Experimental procedures were performed under the United States Public Health Service Guide for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care Committee at (UCLA) (ARC #1992-034-61) on July 1, 2010.

Secretome analysis of human oligodendrocytes derived from neural stem cells

In this study, we investigated the secretome of human oligodendrocytes (F3.Olig2 cells) generated from human neural stem cells by transduction with the gene encoding the Olig2 transcription factor. Using mRNA sequencing and protein cytokine arrays, we identified a number of biologically important secretory proteins whose expression has not been previously reported in oligodendrocytes. We found that F3.Olig2 cells secrete IL-6, PDGF-AA, GRO, GM-CSF, and M-CSF, and showed prominent expression of their corresponding receptors. Co-expression of ligands and receptors suggests that autocrine signaling loops may play important roles in both differentiation and maintenance of oligodendrocytes. We also found that F3.Olig2 cells secrete matrix metalloproteinases and matrix metalloproteinase-associated proteins associated with functional competence of oligodendrocytes. The results of our secretome analysis provide insights into the functional and molecular details of human oligodendrocytes. To the best of our knowledge, this is the first systematic analysis of the secretome of oligodendrocytes.

Brain regeneration in physiology and pathology: the immune signature driving therapeutic plasticity of neural stem cells

Regenerative processes occurring under physiological (maintenance) and pathological (reparative) conditions are a fundamental part of life and vary greatly among different species, individuals, and tissues. Physiological regeneration occurs naturally as a consequence of normal cell erosion, or as an inevitable outcome of any biological process aiming at the restoration of homeostasis. Reparative regeneration occurs as a consequence of tissue damage. Although the central nervous system (CNS) has been considered for years as a "perennial" tissue, it has recently become clear that both physiological and reparative regeneration occur also within the CNS to sustain tissue homeostasis and repair. Proliferation and differentiation of neural stem/progenitor cells (NPCs) residing within the healthy CNS, or surviving injury, are considered crucial in sustaining these processes. Thus a large number of experimental stem cell-based transplantation systems for CNS repair have recently been established. The results suggest that transplanted NPCs promote tissue repair not only via cell replacement but also through their local contribution to changes in the diseased tissue milieu. This review focuses on the remarkable plasticity of endogenous and exogenous (transplanted) NPCs in promoting repair. Special attention will be given to the cross-talk existing between NPCs and CNS-resident microglia as well as CNS-infiltrating immune cells from the circulation, as a crucial event sustaining NPC-mediated neuroprotection. Finally, we will propose the concept of the context-dependent potency of transplanted NPCs (therapeutic plasticity) to exert multiple therapeutic actions, such as cell replacement, neurotrophic support, and immunomodulation, in CNS repair.

Conditional Tet-regulated over-expression of Hoxa2 in CG4 cells increases their proliferation and delays their differentiation into oligodendrocyte-like cells expressing myelin basic protein

Hoxa2 gene was reported to be expressed by oligodendrocytes (OLs) and down-regulated at the terminal differentiation stage during oligodendrogenesis in mice (Nicolay et al. 2004b). To further investigate the role of Hoxa2 in oligodendroglial development, a tetracycline regulated controllable expression system was utilized to establish a stable cell line (CG4-SHoxa2 [sense Hoxa2]), where the expression level of Hoxa2 gene could be up-regulated. The impact of Hoxa2 over-expression on the proliferation and differentiation of CG4-SHoxa2 cells was investigated. Up-regulation of Hoxa2 increased the proliferation of CG4-SHoxa2 cells. The mRNA levels of PDGFαR (platelet-derived growth factor [PDGF] alpha receptor), which is expressed by OL progenitor cells, were not different in CG4-SHoxa2 cells compared to wild-type CG4 cells. Semi-quantitative RT-PCR revealed that the mRNA levels of myelin basic protein (MBP) was lower in CG4-SHoxa2 cells than in wild-type CG4 cells indicating the differentiation of CG4-SHoxa2 cells was delayed when the Hoxa2 gene was up-regulated.

Functional central nervous system myelin repair in an adult mouse model of demyelination caused by proteolipid protein overexpression

Two types of interventions to remyelinate the adult demyelinated central nervous system were investigated in heterozygous transgenic mice overexpressing the proteolipid protein gene. 1) A cocktail of trophic factors, "TS1," was directed toward the activation of the endogenous pool of neural progenitors to increase the number of myelinating oligodendrocytes (OL) in the brain. 2) A combinatorial approach in which OL progenitors were coinjected with TS1 into the corpus callosum of wild-type and He4e transgenic mice that displayed hindlimb paralysis. The levels of locomotor ability in these mice were evaluated after a single treatment. The data showed that a single administration of either one of the interventions had similar therapeutic effects, alleviating the symptoms of demyelination and leading to the recovery of hindlimb function. Histological and immunofluorescent examination of brain sections showed extensive remyelination that was sufficient to reverse hindlimb paralysis in transgenic mice. When the interventions were administered prior to hindlimb paralysis, He4e mice were able to walk up to 1 year of age without paralysis.

Stem cells in genetic myelin disorders

The genetic myelin disorders are a range of diseases that manifest with severe neurological problems, often from infancy. It has been postulated for some time that stem cells might be an effective treatment for these disorders, primarily as agents to restore dysfunctional or lost myelin. Stem cells, however, may offer a wider range of therapeutic potential, for instance as vehicles to replace abnormal enzymes or genes, or to provide trophic support for residual CNS tissue. This article will review several of the more common genetic myelin disorders and currently available therapies, including bone marrow transplantation for adrenoleukodystrophy. Specific stem cell subtypes and their relevance to potential therapeutic use will be discussed and stem cell transplantation in animal model studies will also be reviewed.

Stem cell-based cell therapy in neurological diseases: a review

Human neurological disorders such as Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis (ALS), Alzheimer's disease, multiple sclerosis (MS), stroke, and spinal cord injury are caused by a loss of neurons and glial cells in the brain or spinal cord. Cell replacement therapy and gene transfer to the diseased or injured brain have provided the basis for the development of potentially powerful new therapeutic strategies for a broad spectrum of human neurological diseases. However, the paucity of suitable cell types for cell replacement therapy in patients suffering from neurological disorders has hampered the development of this promising therapeutic approach. In recent years, neurons and glial cells have successfully been generated from stem cells such as embryonic stem cells, mesenchymal stem cells, and neural stem cells, and extensive efforts by investigators to develop stem cell-based brain transplantation therapies have been carried out. We review here notable experimental and preclinical studies previously published involving stem cell-based cell and gene therapies for Parkinson's disease, Huntington's disease, ALS, Alzheimer's disease, MS, stroke, spinal cord injury, brain tumor, and lysosomal storage diseases and discuss the future prospects for stem cell therapy of neurological disorders in the clinical setting. There are still many obstacles to be overcome before clinical application of cell therapy in neurological disease patients is adopted: 1) it is still uncertain what kind of stem cells would be an ideal source for cellular grafts, and 2) the mechanism by which transplantation of stem cells leads to an enhanced functional recovery and structural reorganization must to be better understood. Steady and solid progress in stem cell research in both basic and preclinical settings should support the hope for development of stem cell-based cell therapies for neurological diseases.

Truncated Tau with the Fyn-binding domain and without the microtubule-binding domain hinders the myelinating capacity of an oligodendrocyte cell line

The mechanisms underlying developmental myelination have therapeutic potential following CNS injury and degeneration. We report that transplanted central glial (CG)-4 cells had a diminished myelinating capacity in myelin-deficient (md) rats when cells express a mutated form of Tau (Tau [688]), which binds Fyn but not the microtubules. In the brain of the md rats, Tau [688]-transfected CG-4 cells displayed a decrease in cellular process outgrowth and myelination; in the spinal cord the extent of myelination rostral and caudal to the injection site was decreased. In contrast, control Tau [605]-transfected CG-4 cells formed long cellular processes and substantial areas of myelin both in the brain and spinal cord. In culture, Tau [688]-transfected CG-4 cells displayed a decrease in cellular process outgrowth, and Fyn localized largely in the cell body, not the processes. Thus, Tau in oligodendrocytes plays a key role in myelination, and a functional Tau-Fyn interaction might have therapeutic potential during demyelination and myelin repair following CNS injury and degeneration.

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.

An oligodendrocyte-specific zinc-finger transcription regulator cooperates with Olig2 to promote oligodendrocyte differentiation

Molecular mechanisms that control oligodendrocyte myelination during mammalian central nervous system (CNS) development are poorly understood. In this study, we identified Zfp488, an oligodendrocyte-specific zinc-finger transcription regulator, by screening for genes downregulated in the optic nerves of Olig1-null mice. The predicted primary structure of Zfp488 is evolutionarily conserved in vertebrates and invertebrates. In the developing CNS, Zfp488 is specifically expressed in oligodendrocytes but not their precursors. Its expression increases in parallel with that of major myelin genes Mbp and Plp1. Zfp488 is a nuclear protein that possesses transcriptional repression activity. In the developing chick neural tube, Zfp488 can promote oligodendrocyte precursor formation upon Notch activation. In addition, Zfp488 can interact and cooperate with the bHLH transcription factor Olig2 to promote precocious and ectopic oligodendrocyte differentiation. Furthermore, knockdown of Zfp488 via RNAi in an oligodendroglial cell line leads to the downregulation of myelin gene expression. Taken together, these data suggest that Zfp488 functions as an oligodendrocyte-specific transcription co-regulator important for oligodendrocyte maturation and that zinc-finger/bHLH cooperation can serve as a mechanism for oligodendroglial differentiation.

Stage-specific expression of myelin basic protein in oligodendrocytes involves Nkx2.2-mediated repression that is relieved by the Sp1 transcription factor

The homeodomain-containing protein Nkx2.2 is critical for the development of oligodendrocyte lineage cells, but the target genes of Nkx2.2 regulation have not been identified. In the present study, we found that the myelin basic protein gene is one of the genes that is regulated by Nkx2.2. Expression of Nkx2.2 represses the expression of myelin basic protein in oligodendrocyte progenitors. Two regulatory elements in the myelin basic protein promoter were identified and found to interact with Nkx2.2 in vitro. Despite their sequence divergence, both sites were involved in the Nkx2.2-mediated repression of the myelin basic protein promoter. Binding of Nkx2.2 also blocked and disrupted the binding of the transcriptional activator Puralpha to the myelin basic protein promoter. Additionally Nkx2.2 recruited a histone deacetylase 1-mSin3A complex to the myelin basic protein promoter. We also found that the transcription factor Sp1 was able to compete off the binding of Nkx2.2 to its consensus binding site in vitro and reversed the repressive effect of Nkx2.2 in vivo. Our data revealed a novel role for Nkx2.2 in preventing the precocious expression of myelin basic protein in immature oligodendrocytes. Based on this study and our previous reports, a model for myelin basic protein gene control is proposed.

Genetic programs and responses of neural stem/progenitor cells during demyelination: potential insights into repair mechanisms in multiple sclerosis

In recent years, it has become evident that the adult mammalian CNS contains a population of neural stem cells (NSCs) described as immature, undifferentiated, multipotent cells, that may be called upon for repair in neurodegenerative and demyelinating diseases. NSCs may give rise to oligodendrocyte progenitor cells (OPCs) and other myelinating cells. This article reviews recent progress in elucidating the genetic programs and dynamics of NSC and OPC proliferation, differentiation, and apoptosis, including the response to demyelination. Emerging knowledge of the molecules that may be involved in such responses may help in the design of future stem cell-based treatment of demyelinating diseases such as multiple sclerosis.

The Sp1 family of transcription factors is involved in p27(Kip1)-mediated activation of myelin basic protein gene expression

p27(Kip1) levels increase in many cells as they leave the cell cycle and begin to differentiate. The increase in p27(Kip1) levels generally precedes the expression of differentiation-specific genes. Previous studies from our laboratory showed that the overexpression of p27(Kip1) enhances myelin basic protein (MBP) promoter activity. This activation is specific to p27(Kip1). Additionally, inhibition of cyclin-dependent kinase activity alone is not sufficient to increase MBP expression. In this study, we focused on understanding how p27(Kip1) can activate gene transcription by using the MBP gene in oligodendrocytes as a model. We show that the enhancement of MBP promoter activity by p27(Kip1) is mediated by a proximal region of the MBP promoter that contains a conserved GC box binding sequence. This sequence binds transcription factors Sp1 and Sp3. Increased expression of p27(Kip1) increases the level of Sp1 promoter binding to the GC box but does not change the level of Sp3 binding. The binding of Sp1 to this element activates the MBP promoter. p27(Kip1) leads to increased Sp1 binding through a decrease in Sp1 protein turnover. Enhancement of MBP promoter activity by an increase in the level of p27(Kip1) involves a novel mechanism that is mediated through the stabilization and binding of transcription factor Sp1.

Microfilament and microtubule organization and dynamics in process extension by central glia-4 oligodendrocytes: evidence for a microtubule organizing center

Microfilaments in freshly adhering CG-4 cells and differentiated CG-4 oligodendrocytes are concentrated at the tips and edges of rapidly forming processes while microtubules are concentrated in new processes and extend from a concentrated spot of alpha-tubulin staining in the cell body to the cell periphery. In motile bipolar CG-4 cells, microfilaments are heavily concentrated at the flattened end of one process and along the rim of processes and the cell body: microtubules are concentrated along main processes and splay out into process tips and the cell body. In differentiated CG-4 oligodendrocytes, microfilaments are concentrated at the many process tips, in filopodia and in fine processes, but are not obvious in main processes where separate bundles of microtubules, which diverge at process branch points, are concentrated. gamma-tubulin, involved in microtubule nucleation, is concentrated at a small discrete area in the cell body, indicative of a microtubule organizing center. Polymerization of both actin and tubulin is required for initial process elaboration. Depolymerization of microtubules, but not of microfilaments, causes complete retraction of bipolar CG-4 cell processes. This process retraction does not occur if microfilaments are depolymerized first, indicating that process extension/retraction in motile bipolar CG-4 cells may occur by a balance of motor protein-driven forces as suggested for growth cone motility. Cytoskeleton organization in CG-4 cells is very similar to that reported for oligodendrocytes. CG-4 cells are thus a useful model for investigating the signals and mechanisms regulating oligodendrocyte process dynamics.

Oligodendroglia in developmental neurotoxicity

The developing nervous system has been long recognized as a primary target for a variety of toxicants. To date, most efforts to understand the impact of neurotoxic agents on the brain have focused primarily on neurons and to a lesser degree astroglia as cellular targets. The role of oligodendroglia, the myelin-forming cells in the central nervous system (CNS), in developmental neurotoxicity has been emphasized only in recent years. Oligodendrocytes originate from migratory, mitotic progenitors that mature progressively into postmitotic myelinating cells. During differentiation, oligodendroglial lineage cells pass through a series of distinct phenotypic stages that are characterized by different proliferative capacities and migratory abilities, as well as dramatic changes in morphology with sequential expression of unique developmental markers. In recent years, it has become appreciated that oligodendrocyte lineage cells have important functions other than those related to myelin formation and maintenance, including participation in neuronal survival and development, as well as neurotransmission and synaptic function. Substantial knowledge has accumulated on the control of oligodendroglial survival, migration, proliferation, and differentiation, as well as the cellular and molecular events involved in oligodendroglial development and myelin formation. Recently, studies have been initiated to address the role of oligodendrocyte lineage cells in neurotoxic processes. This article examines recent progress in oligodendroglial biology, focuses attention on the characteristic features of the oligodendrocyte developmental lineage as a model system for neurotoxicological studies, and explores the role of oligodendrocyte lineage cells in developmental neurotoxicity. The potential role of oligodendroglia in environmental lead neurotoxicity is presented to exemplify this thesis.

Selective specification of CNS stem cells into oligodendroglial or neuronal cell lineage: cell culture and transplant studies

Neural stem cells (NSCs) were isolated from embryonic day 16 Sprague-Dawley rats and cultured in a novel serum-free stem cell medium that selected for the growth of NSCs and against the growth of GFAP(+) cells (astrocytes). NSCs maintained in culture for extended periods of time retained immunoreactivity for both nestin and PSA-NCAM, two markers characteristic of the stem cell phenotype. Moreover, using an oligodendrocyte (OL) specification medium, NSCs differentiated into OL as evidenced by their morphology and expression of multiple oligodendrocyte/myelin-specific markers. In addition, NSCs are capable of acquiring a neuronal phenotype as evidenced by expressing neuronal markers, such as neurofilament (NF) and NeuN when cultured in a defined medium for neurons indicating that these cells are also a good source of neuroblasts, which could be used to replace neuronal populations in the brain. We also showed successful propagation and differentiation of NSCs into OL after cryostorage, allowing for the later use of stored NSCs. The long-term goal of culturing NSCs and committed oligodendrocyte progenitors (OLP) is to obtain homogeneous populations for transplantation with the goal of remyelinating the myelin-deficient CNS. Our preliminary experiments carried out on normal and myelin deficient rats demonstrate that these cells survive and migrate extensively in both types of hosts. NSCs grafted as such, as well as cells derived from NSCs exposed to selective specification before grafting, are able to differentiate within the host brain. As expected, NSCs are capable of giving rise to astrocytes in a medium favoring this phenotype.

Cell-based delivery of cytokines allows for the differentiation of a doxycycline inducible oligodendrocyte precursor cell line in vitro

BACKGROUND

Stem cells, having the property of self renewal, offer the promise of lifelong repair of damaged tissue. However, somatic tissue-committed primary stem cells are rare and difficult to expand in vitro. Genetically modified stem-like cells with the ability to expand conditionally provide a valuable tool with which to study stem cell biology, especially the cellular events of proliferation and differentiation. In addition, stem cells may be appropriate candidates for therapeutic applications.

METHODS

Double transgenic mice possesing SV40 T antigen (Tag) under the control of the reverse tetracycline-transactivator (rtTA) were used to establish cell lines. One brain cell line was partially characterized by DNA sequencing, morphology, antigen expression using flow cytometry, confocal microscopy, and electrophysiology using the patch clamp technique. Cell cycle analysis was performed using propidium iodide staining; cell viability and H3-thymidine incorporation assays. The ability of this cell line to differentiate was assessed by confocal microscopy following co-culture with stem cells secreting cytokines.

RESULTS

We report here the establishment and partial characterization of a cell line derived from the brain tissue of rtTA-SV40 Tag transgenic mice. Analysis of the morphology and antigen markers has shown that this cell line mimics some aspects of primary glial precursors. The results of electrophysiology are consistent with this and suggest that the cell line is derived from O2A glial precursor cells. Cell cycle progression of this cell line is doxycycline-dependent. In the absence of doxycycline, cells become apoptotic. Differentiation into mature type 2 astrocytes and (precursor) oligodendrocytes can be induced upon withdrawal of doxycycline and addition of epithelial stem cells secreting cytokine, such as hIL3 (human Interleukine 3) or hIL6 to the culture. In contrast, co-culturing with hCNTF (human Ciliary NeuroTrophic Factor)-secreting epithelial stem cells did not induce them to mature into progeny cell types.

CONCLUSION

The differentiation of this O2A glial precursor line does not occur automatically in culture. Additional external help is required from the cell-based delivery of appropriate transgenic cytokines. Withdrawal of doxycycline from the culture medium removes the proliferation signals and induces a fatal outcome.

Lead exposure delays the differentiation of oligodendroglial progenitors in vitro

Lead (Pb) is an environmental neurotoxicant that can cause hypo- and demyelination. Oligodendrocytes (OLs), the myelin-forming cells in the central nervous system, may be a possible target for Pb toxicity. The present study describes the effect of Pb on the maturation of rat OL progenitor (OP) cells and the developmental expression of myelin-specific galactolipids. Dose-response studies showed that OP cultures were more sensitive to Pb than mature OLs. Pb delayed the differentiation of OL progenitors, as demonstrated by cell morphology and immunostaining with a panel of stage-specific differentiation markers. Pb given prior to and during differentiation caused a decrease in the biosynthesis of galactolipids in both undifferentiated and differentiated OLs, as detected by metabolic radiolabeling with 3H-D-galactose. While the ratios of galacto/gluco-cerebrosides, hydroxy fatty acid/nonhydroxy fatty acid galactolipids, and galactocerebrosides/sulfatides increased in control cultures during cell differentiation, Pb treatment prevented these changes. The results suggest that chronic Pb exposure may impact brain development by interfering with the timely developmental maturation of OL progenitors.

Remyelination of the adult demyelinated mouse brain by grafted oligodendrocyte progenitors and the effect of B-104 cografts

The 4e transgenic mouse is characterized by overexpression of the PLP gene. Heterozygous littermates containing three PLP gene copies develop and myelinate normally. However, a progressive CNS demyelination begins at 3-4 months of age. Despite focal demyelination, these animals survive for one year with hind limb paralysis. We used this CNS demyelination model to determine if grafts of CG4 oligodendrocyte progenitors would survive and myelinate the adult CNS. Either CG4 cells, or co-grafts of CG4/B 104 cells 11:1 ratio respectively) were performed. Grafted cells survived and migrated in the normal and transgenic brain. Non-treated transgenic animals revealed extensive lack of myelin. Three months post-transplant hosts with CG4 or co-transplants displayed a near normal myelin pattern. Double immunofluorescence for neurofilament and myelin basic protein revealed the presence of many naked axons in non-grafted transgenic animals. Those grafted with progenitor CG4 cells or cografts displayed a clear increase in remyelination. This data provides a new direction for the development of cell replacement therapies in demyelinating diseases.

Ethanol exerts different effects on myelin basic protein and 2',3'-cyclic nucleotide 3'-phosphodiesterase expression in differentiating CG-4 oligodendrocytes

Evidence suggests that abnormal myelination is one factor contributing to the neuoropathology associated with fetal alcohol syndrome. We investigated the potential teratogenic effects of ethanol (EtOH) on myelin formation by determining its effects on the developmentally regulated increased expression of myelin basic protein (MBP) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in differentiating CG-4 oligodendrocytes (OLGs). By using CG-4 OLGs in vitro we identified processes altered by ethanol actions exerted directly on OLGs. During the first 8 days of development, EtOH decreased the expression of the major structural 18.5 and 14 kDa MBP isoforms by at least 40% at 4 days of development. EtOH concentrations between 25 and 75 mM inhibited MBP expression in a dose-dependent manner. Adding or withdrawing EtOH on specific days of differentiation reversibly modulated the expression of MBP, and the degree of inhibition was directly related to the length of ethanol exposure. As little as two consecutive days of EtOH exposure either early or late during development caused at least a 20% inhibition, however, no short critical time window of EtOH vulnerability for the inhibition was observed. The ethanol effect was selective for MBP expression, as EtOH did not alter the developmentally-regulated increased expression of CNP isozymes or enzyme activity. The results indicate that one factor contributing to the development of fetal alcohol syndrome may be defective myelination resulting from delayed and decreased MBP expression.

In vitro injury model for oligodendrocytes: development, injury, and recovery

In this study we investigated the effects of severe hypothermia (cryoinjury) on oligodendrocyte (OL) cell marker expression and morphological features. We used a chemically defined cell culture medium, glial development medium (GDM), which favored the optimal expression of the OL phenotype in CG4 cells. Experiments using CG4 cells cultured in 2% serum or in GDM were conducted in parallel. After severe hypothermia, cells were reanimated at 37 degrees C and 4.5% CO(2) and cultured in either GDM or in medium supplemented with 2% serum. In either medium, around 70% of the total number of cells detached within 2 to 4 hours following reanimation. Oligodendroglial markers such as A2B5, O4, Tf, ferritin, tubulin, and MBP were examined by double and triple immunofluorescence. All of these markers except MBP re-appeared at different times during the recovery period for up to 48 hours. Glial fibrillary acidic protein (GFAP) and heat shock protein 60 (HSP-60) were used as injury markers. The presence of serum induced HSP-60 expression, while GDM did not. All CG4 cells expressed HSP-60 in response to hypothermia independently of the cell culture medium used. Cryoinjury induced a spectrum of morphological changes in CG4 cells. The expression of OL specific markers was also influenced by hypothermia. Moreover both, serum and cryoinjury induced the expression of HSP-60 that colocalized with OL and myelin markers. The expression of GFAP by injured cells but not by normal cells corroborated the state of injury of CG4 cells.

Reconstruction of the transected cat spinal cord following NeuroGel implantation: axonal tracing, immunohistochemical and ultrastructural studies

This study examined the ability of NeuroGel, a biocompatible porous poly [N-(2-hydroxypropyl) methacrylamide] hydrogel, to establish a permissive environment across a 3 mm gap in the cat spinal cord in order to promote tissue reconstitution and axonal regeneration across the lesion. Animals with NeuroGel implants were compared to transection-only controls and observed for 21 months. The hydrogel formed a stable bridge between the cord segments. Six months after reconstructive surgery, it was densely infiltrated by a reparative tissue composed of glial cells, capillary vessels and axonal fibres. Axonal labelling and double immunostaining for neurofilaments and myelin basic protein, showed that descending supraspinal axons of the ventral funiculus and afferent fibres of the dorsal column regenerated across the reconstructed lesion. Fifteen months after reconstructive surgery, axons had grown, at least, 12 mm into the distal cord tissue, and in the rostral cord there was labelling of neurons of the intermediate gray matter. Electron microscopy showed that after 9 months, most of the regenerating axons were myelinated, principally by Schwann cells. Newly formed neurons presumably from precursor cells of the ependyma and/or migrating neurons were observed within the reparative tissue after 21 months. Results indicate that functional deficit, as assessed by treadmill training, and morphological changes following double transection of the spinal cord can be modified by the implantation of NeuroGel. This technology offers the potential to promote the formation of a neural tissue equivalent via a reparative neohistogenesis process, that facilitates and supports regenerative growth of axons.

Proliferation and differentiation of progenitor cells throughout the intact adult rat spinal cord

The existence of multipotent progenitor populations in the adult forebrain has been widely studied. To extend this knowledge to the adult spinal cord we have examined the proliferation, distribution, and phenotypic fate of dividing cells in the adult rat spinal cord. Bromodeoxyuridine (BrdU) was used to label dividing cells in 13- to 14-week-old, intact Fischer rats. Single daily injections of BrdU were administered over a 12 d period. Animals were killed either 1 d or 4 weeks after the last injection of BrdU. We observed frequent cell division throughout the adult rodent spinal cord, particularly in white matter tracts (5-7% of all nuclei). The majority of BrdU-labeled cells colocalized with markers of immature glial cells. At 4 weeks, 10% of dividing cells expressed mature astrocyte and oligodendroglial markers. These data predict that 0.75% of all astrocytes and 0.82% of all oligodendrocytes are derived from a dividing population over a 4 week period. To determine the migratory nature of dividing cells, a single BrdU injection was given to animals that were killed 1 hr after the injection. In these tissues, the distribution and incidence of BrdU labeling matched those of the 4 week post injection (pi) groups, suggesting that proliferating cells divide in situ rather than migrate from the ependymal zone. These data suggest a higher level of cellular plasticity for the intact spinal cord than has previously been observed and that glial progenitors exist in the outer circumference of the spinal cord that can give rise to both astrocytes and oligodendrocytes.

Restorative neurosurgery: opportunities for restoration of function in acquired, degenerative, and idiopathic neurological diseases

Historically, neurosurgery has improved the environment of the nervous system to promote maximal spontaneous recovery of function. The population of patients whom we treat at present is a small portion of those who suffer from disabling neurological illnesses. Based on a combination of new technology, and advances in neuroscience, restorative neurosurgery is advancing the frontiers of our specialty, and providing the potential to restore lost function. Significant advancements in gene therapy, the discovery and delivery of neurotrophic factors, and cell transplantation now require neurosurgeons to broaden the scope of our practice so that it includes the restoration of function in an enormous number of patients with acquired, degenerative and idiopathic neurological diseases. In order to meet the present challenge, neurosurgeons must broaden our vision, our role, and our future educational goals. In this review, we summarize the landmark advances in the basic and clinical neurosciences and the results of clinical trials that are driving our evolution from passive reaction to disease to active attempts to restore lost central nervous system function.

Recent developments in drug therapy for multiple sclerosis

Symptomatic treatment of multiple sclerosis (MS) includes a diverse range of drugs intended to relieve the specific symptoms with which a patient may present at a particular point in the progression of the disease. These drugs, not specifically designed for the treatment of MS, may include antispastic agents (e.g. baclofen), drugs to reduce tremor (e.g. clonazepam), anticholinergics (e.g. oxybutynin) which relieve urinary symptoms, anti-epileptics (e.g. carbamazepine) to control neuralgia, stimulants to reduce fatigue (e.g. amantadine), and antidepressants (e.g. fluoxetine) to treat depression. The treatment of acute relapses or exacerbations is dominated by corticosteroids such as methylprednisolone. The most active area of current investigation is the development of drugs which will inhibit the progression of the disease process itself, and in this category the beta- and alpha-interferons are the most effective drugs currently available, although many new treatments are currently in trials, including immunoglobulin, copolymer-1. bovine myelin, T-cell receptor (TCR) peptide vaccines, platelet activating factor (PAF) antagonists, matrix metallo-proteinase inhibitors, campath-1, and insulin-like growth factor (IGF).