MeCP2 in central nervous system glial cells: current updates

avMethyl‑CpG binding protein 2 (MeCP2) is an epigenetic regulator, which preferentially binds to methylated CpG dinucleotides in DNA. MeCP2 mutations have been linked to Rett syndrome, a neurodevelopmental disorder characterized by severe intellectual disability in females. Earlier studies indicated that loss of MeCP2 function in neuronal cells was the sole cause of Rett syndrome. Subsequent studies have linked MeCP2 expression in CNS glial cells to Rett syndrome pathogenesis. In this review, we have discussed the role of MeCP2 in glial subtypes, astrocytes, oligodendrocytes and microglia, and how loss of MeCP2 function in these cells has a profound influence on both glial and neuronal function.

The role of dorsal root ganglia activation and brain-derived neurotrophic factor in multiple sclerosis

Multiple sclerosis (MS) is characterized by focal destruction of the white matter of the brain and spinal cord. The exact mechanisms underlying the pathophysiology of the disease are unknown. Many studies have shown that MS is predominantly an autoimmune disease with an inflammatory phase followed by a demyelinating phase. Recent studies alongside current treatment strategies, including glatiramer acetate, have revealed a potential role for brain-derived neurotrophic factor (BDNF) in MS. However, the exact role of BDNF is not fully understood. We used the experimental autoimmune encephalomyelitis (EAE) model of MS in adolescent female Lewis rats to identify the role of BDNF in disease progression. Dorsal root ganglia (DRG) and spinal cords were harvested for protein and gene expression analysis every 3 days post-disease induction (pdi) up to 15 days. We show significant increases in BDNF protein and gene expression in the DRG of EAE animals at 12 dpi, which correlates with peak neurological disability. BDNF protein expression in the spinal cord was significantly increased at 12 dpi, and maintained at 15 dpi. However, there was no significant change in mRNA levels. We show evidence for the anterograde transport of BDNF protein from the DRG to the dorsal horn of the spinal cord via the dorsal roots. Increased levels of BDNF within the DRG and spinal cord in EAE may facilitate myelin repair and neuroprotection in the CNS. The anterograde transport of DRG-derived BDNF to the spinal cord may have potential implications in facilitating central myelin repair and neuroprotection.

CXCL1 regulation of oligodendrocyte progenitor cell migration is independent of calcium signaling

Cell migration is an indispensable aspect of tissue patterning during embryonic development. Oligodendrocytes, the myelinating cells of the central nervous system, migrate significantly during development of the brain. Several growth factors have been identified as being critical regulators of oligodendrocyte progenitor migration, including platelet derived growth factor-A (PDGFA), and fibroblast growth factor-2 (FGF2). Further, the chemokine CXCL1 has been shown to play a critical role in regulating the dispersal of oligodendrocyte progenitors during development, although the mechanisms underlying this regulation are unknown. Previous studies have also shown that calcium flux is required for oligodendrocyte progenitor migration. CXCL1 induces calcium flux in cells; therefore, we hypothesized that CXCL1 inhibition of oligodendrocyte progenitor migration is regulated via changes in intracellular calcium flux. The current study shows that CXCL1 inhibition of oligodendrocyte progenitor migration is independent of calcium signaling. Further, we show that CXCL1 inhibition of oligodendrocyte progenitor migration is specific to PDGFA induced migration. Finally, we show that CXCL1 inhibition of oligodendrocyte progenitor migration is independent of activation of the cell cycle. Our results provide intriguing results relevant to specific aspects of patterning of white matter tracts in the central nervous system, and may further the understanding of tissue remodeling seen during disease-related processes.

Fatigue and cognition in patients with relapsing multiple sclerosis treated with interferon β

INTRODUCTION

Fatigue and cognitive deficits are common symptoms affecting patients with multiple sclerosis.

METHODS

The effects of interferon beta on fatigue and cognitive deficits were assessed in 50 patients with relapsing multiple sclerosis (recruited at a single center). The pre-treatment assessments were performed on visits 1 and 2 (Months 0 and 3). Patients started treatment with subcutaneous interferon beta-1a or beta-1b, or intramuscular interferon beta-1a at Month 3, with reassessment at visits 3 and 4 (6 and 12 months, respectively). Co-primary endpoints were change in fatigue (Modified Fatigue Impact Scale) and change in cognition (Brief Repeatable Battery of Neuropsychological Tests) from pre-treatment to visits 3 and 4. Follow-up data were obtained for 40 patients.

RESULTS

The pre-treatment demographic and disease characteristics did not differ between groups. Improvements in fatigue levels were reported for patients receiving subcutaneous interferon beta-1a versus patients in the intramuscular interferon beta-1a group (p = .04) and in the interferon beta-1b group (p = .09). Improvements were also reported in five out of 17 cognitive indices for all the treatment groups.

CONCLUSION

The data suggest that interferon beta may reduce fatigue and cognitive deficits in patients with relapsing multiple sclerosis. Larger, randomized, and controlled studies are required to confirm our findings.

Differential effects of growth factors on oligodendrocyte progenitor migration

Oligodendrocytes are myelinating cells of the CNS that originate as progenitor cells (OP) in discrete areas of the developing brain. During brain development, OP migrate significant distances prior to proliferating and myelinating the axons of the putative white matter tracts. Growth factors play a major regulatory role in the behavior of OP. Specifically, platelet-derived growth factor A (PDGF-A) and fibroblast growth factor 2 (FGF2) are two of the most well characterized regulators of OP development. Both growth factors interact with tyrosine kinase receptors, activating various intracellular signaling pathways. The current study advances our earlier research by comparing the effects of both PDGF-A and FGF2 on OP migration. Our results show that activation of ERK is required for OP migration. These findings correlate well with our previous demonstration of the ERK pathway mediating PDGF-A induced OP migration. We also demonstrate the significance of threshold levels of growth factors and temporal regulation for OP migration. In addition, ERK activation alone is not sufficient to induce OP migration. The current research supports the involvement of the non-ERK mediated signaling pathway in OP migration.

Staphylococcus aureus harbouring Enterotoxin A as a possible risk factor for multiple sclerosis exacerbations

BACKGROUND

Staphylococcus aureus may produce superantigens that can non-specifically activate CD4(+) cells to potentially target the myelin basic protein.

OBJECTIVE

This study examined the association between individuals with multiple sclerosis (MS) and colonization with S. aureus harbouring superantigens.

METHODS

Nasal swabs were collected from non-MS subjects and patients with MS who had not experienced a relapse in the past six months (MS stable group) and who had suffered a relapse within 30 days of study recruitment (MS exacerbation group). S. aureus was isolated from the anterior nares of participants following standard procedures and staphylococcal superantigen genes (sea, seb, and tsst-1) were detected using standard laboratory PCR techniques.

RESULTS

The study enrolled 204 patients, 80 in the non-MS and MS stable groups and 44 patients in the MS exacerbation group. Overall, 27.0% of patients were colonized with S. aureus with no significant differences identified between study groups. Amongst individuals colonized with S. aureus, the prevalence of sea was significantly greater in the MS exacerbation versus non-MS study group (p < 0.05; odds ratio 7.9; 95% confidence interval 1.2-49.5).

CONCLUSIONS

The ability to rapidly screen patients for the presence of S. aureus producing sea may serve as a useful marker of a potential MS exacerbation.

A novel decalcification method for adult rodent bone for histological analysis of peripheral-central nervous system connections

Histological analysis of bone encased tissue is severely hampered by technical difficulties associated with sectioning calcified tissue. Cryosectioning of bone is possible but requires significant technical adaptation and expensive materials and is often time-consuming. Some decalcifying reagents in common use result in successful cryosectioning in less time but the integrity of the soft tissue of the spinal column is often compromised during processing. This can result in significant loss of cellular detail. In order to find a method that would allow cryosectioning of the bone without loss of structural integrity of the underlying soft tissue we assessed the efficacy of four different decalcifying reagents with respect to their effects on the cellular structure of the myelin of the grey and white matter of the spinal cord. The antigenic integrity of the spinal cord white matter was evaluated using tissue structural integrity and quality of myelin basic protein immunostaining. The result of this research shows that 6% TCA not only decalcifies intact spinal column suitably for cryosectioning but does so without compromising the antigenic integrity of the tissue. The ease of application, speed of processing and a favorable cost-effective profile were secondary benefits noted with the use of the 6% TCA decalcifying solution. The ability to utilize a decalcifying solution that allows for both histomorphometry and immunohistochemistry in the same spinal column segment represents a novel technique that will provide new insights into pathophysiological aspects and therapeutic approaches ispinal cord damage or disease.

Experimental autoimmune encephalomyelitis-induced upregulation of tumor necrosis factor-alpha in the dorsal root ganglia

Background: Multiple sclerosis (MS) is a chronic, neurological disease characterized by targeted destruction of central nervous system (CNS) myelin. The autoimmune theory is the most widely accepted explanation of disease pathology. Circulating Th1 cells become activated by exposure to CNS-specific antigens such as myelin basic protein. The activated Th1 cells secrete inflammatory cytokines, which are pivotal for inflammatory responses. We hypothesize that enhanced production of inflammatory cytokines triggers cellular events within the dorsal root ganglia (DRG) and/or spinal cord, facilitating the development of neuropathic pain (NPP) in MS. NPP, the second worst disease-induced symptom suffered by patients with MS, is normally regulated by DRG and/or spinal cord.

Objective: To determine gene and protein expression levels of tumor necrosis factor-alpha (TNFα) within DRG and/or spinal cord in an animal model of MS.

Methods: Experimental autoimmune encephalomyelitis (EAE) was induced in adolescent female Lewis rats. Animals were sacrificed every 3 days post-disease induction. DRG and spinal cords were harvested for protein and gene expression analysis.

Results: We show significant increases in TNFα expression in the DRG and of EAE animals at peak disease stage, as assessed by clinical symptoms.

Conclusion: Antigen-induced production of inflammatory cytokines such as TNFα within the DRG identifies a potential novel mechanism for MS-induced NPP.

Toxic effect of blood components on perinatal rat subventricular zone cells and oligodendrocyte precursor cell proliferation, differentiation and migration in culture

The germinal matrix of human brain gives rise to oligodendrocytes and astrocytes after mid-gestation. Hemorrhage in the germinal matrix of premature infants is associated with suppressed cell proliferation. We hypothesize that soluble blood constituents have an adverse effect on the proliferation of cultured rat subventricular zone (SVZ) cells and the proliferation, migration, and differentiation of oligodendrocyte progenitor cells (OPC). Using caspase 3 activation and lactate dehydrogenase release assays, rat plasma, serum, thrombin, and kallikrein killed SVZ cells when grown in the presence (but not absence) of platelet derived growth factor. Plasma and serum killed OPC at 1:1 to 1:100 dilutions. Using a bromodeoxyuridine incorporation assay OPC proliferation was reduced by plasma, serum, thrombin and plasmin. Blood proteins also suppressed OPC migration in a concentration dependent manner. However, differentiation of OPC into myelin basic protein expressing cells was suppressed only by thrombin. We conclude that soluble blood components, particularly thrombin, have an adverse effect on maturing SVZ cells and OPC derived from newborn rat brain.

Initiation of oligodendrocyte progenitor cell migration by a PDGF-A activated extracellular regulated kinase (ERK) signaling pathway

During CNS development, oligodendrocyte progenitor (OP) cells migrate from germinal zones to presumptive white matter tracts to generate myelinating oligodendrocytes. In vitro and in vivo studies indicate that platelet-derived growth factor-A (PDGF-A) is a potent chemoattractant for OP cells and important for normal distribution throughout the developing CNS. However, PDGF-A does not localize in concentration gradients corresponding to OP migratory pathways, as would be expected for a chemoattractant to direct migration. Therefore, the mechanism by which PDGF-A regulates OP distribution remains to be clarified. Here we show that PDGF-A induces OP migration and continuous exposure to PDGF-A is not required to maintain migration. Using pharmacological inhibitors, we show that a self-sustaining extracellular-regulated-kinase signaling pathway drives OP migration for up to 72 hours after the initial PDGF stimulus. These findings indicate PDGF-A may act to mobilize OP cells that then respond to distinct directional signals to distribute appropriately within the CNS.

Serial in vivo MR tracking of magnetically labeled neural spheres transplanted in chronic EAE mice

Neural stem cell (NSC) transplantation has been shown to attenuate the severity of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Central to the future success of NSC transplantation in MS is the ability of transplanted cells to migrate from the site of transplantation to relevant foci of disease. Using magnetically labeled mouse neurospheres and human embryonic stem cell (hESC)-derived neurospheres, we applied serial magnetic resonance imaging (MRI) to assess the biodynamics of transplanted cell migration in a chronic mouse EAE model. Magnetic labeling did not affect the in vitro and in vivo characteristics of cells as multipotential precursors. Cell migration occurred along white matter (WM) tracts (especially the corpus callosum (CC), fimbria, and internal capsule), predominantly early in the acute phase of disease, and in an asymmetric manner. The distance of cell migration correlated well with clinical severity of disease and the number of microglia in the WM tracts, supporting the notion that inflammatory signals promote transplanted cell migration. This study shows for the first time that hESC-derived neural precursors also respond to tissue signals in an MS model, similarly to rodent cells. The results are directly relevant for designing and optimizing cell therapies for MS, and achieving a better understanding of in vivo cell dynamics and cell-tissue interactions.

Noninvasive MRI of endothelial cell response to human breast cancer cells

We have developed a noninvasive magnetic resonance imaging (MRI) assay to characterize human umbilical vein endothelial cell (HUVEC) motility, invasion, and network formation in response to the presence of cancer cells. HUVECs were labeled with a superparamagnetic iron oxide T(2) contrast agent and cocultured with MDA-MB-231 breast cancer cells in the presence of an extracellular matrix (ECM) gel. Invasion into the ECM gel by HUVECs in response to paracrine factors secreted by MDA-MB-231 cancer cells, as well as network formation by HUVECs, was easily tracked with MRI. The invasive behavior of HUVECs was not observed in the absence of cancer cells. This noninvasive assay used to characterize the response of endothelial cells (ECs) can be used to understand the role of proangiogenic or antiangiogenic stimuli, and to study the interactions between ECs and other disease-specific cells in pathologies with aberrant angiogenesis, such as retinopathy and arthritis.

MR evaluation of the glomerular homing of magnetically labeled mesenchymal stem cells in a rat model of nephropathy

PURPOSE

To assess renal glomerular homing of intravenously injected superparamagnetic iron oxide (SPIO)-labeled mesenchymal stem cells (MSCs) at in vivo and ex vivo magnetic resonance (MR) imaging in an experimental rat model of mesangiolysis.

MATERIALS AND METHODS

Animal procedures were performed in accordance with protocols approved by Institutional Animal Care and Use Committee. Fourteen rats were divided into two groups: one pathologic (n = 10), with persistent mesangiolysis following simultaneous injection of OX-7 monoclonal antibody and puromycin aminonucleoside in which 10(7) SPIO- and DiI-labeled MSCs were injected, and one control (n = 4). In vivo and ex vivo MR imaging examinations were performed with 4.7- and 9.4-T spectrometers, respectively, and T2*-weighted sequences. In vivo signal intensity variations were measured in the liver and kidney before and 6 days after MSC injection. Intrarenal signal intensity variations were correlated with histopathologic data by means of colocalization of DiI fluorescence, alpha-actin, and Prussian blue stain-positive cells. Histologic differences between the glomerular homing of MSCs in different kidney portions were correlated to the areas of MR signal intensity decrease with nonparametric statistical tests.

RESULTS

On in vivo images, signal intensity measurements of pathologic kidneys following MSC injection did not show any signal intensity decrease (P = .7), whereas a 34% +/- 14 (mean +/- standard deviation) signal intensity decrease was observed in the liver (P < .01), where a substantial number of labeled cells were trapped. On ex vivo images, pathologic kidneys showed focal cortical (glomerular) areas of signal intensity loss, which was absent in controls. The areas of low signal intensity correlated well with alpha-actin and Prussian blue stain- and DiI-positive areas (P < .01), which indicates that MSCs specifically home to injured tissue. No MSCs were detected in the kidneys of control animals.

CONCLUSION

Intravenously injected MSCs specifically home to focal areas of glomerular damage and can be detected at ex vivo MR imaging.

Quantification of the repair process involved in the repair of a cell monolayer using an in vitro model of mechanical injury

The processes of wound repair were investigated using an in vitro model of mechanical injury on confluent cell monolayers of either human umbilical vein endothelial cells (HUVEC), aortic endothelial (RAEC) or smooth muscle cells (VSMC) of the rat. A mechanical wounder was used to produce 11 parallel (400 microm wide) lesions across the monolayer and the movement of cells into the denuded area was quantified using image analysis. The lesioned area recovered completely in 72h, with proliferation occurring after 24h for endothelial cells and 18h for VSMC, as detected by an increase in cell numbers. The cell migration inhibitor Taxol (1ng/ml) abolished the increase in repair of HUVEC monolayers in the first 24h of repair, while actinomycin D had no effect before 24h but thereafter abolished the further repair which was associated with increased cell numbers. Repair of endothelial cells was accelerated by basic fibroblast growth factor (bFGF), vascular endothelial growth factor or platelet-derived growth factor-BB (PDGF), and in VSMC both bFGF and PDGF increased repair. This simple in vitro model of mechanical injury allows a quantitative study of the repair processes of a previously confluent monolayer and thus is a representation of mechanical damage in vivo.

PDGF and FGF2 regulate oligodendrocyte progenitor responses to demyelination

Acute demyelination of adult CNS, resulting from trauma or disease, is initially followed by remyelination. However, chronic lesions with subsequent functional impairment result from eventual failure of the remyelination process, as seen in multiple sclerosis. Studies using animal models of successful remyelination delineate a progression of events facilitating remyelination. A universal feature of this repair process is extensive proliferation of oligodendrocyte progenitor cells (OPs) in response to demyelination. To investigate signals that regulate OP proliferation in response to demyelination we used murine hepatitis virus-A59 (MHV-A59) infection of adult mice to induce focal demyelination throughout the spinal cord followed by spontaneous remyelination. We cultured glial cells directly from demyelinating and remyelinating spinal cords using conditions that maintain the dramatically enhanced OP proliferative response prior to CNS remyelination. We identify PDGF and FGF2 as significant mitogens regulating this proliferative response. Furthermore, we demonstrate endogenous PDGF and FGF2 activity in these glial cultures isolated from demyelinated CNS tissue. These findings correlate well with our previous demonstration of increased in vivo expression of PDGF and FGF2 ligand and corresponding receptors in MHV-A59 lesions. Together these studies support the potential of these pathways to function in vivo as critical factors in regulating remyelination.

Absence of fibroblast growth factor 2 promotes oligodendroglial repopulation of demyelinated white matter

This study takes advantage of fibroblast growth factor 2 (FGF2) knock-out mice to determine the contribution of FGF2 to the regeneration of oligodendrocytes in the adult CNS. The role of FGF2 during spontaneous remyelination was examined using two complementary mouse models of experimental demyelination. The murine hepatitis virus strain A59 (MHV-A59) model produces focal areas of spinal cord demyelination with inflammation. The cuprizone neurotoxicant model causes extensive corpus callosum demyelination without a lymphocytic cell response. In both models, FGF2 expression is upregulated in areas of demyelination in wild-type mice. Surprisingly, in both models, oligodendrocyte repopulation of demyelinated white matter was significantly increased in FGF2 -/- mice compared with wild-type mice and even surpassed the oligodendrocyte density of nonlesioned mice. This dramatic result indicated that the absence of FGF2 promoted oligodendrocyte regeneration, possibly by enhancing oligodendrocyte progenitor proliferation and/or differentiation. FGF2 -/- and +/+ mice had similar oligodendrocyte progenitor densities in normal adult CNS, as well as similar progenitor proliferation and accumulation during demyelination. To directly analyze progenitor differentiation, glial cultures from spinal cords of wild-type mice undergoing remyelination after MHV-A59 demyelination were treated for 3 d with either exogenous FGF2 or an FGF2 neutralizing antibody. Elevating FGF2 favored progenitor proliferation, whereas attenuating endogenous FGF2 activity promoted the differentiation of progenitors into oligodendrocytes. These in vitro results are consistent with enhanced progenitor differentiation in FGF2 -/- mice. These studies demonstrate that the FGF2 genotype regulates oligodendrocyte regeneration and that FGF2 appears to inhibit oligodendrocyte lineage differentiation during remyelination.

Fibroblast growth factor 2 (FGF2) and FGF receptor expression in an experimental demyelinating disease with extensive remyelination

Fibroblast growth factor 2 (FGF2) is an excellent candidate to regulate remyelination based on its proposed actions in oligodendrocyte lineage cell development in conjunction with its involvement in CNS regeneration. To assess the potential for FGF2 to play a role in remyelination, we examined the expression pattern of FGF2 and FGF receptors (FGFRs) in an experimental demyelinating disease with extensive remyelination. Adult mice were intracranially injected with murine hepatitis virus strain A-59 (MHV-A59) to induce focally demyelinated spinal cord lesions that spontaneously remyelinate, with corresponding recovery of motor function. Using kinetic RT-PCR analysis of spinal cord RNA, we found significantly increased levels of FGF2 mRNA transcripts, which peaked during the initial stage of remyelination. Analysis of tissue sections demonstrated that increased levels of FGF2 mRNA and protein were localized within demyelinated regions of white matter, including high FGF2 expression associated with astrocytes. The expression of corresponding FGF receptors was significantly increased in lesion areas during the initial stage of remyelination. In normal and lesioned white matter, oligodendrocyte lineage cells, including progenitors and mature cells, were found to express multiple FGFR types (FGFR1, FGFR2, and/or FGFR3). In addition, in lesion areas, astrocytes expressed FGFR1, FGFR2, and FGFR3. These findings indicate that, during remyelination, FGF2 may play a role in directly regulating oligodendrocyte lineage cell responses and may also act through paracrine or autocrine effects on astrocytes, which are known to synthesize other growth factors and immunoregulatory molecules that influence oligodendrocyte lineage cells.

Fibroblast growth factor 2 (FGF2) and FGF receptor expression in an experimental demyelinating disease with extensive remyelination

Fibroblast growth factor 2 (FGF2) is an excellent candidate to regulate remyelination based on its proposed actions in oligodendrocyte lineage cell development in conjunction with its involvement in CNS regeneration. To assess the potential for FGF2 to play a role in remyelination, we examined the expression pattern of FGF2 and FGF receptors (FGFRs) in an experimental demyelinating disease with extensive remyelination. Adult mice were intracranially injected with murine hepatitis virus strain A-59 (MHV-A59) to induce focally demyelinated spinal cord lesions that spontaneously remyelinate, with corresponding recovery of motor function. Using kinetic RT-PCR analysis of spinal cord RNA, we found significantly increased levels of FGF2 mRNA transcripts, which peaked during the initial stage of remyelination. Analysis of tissue sections demonstrated that increased levels of FGF2 mRNA and protein were localized within demyelinated regions of white matter, including high FGF2 expression associated with astrocytes. The expression of corresponding FGF receptors was significantly increased in lesion areas during the initial stage of remyelination. In normal and lesioned white matter, oligodendrocyte lineage cells, including progenitors and mature cells, were found to express multiple FGFR types (FGFR1, FGFR2, and/or FGFR3). In addition, in lesion areas, astrocytes expressed FGFR1, FGFR2, and FGFR3. These findings indicate that, during remyelination, FGF2 may play a role in directly regulating oligodendrocyte lineage cell responses and may also act through paracrine or autocrine effects on astrocytes, which are known to synthesize other growth factors and immunoregulatory molecules that influence oligodendrocyte lineage cells.

Fibroblast growth factor 2 (FGF2) and FGF receptor expression in an experimental demyelinating disease with extensive remyelination

Fibroblast growth factor 2 (FGF2) is an excellent candidate to regulate remyelination based on its proposed actions in oligodendrocyte lineage cell development in conjunction with its involvement in CNS regeneration. To assess the potential for FGF2 to play a role in remyelination, we examined the expression pattern of FGF2 and FGF receptors (FGFRs) in an experimental demyelinating disease with extensive remyelination. Adult mice were intracranially injected with murine hepatitis virus strain A-59 (MHV-A59) to induce focally demyelinated spinal cord lesions that spontaneously remyelinate, with corresponding recovery of motor function. Using kinetic RT-PCR analysis of spinal cord RNA, we found significantly increased levels of FGF2 mRNA transcripts, which peaked during the initial stage of remyelination. Analysis of tissue sections demonstrated that increased levels of FGF2 mRNA and protein were localized within demyelinated regions of white matter, including high FGF2 expression associated with astrocytes. The expression of corresponding FGF receptors was significantly increased in lesion areas during the initial stage of remyelination. In normal and lesioned white matter, oligodendrocyte lineage cells, including progenitors and mature cells, were found to express multiple FGFR types (FGFR1, FGFR2, and/or FGFR3). In addition, in lesion areas, astrocytes expressed FGFR1, FGFR2, and FGFR3. These findings indicate that, during remyelination, FGF2 may play a role in directly regulating oligodendrocyte lineage cell responses and may also act through paracrine or autocrine effects on astrocytes, which are known to synthesize other growth factors and immunoregulatory molecules that influence oligodendrocyte lineage cells.

The regulation of proliferation and differentiation in oligodendrocyte progenitor cells by alphaV integrins

We have previously shown that oligodendrocyte progenitor cells exhibit developmental switching between alphav-associated beta integrin subunits to sequentially express alphavbeta1, alphavbeta3 and alphavbeta5 integrins during differentiation in vitro. To understand the role that alphavveta3 integrin may play in regulating oligodendrocyte progenitor cell behaviour, cells of the rat cell line, CG-4, were genetically engineered to constitutively express alphavbeta3 integrin by transfection with full-length human beta3 integrin subunit cDNA. Time-lapse videomicroscopy showed no effect of beta3 expression on cell migration but revealed enhanced proliferation on vitronectin substrata. Comparison of mitotic indices, as measured by 5-bromo-2′-deoxyuridine incorporation, confirmed that human beta3 integrin-expressing cells exhibited enhanced proliferation, as compared to both vector-only transfected, and wild-type CG-4 cells when switched to differentiation medium from growth medium, but only in cultures grown on vitronectin and not on poly-D-lysine. The effects on proliferation were inhibited by a function-blocking antibody specifically directed against the human beta3 integrin subunit. Human beta3 integrin-expressing cells also exhibited reduced differentiation. This differentiation could be reduced still further by a function-blocking monoclonal antibody against alphavbeta5 integrin, as could differentiation in the wild-type CG-4 cells. Taken together, these results suggest that alphavbeta3 integrin may regulate oligodendroglial cell proliferation and that both downregulation of alphavbeta3 integrin expression and signalling through alphavbeta5 integrin may be critical to continued differentiation in vitro.

Integrins mediate a neuronal survival signal for oligodendrocytes

Target-dependent survival of newly differentiated cells is an important part of neural development. In the case of myelin-forming oligodendrocytes, it matches the number of oligodendrocytes to the available axons [1]. In addition to growth factors, an axonal signal regulates this survival: when axons are transected, oligodendrocytes die and, conversely, when the number of axons is increased by genetic manipulation, oligodendrocyte numbers increase [2] [3]. Newly formed oligodendrocytes that fail to contact axons undergo apoptosis, and co-culture experiments that model axon-glial interactions in vitro reveal a neuronal survival effect not present in neuron-conditioned medium [4] [5], suggesting that the signal is non-diffusible and present on the surface of axons. The nature of these neuronal signals is unknown, as are the mechanisms by which they interact with growth-factor-mediated survival signals. As integrins can regulate survival in other cell types [6] [7] [8], we determined whether integrins are involved in the neuronal survival effect. We found that the laminin receptor alpha6beta1 integrin, which is expressed on oligodendrocytes, enhances the sensitivity of oligodendrocytes to the survival effect of growth factors. On the basis of this interaction between integrin and growth-factor-mediated signalling, we propose a simple model by which signals from axons and other cell types might interact to regulate oligodendrocyte cell numbers.

Myelination and behaviour of tenascin-C null transgenic mice

The extracellular matrix glycoprotein tenascin-C is widely expressed during development and repair, making it surprising that few abnormalities have been found in transgenic mice lacking this molecule. We have therefore re-examined the transgenic mice described by Saga et al. [Saga, Y., Yagi, T., Ikawa, Y., Sakakura, T. & Aizawa, S. (1992) Genes Dev., 6 1821-1831] in which tenascin-C was knocked-out by homologous recombination, focusing on two aspects of the nervous system likely to reveal any abnormalities that might follow the loss of tenascin-C. First, we have determined the pattern of myelin and distribution of oligodendrocyte precursor cells in those areas, such as the optic nerve and retina where local concentrations of tenascin-C have been proposed to act as barriers to oligodendrocyte precursor migration and so prevent inappropriate myelination. Secondly, we have examined the behaviour of the mice in a number of well-characterized tests, e.g. beam-walking, passive avoidance and the Morris water maze. We find no abnormalities of myelination or oligodendrocyte precursor distribution in adult mice, showing that local concentrations of tenascin-C are not the sole mechanism responsible for the pattern of myelination in these regions of CNS. However, we do find a number of behavioural abnormalities in these mice and show that hyperlocomotion and deficits in coordination during beam walking can be ascribed to tenascin-C deficiency. The effects on coordination are, however, not seen on a 129 genetic background. Taken together, these results significantly extend the phenotype associated with tenascin-C deficiency but argue against a role in myelination.

Evidence that [3H]-alpha,beta-methylene ATP may label an endothelial-derived cell line 5'-nucleotidase with high affinity

1. In membranes prepared from a permanent cell line of endothelial origin (WEC cells), [3H]-alpha, beta-methylene ATP ([3H]-alpha, beta-meATP) labelled high (pKd = 9.5; Bmax = 3.75 pmol mg-1 protein) and low (pKd = 7.2; Bmax = 23.3 pmol mg-1 protein) affinity binding sites. The high affinity [3H]-alpha, beta-meATP binding sites in the WEC cell membranes could be selectively labelled with a low concentration of the radioligand (1 nM). In competition studies performed at a radioligand concentration of 1 nM, 88.6% of the sites possessed high affinity (pIC50 = 8.26) for alpha, beta-meATP. 2. The high affinity [3H]-alpha, beta-meATP binding sites appeared heterogeneous since in competition studies a number of nucleotide analogues (alpha, beta-meADP, ATP, ADP, AMP, GTP, GppNHp, GMP) and adenosine identified two populations of the sites labelled by 1 nM [3H]-alpha, beta-meATP. The proportion of sites with high affinity for these compounds was found to vary between 42 and 69%. 3. Approximately 60-69% of the binding sites labelled with 1 nM [3H]-alpha, beta-meATP possessed high affinity for alpha, beta-meADP (pIC50 = 8.87), AMP (pIC50 = 7.12), GMP (pIC50 = 7.34), UTP (pIC50 = 6.12), GTP (pIC50 = 7.59), GppNHp (pIC50 = 7.35) and adenosine (pIC50 = 5.45). The sites at which these compounds possessed high affinity were probably the same, since, in the presence of GMP at a concentration (10 microM) sufficient to inhibit selectively the binding of [3H]-alpha,beta-meATP, the [3H]-alpha,beta-meATP binding sites with high affinity for AMP, UTP, alpha, beta-meADP, GTP, GppNHp and adenosine were also occluded.4. WEC cell membranes were able to metabolize a trace concentration (6 nM) of [3H]-AMP to [3H]-adenosine under the conditions of the binding assay. The pIC50 values of adenosine (5.99), GMP (7.55)and the substrate AMP (7.19) for inhibiting this [3H]-AMPase activity were almost identical to their high affinity pIC50 estimates obtained in the binding assay. Although alpha, beta-meADP, alpha, beta-meATP, beta,upsilon-meATP,ATP, ADP and GppNHp identified heterogeneity in the [3H]-AMPase activity of the WEC cells, theirpIC50 values for inhibiting the major portion of the [3H]-AMPase activity were similar to their respective high affinity pIC50 values in the binding assay. It thus seems likely that WEC cells express a form of 5'-nucleotidase that possesses high affinity for both alpha,beta-meADP and alpha,beta-meATP and that this enzyme can be labelled by [3H]-alpha,beta-meATP.5. In the presence of 10 microM GMP, the affinity estimates for alpha,beta-meADP, AMP, GMP, GTP, GppNHp,ADP and adenosine at the high affinity [3H]-alpha,beta4-meATP binding sites that remained available, were lowa nd similar to their affinity estimates at the high affinity [3H]-alpha,beta-meATP binding sites of rat vas deferens. Since the high affinity [3H]-alpha,beta-meATP binding sites in rat vas deferens are thought to be P2x purinoceptors it is possible that the high affinity [3H]-alpha,beta-meATP binding sites in the WEC which possess low affinity for alpha,beta-meADP are also P2x purinoceptors.