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Glia Sep 2008Recent findings suggest that synaptic-type glutamate signaling operates between axons and their supporting glial cells. Glutamate reuptake will be a necessary component... (Comparative Study)
Comparative Study
Recent findings suggest that synaptic-type glutamate signaling operates between axons and their supporting glial cells. Glutamate reuptake will be a necessary component of such a system. Evidence for glutamate-mediated damage of oligodendroglia somata and processes in white matter suggests that glutamate regulation in white matter structures is also of clinical importance. The expression of glutamate transporters was examined in postnatal Day 14-17 (P14-17) mouse and in mature mouse and rat optic nerve using immuno-histochemistry and immuno-electron microscopy. EAAC1 was the major glutamate transporter detected in oligodendroglia cell membranes in both developing and mature optic nerve, while GLT-1 was the most heavily expressed transporter in the membranes of astrocytes. Both EAAC1 and GLAST were also seen in adult astrocytes, but there was little membrane expression of either at P14-17. GLAST, EAAC1, and GLT-1 were expressed in P14-17 axons with marked GLT-1 expression in the axolemma, while in mature axons EAAC1 was abundant at the node of Ranvier. Functional glutamate transport was probed in P14-17 mouse optic nerve revealing Na+-dependent, TBOA-blockable uptake of D-aspartate in astrocytes, axons, and oligodendrocytes. The data show that in addition to oligodendroglia and astrocytes, axons represent a potential source for extracellular glutamate in white matter during ischaemic conditions, and have the capacity for Na(+)-dependent glutamate uptake. The findings support the possibility of functional synaptic-type glutamate release from central axons, an event that will require axonal glutamate reuptake.
Topics: Amino Acid Transport System X-AG; Animals; Axons; Female; Glutamic Acid; Male; Mice; Mice, Knockout; Mice, Transgenic; Neuroglia; Optic Nerve; Protein Transport
PubMed: 18551624
DOI: 10.1002/glia.20703 -
The Journal of Neuroscience : the... Apr 2008Peroxisomal metabolism is essential for normal brain development both in men and in mice. Using conditional knock-out mice, we recently showed that peroxisome deficiency...
Peroxisomal metabolism is essential for normal brain development both in men and in mice. Using conditional knock-out mice, we recently showed that peroxisome deficiency in liver has a severe and persistent impact on the formation of cortex and cerebellum, whereas absence of functional peroxisomes from the CNS only causes developmental delays without obvious alteration of brain architecture. We now report that a substantial fraction of the latter Nes-Pex5 knock-out mice survive into adulthood but develop progressive motoric and coordination problems, impaired exploration, and a deficit in cognition and die before the age of 6 months. Histopathologically, both the white and gray matter of the CNS displayed a region-specific accumulation of neutral lipids, astrogliosis and microgliosis, upregulation of catalase, and scattered cell death. Nes-Pex5 knock-out mice featured a dramatic reduction of myelin staining in corpus callosum, whereas cerebellum and other white matter tracts were less affected or unchanged. This was accompanied by a depletion of alkenylphospholipids in myelin and differentially reduced immunoreactivity of myelin proteins. EM analysis revealed that myelin wrappings around axons did still form, but they showed a reduction in thickness relative to axon diameters. Remarkably, multifocal axonal damage occurred in the corpus callosum. Thereby, debris accumulated between axolemma and inner myelin surface and axons collapsed, although myelin sheaths remained present. These anomalies of myelinated axons were already present in juvenile mice but aggravated in adulthood. Together, loss of CNS peroxisomal metabolism both affects myelin sheaths and axonal integrity possibly via independent pathways.
Topics: Animals; Apoptosis; Ataxia; Axons; Behavior, Animal; Brain; Catalase; Central Nervous System; Central Nervous System Diseases; Demyelinating Diseases; Dyskinesias; Exploratory Behavior; Gliosis; Intermediate Filament Proteins; Lipid Metabolism; Mice; Mice, Knockout; Myelin Sheath; Nerve Degeneration; Nerve Tissue Proteins; Nestin; Peroxisome-Targeting Signal 1 Receptor; Peroxisomes; Phenotype; Receptors, Cytoplasmic and Nuclear; Severity of Illness Index; Spinal Cord; Up-Regulation
PubMed: 18400901
DOI: 10.1523/JNEUROSCI.4968-07.2008 -
The Kobe Journal of Medical Sciences Jan 2009In the present study, the expressions of beta-catenin and integrin-linked kinase (ILK) in the adult mouse peripheral nerve were investigated by means of immunoblotting...
In the present study, the expressions of beta-catenin and integrin-linked kinase (ILK) in the adult mouse peripheral nerve were investigated by means of immunoblotting analyses and electron microscopy using the immunogold pre -embedding method. As a result, beta-catenin and ILK were shown to be expressed both in the axon and the Schwann cell of the myelinated and unmyelinated fibers. By electron microscopy, some molecules of beta-catenin and ILK tended to concentrate under the axolemma in the unmyelinated fibers, while these molecules were distributed in a scattered form throughout the axoplasm in the myelinated fibers. Concerning the cytoplasm of the Schwann cells, the loop region was too slender to detect whether beta-catenin and ILK were associated with the plasmalemma; however, beta-catenin and ILK were distributed diffusely without any relationship in regard to the plasmalemma or the cell organelles around the nucleus region. The density of beta-catenin and ILK around the nucleus region was greater than that within the nucleus region. From these results, some molecules of beta-catenin mediate the axon-Schwann cell adhesion of the unmyelinated fibers, while other molecules are thought to be separated from the cadherin-catenin complex on the plasmalemma. Accordingly, it is hypothesized that the cell-cell adhesion property in the peripheral nerve is not strong but dynamic, and this adhesion is possibly regulated by ILK.
Topics: Animals; Blotting, Western; Mice; Mice, Inbred BALB C; Microscopy, Immunoelectron; Protein Serine-Threonine Kinases; Sciatic Nerve; beta Catenin
PubMed: 19258742
DOI: No ID Found -
Journal of Structural Biology Mar 2008The node of Ranvier is a site for ionic conductances along myelinated nerves and governs the saltatory transmission of action potentials. Defects in the cross-bridging...
The node of Ranvier is a site for ionic conductances along myelinated nerves and governs the saltatory transmission of action potentials. Defects in the cross-bridging and spacing of the cytoskeleton are a prominent pathological feature in diseases of the peripheral nerve. Electron tomography was used to examine cytoskeletal-cytoskeletal, membrane-cytoskeletal, and heterologous cell connections in the paranodal region of the node of Ranvier in peripheral nerves. Focal attachment of cytoskeletal filaments to each other and to the axolemma and paranodal membranes of the Schwann cell via narrow cross-bridges was visualized in both neuronal and glial cytoplasm. A subset of intermediate filaments associates with the cytoplasmic surfaces of supramolecular complexes of transmembrane structures that are presumed to include known and unknown junctional proteins. Mitochondria were linked to both microtubules and neurofilaments in the axoplasm and to neighboring smooth endoplasmic reticulum by narrow cross-bridges. Tubular cisternae in the glial cytoplasm were also linked to the paranodal glial cytoplasmic loop juxtanodal membrane by short cross-bridges. In the extracellular matrix between axon and Schwann cell, junctional bridges formed long cylinders linking the two membranes. Interactions between cytoskeleton, membranes, and extracellular matrix associations in the paranodal region are likely critical not only for scaffolding, but also for intracellular and extracellular communication.
Topics: Animals; Cell Membrane; Cytoskeleton; Extracellular Matrix; Microscopy, Electron; Mitochondria; Peripheral Nerves; Ranvier's Nodes; Rats; Tomography; Ultrasonography
PubMed: 18096402
DOI: 10.1016/j.jsb.2007.10.005 -
Journal of Neurochemistry Nov 2007Understanding the rich complement of sugar chains found in cellular membranes is impeded by the complexity of cell types and membrane diversity. To overcome this, we...
Understanding the rich complement of sugar chains found in cellular membranes is impeded by the complexity of cell types and membrane diversity. To overcome this, we have analyzed the N-linked sugar chain composition of the glycoproteins of CNS myelin, an elaboration of the plasma membranes of oligodendrocytes (OLs) that result in a multilamellar wrapping of neuronal axons, facilitating nerve conduction with dramatic savings of space and energy. Due to an usually high lipid to protein ratio, myelin can be separated readily from other heavier membranes on sucrose gradients and further fractionated into subdomains related to myelin structure and function, including compact myelin and myelin-associated axolemmal membrane (Menon et al. 2003). We analyzed these fractions for N-linked sugar chains, using 2D HPLC following hydrazinolysis and pyridylamination. Our results indicate that compared with total brain homogenate, the amount of N-glycans is 1.3-fold higher in the myelin-associated axolemmal membranes, but it is 0.5-fold less in CM. M5 [Manalpha1-3((Manalpha1-3)(Manalpha1-6)Manalpha1-6)Manbeta1-4GlcNAcbeta1-4GlcNAc] is the most abundant sugar chain in total brain homogenate, compact myelin, and myelin-associated axolemma, constituting approximately 20% of sugar chains. Although the types of sugar chains are similar among the fractions, their expression levels vary significantly. In addition to high mannose type oligosaccharides, the core fucosylated, biantennary N-glycans with bisecting N-acetylglucosamine (GlcNAc) residue, A2G1(3)FB [Galbeta1-4GlcNAcbeta1-2Manalpha1-3(GlcNAcbeta1-2Manalpha1-6)(GlcNAcbeta1-4)Manbeta1-4GlcNAcbeta1-4(Fucalpha1-6)GlcNAc], A2G1(6)FB [GlcNAcbeta1-2Manalpha1-3(Galbeta1-4GlcNAcbeta1-2Manalpha1-6)(GlcNAcbeta1-4)Manbeta1-4GlcNAcbeta1-4 (Fucalpha1-6)GlcNAc] and BA-1 [Manalpha1-3(GlcNAcbeta1-2Manalpha1-6)(GlcNAcbeta1-4)Manbeta1-4GlcNAcbeta1-4(Fucalpha1-6)GlcNAc], and A1(6)G0F [Manalpha1-3(GlcNAcbeta1-2Manalpha1-6)Manbeta1-4GlcNAcbeta1-4(Fucalpha1-6) GlcNAc] are also present in relatively large proportions in compact myelin. We suggest that these differences may be related to myelin-axolemmal function.
Topics: Animals; Carbohydrate Conformation; Carbohydrates; Central Nervous System; Mice; Mice, Inbred ICR; Myelin Sheath; Polysaccharides
PubMed: 17986136
DOI: 10.1111/j.1471-4159.2007.04823.x -
Neuron Glia Biology Aug 2006Mitochondria and other membranous organelles are frequently enriched in the nodes and paranodes of peripheral myelinated axons, particularly those of large caliber. The...
Mitochondria and other membranous organelles are frequently enriched in the nodes and paranodes of peripheral myelinated axons, particularly those of large caliber. The physiologic role(s) of this organelle enrichment and the rheologic factors that regulate it are not well understood. Previous studies suggest that axonal transport of organelles across the nodal/paranodal region is locally regulated. In this study, we have examined the ultrastructure of myelinated axons in the sciatic nerves of mice deficient in the contactin-associated protein (Caspr), an integral junctional component. These mice, which lack the normal septate-like junctions that promote attachment of the glial (paranodal) loops to the axon, contain aberrant mitochondria in their nodal/paranodal regions. These mitochondria are typically large and swollen and occupy prominent varicosities of the nodal axolemma. In contrast, mitochondria located outside the nodal/paranodal regions of the myelinated axons appear normal. These findings suggest that paranodal junctions regulate mitochondrial transport and function in the axoplasm of the nodal/paranodal region of myelinated axons of peripheral nerves. They further implicate the paranodal junctions in playing a role, either directly or indirectly, in the local regulation of energy metabolism in the nodal region.
PubMed: 17460780
DOI: 10.1017/S1740925X06000275 -
The Journal of Comparative Neurology Apr 2006In myelinated axons, action potential conduction is dependent on the discrete clustering of ion channels at specialized regions of the axon, termed nodes of Ranvier....
In myelinated axons, action potential conduction is dependent on the discrete clustering of ion channels at specialized regions of the axon, termed nodes of Ranvier. This organization is controlled, at least in part, by the adherence of myelin sheaths to the axolemma in the adjacent region of the paranode. Age-related disruption in the integrity of internodal myelin sheaths is well described and includes splitting of myelin sheaths, redundant myelin, and fluctuations in biochemical constituents of myelin. These changes have been proposed to contribute to age-related cognitive decline; in previous studies of monkeys, myelin changes correlate with cognitive performance. In the present study, we hypothesize that age-dependent myelin breakdown results in concomitant disruption at sites of axoglial contact, in particular at the paranode, and that this disruption alters the molecular organization in this region. In aged monkey and rat optic nerves, immunolabeling for voltage-dependent potassium channels of the Shaker family (Kv1.2), normally localizing in the adjacent juxtaparanode, were mislocalized to the paranode. Similarly, immunolabeling for the paranodal marker caspr reveals irregular caspr-labeled paranodal profiles, suggesting that there may be age-related changes in paranodal structure. Ultrastructural analysis of paranodal segments from optic nerve of aged monkeys shows that, in a subset of myelinated axons with thick sheaths, some paranodal loops fail to contact the axolemma. Thus, age-dependent myelin alterations affect axonal protein localization and may be detrimental to maintenance of axonal conduction.
Topics: Aging; Animals; Brain; Cell Adhesion Molecules, Neuronal; Image Processing, Computer-Assisted; Immunohistochemistry; Kv1.2 Potassium Channel; Macaca mulatta; Microscopy, Electron, Transmission; Myelin Sheath; Optic Nerve; Ranvier's Nodes; Rats
PubMed: 16485288
DOI: 10.1002/cne.20886 -
Gliomedin mediates Schwann cell-axon interaction and the molecular assembly of the nodes of Ranvier.Neuron Jul 2005Accumulation of Na(+) channels at the nodes of Ranvier is a prerequisite for saltatory conduction. In peripheral nerves, clustering of these channels along the axolemma... (Comparative Study)
Comparative Study
Accumulation of Na(+) channels at the nodes of Ranvier is a prerequisite for saltatory conduction. In peripheral nerves, clustering of these channels along the axolemma is regulated by myelinating Schwann cells through a yet unknown mechanism. We report the identification of gliomedin, a glial ligand for neurofascin and NrCAM, two axonal immunoglobulin cell adhesion molecules that are associated with Na+ channels at the nodes of Ranvier. Gliomedin is expressed by myelinating Schwann cells and accumulates at the edges of each myelin segment during development, where it aligns with the forming nodes. Eliminating the expression of gliomedin by RNAi, or the addition of a soluble extracellular domain of neurofascin to myelinating cultures, which caused the redistribution of gliomedin along the internodes, abolished node formation. Furthermore, a soluble gliomedin induced nodal-like clusters of Na+ channels in the absence of Schwann cells. We propose that gliomedin provides a glial cue for the formation of peripheral nodes of Ranvier.
Topics: Age Factors; Amino Acid Sequence; Animals; Ankyrins; Axons; Blotting, Northern; Blotting, Western; Cell Adhesion Molecules; Cell Adhesion Molecules, Neuronal; Cell Compartmentation; Cells, Cultured; Chlorocebus aethiops; Claudins; Cloning, Molecular; Cytoskeletal Proteins; Fluorescent Antibody Technique; Ganglia, Spinal; Gene Expression Regulation, Developmental; Humans; Macromolecular Substances; Membrane Proteins; Microfilament Proteins; Microscopy, Immunoelectron; Myelin Basic Protein; Myelin-Associated Glycoprotein; Neurofilament Proteins; Phosphoproteins; Protein Binding; Protein Structure, Tertiary; Ranvier's Nodes; Rats; Receptors, Peptide; S100 Proteins; Schwann Cells; Sciatic Nerve; Sodium Channels; Spectrin; Transfection
PubMed: 16039564
DOI: 10.1016/j.neuron.2005.06.026 -
Glia Nov 2005The oligodendrocyte-myelin glycoprotein is a ligand of the neuronal Nogo receptor and a potent inhibitor of neurite outgrowth, but its physiological function remains to... (Comparative Study)
Comparative Study
The oligodendrocyte-myelin glycoprotein is a ligand of the neuronal Nogo receptor and a potent inhibitor of neurite outgrowth, but its physiological function remains to be elucidated. The oligodendrocyte-myelin glycoprotein is anchored solely in the outer leaflet of the plasma membrane via its glycosylphosphatidylinositol anchor, and through its leucine-rich repeat domain, it likely interacts with other proteins. In the present study, we compare its buoyancy and detergent solubility characteristics with those of other myelin proteins. Based on its detergent solubility profile and membrane fractionation using established ultracentrifugation procedures, we conclude that the oligodendrocyte-myelin glycoprotein is a lipid raft component that is closely associated with the axolemma. Moreover, it associates with caveolin-1 and caveolin-1-enriched membranes. We postulate that, by virtue of its concentration in lipid rafts and perhaps through interactions with caveolin-1, the oligodendrocyte-myelin glycoprotein may influence signaling pathways.
Topics: Animals; Axons; Brain; Caveolin 1; Detergents; GPI-Linked Proteins; Membrane Microdomains; Mice; Myelin Proteins; Myelin Sheath; Myelin-Associated Glycoprotein; Myelin-Oligodendrocyte Glycoprotein; Rats; Signal Transduction; Solubility
PubMed: 15968633
DOI: 10.1002/glia.20237 -
Medecine Sciences : M/S Feb 2005Myelination allows the fast propagation of action potentials at a low energetic cost. It provides an insulating myelin sheath regularly interrupted at nodes of Ranvier... (Review)
Review
Myelination allows the fast propagation of action potentials at a low energetic cost. It provides an insulating myelin sheath regularly interrupted at nodes of Ranvier where voltage-gated Na+ channels are concentrated. In the peripheral nervous system, the normal function of myelinated fibers requires the formation of highly differentiated and organized contacts between the myelinating Schwann cells, the axons and the extracellular matrix. Some of the major molecular complexes that underlie these contacts have been identified. Compact myelin which forms the bulk of the myelin sheath results from the fusion of the Schwann cell membranes through the proteins P0, PMP22 and MBP. The basal lamina of myelinating Schwann cells contains laminin-2 which associates with the glial complex dystroglycan/DPR2/L-periaxin. Non compact myelin, found in paranodal loops, periaxonal and abaxonal regions, and Schmidt-Lanterman incisures, presents reflexive adherens junctions, tight junctions and gap junctions, which contain cadherins, claudins and connexins, respectively. Axo-glial contacts determine the formation of distinct domains on the axon, the node, the paranode, and the juxtaparanode. At the paranodes, the glial membrane is tightly attached to the axolemma by septate-like junctions. Paranodal and juxtaparanodal axoglial complexes comprise an axonal transmembrane protein of the NCP family associated in cis and in trans with cell adhesion molecules of the immunoglobulin superfamily (IgSF-CAM). At nodes, axonal complexes are composed of Na+ channels and IgSF-CAMs. Schwann cell microvilli, which loosely cover the node, contain ERM proteins and the proteoglycans syndecan-3 and -4. The fundamental role of the cellular contacts in the normal function of myelinated fibers has been supported by rodent models and the detection of genetic alterations in patients with peripheral demyelinating neuropathies such as Charcot-Marie-Tooth diseases. Understanding more precisely their molecular basis now appears essential as a requisite step to further examine their involvement in the pathogenesis of peripheral neuropathies in general.
Topics: Animals; Basement Membrane; Cell Communication; Humans; Nerve Fibers, Myelinated; Neuroglia; Peripheral Nervous System; Schwann Cells
PubMed: 15691487
DOI: 10.1051/medsci/2005212162