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Journal of Neuropathology and... Dec 2016Congenital hypomyelinating neuropathy is a rare neonatal syndrome responsible for hypotonia and weakness. Nerve microscopic examination shows amyelination or...
Congenital hypomyelinating neuropathy is a rare neonatal syndrome responsible for hypotonia and weakness. Nerve microscopic examination shows amyelination or hypomyelination. Recently, mutations in CNTNAP1 have been described in a few patients. CNTNAP1 encodes contactin-associated protein 1 (caspr-1), which is an essential component of the paranodal junctions of the peripheral and central nervous systems, and is necessary for the establishment of transverse bands that stabilize paranodal axo-glial junctions. We present the results of nerve biopsy studies of three patients from two unrelated, non-consanguineous families with compound heterozygous CNTNAP1 mutations. The lesions were identical, characterized by a hypomyelinating process; on electron microscopy, we detected, in all nodes of Ranvier, subtle lesions that have never been previously described in human nerves. Transverse bands of the myelin loops were absent, with a loss of attachment between myelin and the axolemma; elongated Schwann cell processes sometimes dissociated the Schwann cell and axon membranes that bound the space between them. These lesions were observed in the area where caspr-1 is located and are reminiscent of the lesions reported in sciatic nerves of caspr-1 null mice. CNTNAP1 mutations appear to induce characteristic ultrastructural lesions of the paranodal region.
Topics: Cell Adhesion Molecules, Neuronal; Humans; Infant, Newborn; Male; Mutation; Pedigree; Sural Nerve
PubMed: 27818385
DOI: 10.1093/jnen/nlw093 -
Proceedings of the National Academy of... Apr 1997Crayfish medial giant axons (MGAs) transected in physiological saline form vesicles which interact with each other, pre-existing vesicles, and/or with the plasmalemma to...
Crayfish medial giant axons (MGAs) transected in physiological saline form vesicles which interact with each other, pre-existing vesicles, and/or with the plasmalemma to form an electrical and a physical barrier that seals a cut axonal end within 60 min. The formation of this barrier (seal) was assessed by measuring the decay of injury current at the cut end; its location at the cut end was determined by the exclusion of fluorescent hydrophilic dye at the cut end. When a membrane-incorporating styryl dye was placed in the bath prior to axonal transection and a hydrophilic dye was placed in the bath just after axonal transection, many vesicles near the barrier at the cut axonal end had their limiting membrane labeled with the styryl dye and their contents labeled with the hydrophilic dye, indicating that these vesicles originated from the axolemma by endocytosis. This barrier does not form in Ca2+-free salines. Similar collections of vesicles have been observed at regions of plasmalemmal damage in many cell types. From these and other data, we propose that plasmalemmal lesions in most eukaryotic cells (including axons) are repaired by vesicles, at least some of which arise by endocytosis induced by Ca2+ inflow resulting from the plasmalemmal damage. We describe several models by which vesicles could interact with each other and/or with intact or damaged regions of the plasmalemma to repair small (1-30 microm) plasmalemmal holes or a complete transection of the plasmalemma.
Topics: Animals; Astacoidea; Axons; Calcium; Cell Membrane; Coloring Agents; Endocytosis; Microscopy, Confocal; Microscopy, Interference; Models, Biological
PubMed: 9114062
DOI: 10.1073/pnas.94.9.4745 -
ASN Neuro Mar 2011The ability of an AEF (axolemma-enriched fraction) to influence the proliferation, survival and differentiation of OPC (oligodendrocyte progenitor cells) was evaluated....
The ability of an AEF (axolemma-enriched fraction) to influence the proliferation, survival and differentiation of OPC (oligodendrocyte progenitor cells) was evaluated. Following addition of AEF to cultured OPC, the AEF associated with the outer surface of OPC so that subsequent metabolic events were likely mediated by direct AEF-OPC contact. Addition of AEF to the cultured OPC resulted in a dose- and time-dependent increase in proliferation that was partially dependent on Akt (protein kinase B) and MAPK (mitogen-activated protein kinase) activation. The major mitogen in an AEF-SE (soluble 2.0 M NaCl extract of the AEF) was identified as aFGF (acidic fibroblast growth factor) and accounted for 50% of the mitogenicity. The remaining 50% of the mitogenicity had properties consistent with bFGF (basic fibroblast growth factor) but was not unequivocally identified. Under conditions that limit the survival of OPC in culture, AEF treatment prolonged the survival of the OPC. Antigenic and morphological examination of the AEF-treated OPC indicated that the AEF treatment helped the OPC survive in a more immature state. The potential downstream metabolic pathways potentially activated in OPC by AEF and the consequences of these activated pathways are discussed. The results of these studies are consistent with the view that direct contact of axons with OPC stimulates their proliferation and survival while preventing their differentiation.
Topics: Animals; Animals, Newborn; Cell Count; Cell Differentiation; Cell Proliferation; Cells, Cultured; Cellular Structures; Chromatography, Agarose; Hot Temperature; Mitogen-Activated Protein Kinases; Mitogens; Neurons; Oligodendroglia; Proto-Oncogene Proteins c-akt; Rats; Rats, Sprague-Dawley; Schwann Cells; Stem Cells; Trypsin
PubMed: 21345173
DOI: 10.1042/AN20100035 -
Experimental Neurology Jan 2012Autoantibodies against gangliosides GM1 or GD1a are associated with acute motor axonal neuropathy (AMAN) and acute motor-sensory axonal neuropathy (AMSAN), whereas...
Autoantibodies against gangliosides GM1 or GD1a are associated with acute motor axonal neuropathy (AMAN) and acute motor-sensory axonal neuropathy (AMSAN), whereas antibodies to GD1b ganglioside are detected in acute sensory ataxic neuropathy (ASAN). These neuropathies have been proposed to be closely related and comprise a continuous spectrum, although the underlying mechanisms, especially for sensory nerve involvement, are still unclear. Antibodies to GM1 and GD1a have been proposed to disrupt the nodes of Ranvier in motor nerves via complement pathway. We hypothesized that the disruption of nodes of Ranvier is a common mechanism whereby various anti-ganglioside antibodies found in these neuropathies lead to nervous system dysfunction. Here, we show that the IgG monoclonal anti-GD1a/GT1b antibody injected into rat sciatic nerves caused deposition of IgG and complement products on the nodal axolemma and disrupted clusters of nodal and paranodal molecules predominantly in motor nerves, and induced early reversible motor nerve conduction block. Injection of IgG monoclonal anti-GD1b antibody induced nodal disruption predominantly in sensory nerves. In an ASAN rabbit model associated with IgG anti-GD1b antibodies, complement-mediated nodal disruption was observed predominantly in sensory nerves. In an AMAN rabbit model associated with IgG anti-GM1 antibodies, complement attack of nodes was found primarily in motor nerves, but occasionally in sensory nerves as well. Periaxonal macrophages and axonal degeneration were observed in dorsal roots from ASAN rabbits and AMAN rabbits. Thus, nodal disruption may be a common mechanism in immune-mediated neuropathies associated with autoantibodies to gangliosides GM1, GD1a, or GD1b, providing an explanation for the continuous spectrum of AMAN, AMSAN, and ASAN.
Topics: Acute Disease; Animals; Antibodies; Choline O-Acetyltransferase; Complement C3; Disease Models, Animal; Ganglia, Spinal; Gangliosides; Gangliosidosis, GM1; Injections, Subcutaneous; Microscopy, Electron, Transmission; Neural Conduction; Polyneuropathies; Rabbits; Ranvier's Nodes; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Spectrin; Spinal Cord; Statistics, Nonparametric; Time Factors
PubMed: 22178332
DOI: 10.1016/j.expneurol.2011.11.039 -
The Journal of Cell Biology May 1973Curarized cutaneous pectoris nerve-muscle preparations from frogs were stimulated at 10/s or at 2/s for periods ranging from 20 min to 4 h. End plate potential were...
Curarized cutaneous pectoris nerve-muscle preparations from frogs were stimulated at 10/s or at 2/s for periods ranging from 20 min to 4 h. End plate potential were recorded intracellularly and used to estimate the quantity of transmitter secreted during the period of stimulation. At the ends of the periods of stimulation the preparations were either fixed for electron microscopy or treated with black widow spider venom to determine the quantities of transmitter remainind in the terminal. Horseradish peroxidase or dextran was added to the bathing solution and used as a tracer to detect the formation of vesicles from the axolemma. During 4 h of stimulation at 2/s many new vesicles were formed from the axolemma and the quantity of transmitter secreted was several times greater than the quantity in the initial store. After this period of stimulation, the terminals were severely depleted of transmitter, but not of vesicles, and their general morphological organization was normal. During 20 min of stimulation at 10/s the nerve terminals swelled and were severely depleted both of vesicles and of transmitter. During a subsequent hour of rest the changes in morphology were largely reversed, many new vesicles were formed from the axolemma and the stores of transmitter were partially replenished. These results suggest (a) that synaptic vesicles fuse with, and re-form from, the membrane of the nerve terminal during and after stimulation and (b), that the re-formed vesicles can store and release transmitter.
Topics: Animals; Anura; Axons; Cell Membrane; Curare; Dextrans; Electric Stimulation; Evoked Potentials; Histological Techniques; Microscopy, Electron; Mitochondrial Swelling; Nerve Endings; Neuromuscular Junction; Peroxidases; Rana pipiens; Spiders; Synaptic Transmission; Synaptic Vesicles; Time Factors; Venoms
PubMed: 4348791
DOI: 10.1083/jcb.57.2.499 -
The Journal of Biological Chemistry Jul 1985Two isozymes of the Na,K-ATPase were purified from rat renal medulla and rat brainstem axolemma, and antisera were raised in rabbits. When antibody titers were measured,...
Two isozymes of the Na,K-ATPase were purified from rat renal medulla and rat brainstem axolemma, and antisera were raised in rabbits. When antibody titers were measured, two sera showed specificity for either the kidney or axolemma Na,K-ATPases and had limited cross-reactivity which could be removed by cross-adsorption. In blots of polyacrylamide gels, these sera reacted with only the alpha or alpha (+) Na,K-ATPase catalytic subunits, while they cross-reacted with both types of beta subunits. Two other sera each recognized both alpha and alpha (+), indicating that the catalytic subunit isozymes have additional shared antigenic determinants. A comparison of the Na,K-ATPases from the brains of different vertebrate species indicates that birds and fish differ from mammals and amphibians in the manifestation of Na,K-ATPases isozymes. Neither neuraminidase nor endoglycosidase F treatment eliminated specific antibody reaction or affected the electrophoretic mobilities of the alpha and alpha (+) subunits, although endoglycosidase F increased the mobilities of the two types of beta subunits to similar final apparent molecular weights. Blots of the peptide fragments produced by incomplete papain and trypsin digests of the alpha and alpha (+) subunits were stained with the specific sera, and the patterns of immunoreactive fragments were found to be markedly different. The results suggest that the antigenic differences reside in differences in the primary protein sequences of the two isozymes.
Topics: Animals; Antibody Specificity; Brain Stem; Epitopes; Glycoside Hydrolases; Immune Sera; Immunization; Isoenzymes; Kidney; Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; Molecular Weight; Neuraminidase; Rabbits; Rats; Sodium-Potassium-Exchanging ATPase; Species Specificity
PubMed: 2410405
DOI: No ID Found -
The Journal of Neuroscience : the... Nov 2014In myelinated peripheral axons, Kv1 potassium channels are clustered at the juxtaparanodal region and at an internodal line located along the mesaxon and below the...
In myelinated peripheral axons, Kv1 potassium channels are clustered at the juxtaparanodal region and at an internodal line located along the mesaxon and below the Schmidt-Lanterman incisures. This polarized distribution is controlled by Schwann cells and requires specific cell adhesion molecules (CAMs). The accumulation of Kv1 channels at the juxtaparanodal region depends on the presence of Caspr2 at this site, as well as on the presence of Caspr at the adjacent paranodal junction. However, the localization of these channels along the mesaxonal internodal line still persists in the absence of each one of these CAMs. By generating mice lacking both Caspr and Caspr2 (caspr(-/-)/caspr2(-/-)), we now reveal compensatory functions of the two proteins in the organization of the axolemma. Although Kv1 channels are clustered along the inner mesaxon and in a circumferential ring below the incisures in the single mutants, in sciatic nerves of caspr(-/-)/caspr2(-/-) mice, these channels formed large aggregates that were dispersed along the axolemma, demonstrating that internodal localization of Kv1 channels requires either Caspr or Caspr2. Furthermore, deletion of both Caspr and Caspr2 also resulted in widening of the nodes of Ranvier, suggesting that Caspr2 (which is present at paranodes in the absence of Caspr) can partially compensate for the barrier function of Caspr at this site even without the formation of a distinct paranodal junction. Our results indicate that Caspr and Caspr2 are required for the organization of the axolemma both radially, manifested as the mesaxonal line, and longitudinally, demarcated by the nodal domains.
Topics: Animals; Axons; Cell Adhesion Molecules, Neuronal; Kv1.2 Potassium Channel; Membrane Proteins; Mice; Nerve Tissue Proteins; Protein Transport; Ranvier's Nodes
PubMed: 25378149
DOI: 10.1523/JNEUROSCI.3369-14.2014 -
Brain : a Journal of Neurology Apr 2017See Saporta and Shy (doi:10.1093/awx048) for a scientific commentary on this article.Effective bidirectional signalling between axons and Schwann cells is essential for...
See Saporta and Shy (doi:10.1093/awx048) for a scientific commentary on this article.Effective bidirectional signalling between axons and Schwann cells is essential for both the development and maintenance of peripheral nerve function. We have established conditions by which human induced pluripotent stem cell-derived sensory neurons can be cultured with rat Schwann cells, and have produced for the first time long-term and stable myelinating co-cultures with human neurons. These cultures contain the specialized domains formed by axonal interaction with myelinating Schwann cells, such as clustered voltage-gated sodium channels at the node of Ranvier and Shaker-type potassium channel (Kv1.2) at the juxtaparanode. Expression of type III neuregulin-1 (TIIINRG1) in induced pluripotent stem cell-derived sensory neurons strongly enhances myelination, while conversely pharmacological blockade of the NRG1-ErbB pathway prevents myelination, providing direct evidence for the ability of this pathway to promote the myelination of human sensory axons. The β-secretase, BACE1 is a protease needed to generate active NRG1 from the full-length form. Due to the fact that it also cleaves amyloid precursor protein, BACE1 is a therapeutic target in Alzheimer's disease, however, consistent with its role in NRG1 processing we find that BACE1 inhibition significantly impairs myelination in our co-culture system. In order to exploit co-cultures to address other clinically relevant problems, they were exposed to anti-disialosyl ganglioside antibodies, including those derived from a patient with a sensory predominant, inflammatory neuropathy with mixed axonal and demyelinating electrophysiology. The co-cultures reveal that both mouse and human disialosyl antibodies target the nodal axolemma, induce acute axonal degeneration in the presence of complement, and impair myelination. The human, neuropathy-associated IgM antibody is also shown to induce complement-independent demyelination. Myelinating co-cultures using human induced pluripotent stem cell-derived sensory neurons thus provide insights into the cellular and molecular specialization of axoglial signalling, how pharmacological agents may promote or impede such signalling and the pathogenic effects of ganglioside antibodies.awx012media15372351982001.
Topics: Adult; Animals; Antibodies, Anti-Idiotypic; Cell Differentiation; Coculture Techniques; ErbB Receptors; Female; Humans; Immunoglobulin G; Mice; Myelin Sheath; Neural Stem Cells; Neuregulin-1; Peripheral Nervous System; Rats; Schwann Cells; Sensory Receptor Cells; Transduction, Genetic
PubMed: 28334857
DOI: 10.1093/brain/awx012 -
Frontiers in Molecular Biosciences 2021Around half of the traumatic brain injuries are thought to be axonal damage. Disruption of the cellular membranes, or alternatively cytoskeletal damage has been...
Around half of the traumatic brain injuries are thought to be axonal damage. Disruption of the cellular membranes, or alternatively cytoskeletal damage has been suggested as possible injury trigger. Here, we have used molecular models to have a better insight on the structural and mechanical properties of axon sub-cellular components. We modelled myelin sheath and node of Ranvier as lipid bilayers at a coarse grained level. We built ex-novo a model for the myelin. Lipid composition and lipid saturation were based on the available experimental data. The model contains 17 different types of lipids, distributed asymmetrically between two leaflets. Molecular dynamics simulations were performed to characterize the myelin and node-of-Ranvier bilayers at equilibrium and under deformation and compared to previous axolemma simulations. We found that the myelin bilayer has a slightly higher area compressibility modulus and higher rupture strain than node of Ranvier. Compared to the axolemma in unmyelinated axon, mechanoporation occurs at 50% higher strain in the myelin and at 23% lower strain in the node of Ranvier in myelinated axon. Combining the results with finite element simulations of the axon, we hypothesizes that myelin does not rupture at the thresholds proposed in the literature for axonal injury while rupture may occur at the node of Ranvier. The findings contribute to increases our knowledge of axonal sub-cellular components and help to understand better the mechanism behind axonal brain injury.
PubMed: 34250015
DOI: 10.3389/fmolb.2021.669897 -
The Journal of General Physiology May 1968
PubMed: 19873615
DOI: No ID Found