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Frontiers in Cellular Neuroscience 2021In the central nervous system, myelin is attached to the axon in the paranodal region by a trimolecular complex of Neurofascin155 (NF155) in the myelin membrane,...
In the central nervous system, myelin is attached to the axon in the paranodal region by a trimolecular complex of Neurofascin155 (NF155) in the myelin membrane, interacting with Caspr1 and Contactin1 on the axolemma. Alternative splicing of a single Neurofascin transcript generates several different Neurofascins expressed by several cell types, but NF155, which is expressed by oligodendrocytes, contains a domain in the third fibronectinIII-like region of the molecule that is unique. The immunoglobulin 5-6 domain of NF155 is essential for binding to Contactin1, but less is known about the functions of the NF155-unique third fibronectinIII-like domain. Mutations and autoantibodies to this region are associated with several neurodevelopmental and demyelinating nervous system disorders. Here we used Crispr-Cas9 gene editing to delete a 9 bp sequence of NF155 in this unique domain, which has recently been identified as a thrombin binding site and implicated in plasticity of the myelin sheath. This small deletion results in dysmyelination, eversion of paranodal loops of myelin, substantial enlargement of the nodal gap, a complete loss of paranodal septate junctions, and mislocalization of Caspr1 and nodal sodium channels. The animals exhibit tremor and ataxia, and biochemical and mass spectrometric analysis indicates that while NF155 is transcribed and spliced normally, the NF155 protein is subsequently degraded, resulting in loss of the full length 155 kDa native protein. These findings reveal that this 9 bp region of NF155 in its unique third fibronectinIII-like domain is essential for stability of the protein.
PubMed: 33815060
DOI: 10.3389/fncel.2021.576609 -
Journal of Magnetic Resonance Imaging :... Apr 2021Neurodegeneration is a complex cellular process linked to prompt changes in myelin integrity and gradual neuron loss. Current imaging techniques offer estimations of...
BACKGROUND
Neurodegeneration is a complex cellular process linked to prompt changes in myelin integrity and gradual neuron loss. Current imaging techniques offer estimations of myelin volumes in lesions/remyelinated areas but are limited to detect subtle injury.
PURPOSE
To investigate whether measurements detected by a signal hierarchically isolated as a function of time-to-echo (SHIFT) MRI technique can determine changes in myelin integrity and fiber axolemma.
STUDY TYPE
Prospective animal model.
ANIMAL MODEL
Surgically demyelinated spinal cord (SC) injury model in rodents (n = 6).
FIELD STRENGTH/SEQUENCE
Gradient-echo spin-echo at 3T.
ASSESSMENT
Multicompartment T relaxations were computed by SHIFT MRI in 75-microns-resolution images of the SC injury penumbra region 2 weeks post-trauma. G-ratio and axolemma delamination were assessed by transmission electron microscopy (TEM) in intact and injured samples. SC myelinated nerve fraction was computed by SHIFT MRI prospectively and assessed histologically.
STATISTICAL TESTS
Relations between SHIFT-isolated T -components and TEM measurements were studied using linear regression and t-tests. Pearson's correlation and significance were computed to determine the SHIFT's sensitivity to detect myelinated fibers ratio in gray matter. Regularized least-squares-based ranking analysis was employed to determine SHIFT MRI's ability to discern intact and injured myelinated nerves.
RESULTS
Biexponential signals isolated by SHIFT MRI for intact vs. lesion penumbra exhibited changes in T , shifting from intermediate components (25 ± 2 msec) to long (43 ± 11 msec) in white matter, and similarly in gray matter regions-of-interest (31 ± 2 to 46 ± 16 msec). These changes correlated highly with TEM g-ratio and axon delamination measurements (P < 0.05). Changes in short T components were observed but not statistically significant (8.5 ± 0.5 to 7 ± 3 msec, P = 0.445, and 4.0 ± 0.9 to 7 ± 3 msec, P = 0.075, respectively). SHIFT MRI's ability to detect myelinated fibers within gray matter was confirmed (P < 0.001).
DATA CONCLUSION
Changes detected by SHIFT MRI are associated with abnormal intermembrane spaces formed upon mild injury, directly correlated with early neuro integrity loss. Level of Evidence 1 Technical Efficacy Stage 2.
Topics: Animals; Magnetic Resonance Imaging; Myelin Sheath; Neuropil; Prospective Studies; Spinal Cord; Spinal Cord Injuries
PubMed: 33098256
DOI: 10.1002/jmri.27397 -
Molecular and Cellular Neurosciences Sep 2020Neurotrauma is among main causes of human disability and death. We studied effects of axotomy on ultrastructure and neuronal activity of a simple model object - an...
Neurotrauma is among main causes of human disability and death. We studied effects of axotomy on ultrastructure and neuronal activity of a simple model object - an isolated crayfish stretch receptor that consists of single mechanoreceptor neurons (MRN) enwrapped by multilayer glial envelope. After isolation, MRN regularly fired until spontaneous activity cessation. Axotomy did not change significantly MRN spike amplitude and firing rate. However, the duration of neuron activity from MRN isolation to its spontaneous cessation decreased in axotomized MRN relative to intact neuron. [Ca] in MRN axon and soma increased 3-10 min after axotomy. Ca entry through ion channels in the axolemma accelerated axotomy-stimulated firing cessation. MRN incubation with Caionophore ionomycin accelerated MRN inactivation, whereas Ca-channel blocker Cd prolonged firing. Activity duration of either intact, or axotomized MRN did not change in the presence of ryanodine or dantrolene, inhibitors of ryanodin-sensitive Ca channels in endoplasmic reticulum. Thapsigargin, inhibitor of endoplasmic reticulum Ca-ATPase, or its activator ochratoxin were ineffective. Ultrastructural study showed that the defect in the axon transected by thin scissors is sealed by fused axolemma, glial and collagen layers. Only the 30-50 μm long segment completely lost microtubules and contained swelled mitochondria. The microtubular bundle remained undamaged at 300 μm away from the axotomy site. However, mitochondria within the 200-300 μm segment were strongly condensed and lost matrix and cristae. Glial and collagen layers exhibited greater damage. Swelling and edema of glial layers, collagen disorganization and rupture occurred within this segment. Thus, axotomy stronger damages glia/collagen envelope, axonal microtubules and mitochondria.
Topics: Animals; Axons; Axotomy; Endoplasmic Reticulum; Mechanoreceptors; Mitochondria; Neuroglia; Neurons
PubMed: 32717316
DOI: 10.1016/j.mcn.2020.103534 -
Journal of Neurology, Neurosurgery, and... Jun 2020To describe the pathological features of Guillain-Barré syndrome focusing on macrophage-associated myelin lesions.
OBJECTIVE
To describe the pathological features of Guillain-Barré syndrome focusing on macrophage-associated myelin lesions.
METHODS
Longitudinal sections of sural nerve biopsy specimens from 11 patients with acute inflammatory demyelinating polyneuropathy (AIDP) exhibiting macrophage-associated demyelinating lesions were examined using electron microscopy. A total of 1205 nodes of Ranvier were examined to determine the relationship of the macrophage-associated demyelinating lesions with the nodal regions. Additionally, immunohistochemical and immunofluorescent studies were performed to elucidate the sites of complement deposition.
RESULTS
Overall, 252 macrophage-associated myelin lesions were identified in longitudinal sections. Of these, 40 lesions exhibited complete demyelination with no association with the lamellar structures of myelin. In 183 lesions, macrophage cytoplasm was located at internodes without association with the nodes of Ranvier or paranodes. In particular, these internodal lesions were more frequent in one patient (152 lesions). In the remaining 29 lesions, the involvement of nodal regions was obvious. Lesions involving nodal regions were more frequently observed than those involving internodes in four patients. Invasion of the macrophage cytoplasmic processes into the space between the paranodal myelin terminal loops and the axolemma from the nodes of Ranvier was observed in three of these patients. Immunostaining suggested complement deposition corresponding to putative initial macrophage-associated demyelinating lesions.
CONCLUSIONS
The initial macrophage-associated demyelinating lesions appeared to be located at internodes and at nodal regions. The sites at which the macrophages initiated phagocytosis of myelin might be associated with the location of complement deposition in certain patients with AIDP.
Topics: Aged; Axons; Demyelinating Diseases; Female; Guillain-Barre Syndrome; Humans; Macrophages; Male; Middle Aged; Myelin Sheath; Neurons; Ranvier's Nodes
PubMed: 32245766
DOI: 10.1136/jnnp-2019-322479 -
Frontiers in Neurology 2020Traumatic brain injuries are a leading cause of morbidity and mortality worldwide. With almost 50% of traumatic brain injuries being related to axonal damage,...
Traumatic brain injuries are a leading cause of morbidity and mortality worldwide. With almost 50% of traumatic brain injuries being related to axonal damage, understanding the nature of cellular level impairment is crucial. Experimental observations have so far led to the formulation of conflicting theories regarding the cellular primary injury mechanism. Disruption of the axolemma, or alternatively cytoskeletal damage has been suggested mainly as injury trigger. However, mechanoporation thresholds of generic membranes seem not to overlap with the axonal injury deformation range and microtubules appear too stiff and too weakly connected to undergo mechanical breaking. Here, we aim to shed a light on the mechanism of primary axonal injury, bridging finite element and molecular dynamics simulations. Despite the necessary level of approximation, our models can accurately describe the mechanical behavior of the unmyelinated axon and its membrane. More importantly, they give access to quantities that would be inaccessible with an experimental approach. We show that in a typical injury scenario, the axonal cortex sustains deformations large enough to entail pore formation in the adjoining lipid bilayer. The observed axonal deformation of 10-12% agree well with the thresholds proposed in the literature for axonal injury and, above all, allow us to provide quantitative evidences that do not exclude pore formation in the membrane as a result of trauma. Our findings bring to an increased knowledge of axonal injury mechanism that will have positive implications for the prevention and treatment of brain injuries.
PubMed: 32082244
DOI: 10.3389/fneur.2020.00025 -
Glia Sep 2020Finding causative genetic mutations is important in the diagnosis and treatment of hereditary peripheral neuropathies. This study was conducted to find new genes...
Finding causative genetic mutations is important in the diagnosis and treatment of hereditary peripheral neuropathies. This study was conducted to find new genes involved in the pathophysiology of hereditary peripheral neuropathy. We identified a new mutation in the EBP50 gene, which is co-segregated with neuropathic phenotypes, including motor and sensory deficit in a family with Charcot-Marie-Tooth disease. EBP50 is known to be important for the formation of microvilli in epithelial cells, and the discovery of this gene mutation allowed us to study the function of EBP50 in the nervous system. EBP50 was strongly expressed in the nodal and paranodal regions of sciatic nerve fibers, where Schwann cell microvilli contact the axolemma, and at the growth tips of primary Schwann cells. In addition, EBP50 expression was decreased in mouse models of peripheral neuropathy. Knockout mice were used to study EBP50 function in the peripheral nervous system. Interestingly motor function deficit and abnormal histology of nerve fibers were observed in EBP50 heterozygous mice at 12 months of age, but not 3 months. in vitro studies using Schwann cells showed that NRG1-induced AKT activation and migration were significantly reduced in cells overexpressing the I325V mutant of EBP50 or cells with knocked-down EBP50 expression. In conclusion, we show for the first time that loss of function due to EBP50 gene deficiency or mutation can cause peripheral neuropathy.
Topics: Animals; Charcot-Marie-Tooth Disease; Mice; Mice, Knockout; Mutation; Peripheral Nerves; Peripheral Nervous System
PubMed: 32077526
DOI: 10.1002/glia.23805 -
Cell Jan 2020The propagation of electrical impulses along axons is highly accelerated by the myelin sheath and produces saltating or "jumping" action potentials across internodes,...
The propagation of electrical impulses along axons is highly accelerated by the myelin sheath and produces saltating or "jumping" action potentials across internodes, from one node of Ranvier to the next. The underlying electrical circuit, as well as the existence and role of submyelin conduction in saltatory conduction remain, however, elusive. Here, we made patch-clamp and high-speed voltage-calibrated optical recordings of potentials across the nodal and internodal axolemma of myelinated neocortical pyramidal axons combined with electron microscopy and experimentally constrained cable modeling. Our results reveal a nanoscale yet conductive periaxonal space, incompletely sealed at the paranodes, which separates the potentials across the low-capacitance myelin sheath and internodal axolemma. The emerging double-cable model reproduces the recorded evolution of voltage waveforms across nodes and internodes, including rapid nodal potentials traveling in advance of attenuated waves in the internodal axolemma, revealing a mechanism for saltation across time and space.
Topics: Action Potentials; Animals; Axons; Male; Models, Neurological; Myelin Sheath; Nerve Fibers, Myelinated; Patch-Clamp Techniques; Pyramidal Cells; Ranvier's Nodes; Rats; Rats, Wistar
PubMed: 31883793
DOI: 10.1016/j.cell.2019.11.039 -
Advances in Experimental Medicine and... 2019Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy, and pathophysiologically classified into acute inflammatory demyelinating... (Review)
Review
Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy, and pathophysiologically classified into acute inflammatory demyelinating polyneuropathy (AIDP), acute motor axonal neuropathy (AMAN), and acute motor and sensory axonal neuropathy (AMSAN). The main pathophysiological mechanism is complement-mediated nerve injury caused by antibody-antigen interaction in the peripheral nerves. Antiglycolipid antibodies are most pathogenic factors in the development of GBS, but not found in 40% of patients with GBS. One of the principal target regions in GBS is the node of Ranvier where functional molecules including glycolipids are assembled. Nodal dysfunction induced by the immune response in nodal axolemma, termed "nodopathy," can electrophysiologically show reversible conduction failure, axonal degeneration, or segmental demyelination. To detect new target molecules in antiglycolipid antibody-negative GBS and to elucidate the pathophysiology in the subacute and the subsequent phases of the disorder are the next problems.
Topics: Antibodies; Axons; Complement System Proteins; Glycolipids; Guillain-Barre Syndrome; Humans; Neural Conduction; Peripheral Nerves; Ranvier's Nodes
PubMed: 31760653
DOI: 10.1007/978-981-32-9636-7_20 -
Current Topics in Membranes 2019
Review
Topics: Animals; Axons; Cell Membrane; Humans
PubMed: 31610861
DOI: 10.1016/bs.ctm.2019.07.007 -
Journal of Biomechanical Engineering Dec 2019Diffuse axonal injury (DAI) is the pathological consequence of traumatic brain injury (TBI) that most of all requires a multiscale approach in order to be, first,...
Diffuse axonal injury (DAI) is the pathological consequence of traumatic brain injury (TBI) that most of all requires a multiscale approach in order to be, first, understood and then possibly prevented. While in fact the mechanical insult usually happens at the head (or macro) level, the consequences affect structures at the cellular (or microlevel). The quest for axonal injury tolerances has so far been addressed both with experimental and computational approaches. On one hand, the experimental approach presents challenges connected to both temporal and spatial resolution in the identification of a clear axonal injury trigger after the application of a mechanical load. On the other hand, computational approaches usually consider axons as homogeneous entities and therefore are unable to make inferences about their viability, which is thought to depend on subcellular damages. Here, we propose a computational multiscale approach to investigate the onset of axonal injury in two typical experimental scenarios. We simulated single-cell and tissue stretch injury using a composite finite element axonal model in isolation and embedded in a matrix, respectively. Inferences on axonal damage are based on the comparison between axolemma strains and previously established mechanoporation thresholds. Our results show that, axons embedded in a tissue could withstand higher deformations than isolated axons before mechanoporation occurred and this is exacerbated by the increase in strain rate from 1/s to 10/s.
PubMed: 31556941
DOI: 10.1115/1.4044953