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Pascual-García M, Unkel M, Slotman JA, Bolleboom A, Bouwen B, Houtsmuller AB, Dirven C, Gao Z, Hijazi S, Kushner SA. Morphological correlates of pyramidal cell axonal myelination in mouse and human neocortex. Cereb Cortex 2024; 34:bhae147. [PMID: 38610088 PMCID: PMC11014882 DOI: 10.1093/cercor/bhae147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Revised: 03/16/2024] [Accepted: 03/17/2024] [Indexed: 04/14/2024] Open
Abstract
The axons of neocortical pyramidal neurons are frequently myelinated. Heterogeneity in the topography of axonal myelination in the cerebral cortex has been attributed to a combination of electrophysiological activity, axonal morphology, and neuronal-glial interactions. Previously, we showed that axonal segment length and caliber are critical local determinants of fast-spiking interneuron myelination. However, the factors that determine the myelination of individual axonal segments along neocortical pyramidal neurons remain largely unexplored. Here, we used structured illumination microscopy to examine the extent to which axonal morphology is predictive of the topography of myelination along neocortical pyramidal neurons. We identified critical thresholds for axonal caliber and interbranch distance that are necessary, but not sufficient, for myelination of pyramidal cell axons in mouse primary somatosensory cortex (S1). Specifically, we found that pyramidal neuron axonal segments with a caliber < 0.24 μm or interbranch distance < 18.10 μm are rarely myelinated. Moreover, we further confirmed that these findings in mice are similar for human neocortical pyramidal cell myelination (caliber < 0.25 μm, interbranch distance < 19.00 μm), suggesting that this mechanism is evolutionarily conserved. Taken together, our findings suggest that axonal morphology is a critical correlate of the topography and cell-type specificity of neocortical myelination.
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Affiliation(s)
- Maria Pascual-García
- Department of Psychiatry, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Maurits Unkel
- Department of Psychiatry, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Johan A Slotman
- Erasmus Optical Imaging Centre, Department of Pathology, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Anne Bolleboom
- Department of Neuroscience, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
- Department of Neurosurgery, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Bibi Bouwen
- Department of Neuroscience, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
- Department of Neurosurgery, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Adriaan B Houtsmuller
- Erasmus Optical Imaging Centre, Department of Pathology, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Clemens Dirven
- Department of Neurosurgery, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Zhenyu Gao
- Department of Neuroscience, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
| | - Sara Hijazi
- Department of Psychiatry, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, United Kingdom
| | - Steven A Kushner
- Department of Psychiatry, Erasmus MC, Doctor Molewaterplein 40, Rotterdam, 3015 GD, The Netherlands
- Department of Psychiatry, Columbia University, 1051 Riverside Drive, New York, NY 10032, United States
- SNF Center for Precision Psychiatry & Mental Health, Columbia University, 630 West 168th Street, New York, NY 10032, United States
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Schwann cell functions in peripheral nerve development and repair. Neurobiol Dis 2023; 176:105952. [PMID: 36493976 DOI: 10.1016/j.nbd.2022.105952] [Citation(s) in RCA: 32] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Revised: 11/23/2022] [Accepted: 12/05/2022] [Indexed: 12/12/2022] Open
Abstract
The glial cell of the peripheral nervous system (PNS), the Schwann cell (SC), counts among the most multifaceted cells of the body. During development, SCs secure neuronal survival and participate in axonal path finding. Simultaneously, they orchestrate the architectural set up of the developing nerves, including the blood vessels and the endo-, peri- and epineurial layers. Perinatally, in rodents, SCs radially sort and subsequently myelinate individual axons larger than 1 μm in diameter, while small calibre axons become organised in non-myelinating Remak bundles. SCs have a vital role in maintaining axonal health throughout life and several specialized SC types perform essential functions at specific locations, such as terminal SC at the neuromuscular junction (NMJ) or SC within cutaneous sensory end organs. In addition, neural crest derived satellite glia maintain a tight communication with the soma of sensory, sympathetic, and parasympathetic neurons and neural crest derivatives are furthermore an indispensable part of the enteric nervous system. The remarkable plasticity of SCs becomes evident in the context of a nerve injury, where SC transdifferentiate into intriguing repair cells, which orchestrate a regenerative response that promotes nerve repair. Indeed, the multiple adaptations of SCs are captivating, but remain often ill-resolved on the molecular level. Here, we summarize and discuss the knowns and unknowns of the vast array of functions that this single cell type can cover in peripheral nervous system development, maintenance, and repair.
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van den Bosch AMR, Hümmert S, Steyer A, Ruhwedel T, Hamann J, Smolders J, Nave KA, Stadelmann C, Kole MHP, Möbius W, Huitinga I. Ultrastructural Axon-Myelin Unit Alterations in Multiple Sclerosis Correlate with Inflammation. Ann Neurol 2022; 93:856-870. [PMID: 36565265 DOI: 10.1002/ana.26585] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 12/13/2022] [Accepted: 12/17/2022] [Indexed: 12/25/2022]
Abstract
OBJECTIVE Changes in the normal-appearing white matter (NAWM) in multiple sclerosis (MS) may contribute to disease progression. Here, we systematically quantified ultrastructural and subcellular characteristics of the axon-myelin unit in MS NAWM and determined how this correlates with low-grade inflammation. METHODS Human brain tissue obtained with short postmortem delay and fixation at autopsy enables systematic quantification of ultrastructural characteristics. In this study, we performed high-resolution immunohis tochemistry and quantitative transmission electron microscopy to study inflammation and ultrastructural characteristics of the axon-myelin unit in MS NAWM (n = 8) and control white matter (WM) in the optic nerve. RESULTS In the MS NAWM, there were more activated and phagocytic microglia cells (HLA+ P2RY12- and Iba1+ CD68+ ) and more T cells (CD3+ ) compared to control WM, mainly located in the perivascular space. In MS NAWM compared to control WM, there were, as expected, longer paranodes and juxtaparanodes and larger overlap between paranodes and juxtaparanodes. There was less compact myelin wrapping, a lower g-ratio, and a higher frequency of axonal mitochondria. Changes in myelin and axonal mitochondrial frequency correlated positively with the number of active and phagocytic microglia and lymphocytes in the optic nerve. INTERPRETATION These data suggest that in MS NAWM myelin detachment and uncompact myelin wrapping occurs, potassium channels are unmasked at the nodes of Ranvier, and axonal energy demand is increased, or mitochondrial transport is stagnated, accompanied by increased presence of activated and phagocytic microglia and T cells. These subclinical alterations to the axon-myelin unit in MS NAWM may contribute to disease progression. ANN NEUROL 2023.
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Affiliation(s)
- Aletta M R van den Bosch
- Department of Neuroimmunology, Netherlands Institute for Neuroscience, Royal Netherlands Academy for Arts and Sciences, Amsterdam, the Netherlands
| | - Sophie Hümmert
- Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Anna Steyer
- Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Torben Ruhwedel
- Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Jörg Hamann
- Department of Neuroimmunology, Netherlands Institute for Neuroscience, Royal Netherlands Academy for Arts and Sciences, Amsterdam, the Netherlands.,Department of Experimental Immunology, Amsterdam Institute for Infection and Immunity, Amsterdam University Medical Centers, Amsterdam, the Netherlands
| | - Joost Smolders
- Department of Neuroimmunology, Netherlands Institute for Neuroscience, Royal Netherlands Academy for Arts and Sciences, Amsterdam, the Netherlands.,Department of Neurology and Immunology, Multiple Sclerosis Center ErasMS, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Klaus-Armin Nave
- Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Christine Stadelmann
- Department of Neuropathology, University Medical Center Göttingen, Göttingen, Germany
| | - Maarten H P Kole
- Department of Axonal Signaling, Netherlands Institute for Neuroscience, Royal Netherlands Academy for Arts and Sciences, Amsterdam, the Netherlands.,Cell Biology, Neurobiology, and Biophysics, Department of Biology, Faculty of Science, University of Utrecht, Utrecht, the Netherlands
| | - Wiebke Möbius
- Department of Neurogenetics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Inge Huitinga
- Department of Neuroimmunology, Netherlands Institute for Neuroscience, Royal Netherlands Academy for Arts and Sciences, Amsterdam, the Netherlands.,Center for Neuroscience, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, Amsterdam, the Netherlands
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Chae SA, Kim HS, Lee JH, Yun DH, Chon J, Yoo MC, Yun Y, Yoo SD, Kim DH, Lee SA, Chung SJ, Soh Y, Won CW. Impact of Vitamin B12 Insufficiency on Sarcopenia in Community-Dwelling Older Korean Adults. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2021; 18:ijerph182312433. [PMID: 34886159 PMCID: PMC8656801 DOI: 10.3390/ijerph182312433] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 11/21/2021] [Accepted: 11/23/2021] [Indexed: 10/31/2022]
Abstract
Vitamin B12 (B12) is involved as a cofactor in the synthesis of myelin. A lack of B12 impairs peripheral nerve production, which can contribute to sarcopenia. In this cross-sectional study, we aimed to investigate the relationship between B12 insufficiency and sarcopenia in community-dwelling older Korean adults. A total of 2325 (1112 men; 1213 women) adults aged 70-84 years were recruited. The tools used for sarcopenia were based on the Asian Working Group for Sarcopenia (AWGS) guidelines. Individuals with low appendicular skeletal muscle mass index (ASMI) (<7.0 kg/m2 for men; <5.4 kg/m2 for women) and low hand grip strength (HGS) (<28 kg for men; <18 kg for women) were defined as the sarcopenia group. Among this group, those who showed low physical performance (≤9 points on the Short Physical Performance Battery (SPPB)) were defined as the severe sarcopenia group. B12 concentrations were classified into insufficient (<350 pg/mL) and sufficient (≥350 pg/mL). Univariate and multivariate logistic regression analyses were used to evaluate the relationship between sarcopenia and B12 levels. Low ASMI showed a high incidence in the B12-insufficient group. However, HGS, SPPB, and the severity of sarcopenia showed no correlation with B12. Further, insufficient B12 may affect muscle quantity rather than muscle strength or physical performance.
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Affiliation(s)
- Seon A Chae
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Hee-Sang Kim
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Jong Ha Lee
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Dong Hwan Yun
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Jinmann Chon
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Myung Chul Yoo
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Yeocheon Yun
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
| | - Seung Don Yoo
- Department of Physical Medicine and Rehabilitation, Kyung Hee University Hospital at Gangdong, Seoul 05278, Korea; (S.D.Y.); (D.H.K.); (S.A.L.); (S.J.C.)
| | - Dong Hwan Kim
- Department of Physical Medicine and Rehabilitation, Kyung Hee University Hospital at Gangdong, Seoul 05278, Korea; (S.D.Y.); (D.H.K.); (S.A.L.); (S.J.C.)
| | - Seung Ah Lee
- Department of Physical Medicine and Rehabilitation, Kyung Hee University Hospital at Gangdong, Seoul 05278, Korea; (S.D.Y.); (D.H.K.); (S.A.L.); (S.J.C.)
| | - Sung Joon Chung
- Department of Physical Medicine and Rehabilitation, Kyung Hee University Hospital at Gangdong, Seoul 05278, Korea; (S.D.Y.); (D.H.K.); (S.A.L.); (S.J.C.)
| | - Yunsoo Soh
- Department of Physical Medicine and Rehabilitation Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea; (S.A.C.); (H.-S.K.); (J.H.L.); (D.H.Y.); (J.C.); (M.C.Y.); (Y.Y.)
- Correspondence: (Y.S.); (C.W.W.)
| | - Chang Won Won
- Department of Family Medicine, Kyung Hee University Medical Center, Seoul 02447, Korea
- Correspondence: (Y.S.); (C.W.W.)
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Choi BR, Dobrowolski M, Sockanathan S. GDE2 expression in oligodendroglia regulates the pace of oligodendrocyte maturation. Dev Dyn 2020; 250:513-526. [PMID: 33095500 DOI: 10.1002/dvdy.265] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 09/10/2020] [Accepted: 10/18/2020] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Oligodendrocytes generate specialized lipid-rich sheaths called myelin that wrap axons and facilitate the rapid, saltatory transmission of action potentials. Extrinsic signals and surface-mediated pathways coordinate oligodendrocyte development to ensure appropriate axonal myelination, but the mechanisms involved are not fully understood. Glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5) is a six-transmembrane enzyme that regulates the activity of surface glycosylphosphatidylinositol (GPI)-anchored proteins by cleavage of the GPI-anchor. GDE2 is expressed in neurons where it promotes oligodendrocyte maturation through the release of neuronally-derived soluble factors. GDE2 is also expressed in oligodendrocytes but the function of oligodendroglial GDE2 is not known. RESULTS Using Cre-lox technology, we generated mice that lack GDE2 expression in oligodendrocytes (O-Gde2KO). O-Gde2KOs show normal production and proliferation of oligodendrocyte precursor cells. However, oligodendrocyte maturation is accelerated leading to the robust increase of myelin proteins and increased myelination during development. These in vivo observations are recapitulated in vitro using purified primary oligodendrocytes, supporting cell-autonomous functions for GDE2 in oligodendrocyte maturation. CONCLUSIONS These studies reveal that oligodendroglial GDE2 expression is required for controlling the pace of oligodendrocyte maturation. Thus, the cell-type specific expression of GDE2 is important for the coordination of oligodendrocyte maturation and axonal myelination during neural development.
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Affiliation(s)
- Bo-Ran Choi
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Mateusz Dobrowolski
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Shanthini Sockanathan
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Recovery of sensory function after the implantation of oriented-collagen tube into the resected rat sciatic nerve. Regen Ther 2020; 14:48-58. [PMID: 31988995 PMCID: PMC6965654 DOI: 10.1016/j.reth.2019.12.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 12/03/2019] [Accepted: 12/05/2019] [Indexed: 12/25/2022] Open
Abstract
Introduction In the present study, we examined the effect of oriented collagen tube (OCT) implantation on the recovery of sensory function of the resected rat sciatic nerve. Materials and methods After a 10-mm long portion of the sciatic nerve of a rat was resected, an OCT was placed in the site of nerve defect. Recovery of the sensory function was evaluated using Von Frey test every 3 days after surgery. The regenerated tissue were histologically and ultrastructurally analyzed 2 and 4 weeks after the surgery. Results The sensory reflexes of the OCT group were restored to the level of that of the intact group after 15 days. Hematoxylin and eosin staining revealed the cross-linking between the proximal and distal stumps after 2 weeks. After 4 weeks, Luxol Fast Blue and immunohistochemical staining revealed the presence of myelin sheath from the proximal to distal region of the regenerated tissue and S100B staining confirmed the presence of Schwann cells. Interestingly, no myelin sheath was ultrastructurally observed around the regenerated axons at the central region after 2 weeks. Conclusions These results suggest that OCTs facilitate the recovery of sensory function. Additionally, the non-myelinated axons contributed to the recovery of the sensory function. Von Frey test results in the OCT group on POD 15 were comparable at the sham group. OCT group showed regeneration of unmyelinated axons in 2 weeks. Myelination was observed from proximal to distal after 4 weeks OCT implantation. In the OCT group, a large number of blood vessels were observed in nerve in 2 weeks.
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Rosso G, Guck J. Mechanical changes of peripheral nerve tissue microenvironment and their structural basis during development. APL Bioeng 2019; 3:036107. [PMID: 31893255 PMCID: PMC6932855 DOI: 10.1063/1.5108867] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Accepted: 09/05/2019] [Indexed: 12/15/2022] Open
Abstract
Peripheral nerves are constantly exposed to mechanical stresses associated with body growth and limb movements. Although some aspects of these nerves' biomechanical properties are known, the link between nerve biomechanics and tissue microstructures during development is poorly understood. Here, we used atomic force microscopy to comprehensively investigate the elastic modulus of living peripheral nerve tissue cross sections ex vivo at distinct stages of development and correlated these elastic moduli with various cellular and extracellular aspects of the underlying histological microstructure. We found that local nerve tissue stiffness is spatially heterogeneous and evolves biphasically during maturation. Furthermore, we found the intracellular microtubule network and the extracellular matrix collagens type I and type IV as major contributors to the nerves' biomechanical properties, but surprisingly not cellular density and myelin content as previously shown for the central nervous system. Overall, these findings characterize the mechanical microenvironment that surrounds Schwann cells and neurons and will further our understanding of their mechanosensing mechanisms during nerve development. These data also provide the design of artificial nerve scaffolds to promote biomedical nerve regeneration therapies by considering mechanical properties that better reflect the nerve microenvironment.
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de Moraes AA, de Almeida CAS, Lucas G, Thomazini JA, DeMaman AS. Effect of swimming training on nerve morphological recovery after compressive injury. Neurol Res 2018; 40:955-962. [PMID: 30091393 DOI: 10.1080/01616412.2018.1504180] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
OBJECTIVE This study aims to investigate morphological alterations caused by partial sciatic nerve ligation (PNL) and the efficacy of a moderate-intensity swimming training as therapeutic strategy for nerve regeneration. METHODS A number of 30 male adult mice were equally divided in control, 14 days after PNL (PNL 14 days), 42 days after PNL (PNL 42 days), 70 days after PNL (PNL 70 days) and 5-week exercise training after 7 days post-lesion (PNL trained 35 days) groups. PNL trained 35 days group began with a 10-min session for 3 days and this time was gradually increased by 10 min every three sessions until the animals had swum for 50 min per session. Morphoquantitative analysis was carried out to assess nerve regeneration in each group. RESULTS PNL 14 days group exhibited less degenerating signs than PNL 42 days group, where most post-lesion alterations were visualized. Nerve area and minimum diameter were significantly lower (p < 0.05) than control group. PNL 70 days group showed a greater degree of regenerating fibers and similar morphometric parameters to control group. PNL trained 35 days demonstrated signs of regeneration, reaching control group values in the morphometric analysis. DISCUSSION PNL promotes great histopathological changes, which became more visible at 42 post-injury days. A natural nerve-regeneration tendency was observed throughout time, as observed in PNL 70 days group; nevertheless, moderate swimming training was found to be a therapeutic resource for nerve regeneration, accelerating such process from a morphoquantitative perspective. ABBREVIATIONS ANOVA: One-way analysis of variance; BDNF: Brain-derived neurotrophic factor; FGF-2: Fibroblast growth factor 2; GDNF: Glial cell line derived neurotrophic factor; IGF: Insulin-link growth factor; IL-1β: Interleukin-1β; NGF: Neural growth factor; PBS: Phosphate-buffered saline; PNL: Partial sciatic nerve ligation.
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Affiliation(s)
- Alexa Alves de Moraes
- a Department of Physiotherapy, Center of Biological and Health Sciences , Paraíba State University , Campina Grande , Brazil
| | | | - Guilherme Lucas
- c Department of Physiology, Ribeirão Preto School of Medicine , University of São Paulo , Ribeirão Preto , Brazil
| | - José Antonio Thomazini
- d Department of Surgery and Anatomy, Ribeirão Preto School of Medicine , University of São Paulo , Ribeirão Preto , Brazil
| | - Aline Santos DeMaman
- e Department of Biology, Center of Biological and Health Sciences , Paraíba State University , Campina Grande , Brazil
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Transcriptomic characterization of MRI contrast with focus on the T1-w/T2-w ratio in the cerebral cortex. Neuroimage 2018; 174:504-517. [PMID: 29567503 PMCID: PMC6450807 DOI: 10.1016/j.neuroimage.2018.03.027] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Revised: 03/12/2018] [Accepted: 03/14/2018] [Indexed: 01/24/2023] Open
Abstract
Magnetic resonance (MR) images of the brain are of immense clinical and research utility. At the atomic and subatomic levels, the sources of MR signals are well understood. However, we lack a comprehensive understanding of the macromolecular correlates of MR signal contrast. To address this gap, we used genome-wide measurements to correlate gene expression with MR signal intensity across the cerebral cortex in the Allen Human Brain Atlas (AHBA). We focused on the ratio of T1-weighted and T2-weighted intensities (T1-w/T2-w ratio image), which is considered to be a useful proxy for myelin content. As expected, we found enrichment of positive correlations between myelin-associated genes and the ratio image, supporting its use as a myelin marker. Genome-wide, there was an association with protein mass, with genes coding for heavier proteins expressed in regions with high T1-w/T2-w values. Oligodendrocyte gene markers were strongly correlated with the T1-w/T2-w ratio, but this was not driven by myelin-associated genes. Mitochondrial genes exhibit the strongest relationship, showing higher expression in regions with low T1-w/T2-w ratio. This may be due to the pH gradient in mitochondria as genes up-regulated by pH in the brain were also highly correlated with the ratio. While we corroborate associations with myelin and synaptic plasticity, differences in the T1-w/T2-w ratio across the cortex are more strongly linked to molecule size, oligodendrocyte markers, mitochondria, and pH. We evaluate correlations between AHBA transcriptomic measurements and a group averaged T1-w/T2-w ratio image, showing agreement with in-sample results. Expanding our analysis to the whole brain results in strong positive T1-w/T2-w correlations for immune system, inflammatory disease, and microglia marker genes. Genes with negative correlations were enriched for neuron markers and synaptic plasticity genes. Lastly, our findings are similar when performed on T1-w or inverted T2-w intensities alone. These results provide a molecular characterization of MR contrast that will aid interpretation of future MR studies of the brain.
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Salan T, Jacobs EL, Reddick WE. A 3D model-based simulation of demyelination to understand its effects on diffusion tensor imaging. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2017; 2017:3525-3528. [PMID: 29060658 DOI: 10.1109/embc.2017.8037617] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Demyelination is the progressive damage to the myelin sheath, a protective covering that surrounds a nerve's axon. Due to its high sensitivity to microscopic tissue changes, diffusion tensor imaging (DTI) is a powerful means of detecting signs of demyelination and axonal injury. In this paper, we present a 3D virtual model capable of simulating the complex Brownian motion of water molecules in a bundle of myelinated axons and glial cells for the purpose of synthesizing DTI data, characterizing and verifying the impact of demyelination on DTI. Our model consists of a highly detailed and realistic 3D representation of biological fiber bundles, with a myelin sheath covering the axons and glial cells in between them. The system simulates the Brownian motion of molecules to extract diffusion data. We perform our experiment for progressive stages of demyelination and demonstrate its effect on DTI measurements.
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O'Rourke C, Lee-Reeves C, Drake RA, Cameron GW, Loughlin AJ, Phillips JB. Adapting tissue-engineered in vitro CNS models for high-throughput study of neurodegeneration. J Tissue Eng 2017; 8:2041731417697920. [PMID: 28507726 PMCID: PMC5415290 DOI: 10.1177/2041731417697920] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 02/14/2017] [Indexed: 11/21/2022] Open
Abstract
Neurodegenerative conditions remain difficult to treat, with the continuing failure to see therapeutic research successfully advance to clinical trials. One of the obstacles that must be overcome is to develop enhanced models of disease. Tissue engineering techniques enable us to create organised artificial central nervous system tissue that has the potential to improve the drug development process. This study presents a replicable model of neurodegenerative pathology through the use of engineered neural tissue co-cultures that can incorporate cells from various sources and allow degeneration and protection of neurons to be observed easily and measured, following exposure to neurotoxic compounds – okadaic acid and 1-methyl-4-phenylpyridinium. Furthermore, the technology has been miniaturised through development of a mould with 6 mm length that recreates the advantageous features of engineered neural tissue co-cultures at a scale suitable for commercial research and development. Integration of human-derived induced pluripotent stem cells aids more accurate modelling of human diseases, creating new possibilities for engineered neural tissue co-cultures and their use in drug screening.
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Affiliation(s)
- Caitriona O'Rourke
- Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, University College London, London, UK.,Department of Life, Health and Chemical Sciences, The Open University, Milton Keynes, UK
| | - Charlotte Lee-Reeves
- Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, University College London, London, UK
| | | | | | - A Jane Loughlin
- Department of Life, Health and Chemical Sciences, The Open University, Milton Keynes, UK
| | - James B Phillips
- Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, University College London, London, UK
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Kakihata CMM, Malanotte JA, Karvat J, Brancalhão RMC, de Fátima Chasko Ribeiro L, Bertolini GRF. The morphological and functional effects of exercise in the aquatic environment, performed before and/or after sciatic nerve compression in Wistar rats. J Exerc Rehabil 2016; 12:393-400. [PMID: 27807516 PMCID: PMC5091053 DOI: 10.12965/jer.1632670.335] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 09/27/2016] [Indexed: 12/30/2022] Open
Abstract
The aim of this study was to evaluate the effects of exercise in the aquatic environment, performed before and/or after sciatic nerve compression in Wistar rats on morphological and functional parameters. Twenty-five Wistar rats were divided into the following groups: control (C), lesion (L), trained+lesion (TL), lesion+exercise (LE), and training+lesion+exercise (TLE), who underwent right sciatic nerve compression on day 21 of the experiment. The TL and TLE groups were submitted to a jumping exercise in a water environment for 20 days prior to injury and the LE and TLE groups after injury. The functional analysis was carried out using the sciatic functional index (SFI). On the last day of the experiment, the right sciatic nerves were collected, processed and analysed according to morphology and morphometry. The C group showed higher SFI in relation to the other groups. In the morphometric analysis, in comparison to C, all groups showed a decrease in the diameter of the injured nerve fibre, the myelin sheath and an increase in the percentage of connective tissue. There was a decrease in axon diameter in L, TL, and LE groups and a decrease in the density of nerve fibres in the TL and LE groups. The exercise did not affect functional recovery. However, the exercise prior to the injury improved morphology of the nervous tissue, and when performed pre- and postinjury, there was also an improvement in nerve regeneration, but this was not the case with exercise performed after the injury demonstrating worse results.
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Affiliation(s)
| | | | - Jhenifer Karvat
- Universidade Estadual do Oeste do Paraná, Cascavel, Brazil; Universidade Federal de Santa Catarina, Florianópolis, Brazil
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Micheva KD, Wolman D, Mensh BD, Pax E, Buchanan J, Smith SJ, Bock DD. A large fraction of neocortical myelin ensheathes axons of local inhibitory neurons. eLife 2016; 5. [PMID: 27383052 PMCID: PMC4972537 DOI: 10.7554/elife.15784] [Citation(s) in RCA: 167] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Accepted: 07/05/2016] [Indexed: 12/30/2022] Open
Abstract
Myelin is best known for its role in increasing the conduction velocity and metabolic efficiency of long-range excitatory axons. Accordingly, the myelin observed in neocortical gray matter is thought to mostly ensheath excitatory axons connecting to subcortical regions and distant cortical areas. Using independent analyses of light and electron microscopy data from mouse neocortex, we show that a surprisingly large fraction of cortical myelin (half the myelin in layer 2/3 and a quarter in layer 4) ensheathes axons of inhibitory neurons, specifically of parvalbumin-positive basket cells. This myelin differs significantly from that of excitatory axons in distribution and protein composition. Myelin on inhibitory axons is unlikely to meaningfully hasten the arrival of spikes at their pre-synaptic terminals, due to the patchy distribution and short path-lengths observed. Our results thus highlight the need for exploring alternative roles for myelin in neocortical circuits.
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Affiliation(s)
- Kristina D Micheva
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States
| | - Dylan Wolman
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
| | - Brett D Mensh
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
| | - Elizabeth Pax
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
| | - JoAnn Buchanan
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States
| | - Stephen J Smith
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, United States
| | - Davi D Bock
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States
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Rao SNR, Pearse DD. Regulating Axonal Responses to Injury: The Intersection between Signaling Pathways Involved in Axon Myelination and The Inhibition of Axon Regeneration. Front Mol Neurosci 2016; 9:33. [PMID: 27375427 PMCID: PMC4896923 DOI: 10.3389/fnmol.2016.00033] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 05/02/2016] [Indexed: 01/06/2023] Open
Abstract
Following spinal cord injury (SCI), a multitude of intrinsic and extrinsic factors adversely affect the gene programs that govern the expression of regeneration-associated genes (RAGs) and the production of a diversity of extracellular matrix molecules (ECM). Insufficient RAG expression in the injured neuron and the presence of inhibitory ECM at the lesion, leads to structural alterations in the axon that perturb the growth machinery, or form an extraneous barrier to axonal regeneration, respectively. Here, the role of myelin, both intact and debris, in antagonizing axon regeneration has been the focus of numerous investigations. These studies have employed antagonizing antibodies and knockout animals to examine how the growth cone of the re-growing axon responds to the presence of myelin and myelin-associated inhibitors (MAIs) within the lesion environment and caudal spinal cord. However, less attention has been placed on how the myelination of the axon after SCI, whether by endogenous glia or exogenously implanted glia, may alter axon regeneration. Here, we examine the intersection between intracellular signaling pathways in neurons and glia that are involved in axon myelination and axon growth, to provide greater insight into how interrogating this complex network of molecular interactions may lead to new therapeutics targeting SCI.
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Affiliation(s)
- Sudheendra N R Rao
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine Miami, FL, USA
| | - Damien D Pearse
- The Miami Project to Cure Paralysis, University of Miami Miller School of MedicineMiami, FL, USA; The Department of Neurological Surgery, University of Miami Miller School of MedicineMiami, FL, USA; The Neuroscience Program, University of Miami Miller School of MedicineMiami, FL, USA; The Interdisciplinary Stem Cell Institute, University of Miami Miller School of MedicineMiami, FL, USA; Bruce W. Carter Department of Veterans Affairs Medical CenterMiami, FL, USA
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Mehrshad A, Seddighnia A, Shadabi M, Najafpour A, Mohammadi R. Local Effect of Heparin Binding Neurotrophic Factor Combined With Chitosan Entubulization on Sciatic Nerve Repair in Rats. Bull Emerg Trauma 2016; 4:80-87. [PMID: 27331064 PMCID: PMC4897988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Revised: 03/22/2016] [Accepted: 03/27/2016] [Indexed: 06/06/2023] Open
Abstract
OBJECTIVE To assess the effect of on sciatic nerve regeneration in animal model of rat. METHODS Seventy-five male Wistar rats were divided into five experimental groups randomly (each group containing 15 animals): Sham operation group (SHAM), autograft group (AUTO), transected control (TC), chitosan conduit (CHIT) and heparin binding neurotrophic factor treated group (CHIT/HBNF). In AUTO group a segment of sciatic nerve was transected and reimplanted reversely. In SHAM group sciatic nerve was exposed and manipulated. In transected group left sciatic nerve was transected and stumps were fixed in adjacent muscle (TC). In treatment group defect was bridged using a chitosan conduit (CHIT) filled with 10 µL HBNF (CHIT/HBNF). Each group was subdivided into four subgroups of five animals each and nerve fibers were studied in a 12-week period. RESULTS Behavioral, functional, biomechanical, electrophysiological and gastrocnemius muscle mass findings and morphometric indices confirmed faster recovery of regenerated axons in treatment group than in CHIT group (P=0.001). Immunohistochemical reactions to S-100 in treatment group were more positive than that in CHIT group. CONCLUSION Local administration of improved functional recovery and morphometric indices of sciatic nerve. It could be considered as an effective treatment for peripheral nerve repair in practice.
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Affiliation(s)
- Ali Mehrshad
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Urmia Branch, Islamic Azad University, Urmia, Iran
| | - Ashkan Seddighnia
- Department of Basic Sciences, Faculty of Veterinary Medicine, Urmia Branch, Islamic Azad University, Urmia, Iran
| | - Mohammadreza Shadabi
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Urmia Branch, Islamic Azad University, Urmia, Iran
| | - Alireza Najafpour
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Urmia Branch, Islamic Azad University, Urmia, Iran
| | - Rahim Mohammadi
- Department of Surgery and Diagnostic Imaging, Faculty of Veterinary Medicine, Urmia University, Urmia 57153 1177, Iran
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Tajdaran K, Gordon T, Wood MD, Shoichet MS, Borschel GH. A glial cell line-derived neurotrophic factor delivery system enhances nerve regeneration across acellular nerve allografts. Acta Biomater 2016; 29:62-70. [PMID: 26441127 DOI: 10.1016/j.actbio.2015.10.001] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 09/29/2015] [Accepted: 10/01/2015] [Indexed: 10/22/2022]
Abstract
Acellular nerve allografts (ANAs) are used clinically to bridge nerve gaps but these grafts, lacking Schwann cells and therapeutic levels of neurotrophic factors, do not support regeneration to the same extent as autografts. Here we investigated a local drug delivery system (DDS) for glial cell line-derived neurotrophic factor (GDNF) controlled release to implanted ANAs in rats using drug-loaded polymeric microspheres (MSs) embedded in a fibrin gel. In a rat hindlimb nerve gap model, a 10mm ANA was used to bridge a 5mm common peroneal (CP) nerve gap. Experimental groups received DDS treatment at both suture sites of the allografts releasing GDNF for either 2 weeks or 4 weeks. In negative control groups, rats received no DDS treatment or empty DDS. Rats receiving nerve isografts served as the positive control group. The numbers of motor and sensory neurons that regenerated their axons in all the groups with GDNF MS and isograft treatment were indistinguishable and significantly higher as compared to the negative control groups. Nerve histology distal to the nerve graft demonstrated increased axon counts and a shift to larger fiber diameters due to GDNF MS treatment. The sustained delivery of GDNF to the implanted ANA achieved in this study demonstrates the promise of this DDS for the management of severe nerve injuries in which allografts are placed. STATEMENT OF SIGNIFICANCE This work addresses the common clinical situation in which a nerve gap is bridged using acellular nerve allografts. However, these allografts are not as effective in supporting nerve regeneration as the gold standard method of autografting. The novel local drug delivery system used in this study provides sustained and controlled release of glial cell line-derived neurotrophic factor (GDNF), one of the most potent neurotrophic factors, which significantly improves nerve regeneration following severe nerve injuries. Results from this research will provide a mean of improving nerve allografts with locally delivered GDNF. This strategy may lead to a novel "off the shelf" alternative to the current management of severe nerve injuries.
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17
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A comparative study of acellular nerve xenografts and allografts in repairing rat facial nerve defects. Mol Med Rep 2015; 12:6330-6. [DOI: 10.3892/mmr.2015.4123] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 06/26/2015] [Indexed: 11/05/2022] Open
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Effect of local administration of fibroblastic growth factor with chitosan conduit on peripheral nerve regeneration: a rat sciatic nerve transection model. ACTA ACUST UNITED AC 2014. [DOI: 10.1007/s00580-014-1976-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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19
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Functional effect of local administration of glial derived neurotrophic factor combined with inside-out artery graft on sciatic nerve regeneration in rat. Int J Surg 2014; 12:457-63. [DOI: 10.1016/j.ijsu.2014.03.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Revised: 01/29/2014] [Accepted: 03/28/2014] [Indexed: 11/19/2022]
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20
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Jesuraj NJ, Santosa KB, Macewan MR, Moore AM, Kasukurthi R, Ray WZ, Flagg ER, Hunter DA, Borschel GH, Johnson PJ, Mackinnon SE, Sakiyama-Elbert SE. Schwann cells seeded in acellular nerve grafts improve functional recovery. Muscle Nerve 2013; 49:267-76. [PMID: 23625513 DOI: 10.1002/mus.23885] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/15/2013] [Indexed: 12/14/2022]
Abstract
INTRODUCTION This study evaluated whether Schwann cells (SCs) from different nerve sources transplanted into cold-preserved acellular nerve grafts (CP-ANGs) would improve functional regeneration compared with nerve isografts. METHODS SCs isolated and expanded from motor and sensory branches of rat femoral and sciatic nerves were seeded into 14mm CP-ANGs. Growth factor expression, axonal regeneration, and functional recovery were evaluated in a 14-mm rat sciatic injury model and compared with isografts. RESULTS At 14 days, motor or sensory-derived SCs increased expression of growth factors in CP-ANGs versus isografts. After 42 days, histomorphometric analysis found CP-ANGs with SCs and isografts had similar numbers of regenerating nerve fibers. At 84 days, muscle force generation was similar for CP-ANGs with SCs and isografts. SC source did not affect nerve fiber counts or muscle force generation. CONCLUSIONS SCs transplanted into CP-ANGs increase functional regeneration to isograft levels; however SC nerve source did not have an effect.
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Affiliation(s)
- Nithya J Jesuraj
- Department of Biomedical Engineering, Washington University, Campus Box 1097, One Brookings Drive, St. Louis, Missouri, 63130, USA
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21
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Pace LA, Plate JF, Mannava S, Barnwell JC, Koman LA, Li Z, Smith TL, Van Dyke M. A human hair keratin hydrogel scaffold enhances median nerve regeneration in nonhuman primates: an electrophysiological and histological study. Tissue Eng Part A 2013; 20:507-17. [PMID: 24083825 DOI: 10.1089/ten.tea.2013.0084] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
A human hair keratin biomaterial hydrogel scaffold was evaluated as a nerve conduit luminal filler following median nerve transection injury in 10 Macaca fascicularis nonhuman primates (NHP). A 1 cm nerve gap was grafted with a NeuraGen® collagen conduit filled with either saline or keratin hydrogel and nerve regeneration was evaluated by electrophysiology for a period of 12 months. The keratin hydrogel-grafted nerves showed significant improvement in return of compound motor action potential (CMAP) latency and recovery of baseline nerve conduction velocity (NCV) compared with the saline-treated nerves. Histological evaluation was performed on retrieved median nerves and abductor pollicis brevis (APB) muscles at 12 months. Nerve histomorphometry showed a significantly larger nerve area in the keratin group compared with the saline group and the keratin APB muscles had a significantly higher myofiber density than the saline group. This is the first published study to show that an acellular biomaterial hydrogel conduit filler can be used to enhance peripheral nerve regeneration and motor recovery in an NHP model.
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Affiliation(s)
- Lauren A Pace
- 1 Wake Forest Institute for Regenerative Medicine, Wake Forest School of Medicine , Winston-Salem, North Carolina
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22
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Wood MD, Gordon T, Kim H, Szynkaruk M, Phua P, Lafontaine C, Kemp SW, Shoichet MS, Borschel GH. Fibrin gels containing GDNF microspheres increase axonal regeneration after delayed peripheral nerve repair. Regen Med 2013; 8:27-37. [PMID: 23259803 DOI: 10.2217/rme.12.105] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
AIM Recovery following nerve transection declines when target reconnection is delayed for prolonged periods. GDNF has previously been shown to promote motor axon regeneration following delayed nerve repair. MATERIALS & METHODS We constructed delivery systems using fibrin gels containing free GDNF or poly(lactide-co-glycolide) microspheres with GDNF. The delivery systems were implanted with fluorescent fibrinogen surrounding the common fibular (CF; peroneal) nerve in transgenic Thy-1 GFP rats (whose axons express GFP) to track degradation of the system. A delayed nerve repair model was designed by transecting the rat CF nerve, where nerve regeneration was prevented by ligating the two stumps to surrounding muscle for 2 months prior to resuture. At resuture, either a delivery system with GDNF or an additional group consisting of fibrin gels with empty microspheres were implanted surrounding the repair site. In an additional positive control, the CF was transected and repaired immediately without delay. RESULTS ELISA assays demonstrated GDNF release in vitro for 2 weeks from fibrin gels with GDNF microspheres. Implanted delivery systems, including GDNF microspheres, remained surrounding the nerve for at least 10 days compared with 3 days for free GDNF. Four weeks after repair, histomorphometry of distal nerve cross-sections taken 20 mm from the repair site demonstrated increased fiber diameter and myelin thickness due to release of GDNF from microspheres compared with empty microspheres. Additionally, the number of motoneurons that regenerated their axons to the same site increased to comparable levels as immediate repair due to the extended delivery of GDNF from microspheres. CONCLUSION These findings demonstrate that early measures of nerve regeneration after delayed nerve repair is improved by GDNF microspheres implanted at the coaptation site.
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Affiliation(s)
- Matthew D Wood
- Division of Plastic & Reconstructive Surgery, The Hospital for Sick Children, Toronto, ON, Canada.
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Wood MD, Kemp SWP, Liu EH, Szynkaruk M, Gordon T, Borschel GH. Rat-derived processed nerve allografts support more axon regeneration in rat than human-derived processed nerve xenografts. J Biomed Mater Res A 2013; 102:1085-91. [DOI: 10.1002/jbm.a.34773] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 04/22/2013] [Accepted: 04/23/2013] [Indexed: 11/05/2022]
Affiliation(s)
- Matthew D. Wood
- Division of Plastic and Reconstructive Surgery; The Hospital for Sick Children; 555 University Ave Toronto ON Canada M5G 1X8
- Program in Physiology and Experimental Medicine; The Hospital for Sick Children Research Institute; Elizabeth McMaster Building Toronto ON Canada M5G 1X8
| | - Stephen W. P. Kemp
- Division of Plastic and Reconstructive Surgery; The Hospital for Sick Children; 555 University Ave Toronto ON Canada M5G 1X8
- Program in Physiology and Experimental Medicine; The Hospital for Sick Children Research Institute; Elizabeth McMaster Building Toronto ON Canada M5G 1X8
| | - Edward H. Liu
- Division of Plastic and Reconstructive Surgery; The Hospital for Sick Children; 555 University Ave Toronto ON Canada M5G 1X8
| | - Mark Szynkaruk
- Division of Plastic and Reconstructive Surgery; The Hospital for Sick Children; 555 University Ave Toronto ON Canada M5G 1X8
- Program in Physiology and Experimental Medicine; The Hospital for Sick Children Research Institute; Elizabeth McMaster Building Toronto ON Canada M5G 1X8
| | - Tessa Gordon
- Division of Plastic and Reconstructive Surgery; The Hospital for Sick Children; 555 University Ave Toronto ON Canada M5G 1X8
- Program in Physiology and Experimental Medicine; The Hospital for Sick Children Research Institute; Elizabeth McMaster Building Toronto ON Canada M5G 1X8
| | - Gregory H. Borschel
- Division of Plastic and Reconstructive Surgery; The Hospital for Sick Children; 555 University Ave Toronto ON Canada M5G 1X8
- Program in Physiology and Experimental Medicine; The Hospital for Sick Children Research Institute; Elizabeth McMaster Building Toronto ON Canada M5G 1X8
- Institute of Biomaterials and Biomedical Engineering; University of Toronto; 164 College Street Toronto Ontario Canada M5G 1X8
- Division of Plastic and Reconstructive Surgery; Department of Surgery, University of Toronto; 100 College Street Toronto Ontario Canada M5G 1X8
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The association of white matter volume in psychotic disorders with genotypic variation in NRG1, MOG and CNP: a voxel-based analysis in affected individuals and their unaffected relatives. Transl Psychiatry 2012; 2:e167. [PMID: 23032943 PMCID: PMC3565820 DOI: 10.1038/tp.2012.82] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We investigated the role of variation in putative psychosis genes coding for elements of the white matter system by examining the contribution of genotypic variation in three single-nucleotide polymorphisms (SNPs) neuregulin 1 (NRG1) SNP8NRG221533, myelin oligodendrocytes glycoprotein (MOG) rs2857766 and CNP (rs2070106) and one haplotype HAP(ICE) (deCODE) to white matter volume in patients with psychotic disorder and their unaffected relatives. Structural magnetic resonance imaging and blood samples for genotyping were collected on 189 participants including patients with schizophrenia (SZ) or bipolar I disorder (BDI), unaffected first-degree relatives of these patients and healthy volunteers. The association of genotypic variation with white matter volume was assessed using voxel-based morphometry in SPM5. The NRG1 SNP and the HAP(ICE) haplotype were associated with abnormal white matter volume in the BDI group in the fornix, cingulum and parahippocampal gyrus circuit. In SZ the NRG1 SNP risk allele was associated with lower white matter volume in the uncinate fasciculus (UF), right inferior longitudinal fasciculus and the anterior limb of the internal capsule. Healthy G-homozygotes of the MOG SNP had greater white matter volume in areas of the brainstem and cerebellum; this relationship was absent in those with a psychotic disorder and the unaffected relatives groups. The CNP SNP did not contribute to white matter volume variation in the diagnostic groups studied. Variation in the genes coding for structural and protective components of myelin are implicated in abnormal white matter volume in the emotion circuitry of the cingulum, fornix, parahippocampal gyrus and UF in psychotic disorders.
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Saueressig F, Xavier LL, Bagatini PB, Nique PS, DaCosta JC, Gomes I, Cherubini K. Morphofunctional analysis of sciatic nerve and motor performance of rats after cryotherapy with liquid nitrogen. Oral Surg Oral Med Oral Pathol Oral Radiol 2012; 113:319-26. [PMID: 22676823 DOI: 10.1016/j.tripleo.2011.03.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2011] [Revised: 02/17/2011] [Accepted: 03/13/2011] [Indexed: 11/27/2022]
Abstract
OBJECTIVE This work evaluated sciatic nerve regeneration after cryotherapy. STUDY DESIGN Rats underwent surgical access of the sciatic nerve and subsequent cryotherapy, crush lesion, or no manipulation. Walking-track, electroneuromyographic, and histomorphometric analyses were performed at 15, 30, and 70 postoperative days. RESULTS At 15 days, the crush and cryotherapy groups showed significant morphofunctional impairment. At 30 days, functional loss was significant in the walking-track, but at 70 days, there were no significant differences between the groups. Amplitude was near zero for the crush group at 15 and 30 days and zero for the cryotherapy group. Measurement of latency was not possible in the latter group. Crush and cryotherapy groups showed greater amounts of myelinated fibers (by 30 days), with axonal diameter and width of the myelin sheath being less than in control group. CONCLUSIONS Sciatic nerve lesion by application of liquid nitrogen is classified as axonotmesis, which is reversible.
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Affiliation(s)
- Frederico Saueressig
- Dental College, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil
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26
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Swimming exercise in the acute or late phase after sciatic nerve crush accelerates nerve regeneration. Neural Plast 2011; 2011:783901. [PMID: 21876821 PMCID: PMC3159303 DOI: 10.1155/2011/783901] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Revised: 03/06/2011] [Accepted: 05/23/2011] [Indexed: 12/30/2022] Open
Abstract
There is no consensus about the best time to start exercise after peripheral nerve injury. We evaluated the morphological and functional characteristics of the sciatic nerves of rats that began to swim immediately after crush nerve injury (CS1), those that began to swim 14 days after injury (CS14), injured rats not submitted to swimming (C), and uninjured rats submitted to swimming (S). After 30 days the number of axons in CS1 and CS14 was lower than in C (P < 0.01). The diameter of axons and nerve fibers was larger in CS1 (P < 0.01) and CS14 (P < 0.05) than in C, and myelin sheath thickness was lower in all crushed groups (P < 0.05). There was no functional difference between CS1 and CS14 (P > 0.05). Swimming exercise applied during the acute or late phase of nerve injury accelerated nerve regeneration and synaptic elimination after axonotmesis, suggesting that exercise may be initiated immediately after injury.
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27
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Wood MD, MacEwan MR, French AR, Moore AM, Hunter DA, Mackinnon SE, Moran DW, Borschel GH, Sakiyama-Elbert SE. Fibrin matrices with affinity-based delivery systems and neurotrophic factors promote functional nerve regeneration. Biotechnol Bioeng 2010; 106:970-9. [PMID: 20589674 DOI: 10.1002/bit.22766] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Glial-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) have both been shown to enhance peripheral nerve regeneration following injury and target different neuronal populations. The delivery of either growth factor at the site of injury may, therefore, result in quantitative differences in motor nerve regeneration and functional recovery. In this study we evaluated the effect of affinity-based delivery of GDNF or NGF from fibrin-filled nerve guidance conduits (NGCs) on motor nerve regeneration and functional recovery in a 13 mm rat sciatic nerve defect. Seven experimental groups were evaluated consisting of GDNF or NGF and the affinity-based delivery system (DS) within NGCs, control groups excluding the DS and/or growth factor, and nerve isografts. Groups with growth factor in the conduit demonstrated equivalent or superior performance in behavioral tests and relative muscle mass measurements compared to isografts at 12 weeks. Additionally, groups with GDNF demonstrated greater specific twitch and tetanic force production in extensor digitorum longus (EDL) muscle than the isograft control, while groups with NGF produced demonstrated similar force production compared to the isograft control. Assessment of motor axon regeneration by retrograde labeling further revealed that the number of ventral horn neurons regenerating across NGCs containing GDNF and NGF DS was similar to the isograft group and these counts were greater than the groups without growth factor. Overall, the GDNF DS group demonstrated superior functional recovery and equivalent motor nerve regeneration compared to the isograft control, suggesting it has potential as a treatment for motor nerve injury.
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Affiliation(s)
- Matthew D Wood
- Department of Biomedical Engineering, Washington University, Campus Box 1097, One Brookings Drive, St. Louis, Missouri 63130, USA
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28
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Wood MD, Hunter D, Mackinnon SE, Sakiyama-Elbert SE. Heparin-binding-affinity-based delivery systems releasing nerve growth factor enhance sciatic nerve regeneration. JOURNAL OF BIOMATERIALS SCIENCE-POLYMER EDITION 2010; 21:771-87. [PMID: 20482984 DOI: 10.1163/156856209x445285] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The controlled delivery of nerve growth factor (NGF) to the peripheral nervous system has been shown to enhance nerve regeneration following injury, although the effect of release rate has not been previously studied with an affinity-based delivery system (DS). The goal of this research was to determine if the binding site affinity of the DS affected nerve regeneration in vivo using nerve guidance conduits (NGCs) in a 13-mm rat sciatic nerve defect. These DSs consisted of bi-domain peptides that varied in heparin-binding affinity, heparin and NGF, which binds to heparin with moderate affinity. Eight experimental groups were evaluated consisting of NGF with DS, control groups excluding one or more components of the DS within silicone conduits and nerve isografts. Nerves were harvested 6 weeks after treatment for analysis by histomorphometry. These DSs with NGF resulted in a higher frequency of nerve regeneration compared to control groups and were similar to the nerve isograft group in measures of nerve fiber density and percent neural tissue, but not in total nerve fiber count. In addition, these DSs with NGF contained a significantly greater percentage of larger diameter nerve fibers, suggesting more mature regenerating nerve content. While there were no differences in nerve regeneration due to varying peptide affinity with these DSs, their use with NGF enhanced peripheral nerve regeneration through a NGC across a critical nerve gap.
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Affiliation(s)
- Matthew D Wood
- Department of Biomedical Engineering, Washington University, Campus Box 1097, One Brookings Drive, St. Louis, MO 63130, USA
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Whitlock EL, Kasukurthi R, Yan Y, Tung TH, Hunter DA, Mackinnon SE. Fibrin glue mitigates the learning curve of microneurosurgical repair. Microsurgery 2010; 30:218-22. [DOI: 10.1002/micr.20754] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Wood MD, Moore AM, Hunter DA, Tuffaha S, Borschel GH, Mackinnon SE, Sakiyama-Elbert SE. Affinity-based release of glial-derived neurotrophic factor from fibrin matrices enhances sciatic nerve regeneration. Acta Biomater 2009; 5:959-68. [PMID: 19103514 PMCID: PMC2678870 DOI: 10.1016/j.actbio.2008.11.008] [Citation(s) in RCA: 128] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Revised: 10/20/2008] [Accepted: 11/19/2008] [Indexed: 12/13/2022]
Abstract
Glial-derived neurotrophic factor (GDNF) promotes both sensory and motor neuron survival. The delivery of GDNF to the peripheral nervous system has been shown to enhance regeneration following injury. In this study, we evaluated the effect of affinity-based delivery of GDNF from a fibrin matrix in a nerve guidance conduit on nerve regeneration in a 13 mm rat sciatic nerve defect. Seven experimental groups were evaluated which received GDNF or nerve growth factor (NGF) with the delivery system within the conduit, control groups excluding one or more components of the delivery system, and nerve isografts. Nerves were harvested 6 weeks after treatment for analysis by histomorphometry and electron microscopy. The use of the delivery system (DS) with either GDNF or NGF resulted in a higher frequency of nerve regeneration vs. control groups, as evidenced by a neural structure spanning the 13 mm gap. The GDNF DS and NGF DS groups were also similar to the nerve isograft group in measures of nerve fiber density, percent neural tissue and myelinated area measurements, but not in terms of total fiber counts. In addition, both groups contained a significantly greater percentage of larger diameter fibers, with GDNF DS having the largest in comparison to all groups, suggesting more mature neural content. The delivery of GDNF via the affinity-based delivery system can enhance peripheral nerve regeneration through a silicone conduit across a critical nerve gap and offers insight into potential future alternatives to the treatment of peripheral nerve injuries.
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Affiliation(s)
- Matthew D. Wood
- Department of Biomedical Engineering, Washington University, Campus Box 1097, One Brookings Drive, St. Louis, MO 63130, USA
| | - Amy M. Moore
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, Campus Box 8238, 660 South Euclid Avenue, St. Louis, MO 63110, USA
| | - Daniel A. Hunter
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, Campus Box 8238, 660 South Euclid Avenue, St. Louis, MO 63110, USA
| | - Sami Tuffaha
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, Campus Box 8238, 660 South Euclid Avenue, St. Louis, MO 63110, USA
| | - Gregory H. Borschel
- Department of Biomedical Engineering, Washington University, Campus Box 1097, One Brookings Drive, St. Louis, MO 63130, USA
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, Campus Box 8238, 660 South Euclid Avenue, St. Louis, MO 63110, USA
| | - Susan E. Mackinnon
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, Campus Box 8238, 660 South Euclid Avenue, St. Louis, MO 63110, USA
| | - Shelly E. Sakiyama-Elbert
- Department of Biomedical Engineering, Washington University, Campus Box 1097, One Brookings Drive, St. Louis, MO 63130, USA
- Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, Campus Box 8238, 660 South Euclid Avenue, St. Louis, MO 63110, USA
- Center for Materials Innovation, Washington University, Campus Box 1105, One Brookings Drive, St. Louis, MO 63130, USA
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Patel M, Vandevord PJ, Matthew HW, De Silva S, Bin Wu, Wooley PH. Collagen—Chitosan Nerve Guides for Peripheral Nerve Repair: A Histomorphometric Study. J Biomater Appl 2008; 23:101-21. [DOI: 10.1177/0885328207084521] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Currently a wide variety of polymer materials are being applied to fabricate nerve guide tubes to repair injured peripheral nerves. In this study we have examined whether collagen—chitosan nerve guides promotes nerve repair compared to chitosan nerve guides using histological analysis. Results indicates that the enclosed structure of the nerve guide both promotes and supports axonal sprouting. Collagen—chitosan guides improved axonal maturation measured by a significant increase in axon diameter and axon area. These findings indicate that the collagen—chitosan nerve guides can be applied to repair severed peripheral nerve ends.
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Affiliation(s)
- Minal Patel
- Department of Biomedical Engineering, Wayne State University 818 W. Hancock St, Detroit, MI, 48201, USA, Department of Orthopaedic Surgery, University Health Center St. Antoine St, Detroit, MI, 48201, USA
| | - Pamela J. Vandevord
- Department of Biomedical Engineering, Wayne State University 818 W. Hancock St, Detroit, MI, 48201, USA
| | - Howard W. Matthew
- Department of Biomedical Engineering, Wayne State University 818 W. Hancock St, Detroit, MI, 48201, USA, Department of Chemical Engineering and Material Science Wayne State University, 5050 Anthony Wayne Dr., Detroit, MI, 48202, USA
| | - Stephen De Silva
- Department of Orthopaedic Surgery, University Health Center St. Antoine St, Detroit, MI, 48201, USA
| | - Bin Wu
- Department of Orthopaedic Surgery, University Health Center St. Antoine St, Detroit, MI, 48201, USA
| | - Paul H. Wooley
- Department of Biomedical Engineering, Wayne State University 818 W. Hancock St, Detroit, MI, 48201, USA, , Department of Orthopaedic Surgery, University Health Center St. Antoine St, Detroit, MI, 48201, USA
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Lang EM, Schlegel N, Reiners K, Hofmann GO, Sendtner M, Asan E. Single-Dose Application of CNTF and BDNF Improves Remyelination of Regenerating Nerve Fibers after C7 Ventral Root Avulsion and Replantation. J Neurotrauma 2008; 25:384-400. [DOI: 10.1089/neu.2007.0396] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Affiliation(s)
- Eva M. Lang
- Department of Plastic and Hand Surgery, Albert Ludwigs University, Freiburg, Germany
| | - Nicholas Schlegel
- Institute of Anatomy and Cell Biology, University of Wuerzburg, Wuerzburg, Germany
| | - Karlheinz Reiners
- Department of Neurology, University of Wuerzburg, Wuerzburg, Germany
| | - Gunther O. Hofmann
- Clinic of Trauma Surgery, Friedrich Schiller University, Jena, and BG-TraumaCenter, Halle, Germany
| | - Michael Sendtner
- Institute of Clinical Neurobiology, University of Wuerzburg, Wuerzburg, Germany
| | - Esther Asan
- Institute of Anatomy and Cell Biology, University of Wuerzburg, Wuerzburg, Germany
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Tolwani RJ, Cosgaya JM, Varma S, Jacob R, Kuo LE, Shooter EM. BDNF overexpression produces a long-term increase in myelin formation in the peripheral nervous system. J Neurosci Res 2004; 77:662-9. [PMID: 15352212 DOI: 10.1002/jnr.20181] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The neurotrophin brain-derived neurotrophic factor (BDNF) is an endogenous regulator of the myelination process during development in the peripheral nervous system. Enhancement of myelin formation by BDNF is mediated by the neurotrophin receptor p75(NTR). Although this neurotrophin is a positive modulator of myelination during early development, the final effects of BDNF on myelin sheaths after active myelination is completed are largely unknown. Using BDNF transgenic mice, we examined the long-term effects of BDNF on myelination of the peripheral nervous system in vivo. Elevation of BDNF levels in the transgenic mice produced an increase in both the rate and extent of the myelination process. BDNF enhanced and accelerated myelin formation during early development and this increase in myelin content and thickness was maintained in adulthood. Besides enhanced myelination, BDNF also influenced axon caliber size but to a lesser extent. This lagging increase in axon caliber compared to myelin suggests that the axon size is not the only determinant of myelin thickness.
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Affiliation(s)
- Ravi J Tolwani
- Department of Comparative Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.
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Chan JR, Watkins TA, Cosgaya JM, Zhang C, Chen L, Reichardt LF, Shooter EM, Barres BA. NGF controls axonal receptivity to myelination by Schwann cells or oligodendrocytes. Neuron 2004; 43:183-91. [PMID: 15260955 PMCID: PMC2758239 DOI: 10.1016/j.neuron.2004.06.024] [Citation(s) in RCA: 235] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2004] [Revised: 05/19/2004] [Accepted: 06/16/2004] [Indexed: 10/26/2022]
Abstract
Axons dictate whether or not they will become myelinated in both the central and peripheral nervous systems by providing signals that direct the development of myelinating glia. Here we identify the neurotrophin nerve growth factor (NGF) as a potent regulator of the axonal signals that control myelination of TrkA-expressing dorsal root ganglion neurons (DRGs). Unexpectedly, these NGF-regulated axonal signals have opposite effects on peripheral and central myelination, promoting myelination by Schwann cells but reducing myelination by oligodendrocytes. These findings indicate a novel role for growth factors in regulating the receptivity of axons to myelination and reveal that different axonal signals control central and peripheral myelination.
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Affiliation(s)
- Jonah R. Chan
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
| | - Trent A. Watkins
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
- Correspondence:
| | - José M. Cosgaya
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
| | - ChunZhao Zhang
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
| | - Lian Chen
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
| | - Louis F. Reichardt
- Department of Physiology, University of California, San Francisco, San Francisco, California 94143
| | - Eric M. Shooter
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
| | - Ben A. Barres
- Department of Neurobiology, Stanford University School of Medicine, Fairchild Science Building D235, Stanford, California 94305
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