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Anti-GD1a antibody targeted disruption of the node of Ranvier in a mouse model of acute motor axonal neuropathy

McGonigal, Rhona (2009) Anti-GD1a antibody targeted disruption of the node of Ranvier in a mouse model of acute motor axonal neuropathy. PhD thesis, University of Glasgow.

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Abstract

Guillain-Barré syndrome (GBS) is a peripheral neuropathy characterised by acute flaccid paralysis. The axonal variant is associated with anti-GD1a ganglioside antibody-dependent, complement-mediated injury to the peripheral axon with conduction block. The blood-nerve barrier (BNB) relatively protects axons from factors in the extra-neural environment; however, it does not extend over the neuromuscular junction, leaving this terminal portion of the axon unprotected. It is here that susceptibility to antibody attack in a mouse model of GBS has previously been demonstrated. It was the aim of this thesis to determine to what extent more proximal portions of the distal axon are at risk from circulating antibody and what exogenous protection can be provided therapeutically. GD1a is expressed at the nodes of Ranvier (NoR) of intramuscular axons. To investigate the injury caused by anti-GD1a antibodies in relation to BNB permeability, anti-GD1a antibodies were applied to mice genetically engineered both to over-express GD1a and to express cyan fluorescent protein (CFP) in the cytoplasm of axons. Endogenous fluorescence allowed identification of intramuscular nerve bundles and their terminal branches, which were categorized depending on bundle size. Within these categories, IgG and the final product of the complement pathway (membrane attack complex, MAC) deposition were quantified after an acute injury, alongside the deleterious effects on NoR protein’s. Nerve conduction studies were also performed to better elucidate the pathological pathway. IgG and MAC were localized in a gradient-dependent manner, with significantly more deposition at NoR as the bundles progressively branch to a single terminating fibre. Furthermore, MAC deposition was associated with the loss or disruption to immunostaining for nodal protein’s including voltage gated sodium channel and ankyrin G. This is indicative of targeted injury to this region of the distal axon in an acute model. The loss of nodal protein staining is associated with the activation of complement and the Ca2+-dependent protease calpain as determined by the protection of staining by the complement inhibitor Eculizumab and the calpain inhibitor AK295. A similar disruption to nodal protein staining is also shown at the proximal NoR of the desheathed phrenic nerve. Extracellular nerve recordings demonstrate a detrimental effect on function as there is a decrease in the peak of the compound nerve action potential over time, which can be associated with Nav channel staining loss. This study is suggestive of a resilient proximal barrier that becomes more permeable towards the nerve terminal. Therefore, it is not only the axon at the terminal that can be a target of injury, but also the distal axons at their nodes of Ranvier, resulting in disruption at this site. Prevention of staining loss by Eculizumab and AK295 exemplify the route of injury and identify a potential point of therapeutic intervention in human disease.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: GD1a ganglioside, node of Ranvier, complement, calpain, acute motor axonal neuropathy
Subjects: Q Science > Q Science (General)
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Supervisor's Name: Willison, Professor H.J.
Date of Award: 2009
Depositing User: Rhona McGonigal
Unique ID: glathesis:2009-1453
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 18 Mar 2010
Last Modified: 10 Dec 2012 13:40
URI: http://theses.gla.ac.uk/id/eprint/1453

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