title: Absence of SOD1 leads to oxidative stress in peripheral nerve and causes a progressive distal motor axonopathy.
abstract: Oxidative stress is commonly implicated in the pathogenesis of motor neuron disease. However, the cause and effect relationship between oxidative stress and motor neuron degeneration is poorly defined. We recently identified denervation at the neuromuscular junction in mice lacking the antioxidant enzyme, Cu,Zn-superoxide dismutase (SOD1) (Fischer et al., 2011). These mice show a phenotype of progressive muscle atrophy and weakness in the setting of chronic oxidative stress. Here, we investigated further the extent of motor neuron pathology in this model, and the relationship between motor pathology and oxidative stress. We report preferential denervation of fast-twitch muscles beginning between 1 and 4 months of age, with relative sparing of slow-twitch muscle. Motor axon terminals in affected muscles show widespread sprouting and formation of large axonal swellings. We confirmed, as was previously reported, that spinal motor neurons and motor and sensory nerve roots in these mice are preserved, even out to 18 months of age. We also found preservation of distal sensory fibers in the epidermis, illustrating the specificity of pathology in this model for distal motor axons. Using HPLC measurement of the glutathione redox potential, we quantified oxidative stress in peripheral nerve and muscle at the onset of denervation. SOD1 knockout tibial nerve, but not gastrocnemius muscle, showed significant oxidation of the glutathione pool, suggesting that axonal degeneration is a consequence of impaired redox homeostasis in peripheral nerve. We conclude that the SOD1 knockout mouse is a model of oxidative stress-mediated motor axonopathy. Pathology in this model primarily affects motor axon terminals at the neuromuscular junction, demonstrating the vulnerability of this synapse to oxidative injury.
authors.affiliation: Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Lindsey R
authors.initials: LR
authors.lastname: Fischer
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Li
authors.forename: Seneshaw A
authors.initials: SA
authors.lastname: Asress
authors.forename: Dean P
authors.initials: DP
authors.lastname: Jones
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Glass
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology / Q000627:therapeutic use; D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D001369:Axons / Q000473:pathology*; D001426:Bacterial Proteins / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004268:DNA-Binding Proteins / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology / Q000627:therapeutic use; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000378:metabolism; D009121:Muscle Denervation / Q000379:methods; D018482:Muscle, Skeletal / Q000503:physiopathology; D009412:Nerve Fibers / Q000473:pathology; D009469:Neuromuscular Junction / Q000503:physiopathology; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000235:genetics*; D010525:Peripheral Nerves / Q000378:metabolism*; D010523:Peripheral Nervous System Diseases / Q000473:pathology* / Q000503:physiopathology*; D017729:Presynaptic Terminals / Q000378:metabolism / Q000473:pathology; D012867:Skin / Q000294:innervation / Q000473:pathology; D013482:Superoxide Dismutase / Q000172:deficiency*; D000072105:Superoxide Dismutase-1; D043222:Ubiquitin Thiolesterase / Q000378:metabolism; D014452:Ubiquitins / Q000378:metabolism
chemical_list: C491049:Aif1 protein, mouse; D001426:Bacterial Proteins; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D016166:Free Radical Scavengers; D005904:Glial Fibrillary Acidic Protein; D008164:Luminescent Proteins; D008840:Microfilament Proteins; D014452:Ubiquitins; C054562:yellow fluorescent protein, Bacteria; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D043222:Ubiquitin Thiolesterase; C496976:Uchl1 protein, mouse; D005978:Glutathione; D019803:Glutathione Disulfide; D000111:Acetylcysteine