title: Direct and indirect mechanisms for wild-type SOD1 to enhance the toxicity of mutant SOD1 in bigenic transgenic mice.
abstract: Co-expression of wild-type human superoxide dismutase 1 (WT-hSOD1) with ALS mutant hSOD1 accelerates disease onset relative to mice expressing only mutant protein. Here, we analyzed the effect of co-expressed WT-hSOD1 in two established mutant mouse models (L126Z and G37R), and a new model that expresses the first 102 amino acids of SOD1 with mutations at histidines 46, 48 and 63 to eliminate Cu binding (Cu-V103Z). A subset of Cu-V103Z mice developed paralysis between 500 and 730 days. Similar to mice expressing L126Z-SOD1, the spinal cords of this new model showed SOD1 immunoreactive fibrillar inclusions. Co-expression of WT-hSOD1 with Cu-V103Z SOD1 moderately accelerated the age to paralysis, similar in magnitude to WT/L126Z mice. In either combination of these bigenic mice, the severity of fibrillar inclusion pathology was diminished and unreactive to antibodies specific for the C terminus of WT protein. Co-expression of WT-hSOD1 fused to yellow fluorescent protein (WT-hSOD1:YFP) with G37R-hSOD1 produced earlier disease, and spinal cords of paralyzed bigenic mice showed YFP fluorescent inclusion-like structures. In bigenic L126Z/WT-hSOD1:YFP mice, disease was not accelerated and WT-hSOD1:YFP remained diffusely distributed. A combination of split luciferase complementation assays and affinity capture-binding assays demonstrated that soluble G37R-hSOD1 efficiently and tightly bound soluble WT-hSOD1, whereas soluble forms of the Cu-V103Z and L126Z variants demonstrated low affinity. These data indicate that WT-hSOD1 may indirectly augment the toxicity of mutant protein by competing for protective factors, but disease onset seems to be most accelerated when WT-hSOD1 interacts with mutant SOD1 and becomes misfolded.
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease, SantaFe HealthCare Alzheimer's Disease Research Center and.
authors.forename: Guilian
authors.initials: G
authors.lastname: Xu
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease.
authors.forename: Jacob I
authors.initials: JI
authors.lastname: Ayers
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease.
authors.forename: Brittany L
authors.initials: BL
authors.lastname: Roberts
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease, SantaFe HealthCare Alzheimer's Disease Research Center and.
authors.forename: Hilda
authors.initials: H
authors.lastname: Brown
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease, SantaFe HealthCare Alzheimer's Disease Research Center and.
authors.forename: Susan
authors.initials: S
authors.lastname: Fromholt
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease.
authors.forename: Cameron
authors.initials: C
authors.lastname: Green
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease, SantaFe HealthCare Alzheimer's Disease Research Center and McKnight Brain Institute, University of Florida, PO Box 100159 Center Drive, Gainesville, FL 32610, USA drb1@ufl.edu borchelt@mbi.ufl.edu.
authors.forename: David R
authors.initials: DR
authors.lastname: Borchelt
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism / Q000401:mortality; D000818:Animals; D002460:Cell Line; D004195:Disease Models, Animal; D005260:Female; D015870:Gene Expression; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D055503:Protein Multimerization; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000072105:Superoxide Dismutase-1
chemical_list: D050505:Mutant Proteins; D012333:RNA, Messenger; C000606290:SOD1 protein, human; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1