Article

Disulphide-reduced superoxide dismutase-1 in CNS of transgenic amyotrophic lateral sclerosis models

Department of Medical Biosciences, Umeå University, Umeå, Sweden.
Brain (Impact Factor: 9.2). 03/2006; 129(Pt 2):451-64. DOI: 10.1093/brain/awh704
Source: PubMed

ABSTRACT

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease afflicting the voluntary motor system. More than 100 different mutations in the ubiquitously expressed enzyme superoxide dismutase-1 (SOD1) have been associated with the disease. To search for the nature of the cytotoxicity of mutant SOD1s, amounts, enzymic activities and structural properties of the protein as well as the CNS histopathology were examined in multiple transgenic murine models. In order to generate the ALS phenotype within the short lifespan of the mouse, more than 20-fold increased rates of synthesis of mutant SOD1s appear to be required. The organs of transgenic mice expressing human wild-type SOD1 or either of the G93A and D90A mutant proteins showed high steady-state protein levels. The major proportion of these SOD1s in the CNS were inactive due to insufficient Cu charging and all contained subfractions with a reduced C57-C146 intrasubunit disulphide bond. Both G85R and the truncated G127insTGGG mutant showed low steady-state protein levels, lacked enzyme activity and had no C57-C146 disulphide bond. These mutants were also enriched in the CNS relative to other organs, suggesting inefficient recognition and degradation of misfolded disulphide-reduced SOD1 in susceptible tissues. In end-stage disease, despite 35-fold differences in levels of mutant SOD1s, similar amounts of detergent-resistant aggregates accumulated in the spinal cord. Small granular as well as larger more diffuse human SOD1 (hSOD1)-inclusions developed in all strains, the latter more pronounced in those with high hSOD1 levels. Widespread vacuolizations were seen in the strains with high levels of hSOD1 but not those with low, suggesting these alterations to be artefacts related to high hSOD1 levels and not to the ALS-causing cytotoxicity. The findings suggest that the motoneuron degeneration could be due to long-term exposure to misfolded aggregation-prone disulphide-reduced SOD1, which constitutes minute subfractions of the stable mutants and larger proportions of the unstable mutants.

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Available from: Karin Sixtensdotter Graffmo, Mar 22, 2014
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    • "The model is aggressive, with early onset of symptoms and a short lifespan. The concentration of mutant hSOD1 is 17-fold higher than that of the endogenous murine SOD1, causing overexpression artifacts[4,29]. Moreover, over 95 % of the protein is natively folded, making analysis of misfolded hSOD1 conformers complicated[54,55]. "
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    • "Only 20% of the fALS cases are attributed to SOD1 mutations and although treatment that benefit the mSOD1 have been mostly unsuccessful when tested in humans (Rothstein, 2009), these animal models have been vital in identifying several ALS-related pathogenic mechanisms. More than 10 different mSOD1 murine models have been created (Bruijn et al., 1997; Jonsson et al., 2006; Nicholson et al., 2000). Within them the transgenic line harboring the Gly93→Ala amino acid substitution (SOD1G93A) has been used most extensively to study the ALS pathophysiology (Gurney et al., 1994), followed by the SOD1G37R, SOD1G85R and SOD1G86R models. "
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    • "Also recently, even in the presence of the disulfide bond, destabilization of apo-SOD1 was found to allow the disulfide bond to be shuffled among four Cys residues, resulting in the formation of disulfide cross-linked oligomers in vitro [9]. While disulfide cross-linking of mutant SOD1 would be a secondary event for formation of the insoluble aggregates [10], abnormal accumulation of disulfide-reduced SOD1 was observed in fALS model mice [11]. Despite this, a C57S/C146S double mutation, by which the conserved disulfide bond cannot form, did not affect toxicity of mutant SOD1 toward cultured cells [12] [13]. "
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