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Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients.

ABSTRACT: Mutations in superoxide dismutase-1 (SOD1) are a common known cause of amyotrophic lateral sclerosis (ALS). The neurotoxicity of mutant SOD1s is most likely caused by misfolded molecular species, but disease pathogenesis is still not understood. Proposed mechanisms include impaired mitochondrial function, induction of endoplasmic reticulum stress, reduction in the activities of the proteasome and autophagy, and the formation of neurotoxic aggregates. Here we examined whether perturbations in these cellular pathways in turn influence levels of misfolded SOD1 species, potentially amplifying neurotoxicity. For the study we used fibroblasts, which express SOD1 at physiological levels under regulation of the native promoter. The cells were derived from ALS patients expressing 9 different SOD1 mutants of widely variable molecular characteristics, as well as from patients carrying the GGGGCC-repeat-expansion in C9orf72 and from non-disease controls. A specific ELISA was used to quantify soluble, misfolded SOD1, and aggregated SOD1 was analysed by western blotting. Misfolded SOD1 was detected in all lines. Levels were found to be much lower in non-disease control and the non-SOD1 C9orf72 ALS lines. This enabled us to validate patient fibroblasts for use in subsequent perturbation studies. Mitochondrial inhibition, endoplasmic reticulum stress or autophagy inhibition did not affect soluble misfolded SOD1 and in most cases, detergent-resistant SOD1 aggregates were not detected. However, proteasome inhibition led to uniformly large increases in misfolded SOD1 levels in all cell lines and an increase in SOD1 aggregation in some. Thus the ubiquitin-proteasome pathway is a principal determinant of misfolded SOD1 levels in cells derived both from patients and controls and a decline in activity with aging could be one of the factors behind the mid-to late-life onset of inherited ALS.

SUBMITTER: Keskin I

PROVIDER: S-EPMC4769150 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients.

Keskin Isil I Forsgren Elin E Lange Dale J DJ Weber Markus M Birve Anna A Synofzik Matthis M Gilthorpe Jonathan D JD Andersen Peter M PM Marklund Stefan L SL

PloS one 20160226 2

Mutations in superoxide dismutase-1 (SOD1) are a common known cause of amyotrophic lateral sclerosis (ALS). The neurotoxicity of mutant SOD1s is most likely caused by misfolded molecular species, but disease pathogenesis is still not understood. Proposed mechanisms include impaired mitochondrial function, induction of endoplasmic reticulum stress, reduction in the activities of the proteasome and autophagy, and the formation of neurotoxic aggregates. Here we examined whether perturbations in the ...[more]

PMID: 26919046

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Project description:BackgroundMutations in superoxide dismutase 1 (SOD1), which are one cause of familial amyotrophic lateral sclerosis (fALS), induce misfolding and aggregation of the protein. Misfolding can be detected by the binding of antibodies raised against peptide epitopes that are normally buried in the native conformation, shifts in solubility in non-ionic detergents, and the formation of macromolecular inclusions. In the present study, we investigate the relationship between detergent-insoluble and sedimentable forms of mutant SOD1, forms of mutant SOD1 with aberrantly accessible epitopes, and mutant protein in inclusions with the goal of defining the spectrum of misfolded states that mutant SOD1 can adopt.ResultsUsing combined approaches in cultured cell models, we demonstrate that a substantial fraction of mutant SOD1 adopts a non-native conformation that remains soluble and freely mobile. We also show that mutant SOD1 can produce multimeric assemblies of which some are insoluble in detergent and large enough to sediment by ultracentrifugation and some are large enough to detect visually. Three conformationally restricted antibodies were found to be useful in discriminating mal-folded forms of mutant SOD1. An antibody termed C4F6 displays properties consistent with recognition of soluble, freely mobile, mal-folded mutant SOD1. An antibody termed SEDI, which recognizes C-terminal residues, detects larger inclusion structures as well as soluble misfolded entities. An antibody termed hSOD1, which recognizes aa 24-36, detects an epitope shared by soluble non-natively folded WT and mutant SOD1. This epitope becomes inaccessible in aggregates of mutant SOD1.ConclusionsOur studies demonstrate how different methods of detecting misfolding and aggregation of mutant SOD1 reveal different forms of aberrantly folded protein. Immunological and biochemical methods can be used in combination to detect soluble and insoluble misfolded forms of mutant SOD1. Our findings support the view that mutant SOD1 can adopt multiple misfolded conformations with the potential that different structural variants mediate different aspects of fALS.

Dataset Information

Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients.

Publications

Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients.

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