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SOD, ORF and ALS: On the role of SOD1 and C9ORF72 in the pathogenesis of ALS
Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Clinical Neuroscience.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amyotrophic lateral sclerosis (ALS) is characterized by adult-onset degeneration of upper and lower motor neurons. Symptoms begin focally in one muscle and then spread contiguously, resulting in progressive paralysis and death from respiratory failure. Hexanucleotide repeat expansion in C9ORF72 is the most common genetic cause, however, mutations in SOD1 were the first identified and are found in 1-9% of patients. Misfolded SOD1 aggregates in the CNS are hallmarks of ALS associated with SOD1 mutations. However, accumulation of misfolded or aggregated SOD1 protein has also been reported in sporadic and familial ALS without SOD1 mutations, suggesting that wild-type SOD1 could play a role in ALS pathology in general.

The aims of this thesis are: 1) To describe the resulting disease phenotype and specific characteristics of the SOD1 protein carrying the stable disease- associated mutation L117V. 2) To set up cell-based in vitro models to study the mechanisms of SOD1 misfolding and aggregation under physiologically relevant expression levels. 3) To compare SOD1 activity in patient-derived samples and screen for underlying causes of deviant SOD1 activities in individuals lacking SOD1 mutations.

1) We identified a novel L117V SOD1 mutant in two families of Syrian origin that co-segregated with the disease. This mutation was associated with slow disease progression, reduced penetrance and a uniform phenotype. The L117V mutant protein was indistinguishable from wild-type SOD1 in terms of stability, dismutation activity and misfolding in patient-derived cell lines.

2) We established patient-derived fibroblast and iPSC-MN lines expressing mutant SOD1 at physiological levels as in vitro models to study misfolding and aggregation of SOD1. We investigated the effects of several cellular pathway disturbances on SOD1 misfolding. Misfolded SOD1 was increased by inhibition of the ubiquitin-proteasome pathway in fibroblasts derived from both patients and controls. An age-related decline in proteasome activity could contribute to the late onset of ALS.

Next, we studied the effects of low oxygen tension on misfolding and aggregation of SOD1 in patient-derived cells. Low O2 tensions were found to markedly increase C57-C146 disulphide reduction, misfolding and aggregation of SOD1. Importantly, the largest effects were detected in iPSC-MNs. This suggests that motor neurons are specifically vulnerable to misfolding and aggregation of SOD1 under low O2 tension.

3) We compared the enzymatic activity of SOD1 in blood samples from a large number of ALS patients and controls. We screened for potential underlying causes of deviant SOD1 activities in individuals lacking SOD1 mutations. No aberrations in copy number, other large structural changes in introns and exons or intronic mutations in the 30-50 bp flanking the exons were found in the 142 outliers, with either very low or very high SOD1 dismutation activities. However, hemoglobinopathies, including thalassemias and iron deficiency anemia, were associated with high SOD1/mg Hb ratios. Erythrocytes from patients with destabilizing SOD1 mutations showed half the normal activity. There were no significant differences in SOD1 activity between control individuals and ALS patients without a coding SOD1 mutation, or carriers of TBK1 mutations or the hexanucleotide repeat expansion in C9ORF72. Our result suggests that SOD1 enzymatic activity is not associated with the disease in non-SOD1 mutation ALS.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2016. , 89 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1829
Keyword [en]
ALS, SOD1, Misfolded species
National Category
Biochemistry and Molecular Biology Neurology
Identifiers
URN: urn:nbn:se:umu:diva-124917ISBN: 978-91-7601-531-5OAI: oai:DiVA.org:umu-124917DiVA: diva2:956775
Public defence
2016-09-23, Föreläsningssal A, Unod T 9, Norrlands universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2016-09-02 Created: 2016-08-30 Last updated: 2016-09-01Bibliographically approved
List of papers
1. Mutant superoxide dismutase-1 indistinguishable from wild-type causes ALS
Open this publication in new window or tab >>Mutant superoxide dismutase-1 indistinguishable from wild-type causes ALS
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2012 (English)In: Human Molecular Genetics, ISSN 0964-6906, E-ISSN 1460-2083, Vol. 21, no 16, 3568-3574 p.Article in journal (Refereed) Published
Abstract [en]

A reason for screening amyotrophic lateral sclerosis (ALS) patients for mutations in the superoxide dismutase-1 (SOD1) gene is the opportunity to find novel mutations with properties that can give information on pathogenesis. A novel c.352CG (L117V) SOD1 mutation was found in two Syrian ALS families living in Europe. The disease showed unusually low penetrance and slow progression. In erythrocytes, the total SOD1 activity, as well as specific activity of the mutant protein, was equal in carriers of the mutation and family controls lacking SOD1 mutations. The structural stabilities of the L117V mutant and wild-type SOD1 under denaturing conditions were likewise equal, but considerably lower than that of murine SOD1. As analyzed with an ELISA specific for misfolded SOD1 species, no differences were found in the content of misfolded SOD1 protein between extracts of fibroblasts from wild-type controls and from an L117V patient. In contrast, elevated levels of misfolded SOD1 protein were found in fibroblasts from ALS patients carrying seven other mutations in the SOD1 gene. We conclude that mutations in SOD1 that result in a fully stable protein are associated with low disease penetrance for ALS and may be found in cases of apparently sporadic ALS. Wild-type human SOD1 is moderately stable, and was found here to be within the stability range of ALS-causing SOD1 variants, lending support to the hypothesis that wild-type SOD1 could be more generally involved in ALS pathogenesis.

National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-59717 (URN)10.1093/hmg/dds188 (DOI)000306964700005 ()
External cooperation:
Available from: 2012-10-26 Created: 2012-09-25 Last updated: 2016-09-01Bibliographically approved
2. Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients
Open this publication in new window or tab >>Effects of Cellular Pathway Disturbances on Misfolded Superoxide Dismutase-1 in Fibroblasts Derived from ALS Patients
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2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 2, e0150133Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Superoxides, Amyotrophic Lateral Sclerosis
National Category
Neurosciences
Identifiers
urn:nbn:se:umu:diva-118791 (URN)10.1371/journal.pone.0150133 (DOI)000371274400090 ()26919046 (PubMedID)
Available from: 2016-04-08 Created: 2016-04-04 Last updated: 2016-08-31Bibliographically approved
3. Low oxygen tension induces misfolding and aggregation of superoxide dismutase in ALS patient-derived motor neurons
Open this publication in new window or tab >>Low oxygen tension induces misfolding and aggregation of superoxide dismutase in ALS patient-derived motor neurons
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(English)Manuscript (preprint) (Other academic)
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-124954 (URN)
External cooperation:
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2016-09-01Bibliographically approved
4. Comprehensive analysis to explain reduced or increased SOD1 enzymatic activity in erythrocytes in ALS patients and their relatives
Open this publication in new window or tab >>Comprehensive analysis to explain reduced or increased SOD1 enzymatic activity in erythrocytes in ALS patients and their relatives
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Our objective was to in blood samples from 3723 individuals including ALS patients without a coding SOD1 mutation and 372 control individuals characterize stabilities of mutant SOD1s, compare SOD1 enzymatic activities between patients with different genetic causes of ALS, and search for underlying causes of deviant SOD1 activities in individuals lacking SOD1 mutations. Erythrocyte SOD1 enzymatic activities normalized to hemoglobin content were determined. Coding SOD1 sequences were analyzed by Sanger sequencing, copy number variations by fragment length analysis and by TaqMan Assay. Hemoglobin disorders were searched for. Of the 46 SOD1 mutations found, ¾ caused severe destabilization of the mutant protein but in ¼ SOD1 was essentially physically stable. Mutations producing structural changes all caused halved SOD activities. There were no differences in SOD1 activities between controls and patients without any detected SOD1 mutations or patients with C9ORF72HRE or TBK1 mutations. In the low and high SOD1 activity groups no deviations were found in exon copy numbers and intron gross structures. Also, no uncommon variants in exon-flanking sequences were detected. Thalassemias and iron deficiency anemia were associated with increased SOD1 activity/hemoglobin ratios. In conclusion, adjunct erythrocyte SOD activity analysis is of value to signal the presence of exon and splice-site-intron mutations that influence the SOD1 structure.

National Category
Biochemistry and Molecular Biology Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-124955 (URN)
External cooperation:
Available from: 2016-08-31 Created: 2016-08-31 Last updated: 2016-09-01Bibliographically approved

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