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Altered p53 and NOX1 activity cause bioenergetic defects in a SCA7 polyglutamine disease model
Stockholm University, Faculty of Science, Department of Neurochemistry.ORCID iD: 0000-0001-9064-5432
Stockholm University, Faculty of Science, Department of Neurochemistry.ORCID iD: 0000-0001-9834-4554
Stockholm University, Faculty of Science, Department of Neurochemistry.
Stockholm University, Faculty of Science, Department of Neurochemistry.
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Number of Authors: 6
2015 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1847, no 4-5, 418-428 p.Article in journal (Refereed) Published
Abstract [en]

Spinocerebellar ataxia type 7 (SCA7) is one of the nine neurodegenerative disorders caused by expanded polyglutamine (polyQ) domains. Common pathogenic mechanisms, including bioenergetics defects, have been suggested for these so called polyQ diseases. However, the exact molecular mechanism(s) behind the metabolic dysfunction is still unclear. In this study we identified a previously unreported mechanism, involving disruption of p53 and NADPH oxidase 1 (NOX1) activity, by which the expanded SCA7 disease protein ATXN7 causes metabolic dysregulation. The NOX1 protein is known to promote glycolytic activity, whereas the transcription factor p53 inhibits this process and instead promotes mitochondrial respiration. In a stable inducible PC12 model of SCA7, p53 and mutant ATXN7 co-aggregated and the transcriptional activity of p53 was reduced, resulting in a 50% decrease of key p53 target proteins, like AIF and TIGAR. In contrast, the expression of NOX1 was increased approximately 2 times in SCA7 cells. Together these alterations resulted in a decreased respiratory capacity, an increased reliance on glycolysis for energy production and a subsequent 20% reduction of ATP in SCA7 cells. Restoring p53 function, or suppressing NOX1 activity, both reversed the metabolic dysfunction and ameliorated mutant ATXN7 toxicity. These results hence not only enhance the understanding of the mechanisms causing metabolic dysfunction in SCA7 disease, but also identify NOX1 as a novel potential therapeutic target in SCA7 and possibly other polyQ diseases.

Place, publisher, year, edition, pages
2015. Vol. 1847, no 4-5, 418-428 p.
Keyword [en]
Neurodegeneration, NADPH oxidase, Oxidative phosphotylation, Metabolism, p53
National Category
Chemical Sciences Biological Sciences
Research subject
Neurochemistry with Molecular Neurobiology
Identifiers
URN: urn:nbn:se:su:diva-116946DOI: 10.1016/j.bbabio.2015.01.012ISI: 000351793600004PubMedID: 25647692OAI: oai:DiVA.org:su-116946DiVA: diva2:846585
Available from: 2015-08-17 Created: 2015-05-04 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Molecular mechanism(s) underlying neurodegeneration in SCA7 disease: Role of NOX enzymes and oxidative stress
Open this publication in new window or tab >>Molecular mechanism(s) underlying neurodegeneration in SCA7 disease: Role of NOX enzymes and oxidative stress
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide expansion in the SCA7 gene resulting in progressive ataxia and retinal dystrophy. SCA7 belongs to a group of neurodegenerative disorders called polyglutamine (polyQ) diseases, that share the common feature of glutamine tract expansions within otherwise unrelated proteins. Common suggested mechanisms by which polyQ expanded proteins induce toxicity include aggregation and induction of oxidative stress. 

In this work we examined the connection between oxidative stress, aggregation and toxicity in SCA7 disease. We show that expression of the SCA7 disease protein, ataxin-7 (ATXN7), results in elevated levels of ROS and oxidative stress which in turn lead to toxicity. Our results also revealed that the oxidative stress further contributes to mutant ATXN7 aggregation. Moreover, we show, for the first time, that the major source of the elevated ROS in mutant ATXN7 cells is the increased activation of NOX1 enzymes. Interestingly, our results further revealed that the increased level of NOX1 activity together with altered p53 function leads to a metabolic shift in mutant ATXN7 expressing cells. Treatments with antioxidants, a NOX1 specific inhibitor or NOX1 knock-down, all decreased the ROS level, restored the metabolic shift and ameliorated the mutant ATXN7 induced toxicity. Taken together, we conclude that mutant ATXN7 activate NOX1 enzymes which results in oxidative stress, increased mutant ATXN7 aggregation, metabolic dysfunction and toxicity. NOX1 specific inhibition could thus be a potential therapeutic strategy for SCA7.

Place, publisher, year, edition, pages
Stockholm: Department of Neurochemistry, Stockholm University, 2015. 56 p.
Keyword
neurodegeneration, oxidative stress, NOX, metabolism, p53
National Category
Chemical Sciences
Research subject
Neurochemistry with Molecular Neurobiology
Identifiers
urn:nbn:se:su:diva-119846 (URN)978-91-7649-257-4 (ISBN)
Public defence
2015-10-16, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2015-09-24 Created: 2015-08-26 Last updated: 2015-09-16Bibliographically approved
2. Studies of polyglutamine expanded Ataxin-7 toxicity
Open this publication in new window or tab >>Studies of polyglutamine expanded Ataxin-7 toxicity
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant inherited neurodegenerative disease for which there is no cure. SCA7 belongs to the group of polyglutamine disorders, which are all caused by the expansion of a polyglutamine tract in different disease proteins. Common toxic mechanisms have been proposed for polyglutamine diseases; however the exact pathological mechanism(s) are still unclear.

The aim of this thesis was to identify and characterize the molecular mechanisms by which polyglutamine expansion in the ATXN7 protein cause SCA7 and how this can be counteracted. We found that mutant ATXN7 can be degraded by the ubiquitin proteasome system (UPS) and autophagy, the two main cellular degradation pathways. However aggregation stabilized the protein against degradation. Moreover, we found that mutant ATXN7 blocked the induction of autophagy by interfering with p53 and the ULK1-ATG13-FIP200 complex. Pharmacological stimulation of autophagy ameliorated aggregation, as well as toxicity.

We also found that oxidative stress plays an important role in mutant ATXN7 toxicity and that the oxidative stress is generated by activation of NADPH oxidase 1 (NOX1) complexes. Furthermore, we showed that the increased NOX1 activity, together with polyQ expanded ATXN7 mediated disruption of the transcription factor p53, results in metabolic alterations in SCA7 cells. The expression of key p53 regulated metabolic proteins like AIF, TIGAR and GLUT1 was altered in SCA7 cells and resulted in reduced mitochondrial respiration, a higher dependence on glycolysis and reduced ATP levels.

In summary, our data indicate that mutant ATXN7 mediated dysregulation of p53, resulting in autophagic and metabolic alterations, could play a key role in SCA7 and possibly other polyglutamine diseases.

Place, publisher, year, edition, pages
Stockholm: Department of Neurochemistry, Stockholm University, 2015. 74 p.
Keyword
neurodegeneration, SCA7, protein degradation, aggregation, p53, oxidative stress, NOX
National Category
Biochemistry and Molecular Biology
Research subject
Neurochemistry with Molecular Neurobiology
Identifiers
urn:nbn:se:su:diva-121116 (URN)978-91-7649-249-9 (ISBN)
Public defence
2015-11-13, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 09:30 (English)
Opponent
Supervisors
Available from: 2015-10-22 Created: 2015-09-24 Last updated: 2015-10-09Bibliographically approved

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