Molecular mechanism(s) underlying neurodegeneration in SCA7 disease : Role of NOX enzymes and oxidative stress

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could thus be a potential therapeutic strategy for SCA7.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.