Expression Profiling of brain samples from wt and SCA3 tg animals after CCI-779 and placebo treatment

Spinocerebellar ataxia type 3 is a neurodegenerative disorder caused by the expansion of the polyglutamine repeat region within the ataxin-3 protein. The mutant protein forms intracellular aggregates in the brain. However, the cellular mechanisms causing toxicity are still poorly understood and there are currently no effective treatments. In this study we show that administration of a rapamycin ester, CCI-779, improves motor performance in a transgenic mouse model of SCA3. CCI-779 inhibits mammalian target of rapamycin (mTOR) and hence upregulates protein degradation by autophagy. CCI-779 reduces the number of aggregates seen in the brains of transgenic mice and decreases levels of cytosolic soluble mutant ataxin-3, while endogenous wild-type protein levels remain unaffected. CCI-779 is designed for long-term use in patients and therefore represents a possible therapeutic strategy for the treatment of SCA3. Using this disease model and treatment paradigm we employed a microarray approach to investigate transcriptional changes that might be important in the pathogenesis of SCA3. This approach identified Usp15, which showed expression changes at both the mRNA and protein level. Usp15 levels were also changed in mice expressing another mutant polyglutamine protein, huntingtin. In total we identified 16 transcripts that were decreased in transgenic ataxin-3 mice that were normalised following CCI-779 treatment, as the number of transcripts changed was low and the magnitude of these changes was small we suggest that transcriptional dysregulation may not be an important step in the primary pathogenesis of SCA3.

19