Ataxin-3 protein modification as a treatment strategy for spinocerebellar ataxia type 3: removal of the CAG containing exon

Abstract

Spinocerebellar ataxia type 3 is caused by a polyglutamine expansion in the ataxin-3 protein, resulting in gain of toxic function of the mutant protein. The expanded glutamine stretch in the protein is the result of a CAG triplet repeat expansion in the penultimate exon of the ATXN3 gene. Several gene silencing approaches to reduce mutant ataxin-3 toxicity in this disease aim to lower ataxin-3 protein levels, but since this protein is involved in deubiquitination and proteasomal protein degradation, its long-term silencing might not be desirable. Here, we propose a novel protein modification approach to reduce mutant ataxin-3 toxicity by removing the toxic polyglutamine repeat from the ataxin-3 protein through antisense oligonucleotide-mediated exon skipping while maintaining important wild type functions of the protein. In vitro studies showed that exon skipping did not negatively impact the ubiquitin binding capacity of ataxin-3. Our in vivo studies showed no toxic properties of the novel truncated ataxin-3 protein. These results suggest that exon skipping may be a novel therapeutic approach to reduce polyglutamine-induced toxicity in spinocerebellar ataxia type 3.

Keywords: AON; ATXN3; Ataxin-3; CAG repeat; DMD; Duchenne muscular dystrophy; Exon skipping; ICV; MJD; Machado–Joseph disease; NES; NLS; PolyQ; Polyglutamine disorder; Polyglutamine repeat; RNA interference; RNAi; SCA3; SNP; Spinocerebellar ataxia type 3; UIMs; VCP; antisense oligonucleotide; ataxin-3; intra-cerebral ventricular; nuclear export signal; nuclear localization signal; polyglutamine; single nucleotide polymorphism; spinocerebellar ataxia type 3; ubiquitin interacting motifs; valosin containing protein.