Antisense Oligonucleotide-Mediated Removal of the Polyglutamine Repeat in Spinocerebellar Ataxia Type 3 Mice.

Lodewijk J.A Toonen,Willeke M.C Van Roon-Mom,Frank Rigo,Haico Van Attikum

doi:10.1016/j.omtn.2017.06.019

Lodewijk J.A Toonen, Willeke M.C Van Roon-Mom + Show 2 more

Open Access

https://doi.org/10.1016/j.omtn.2017.06.019

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Abstract

Spinocerebellar ataxia type 3 (SCA3) is a currently incurable neurodegenerative disorder caused by a CAG triplet expansion in exon 10 of the ATXN3 gene. The resultant expanded polyglutamine stretch in the mutant ataxin-3 protein causes a gain of toxic function, which eventually leads to neurodegeneration. One important function of ataxin-3 is its involvement in the proteasomal protein degradation pathway, and long-term downregulation of the protein may therefore not be desirable. In the current study, we made use of antisense oligonucleotides to mask predicted exonic splicing signals, resulting in exon 10 skipping from ATXN3 pre-mRNA. This led to formation of a truncated ataxin-3 protein lacking the toxic polyglutamine expansion, but retaining its ubiquitin binding and cleavage function. Repeated intracerebroventricular injections of the antisense oligonucleotides in a SCA3 mouse model led to exon skipping and formation of the modified ataxin-3 protein throughout the mouse brain. Exon skipping was long lasting, with the modified protein being detectable for at least 2.5 months after antisense oligonucleotide injection. A reduction in insoluble ataxin-3 and nuclear accumulation was observed following antisense oligonucleotide treatment, indicating a beneficial effect on pathogenicity. Together, these data suggest that exon 10 skipping is a promising therapeutic approach for SCA3.

Highlights

Spinocerebellar ataxia type 3 (SCA3) is a hereditary neurodegenerative disorder characterized by ataxia, usually presenting in the third to sixth decade of life.[1]
In the case of SCA3, the CAG repeat expansion is located in exon 10 of the ATXN3 gene, encoding the ataxin-3 protein.[4]
Our therapeutic approach removes the polyQ repeat from the protein and removes the cause of SCA3

Summary

Introduction

Spinocerebellar ataxia type 3 (SCA3) is a hereditary neurodegenerative disorder characterized by ataxia, usually presenting in the third to sixth decade of life.[1]. Pathoanatomical studies of SCA3 patient brains have shown neurodegeneration in the cerebellum, thalamus, midbrain, pons, medulla, and spinal cord.[2]. SCA3 is one of nine known polyglutamine (polyQ) disorders. The causative mutation for polyQ disorders is a CAG codon repeat expansion in the coding region of a gene, which upon translation leads to an expanded glutamine amino acid stretch in the causative protein. It is thought that the polyQ expansion leads to a gain of toxic protein function.[3]. In the case of SCA3, the CAG repeat expansion is located in exon 10 of the ATXN3 gene, encoding the ataxin-3 protein.[4]. An ATXN3 CAG repeat length of 10 to 51 repeats is observed, while SCA3 patients have repeat lengths of 55 or longer.[5]

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