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Updated: Jun 27, 2025
A Simple Composite Phenotype Scoring System for Evaluating Mouse Models of Cerebellar Ataxia
Published on: May 21, 2010
AAV-Mediated CAG-Targeting Selectively Reduces Polyglutamine-Expanded Protein and Attenuates Disease Phenotypes in a
Anna Niewiadomska-Cimicka1, Lorraine Fievet1, Magdalena Surdyka2
1Institute of Genetics and Molecular and Cellular Biology, INSERM U1258, CNRS UMR7104, University of Strasbourg, 67404 Illkirch, France.
Abstract:
Polyglutamine (polyQ)-encoding CAG repeat expansions represent a common disease-causing mutation responsible for several dominant spinocerebellar ataxias (SCAs). PolyQ-expanded SCA proteins are toxic for cerebellar neurons, with Purkinje cells (PCs) being the most vulnerable. RNA interference (RNAi) reagents targeting transcripts with expanded CAG reduce the level of various mutant SCA proteins in an allele-selective manner in vitro and represent promising universal tools for treating multiple CAG/polyQ SCAs. However, it remains unclear whether the therapeutic targeting of CAG expansion can be achieved in vivo and if it can ameliorate cerebellar functions. Here, using a mouse model of SCA7 expressing a mutant Atxn7 allele with 140 CAGs, we examined the efficacy of short hairpin RNAs (shRNAs) targeting CAG repeats expressed from PHP.eB adeno-associated virus vectors (AAVs), which were introduced into the brain via intravascular injection. We demonstrated that shRNAs carrying various mismatches with the CAG target sequence reduced the level of polyQ-expanded ATXN7 in the cerebellum, albeit with varying degrees of allele selectivity and safety profile. An shRNA named A4 potently reduced the level of polyQ-expanded ATXN7, with no effect on normal ATXN7 levels and no adverse side effects. Furthermore, A4 shRNA treatment improved a range of motor and behavioral parameters 23 weeks after AAV injection and attenuated the disease burden of PCs by preventing the downregulation of several PC-type-specific genes. Our results show the feasibility of the selective targeting of CAG expansion in the cerebellum using a blood-brain barrier-permeable vector to attenuate the disease phenotype in an SCA mouse model. Our study represents a significant advancement in developing CAG-targeting strategies as a potential therapy for SCA7 and possibly other CAG/polyQ SCAs.
Insights
This study shows that targeting expanded CAG repeats in the brain using shRNAs delivered by AAV vectors can effectively reduce toxic proteins and improve motor function in a mouse model of spinocerebellar ataxia type 7 (SCA7). This offers a promising therapeutic strategy for SCA7 and other polyglutamine diseases.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Dominant spinocerebellar ataxias (SCAs) are caused by polyglutamine (polyQ)-encoding CAG repeat expansions, leading to toxic mutant SCA proteins that damage cerebellar neurons, particularly Purkinje cells (PCs).
- RNA interference (RNAi) using short hairpin RNAs (shRNAs) has shown potential in vitro for allele-selectively reducing mutant SCA proteins, but in vivo efficacy for treating SCAs remains largely unproven.
- Developing effective in vivo strategies is crucial for treating SCAs, as current treatments are limited and the disease burden on cerebellar function is significant.
Purpose of the Study:
- To investigate the in vivo efficacy of shRNAs targeting CAG repeats delivered via blood-brain barrier-permeable adeno-associated virus (AAV) vectors in a mouse model of SCA7.
- To determine if this approach can selectively reduce polyglutamine-expanded ATXN7 protein levels and ameliorate cerebellar dysfunction and PC degeneration.
- To assess the potential of this strategy as a universal therapeutic tool for various CAG/polyQ SCAs.
Main Methods:
- Utilized a mouse model of SCA7 expressing a mutant Atxn7 allele with 140 CAG repeats.
- Administered PHP.eB AAV vectors encoding shRNAs targeting CAG repeats via intravascular injection into the brain.
- Assessed the reduction of polyQ-expanded ATXN7, allele selectivity, safety profiles, motor and behavioral improvements, and PC gene expression changes.
Main Results:
- shRNAs targeting CAG repeats reduced polyQ-expanded ATXN7 levels in the cerebellum with varying degrees of selectivity and safety.
- A specific shRNA, A4, potently reduced mutant ATXN7 without affecting normal ATXN7 or causing adverse effects.
- A4 shRNA treatment led to significant improvements in motor and behavioral parameters and prevented PC gene downregulation, attenuating disease burden.
Conclusions:
- Selective targeting of CAG expansion in the cerebellum is feasible using blood-brain barrier-permeable AAV vectors.
- This strategy effectively attenuates the disease phenotype in an SCA mouse model, demonstrating therapeutic potential.
- The findings represent a significant advancement for developing CAG-targeting therapies for SCA7 and other CAG/polyQ SCAs.
