CAG-targeted brain-permeable therapy tested in biallelic humanized polyQ mouse models

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Polyglutamine (polyQ) diseases, such as Huntington disease (HD) and spinocerebellar ataxia type 3 (SCA3), are caused by expanded CAG repeats leading to toxic protein accumulation.
• Current therapeutic strategies aim to reduce these pathogenic proteins, but effective in vivo targeting remains a challenge.

Purpose of the Study:

• To evaluate the in vivo efficacy and safety of CAG-directed short hairpin RNAs (shRNAs) as a therapeutic strategy for polyglutamine diseases.
• To assess reagent design, toxicity, delivery, brain region transduction, silencing efficiency, and allele preference of novel shRNA constructs.

Main Methods:

• Designed and tested CAG-directed shRNAs (A4(P10) and A4(P10,11)) in humanized mouse models of HD and SCA3.
• Administered AAV-PHP.eB shRNA-encoding vectors systemically via intravenous injection to assess blood-brain barrier penetration and brain targeting.
• Evaluated protein reduction, aggregate formation, toxicity, and regional specificity of shRNA-mediated gene silencing.

Main Results:

• Optimized CAG-targeted shRNAs (A4(P10) and A4(P10,11)) successfully lowered mutant huntingtin and ataxin-3 protein levels and reduced aggregates in relevant brain regions.
• Demonstrated selective brain region transduction and diminished toxicity compared to other tested shRNAs.
• Showcased potential for targeting somatic expansions and highlighted the importance of transduction region and dose for silencing efficiency.

Conclusions:

• CAG-directed shRNA therapy is a viable strategy for reducing pathogenic proteins in polyglutamine diseases.
• Optimized reagents offer a promising avenue for developing targeted therapies for HD, SCA3, and potentially other polyQ disorders.
• This approach may accelerate drug development for debilitating neurodegenerative conditions.