Base editing strategies to convert CAG to CAA diminish the disease-causing mutation in Huntington's disease

Area of Science:

• Genetics
• Molecular Biology
• Neurodegenerative Diseases

Background:

• Huntington's disease (HD) is caused by an expanded CAG repeat in the huntingtin gene (HTT).
• The length of the uninterrupted CAG repeat, not the polyglutamine tract, correlates with the age of HD onset.
• Targeting CAG repeat length is a potential therapeutic strategy for HD.

Purpose of the Study:

• To develop and evaluate base editing strategies for converting CAG repeats to CAA repeats.
• To assess the molecular outcomes and effects on disease phenotypes of these base editing strategies.

Main Methods:

• Utilized combinations of cytosine base editors (CBEs) and guide RNAs (gRNAs) to target CAG repeats.
• Assessed base editing efficiency, specificity (indels, off-target edits), and transcriptome alterations.
• Evaluated the impact of base editing on somatic CAG repeat expansion in HD knock-in mouse models.

Main Results:

• Base editing strategies efficiently converted CAG to CAA at various sites within the repeat with high specificity.
• No significant indels, off-target edits, or transcriptome alterations were observed.
• Somatic CAG repeat expansion was significantly reduced in the liver of treated HD mice.
• CAG repeat expansion was completely abolished in mice with CAA-interrupted repeats.

Conclusions:

• CAG-to-CAA conversion via base editing is a feasible and specific strategy for Huntington's disease.
• This approach effectively reduces somatic CAG repeat expansion, a key driver of HD pathology.
• Base editing of CAG repeats holds therapeutic potential for Huntington's disease and other repeat expansion disorders.