Durable HTT silencing using non-evolved dCas9 epigenome editors in patient-derived cells
Jennifer J Waldo1,2,3,4,5,6, Julian A N M Halmai1,2,3,4,5,6, Ankita Singh1,2,3,4,5,6
1Ctr. for Interventional Genetics, University of California Davis Health, Sacramento, CA, USA.
Molecular Therapy. Nucleic Acids
|June 16, 2025
Summary
This study demonstrates that SpCas9 epigenetic editing effectively downregulates the huntingtin (HTT) gene in Huntington's disease models. This approach shows promise as a stable, targeted therapy for this neurodegenerative disorder.
Area of Science:
- Neurogenetics
- Gene Therapy
- Epigenetic Regulation
Background:
- Huntington's disease (HD) is a neurodegenerative disorder caused by a trinucleotide repeat expansion in the huntingtin (HTT) gene.
- Epigenetic editing using nuclease-deficient Cas9 (dCas9) offers a potential therapeutic strategy for HD by downregulating the causative HTT gene.
Purpose of the Study:
- To screen dCas9 variants fused to KRAB and DNMT3A/L for their ability to downregulate HTT expression.
- To evaluate the efficacy and specificity of the most effective dCas9 variant for HTT gene silencing in disease-relevant cell types.
Main Methods:
- Screening of dCas9 variants (SpCas9, dxCas9, dCas9-VQR) fused to epigenetic modifiers (KRAB, DNMT3A/L) to assess HTT downregulation.
- Reduced representation bisulfite sequencing (RRBS) to analyze on-target and off-target DNA methylation changes.
- Assessment of HTT silencing stability in a rapidly dividing cell line and in patient-derived neuronal stem cells.
Main Results:
- Only SpCas9 significantly downregulated HTT expression, while other variants were less effective.
- The SpCas9-based system induced high on-target DNA methylation with minimal off-target effects.
- HTT silencing was mitotically stable for up to 6 weeks and effective in patient-derived neuronal stem cells.
Conclusions:
- SpCas9-based epigenetic editing is a potent and specific strategy for downregulating the HTT gene in Huntington's disease.
- This approach demonstrates therapeutic potential for Huntington's disease, offering a novel pathway for gene silencing.
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