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Blocking somatic repeat expansion and lowering huntingtin by RNAi synergize to attenuate Huntington's disease

Jillian Belgrad1, Ashley Summers1, Christian Landles2

  • 1UMass Chan Medical School, RNA Therapeutics Institute, Worcester, MA 01605, USA.

Science Translational Medicine
|August 12, 2026
PubMed

Insights

Targeting somatic expansion via MSH3 silencing, alone or with huntingtin (HTT) lowering, shows promise for Huntington's disease (HD). Combined MSH3/HTT RNAi therapy effectively reduced toxic HTT and restored gene expression in HD mice.

Area of Science:

  • Neuroscience
  • Genetics
  • Molecular Biology

Background:

  • Huntington's disease (HD) is a progressive neurodegenerative disorder lacking effective treatments.
  • Current huntingtin (HTT)-lowering strategies have shown limited clinical success.
  • Somatic expansion and toxic HTT species are key drivers of HD pathology.

Purpose of the Study:

  • To compare the long-term effects of targeting somatic expansion (MSH3) versus HTT, or both, in an HD mouse model.
  • To evaluate the potential of RNA interference (RNAi)-based cosilencing for HD therapy.

Main Methods:

  • Utilized therapeutic divalent siRNAs to silence MSH3, HTT, or both in Q111 HD mice.
  • Assessed long-term impact on somatic expansion, HTT inclusions, and gene expression.
  • Evaluated safety in wild-type mice.

Main Results:

  • MSH3 silencing alone blocked somatic expansion, reduced HTT inclusions, and normalized gene expression.
  • HTT silencing had minimal effects.
  • Combined MSH3/HTT silencing synergistically eliminated inclusions and restored transcriptomic profiles.
  • No toxicity observed in wild-type mice.

Conclusions:

  • Somatic expansion is a viable therapeutic target for HD.
  • RNAi-based cosilencing of MSH3 and HTT represents a potential disease-modifying strategy for HD.
  • Combined targeting offers synergistic benefits over single-target approaches.

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