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Blocking somatic repeat expansion and lowering huntingtin via RNA interference synergize to prevent Huntingtons disease pathogenesis in mice

Belgrad, J.; Summers, A.; Landles, C.; Greene, J. R.; Hildebrand, S.; Knox, E.; Sapp, E.; Yamada, N.; Furgal, R.; Miller, R.; Osborne, G. F.; Chase, K.; Luu, E.; Freedman, J.; Bramato, B.; McHugh, N.; Benoit, V.; OReilly, D.; Greer, P.; Bates, G. P.; Vogt, T. F.; Lee, R.; Howland, D.; DiFiglia, M.; Aronin, N.; Khvorova, A.

2025-06-25 neuroscience
10.1101/2025.06.24.661398 bioRxiv
Show abstract

Huntingtons disease (HD) is a progressive neurodegenerative disorder with no approved therapies. Two major molecular drivers--somatic expansion of inherited CAG repeats and toxic mutant HTT (mHTT) variants--lead to neuronal dysfunction. Despite multiple trials, HTT-lowering strategies have not shown meaningful clinical benefit. Using therapeutic divalent siRNAs, we assessed the long-term impact of silencing MSH3 (a key regulator of somatic expansion), HTT, or both. In Q111 HD mice (>110 CAGs), which exhibit robust expansion, mHTT inclusions, and transcriptional dysregulation by 12 months, long-term MSH3 silencing blocked expansion, reduced inclusions, and reversed gene expression changes. HTT silencing alone had limited effect, but combined MSH3/HTT targeting synergistically eliminated inclusions and restored transcriptomic profiles. Parallel treatment in wild-type mice showed no toxicity, supporting the safety of long-term intervention. These findings position somatic expansion as a promising therapeutic target and demonstrate the potential of RNAi-based co-silencing of MSH3 and HTT as a disease-modifying strategy for HD.

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