Di-valent siRNA-mediated silencing of MSH3 blocks somatic repeat expansion in mouse models of Huntington’s disease

• Published in: Molecular therapy 2023-06, Vol.31 (6), p.1661-1674
• Main Authors: O'Reilly, Daniel, Belgrad, Jillian, Ferguson, Chantal, Summers, Ashley, Sapp, Ellen, McHugh, Cassandra, Mathews, Ella, Boudi, Adel, Buchwald, Julianna, Ly, Socheata, Moreno, Dimas, Furgal, Raymond, Luu, Eric, Kennedy, Zachary, Hariharan, Vignesh, Monopoli, Kathryn, Yang, X. William, Carroll, Jeffery, DiFiglia, Marian, Aronin, Neil, Khvorova, Anastasia
• Format: Article
• Language: English
• Subjects: Animals; CAG expansion disorders; Corpus Striatum - metabolism; DNA instability; Huntingtin Protein - genetics; Huntingtin Protein - metabolism; Huntington Disease - genetics; Huntington Disease - metabolism; Huntington Disease - therapy; Huntington’s disease; Mice; mismatch repair; MutS Homolog 3 Protein - genetics; Neostriatum - metabolism; neurodegeneration; oligonucleotide therapeutics; Original; RNA, Double-Stranded; RNA, Small Interfering - genetics; RNA, Small Interfering - metabolism; siRNA; Trinucleotide Repeat Expansion - genetics
• ISSN: 1525-0016; 1525-0024; 1525-0024
• DOI: 10.1016/j.ymthe.2023.05.006

Huntington’s disease (HD) is a severe neurodegenerative disorder caused by the expansion of the CAG trinucleotide repeat tract in the huntingtin gene. Inheritance of expanded CAG repeats is needed for HD manifestation, but further somatic expansion of the repeat tract in non-dividing cells, particularly striatal neurons, hastens disease onset. Called somatic repeat expansion, this process is mediated by the mismatch repair (MMR) pathway. Among MMR components identified as modifiers of HD onset, MutS homolog 3 (MSH3) has emerged as a potentially safe and effective target for therapeutic intervention. Here, we identify a fully chemically modified short interfering RNA (siRNA) that robustly silences Msh3 in vitro and in vivo. When synthesized in a di-valent scaffold, siRNA-mediated silencing of Msh3 effectively blocked CAG-repeat expansion in the striatum of two HD mouse models without affecting tumor-associated microsatellite instability or mRNA expression of other MMR genes. Our findings establish a promising treatment approach for patients with HD and other repeat expansion diseases. [Display omitted] Khvorova and colleagues demonstrate that the delivery of a di-valent siRNA to the CNS silences MSH3 and blocks disease-associated somatic expansion of CAG repeats in two Huntington’s disease mouse models.