Figure 3.

MSH3 silencing with di-siRNA blocks somatic repeat expansion in striatum of BAC-CAG HD mice

(A) Di-valent chemically modified siRNA structure including the chemical structure used. (B) BAC-CAG study plan, injecting groups at 12 weeks of age: PBS, NTC, siHTT_10150, and siMSH3_1000. Mice were injected with 125 μg per ventricle of di-valent siRNA and were euthanized at 20 weeks. (C) MSH3 protein measured in PBS, NTC, and siMSH3_1000 groups showing 40%–50% silencing of the Msh3 protein in the striatum, cortex, and thalamus. (D) mutHTT protein expression of PBS, NTC, and siHTT_10150 showing >90% silencing in the striatum, cortex, and thalamus. Data shown are the mean ± standard deviation. n = 5–6 mice per condition. (E) Representative fragment analysis of the expanded CAG locus in striatum of PBS-, NTC-, siMSH3_1000-, and siHTT_10150-treated BAC-CAG mice 8 weeks post-injection. Primers are reported in the materials and methods. (F) Somatic instability index calculated with a 5% signal-to-noise threshold as described in the materials and methods. Each data point is one mouse. Instability index is compared with NTC (one-way ANOVA treatment with Dunnett’s multiple comparison test; ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001, ∗∗∗∗p < 0.0001). Data shown are the mean ± standard deviation.