Figure 3.

Dose escalation of tetra-siRNA^Htt in mouse

(A) Retinal cross-sections of mice 2 months postinjection of 2 μL siRNA (doses indicated in each individual section shown in panel). Seen is the siRNA distribution through the fluorescence of the attached Cy3 fluorophore. (B) Dose response at 2 months postinjection using the same doses and injection volume as shown in (A). Shown is the percentage of the remaining HTT protein compared to the NTC. (C) Scotopic (first graph) and photopic (second graph) a-wave amplitudes from ERG recordings at 2 months postinjection. N = 6 for (A)–(C); error bars: SD; significance is compared to NTC; n.s., not significant. ∗p < 0.05; ∗∗p < 0.01; ∗∗∗p < 0.001. (D and E) Retinal cross-sections shown in (A) stained for Iba1 (D: green signal) and GFAP (E: red signal) to visualize migrating microglia and activation of gliosis, respectively. Except for the highest dose (60 μg), there are no microglia (white arrowheads) seen in the ONL or where PR cell segments reside. Blue: nuclei marked with DAPI; green: Iba1 in (D) and peanut agglutinin lectin (PNA) marking cone PR cell segments in (E); red: siRNA in (D) marked through Cy3 label and GFAP in (E). In each part of (D), half of the blue and red signal was removed to better visualize the green signal. Histology in (A), (D), and (E) was repeated with at least N = 3 retinas. PS, photoreceptor segments. White arrowheads mark microglia in the subretinal space; vertical bars indicate height of different layers. Scale bars: 50 μm.