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. 2016 Jun 2;98(6):1101-1113.
doi: 10.1016/j.ajhg.2016.03.028. Epub 2016 May 26.

RNA Interference Prevents Autosomal-Dominant Hearing Loss

Seiji B Shibata  1 , Paul T Ranum  2 , Hideaki Moteki  3 , Bifeng Pan  4 , Alexander T Goodwin  5 , Shawn S Goodman  6 , Paul J Abbas  6 , Jeffrey R Holt  4 , Richard J H Smith  7
Affiliations

RNA Interference Prevents Autosomal-Dominant Hearing Loss

Seiji B Shibata et al. Am J Hum Genet. .

Abstract

Hearing impairment is the most common sensory deficit. It is frequently caused by the expression of an allele carrying a single dominant missense mutation. Herein, we show that a single intracochlear injection of an artificial microRNA carried in a viral vector can slow progression of hearing loss for up to 35 weeks in the Beethoven mouse, a murine model of non-syndromic human deafness caused by a dominant gain-of-function mutation in Tmc1 (transmembrane channel-like 1). This outcome is noteworthy because it demonstrates the feasibility of RNA-interference-mediated suppression of an endogenous deafness-causing allele to slow progression of hearing loss. Given that most autosomal-dominant non-syndromic hearing loss in humans is caused by this mechanism of action, microRNA-based therapeutics might be broadly applicable as a therapy for this type of deafness.

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Figures

Figure 1
Figure 1
miRNA Design, Screening, and Viral-Vector Selection (A) Cartoon depiction of a possible configuration of TMC1 highlights the position of the Bth mutation. (B) Multiple-sequence alignment shows conservation of Met412 in vertebrates and the Met412Lys change in the Tmc1Bth/+ mouse. (C) siRNA sequence #16 embedded in an artificial miRNA scaffold. Of all miRNAs tested, #16 had the most specific and selective suppression of the mutant Tmc1 c.1235T>A allele. Blue and red arrows depict predicted Drosha and Dicer cleavage sites, respectively; the dashed box shows the core #16 sequence targeting the mutant Tmc1 variant. (D) Real-time qPCR analysis of total RNA isolated from COS-7 cells cotransfected with constructs expressing both miRNA #16 and miSafe (a sequence specifically selected for its validated low off-targeting potential6) and either wild-type Tmc1 or mutant Tmc1 c.1235T>A. Relative mRNA expression levels were calculated with the ΔΔCt algorithm. Error bars represent the SD of three biological and nine technical replicates.
Figure 2
Figure 2
Evaluation of the Efficiency and Specificity of AAV Transduction (A) Comparative transduction efficiency and specificity of rAAV2/1 and rAAV2/9 carrying a CMV-eGFP expression construct delivered to wild-type murine cochlea at P0–P2 via a trans-RWM approach. rAAV2/1 transduces IHCs, OHCs, spiral ganglion cells (arrow), and inner sulcus cells (arrowhead) in the osseous spiral lamina (OSL). Overlapping MYO7A and eGFP localization represents positive hair cell transduction. Note that compared to rAAV2/1, rAAV2/9 shows specific IHC transduction. Scale bars represent 50 μm. (B) The efficiency of viral transuction in IHCs was assessed in 400 μm segments in the apical and basal turns (rAAV2/1 [gray] and rAAV2/9 [black]). Note the high (∼74%) rAAV2/9 IHC transduction in the apical turn. Error bars represent the SD (n = 3). ∗p < 0.05, ∗∗p < 0.005.
Figure 3
Figure 3
rAAV2/9-Mediated miTmc Suppresses Expression of Tmc1 c.1235T>A In Vivo (A) Dual-promoter viral insert in which the U6 promoter drives miTmc miRNA expression and the CMV promoter drives eGFP expression. miSafe was specifically selected for its validated low off-targeting potential. (B) Two weeks after trans-RWM injection of miTmc at P0–P2, native eGFP localization was visible in transduced IHCs and OHCs in the organ of Corti. (C) Expression of wild-type Tmc1 and Bth Tmc1 mRNA was measured by real-time qPCR using allele-specific primers. Allele-specific qPCR amplification was carried out on groups of individually isolated auditory hair cells (Movie S1). All samples were normalized to β-actin. Expression of wild-type Tmc1 mRNA measured in the untreated contralateral sample was set at a value of 1. mRNA abundance was calculated in relation to that of this untreated contralateral sample with wild-type Tmc1. Abundance of both wild-type Tmc1 and Bth Tmc1 were measured in samples containing 12 cells collected from either miTmc-treated ears or untreated contralateral ears from five 4-week-old Tmc1Bth/+ mice. Cells collected from untreated contralateral ears were GFP negative, whereas cells collected from miTmc-injected ears were GFP positive. mRNA abundance was calculated by the ΔΔCt method. The range indicated by the error bars represents the SD of ΔΔCt on the basis of the fold-difference calculation 2−ΔΔCt, where ΔΔCt + S and ΔΔCt − S.
Figure 4
Figure 4
miTmc Lowers Mechanotransduction Currents in Tmc1Bth/− Mice (A) Families of mechanotransduction currents were recorded from eight different IHCs (P8–P10) under four different conditions. Currents were evoked by step hair-bundle deflections that ranged in amplitude from −0.2 to 1 μm. (B) Scatter plot shows maximal mechanotransduction currents recorded from 74 IHCs (open symbols) under four different conditions. Filled symbols indicate the mean ± SE (box) and SD (bars) for each condition. The number of cells for each condition is indicated at the bottom.
Figure 5
Figure 5
miTmc Gene Therapy Slows Progression of Hearing Loss in Tmc1Bth/+ Mice (A) Experimental timeline catalogs the experimental procedures in Tmc1Bth/+ mice and controls from the time of artificial miRNA injection to the time of tissue collection. (B) Click ABR thresholds in wild-type, Tmc1Bth/++miTmc contralateral, Tmc1Bth/++miSafe, and Tmc1Bth/++miTmc animals. The two best-performing and two worst-performing Tmc1Bth/++miTmc-treated animals are shown as dashed and dotted blue lines, respectively, to illustrate variability in performance within the treated cohort. (C) Representative 8 kHz ABR traces recorded from the wild-type, non-injected Tmc1Bth/++miTmc contralateral, and Tmc1Bth/++miTmc 13-week-old mice. (D and E) Tone-burst ABR thresholds (D) and DPOAE amplitudes and noise floors (E) in wild-type, Tmc1Bth/+, Tmc1Bth/++miSafe, and Tmc1Bth/++miTmc animals at 4, 8, 13, 26, and 35 weeks. The dotted black line indicates the average noise floor for each group of DPOAEs. Black arrows indicate no response at equipment limits. ∗p < 0.05, ∗∗p < 0.005. See also Figures S4 and S5.
Figure 6
Figure 6
miTmc Gene Therapy Improves Hair Cell Survival Wild-type, Tmc1Bth/+, Tmc1Bth/++miSafe, and Tmc1Bth/++miTmc animals sacrificed 35 weeks after treatment. Ears were fixed, dissected, and stained as cochlear whole mounts. (A) 10× images of representative whole-mount apical turns from wild-type, Tmc1Bth/++miTmc, Tmc1Bth/++miSafe, and Tmc1Bth/+ animals. Samples were stained with MYO7A (red) and phalloidin (green) for labeling hair cells and filamentous actin, respectively. Arrowheads show the apical tip and 8 and 16 kHz regions along the apical turn of the cochlea. Note IHC preservation in the Tmc1Bth/++miTmc animals. The white cross shows the area devoid of IHCs. Scale bars represent 150 μm. (B) 40× magnification at the indicated position in relation to the cochlear apex. The three rows of OHCs (1–3), pillar cells (P), and IHCs are shown. Areas with dark hallows illustrate OHC or IHC loss. The white cross shows the area devoid of IHCs. Scale bars represent 50 μm. (C and D) IHC (C) and OHC (D) survival was quantified with 20×–40× images of whole-mount cochlea compiled into cochleograms at 35 weeks. Hair cells were counted in 0.25 mm segments and plotted against the distance (%) from the apex. Tmc1Bth/++miSafe, Tmc1Bth/++miTmc, and Tmc1Bth/++miTmc best performers (n = 2) are shown. ∗p < 0.05, ∗∗p < 0.005.
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