Clarin-1 gene transfer rescues auditory synaptopathy in model of Usher syndrome
Didier Dulon, … , Christine Petit, Aziz El-Amraoui
Didier Dulon, … , Christine Petit, Aziz El-Amraoui
Published July 9, 2018
Citation Information: J Clin Invest. 2018;128(8):3382-3401. https://doi.org/10.1172/JCI94351.
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Clarin-1 gene transfer rescues auditory synaptopathy in model of Usher syndrome

Abstract

Clarin-1, a tetraspan-like membrane protein defective in Usher syndrome type IIIA (USH3A), is essential for hair bundle morphogenesis in auditory hair cells. We report a new synaptic role for clarin-1 in mouse auditory hair cells elucidated by characterization of Clrn1 total (Clrn1ex4–/–) and postnatal hair cell–specific conditional (Clrn1ex4fl/fl Myo15-Cre+/–) knockout mice. Clrn1ex4–/– mice were profoundly deaf, whereas Clrn1ex4fl/fl Myo15-Cre+/– mice displayed progressive increases in hearing thresholds, with, initially, normal otoacoustic emissions and hair bundle morphology. Inner hair cell (IHC) patch-clamp recordings for the 2 mutant mice revealed defective exocytosis and a disorganization of synaptic F-actin and CaV1.3 Ca2+ channels, indicative of a synaptopathy. Postsynaptic defects were also observed, with an abnormally broad distribution of AMPA receptors associated with a loss of afferent dendrites and defective electrically evoked auditory brainstem responses. Protein-protein interaction assays revealed interactions between clarin-1 and the synaptic CaV1.3 Ca2+ channel complex via the Cavβ2 auxiliary subunit and the PDZ domain–containing protein harmonin (defective in Usher syndrome type IC). Cochlear gene therapy in vivo, through adeno-associated virus–mediated Clrn1 transfer into hair cells, prevented the synaptic defects and durably improved hearing in Clrn1ex4fl/fl Myo15-Cre+/– mice. Our results identify clarin-1 as a key organizer of IHC ribbon synapses, and suggest new treatment possibilities for USH3A patients.

Authors

Didier Dulon, Samantha Papal, Pranav Patni, Matteo Cortese, Philippe F.Y. Vincent, Margot Tertrais, Alice Emptoz, Abdelaziz Tlili, Yohan Bouleau, Vincent Michel, Sedigheh Delmaghani, Alain Aghaie, Elise Pepermans, Olinda Alegria-Prevot, Omar Akil, Lawrence Lustig, Paul Avan, Saaid Safieddine, Christine Petit, Aziz El-Amraoui

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Figure 8

Intracochlear AAV2/8-mediated delivery of clarin-1 in Clrn1ex4–/– mice leads to moderate hearing preservation.

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Intracochlear AAV2/8-mediated delivery of clarin-1 in Clrn1ex4–/– mice l...
(A) The schematic diagram (top panel) shows the AAV2/8-Clrn1-IRES-GFP vector used for gene delivery to the cochlea on P2–P3. The histogram indicates the percentage of GFP-labeled IHCs and OHCs on P20–P30 in Clrn1ex4–/– mice. (B) Injections of either AAV2/8-Clrn1-IRES-GFP or AAV2/8-GFP had no effect on click ABR thresholds in WT mice. Injections of AAV2/8-GFP also had no impact on ABR thresholds in Clrn1ex4fl/fl Myo15-Cre+/– mice (unpaired Student’s t test). (C) ABR thresholds (mean ± SEM) in treated (purple, n = 9) and untreated (blue, n = 9) inner ears of P22–P24 Clrn1ex4–/– and control (black, n = 5) mice. A decrease of about 10–15 dB in ABR thresholds relative to untreated ears was observed in Clrn1ex4–/– ears after injection. **P < 0.01 (unpaired Student’s t test). (D) Early postnatal AAV2/8-mediated delivery of clarin-1 into Clrn1ex4–/– ears did not prevent or correct the misshaping of the hair bundles. Both IHC and OHC hair bundles presented alterations in shape and a loss of short-row stereocilia due to the embryonic loss of clarin-1 (representative of 8 mice between P25 and P30). Scale bars: 1 μm.