Gene therapy against deafness: a proof of concept study demonstrates partial rescue of hearing in a mouse model for deafness DFNB9

Introduction:

Inherited forms of deafness are currently treated with cochlear implantation, which are limited in frequency resolution and sound pressure level dynamics. Here, we tested a gene therapy for the recessively inherited form of profound prelingual deafness DFNB9, where the inner ear is morphologically preserved into childhood, therefore presumably allowing treatment after birth. Otoferlin, the protein encoded by the DFNB9 gene, is required for synaptic transmission from inner hair cells (IHCs) to subsequent neurons.

Materials and Methods:

We tested a gene replacement by viral transduction of IHCs with otoferlin cDNA in otoferlin knock-out (KO) mouse models. To circumvent the limited cargo capacity of adeno-associated viruses (AAVs), we split the 6kb otoferlin cDNA to two separate AAVs, which we co-injected into cochleae of otoferlin KO mice (n = 22). We then compared otoferlin immunofluorescence, IHC exocytosis and auditory brainstem responses (ABRs) to non-transduced otoferlin KO and wild-type mice.

Results:

Upon cochlear injection, the split otoferlin cDNA transduced via the two AAVs re-assembled in up to 50% of IHCs and led to expression of full-length otoferlin protein with levels of ˜30% of wild-type values. Fast neurotransmitter release from IHCs was fully rescued, and sustained exocytosis was partially restored. Dual-AAV injection into cochleae of otoferlin KO mice rescued ABRs with thresholds of 40 – 60dB in response to acoustic clicks, but ABR wave amplitudes were smaller than in wild-type mice.

Conclusion:

Given that optimized otoferlin dual-AAVs leads to higher otoferlin expression levels, this approach is presumed to fully restore hearing and will be a straightforward therapeutical option for children with DFNB9 in the future.

Publication History

Publication Date:
23 April 2019 (online)