In Vivo Gene Transfer into Neonatal Mice Cochlea Using Adeno‐ Associated Viral Vectors

Abstract

Objectives: Although sensory hearing loss is the most common sensory disorder, with more than 75% of genetic origin, there are no curative treatments available. A promising approach to restore inherited hearing loss consists of introducing a functional copy of the deficient gene using gene therapy. The present study develops a non-invasive surgical approach using adeno-associated viruses (AAV) vector to introduce reporter genes into neonatal mice cochleae, without affecting the normal development of hearing. Methods: AAV2, AAV2/8, AAV2/1, and AAV8, carrying green fluorescent protein (GFP) reporter gene, were tested using 150 neonatal mice. Two microliters of vectors, with titer of 1013 vg/ml, were injected into the scala tympani through the round window. Two weeks after viral injection, evoked auditory brain-stem responses (ABR) were recorded; cellular expression and distribution of GFP were analyzed by immunohistochemistry and confocal imaging. Results: AAV2/8 vector transduced cochlear inner hair cells with high efficiency (80%) and to a lesser degree supporting cells (40%). Serotype 8 transduced mostly neurons (30%). The efficiency of serotypes 2/1, 1, and 2 varied from 5% to 80% of the inner hair cells and from 35% to 80% of supporting cells. The recording of the evoked ABR responses of the injected mice at P16 showed that cochlear function is not affected. Conclusions: We have developed a surgical procedure that might be useful for AAV gene transfer into the cochlea to treat genetic deafness. As a next step, a therapeutic gene will be transferred into a mouse model for human deafness to correct hearing loss.