Abstract
Cochlear gene therapy holds promise for the treatment of genetic deafness. Assessing its impact in adult murine models of hearing loss, however, has been hampered by technical challenges that have made it difficult to establish a robust method to deliver transgenes to the mature murine inner ear. Here in we demonstrate the feasibility of a combined round window membrane injection and semi-circular canal fenestration technique in the adult cochlea. Injection of both AAV2/9 and AAV2/Anc80L65 via this approach in P15–16 and P56–60 mice permits robust eGFP transduction of virtually all inner hair cells throughout the cochlea with variable transduction of vestibular hair cells. Auditory thresholds are not compromised. Transduction rate and cell tropism is primarily influenced by viral titer and AAV serotype but not age at injection. This approach is safe, versatile and efficient. Its use will facilitate studies using cochlear gene therapy in murine models of hearing loss over a wide range of time points.
Highlights
Current clinical treatment options for hereditary hearing loss are limited to hearing aids and cochlear implantation[1]
The injection of AAV2/9 (3.90 × 1013 vg/ml) at P15–16 using the round window membrane (RWM) + CF approach resulted in robust transduction of inner hair cells (IHCs) throughout the cochlea: apex 94.6%, middle 96.8% and base 94.2% (Fig. 2c and e). eGFP expression in outer hair cells (OHCs) was limited (Fig. 2c)
Auditory thresholds and Peak 1 (P1) latencies and amplitudes in injected and uninjected ears were comparable (Fig. 2d and Supplementary Fig. S1). These findings suggest that cochlear gene delivery using a RWM + CF approach facilitates high and uniform transduction of IHCs throughout the cochlea without altering auditory function
Summary
Current clinical treatment options for hereditary hearing loss are limited to hearing aids and cochlear implantation[1]. For example, injected AAV8-CMV-eGFP through the RWM and showed that transduction efficiency of inner hair cells (IHCs) was 12–31% with apical to basal gradient. These mice sustained a 30 dB auditory brainstem response (ABR) threshold shift, consistent with injection-associated cochlear damage[12]. Suzuki et al showed that direct infusion of AAV2/Anc80L65 into the posterior semicircular canal (PSCC) in the cochlea of 6-week-old mice resulted in transduction of all IHCs throughout the spiral duct and most apical turn outer hair cells (OHCs), while preserving auditory function[16]. One technical difficulty of the PSCC canalostomy injection is that it is impossible to determine whether the viral suspension is administered into the endolymphatic or perilymphatic space of PSCC19,20
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