Cochleovestibular gene transfer in neonatal mice by canalostomy

Abstract

Impairments of the inner ear result in sensorineural hearing loss and vestibular dysfunction in humans. A large proportion of these disorders are congenital, and involve both auditory and vestibular systems. Therefore, genetic interventions to correct deficits must be administered during early developmental stages. In this study, we evaluated inner ear gene transfer in neonatal mice by canalostomy using an adeno-associated virus serotype 8 (AAV8) vector. AAV8 with the green fluorescence protein (GFP) gene was inoculated into the inner ear of the neonatal mice through the posterior semicircular canal (canalostomy). At 30 days following surgery, animals were subjected to swim tests and auditory brainstem response measurements. Then, the animals were euthanized and temporal bones were harvested for whole-mount preparation. GFP expression and morphological changes in the inner ear were assessed by immunohistochemistry. After surgery, no signs of vestibular dysfunction were found, and there were no significant differences in the auditory brainstem response threshold between AAV8-inoculated ears and nonsurgery ears. In the surgery ears, extensive GFP expression and no morphological lesions were detected in the cochlear and vestibular end organs. Robust GFP expression was found in inner hair cells, marginal cells, vestibular hair cells, and vestibular supporting cells. In conclusion, AAV8 inoculation through canalostomy into the inner ears of neonatal mice led to extensive overexpression of exogenous genes in the inner ear without affecting hearing or vestibular function. It serves as a promising approach for gene therapy of congenital cochleovestibular diseases.

Canalostomy As a Surgical Approach to Local Drug Delivery into the Inner Ears of Adult and Neonatal Mice

“…To evaluate the safety and efficiency of canalostomy for inner ear gene delivery, AAV8-GFP was injected into the inner ear of adult and neonatal mice. All animals exhibited normal ABR thresholds and swimming test scores after AAV8-GFP injection 18,30 . Immunohistology revealed that, in the auditory sensory epithelium, inner hair cells (IHCs) and a few outer hair cells (OHCs) of the basal turn showed robust GFP expression .…”

Enhanced viral-mediated cochlear gene delivery in adult mice by combining canal fenestration with round window membrane inoculation

“…One limitation of this study was that it focused solely on the utilization of AAV2/Anc80L65; other serotypes were not screened. Of note, in neonatal mice injected with AAV8 via a PSCC canalostomy, transduction of IHCs was 69–76% 18 , suggesting that transduction efficiency with this approach may be serotype dependent. Additionally, 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 PSCC 19 , 20 .…”

Anatomical and Surgical Evaluation of the Common Marmoset as an Animal Model in Hearing Research

“…A previous study reported that direct injection of adenovirus via the semicircular canal in mice led to transduction, predominantly in the vestibular organ (Kawamoto et al, 2001). Other mouse studies demonstrated that viral vectors injected from the semicircular canal diffuse into the cochlea, introducing transgene expression in cochlear hair cells (Pfannenstiel et al, 2009; Guo et al, 2017). Therefore, further studies are required to evaluate the efficiency of injection from the semicircular canal and diffusion of the injected solution into the inner ear canal in the common marmoset.…”