What question did this study set out to answer?

The central aim is to explore minimally invasive light-based methods for activating gene expression in the inner ear to enhance gene therapy applications.

February 6, 2026

Less Invasive Light Irradiation Methods for Inner Ear Gene Therapy Based on Photoswitch Technology: Toward Clinical Translation

Key Points

The central aim is to explore minimally invasive light-based methods for activating gene expression in the inner ear to enhance gene therapy applications.
Developed a photoactivatable Cre recombinase (PA-Cre) system for gene expression regulation.
Injected AAV9/3 vectors encoding PA-Cre into the cochlea of mice.
Evaluated three irradiation methods: direct cochlear, tympanic membrane, and external auditory canal.
Measured recombination efficiency using whole-mount immunohistochemistry after seven days.
Direct cochlear irradiation showed an 88.4% recombination rate.
Tympanic membrane and external auditory canal irradiation achieved conversion efficiencies of 95.8% and 97.6%, respectively.
Diminished tdTomato expression in the absence of light confirmed low Cre leak activity.

Abstract

Hearing impairment, one of the most prevalent sensory disorders, remains a major risk factor for dementia in the aging population. Although interventions such as hearing aids and cochlear implants provide partial benefit, they do not address the underlying pathology of sensorineural hearing loss. Inner ear gene therapy has attracted significant attention as a promising approach; however, its clinical translation requires minimally invasive and controllable methods for gene activation. We previously developed a photoactivatable Cre recombinase (PA-Cre) system for spatiotemporal regulation of gene expression. In this study, we evaluated the feasibility of irradiating the external auditory canal (EAC) and tympanic membrane (TM) as minimally invasive approaches for activating cochlear gene expression. Tyrosine-mutant AAV9/3 vectors (AAV.GTX) encoding PA-Cre and a Cre-dependent reporter (sfGFP-to-tdTomato) were injected via the round window membrane in 9-week-old C57BL/6J mice. Seven days later, light irradiation was applied using three approaches: (1) Direct cochlear irradiation via postauricular access, (2) TM irradiation with a fiber-optic probe, and (3) noninvasive EAC irradiation through the intact TM. Recombination efficiency in inner hair cells (IHCs) was quantified using whole-mount immunohistochemistry. AAV.GTX efficiently transduced IHCs and drove robust sfGFP expression. In the absence of light, tdTomato expression remained minimal (<5%), indicating low basal Cre leak activity. Direct cochlear irradiation produced strong recombination (conversion rate: 88.4 ± 1.5%), confirming the functionality of PA-Cre in the mouse inner ear. TM and EAC irradiation yielded high conversion efficiencies (95.8 ± 1.7% and 97.6 ± 1.2%, respectively), comparable to direct irradiation, while preserving cochlear integrity. These findings indicate that PA-Cre functions effectively in the mouse cochlea with minimal leak activity and that TM and EAC irradiation enable robust, minimally invasive gene activation. This strategy highlights the light-mediated, noninvasive modulation of cochlear gene expression, informing future translational development.

Mark Helpful

Bookmark

Relay