Cabp2-Gene Therapy Restores Inner Hair Cell Calcium Currents and Improves Hearing in a DFNB93 Mouse Model.

David Oestreicher,Tobias Moser,Maria Magdalena Picher,Vladan Rankovic,Tina Pangrsic

doi:10.3389/fnmol.2021.689415

Abstract

Clinical management of auditory synaptopathies like other genetic hearing disorders is currently limited to the use of hearing aids or cochlear implants. However, future gene therapy promises restoration of hearing in selected forms of monogenic hearing impairment, in which cochlear morphology is preserved over a time window that enables intervention. This includes non-syndromic autosomal recessive hearing impairment DFNB93, caused by defects in the CABP2 gene. Calcium-binding protein 2 (CaBP2) is a potent modulator of inner hair cell (IHC) voltage-gated calcium channels CaV1.3. Based on disease modeling in Cabp2–/– mice, DFNB93 hearing impairment has been ascribed to enhanced steady-state inactivation of IHC CaV1.3 channels, effectively limiting their availability to trigger synaptic transmission. This, however, does not seem to interfere with cochlear development and does not cause early degeneration of hair cells or their synapses. Here, we studied the potential of a gene therapeutic approach for the treatment of DFNB93. We used AAV2/1 and AAV-PHP.eB viral vectors to deliver the Cabp2 coding sequence into IHCs of early postnatal Cabp2–/– mice and assessed the level of restoration of hair cell function and hearing. Combining in vitro and in vivo approaches, we observed high transduction efficiency, and restoration of IHC CaV1.3 function resulting in improved hearing of Cabp2–/– mice. These preclinical results prove the feasibility of DFNB93 gene therapy.

Highlights

According to the World Health Organization, ∼466 M people worldwide are affected by disabling hearing loss, which can have a big functional, emotional and socio-economic impact on their life, and society
We asked whether AAV-mediated gene therapy could be applicable in a knock-out mouse model of non-syndromic hearing impairment DFNB93 (Picher et al, 2017), characterized by moderate to severe hearing loss in patients (Tabatabaiefar et al, 2011; Schrauwen et al, 2012; Bademci et al, 2016; Marková et al, 2016; Picher et al, 2017; Koohiyan et al, 2019; Park et al, 2020; Safka Brozkova et al, 2020)
Plasmids encoding for bicistronic expression of calcium-binding protein 2 (Cabp2) and eGFP via the P2A peptide driven by the hCMV/hBA promoter and followed by the WPRE and bGH posttranscriptional elements were packaged into AAV2/1, and PHP.eB capsids (Figure 1A and Supplementary Figure 1)

Summary

Introduction

According to the World Health Organization, ∼466 M people worldwide are affected by disabling hearing loss, which can have a big functional, emotional and socio-economic impact on their life, and society. Besides factors like aging or noise, a large proportion of hearing impairment is caused by genetic factors, and has mostly monogenic origins The treatment of sensorineural hearing loss is limited to the use of conventional hearing aids or, in cases of severe and profound deafness, cochlear implants. Despite their phenomenal success, cochlear implants have their drawbacks. Novel methods for improved hearing restoration are currently being developed, including gene replacement, and editing or silencing as well as optogenetics (reviewed in Kleinlogel et al, 2020). The potential of a therapeutic approach using AAVmediated gene transfer has been tested in a few animal deafness models (e.g., Akil et al, 2012, 2019; Jung et al, 2015; Pan et al, 2017; Al-Moyed et al, 2019; Nist-Lund et al, 2019; Rankovic et al, 2021; Taiber et al, 2021)

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