Rescue of stereocilia architecture and hearing function by AAV-CIB2 and AAV-CIB3 in a mouse model of recessive deafness DFNB48.

Pathogenic variants in the calcium and integrin-binding protein 2 (CIB2) are among the leading causes of nonsyndromic prelingual hearing loss (DFNB48). Loss of Cib2 in mice causes severe stereocilia bundle defects, impaired mechanoelectrical transduction (MET), and profound hearing loss. To determine whether a critical window of opportunity exists to restore the stereocilia architecture and to rescue hearing function, we developed and investigated the effect of adeno-associated virus (AAV)-mediated gene delivery in Cib2 mutant mice. A single administration of the AAV-Cib2 vector was performed via semicircular canal injections in Cib2ko/ko mice at several different ages within the early postnatal period. We observed sustained, but partial, recovery of hearing function and restoration of stereocilia architecture in the apical to middle cochlear turns in mice having received AAV-Cib2 between postnatal day 0 (P0) and P4. Both CIB2 and a closely related protein family member, CIB3, are known to bind to TMC1/2 proteins and regulate MET function. Thus, we also investigated the impact of human CIB3 (hCIB3) overexpression on hearing in Cib2ko/ko mice. Intriguingly, administration of AAV-CIB3 gene via semicircular canal injections at P0-P1 also restored hearing function at frequencies corresponding to the apical to middle cochlear turns in Cib2ko/ko mice. Taken together, our data provide a critical timeline in which stereocilia architecture and hearing function can be restored in CIB2-deficient mice and lay the foundation for future gene therapy trials for DFNB48 patients.