Impacts of an age-related hearing loss allele of cadherin 23 on severity of hearing loss in ICR and NOD/Shi mice

The age-related hearing loss allele (Cdh23^ahl) of the cadherin 23 gene leads to a more severe hearing loss phenotype through additive effects with risk alleles for hearing loss. In this study, we genome edited the Cdh23^ahl allele to the wild-type Cdh23⁺ allele in outbred ICR mice and inbred NOD/Shi mice established from ICR mice and investigated their effects on hearing phenotypes. Several hearing tests confirmed that ICR mice developed early onset high-frequency hearing loss and exhibited individual differences in hearing loss onset times. Severe loss of cochlear hair cells was also detected in the high-frequency areas in ICR mice. These phenotypes were rescued by genome editing the Cdh23^ahl allele to Cdh23⁺, suggesting that abnormal hearing phenotypes develop because of the interaction of the Cdh23^ahl and risk alleles in the genetic background of ICR mice. NOD/Shi mice developed more severe hearing loss and hair cell degeneration than ICR mice. Hearing loss was detected at 1 month old. Hair cell loss, including degeneration of cell bodies and stereocilia, was observed in all regions of the cochlea in NOD/Shi mice. Although these phenotypes were partially rescued by genome editing to the Cdh23⁺ allele, the phenotypes associated with high-frequency hearing were mostly unrecovered in NOD/Shi mice. These results strongly suggest that the genetic background of NOD/Shi mice contain a potential risk allele for the acceleration of early onset high-frequency hearing loss.