Investigation of the Effects of Cadherin 23 and Oncomodulin on Early Progressive Hearing Loss Using a New Oncomodulin Mouse Model

Oncomodulin (OCM) is the most abundant Ca2+ buffering protein found in mature outer hair cells (OHCs). Cadherin 23 (CDH23) is a crucial component of the tip-links in hair cell stereocilia. The absence or dysfunction of these two proteins contributes to the early onset of age-related hearing loss (AHL). In this study, we investigated the effects of the Cdh23753G→A mutation on OHC function using new Ocm-knockout (KO) mouse models (Ocmtm1a/tm1a) with or without the Cdh23753G→A mutation. Despite having the same genetic background, Ocm-KO mice carrying the Cdh23753G→A mutation displayed significant hearing loss and a notable decline in OHC function across all measured frequencies as early as three months of age. In contrast, Ocm-KO mice without the Cdh23753G→A mutation did not exhibit comparable hearing loss until they reached twelve months of age. Additionally, we examined the role of OCM in preserving OHC function under ototoxic stress induced by HPβCD (2-hydroxypropyl-β-cyclodextrin). The administration of HPβCD resulted in a more pronounced decline in OHC function in Ocm-KO mice compared to wild-type (WT) mice, as indicated by distortion product otoacoustic emissions (DPOAE) measurements. Furthermore, HPβCD treatment led to greater structural deterioration and more rapid rupture events in OHCs from Ocm-KO mice than in those from WT mice, as demonstrated by in vitro live imaging. These findings suggest that the Cdh23753G→A mutation, rather than other potential strain-specific genetic factors associated with AHL, solely exacerbates the early onset of AHL phenotypes in Ocm-KO mice. Furthermore, our data indicates that OCM proteins in OHCs enhance their ability to withstand ototoxic stimuli.