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

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 Cdh23^753G→A mutation on OHC function using new Ocm-knockout (KO) mouse models (Ocm^tm1a/tm1a) with or without the Cdh23^753G→A mutation. Despite having the same genetic background, Ocm-KO mice carrying the Cdh23^753G→A mutation displayed a notable decline in OHC function across all measured frequencies as early as three months of age. In contrast, Ocm-KO mice without the Cdh23^753G→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 distortion product otoacoustic emission data show that the administration of HPβCD resulted in a more pronounced decline in OHC function in Ocm-KO mice compared to wild-type (WT) mice. Time-lapse recording also shows that HPβCD treatment led to greater structural deterioration and more rapid rupture events in OHCs from Ocm-KO mice than in those from WT mice. These findings suggest that the Cdh23^753G→A mutation, rather than other potential strain-specific genetic factors associated with AHL, significantly exacerbates the early onset of AHL phenotypes in Ocm-KO mice. Furthermore, our data indicates that the OCM protein in OHCs enhances their ability to withstand ototoxic stimuli.