The motor protein prestin, found in the inner ear’s outer hair cells (OHCs), is responsible for high sensitivity and sharp frequency selectivity in mammalian hearing. Some studies have suggested that prestin could be a serological biomarker for cochlear damage, as OHCs are highly vulnerable to damage from various sources. However, the reported data are inconsistent and lack appropriate negative controls. To investigate whether prestin can be used as a serological biomarker for cochlear damage or stress, we measured prestin quantities in the bloodstreams of mice using ELISA kits from different companies. Wildtype (WT) mice were exposed to different ototoxic treatments, including noise exposure and ototoxic reagents that rapidly kill OHCs. Prestin-knockout (KO) mice were used as a negative control. Our data show that some ELISA kits were not able to detect prestin specifically. The ELISA kit that could detect the prestin protein from cochlear homogenates failed to detect prestin in the bloodstream, despite there being significant damage to OHCs in the cochleae. Furthermore, the optical densities of the serum samples, which correlate to prestin quantities, were significantly influenced by hemolysis in the samples. In conclusion, Prestin from OHCs is not a sensitive and reliable serological biomarker for detecting cochlear damage in mice using ELISA.

The motor protein Prestin found in the outer hair cells (OHCs) of the inner ear is responsible for producing high sensitivity and sharp frequency selectivity for mammalian hearing. Some studies have suggested that Prestin could serve as a serological biomarker for cochlear damage since OHCs are highly vulnerable to damage from various sources of insults. However, the reported data are inconsistent and lack appropriate negative controls. To investigate this further, we measured Prestin quantities in the bloodstream using ELISA kits from different companies. Wildtype (WT) mice were exposed to different ototoxic treatments, including noise exposure and ototoxic reagents that kill OHCs rapidly. Prestin-knockout (KO) mice were used as a negative control. Our data show that some ELISA kits were not able to detect Prestin specifically. The ELISA kit that could detect Prestin protein from cochlear homogenates failed to detect Prestin in the bloodstream despite significant damage to OHCs in cochleae. Furthermore, the optical densities of samples, which correlate to Prestin quantities, were significantly influenced by hemolysis in the samples. In conclusion, Prestin from OHCs is not a sensitive and reliable serological biomarker for detecting cochlear damage in mice.

High-resolution visualization of cochlear cisplatin distribution is essential for understanding its pharmacokinetics and ototoxicity. We employed synchrotron X-ray fluorescence microscopy (XFM) to map platinum (Pt) at sub-micron resolution. Adult male FVB mice received cisplatin (10 mg/kg) through intravenous (i.v.) or intraperitoneal (i.p.) administration. Cochleae were collected on days 1, 7, and 14, cryo-sectioned, and scanned using XFM. Cochlear Pt signal increased progressively through day 14. Notably, i.v. administration led to higher Pt levels than the i.p. route, with the highest increase observed in the organ of Corti on day 14. These results provided the first cell-specific mapping of cochlear Pt distribution and revealed a persistent Pt accumulation long after systemic cisplatin clearance from plasma. Although no significant hearing loss was detected on day 14, the distinct of Pt kinetics between administration routes highlighted critical disconnections in cispla-tin-induced hearing loss between clinical chemotherapy and current preclinical animal models.

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.

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 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 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 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 Cdh23^753G→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.

Cisplatin-induced hearing loss (CIHL) is a debilitating side effect in cancer patients undergoing chemotherapy. So far, epigenetic studies in the inner ear have largely focused on developmental biology to regenerate hair cells. In post-mitotic hair cells, on the other hand, DNA methylation regulates transcriptomic response to external stimuli. Adult mammalian hair cells are locked in the G0 phase, and passive demethylation via DNA replication does not occur under normal physiological conditions. However, external stimuli such as cisplatin can aberrantly upregulate DNMT methyltransferases (DNMTs), resulting in promoter methylation and silencing protective genes. From this angle, DNMTs modulation is an attractive therapeutic strategy to protect hearing during chemotherapy. Recent studies suggest that non-nucleoside inhibitors such as RG108 and natural polyphenolic compounds downregulate DNMTs, and at the same time, protect auditory cells. These compounds function via the inhibition of the DNMT catalytic site but can also act through downregulating DNMT1 and DNMT3A/B at mRNA and protein levels. Polyphenols are also antioxidants, decreasing reactive oxygen species, thereby increasing cell survival. Furthermore, it is suggested that upregulating TET-mediated active demethylation can be another angle to modify DNA methylation in cancer and CIHL models. However, functional DNA methylation should be distinguished from non-functional, passenger DNA methylation to elucidate the compounds’ otoprotective effects. In addition, the candidate compounds should not interfere with cisplatin’s antitumor effect. In this review, we investigate the relationship between DNA methylation and CIHL in the post-mitotic inner ear and evaluate the therapeutic potential of candidate DNMT inhibitors.