Down-regulation of the large conductance Ca(2+)-activated K(+) channel expression in C57BL/6J cochlea

Downregulation of KCNMA1 in mice accelerates auditory hair cells senescence via ferroptosis

KCNMA1 encodes the K+ potassium channel α-subunit that plays a significant role in the auditory system. Our previous studies indicated that KCNMA1 is associated with age-related hearing loss(AHL). However, the detailed mechanism of KCNMA1 involvement in auditory age-related degradation has not been fully clarified. Therefore, we explored the expression of KCNMA1 in the peripheral auditory of 2-month-old and 12-month-old mice by Western blotting and immunofluorescence. The results of animal experiments showed that KCNMA1 expression was decreased in 12-month-old mice compared with 2-month-old mice, whereas the ferroptosis level was increased. To verify the role of KCNMA1 in AHL, we downregulated KCNMA1 in HEI-OC1 cells by transfecting shRNA. After downregulation, the ferroptosis level was increased and the aging process was accelerated. Furthermore, the aging process was affected by the expression of ferroptosis. In conclusion, these results revealed that KCNMA1 is associated with the aging process in auditory hair cells by regulating ferroptosis, which deepens our understanding of age-related hearing loss.

Bile Acid Application in Cell-Targeting for Molecular Receptors in Relation to Hearing: A Comprehensive Review

Bile acids play important roles in the human body, and changes in their pool can be used as markers for various liver pathologies. In addition to their functional effects in modulating inflammatory responses and cellular survivability, the unconjugated or conjugated, secondary, or primary nature of bile acids accounts for their various ligand effects. The common hydrophilic bile acids have been used successfully as local treatment to resolve drug-induced cell damage or to ameliorate hearing loss. From various literature references, bile acids show concentration and tissue-dependent effects. Some hydrophobic bile acids act as ligands modulating vitamin D receptors, muscarinic receptors, and calcium-activated potassium channels, important proteins in the inner ear system. Currently, there are limited resources investigating the therapeutic effects of bile acid on hearing loss and little to no information on detecting bile acids in the remote ear system, let alone baseline bile acid levels and their prevalence in healthy and disease conditions. This review presents both hydrophilic and hydrophobic human bile acids and their tissue-specific effects in modulating cellular integrity, thus considering the possible effects and extended therapeutic applicability of bile acids to the inner ear tissue.

Factors influencing the relationship between cochlear health measures and speech recognition in cochlear implant users

Background

One factor which influences the speech intelligibility of cochlear implant (CI) users is the number and the extent of the functionality of spiral ganglion neurons (SGNs), referred to as "cochlear health." To explain the interindividual variability in speech perception of CI users, a clinically applicable estimate of cochlear health could be insightful. The change in the slope of the electrically evoked compound action potentials (eCAP), amplitude growth function (AGF) as a response to increased interphase gap (IPG) (IPGE_slope) has been introduced as a potential measure of cochlear health. Although this measure has been widely used in research, its relationship to other parameters requires further investigation.

Methods

This study investigated the relationship between IPGE_slope, demographics and speech intelligibility by (1) considering the relative importance of each frequency band to speech perception, and (2) investigating the effect of the stimulus polarity of the stimulating pulse. The eCAPs were measured in three different conditions: (1) Forward masking with anodic-leading (FMA) pulse, (2) Forward masking with cathodic-leading (FMC) pulse, and (3) with alternating polarity (AP). This allowed the investigation of the effect of polarity on the diagnosis of cochlear health. For an accurate investigation of the correlation between IPGE_slope and speech intelligibility, a weighting function was applied to the measured IPGE_slopes on each electrode in the array to consider the relative importance of each frequency band for speech perception. A weighted Pearson correlation analysis was also applied to compensate for the effect of missing data by giving higher weights to the ears with more successful IPGE_slope measurements.

Results

A significant correlation was observed between IPGE_slope and speech perception in both quiet and noise for between-subject data especially when the relative importance of frequency bands was considered. A strong and significant correlation was also observed between IPGE_slope and age when stimulation was performed with cathodic-leading pulses but not for the anodic-leading pulse condition.

Conclusion

Based on the outcome of this study it can be concluded that IPGE_slope has potential as a relevant clinical measure indicative of cochlear health and its relationship to speech intelligibility. The polarity of the stimulating pulse could influence the diagnostic potential of IPGE_slope.

Downregulation of Cav3.1 T-type Calcium Channel Expression in Age-related Hearing Loss Model

OBJECTIVE

Age-related hearing loss (AHL), characterized by degeneration of cochlea structures, is the most common sensory disorder among the elderly worldwide. The calcium channel is considered to contribute to normal hearing. However, the role of the T-type voltage-activated calcium channel, Cav3.1, remains unclear in AHL. Here, we investigate the age-related change of Cav3.1 expression in the cochlea and D-gal-induced senescent HEI-OC1 cells.

METHODS

Cochleae from C57BL/6 mice at 2 months and 12 months of age were assessed. Senescence in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells was induced by D-gal treatment. The immunofluorescence technique was employed to investigate the distribution of Cav3.1 in vivo and in vitro. Quantitative assessment was achieved by Western blotting and real-time PCR.

RESULTS

In comparison with 2-month-old animals, 12-month old C57BL/6 mice exhibited great loss of hair cells and elevated auditory brainstem threshold. The Cav3.1 was located in hair cells, spiral ganglion cells, lateral walls, and the expression of Cav3.1 protein and mRNA decreased in the aged cochleae. D-gal-induced senescence assay confirmed the down-regulation of Cav3.1 expression in senescent HEI-OC1 cells.

CONCLUSION

Our results show that age-related down-regulated expression of Cav3.1 in the cochleae is associated with AHL and may contribute to the pathogenesis of AHL.