Correlation of PDCD5 and apoptosis in hair cells and spiral ganglion neurons of different age of C57BL/6J mice

Downregulation of inwardly rectifying potassium channel 5.1 expression in C57BL/6J cochlear lateral wall

Age-related hearing loss (AHL) is one of the most common sensory disorders among elderly persons. The inwardly rectifying potassium channel 5.1 (Kir5.1) plays a vital role in regulating cochlear K(+) circulation which is necessary for normal hearing. The distribution of Kir5.1 in C57BL/6J mice cochleae, and the relationship between the expression of Kir5.1 and the etiology of AHL were investigated. Forty C57BL/6J mice were randomly divided into four groups at 4, 12, 24 and 52 weeks of age respectively. The location of Kir5.1 was detected by immunofluorescence technique. The mRNA and protein expression of Kir5.1 was evaluated in mice cochleae using real-time polymerase-chain reactions (RT-PCR) and Western blotting respectively. Kir5.1 was detected in the type II and IV fibrocytes of the spiral ligament in the cochlear lateral wall of C57BL/6J mice. The expression levels of Kir5.1 mRNA and protein in the cochleae of aging C57BL/6J mice were down-regulated. It was suggested that the age-related decreased expression of Kir5.1 in the lateral wall of C57BL/6J mice was associated with hearing loss. Our results indicated that Kir5.1 may play an important role in the pathogenesis of AHL.

Differential effects of Cdh23(753A) on auditory and vestibular functional aging in C57BL/6J mice

The C57BL/6J (B6) mouse strain carries a cadherin 23 mutation (Cdh23(753A), also known as Ahl), which affects inner ear structures and results in age-related hearing loss. The B6.CAST strain harbors the wild type Cdh23 gene, and hence, the influence of Ahl is absent. The purpose of the present study was to characterize the effect of age and gender on gravity receptor function in B6 and B6.CAST strains and to compare functional aging between auditory and vestibular modalities. Auditory sensitivity declined at significantly faster rates than gravity receptor sensitivity for both strains. Indeed, vestibular functional aging was minimal for both strains. The comparatively smaller loss of macular versus cochlear sensitivity in both the B6 and B6.CAST strains suggests that the contribution of Ahl to the aging of the vestibular system is minimal, and thus very different than its influence on aging of the auditory system. Alternatively, there exist unidentified genes or gene modifiers that serve to slow the degeneration of gravity receptor structures and maintain gravity receptor sensitivity into advanced age.

Age-related change in the expression of NKCC1 in the cochlear lateral wall of C57BL/6J mice

CONCLUSIONS

Na(+)-K(+)-2Cl(-) co-transporter isoform 1 (NKCC1) mRNA and protein decrease with increasing age in the cochlear lateral wall of C57BL/6J (C57) mice. The down-regulation of NKCC1 may influence the K(+) transport efficiency and the homeostasis of ion transport cells, and cause the irreversible damage of cochlear cells in old C57 mice. Our results indicate that NKCC1 may play an important role in the pathogenesis of age-related hearing loss (AHL).

OBJECTIVES

The aim of the present study was to investigate the relationship between the functional expression of NKCC1 transporter and the etiology of AHL.

METHODS

C57 mice were used and randomly divided into four groups according to age (4 weeks, 14 weeks, 26 weeks, and 52 weeks). Immunofluorescence technique, quantitative real-time PCR, and western blot were applied to detect the expression of NKCC1 in the cochlear lateral wall of C57 mice at the various ages.

RESULTS

In all four groups, the expression of NKCC1 was observed in the stria vascularis and type II fibrocytes of the spiral ligament. Also, the expression of NKCC1 appeared to decrease with age at both the transcriptional level and the protein level.