Dock4 is required for the maintenance of cochlear hair cells and hearing function

Gene expression analysis of oxidative stress-related genes in the apical, middle, and basal turns of the cochlea

It can be observed from aminoglycoside-induced hair cell damage that the cochlea basal turn is more susceptible to trauma than the apex. Drug-induced hearing loss is closely related to oxidative damage. The basilar membrane directly exposed to these ototoxic drugs exhibits differences in damage, indicating that there is an inherent difference in the sensitivity to oxidative damage from the apex to the base of the cochlea. It has been reported that the morphology and characteristics of the cochlea vary from the apex to the base. Therefore, we investigated oxidative stress-related gene expression profiles in the apical, middle, and basal turns of the cochlea. The Oxidative Stress RT2 Profiler™ PCR Array revealed that three of the 84 genes (Mb, Mpo, and Ncf1) were upregulated in the middle turn compared to their level in the apical turn. Moreover, eight genes (Mb, Duox1, Ncf1, Ngb, Fmo2, Gpx3, Mpo, and Gstk1) were upregulated in the basal turn compared to their level in the apical turn. The qPCR verification data were similar to that of the PCR Array. We found that MPO was expressed in the rat cochlea and protected against gentamicin-induced hair cell death. This study summarized the data for the gradient of expression of oxidative stress-related genes in the cochlea and found potential candidate targets for prevention of ototoxic deafness, which may provide new insights for cochlear pathology.

SIRT3/GLUT4 signaling activation by metformin protect against cisplatin-induced ototoxicity in vitro

Cisplatin is highly effective for killing tumor cells. However, as one of its side effects, ototoxicity limits the clinical application of cisplatin. The mechanisms of cisplatin-induced ototoxicity have not been fully clarified yet. SIRT3 is a deacetylated protein mainly located in mitochondria, which regulates a variety of physiological processes in cells. The role of SIRT3 in cisplatin-induced hair cell injury has not been founded. In this study, primary cultured cochlear explants exposed to 5 μM cisplatin, as well as OC-1 cells exposed to 10 μM cisplatin, were used to establish models of cisplatin-induced ototoxicity in vitro. We found that when combined with cisplatin, metformin (75 μM) significantly up-regulated the expression of SIRT3 and alleviated cisplatin-induced apoptosis of hair cells. We regulated the expression of SIRT3 to explore the role of SIRT3 in cisplatin-induced auditory hair cell injury. Overexpression of SIRT3 promoted the survival of auditory hair cells and alleviated the apoptosis of auditory hair cells. In contrast, knockdown of SIRT3 impaired the protective effect of metformin and exacerbated cisplatin injury. In addition, we found that the protective effect of SIRT3 may be achieved by regulating GLUT4 translocation and rescuing impaired glucose uptake caused by cisplatin. Our study confirmed that upregulation of SIRT3 may antagonize cisplatin-induced ototoxicity, and provided a new perspective for the study of cisplatin-induced ototoxicity.

ftr82 is necessary for hair cell morphogenesis and auditory function during zebrafish development

Damages of sensory hair cells (HCs) are mainly responsible for sensorineural hearing loss, while the pathological mechanism remains not fully understood due to the many potential deafness genes unidentified. ftr82, a member of the largely TRIMs family in fish, has been found specifically expressed in the otic vesicle while its function is still unclear. Here, we investigate the roles of ftr82 in HC development and hearing function utilizing the zebrafish model. The results of in situ hybridization illustrate that ftr82 is always restricted to localize in otic vesicles at different stages. The defects of HCs are observed both in ftr82 morphants and mutants, including significantly decreased crista HCs, shortened cilia as well as remarkably reduced functional HCs in neuromasts, which could be successfully rescued by co-injection of exogenous ftr82 mRNA. The behavior assay of startle response indicates that larvae lacking of ftr82 exhibits lower sensitivity to external sound stimuli. Further research reveals that the loss of HCs is mainly caused by cell apoptosis mediated by caspase-3 activation. Our study demonstrates that ftr82 is a crucial hearing-related gene that regulates the HC morphogenesis and auditory function performing, which provides new insight into the rapid identification of the deafness gene.

Adenovirus-mediated SIRT1 protects cochlear strial marginal cells in a D-gal-induced senescent model in vitro

BACKGROUND

A primary obstacle in age-related hearing loss (ARHL) study is the lack of accelerated senescent models in vitro that explore the precise underlying mechanism in different types of ARHL. The damage to strial marginal cells (SMCs) is a subset of strial presbycusis-associated pathological changes. We aimed to establish a D-galactose (D-gal)-induced SMCs senescent model and study the effect of deacetylase sirtuin 1 (SIRT1) on presbycusis in vitro.

METHODS

SMCs from C57BL/6J neonatal mice were cultured and treated with D-gal to establish accelerated senescent models. And then D-gal-induced SMCs were transfected with adenovirus (Ad)-SIRT1-GFP or Ad-GFP. Oxidative stress and mitochondrial DNA (mtDNA) damage were determined by histological analysis or RT-PCR. Western blotting (WB) and RT-PCR were used to evaluate protein and mRNA levels of superoxide dismutase 2 (SOD2) and SIRT1, respectively. Additionally, apoptosis was investigated by WB and TUNEL staining.

RESULTS

D-gal-induced SMCs exhibited several characteristics of senescence, including increased the level of 8-hydroxy-2'-deoxyguanosine, which is a marker of DNA oxidative damage, and elevated the amount of mtDNA 3860-bp deletion, which is a common type of mtDNA damage in the auditory system of mice. SIRT1 overexpression effectively inhibited these changes by upregulating the level of SOD2, thereby inhibiting cytochrome c translocation from mitochondria to cytoplasm, inhibiting cell apoptosis, and ultimately delaying aging in the D-gal-induced senescent SMCs.

CONCLUSIONS

Altogether, the evidence suggests that the D-gal-induced SMCs accelerated aging model is successfully established, and SIRT1 overexpression protects SMCs against oxidative stress by enhancing SOD2 expression in ARHL.

Characteristics of sound localization in children with unilateral microtia and atresia and predictors of localization improvement when using a bone conduction device

This study aimed to determine the characteristics of sound localization in children with unilateral microtia and atresia (UMA) and the influence of a non-surgical bone conduction device (BCD). Hearing benefits were evaluated by the word recognition score (WRS), speech reception threshold, the international outcome inventory for hearing aids (IOI-HA), and the Speech, Spatial, and Qualities of Hearing Test for Parent (SSQ-P). Sound localization was measured using broadband noise stimuli randomly played from seven loudspeakers at different stimulus levels [65, 70, and 75 dB sound pressure levels (SPLs)]. The average unaided WRS and speech-to-noise ratio (SNR) for UMA patients was 18.27 ± 14.63 % and -5 ± 1.18 dB SPL, and the average aided WRS and SNR conspicuously changed to 85.45 ± 7.38 % and -7.73 ± 1.42 dB SPL, respectively. The mean IOI-HA score was 4.57 ± 0.73. Compared to the unaided condition, the mean SSQ-P score in each domain improved from 7.08 ± 2.5, 4.86 ± 2.27, and 6.59 ± 1.4 to 8.72 ± 0.95, 7.61 ± 1.52, and 8.55 ± 1.09, respectively. In the sound localization test, some children with UMA were able to detect sound sources quite well and the sound localization abilities did not deteriorate with the non-surgical BCD. Our study concludes that for children with UMA, the non-surgical BCD provided a definite benefit on speech recognition and high satisfaction without deteriorating their sound localization abilities. It is an efficient and safe solution for the early hearing intervention of these patients.