Caspase-Mediated Apoptosis in the Cochleae Contributes to the Early Onset of Hearing Loss in A/J Mice

A/J and C57BL/6 J (B6) mice share a mutation in Cdh23 (ahl allele) and are characterized by age-related hearing loss. However, hearing loss occurs much earlier in A/J mice at about four weeks of age. Recent study has revealed that a mutation in citrate synthase (Cs) is one of the main contributors, but the mechanism is largely unknown. In the present study, we showed that A/J mice displayed more severe degeneration of hair cells, spiral ganglion neurons, and stria vascularis in the cochleae compared with B6 mice. Moreover, messenger RNA accumulation levels of caspase-3 and caspase-9 in the inner ears of A/J mice were significantly higher than those in B6 mice at 2 and 8 weeks of age. Immunohistochemistry localized caspase-3 expression mainly to the hair cells, spiral ganglion neurons, and stria vascularis in cochleae. In vitro transfection with Cs short hairpin RNA (shRNA) alone or cotransfection with Cs shRNA and Cdh23 shRNA significantly increased the levels of caspase-3 in an inner ear cell line (HEI-OC1). Finally, a pan-caspase inhibitor Z-VAD-FMK could preserve the hearing of A/J mice by lowering about 15 decibels of the sound pressure level for the auditory-evoked brainstem response thresholds. In conclusion, our results suggest that caspase-mediated apoptosis in the cochleae, which may be related to a Cs mutation, contributes to the early onset of hearing loss in A/J mice.     

噪声所致听力损失现象的物种差异及可能生理机制研究进展

噪声广泛存在于人和动物的生活环境中,从无脊椎动物到哺乳动物乃至人类,都会受到噪声的负面影响.强烈的噪声会损伤听觉系统的结构和功能,引起噪声性听力损失(noise-induced hearing loss,NIHL).本文对噪声性听力损失的类型、影响因素、噪声所致不同程度听力损失形成的可能机制进行了总结,发现NIHL主要与突触结构肿胀、谷氨酸引起的可逆兴奋性中毒以及活性氧引起的氧化应激、细胞凋亡、带状体损伤、α激动型鸟嘌呤核苷酸结合蛋白(guanine nucleotide binding protein alpha stimulating,GNAS)基因的mRNA及其上游lncRNA Sept7的表达量上调等因素有关.比较噪声暴露后不同物种听力损失情况的差异,发现鱼类和鸟类由于具有毛细胞再生能力而能够较快从听力损伤中恢复,啮齿类较容易受到噪声影响,而回声定位鲸类噪声暴露后的暂时性听觉阈移较小,非常有趣的是回声定位蝙蝠在噪声高强度暴露后未表现出暂时性听觉阈移的现象.上述结论提示,对不同物种的比较生理研究可深入揭示NIHL机制,并为听力保护以及噪声所致的听力损伤后修复等提供理论参考.     

DKK1 Mediated Inhibition of Wnt Signaling in Postnatal Mice Leads to Loss of TEC Progenitors and Thymic Degeneration

Background

Thymic epithelial cell (TEC) microenvironments are essential for the recruitment of T cell precursors from the bone marrow, as well as the subsequent expansion and selection of thymocytes resulting in a mature self-tolerant T cell repertoire. The molecular mechanisms, which control both the initial development and subsequent maintenance of these critical microenvironments, are poorly defined. Wnt signaling has been shown to be important to the development of several epithelial tissues and organs. Regulation of Wnt signaling has also been shown to impact both early thymocyte and thymic epithelial development. However, early blocks in thymic organogenesis or death of the mice have prevented analysis of a role of canonical Wnt signaling in the maintenance of TECs in the postnatal thymus.

Methodology/Principal Findings

Here we demonstrate that tetracycline-regulated expression of the canonical Wnt inhibitor DKK1 in TECs localized in both the cortex and medulla of adult mice, results in rapid thymic degeneration characterized by a loss of ΔNP63⁺ Foxn1⁺ and Aire⁺ TECs, loss of K5K8DP TECs thought to represent or contain an immature TEC progenitor, decreased TEC proliferation and the development of cystic structures, similar to an aged thymus. Removal of DKK1 from DKK1-involuted mice results in full recovery, suggesting that canonical Wnt signaling is required for the differentiation or proliferation of TEC populations needed for maintenance of properly organized adult thymic epithelial microenvironments.

Conclusions/Significance

Taken together, the results of this study demonstrate that canonical Wnt signaling within TECs is required for the maintenance of epithelial microenvironments in the postnatal thymus, possibly through effects on TEC progenitor/stem cell populations. Downstream targets of Wnt signaling, which are responsible for maintenance of these TEC progenitors may provide useful targets for therapies aimed at counteracting age associated thymic involution or the premature thymic degeneration associated with cancer therapy and bone marrow transplants.     

The expression of PHB2 in the cochlea: Possible relation to age-related hearing loss

Age-related hearing loss (ARHL) is the most prevalent sensory deficit in the elderly, but its mechanism remains unclear. Scaffold protein prohibitin 2 (PHB2) has been widely involved in aging and neurodegeneration. However, the role of PHB2 in ARHL is undeciphered to date. To investigate the expression pattern and the role of PHB2 in ARHL, we used C57BL/6 mice and HEI-OC1 cell line as models. In our study, we have found PHB2 exists in the cochlea and is expressed in hair cells, spiral ganglion neurons, and HEI-OC1 cells. In mice with ARHL, mitophagy is reduced and correspondingly the expression level of PHB2 is decreased. Moreover, after H₂O₂ treatment the mitophagy is activated and the PHB2 expression is increased. These findings indicate that PHB2 may exert an important role in ARHL through mitophagy. Findings from this study will be helpful for elucidating the mechanism underlying the ARHL and for providing a new target for ARHL treatment.     

血脂及血液流变学指标与突发性聋患者听力曲线类型的关系及其临床疗效的影响因素分析

摘要 目的：探究血脂及血液流变学指标与突发性聋（SSHL）患者听力曲线类型的关系,并分析临床疗效的影响因素。方法：选取2020年6月-2022年1月我院收治的103例SSHL患者设为SSHL组,另选取103例体检健康者设为健康组,分析两组血脂水平及血液流变学指标,比较不同听力曲线类型的SSHL患者血脂水平及血液流变学指标,Spearman相关分析血脂水平及血液流变学指标与SSHL患者听力曲线类型的关系,单因素和多因素Logistic回归模型分析SSHL患者临床疗效的影响因素。结果：与健康组比较,SSHL组总胆固醇（TC）、三酰甘油（TG）与全血高切、中切、低切粘度及血浆粘度明显增高（P＜0.05）,高密度脂蛋白-C（HDL-C）、低密度脂蛋白-C（LDL-C）差异比较无统计学意义（P＞0.05）。不同听力曲线类型的SSHL患者各项血脂指标比较差异均无统计学意义（P＞0.05）,不同听力曲线类型的SSHL患者各项血液流变学指标比较差异均有统计学意义（P＜0.05）,其中全聋型患者各项血液流变学指标显著高于低频下降型患者（P＜0.05）。血脂四项与SSHL听力曲线类型无显著相关性（P＞0.05）,而血液流变学指标与SSHL听力曲线类型显著相关（P<0.05）。治疗无效组患者双耳患病比例、听力曲线类型为全聋型比例、全血高切粘度、全血低切粘度、血浆粘度显著高于有效组患者（P＜0.05）,多因素Logistic分析结果显示：双耳患病、听力曲线类型为全聋型、血浆粘度增加为SSHL患者治疗无效的危险因素（P＜0.05）。结论：SSHL患者存在血脂及血液流变学异常,血液流变学与SSHL患者听力曲线类型和临床疗效有一定关系,其中双耳患病、全聋型、血浆粘度增加为SSHL患者治疗无效的危险因素,检测血脂和血液流变学对于SSHL诊治具有一定临床指导意义。     

Reduced acoustic startle response and peripheral hearing loss in the 5xFAD mouse model of Alzheimer's disease

Hearing dysfunction has been associated with Alzheimer's disease (AD) in humans, but there is little data on the auditory function of mouse models of AD. Furthermore, characterization of hearing ability in mouse models is needed to ensure that tests of cognition that use auditory stimuli are not confounded by hearing dysfunction. Therefore, we assessed acoustic startle response and pre‐pulse inhibition in the double transgenic 5xFAD mouse model of AD from 3–4 to 16 months of age. The 5xFAD mice showed an age‐related decline in acoustic startle as early as 3–4 months of age. We subsequently tested auditory brainstem response (ABR) thresholds at 4 and 13–14 months of age using tone bursts at frequencies of 2–32 kHz. The 5xFAD mice showed increased ABR thresholds for tone bursts between 8 and 32 kHz at 13–14 months of age. Finally, cochleae were extracted and basilar membranes were dissected to count hair cell loss across the cochlea. The 5xFAD mice showed significantly greater loss of both inner and outer hair cells at the apical and basal ends of the basilar membrane than wild‐type mice at 15–16 months of age. These results indicate that the 5xFAD mouse model of AD shows age‐related decreases in acoustic startle responses, which are at least partially due to age‐related peripheral hearing loss. Therefore, we caution against the use of cognitive tests that rely on audition in 5xFAD mice over 3–4 months of age, without first confirming that performance is not confounded by hearing dysfunction.     

Biochemical and molecular analyses of copper-zinc superoxide dismutase from a C4 plant Pennisetum glaucum reveals an adaptive role in response to oxidative stress

Cadherin 23 (CDH23) is an important constituent of the hair cell tip link in the organ of Corti. Mutations in cdh23 are associated with age-related hearing loss (AHL). In this study, we proposed that the Cdh23(nmf308/nmf308) mice with progressive hair cell loss had specific morphological changes and suffered a base to apex gradient and age-related hearing loss, and that mutations in cdh23 were linked to AHL. The Cdh23(nmf308/nmf308) mice produced by the N-nitrosourea (ENU) mutagenesis program were used as an animal model to study AHL and progressive hair cell loss. RT-PCR was performed to confirm the cdh23 mutation in Cdh23(nmf308/nmf308) mice and genetic analysis was used to map the specific mutation site. Distortion product otoacoustic emission (DPOAE) assay and acoustic brainstem evoked response (ABR) threshold analysis were carried out to evaluate the AHL. Cochlear histology was examined with scanning electron microscope (SEM) and transmission electron microscope (TEM), as well as the nuclear labeling by propidium iodide staining; terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay and caspase-3 activities were examined to evaluate cell apoptosis. Genetic mapping identified the candidate gene linking AHL in Cdh23(nmf308/nmf308) mice as cdh23. A mutation in exon3 (63 T>C) was screened as compared with the sequence of the same position of the gene from B6 (+/+) mice. The cochleae outer hair cells were reduced from 5-10% at one month to 100% at three months in the basal region. DPOAE and ABR exhibited an increasing threshold at high frequencies (≥16kHz) from one month of age. Morphological and cellular analysis showed that Cdh23(nmf308/nmf308) mice exhibited a time course of histological alterations and cell apoptosis of outer hair cells. Our results suggest that the cdh23 mutation may be harmful to the stereociliary tip link and cause the hair cell apoptosis. Due to the same cdh23 mutations in human subjects with presbycusis (Petit et al., 2001; Zheng et al., 2005), the Cdh23(nmf308/nmf308) mouse is an excellent animal model for investigating the mechanisms involved in human AHL.     

Sex-Specific Associations Between Diabetes Mellitus and Hearing Loss in the Middle-Aged and Elderly Individuals: A National Cohort Study of Chinese Adults

ObjectiveTo examine the association between diabetes and hearing loss and whether the association varied by sex.MethodsThis cohort study based on nationally representative data from the China Health and Retirement Longitudinal Study included 16 140 Chinese adults aged >45 years between 2011 and 2018. Diabetes was identified by blood glucose levels, HbA1c levels, and a self-reported diagnosis at baseline. The main outcome was self-reported incident hearing loss. Cox proportional hazards regression models were performed to estimate the risk of hearing loss.ResultsWe documented 2388 cases of hearing loss during a median 6.9 years of follow-up. The incidence rates were 29.64 (95% CI, 28.07-31.29) per 1000 person-years in women and 25.23 (95% CI, 23.77-26.78) per 1000 person-years in men. After adjustment, the hazard ratios of hearing loss associated with diabetes were 1.20 (95% CI, 1.01-1.42) for women and 0.97 (95% CI, 0.78-1.19) for men. Compared with poor control of the blood sugar levels, the odds ratio for hearing loss for women with good glycemic control was reduced from 5.08 (95% CI, 1.31-19.66) to 1.26 (95% CI, 0.69-2.28), and the corresponding odds ratio for men was 1.65 (95% CI, 0.61-4.44) to 0.50 (95% CI, 0.18-1.38).ConclusionIn conclusion, we identified a differential effect of sex on hearing loss risk with more pronounced effects for women. Our data suggest that good blood glucose level control is helpful to prevent hearing loss.