Damage of Inner Ear Sensory Hair Cells via Mitochondrial Loss in a Murine Model of Sleep Apnea With Chronic Intermittent Hypoxia

The common link between sleep apnea syndrome and osteoarthritis: a literature review

Patients with Osteoarthritis (OA) often also suffer from Sleep Apnea Syndrome (SAS), and many scholars have started to notice this link, although the relationship between the two is still unclear. In this review, we aim to summarize the current literature on these two diseases, integrate evidence of the OA and OSA connection, explore and discuss their potential common mechanisms, and thus identify effective treatment methods for patients with both OA and SAS. Some shared characteristics of the two conditions have been identified, notably aging and obesity as mutual risk factors. Both diseases are associated with various biological processes or molecular pathways, including mitochondrial dysfunction, reactive oxygen species production, the NF-kB pathway, HIF, IL-6, and IL-8. SAS serves as a risk factor for OA, and conversely, OA may influence the progression of SAS. The effects of OA on SAS are underreported in the literature and require more investigation. To effectively manage these patients, timely intervention for SAS is necessary while treating OA, with weight reduction being a primary requirement, alongside combined treatments such as Continuous positive airway pressure (CPAP) and medications. Additionally, numerous studies in drug development are now aimed at inhibiting or clearing certain molecular pathways, including ROS, NF-KB, IL-6, and IL-8. Improving mitochondrial function might represent a viable new strategy, with further research into mitochondrial updates or transplants being essential.

Shengmaisan combined with Liuwei Dihuang Decoction alleviates chronic intermittent hypoxia-induced cognitive impairment by activating the EPO/EPOR/JAK2 signaling pathway

Chronic intermittent hypoxia (CIH), a principal pathophysiological aspect of obstructive sleep apnea (OSA), is associated with cognitive deficits. Clinical evidence suggests that a combination of Shengmaisan and Liuwei Dihuang Decoctions (SMS-LD) can enhance cognitive function by nourishing yin and strengthening the kidneys. This study aimed to assess the efficacy and underlying mechanisms of SMS-LD in addressing cognitive impairments induced by CIH. We exposed C57BL/6N mice to CIH for five weeks (20%-5% O2, 5 min/cycle, 8 h/day) and administered SMS-LD intragastrically (15.0 or 30 g·kg-1·day) 30 min before each CIH session. Additionally, AG490, a JJanus kinase 2 (JAK2) inhibitor, was administered via intracerebroventricular injection. Cognitive function was evaluated using the Morris water maze, while synaptic and mitochondrial structures were examined by transmission electron microscopy. Oxidative stress levels were determined using DHE staining, and the activation of the erythropoietin (ER)/ER receptor (EPOR)/JAK2 signaling pathway was analyzed through immunohistochemistry and Western blotting. To further investigate molecular mechanisms, HT22 cells were treated in vitro with either SMS-LD medicated serum alone or in combination with AG490 and then exposed to CIH for 48 h. Our results indicate that SMS-LD significantly mitigated CIH-induced cognitive impairments in mice. Specifically, SMS-LD treatment enhanced dendritic spine density, ameliorated mitochondrial dysfunction, reduced oxidative stress, and activated the EPO/EPOR/JAK2 signaling pathway. Conversely, AG490 negated SMS-LD's neuroprotective and cognitive improvement effects under CIH conditions. These findings suggest that SMS-LD's beneficial impact on cognitive impairment and synaptic and mitochondrial integrity under CIH conditions may predominantly be attributed to the activation of the EPO/EPOR/JAK2 signaling pathway.

Associations of sleep characteristics in late midlife with late-life hearing loss in the Atherosclerosis Risk in Communities-Sleep Heart Health Study (ARIC-SHHS)

OBJECTIVES

This study investigated associations of late midlife sleep characteristics with late-life hearing, which adds to the existing cross-sectional evidence and is novel in examining polysomnographic sleep measures and central auditory processing.

METHODS

A subset of Atherosclerosis Risk in Communities Study participants underwent sleep assessment in the Sleep Heart Health Study in 1996-1998 and hearing assessment in 2016-2017. Peripheral hearing thresholds (0.5-4kHz) assessed by pure-tone audiometry were averaged to calculate speech-frequency pure-tone average in better-hearing ear (higher pure-tone average=worse hearing). Central auditory processing was measured by the Quick Speech-in-Noise Test (lower score=worse performance). Sleep was measured using polysomnography (time spent in stage 1, stage 2, stage 3/4, rapid eye movement sleep; sleep-disordered breathing [apnea-hypopnea index ≥5]) and self-report (habitual sleep duration; excessive daytime sleepiness [Epworth Sleepiness Scale 10]). Linear regression models adjusted for demographic and lifestyle factors with additional adjustment for cardiovascular factors.

RESULTS

Among 719 Atherosclerosis Risk in Communities-Sleep Heart Health Study participants (61 ± 5years, 54% female, 100% White), worse speech-frequency pure-tone average was found with sleep-disordered breathing (2.51dB, 95% confidence interval: 0.27, 4.75) and excessive daytime sleepiness (3.35 dB, 95% confidence interval: 0.81, 5.90). Every additional hour of sleep when sleeping >8 hours was associated with worse Quick Speech-in-Noise score (1.61 points, 95% confidence interval: 0.03, 3.19). Every 10-minute increase in rapid eye movement sleep was associated with 0.14-point better Quick Speech-in-Noise score (95% confidence interval: 0.02, 0.25).

CONCLUSIONS

Sleep abnormalities might be risk factors for late-life hearing loss. Future longitudinal studies are needed to confirm these novel findings and clarify the mechanisms.

D-Galactose and Hypoxia Induce the Early Onset of Age-Related Hearing Loss Deterioration in a Mouse Model

BACKGROUND

We previously showed that aging accelerates after 3 months of exposure to hypoxia and environmental change but not genetic modifications. Here, we aimed to simply induce early-onset age-related hearing loss within a short period based on our previous method.

METHODS

We randomly divided 16 C57BL/6 mice into four groups that were maintained under conditions of normoxia and hypoxia with or without injected D-galactose for 2 months. Deteriorated hearing, the expression of age-related factors, and oxidative stress responses were detected using the click and tone burst auditory brainstem response test, reverse transcription-polymerase chain reaction, and by measuring superoxide dismutase (SOD).

RESULTS

The group maintained under hypoxia combined with D-galactose lost hearing particularly at 24 Hz and 32 Hz at 6 weeks compared with the other groups. Aging-related factors were also significantly decreased in the hypoxia and D-galactose groups. However, SOD levels did not significantly differ among the groups.

CONCLUSION

Age-related hearing loss is an environmental disorder induced by chronic oxidative stress associated with genetic backgrounds. Our findings suggested that D-galactose and hypoxia can induce the phenotypes of age-related hearing loss and aging-associated molecules in a murine model within a short time with environmental stimulation alone.

Oxidative Stress in Obstructive Sleep Apnea Syndrome: Putative Pathways to Hearing System Impairment

INTRODUCTION

OSAS is a disease that affects 2% of men and 4% of women of middle age. It is a major health public problem because untreated OSAS could lead to cardiovascular, metabolic, and cerebrovascular complications. The more accepted theory relates to oxidative stress due to intermittent hypoxia, which leads, after an intense inflammatory response through multiple pathways, to endothelial damage. The objective of this study is to demonstrate a correlation between OSAS and hearing loss, the effect of the CPAP on hearing function, and if oxidative stress is also involved in the damaging of the hearing system.

METHODS

A review of the literature has been executed. Eight articles have been found, where seven were about the correlation between OSAS and the hearing system, and only one was about the CPAP effects. It is noted that two of the eight articles explored the theory of oxidative stress due to intermittent hypoxia.

RESULTS

All studies showed a significant correlation between OSAS and hearing function (p < 0.05).

CONCLUSIONS

Untreated OSAS affects the hearing system at multiple levels. Oxidative stress due to intermittent hypoxia is the main pathogenetic mechanism of damage. CPAP has no effects (positive or negative) on hearing function. More studies are needed, with the evaluation of extended high frequencies, the execution of vocal audiometry in noisy environments, and the evaluation of potential biomarkers due to oxidative stress.

Is sleep apnea truly associated with hearing loss? A nationwide, population-based study with STOP-BANG questionnaire

Objectives

We aimed to investigate the effect of obstructive sleep apnea (OSA) on hearing ability.

Methods

We retrospectively reviewed the population-based survey data collected by the Korean National Health and Nutrition Examination Survey between January 1, 2019 and December 31, 2020. The data included 3,575 participants who completed the STOP-BANG questionnaire (SBQ) and pure-tone audiometry. OSA risk was assessed using the SBQ, and the hearing level was compared between the risk groups.

Results

Among the 3,575 participants, 2,152 (60.2%), 891 (24.9%), and 532 (14.9%) were classified as being low, intermediate, and high risk, respectively. The intermediate- and high-risk groups showed significantly worse hearing levels than the low-risk group. When age and sex were adjusted, the hearing level did not differ between the risk groups.

Conclusion

The study found that the presence of OSA minimally affected hearing level. Because hearing loss due to hypoxic damage develops over a long period of time, further research on the association between the duration of OSA, rather than the presence or severity of OSA, and hearing loss is needed.

Mitochondrial replication, transcription, and function in obstructive sleep apnea

We assessed mitochondrial replication, transcription, and function in the upper airways of obstructive sleep apnea (OSA) patients and the effects of uvulopalatopharyngoplasty. Twenty subjects with mild and 40 with moderate to severe OSA requiring uvulopalatopharyngoplasty were included. Mitochondrial transcription factor A (TFAM) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) in uvula specimens were assessed by immunohistochemical staining, and their mRNA and protein expression was examined using reverse-transcription polymerase chain reaction and western blotting, respectively. The mitochondrial to nuclear DNA (Mt/N) ratio in the blood, exhaled breath condensate (EBC), and uvula was measured using quantitative reverse-transcription polymerase chain reaction. TFAM and PGC-1α protein concentrations in the plasma and EBC were determined using enzyme-linked immunosorbent assay. All tested parameters were higher in the OSA group than in the control. Three months later, 21 uvulopalatopharyngoplasty-responsive patients with OSA showed decreased TFAM and PGC-1α concentrations and EBC Mt/N ratio while these remained high in 19 uvulopalatopharyngoplasty-unresponsive patients. The OSA group showed severe inflammation, increased mitochondrial replication and transcription-related signaling, and mitochondrial dysfunction in the uvula. Successful OSA treatment using uvulopalatopharyngoplasty restored the TFAM and PGC-1α levels and EBC Mt/N ratio.

Molecular Pathology, Oxidative Stress, and Biomarkers in Obstructive Sleep Apnea

Obstructive sleep apnea syndrome (OSAS) is characterized by intermittent hypoxia (IH) during sleep due to recurrent upper airway obstruction. The derived oxidative stress (OS) leads to complications that do not only concern the sleep-wake rhythm but also systemic dysfunctions. The aim of this narrative literature review is to investigate molecular alterations, diagnostic markers, and potential medical therapies for OSAS. We analyzed the literature and synthesized the evidence collected. IH increases oxygen free radicals (ROS) and reduces antioxidant capacities. OS and metabolic alterations lead OSAS patients to undergo endothelial dysfunction, osteoporosis, systemic inflammation, increased cardiovascular risk, pulmonary remodeling, and neurological alterations. We treated molecular alterations known to date as useful for understanding the pathogenetic mechanisms and for their potential application as diagnostic markers. The most promising pharmacological therapies are those based on N-acetylcysteine (NAC), Vitamin C, Leptin, Dronabinol, or Atomoxetine + Oxybutynin, but all require further experimentation. CPAP remains the approved therapy capable of reversing most of the known molecular alterations; future drugs may be useful in treating the remaining dysfunctions.

UHRF1-induced connexin26 methylation is involved in hearing damage triggered by intermittent hypoxia in neonatal rats

Ubiquitin-like with plant homeodomain and ring finger domains 1 (UHRF1) promotes the maintenance of established patterns of DNA methylation in mammalian cells. Extensive methylation of connexin26 (COX26) during hearing impairment has been demonstrated. The present study aims to determine whether UHRF1 can induce the methylation of COX26 in cochlea damaged by intermittent hypoxia (IH). After the establishment of the cochlear injury model through IH treatment or isolation of the cochlea containing Corti's organ, pathological changes were observed via HE staining. Expressions of COX26 and UHRF1 were detected by quantitative reverse-transcription polymerase chain reaction and Western blot. The effect of COX26 methylation levels was analyzed by methylation-specific PCR (MSP). Phalloidin/immunofluorescence staining was used to observe structural changes. The binding relationship between UHRF1 and COX26 was verified by chromatin immunoprecipitation. IH caused cochlear damage, accompanied by increased methylation of COX26 and expression of UHRF1 in the cochlea of neonatal rats. CoCl₂ treatment caused the loss of cochlear hair cells, downregulation and hypermethylation of COX26, abnormal upregulation of UHRF1, and disordered expressions of apoptosis-related proteins. UHRF1 in cochlear hair cells binds to COX26, and its knockdown upregulated COX26 level. Overexpressed COX26 partially alleviated the CoCl₂-caused cell damage. UHRF1 induces COX26 methylation and aggravates the cochlear damage caused by IH.

Determining the effect of obstructive sleep apnea syndrome on peripheral vestibular system and hearing

There have been studies in the literature regarding the effect of obstructive sleep apnea syndrome on hearing function, but studies on the effect of obstructive sleep apnea syndrome on the peripheral vestibular system are limited. The aim of the present study was to determine whether obstructive sleep apnea syndrome causes functional neurological changes, particularly in the peripheral vestibular system, using the video head impulse test. Overall, 57 patients with obstructive sleep apnea syndrome were included; the 'Snorers' group comprised 20 volunteers diagnosed with simple snoring in the polysomnography test. The severity of apnea was assessed by monitoring cardiac and respiratory functions during sleep in both groups. The video head impulse test and audiological evaluations were performed in both groups. Statistically significant differences were found in the cochlea and semicircular canals of our patients in the video head impulse test and audiological battery tests. It may be assumed that decreased blood oxygen concentrations and chronic hypoxaemia have negative effects on the vestibule, cochlear sensory epithelium, and the auditory pathways. We think that inner ear structures and pathways may be affected due to hypoxia in obstructive sleep apnea syndrome. Therefore, screening patients with obstructive sleep apnea syndrome with an audiometry battery may help to detect inner ear pathologies early.

Advances in Molecular Pathology of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a common syndrome that features a complex etiology and set of mechanisms. Here we summarized the molecular pathogenesis of OSA, especially the prospective mechanism of upper? airway dilator fatigue and the current breakthroughs. Additionally, we also introduced the molecular mechanism of OSA in terms of related studies on the main signaling pathways and epigenetics alterations, such as microRNA, long non-coding RNA, and DNA methylation. We also reviewed small molecular compounds, which are potential targets for gene regulations in the future, that are involved in the regulation of OSA. This review will be beneficial to point the way for OSA research within the next decade.

Effects of Diet and Lifestyle on Audio-Vestibular Dysfunction in the Elderly: A Literature Review

BACKGROUND

The world's age-related health concerns continue to rise. Audio-vestibular disorders, such as hearing loss, tinnitus, and vertigo, are common complaints in the elderly and are associated with social and public health burdens. Various preventative measures can ease their impact, including healthy food consumption, nutritional supplementation, and lifestyle modification. We aim to provide a comprehensive summary of current possible strategies for preventing the age-related audio-vestibular dysfunction.

METHODS

A PubMed, Embase, and Cochrane review databases search was conducted to identify the relationship between diet, lifestyle, and audio-vestibular dysfunction. "Diet", "nutritional supplement", "lifestyle", "exercise", "physical activity", "tinnitus", "vertigo" and "age-related hearing loss" were used as keywords.

RESULTS

Audio-vestibular dysfunction develops and progresses as a result of age-related inflammation and oxidative stress. Diets with anti-inflammatory and antioxidant effects have been proposed to alleviate this illness. A high-fat diet may induce oxidative stress and low protein intake is associated with hearing discomfort in the elderly. Increased carbohydrate and sugar intake positively correlate with the incidence of audio-vestibular dysfunction, whereas a Mediterranean-style diet can protect against the disease. Antioxidants in the form of vitamins A, C, and E; physical activity; good sleep quality; smoking cessation; moderate alcohol consumption; and avoiding noise exposure are also beneficial.

CONCLUSIONS

Adequate diet or nutritional interventions with lifestyle modification may protect against developing audio-vestibular dysfunction in elderly individuals.

Evaluating the role of rare genetic variation in sleep duration

OBJECTIVES

To explore the roles of rare and high-impact variants in sleep duration.

DESIGN

Based on the recently released UK Biobank 200k exome dataset, an exome-wide association study was conducted to detect rare variants (minor allele frequency <0.01) contributing to sleep duration. Variant annotations were performed by the software tool ANNOVAR. Gene-based burden tests of sleep duration were conducted by the SKAT R-package. After quality control, 137,047 subjects were included in this study. CAUSALdb database was used to explore the related mental traits of identified genes.

RESULTS

We detected 730,572 variants with MAF < 1%, including 3873 frameshift variants, 3977 nonframeshift variants, 449,632 nonsynonymous variants, 1293 startloss variants, 10,254 stopgain variants, 413 stoploss variants, 261,130 synonymous variants, and 3102 variants are annotated as unknown. The burden test of exonic variants detected two exome-wide significant associations for sleep duration including TMIE at 3p21.31 (P_{Bonferroni adjusted} = 0.015) and ZIC2 at 13q32.3 (P_{Bonferroni adjusted} = 0.047). There are only nonsynonymous contained in TMIE; as for ZIC2, we detected 2 annotations of variants: nonsynonymous (P_{Bonferroni adjusted} =2.04 × 10^-4) and nonframeshift (P_{Bonferroni adjusted} =0.85). TMIE and ZIC2 were reported to be associated with several mental traits, such as chronotype, depression, and brain natriuretic peptide in published study.

CONCLUSION

This study reported 2 novel candidate genes for a sleep duration, supporting the roles of rare genetic variants in the regulation of sleep duration.

Obstructive Sleep Apnea and Auditory Dysfunction—Does Snoring Sound Play a Role?

The objective of the study was to investigate the relationship between obstructive sleep apnea (OSA) and auditory dysfunction, and to clarify the role of snoring sounds in contributing to auditory dysfunction. A comprehensive assessment of OSA and the auditory system was performed, including overnight polysomnography, detection of the intra-ear canal snoring sound energy (SSE), pure tone average (PTA), tinnitus pitch matching, the tinnitus handicap inventory (THI), and the Epworth sleepiness scale (ESS). The patients were identified as having tinnitus if their THI score was higher than zero or their tinnitus pitches were matched to specific frequencies. The median age, body mass index, and apnea–hypopnea index score were 41 years, 26.4 kg/m², and 29.9 events/h, respectively. Among the 50 participants, 46 (92%) had a normal PTA, and only 4 (8%) patients had mild hearing loss. There was no significant difference in PTA among OSA severities (p = 0.52). Among the 50 participants, 33 patients (66%) were identified as having tinnitus. In the tinnitus group (n = 33), the ESS score (p = 0.01) and intra-ear canal SSE of 851–1500 Hz (p = 0.04) were significantly higher than those in the non-tinnitus group (n = 17). OSA patients with a higher ESS score had a higher risk of tinnitus (odds ratio 1.22 [95% CI: 1.01–1.46]). OSA-related auditory dysfunction emerged in tinnitus rather than in hearing impairment. OSA patients with daytime sleepiness had a higher risk of tinnitus. High-frequency SSE can jeopardize cochlea and is a potential mechanism contributing to tinnitus. Detection of snoring sounds through an intra-ear canal device may be more precise in assessing acoustic trauma from snoring sounds to vulnerable auditory system and thus warrants further research.

Obstructive sleep apnea risk and hearing impairment among occupational noise-exposed male workers

This study aimed to investigate the association between obstructive sleep apnea (OSA) risk and hearing impairment among workers exposed to occupational noise. A cross-sectional study was conducted among 607 healthy male workers at a tire-manufacturing factory. The subjects underwent audiometric testing, and their OSA risk was examined based on the STOP-Bang questionnaire. Hearing impairment was defined as a hearing threshold >25 dB hearing level (HL) in any frequency of 1, 2, 3 and 4 kHz in either ear. High OSA risk was defined as a STOP-bang score of ≥3. Hearing thresholds at 1, 2, 3 and 4 kHz in both ears were significantly higher among workers with high OSA risk than among those with low OSA risk after adjusting for confounders. Multiple logistic regression analysis examining the association of OSA risk and STOP-Bang score with hearing impairment revealed an odds ratio of 1.738 (95% confidence interval [CI] 1.113-2.713, p = 0.015) and 1.256 (95% CI 1.031-1.529, p = 0.023), respectively, after adjusting for confounders. In addition, when the hearing impairment was reclassified into high- and low-frequency hearing impairment, a statistically significant OR was seen for high-frequency hearing impairment. In conclusion, high OSA risk was associated with hearing impairment in occupational noise-exposed workers, especially in the high-frequency range of 3 and 4 kHz. More efforts are required to improve the management of OSA and its risk factors to preserve hearing in occupational noise-exposed workers.

Continuous positive airway pressure affects mitochondrial function and exhaled PGC1-α levels in obstructive sleep apnea

Purpose: Subjects with obstructive sleep apnea (OSA) exhibit systemic and upper airway oxidative stress and inflammation, which cause mitochondrial dysfunction. The intend of this study is to estimate mitochondrial function (mitochondrial DNA/nuclear DNA [Mt/N] ratio) and protein levels of peroxisome proliferator-coactivated receptor gamma co-activator 1-alpha (PGC1-α) in the exhaled breath condensate (EBC) and plasma before and after continuous positive airway pressure (CPAP) treatment. Materials and methods: Twenty healthy individuals (control) and 40 subjects with severe or moderate OSA were recruited to undergo CPAP treatment and evaluation in a sleep study. The Mt/N ratio in the EBC and blood were assayed by quantitative real-time polymerase chain reaction. Enzyme-linked immunosorbent assay was used to measure the protein concentration of PGC1-α in the EBC and plasma. All experiments were performed after 3 months of CPAP treatment in subjects with OSA. Results: We observed no noteworthy differences between the control and treatment groups. Moreover, there were no differences in the Mt/N ratio in the blood and plasma levels of PGC1-α in subjects with OSA before and after treatment. However, the Mt/N ratio and protein levels of PGC1-α in the EBC of OSA subjects were higher than those in the control group and returned to normal levels after CPAP treatment. Conclusions: We successfully treated subjects with OSA by CPAP, which restored the Mt/N ratio and levels of PGC1-α in the EBC.

Cochlear Inflammaging in Relation to Ion Channels and Mitochondrial Functions

The slow accumulation of inflammatory biomarker levels in the body-also known as inflammaging-has been linked to a myriad of age-related diseases. Some of these include neurodegenerative conditions such as Parkinson's disease, obesity, type II diabetes, cardiovascular disease, and many others. Though a direct correlation has not been established, research connecting age-related hearing loss (ARHL)-the number one communication disorder and one of the most prevalent neurodegenerative diseases of our aged population-and inflammaging has gained interest. Research, thus far, has found that inflammatory markers, such as IL-6 and white blood cells, are associated with ARHL in humans and animals. Moreover, studies investigating ion channels and mitochondrial involvement have shown promising relationships between their functions and inflammaging in the cochlea. In this review, we summarize key findings in inflammaging within the auditory system, the involvement of ion channels and mitochondrial functions, and lastly discuss potential treatment options focusing on controlling inflammation as we age.

Sleep Characteristics and Hearing Loss in Older Adults: The National Health and Nutrition Examination Survey 2005-2006

BACKGROUND

Sleep characteristics might be associated with hearing loss through disturbed energy metabolism and disrupted cochlear blood flow, but prior evidence is limited. This study aims to investigate cross-sectional associations of sleep duration and signs/symptoms of sleep-disordered breathing with hearing in a nationally representative cohort of U.S. older adults aged 70 and over.

METHODS

We studied 632 older adults aged 70+ years from the 2005-2006 cycle of National Health and Nutrition Examination Survey (NHANES). Hearing thresholds were measured using pure-tone audiometry and were averaged to create speech-frequency (0.5-4 kHz), low-frequency (0.5-2 kHz) and high-frequency (4-8 kHz) pure-tone averages (PTAs) in better-hearing ear, with higher values indicate worse hearing. Sleep duration and signs/symptoms of sleep-disordered breathing (snoring, snorting/stopping breathing, excessive sleepiness) were collected through questionnaire. Multivariable-adjusted spline models with knots at 6 and 8 hours were fitted for associations between sleep duration and PTAs. Multivariable-adjusted linear regression was used for associations between sleep-disordered breathing and PTAs. Primary models adjusted for demographic and lifestyle factors, secondary models additionally adjusted for cardiovascular factors.

RESULTS

When sleep duration exceeded 8 hours, every additional hour of sleep duration was marginally associated with higher(poorer) high-frequency PTA (Primary:2.45 dB HL, 95% CI:-0.34, 5.24; Secondary:2.89 dB HL, 95% CI:0.02, 5.76). No associations were observed between sleep-disordered breathing and hearing.

CONCLUSIONS

Longer sleep duration is marginally associated with poorer high-frequency hearing among older adults sleeping more than 8 hours. However, we cannot infer temporality given the cross-sectional design. Future longitudinal studies are needed to establish temporality and clarify mechanisms.

CPAP Treatment Improves Pure Tone Audiometry Threshold in Sensorineural Hearing Loss Patients with Sleep-Disordered Breathing

This article investigates the effects of continuous positive airway pressure (CPAP) on hearing impairment in sensorineural hearing loss (SNHL) patients with sleep-disordered breathing (SDB). This retrospective and observational study took place from September 2016 to February 2021, accumulating 77 subjects with SNHL and SDB (60.7 ± 11.1 years). Of which, 28 received CPAP treatment (63.0 ± 8.5 years). In our methodology, hearing thresholds at low, medium, high, and average frequencies are assessed by pure-tone audiometry at baseline (BL), three (3 m), six (6 m), and 12 (12 m) months. Our results show that the BL of at least three frequencies in all subjects is positively associated with old age, males, smoking, alcohol, coronary artery disease, hypertension, and apnea-hypopnea index [AHI] (all p < 0.05). Moreover, low, medium, and average frequencies are negatively correlated at CPAP-6 m (-5.60 ± 2.33, -5.82 ± 2.56, and -5.10 ± 2.26 dB; all p < 0.05) and CPAP-12 m (-7.97 ± 2.74, -8.15 ± 2.35, and -6.67 ± 2.37 dB; all p < 0.01) against corresponding measures of CPAP-BL. High, medium, and average frequencies positively correlated with age (p < 0.001 for high and average frequencies and <0.01 for medium frequencies). We conclude that in SNHL patients with SDB, hearing thresholds at low and medium frequencies improves under CPAP use after six months, which persists at least to the end of one year.

Standardized Methodologies to Utilize Exosome Treatment as Potential Nano Substances in Hearing Loss

Recently, studies on the mechanism and clinical application of stem cell-derived exosomes have increased. Although the number of patients with hearing loss is increasing, there is no ideal therapy for the recovery of auditory cells of an independent organ in humans. In this review, we proposed the use of stem cell-derived exosomes for treating hearing loss and summarized the exosome research strategy platform for preclinical studies. It is necessary to select a research direction to assess direct or indirect effects on recipients based on the physiological mechanisms of exosomes that deliver useful molecules (called payloads) to recipient cells or tissues. To apply exosomes in the auditory field, researchers should select a model for assessing the toxicity to the auditory cells and analyzing their mechanisms in the recipient tissue. Such in vitro, ex vivo, and in vivo models have been designed and reported in previous studies. The analytical strategies in various models can evaluate the mechanism of exosomes based on exosome surface markers or the payload, thus helping the researchers in finding evidence regarding the efficacy of exosomes. Here, we propose three strategies for exosome application research in the auditory field.

Induced Short-Term Hearing Loss due to Stimulation of Age-Related Factors by Intermittent Hypoxia, High-Fat Diet, and Galactose Injection

Age-related hearing loss (ARHL) is the most common sensory disorder among the elderly, associated with aging and auditory hair cell death due to oxidative-stress-induced mitochondrial dysfunction. Although transgenic mice and long-term aging induction cultures have been used to study ARHL, there are currently no ARHL animal models that can be stimulated by intermittent environmental changes. In this study, an ARHL animal model was established by inducing continuous oxidative stress to promote short-term aging of cells, determined on the basis of expression of hearing-loss-induced phenotypes and aging-related factors. The incidence of hearing loss was significantly higher in dual- and triple-exposure conditions than in intermittent hypoxic conditions, high-fat diet (HFD), or d-galactose injection alone. Continuous oxidative stress and HFD accelerated cellular aging. An increase in Ucp2, usually expressed during mitochondrial dysfunction, was observed. Expression of Cdh23, Slc26a4, Kcnq4, Myo7a, and Myo6, which are ARHL-related factors, were modified by oxidative stress in the cells of the hearing organ. We found that intermittent hypoxia, HFD, and galactose injection accelerated cellular aging in the short term. Thus, we anticipate that the development of this hearing loss animal model, which reflects the effects of intermittent environmental changes, will benefit future research on ARHL.

Evaluation of the changes in the hearing system over the years among patients with OSAS using a CPAP device

OBJECTIVE

To evaluate whether patients using a continuous positive airway pressure (CPAP) device for obstructive sleep apnea syndrome (OSAS) have improvement or deterioration in their auditory systems.

METHODS

Charts of OSAS patients who were followed up at the ENT clinic were retrospectively reviewed starting from 2018. The hearing tests performed at least 2 years before and after CPAP use in patients were compared with themselves and with the test results of patients with no CPAP use.

RESULTS

No improvement in the hearing system on the patients using a CPAP device was detected. Deterioration in hearing was detected in 13.63% and 9.09% of the patients with and without CPAP use, respectively. No statistically significant difference was found between the two groups.

CONCLUSION

The use of a CPAP device does not affect hearing positively or negatively.

Sleep apnoea is associated with hearing impairment: The Paris prospective study 3

OBJECTIVES

Hearing impairment (HI) is a leading impairment worldwide, and identifying modifiable risk factors of HI may have major public health implications. The aim of this study was to investigate the association between obstructive sleep apnoea (OSA) and HI.

DESIGN

Observational longitudinal study (the Paris Prospective Study 3).

SETTING

Population-based.

PARTICIPANTS

Volunteers aged 50-75 years and consulting at a preventive medical centre were included between 2008 and 2012. 6797 participants were included in the present analysis.

MAIN OUTCOME MEASURES

Audiometry testing was performed in both ears in all participants, and HI was defined by a pure-tone average (PTA) >25 decibels (dB) hearing level in the better ear.

RESULTS

Obstructive sleep apnoea (estimated by the Berlin questionnaire) was present in 18.6% (n = 1267) and HI in 13.9% (n = 947) of the participants. Mean age was 59.5 years (SD 6.2) and 63.5% were male (n = 4317). In multiple logistic regression modelling, OSA was significantly associated with a 1.21-increased odds of HI (95% confidence interval 1.01-1.44). Several sensitivity analyses supported this finding.

CONCLUSION

Obstructive sleep apnoea is associated with a 21% increased odds of HI. These results support active screening of HI in subjects with OSA, and future studies should evaluate whether the treatment of OSA can delay the onset of HI.

miRNA-Mediated Suppression of a Cardioprotective Cardiokine as a Novel Mechanism Exacerbating Post-MI Remodeling by Sleep Breathing Disorders

Rationale:

Obstructive sleep apnea-hypopnea syndrome, a sleep breathing disorder in which chronic intermittent hypoxia (CIH) is the primary pathology, is associated with multiple cardiovascular diseases. However, whether and how CIH may affect cardiac remodeling following myocardial infarction (MI) remains unknown.

Objective:

To determine whether CIH exposure at different periods of MI may exacerbate post-MI heart failure and to identify the mechanisms underlying CIH-exacerbated post-MI remodeling.

Methods and Results:

Adult male mice were subjected to MI (4 weeks) with and without CIH (4 or 8 weeks). CIH before MI (CIH+MI) had no significant effect on post-MI remodeling. However, double CIH exposure (CIH+MI+CIH) or CIH only during the MI period (MI+CIH) significantly exacerbated pathological remodeling and reduced survival rate. Mechanistically, CIH activated TGF-β (tumor growth factor-β)/Smad (homologs of both the Drosophila protein MAD and the C. elegans protein SMA) signaling and enhanced cardiac epithelial to mesenchymal transition, markedly increasing post-MI cardiac fibrosis. Transcriptome analysis revealed that, among 15 genes significantly downregulated (MI+CIH versus MI), Ctrp9 (a novel cardioprotective cardiokine) was one of the most significantly inhibited genes. Real-time polymerase chain reaction/Western analysis confirmed that cardiomyocyte CTRP9 expression was significantly reduced in MI+CIH mice. RNA-sequencing, real-time polymerase chain reaction, and dual-luciferase reporter assays identified that microRNA-214-3p is a novel Ctrp9 targeting miRNA. Its upregulation is responsible for Ctrp9 gene suppression in MI+CIH. Finally, AAV9 (adeno-associated virus 9)-mediated cardiac-specific CTRP9 overexpression or rCTRP9 (recombinated CTRP9) administration inhibited TGF-β/Smad and Wnt/β-catenin pathways, attenuated interstitial fibrosis, improved cardiac function, and enhanced survival rate in MI+CIH animals.

Conclusions:

This study provides the first evidence that MI+CIH upregulates miR-214-3p, suppresses cardiac CTRP9 (C1q tumor necrosis factor-related protein-9) expression, and exacerbates cardiac remodeling, suggesting that CTRP9 may be a novel therapeutic target against pathological remodeling in MI patients with obstructive sleep apnea-hypopnea syndrome.

Inhibition of DRP-1-Dependent Mitophagy Promotes Cochlea Hair Cell Senescence and Exacerbates Age-Related Hearing Loss

Background: Mitochondrial dysfunction is considered to contribute to the development of age-related hearing loss (AHL). The regulation of mitochondrial function requires mitochondrial quality control, which includes mitophagy and dynamics. Dynamin-related Protein 1 (DRP-1) is believed to play a central role in this regulation. However, the underlying mechanism of DRP-1 in AHL remains unclear. Here, we examined whether the decline of DRP-1-dependent mitophagy contributes to the development of AHL. Methods: We induced cellular and cochlear senescence using hydrogen peroxide (H₂O₂) and evaluated the level of senescence through senescence-associated β-galactosidase staining. We evaluated mitophagy levels via fluorescence imaging and Western Blotting of LC3II and P62. Mitochondrial function was assessed by ATP assay, mtDNA assay, and JC-1. Results: We found that both the expression of DRP-1 and the mitophagy level decreased in senescent cells and aged mice. DRP-1 overexpression in HEI-OC1 cells initiated mitophagy and preserved mitochondrial function when exposed to H₂O₂, while cells with DRP-1 silencing displayed otherwise. Moreover, inhibition of DRP-1 by Mdivi-1 blocked mitophagy and exacerbated hearing loss in aged C57BL/6 mice. Conclusion: These results indicated that DRP-1 initiated mitophagy, eliminated mitochondrial dysfunction, and may protect against oxidative stress-induced senescence. These results provide a potential therapeutic target for AHL.

The association between obstructive sleep apnea and hearing loss: a cross-sectional analysis

PURPOSE

To determine if sleep apnea had significant effects on hearing functions and to investigate the polysomnography parameters that might be associated with hearing impairment in sleep apnea patients.

METHODS

We included 120 patients who were admitted to sleep disorders outpatient clinic. We constituted four groups by reference to the apnea-hypopnea index (including control group), and compared the audiometric parameters of the groups. Additionally, we investigated the correlation of apnea-hypopnea index, desaturation index and min. oxygen saturations with pure-tone thresholds, speech recognition thresholds and speech discrimination scores.

RESULTS

The median pure-tone thresholds at 250, 500, 1000, 2000, 4000 and 8000 mHz, the median speech recognition thresholds and the median speech discrimination scores on both ears did significantly differ among four groups (p < 0.001). Moderate sleep apnea affected high-frequency hearing functions and speech discrimination scores, and severe sleep apnea had significant effects on all hearing functions. Pure-tone thresholds and speech recognition thresholds on the both ears were positively correlated with apnea-hypopnea index and desaturation index, and negatively correlated with min. oxygen saturation (p < 0.001). Speech discrimination scores on the both ears were negatively correlated with apnea-hypopnea index and desaturation index, and positively correlated with min. oxygen saturation (p < 0.001).

CONCLUSION

Obstructive sleep apnea syndrome (OSA) had several effects on hearing, and hearing impairment might be associated with the severity of OSA. Moderate OSA affected high-frequency hearing functions and severe OSA affected all hearing functions negatively.

Histological, Ultrastructural, and Physiological Evaluation of a Rat Model of Obstructive Sleep Apnea Syndrome

BACKGROUND Patients with obstructive sleep apnea syndrome (OSAS) are at an increased risk of cardiovascular disease. The aims of this study were to develop a rat model of OSAS and to validate the use of the model by investigating respiratory and cardiovascular physiological parameters and morphological changes by light microscopy and electron microscopy. MATERIAL AND METHODS Sixty 3-month-old Sprague-Dawley rats were assigned to the model group (n=30) and the control group (n=30). The rats in the OSAS model group were injected with 0.1 ml sodium hyaluronate solution into the upper respiratory tract at the junction between the hard and soft palate. After one month, the model and normal rats were compared using tests of respiratory and cardiac function, and histology and electron microscopy of the lung and cardiac tissue. RESULTS In the rat model of OSAS, airway obstruction resulted in the collapse of the upper airway. Tests of respiratory function showed that the oxygen partial pressure, oxygen concentration, and oxygen saturation in the model group were significantly lower when compared with the control group. In the model group, histology of the heart showed cardiac myocyte disarray, and electron microscopy showed vacuolar degeneration and mitochondrial abnormalities. The rat model of upper airway occlusion showed pulmonary and cardiac changes that have been described in OSAS. CONCLUSIONS A rat model of upper airway occlusion resulted in physiological and morphological changes in the lung and heart due to hypoxia, and may be used for future studies on OSAS.

Recombinant human glucagon-like peptide-1 protects against chronic intermittent hypoxia by improving myocardial energy metabolism and mitochondrial biogenesis

BACKGROUND AND AIMS

Obstructive sleep apnea syndrome is a chronic disease associated with intermittent hypoxia (IH) and is an important risk factor for cardiovascular disease. Glucagon-like peptide (GLP-1) is a naturally occurring incretin used as a promising therapeutic agent in the treatment of acute myocardial infarction, dilated cardiomyopathy, and advanced heart failure. However, whether GLP-1 can protect against IH-induced cardiac injury is still unclear. Accordingly, in this study, we evaluated the effects of recombinant human GLP-1 (rhGLP-1) on cardiac health in mice.

METHODS

Mice were subjected to repetitive 5% O₂ for 30 s and 21% O₂ for 30 s, for a total of 8 h/day for 4 weeks. Subsequently, mice received subcutaneous injection of saline or rhGLP-1 (100 μg/kg, three times per day). Cardiac function, myocardial apoptosis and fibrosis, energy metabolism, and mitochondrial biogenesis were examined for evaluation of cardiac injury.

RESULTS

A reduction in diastolic function (E/A ratio) in mice exposed to IH was significantly reversed by rhGLP-1. IH induced marked cardiomyocyte apoptosis and myocardial fibrosis. Additionally, IH resulted in a shift from fatty acid to glucose metabolism in the myocardium with downregulation of peroxisome proliferator-activated receptor (PPAR) α and PPARγ. Moreover, IH caused a reduction in mitochondrial DNA (mtDNA) replication and transcription, together with reduced mtDNA content and impaired mitochondrial ultrastructure. These changes were abolished by rhGLP-1 via activation of PGC-1α and Akt signaling.

CONCLUSIONS

rhGLP-1 protects against IH-induced cardiac injury by improving myocardial energy metabolism and enhancing the early adaptive changes of mitochondrial biogenesis.

Codeficiency of Lysosomal Mucolipins 3 and 1 in Cochlear Hair Cells Diminishes Outer Hair Cell Longevity and Accelerates Age-Related Hearing Loss

Acquired hearing loss is the predominant neurodegenerative condition associated with aging in humans. Although mutations on several genes are known to cause congenital deafness in newborns, few genes have been implicated in age-related hearing loss (ARHL), perhaps because its cause is likely polygenic. Here, we generated mice lacking lysosomal calcium channel mucolipins 3 and 1 and discovered that both male and female mice suffered a polygenic form of hearing loss. Whereas mucolipin 1 is ubiquitously expressed in all cells, mucolipin 3 is expressed in a small subset of cochlear cells, hair cells (HCs) and marginal cells of the stria vascularis, and very few other cell types. Mice lacking both mucolipins 3 and 1, but not either one alone, experienced hearing loss as early as at 1 month of age. The severity of hearing impairment progressed from high to low frequencies and increased with age. Early onset of ARHL in these mice was accompanied by outer HC (OHC) loss. Adult mice conditionally lacking mucolipins in HCs exhibited comparable auditory phenotypes, thereby revealing that the reason for OHC loss is mucolipin codeficiency in the HCs and not in the stria vascularis. Furthermore, we observed that OHCs lacking mucolipins contained abnormally enlarged lysosomes aggregated at the apical region of the cell, whereas other organelles appeared normal. We also demonstrated that these aberrant lysosomes in OHCs lost their membrane integrity through lysosomal membrane permeabilization, a known cause of cellular toxicity that explains why and how OHCs die, leading to premature ARHL.SIGNIFICANCE STATEMENT Presbycusis, or age-related hearing loss (ARHL), is a common characteristic of aging in mammals. Although many genes have been identified to cause deafness from birth in both humans and mice, only a few are known to associate with progressive ARHL, the most prevalent form of deafness. We have found that mice lacking two lysosomal channels, mucolipins 3 and 1, suffer accelerated ARHL due to auditory outer hair cell degeneration, the most common cause of hearing loss and neurodegenerative condition in humans. Lysosomes lacking mucolipins undergo organelle membrane permeabilization and promote cytotoxicity with age, revealing a novel mechanism of outer hair cell degeneration and ARHL. These results underscore the importance of lysosomes in hair cell survival and the maintenance of hearing.