Pre-treatment With Fasudil Prevents Neomycin-Induced Hair Cell Damage by Reducing the Accumulation of Reactive Oxygen Species

Fasudil protects spiral ganglion neurons and hair cells against cisplatin-induced apoptosis by inhibiting reactive oxygen species accumulation and regulating the ROCK/PTEN/AKT signaling pathway

Cisplatin causes hearing loss in at least 60% of chemotherapy patients, leading to impairments in the patient's life quality. Spiral ganglion neurons (SGNs) and hair cells (HCs) are the main cell types affected by cisplatin accumulation in the inner ear. Fasudil is an FDA-approved drug and has been reported to exert neuroprotective effects in previous research. However, whether fasudil possesses protective effects in cisplatin-induced SGN and HC damage and the potential mechanisms remain unknown. In this study, we investigated whether fasudil has a protective effect on cisplatin-induced damage to inner ear SGNs and HCs. We first observed the effect of different concentrations of fasudil on cisplatin-induced cell loss of SGNs and HCs. We also studied the effects of fasudil on cisplatin-induced apoptosis of SGNs and HCs and detected the mitochondrial reactive oxygen species (ROS) level. Furthermore, we investigated the mechanisms of fasudil in protecting the SGNs and HCs from cisplatin- induced cells apoptosis. We found that fasudil treatment significantly ameliorated SGNs and HCs loss and attenuated cell apoptosis after cisplatin exposure. Moreover, fasudil attenuated the cisplatin-induced ROS generation in SGN- and HC-explants culture. Further mechanistic studies revealed that fasudil regulated the ROCK/PTEN/AKT signaling pathway in SGN- and HC-explants after cisplatin exposure. This study indicates that fasudil might be a novel therapeutic target for preventing cisplatin-induced SGNs and HCs damage.

Development of the inner ear and regeneration of hair cells after hearing impairment

Hearing loss, as a sensory disorder, is the most common occurrence among humans, which has received increasing attention from society. It is mainly caused by the damage of inner ear hair cells (HCs) or the degeneration of spiral ganglion neurons. In mammals, cochlear HCs cannot regenerate naturally after injury, leading to irreversible hearing loss. Therefore, HCs are essential for hearing protection. In recent years, the protection of drug-related ototoxicity, inner ear stem cells, gene therapy, new materials, and signal regulation have become important ways to develop regeneration strategies of HCs. An in-depth study of the causes of the occurrence and development of hearing impairment and the regeneration of hearing loss for effective prevention, discovery, and treatment of deafness has great significance. This review aimed to analyze the development of the inner ear and summarize the related factors leading to HCs injury and the research progress of regeneration after injury.

Protective Effects of Fasudil Against Cisplatin-Induced Ototoxicity in Zebrafish: An In Vivo Study

While cisplatin is an effective anti-tumor treatment, it induces ototoxicity through mechanisms involving DNA damage, oxidative stress, and programmed cell death. Rho-associated coiled-coil-containing protein kinase (ROCK) is essential for numerous cellular processes, including apoptosis regulation. Studies have suggested that ROCK inhibitors could prevent apoptosis and promote regeneration. We aimed to investigate the protective effects of the ROCK inhibitor fasudil against cisplatin-induced ototoxicity in a zebrafish model. The zebrafish larvae were exposed to 1 mM cisplatin alone or 1 mM cisplatin co-administered with varying concentrations of fasudil for 4 h. The surviving hair cell counts, apoptosis, reactive oxygen species (ROS) levels, mitochondrial membrane potential (ΔΨm), caspase 3 activity, and autophagy activation were assessed. Rheotaxis behavior was also examined. Cisplatin reduced hair cell counts; increased apoptosis, ROS production, and ΔΨm loss; and activated caspase 3 and autophagy. Fasudil (100 and 500 µM) mitigated cisplatin-induced hair cell loss, reduced apoptosis, and inhibited caspase 3 and autophagy activation. Rheotaxis in zebrafish was preserved by the co-administration of fasudil with cisplatin. Cisplatin induces hair cell apoptosis in zebrafish, whereas fasudil is a promising protective agent against cisplatin-induced ototoxicity.

Rodent models in sensorineural hearing loss research: A comprehensive review

Sensorineural hearing loss (SNHL) constitutes a major global health challenge, affecting millions of individuals and substantially impairing social integration and quality of life. The complexity of the auditory system and the multifaceted nature of SNHL necessitate advanced methodologies to understand its etiology, progression, and potential therapeutic interventions. This review provides a comprehensive overview of the current animal models used in SNHL research, focusing on their selection based on specific characteristics and their contributions to elucidating pathophysiological mechanisms and evaluating novel treatment strategies. It discusses the most commonly used rodent models in hearing research, including mice, rats, guinea pigs, Mongolian gerbils, and chinchillas. Through a comparative analysis, this review underscores the importance of selecting models that align with specific research objectives in SNHL studies, discussing the advantages and limitations of each model. By advocating for a multidisciplinary approach that leverages the strengths of various animal models with technological advancements, this review aims to facilitate significant advancements in the prevention, diagnosis, and treatment of sensorineural hearing loss.

Colorimetric detection of neomycin sulfate in serum based on ultra-small gold nanoparticles with peroxidase-like activity

Neomycin sulfate (NEO) is a kind of aminoglycoside antibiotics. Because of its strong ototoxicity, nephrotoxicity and other side effects, its content in the body should be strictly monitored during use. In this paper, a rapid colorimetric detection method for NEO based on ultrasmall polyvinylpyrrolidone modified gold nanoparticles (PVP/Au NPs) with peroxidase-like activity was developed. Firstly, ultra small PVP/Au NPs with weak peroxidase-like activity were synthetized. When they were mixed with NEO, strong hydrogen bonds were formed between NEO and PVP, resulting in the aggregation of PVP/Au NPs, and the aggregated PVP/Au NPs showed stronger peroxidase-like activity. Therefore, rapid colorimetric detection of NEO was achieved by utilizing the enhanced peroxidase-like activity mechanism caused by the aggregation of ultra small PVP/Au NPs. The naked eye detection limit of this method is 50 nM. Within the range of 1 nM-300 nM, there was a good linear relationship between NEO concentration and the change in absorbance intensity of PVP/Au NPs-H2O2-TMB solution at 652 nm, with the regression curve of y = 0.0045x + 0.0525 (R2 = 0.998), and the detection limit is 1 nM. In addition, this method was successfully applied to the detection of NEO in mouse serum. The recoveries were 104.4 % -107.6 % compared with HPLC assay results, indicating that this method for NEO detection based on PVP/Au NPs has great potential in actual detection of NEO in serum.

PGC-1α-mediated imbalance of mitochondria-lipid droplet homeostasis in neomycin-induced ototoxicity and nephrotoxicity

Ototoxicity and nephrotoxicity are the most prevalent side effects of aminoglycoside antibiotics (gentamicin, amikacin, neomycin) and platinum anti-tumor drugs (cisplatin, carboplatin). The inner ear and kidney share similarities in drug deposition and toxicity, but the underlying pathophysiological mechanisms remain unclear. Investigating the shared mechanisms and metabolic alterations in these distinct organs will provide valuable insights for clinical therapy. A strong correlation has been identified between the spatiotemporal accumulation patterns of neomycin and the specific occurrence of lipid metabolism disorders in these two organs. The primary allocation of neomycin to mitochondria results in a notable escalation in the accumulation of lipid droplets (LDs) and more interactions between mitochondria and LDs, leading to a sequence of disturbances in lipid metabolism, such as increased lipid ROS and the blocked transfer of fatty acids from LDs to mitochondria. PGC-1α deficiency worsens the neomycin-induced disorders in lipid metabolism and intensifies the pathological interactions between mitochondria and LDs, as indicated by the exacerbated disturbance of dynamic LD turnover, increased level of oxidized lipids and decreased use of fatty acids. This investigation provides a fresh perspective on the lipid metabolic dysfunction related to mitochondria-LD interactions in drug-induced ototoxicity and nephrotoxicity, potentially providing novel avenues for intervention strategies.

Nanodelivery of antioxidant Agents: A promising strategy for preventing sensorineural hearing loss

Sensorineural hearing loss (SNHL), often stemming from reactive oxygen species (ROS) generation due to various factors such as ototoxic drugs, acoustic trauma, and aging, remains a significant health concern. Oxidative stress-induced damage to the sensory cells of the inner ear, particularly the non-regenerating hair cells, is a critical pathologic mechanism leading to SNHL. Despite the proven efficacy of antioxidants in mitigating oxidative stress, their clinical application for otoprotection is hindered by the limitations of conventional drug delivery methods. This review highlights the challenges associated with systemic and intratympanic administration of antioxidants, including the blood-labyrinthine barrier, restricted permeability of the round window membrane, and inadequate blood flow to the inner ear. To overcome these hurdles, the application of nanoparticles as a delivery platform for antioxidants emerges as a promising solution. Nanocarriers facilitate indirect drug delivery to the cochlea through the round and oval window membrane, optimising drug absorption while reducing dosage, Eustachian tube clearance, and associated side effects. Furthermore, the development of nanoparticles carrying antioxidants tailored to the intracochlear environment holds immense potential. This literature research aimed to critically examine the root causes of SNHL and ROS overproduction in the inner ear, offering insights into the application of nanoparticle-based drug delivery systems for safeguarding sensorineural hair cells. By focusing on the intricate interplay between oxidative stress and hearing loss, this research aims to contribute to the advancement of innovative therapeutic strategies for the prevention of SNHL.

Berberine protects against neomycin-induced ototoxicity by reducing ROS generation and activating the PI3K/AKT pathway

In mammals, aminoglycoside antibiotic-induced injury to hair cells (HCs) and associated spiral ganglion neurons (SGNs) is irreversible and eventually leads to permanent hearing loss. Efforts have been directed towards the advancement of efficacious therapeutic treatments to protect hearing loss, but the ideal substance for treating the damaged cochlear sensory epithelium has yet to be identified. Berberine (BBR), a quaternary ammonium hydroxide extracted from Coptis chinensis, has been found to display potential anti-oxidant and neuroprotective properties. However, its involvement in aminoglycoside antibiotic-induced ototoxicity has yet to be explored or assessed. In the present study, we explored the possible anti-oxidative properties of BBR in mitigating neomycin-triggered ototoxicity. An improved survival of HCs and SGN nerve fibers (NFs) in organ of Corti (OC) explants after neomycin with BBR co-treatment was observed, and BBR treatment attenuated reactive oxygen species (ROS) generation and reduced cleaved caspase-3 signaling by activating six phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling relative subtypes, and the addition of PI3K/AKT suppressor LY294002 resulted in a decrease in the protective effect. The protective effect of BBR against ototoxicity was also evident in a neomycin-injured animal model, as evidenced by the preservation of HC and SGN in mice administered subcutaneous BBR for 7 days. In summary, all results suggest that BBR has potential as a new and effective otoprotective agent, operating via the PI3K/AKT signaling pathway.

Loxhd1b inhibits the hair cell development in zebrafish: Possible relation to the BDNF/TrkB/ERK pathway

Background

Mutations in lipoxygenase homology domain 1 (LOXHD1) cause autosomal recessive inheritance, leading to high-frequency and intermediate-frequency hearing losses in patients. To date, studies on the localization of LOXHD1 gene expression are limited. In this study, we aimed to observe the expressions of Loxhd1b in zebrafish, C57BL/6 murine cochlea, and HEI-OC1 cells.

Methods

The expression of Loxhd1b in the auditory system of zebrafish was explored by in situ hybridization experiments of zebrafish embryos. The expression of Loxhd1b in cochlear and HEI-OC1 cells of C57BL/6 mice was analyzed by immunofluorescence staining. Confocal microscopic in vivo imaging was used to detect the number and morphological characteristics of lateral line neuromasts and inner ear hair cells in zebrafish that knocked down Loxhd1b gene. The effect of knockdown Loxhd1b gene on the development of zebrafish otolith and semicircular canal was observed using microscopic. Transcriptome sequencing was used to identify downstream molecules and associated signaling pathways and validated by western blotting, immunostaining, and rescue experiments.

Results

Results of the in situ hybridization with zebrafish embryos at different time points showed that Loxhd1b was expressed in zebrafish at the inner ear and olfactory pores, while the immunostaining showed that Loxhd1 was expressed in both C57BL/6 mouse cochlea and HEI-OC1 cells. Loxhd1b knockdown causes a decrease in the number of spinal and lateral line neuromasts in the inner ear of zebrafish, accompanied by weakened hearing function, and also leads to developmental defects of otoliths and ear follicles. The results of transcriptomics analysis revealed the downstream molecule brain-derived neurotrophic factor (BDNF) and verified that Loxhd1b and BDNF regulate the formation of zebrafish hair cells by synergistic regulation of BDNF/TrkB/ERK pathway based on western blotting, immunostaining, and rescue experiments.

Conclusion

This was the first time that the BDNF/TrkB/ERK pathway was identified to play a critical role in the molecular regulation of the development of zebrafish hair cells and the auditory development by Loxhd1b.

FGF22 deletion causes hidden hearing loss by affecting the function of inner hair cell ribbon synapses

Ribbon synapses are important structures in transmitting auditory signals from the inner hair cells (IHCs) to their corresponding spiral ganglion neurons (SGNs). Over the last few decades, deafness has been primarily attributed to the deterioration of cochlear hair cells rather than ribbon synapses. Hearing dysfunction that cannot be detected by the hearing threshold is defined as hidden hearing loss (HHL). The relationship between ribbon synapses and FGF22 deletion remains unknown. In this study, we used a 6-week-old FGF22 knockout mice model (Fgf22^–/–) and mainly focused on alteration in ribbon synapses by applying the auditory brainstem response (ABR) test, the immunofluorescence staining, the patch-clamp recording, and quantitative real-time PCR. In Fgf22^–/– mice, we found the decreased amplitude of ABR wave I, the reduced vesicles of ribbon synapses, and the decreased efficiency of exocytosis, which was suggested by a decrease in the capacitance change. Quantitative real-time PCR revealed that Fgf22^–/– led to dysfunction in ribbon synapses by downregulating SNAP-25 and Gipc3 and upregulating MEF2D expression, which was important for the maintenance of ribbon synapses’ function. Our research concluded that FGF22 deletion caused HHL by affecting the function of IHC ribbon synapses and may offer a novel therapeutic target to meet an ever-growing demand for deafness treatment.

SIRT3-mediated deacetylation protects inner hair cell synapses in a H2O2-induced oxidative stress model in vitro

Oxidative stress is considered a driving event in the damage to inner hair cell (IHC) synapses. Mitochondrial deacetylase Sirtuin 3 (SIRT3) is an important regulator of reactive oxygen species (ROS) production. However, the effect of SIRT3 on IHC synapses remains elusive. In this study, we treated cochlear basilar membrane (CBM) with hydrogen peroxide (H₂O₂) to establish an oxidative stress model in vitro. The H₂O₂-induced CBM exhibited decreased the number of IHC synapses with low levels of ATP and mitochondrial membrane potential. Additionally, H₂O₂-incuded CBM showed markedly reduced levels of forkhead box protein O 3a (FOXO3a), superoxide dismutase 2 (SOD2), and isocitrate dehydrogenase 2 (IDH2), thereby increasing ROS generation. SIRT3 overexpression via administrating nicotinamide riboside in the H₂O₂-induced CBM protected IHC synapses against oxidative stress and inhibited hair cell apoptosis. We further demonstrated that SIRT3 overexpression led to upregulation of IDH2, and hypoacetylation of several proteins, such as FOXO3a and SOD2, which in turn reduced the levels of ROS and improved mitochondrial function. Collectively, these findings reveal that SIRT3 may be a potential therapeutic approach for damaged IHC synapses induced by oxidative stress.

Graphene Substrates Promote the Differentiation of Inner Ear Lgr5+ Progenitor Cells Into Hair Cells

The ideal treatment for sensory hearing loss is to regenerate inner ear hair cells (HCs) through stem cell therapy, thereby restoring the function and structure of the cochlea. Previous studies have found that Lgr5+ supporting cells (SCs) in the inner ear can regenerate HCs, thus being considered inner ear progenitor cells. In addition to traditional biochemical factors, physical factors such as electrical conductivity also play a crucial role in the regulation of stem cell proliferation and differentiation. In this study, the graphene substrates were used to culture Lgr5+ progenitor cells and investigated their regulatory effects on cells. It was demonstrated that the graphene substrates displayed great cytocompatibility for Lgr5+ progenitors and promoted their sphere-forming ability. Moreover, more Myosin7a+ cells were found on the graphene substrates compared with tissue culture polystyrene (TCPS). These results suggest that graphene is an efficient interface that can promote the differentiation of Lgr5+ progenitors into HCs, which is great significance for its future application in combination with Lgr5+ cells to regenerate HCs in the inner ear.

Regeneration of Hair Cells in the Human Vestibular System

The vestibular system is a critical part of the human balance system, malfunction of this system will lead to balance disorders, such as vertigo. Mammalian vestibular hair cells, the mechanical receptors for vestibular function, are sensitive to ototoxic drugs and virus infection, and have a limited restorative capacity after damage. Considering that no artificial device can be used to replace vestibular hair cells, promoting vestibular hair cell regeneration is an ideal way for vestibular function recovery. In this manuscript, the development of human vestibular hair cells during the whole embryonic stage and the latest research on human vestibular hair cell regeneration is summarized. The limitations of current studies are emphasized and future directions are discussed.

Shikonin Attenuates Cochlear Spiral Ganglion Neuron Degeneration by Activating Nrf2-ARE Signaling Pathway

The molecular mechanisms that regulate the proliferation and differentiation of inner ear spiral ganglion cells (SGCs) remain largely unknown. Shikonin (a naphthoquinone pigment isolated from the traditional Chinese herbal medicine comfrey root) has anti-oxidation, anti-apoptosis and promoting proliferation and differentiation effects on neural progenitor cells. To study the protective effect of shikonin on auditory nerve damage, we isolated spiral ganglion neuron cells (SGNs) and spiral ganglion Schwann cells (SGSs) that provide nutrients in vitro and pretreated them with shikonin. We found that shikonin can reduce ouabain, a drug that can selectively destroy SGNs and induce auditory nerve damage, caused SGNs proliferation decreased, neurite outgrowth inhibition, cells apoptosis and mitochondrial depolarization. In addition, we found that shikonin can increase the expression of Nrf2 and its downstream molecules HO-1 and NQO1, thereby enhancing the antioxidant capacity of SGNs and SGSs, promoting cells proliferation, and inhibiting cells apoptosis by activating the Nrf2/antioxidant response elements (ARE) signal pathway. However, knockdown of Nrf2 rescued the protective effect of shikonin on SGNs and SGSs damage. In addition, we injected shikonin pretreatment into mouse that ouabain-induced hearing loss and found that shikonin pretreatment has a defensive effect on auditory nerve damage. In summary, the results of this study indicate that shikonin could attenuate the level of oxidative stress in SGNs and SGSs through the Nrf2-ARE signaling pathway activated, induce the proliferation and differentiation of SGNs, and thereby improve the neurological hearing damage in mice. Therefore, shikonin may be a candidate therapeutic drug for endogenous antioxidants that can be used to treat neurological deafness.

Inhibition of PRMT6 reduces neomycin-induced inner ear hair cell injury through the restraint of FoxG1 arginine methylation

OBJECTIVE

Hair cells in the inner ear have been demonstrated to be sensitive to the ototoxicity from some beneficial pharmaceutical drugs. This study aimed to explore the role of protein arginine methyltransferase 6 (PRMT6) in the process of neomycin-induced hearing loss and the underlying mechanism.

METHODS

The neomycin-induced hearing loss mouse model and hair cell injury in vitro model were established. We took advantage of the HEI-OC1 cell line to evaluate PRMT6 expression in neomycin-induced hair cells, and the effect of PRMT6 on mitochondrial function and FoxG1 arginine methylation. Apoptotic cells were assessed and apoptotic marker cleaved caspase-3 level was detected. Reactive oxygen species (ROS) level and mitochondrial membrane potential (MMP) were subsequently measured.

RESULT

The result showed that PRMT6 was significantly upregulated in neomycin-induced HEI-OC-1 cells, and PRMT6 silencing prevented MMP loss, reduced ROS production, as well as decreased cell apoptosis under neomycin treatment. Further results showed that FoxG1 was downregulated in neomycin-induced HEI-OC-1 cells, and PRMT6 promoted the FoxG1-mediated luciferase activity, while PRMT6 silencing reversed this effect. Mechanistic experiments revealed that PRMT6 silencing reduced the arginine methylation level of FoxG1 protein. In vivo, neomycin-induced upregulation of hearing thresholds and increased cell apoptosis, whereas PRMT6 inhibitor partly reversed these effects.

CONCLUSION

Our findings suggested that inhibition of PRMT6 reduced neomycin-induced inner ear hair cell injury through the restraint of FoxG1 arginine methylation.

Novel m.4268T>C mutation in the mitochondrial tRNAIle gene is associated with hearing loss in two Chinese families

BACKGROUND

Herein, we report the genetic, clinical, molecular and biochemical features of two Han Chinese pedigrees with suggested maternally transmitted non-syndromic hearing loss.

AIM

To investigate the pathophysiology of hearing loss associated with mitochondrial tRNA mutations.

METHODS

Sixteen subjects from two Chinese families with hearing loss underwent clinical, genetic, molecular, and biochemical evaluations. Biochemical characterizations included the measurements of tRNA levels using lymphoblastoid cell lines derived from five affected matrilineal relatives of these families and three control subjects.

RESULTS

Three of the 16 matrilineal relatives in these families exhibited a variable seriousness and age-at-onset (8 years) of deafness. Analysis of mtDNA mutation identified the novel homoplasmic tRNA^Ile 4268T>C mutation in two families both belonging to haplogroup D4j. The 4268T>C mutation is located in a highly conserved base pairing (6U–67A) of tRNA^Ile. The elimination of 6U–67A base-pairing may change the tRNA^Ile metabolism. Functional mutation was supported by an approximately 64.6% reduction in the level of tRNA^Ile observed in the lymphoblastoid cell lines with the 4268T>C mutation, in contrast to the wild-type cell lines. The reduced level of tRNA was below the proposed threshold for normal respiration in lymphoblastoid cells. However, genotyping analysis did not detect any mutations in the prominent deafness-causing gene GJB2 in any members of the family.

CONCLUSION

These data show that the novel tRNA^Ile 4268T>C mutation was involved in maternally transmitted deafness. However, epigenetic, other genetic, or environmental factors may be attributed to the phenotypic variability. These findings will be useful for understanding families with maternally inherited deafness.

Cisplatin induces damage of auditory cells: Possible relation with dynamic variation in calcium homeostasis and responding channels

AIMS

The present study was aimed to explore the possible mechanism(s) underlying the action of cisplatin on auditory cells of mice in vitro, with special attention given to the dynamic variation in calcium homeostasis and responding channels.

METHODS

The apoptosis of auditory cells was tested by flow cytometry and TUNEL staining. The expressions of inositol 1,4,5-trisphosphate receptors (IP3R), voltage-dependent anion channel 1 (VDAC1), phosphorylated protein kinase R-like ER kinase (p-PERK), activating transcription factor 6 (ATF6), caspase-12, bcl-2, bax, cleaved caspase-9, cleaved caspase-3, beclin-1 and light chain 3β (LC3B) were measured by immunofluorescence or Western blotting. The calcium variations in subcellular structures were evaluated by Rhod-2 AM and Mag-Fluo-4 AM staining. The colocalization ratio between IP3R and beclin-1 was determined by immunocytochemistry.

RESULTS

We found that cisplatin exposure induced the apoptosis of HEI-OC1 cells and hair cells (HCs) in a caspase-3 dependent manner. This apoptotic process was attributed to the activation of endoplasmic reticulum (ER) stress and mitochondrial pathway and, meanwhile, accompanied by variation in calcium homeostasis and responding channels. Interestingly, we also observed that IP3R might dissociate from beclin-1 to motivate autophagy under the cisplatin insult.

CONCLUSIONS

Overall, the findings from this work indicate that cisplatin leads to auditory cell damage of mice in vitro, which is closely relevant to dynamic variation in calcium homeostasis and responding channels in subcellular structure.

D-Galactose-Induced Accelerated Aging Model on Auditory Cortical Neurons by Regulating Oxidative Stress and Apoptosis in Vitro

OBJECTIVES

Age-related hearing loss (ARHL) is much more prevalent with age, affecting not only peripheral but central auditory system. We have previously established an aging model of peripheral auditory system in vitro using cultured cochlear basilar membrane. However, there is no ideal accelerated aging model on central auditory system in vitro. To establish the aging model, auditory cortical neurons (ACNs) were primary cultured and treated with either vehicle or different doses of D-galactose (D-gal). We studied the effect of D-gal on ACNs by evaluating the hallmarks of aging, including cell proliferation, oxidative stress, mitochondrial function, and neuronal apoptosis. Compared with the control group, cell viability was significantly inhibited in the D-gal-treated group in a dose-dependent manner. The production of reactive oxygen species was strongly increased in the D-gal-treated group. Meanwhile, the level of 8-hydroxy-2'-deoxyguanosine, which is a biomarker of DNA oxidative damage, was even higher in the D-gal-treated group than that in the control group. Conversely, the levels of ATP and mitochondrial membrane potential were notably decreased in the D-gal-treated group contrast to that in the control group. Furthermore, the number of neuronal apoptosis in the D-gal-treated group, compared with that in the control group, was dramatically increased in a dose-dependent approach. Together, our results demonstrate that ACNs treated with D-gal in vitro display senescence characteristics by regulating oxidative stress and apoptosis, indicating accelerated aging model on ACNs are successfully established. And the model provides a promising approach for exploring underlying mechanisms of the ARHL.

Sirtuin-3 Protects Cochlear Hair Cells Against Noise-Induced Damage via the Superoxide Dismutase 2/Reactive Oxygen Species Signaling Pathway

Mitochondrial oxidative stress is involved in hair cell damage caused by noise-induced hearing loss (NIHL). Sirtuin-3 (SIRT3) plays an important role in hair cell survival by regulating mitochondrial function; however, the role of SIRT3 in NIHL is unknown. In this study, we used 3-TYP to inhibit SIRT3 and found that this inhibition aggravated oxidative damage in the hair cells of mice with NIHL. Moreover, 3-TYP reduced the enzymatic activity and deacetylation levels of superoxide dismutase 2 (SOD2). Subsequently, we administered adeno-associated virus-SIRT3 to the posterior semicircular canals and found that SIRT3 overexpression significantly attenuated hair cell injury and that this protective effect of SIRT3 could be blocked by 2-methoxyestradiol, a SOD2 inhibitor. These findings suggest that insufficient SIRT3/SOD2 signaling leads to mitochondrial oxidative damage resulting in hair cell injury in NIHL. Thus, ameliorating noise-induced mitochondrial redox imbalance by intervening in the SIRT3/SOD2 signaling pathway may be a new therapeutic target for hair cell injury.

Caffeine Induces Autophagy and Apoptosis in Auditory Hair Cells via the SGK1/HIF-1α Pathway

Caffeine is being increasingly used in daily life, such as in drinks, cosmetics, and medicine. Caffeine is known as a mild stimulant of the central nervous system, which is also closely related to neurologic disease. However, it is unknown whether caffeine causes hearing loss, and there is great interest in determining the effect of caffeine in cochlear hair cells. First, we explored the difference in auditory brainstem response (ABR), organ of Corti, stria vascularis, and spiral ganglion neurons between the control and caffeine-treated groups of C57BL/6 mice. RNA sequencing was conducted to profile mRNA expression differences in the cochlea of control and caffeine-treated mice. A CCK-8 assay was used to evaluate the approximate concentration of caffeine. Flow cytometry, TUNEL assay, immunocytochemistry, qRT-PCR, and Western blotting were performed to detect the effects of SGK1 in HEI-OC1 cells and basilar membranes. In vivo research showed that 120 mg/ kg caffeine injection caused hearing loss by damaging the organ of Corti, stria vascularis, and spiral ganglion neurons. RNA-seq results suggested that SGK1 might play a vital role in ototoxicity. To confirm our observations in vitro, we used the HEI-OC1 cell line, a cochlear hair cell-like cell line, to investigate the role of caffeine in hearing loss. The results of flow cytometry, TUNEL assay, immunocytochemistry, qRT-PCR, and Western blotting showed that caffeine caused autophagy and apoptosis via SGK1 pathway. We verified the interaction between SGK1 and HIF-1α by co-IP. To confirm the role of SGK1 and HIF-1α, GSK650394 was used as an inhibitor of SGK1 and CoCl₂ was used as an inducer of HIF-1α. Western blot analysis suggested that GSK650394 and CoCl₂ relieved the caffeine-induced apoptosis and autophagy. Together, these results indicated that caffeine induces autophagy and apoptosis in auditory hair cells via the SGK1/HIF-1α pathway, suggesting that caffeine may cause hearing loss. Additionally, our findings provided new insights into ototoxic drugs, demonstrating that SGK1 and its downstream pathways may be potential therapeutic targets for hearing research at the molecular level.

Fasudil prevents neomycin-induced hair cell damage by inhibiting autophagy through the miR-489/NDP52 signaling pathway in HEI-OC1 cells

Hearing loss is a common sensory disorder that is mainly caused by the loss of hair cells (HCs). Drug-induced deafness, for which there is currently no effective treatment, is mainly caused by the inappropriate use of aminoglycoside antibiotics. Fasudil (Fas), a novel isoquinoline sulfonamide derivative, has exhibited antioxidant abilities in a number of previous studies. The aim of the present study was to investigate the potential effects of Fas against neomycin (Neo)-induced hair cell damage and elucidate the underlying mechanism. Flow cytometry and western blot analysis were used to detect the effects of Fas on cell apoptosis and to determine the expression levels of autophagy-related proteins, LC3B and Beclin 1, induced by Neo. Mitochondrial membrane potential and reactive oxygen species (ROS) levels were detected using fluorescent probes. The effect of Fas on Neo-induced hair cell injury marker, GFP-LC3B, was also examined using the immunofluorescence technique. Fas was found to inhibit Neo-induced mitochondrial autophagy and mitochondrial membrane potential decline, in addition to reducing ROS levels and cell apoptosis caused by Neo treatment. However, Fas failed to inhibit the Neo-induced these above changes in cells with NDP52 overexpression. The putative binding sites of microRNA (miR)-489 on the 3'-untranslated region of nuclear dot protein 52 (NDP52) were predicted using the TargetScan 7.0 online tool, and this association was further verified using a dual-luciferase reporter assay. Moreover, the expression of miR-489 negatively regulated the expression of NDP52. Fas and miR-489 mimic inhibited the Neo-induced mitochondrial autophagy and mitochondrial membrane potential decline, in addition to reducing ROS levels and cell apoptosis. Knockdown of miR-489 expression using a miR-489 inhibitor blocked the inhibitory effects of Fas on the mitochondrial membrane potential, cell apoptosis and ROS production. Therefore, Fas may upregulate the expression of miR-489 to negatively regulate the expression of NDP52 at the post-transcriptional level, which in turn inhibits the activation of mitophagy and cell injury induced by Neo. Thus, Fas may act as a novel therapeutic option in the clinical treatment of hearing loss in the future.

Long-Term Release of Dexamethasone With a Polycaprolactone-Coated Electrode Alleviates Fibrosis in Cochlear Implantation

Cochlear implantation (CI) is the major treatment for severe sensorineural hearing loss. However, the fibrotic tissue forming around the electrodes reduces the treatment effectiveness of CI. Dexamethasone (DEX) is usually applied routinely in perioperative treatment of cochlear implantation (CI), but its diffusion in the inner ear after systemic administration is limited. In the present study, an electrode coated with polycaprolactone (PCL) loaded with dexamethasone was developed with a simple preparation process to maintain the stability of the electrode itself. The DEX-loaded PCL coating has good biocompatibility and does not change the smoothness, flexibility, or compliance of the implant electrode. Stable and effective DEX concentrations were maintained for more than 9 months. Compared with the pristine electrode, decreasing intracochlear fibrosis, protection of hair cells and spiral ganglion cells, and better residual hearing were observed 5 weeks after PCL-DEX electrode implantation. The PCL-DEX electrode has great potential in preventing hearing loss and fibrosis by regulating macrophages and inhibiting the expression of the fibrosis-related factors IL-1β, TNF-α, IL-4, and TGF-β1. In conclusion, the PCL-DEX electrode coating shows promising application in CI surgery.

MECOM promotes supporting cell proliferation and differentiation in cochlea

Permanent damage to hair cells (HCs) is the leading cause of sensory deafness. Supporting cells (SCs) are essential in the restoration of hearing in mammals because they can proliferate and differentiate to HCs. MDS1 and EVI1 complex locus (MECOM) is vital in early development and cell differentiation and regulates the TGF-β signaling pathway to adapt to pathophysiological events, such as hematopoietic proliferation, differentiation and cells death. In addition, MECOM plays an essential role in neurogenesis and craniofacial development. However, the role of MECOM in the development of cochlea and its way to regulate related signaling are not fully understood. To address this problem, this study examined the expression of MECOM during the development of cochlea and observed a significant increase of MECOM at the key point of auditory epithelial morphogenesis, indicating that MECOM may have a vital function in the formation of cochlea and regeneration of HCs. Meanwhile, we tried to explore the possible effect and potential mechanism of MECOM in SC proliferation and HC regeneration. Findings from this study indicate that overexpression of MECOM markedly increases the proliferation of SCs in the inner ear, and the expression of Smad3 and Cdkn2b related to TGF signaling is significantly down-regulated, corresponding to the overexpression of MECOM. Collectively, these data may provide an explanation of the vital function of MECOM in SC proliferation and trans-differentiation into HCs, as well as its regulation. The interaction between MECOM, Wnt, Notch and the TGF-β signaling may provide a feasible approach to induce the regeneration of HCs.

Auditory Neuropathy as the Initial Phenotype for Patients With ATP1A3 c.2452 G > A: Genotype-Phenotype Study and CI Management

Objective: The objective of this study is to analyze the genotype–phenotype correlation of patients with auditory neuropathy (AN), which is a clinical condition featuring normal cochlear responses and abnormal neural responses, and ATP1A3 c.2452 G > A (p.E818K), which has been generally recognized as a genetic cause of cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS) syndrome.

Methods: Four patients diagnosed as AN by clinical evaluation and otoacoustic emission and auditory brainstem responses were recruited and analyzed by next-generation sequencing to identify candidate disease-causing variants. Sanger sequencing was performed on the patients and their parents to verify the results, and short tandem repeat-based testing was conducted to confirm the biological relationship between the parents and the patients. Furthermore, cochlear implantation (CI) was performed in one AN patient to reconstruct hearing.

Results: Four subjects with AN were identified to share a de novo variant, p.E818K in the ATP1A3 gene. Except for the AN phenotype, patients 1 and 2 exhibited varying degrees of neurological symptoms, implying that they can be diagnosed as CAPOS syndrome. During the 15 years follow-up of patient 1, we observed delayed neurological events and progressive bilateral sensorineural hearing loss in pure tone threshold (pure tone audiometry, PTA). Patient 2 underwent CI on his left ear, and the result was poor. The other two patients (patient 3 and patient 4, who were 8 and 6 years old, respectively) denied any neurological symptoms.

Conclusion:ATP1A3 p.E818K has rarely been documented in the Chinese AN population. Our study confirms that p.E818K in the ATP1A3 gene is a multiethnic cause of AN in Chinese individuals. Our study further demonstrates the significance of genetic testing for this specific mutation for identifying the special subtype of AN with somewhat favorable CI outcome and offers a more accurate genetic counseling about the specific de novo mutation.

Promising Applications of Nanoparticles in the Treatment of Hearing Loss

Hearing loss is one of the most common disabilities affecting both children and adults worldwide. However, traditional treatment of hearing loss has some limitations, particularly in terms of drug delivery system as well as diagnosis of ear imaging. The blood–labyrinth barrier (BLB), the barrier between the vasculature and fluids of the inner ear, restricts entry of most blood-borne compounds into inner ear tissues. Nanoparticles (NPs) have been demonstrated to have high biocompatibility, good degradation, and simple synthesis in the process of diagnosis and treatment, which are promising for medical applications in hearing loss. Although previous studies have shown that NPs have promising applications in the field of inner ear diseases, there is still a gap between biological research and clinical application. In this paper, we aim to summarize developments and challenges of NPs in diagnostics and treatment of hearing loss in recent years. This review may be useful to raise otology researchers’ awareness of effect of NPs on hearing diagnosis and treatment.

The Ganglioside Monosialotetrahexosylganglioside Protects Auditory Hair Cells Against Neomycin-Induced Cytotoxicity Through Mitochondrial Antioxidation: An in vitro Study

Neomycin is a common ototoxic aminoglycoside antibiotic that causes sensory hearing disorders worldwide, and monosialotetrahexosylganglioside (GM1) is reported to have antioxidant effects that protect various cells. However, little is known about the effect of GM1 on neomycin-induced hair cell (HC) ototoxic damage and related mechanism. In this study, cochlear HC-like HEI-OC-1 cells along with whole-organ explant cultures were used to establish an in vitro neomycin-induced HC damage model, and then the apoptosis rate, the balance of oxidative and antioxidant gene expression, reactive oxygen species (ROS) levels and mitochondrial membrane potential (MMP) were measured. GM1 could maintain the balance of oxidative and antioxidant gene expression, inhibit the accumulation of ROS and proapoptotic gene expression, promoted antioxidant gene expression, and reduce apoptosis after neomycin exposure in HEI-OC-1 cells and cultured cochlear HCs. These results suggested that GM1 could reduce ROS aggregation, maintain mitochondrial function, and improve HC viability in the presence of neomycin, possibly through mitochondrial antioxidation. Hence, GM1 may have potential clinical value in protecting against aminoglycoside-induced HC injury.

Opa1 Prevents Apoptosis and Cisplatin-Induced Ototoxicity in Murine Cochleae

Optic atrophy1 (OPA1) is crucial for inner mitochondrial membrane (IMM) fusion and essential for maintaining crista structure and mitochondrial morphology. Optic atrophy and hearing impairment are the most prevalent clinical features associated with mutations in the OPA1 gene, but the function of OPA1 in hearing is still unknown. In this study, we examined the ability of Opa1 to protect against cisplatin-induced cochlear cell death in vitro and in vivo. Our results revealed that knockdown of Opa1 affects mitochondrial function in HEI-OC1 and Neuro 2a cells, as evidenced by an elevated reactive oxygen species (ROS) level and reduced mitochondrial membrane potential. The dysfunctional mitochondria release cytochrome c, which triggers apoptosis. Opa1 expression was found to be significantly reduced after cell exposed to cisplatin in HEI-OC1 and Neuro 2a cells. Loss of Opa1 aggravated the apoptosis and mitochondrial dysfunction induced by cisplatin treatment, whereas overexpression of Opa1 alleviated cisplatin-induced cochlear cell death in vitro and in explant. Our results demonstrate that overexpression of Opa1 prevented cisplatin-induced ototoxicity, suggesting that Opa1 may play a vital role in ototoxicity and/or mitochondria-associated cochlear damage.

Familial Temperature-Sensitive Auditory Neuropathy: Distinctive Clinical Courses Caused by Variants of the OTOF Gene

Objective: To investigate the clinical course and genetic etiology of familial temperature-sensitive auditory neuropathy (TSAN), which is a very rare subtype of auditory neuropathy (AN) that involves an elevation of hearing thresholds due to an increase in the core body temperature, and to evaluate the genotype-phenotype correlations in a family with TSAN. Methods: Six members of a non-consanguineous Chinese family, including four siblings complaining of communication difficulties when febrile, were enrolled in this study. The clinical and audiological profiles of the four siblings were fully evaluated during both febrile and afebrile episodes, and the genetic etiology of hearing loss (HL) was explored using next-generation sequencing (NGS) technology. Their parents, who had no complaints of fluctuating HL due to body temperature variation, were enrolled for the genetics portion only. Results: Audiological tests during the patients' febrile episodes met the classical diagnostic criteria for AN, including mild HL, poor speech discrimination, preserved cochlear microphonics (CMs), and absent auditory brainstem responses (ABRs). Importantly, unlike the pattern observed in previously reported cases of TSAN, the ABRs and electrocochleography (ECochG) signals of our patients improved to normal during afebrile periods. Genetic analysis identified a compound heterozygous variant of the OTOF gene (which encodes the otoferlin protein), including one previously reported pathogenic variant, c.5098G > C (p.Glu1700Gln), and one novel variant, c.4882C > A (p.Pro1628Thr). Neither of the identified variants affected the C2 domains related to the main function of otoferlin. Both variants faithfully cosegregated with TSAN within the pedigree, suggesting that OTOF is the causative gene of the autosomal recessive trait segregation in this family. Conclusion: The presence of CMs with absent (or markedly abnormal) ABRs is a reliable criterion for diagnosing AN. The severity of the phenotype caused by dysfunctional neurotransmitter release in TSAN may reflect variants that alter the C2 domains of otoferlin. The observations from this study enrich the current understanding of the phenotype and genotype of TSAN and may lay a foundation for further research on its pathogenesis.

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 H₂ O₂ 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.

A Model of Waardenburg Syndrome Using Patient-Derived iPSCs With a SOX10 Mutation Displays Compromised Maturation and Function of the Neural Crest That Involves Inner Ear Development

Waardenburg syndrome (WS) is an autosomal dominant inherited disorder that is characterized by sensorineural hearing loss and abnormal pigmentation. SOX10 is one of its main pathogenicity genes. The generation of patient-specific induced pluripotent stem cells (iPSCs) is an efficient means to investigate the mechanisms of inherited human disease. In our work, we set up an iPSC line derived from a WS patient with SOX10 mutation and differentiated into neural crest cells (NCCs), a key cell type involved in inner ear development. Compared with control-derived iPSCs, the SOX10 mutant iPSCs showed significantly decreased efficiency of development and differentiation potential at the stage of NCCs. After that, we carried out high-throughput RNA-seq and evaluated the transcriptional misregulation at every stage. Transcriptome analysis of differentiated NCCs showed widespread gene expression alterations, and the differentially expressed genes (DEGs) were enriched in gene ontology terms of neuron migration, skeletal system development, and multicellular organism development, indicating that SOX10 has a pivotal part in the differentiation of NCCs. It's worth noting that, a significant enrichment among the nominal DEGs for genes implicated in inner ear development was found, as well as several genes connected to the inner ear morphogenesis. Based on the protein-protein interaction network, we chose four candidate genes that could be regulated by SOX10 in inner ear development, namely, BMP2, LGR5, GBX2, and GATA3. In conclusion, SOX10 deficiency in this WS subject had a significant impact on the gene expression patterns throughout NCC development in the iPSC model. The DEGs most significantly enriched in inner ear development and morphogenesis may assist in identifying the underlying basis for the inner ear malformation in subjects with WS.

Disruption of Glutamate Release and Uptake-Related Protein Expression After Noise-Induced Synaptopathy in the Cochlea

High-intensity noise can cause permanent hearing loss; however, short-duration medium-intensity noise only induces a temporary threshold shift (TTS) and damages synapses formed by inner hair cells (IHCs) and spiral ganglion nerves. Synaptopathy is generally thought to be caused by glutamate excitotoxicity. In this study, we investigated the expression levels of vesicle transporter protein 3 (Vglut3), responsible for the release of glutamate; glutamate/aspartate transporter protein (GLAST), responsible for the uptake of glutamate; and Na⁺/K⁺-ATPase α1 coupled with GLAST, in the process of synaptopathy in the cochlea. The results of the auditory brainstem response (ABR) and CtBP2 immunofluorescence revealed that synaptopathy was induced on day 30 after 100 dB SPL noise exposure in C57BL/6J mice. We found that GLAST and Na⁺/K⁺-ATPase α1 were co-localized in the cochlea, mainly in the stria vascularis, spiral ligament, and spiral ganglion cells. Furthermore, Vglut3, GLAST, and Na⁺/K⁺-ATPase α1 expression were disrupted after noise exposure. These results indicate that disruption of glutamate release and uptake-related protein expression may exacerbate the occurrence of synaptopathy.

Hair Cell Protection from Ototoxic Drugs

Hearing loss is often caused by death of sensory hair cells (HCs) in the inner ear. HCs are vulnerable to some ototoxic drugs, such as aminoglycosides(AGs) and the cisplatin.The most predominant form of drug-induced cell death is apoptosis. Many efforts have been made to protect HCs from cell death after ototoxic drug exposure. These mechanisms and potential targets of HCs protection will be discussed in this review.And we also propose further investigation in the field of HCs necrosis and regeneration, as well as future clinical utilization.

Noise-Induced Hearing Loss: Updates on Molecular Targets and Potential Interventions

Noise overexposure leads to hair cell loss, synaptic ribbon reduction, and auditory nerve deterioration, resulting in transient or permanent hearing loss depending on the exposure severity. Oxidative stress, inflammation, calcium overload, glutamate excitotoxicity, and energy metabolism disturbance are the main contributors to noise-induced hearing loss (NIHL) up to now. Gene variations are also identified as NIHL related. Glucocorticoid is the only approved medication for NIHL treatment. New pharmaceuticals targeting oxidative stress, inflammation, or noise-induced neuropathy are emerging, highlighted by the nanoparticle-based drug delivery system. Given the complexity of the pathogenesis behind NIHL, deeper and more comprehensive studies still need to be fulfilled.

Autophagy: A Novel Horizon for Hair Cell Protection

As a general sensory disorder, hearing loss was a major concern worldwide. Autophagy is a common cellular reaction to stress that degrades cytoplasmic waste through the lysosome pathway. Autophagy not only plays major roles in maintaining intracellular homeostasis but is also involved in the development and pathogenesis of many diseases. In the auditory system, several studies revealed the link between autophagy and hearing protection. In this review, we aimed to establish the correlation between autophagy and hair cells (HCs) from the aspects of ototoxic drugs, aging, and acoustic trauma and discussed whether autophagy could serve as a potential measure in the protection of HCs.

Atrial Natriuretic Peptide Promotes Neurite Outgrowth and Survival of Cochlear Spiral Ganglion Neurons in vitro Through NPR-A/cGMP/PKG Signaling

Sensorineural hearing loss (SNHL) is a dominant public health issue affecting millions of people around the globe, which is correlated with the irreversible deterioration of the hair cells and spiral ganglion neurons (SGNs) within the cochlea. Strategies using bioactive molecules that regulate neurite regeneration and neuronal survival to reestablish connections between auditory epithelium or implanted electrodes and SGN neurites would become attractive therapeutic candidates for SNHL. As an intracellular second messenger, cyclic guanosine-3’,5’-monophosphate (cGMP) can be synthesized through activation of particulate guanylate cyclase-coupled natriuretic peptide receptors (NPRs) by natriuretic peptides, which in turn modulates multiple aspects of neuronal functions including neuronal development and neuronal survival. As a cardiac-derived hormone, atrial natriuretic peptide (ANP), and its specific receptors (NPR-A and NPR-C) are broadly expressed in the nervous system where they might be involved in the maintenance of diverse neural functions. Despite former literatures and our reports indicating the existence of ANP and its receptors within the inner ear, particularly in the spiral ganglion, their potential regulatory mechanisms underlying functional properties of auditory neurons are still incompletely understood. Our recently published investigation revealed that ANP could promote the neurite outgrowth of SGNs by activating NPR-A/cGMP/PKG cascade in a dose-dependent manner. In the present research, the influence of ANP and its receptor-mediated downstream signaling pathways on neurite outgrowth, neurite attraction, and neuronal survival of SGNs in vitro was evaluated by employing cultures of organotypic explant and dissociated neuron from postnatal rats. Our data indicated that ANP could support and attract neurite outgrowth of SGNs and possess a high capacity to improve neuronal survival of SGNs against glutamate-induced excitotoxicity by triggering the NPR-A/cGMP/PKG pathway. The neuroregenerative and neuroprotective effects of ANP/NPRA/cGMP/PKG-dependent signaling on SGNs would represent an attractive therapeutic candidate for hearing impairment.

Key Signaling Pathways Regulate the Development and Survival of Auditory Hair Cells

The loss of auditory sensory hair cells (HCs) is the most common cause of sensorineural hearing loss (SNHL). As the main sound transmission structure in the cochlea, it is necessary to maintain the normal shape and survival of HCs. In this review, we described and summarized the signaling pathways that regulate the development and survival of auditory HCs in SNHL. The role of the mitogen-activated protein kinase (MAPK), phosphoinositide-3 kinase/protein kinase B (PI3K/Akt), Notch/Wnt/Atoh1, calcium channels, and oxidative stress/reactive oxygen species (ROS) signaling pathways are the most relevant. The molecular interactions of these signaling pathways play an important role in the survival of HCs, which may provide a theoretical basis and possible therapeutic interventions for the treatment of hearing loss.

Dose-Dependent Pattern of Cochlear Synaptic Degeneration in C57BL/6J Mice Induced by Repeated Noise Exposure

It is widely accepted that even a single acute noise exposure at moderate intensity that induces temporary threshold shift (TTS) can result in permanent loss of ribbon synapses between inner hair cells and afferents. However, effects of repeated or chronic noise exposures on the cochlear synapses especially medial olivocochlear (MOC) efferent synapses remain elusive. Based on a weeklong repeated exposure model of bandwidth noise over 2-20 kHz for 2 hours at seven intensities (88 to 106 dB SPL with 3 dB increment per gradient) on C57BL/6J mice, we attempted to explore the dose-response mechanism of prolonged noise-induced audiological dysfunction and cochlear synaptic degeneration. In our results, mice repeatedly exposed to relatively low-intensity noise (88, 91, and 94 dB SPL) showed few changes on auditory brainstem response (ABR), ribbon synapses, or MOC efferent synapses. Notably, repeated moderate-intensity noise exposures (97 and 100 dB SPL) not only caused hearing threshold shifts and the inner hair cell ribbon synaptopathy but also impaired MOC efferent synapses, which might contribute to complex patterns of damages on cochlear function and morphology. However, repeated high-intensity (103 and 106 dB SPL) noise exposures induced PTSs mainly accompanied by damages on cochlear amplifier function of outer hair cells and the inner hair cell ribbon synaptopathy, rather than the MOC efferent synaptic degeneration. Moreover, we observed a frequency-dependent vulnerability of the repeated acoustic trauma-induced cochlear synaptic degeneration. This study provides a sight into the hypothesis that noise-induced cochlear synaptic degeneration involves both afferent (ribbon synapses) and efferent (MOC terminals) pathology. The pattern of dose-dependent pathological changes induced by repeated noise exposure at various intensities provides a possible explanation for the complicated cochlear synaptic degeneration in humans. The underlying mechanisms remain to be studied in the future.

PIN1 Protects Hair Cells and Auditory HEI-OC1 Cells against Senescence by Inhibiting the PI3K/Akt/mTOR Pathway

A growing amount of evidence has confirmed the crucial role of the prolyl isomerase PIN1 in aging and age-related diseases. However, the mechanism of PIN1 in age-related hearing loss (ARHL) remains unclear. Pathologically, ARHL is primarily due to the loss and dysfunction of hair cells (HCs) and spiral ganglion cells (SGCs) in the cochlea. Therefore, in this study, we aimed to investigate the role of PIN1 in protecting hair cells and auditory HEI-OC1 cells from senescence. Enzyme-linked immunosorbent assays, immunohistochemistry, and immunofluorescence were used to detect the PIN1 protein level in the serum of ARHL patients and C57BL/6 mice in different groups, and in the SGCs and HCs of young and aged C57BL/6 mice. In addition, a model of HEI-OC1 cell senescence induced by H2O2 was used. Adult C57BL/6 mice were treated with juglone, or juglone and NAC, for 4 weeks. Interestingly, we found that the PIN1 protein expression decreased in the serum of patients with ARHL, in senescent HEI-OC1 cells, and in the cochlea of aged mice. Moreover, under H2O2 and juglone treatment, a large amount of ROS was produced, and phosphorylation of p53 was induced. Importantly, PIN1 expression was significantly increased by treatment with the p53 inhibitor pifithrin-α. Overexpression of PIN1 reversed the increased level of p-p53 and rescued HEI-OC1 cells from senescence. Furthermore, PIN1 mediated cellular senescence by the PI3K/Akt/mTOR signaling pathway. In vivo data from C57BL/6 mice showed that treatment with juglone led to hearing loss. Taken together, these findings demonstrated that PIN1 may act as a vital modulator in hair cell and HEI-OC1 cell senescence.

Deletion of Clusterin Protects Cochlear Hair Cells against Hair Cell Aging and Ototoxicity

Hearing loss is a debilitating disease that affects 10% of adults worldwide. Most sensorineural hearing loss is caused by the loss of mechanosensitive hair cells in the cochlea, often due to aging, noise, and ototoxic drugs. The identification of genes that can be targeted to slow aging and reduce the vulnerability of hair cells to insults is critical for the prevention of sensorineural hearing loss. Our previous cell-specific transcriptome analysis of adult cochlear hair cells and supporting cells showed that Clu, encoding a secreted chaperone that is involved in several basic biological events, such as cell death, tumor progression, and neurodegenerative disorders, is expressed in hair cells and supporting cells. We generated Clu-null mice (C57BL/6) to investigate its role in the organ of Corti, the sensory epithelium responsible for hearing in the mammalian cochlea. We showed that the deletion of Clu did not affect the development of hair cells and supporting cells; hair cells and supporting cells appeared normal at 1 month of age. Auditory function tests showed that Clu-null mice had hearing thresholds comparable to those of wild-type littermates before 3 months of age. Interestingly, Clu-null mice displayed less hair cell and hearing loss compared to their wildtype littermates after 3 months. Furthermore, the deletion of Clu is protected against aminoglycoside-induced hair cell loss in both in vivo and in vitro models. Our findings suggested that the inhibition of Clu expression could represent a potential therapeutic strategy for the alleviation of age-related and ototoxic drug-induced hearing loss.

Claudin h Is Essential for Hair Cell Morphogenesis and Auditory Function in Zebrafish

Hereditary hearing loss caused by defective hair cells is one of the most common congenital diseases, whose nosogenesis is still unclear because many of the causative genes remain unidentified. Claudins are one kind of transmembrane proteins that constitute the most important components of the tight junctions and paracellular barrier and play important roles in neurodevelopment. In this study, we investigated the function of claudin h in morphogenesis and auditory function of the hair cell in zebrafish. The results of in situ hybridization showed that claudin h was specifically localized in the otic vesicle and neuromasts in zebrafish embryos. The deficiency of claudin h caused significant reduction of otic vesicle size and loss of utricle otolith. Moreover, the startle response and vestibulo-ocular reflex experiments revealed that loss of claudin h led to serious hearing loss and vestibular dysfunction. Importantly, the confocal microscopy observation found that compared to the control zebrafish, the claudin h morphants and mutants displayed significantly reduced the number of cristae hair cells and shortened kinocilia. Besides, the deficiency of claudin h also caused the loss of hair cells in neuromasts which could be rescued by injecting claudin h mRNA into the mutant embryos at one cell stage. Furthermore, the immunohistochemistry experiments demonstrated remarkable apoptosis of hair cells in the neuromasts, which might contribute to the loss of hair cells number. Overall, these data indicated that claudin h is indispensable for the development of hair cells, vestibular function, and hearing ability of zebrafish.

Next-Generation Sequencing Identifies Pathogenic Variants in HGF, POU3F4, TECTA, and MYO7A in Consanguineous Pakistani Deaf Families

Background

Approximately 70% of congenital deafness is attributable to genetic causes. Incidence of congenital deafness is known to be higher in families with consanguineous marriage. In this study, we investigated the genetic causes in three consanguineous Pakistani families segregating with prelingual, severe-to-profound deafness.

Results

Through targeted next-generation sequencing of 414 genes known to be associated with deafness, homozygous variants c.536del (p. Leu180Serfs∗20) in TECTA, c.3719 G>A (p. Arg1240Gln) in MYO7A, and c.482+1986_1988del in HGF were identified as the pathogenic causes of enrolled families. Interestingly, in one large consanguineous family, an additional c.706G>A (p. Glu236Lys) variant in the X-linked POU3F4 gene was also identified in multiple affected family members causing deafness. Genotype-phenotype cosegregation was confirmed in all participating family members by Sanger sequencing.

Conclusions

Our results showed that the genetic causes of deafness are highly heterogeneous. Even within a single family, the affected members with apparently indistinguishable clinical phenotypes may have different pathogenic variants.

Transcriptomic Analysis Reveals an Altered Hcy Metabolism in the Stria Vascularis of the Pendred Syndrome Mouse Model

PURPOSE

Slc26a4-/- mice exhibit severer defects in the development of the cochlea and develop deafness, while the underlying mechanisms responsible for these effects remain unclear. Our study was to investigate the potential mechanism linking SLC26A4 deficiency to hearing loss.

MATERIALS AND METHODS

RNA sequencing was applied to analyze the differential gene expression of the stria vascularis (SV) from wildtype and Slc26a4-/- mice. GO and KEGG pathway analysis were performed. Quantitative RT-PCR was applied to validate the expression of candidate genes affected by Slc26a4. ELISA and immunofluorescence technique were used to detect the homocysteine (Hcy) level in serum, brain, and SV, respectively.

RESULTS

183 upregulated genes and 63 downregulated genes were identified in the SV associated with Slc26a4 depletion. Transcriptomic profiling revealed that Slc26a4 deficiency significantly affected the expression of genes associated with cell adhesion, transmembrane transport, and the biogenesis of multicellular organisms. The SV from Slc26a4-/- mice exhibited a higher expression of Bhmt mRNAs, as well as altered homocysteine (Hcy) metabolism.

CONCLUSIONS

The altered expression of Bhmt results in a dramatic change in multiple biochemical reactions and a disruption of nutrient homeostasis in the endolymph which may contribute to hearing loss of Slc26a4 knockout mouse.

Identification and Characterization of a Cryptic Genomic Deletion-Insertion in EYA1 Associated with Branchio-Otic Syndrome

Branchio-oto-renal spectrum disorder (BORSD) is characterized by hearing loss accompanied by ear malformations, branchial cysts, and fistulae, with (branchio-oto-renal syndrome (BORS)) or without renal abnormalities (BOS (branchio-otic syndrome)). As the most common causative gene for BORSD, dominant mutations in EYA1 are responsible for approximately 40% of the cases. In a sporadic deaf patient diagnosed as BOS, we identified an apparent heterozygous genomic deletion spanning the first four coding exons and one 5′ noncoding exon of EYA1 by targeted next-generation sequencing of 406 known deafness genes. Real-time PCR at multiple regions of EYA1 confirmed the existence of this genomic deletion and extended its 5′ boundary beyond the 5′-UTR. Whole genome sequencing subsequently located the 5′ and 3′ breakpoints to 19268 bp upstream to the ATG initiation codon and 3180 bp downstream to exon 5. PCR amplification across the breakpoints in both the patient and his parents showed that the genomic alteration occurred de novo. Sanger sequencing of this PCR product revealed that it is in fact a GRCh38/hg38:chr8:g.71318554_71374171delinsTGCC genomic deletion-insertion. Our results showed that the genomic variant is responsible for the hearing loss associated with BOS and provided an example for deciphering such cryptic genomic alterations following pipelines of comprehensive exome/genome sequencing and designed verification.

N-Acetylcysteine Combined With Dexamethasone Treatment Improves Sudden Sensorineural Hearing Loss and Attenuates Hair Cell Death Caused by ROS Stress

Sudden sensorineural hearing loss (SSNHL) is a common emergency in the world. Increasing evidence of imbalance of oxidant–antioxidant were found in SSNHL patients. Steroids combined with antioxidants may be a potential strategy for the treatment of SSNHL. In cochlear explant experiment, we found that N-acetylcysteine (NAC) combined with dexamethasone can effectively protect hair cells from oxidative stress when they were both at ineffective concentrations alone. A clinic trial was designed to explore whether oral NAC combined with intratympanic dexamethasone (ITD) as a salvage treatment has a better therapeutic effect. 41 patients with SSNHL were randomized to two groups. 23 patients in control group received ITD therapy alone, while 18 patient s in NAC group were treated with oral NAC and ITD. The patients were followed-up on day 1st (initiation of treatment) and day 14th. Overall, there was no statistical difference in final pure-tone threshold average (PTA) improvement between those two groups. However, a significant hearing gain at 8,000 Hz was observed in NAC group. Moreover, the hearing recovery rates of NAC group is much higher than that in control group. These results demonstrated that oral NAC in combination with ITD therapy is a more effective therapy for SSNHL than ITD alone.

Mitochondrial Dysfunction and Sirtuins: Important Targets in Hearing Loss

Mitochondrial dysfunction has been suggested to be a risk factor for sensorineural hearing loss (SNHL) induced by aging, noise, ototoxic drugs, and gene. Reactive oxygen species (ROS) are mainly derived from mitochondria, and oxidative stress induced by ROS contributes to cochlear damage as well as mitochondrial DNA mutations, which may enhance the sensitivity and severity of hearing loss and disrupt ion homeostasis (e.g., Ca2+ homeostasis). The formation and accumulation of ROS further undermine mitochondrial components and ultimately lead to apoptosis and necrosis. SIRT3–5, located in mitochondria, belong to the family of sirtuins, which are highly conserved deacetylases dependent on nicotinamide adenine dinucleotide (NAD+). These deacetylases regulate diverse cellular biochemical activities. Recent studies have revealed that mitochondrial sirtuins, especially SIRT3, modulate ROS levels in hearing loss pathologies. Although the precise functions of SIRT4 and SIRT5 in the cochlea remain unclear, the molecular mechanisms in other tissues indicate a potential protective effect against hearing loss. In this review, we summarize the current knowledge regarding the role of mitochondrial dysfunction in hearing loss, discuss possible functional links between mitochondrial sirtuins and SNHL, and propose a perspective that SIRT3–5 have a positive effect on SNHL.

Molecular Behavior of HMGB1 in the Cochlea Following Noise Exposure and in vitro

Noise-induced hearing loss (NIHL) is characterized by cellular damage to the inner ear, which is exacerbated by inflammation. High-mobility group box 1 (HMGB1), a representative damage-associated molecular pattern (DAMP), acts as a mediator of inflammation or an intercellular messenger according to its cellular localization. Blocking or regulating HMGB1 offers an attractive approach in ameliorating NIHL. However, the precise therapeutic intervention must be based on a deeper understanding of its dynamic molecular distribution and function in cochlear pathogenesis after acoustic trauma. Here, we have presented the spatiotemporal dynamics of the expression of HMGB1, exhibiting distribution variability in specific cochlear regions and cells following noise exposure. After gene manipulation, we further investigated the characteristics of cellular HMGB1 in HEI-OC1 cells. The higher cell viability observed in the HMGB1 knocked-down group after stimulation with H₂O₂ indicated the possible negative effect of HMGB1 on cellular lifespan. In conclusion, this study demonstrated that HMGB1 is involved in NIHL pathogenesis and its molecular biology has essential and subtle influences, preserving a translational potential for pharmacological intervention.

Differences in Calcium Clearance at Inner Hair Cell Active Zones May Underlie the Difference in Susceptibility to Noise-Induced Cochlea Synaptopathy of C57BL/6J and CBA/CaJ Mice

Noise exposure of a short period at a moderate level can produce permanent cochlear synaptopathy without seeing lasting changes in audiometric threshold. However, due to the species differences in inner hair cell (IHC) calcium current that we have recently discovered, the susceptibility to noise exposure may vary, thereby impact outcomes of noise exposure. In this study, we investigate the consequences of noise exposure in the two commonly used animal models in hearing research, CBA/CaJ (CBA) and C57BL/6J (B6) mice, focusing on the functional changes of cochlear IHCs. In the CBA mice, moderate noise exposure resulted in a typical fully recovered audiometric threshold but a reduced wave I amplitude of auditory brainstem responses. In contrast, both auditory brainstem response threshold and wave I amplitude fully recovered in B6 mice at 2 weeks after noise exposure. Confocal microscopy observations found that ribbon synapses of IHCs recovered in B6 mice but not in CBA mice. To further characterize the molecular mechanism underlying these different phenotypes in synaptopathy, we compared the ratio of Bax/Bcl-2 with the expression of cytochrome-C and found increased activity in CBA mice after noise exposure. Under whole-cell patch clamped IHCs, we acquired two-photon calcium imaging around the active zone to evaluate the Ca²⁺ clearance rate and found that CBA mice have a slower calcium clearance rate. Our results indicated that excessive accumulation of calcium due to acoustic overexposure and slow clearance around the presynaptic ribbon might lead to disruption of calcium homeostasis, followed by mitochondrial dysfunction of IHCs that cause susceptibility of noise-induced cochlear synaptopathy in CBA mice.

Autophagy impairment as a key feature for acetaminophen-induced ototoxicity

Macroautophagy/autophagy is a highly conserved self-digestion pathway that plays an important role in cytoprotection under stress conditions. Autophagy is involved in hepatotoxicity induced by acetaminophen (APAP) in experimental animals and in humans. APAP also causes ototoxicity. However, the role of autophagy in APAP-induced auditory hair cell damage is unclear. In the present study, we investigated autophagy mechanisms during APAP-induced cell death in a mouse auditory cell line (HEI-OC1) and mouse cochlear explant culture. We found that the expression of LC3-II protein and autophagic structures was increased in APAP-treated HEI-OC1 cells; however, the degradation of SQSTM1/p62 protein, the yellow puncta of mRFP-GFP-LC3 fluorescence, and the activity of lysosomal enzymes decreased in APAP-treated HEI-OC1 cells. The degradation of p62 protein and the expression of lysosomal enzymes also decreased in APAP-treated mouse cochlear explants. These data indicate that APAP treatment compromises autophagic degradation and causes lysosomal dysfunction. We suggest that lysosomal dysfunction may be directly responsible for APAP-induced autophagy impairment. Treatment with antioxidant N-acetylcysteine (NAC) partially alleviated APAP-induced autophagy impairment and apoptotic cell death, suggesting the involvement of oxidative stress in APAP-induced autophagy impairment. Inhibition of autophagy by knocking down of Atg5 and Atg7 aggravated APAP-induced ER and oxidative stress and increased apoptotic cell death. This study provides a better understanding of the mechanism responsible for APAP ototoxicity, which is important for future exploration of treatment strategies for the prevention of hearing loss caused by ototoxic medications.

Protection of Cochlear Ribbon Synapses and Prevention of Hidden Hearing Loss

In the auditory system, ribbon synapses are vesicle-associated structures located between inner hair cells (IHCs) and spiral ganglion neurons that are implicated in the modulation of trafficking and fusion of synaptic vesicles at the presynaptic terminals. Synapse loss may result in hearing loss and difficulties with understanding speech in a noisy environment. This phenomenon happens without permanent hearing loss; that is, the cochlear synaptopathy is "hidden." Recent studies have reported that synapse loss might be critical in the pathogenesis of hidden hearing loss. A better understanding of the molecular mechanisms of the formation, structure, regeneration, and protection of ribbon synapses will assist in the design of potential therapeutic strategies. In this review, we describe and summarize the following aspects of ribbon synapses: (1) functional and structural features, (2) potential mechanisms of damage, (3) therapeutic research on protecting the synapses, and (4) the role of synaptic regeneration in auditory neuropathy and the current options for synapse rehabilitation.

Development and validation of a survival model for thyroid carcinoma based on autophagy-associated genes

Abnormalities in autophagy-related genes (ARGs) are closely related to the occurrence and development of thyroid carcinoma (THCA). However, the effect of ARGs on the prognosis of THCA remains unclear. Here, by analyzing data from TCGA, 26 differentially expressed ARGs were screened. Cox regression and Lasso regression were utilized to analyze the prognosis of the training group, and a risk model was constructed. Our results show that low-risk patients had better overall survival (OS) than high-risk patients, and the area under the ROC curve in the training and testing groups was significant (3-year AUC, 0.735 vs 0.796; 5-year AUC, 0.821 vs 0.804). In addition, a comprehensive analysis of the 5 identified ARGs demonstrated that most of them were related to OS in THCA patients, and two of them (CX3CL1 and CDKN2A) were differentially expressed in THCA and normal thyroid tissues at the protein level. GSEA suggested that the inactivation of the cell defense system and the activation of some classical tumor signaling pathways are important driving forces for the progression of THCA. This study demonstrated that the 5 ARGs in the survival model are promising multidimensional biomarkers for the diagnosis, prognosis, and treatment of THCA.