Auditory Research publications

Kanamycin (KM), a widely used aminoglycoside antibiotic, is limited by its ototoxic side effects, primarily targeting cochlear outer hair cells (OHCs) and leading to irreversible sensorineural hearing loss. Our previous work showed that silencing AMP‐activated protein kinase alpha 1 (AMPKα1) prevents noise‐induced hearing loss through a redox‐sensitive regulatory mechanism. Given that both noise‐induced and aminoglycoside‐induced hearing loss share oxidative stress as a key pathological feature, we tested whether AMPKα1 silencing could mitigate KM‐induced damage using an acute ototoxic model combining KM with furosemide (KM + FU). KM + FU exposure markedly increased AMPKα phosphorylation at Thr172. Targeted siRNA‐mediated silencing via posterior semicircular canal delivery in CBA/J mice significantly reduced AMPKα1 expression in OHCs and effectively prevented KM + FU‐induced OHC loss and hearing impairment. This preventive effect was independent of stria vascularis permeability or cochlear KM uptake. These findings identify AMPKα as a contributor to KM + FU‐induced acute ototoxicity and suggest that its inhibition may be a promising strategy for hearing preservation.

Age-related hearing loss (ARHL), or presbycusis, is one of the most prevalent sensory deficits in older adults and has been increasingly implicated in cognitive decline and dementia. This study characterizes ARHL in a rhesus macaque model by combining histological, physiological, and cognitive assessments. Aged macaques exhibited progressive cochlear degeneration, with marked outer hair cell loss at mid-to-high frequencies, elevated auditory thresholds, reduced distortion product otoacoustic emissions, and impaired auditory brainstem responses including amplitude reduction, latency prolongation, and diminished temporal precision. Despite modest reductions in inner hair cell ribbon synapse counts, hypertrophic changes were observed. These auditory deficits correlated with subtle impairments in visual working memory, as measured by a delayed match-to-sample task, underscoring a potential sensory-cognitive link. By capturing cross-domain aging markers in a translationally relevant primate model, this work lays a foundation for mechanistic studies and therapeutic interventions targeting both hearing and cognition in aging populations.

Age-related hearing loss (ARHL) is a prevalent neurodegenerative condition characterized by the progressive loss of spiral ganglion neurons (SGNs). Although oxidative stress is recognized as a central pathogenic driver of ARHL, the precise molecular triggers that initiate and amplify SGN damage remain elusive. Here, we investigated the role of the Transient Receptor Potential Vanilloid 2 (TRPV2) channel in ARHL. We found that TRPV2 expression was significantly upregulated in the SGNs of aged mice, which was associated with elevated oxidative stress. Pharmacological activation of TRPV2 in 6-month-old mice (a pre-senescent stage with preserved baseline hearing) accelerated the onset of high-frequency hearing damage, as evidenced by auditory brainstem response (ABR) measurements. Consistently, TRPV2 activation exacerbated oxidative damage (assessed by 4-HNE staining) and increased apoptotic cell death (detected via TUNEL) in the SGN population. In primary SGN cultures, TRPV2 overexpression aggravated oxidative stress, whereas TRPV2 knockdown in SH-SY5Y cells (a human neuroblastoma cell line) markedly mitigated the oxidative injury as reflected by reduced 4-HNE. Our findings establish that the age-related upregulation of TRPV2 sensitizes SGNs to oxidative stress, thereby promoting neuronal damage and exacerbating ARHL. This work highlights TRPV2 as a promising therapeutic target for intervening in the progression of ARHL.

Noise‐induced hearing loss (NIHL) is a common cause of acquired sensorineural hearing loss. Excessive endoplasmic reticulum (ER) stress‐induced apoptosis of cochlear hair cells contributes to NIHL. ER autophagy (ER‐phagy) is a critical pathway for maintaining ER homeostasis and cell survival. DDRGK1 (DDRGK domain containing 1) is a crucial receptor in ER‐phagy, essential for the removal of injured ER components. This work investigates the involvement of DDRGK1‐mediated ER‐phagy in NIHL, which has remained unclear. ER‐phagy flux is inhibited in HEI‐OC1 cells treated with hydrogen peroxide. Noise exposure reduces XIAP (X‐linked inhibitor of apoptosis protein) and DDRGK1 protein levels in these cells. Moreover, XIAP binds to DDRGK1, increasing the stability of DDRGK1 and activating ER‐phagy. Notably, in noise‐exposed CBA/CaJ mice, gastrodin, a traditional Chinese medicine ingredient, reduces noise‐induced loss of cochlear hair cells, ribbon synaptic damage, and hearing loss by promoting XIAP expression, thereby increasing DDRGK1 protein levels and activating ER‐phagy. These findings highlight XIAP‐DDRGK1‐mediated ER‐phagy as a novel therapeutic target for NIHL treatment.

Proper orientation of the apical cytoskeleton in auditory and vestibular hair cells is essential for their sensory function. A recently identified regulator of hair cell orientation is the G protein-coupled receptor GPR156, which signals through inhibitory heterotrimeric G proteins. In hair cells expressing the transcription factor EMX2, GPR156 is apically enriched and polarized at cell junctions. There, GPR156 signaling reverses the interpretation of tissue-level core planar cell polarity cues, effectively reversing the orientation of Emx2 -positive compared to Emx2 -negative hair cells. This mechanism establishes key anatomical features, such as the correct alignment of auditory outer hair cells and the line of polarity reversal in the otolith organs of the vestibular system. Null mice with constitutive Gpr156 inactivation exhibit severe hearing loss, mirroring congenital hearing impairment in human patients with homozygous GPR156 variants. These null mutants also display impaired swimming and vestibulo-ocular reflexes, although the nature of these vestibular deficits differs from those reported in Emx2 mutants. Here, to determine the extent to which functional deficits arise from hair cell misorientation, we conditionally inactivated Gpr156 in postmitotic hair cells in the inner ear. This targeted deletion approach recapitulated the misorientation phenotype observed in null mutants. Notably, 30–40% of cochlear and utricular hair cells affected in the null background retained normal orientation in conditional mutants, likely due to the later timing of Gpr156 inactivation. Despite reduced efficiency, conditional mutants exhibited similar, albeit predictably milder, auditory and vestibular dysfunction. As hair cells can carry out mechano-electrical transduction without GPR156, we conclude that sensory deficits mainly result from its essential role in hair cell orientation.

Hearing impairments, as a prevalent and debilitating non-motor symptom of Parkinson's disease (PD), remain unclear in mechanisms. In this work, we established PD mouse and rat models by using 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), respectively, and investigated their hearing functions and potential mechanisms through auditory brainstem response (ABR), distortion product otoacoustic Emissions (DPOAE), noise exposure, immunofluorescence labeling, volumetric measurement, and colocalization analysis. In MPTP-induced PD mice, we observed significant cholinergic fibers decompensation, heterogeneous dopaminergic fibers damage of cochlear efferent fibers, and adrenergic sympathetic fibers marked loss in the osseous spiral lamina (OSL), corresponding to insignificant cochlear hair cells, ribbon synapse alteration, and auditory sensitivity injury. While in 6-OHDA-induced PD rats, asymmetric alterations in cochlear cholinergic, dopaminergic fibers were found, accompanied by inconsistent adrenergic changes in the OSL, which matched unilateral hair cells, ribbon synapse damage, and hearing loss. Overall, findings from this work indicate that pathological alterations in the cochlea of PD mice and rats, particularly in efferent fibers, may be closely relevant to peripheral hearing alterations.

The gene therapy achieved by AAV-mediated otoferlin-overexpression is an effective therapeutic strategy for congenital deafness. However, achieving its physiological and endogenous patterns of expression remains challenging. Here, we generate the homologous mutation Otof c.1315 C > T (p.R439*), equivalent to OTOF c.1273 C > T (p.R425*) found in humans with profound deafness, to create a nonsense mutation-induced deaf mouse model. We then deliver the ‘RESTART v3’ system, which is a CRISPR-free RNA base editor for nonsense mutation suppression, into the cochlea of the mice. We achieve physiological otoferlin expression, and the edited premature termination codon is reverse-mutated to the original amino acid. We observe significant hearing restoration and enhancement of the behavioral auditory startle reflex. Thus, our study presents a successful RNA editing strategy to significantly restore hereditary deafness in mice carrying the specific Otof nonsense mutation, which holds great promise for future clinical translation.

Noise-induced hearing loss can lead to degeneration of spiral ganglion neurons (SGN), resulting in impairment of auditory signalling. However, the specific mechanism is unclear. In our study, we investigated the function of mitochondrial activity following noise exposure. Findings revealed a reduction in ATP synthesis and alterations in the levels of mitochondrial electron transport chain complexes II, Ⅲ, IV and complex I subunit ND3 reduction by the seventh day post-noise exposure. These findings indicate that SGN mitochondrial dysfunction can impair SGN function. This is further demonstrated by the reduced expression of the mitochondrial marker protein Tom20 and apoptosis-inducing factor (AIF) showed inner membrane but not outer membrane resulted in changes in mitochondrial ETC complexes. And the findings of calpain 2 but not calpain 1 high expression was accompanied in AIF reduction, suggesting AIF has not yet caused SGN deaths. Calpain 2 regulated decreased expression of AIF may relieve the low function of mitochondrion in SGN after noise.

Acquired sensorineural hearing loss (SNHL) is primarily caused by the damage or loss of hair cells (HCs), induced by factors such as noise exposure and ototoxic drugs. However, clinical treatments for SNHL remain limited. Here, the role of the apoptosis‐inducing gene Cidea in SNHL is investigated. It is initially observed that Cidea expression is specifically increased in neomycin‐damaged HCs at both the protein and mRNA levels. To further explore its role, Cidea knockout (Cidea‐/‐) mice are obtained, and it is found that the absence of Cidea effectively alleviates HC apoptosis caused by neomycin treatment and noise exposure in vivo. Moreover, a novel therapeutic strategy for SNHL has been developed by delivering CRISPR/SlugCas9‐HF via AAV to edit Cidea , and this approach significantly reduced HC loss induced by both neomycin and noise exposure. These findings suggest that Cidea may serve as a promising target for the prevention of neomycin‐ and noise‐induced SNHL in clinical settings.

Noise-induced hearing loss (NIHL) involves a biphasic pathophysiology. Intense noise exposure causes immediate cochlear vasoconstriction and ischemia, leading to transient hypoxia. Subsequent reperfusion triggers excess reactive oxygen species (ROS) production, resulting in oxidative stress and hair cell injury. This study therefore developed two oxygenated albumin microbubble (OMB) formulations-ionic-bond metformin-coated (iMet-OMBs) and covalent-bond metformin-encapsulated (cMet-OMBs)-and combined them with transcranial ultrasound (US) to enhance targeted delivery to the cochlea. This approach aims to provide transient oxygen supplementation while simultaneously reducing ROS-mediated injury. Microbubbles were characterized for morphology, oxygen loading, and metformin content. Based on their superior stability and drug-loading profile, cMet-OMBs were selected for in vivo evaluation. In a mouse NIHL model, animals were administered cMet-OMBs systemically via retro-orbital injection, followed by US triggering over the temporal bone. Auditory brainstem response (ABR) thresholds, cochlear oxygen tension, and outer hair cell (OHC) survival were assessed. US-mediated cMet-OMBs rupture transiently increased intracochlear oxygen tension, counteracting early hypoxia after noise exposure. Metformin released from cMet-OMBs attenuated ROS production through mitochondrial complex I inhibition and antioxidant pathway activation. Mice treated with cMet-OMBs + US showed significantly lower ABR threshold shifts and better OHC preservation compared with controls. This dual-action strategy combines transient oxygen supplementation from OMBs with sustained antioxidant protection from metformin. While oxygen delivery raises intracochlear oxygen tension, metformin suppresses ROS generation through mitochondrial complex I inhibition and AMPK/Nrf2 activation. This controlled, US-triggered release achieves net cochlear protection against NIHL without excessive oxidative burden.

Significant breakthroughs have been made in translation of adeno-associated virus (AAV) vectors for hearing disorders targeting auditory hair cells (HCs). In addition to HCs, spiral ganglion neurons (SGNs) are also impacted in a large number of sensorineural hearing loss cases in adults. However when administered directly into the cochlea in rodents aged older than P1-P3, AAV-mediated SGN transduction efficiency decreases dramatically. An efficient gene-delivery method to transduce adult SGNs is needed. Our group has a track record of utilizing axonal transport to transduce brain structures distal from the site of AAV injection. We investigated whether SGNs could be transduced in adult rats following intraparenchymal AAV administration to the olivary complex. Cochlear transduction was observed with the following common AAV serotypes expressing green fluorescent protein: AAV6, AAV9, AAV-Anc80, and AAV-PhP.B. Cochlear transduction was observed with all serotypes, but the cellular tropism and efficiency of gene transfer varied across the cochlear spiral (apex, middle, base) with different AAV serotypes, with some transducing both SGNs and HCs, while others transduced SGNs or HCs exclusively. This study provides proof of concept that AAV delivery to the olivary complex can efficiently deliver transgenes to SGNs in the adult mammalian cochlea.

Most patients with sensorineural hearing loss (SNHL) may initially experience high‐frequency hearing loss linked to greater vulnerability of outer hair cells (OHCs) in the cochlear basal turn. However, the molecular mechanism underlying this susceptibility in the high‐frequency region remains unclear. Here, NOX2 is first identified as a differentially expressed gene related to oxidative damage in the apical and basal turns through single‐cell RNA sequencing. In mouse cochleae damaged by neomycin and noise, Nox2‐positive OHCs increase progressively from the apex to base, indicating that NOX2 expression clearly differed significantly between the apical and basal OHCs. In NOX2 knockout mice, OHC damage caused by neomycin and noise exposure is significantly reduced. Furthermore, knocking out NOX2 increases the expression of Nrf2 in the cytoplasm and Nrf2 nuclear translocation in OHCs. In addition, Nrf2 inhibitors counteract the protective effect of NOX2 knockout against neomycin. Finally, when Nox2 is used as the target, ginsenoside Rg1 is identified as a compound with protective effects against neomycin‐induced hearing loss. In summary, these results indicate NOX2 is highly correlated with high‐frequency OHCs vulnerability in the cochlea and is a potential intervention target for the clinical treatment of SNHL.

Introduction Prenatal exposure to valproic acid (VPA) is a common environmental cause of autism spectrum disorder (ASD) and often leads to expressive and receptive language impairments. Similar communication difficulties among individuals with ASD are often linked to abnormal subcortical and cortical sound processing. Rodents prenatally exposed to VPA exhibit degraded cortical responses to speech and an impaired ability to behaviorally discriminate speech sounds. Methods We sought to determine whether sound processing could be restored with paired vagus nerve stimulation (VNS). In a first experiment, we evaluated whether sound-paired VNS would alter in vivo extracellular multi-unit responses to tones, noise burst trains, and speech sounds from the anterior auditory field. We next sought to evaluate whether improvements to neural sound processing led to improvements in sound discrimination ability. In a second experiment, rats underwent go/no-go sound discrimination testing where VNS was paired with successful trials. Results We found that VPA-exposed rats had degraded spectral, temporal, and speech sound processing compared to saline-exposed control rats. VPA-exposed rats which received sound-paired VNS exhibited a partial or full restoration of processing across sound types. However, across several sound discrimination tasks, we did not observe changes in behavioral performance in response to prenatal exposure to VPA or VNS. Discussion Our study is the first to show that speech-paired VNS leads to a generalized improvement in cortical sound processing across sound types, rescuing neural processing among VPA-exposed rats. These results provide a framework for future studies to develop VNS-based interventions for communication disorders.

Noise-induced hearing loss (NIHL) poses an emerging global health problem with only ear protection or sound avoidance as preventive strategies. The cochlea receives some protection from medial olivocochlear efferent neurons, providing a potential target for therapeutic enhancement. Cholinergic efferents release acetylcholine (ACh) to hyperpolarize and shunt the outer hair cells (OHCs), reducing sound-evoked activation. The (α9)2(α10)3 nicotinic ACh receptor (nAChR) on the OHCs mediates this effect. Transgenic knockin mice with a gain-of-function nAChR (α9L9'T) suffer less NIHL. α9 knockout mice are more vulnerable to NIHL but can be rescued by viral transduction of the α9L9'T subunit. In this study, an HA-tagged gain-of-function α9 isoform was expressed in wild-type mice to reduce NIHL. Synaptic integration of the virally expressed nAChR subunit was confirmed by HA immunopuncta localized to the postsynaptic membrane of OHCs. After noise exposure, AAV2.7m8-CAG-α9L9'T-HA (α9L9'T-HA)-injected mice had less hearing loss (auditory brainstem response [ABR] thresholds and threshold shifts) than did control mice. ABRs of α9L9'T-HA-injected mice also had larger wave-1 amplitudes and better recovery of wave-1 amplitudes post noise exposure. Thus, virally expressed α9L9'T combines effectively with native α9 and α10 subunits to mitigate NIHL in wild-type cochleas.

Aminoglycoside antibiotics remain indispensable despite their ototoxicity. Like other sensorineural forms, aminoglycoside-induced hearing loss (AGIHL) has no effective pharmacotherapy. Oxidative stress, apoptosis, excitotoxicity and inflammation are key pathological factors of the disease. We hypothesised that selegiline, an irreversible monoamine oxidase-B (MAO-B) inhibitor used in Parkinson’s disease, could be repurposed as an otoprotective agent against AGIHL and its effect on dopamine (DA) release from lateral olivocochlear (LOC) fibres, the efferent division of a protective feedback loop plays a major role in the protection against excitotoxicity. Selegiline mitigated AGIHL in BALB/c mice in a dose-dependent manner at different auditory brainstem response frequencies, including 16 kHz, the hearing sensitivity optimum of the animals. It also enhanced the action potential-evoked DA release from LOC efferents in mouse cochlear preparation dose-dependently. Inhibition of DA reuptake contributed to its basic effect of saving DA from metabolism. Among four selegiline analogues tested, the one that increased LOC DA release also provided otoprotection. In contrast, neither safinamide (a reversible MAO-B inhibitor) nor LJP-1207 (a selective semicarbazide-sensitive amine oxidase/vascular-adhesion protein 1 (SSAO/VAP1) inhibitor) prevented AGIHL, despite their antioxidant and anti-inflammatory properties. The reversibility or lack of MAO-B inhibition in safinamide and LJP-1207, respectively, as well as the absence of the propargylamine moiety with known intrinsic neuroprotective activity in both molecules, may explain their ineffectiveness. Selegiline, or certain propargylamine analogues of it, offer a promising therapy against AGIHL by addressing its multifactorial pathology through antioxidant, antiapoptotic, neuroprotective, and anti-inflammatory actions, while enhancing endogenous DAergic protective mechanisms.

Aims This study examined the effect of 4,4′‐diisothiocyanostilbene‐2,2′‐disulfonic acid (DIDS), an anion channel blocker of voltage‐dependent anion channel 1 (VDAC1), on noise‐induced hearing loss (NIHL) and its underlying mechanisms. Methods Cochlear explants and House Ear Institute‐Organ of Corti 1 (HEI‐OC1) cells were used to assess the effect of DIDS in vitro. Auditory brainstem responses were used to assess auditory functions in mice. Immunofluorescence staining of myosin 7a and CTBP2 were used to examine hair cells and synaptic ribbons. The accumulation of reactive oxygen species (ROS) was measured by 4‐HNE staining. The gene expression changes of cochlea were analyzed using RNA sequencing. Results DIDS reduced the levels of ROS in cochlear explants and attenuated cell death caused by hydrogen peroxide in both cochlear explants and HEI‐OC1 cells. In C57BL/6 mice, DIDS reduced ROS generation and tumor necrosis factor‐α induced by noise exposure, thereby protecting outer hair cells and inner hair cell synaptic ribbons from noise‐induced damage through a mechanism involving the PINK1/Parkin signaling pathway. The preventive effect of DIDS in cochlear explants was eliminated by mitophagy inhibition. Conclusion VDAC1 inhibition enhances mitophagy in cochlear hair cells, playing a critical role in defending against oxidative stress and inflammation. Downregulation of VDAC1 may thus be considered a therapeutic strategy for preventing cochlear hair cell damage and reducing NIHL.

Human cytomegalovirus (HCMV) is the most common viral infection acquired in utero and a leading cause of neurodevelopmental abnormalities, including sensorineural hearing loss (SNHL). In previous studies using a murine model of HCMV induced SNHL, hearing loss was correlated with virus-induced cochlear inflammation but not cochlear viral load. However, these previous findings were determined at the time of auditory testing, a time poiont well past critical periods of auditory development. In the current study, cochlear virus load early in auditory development could be correlated with the magnitude of virus-induced cochlear inflammation, cochlear histopathology and the development of hearing loss. Transcriptional profiling at early times after infection revealed dysregulation of multiple well described deafness-related genes (DRG). Treatment with antiviral antibodies early after infection decreased cochlear virus load, cochlear inflammation, cochlear histopathology, and normalized DRG expression arguing that virus-induced cochlear inflammation can result in pleiotropic effects on the developing auditory system. Finally, this model also demonstrated that sterilizing immunity was unnecessary for prevention of SNHL, thus providing a rationale for inteventions that could limit, but not completely prevent HCMV infection of the developing auditory system.

While soundscapes shape the structure and function of auditory systems over evolutionary timescales, there is limited information regarding the adaptation of wild fish populations to their natural acoustic environments. This is particularly relevant for freshwater ecosystems, which are extremely diverse and face escalating pressures from human activities and associated noise pollution. The Siamese fighting fish Betta splendens is one of the most important cultured species in the global ornamental fish market and is increasingly recognized as a model organism for genetics and behavioural studies. This air-breathing species (Anabantoidei), characterized by the presence of a suprabranchial labyrinth organ that enhances auditory sensitivity, is native to Southeast Asia and inhabits low flow freshwater ecosystems that are increasingly threatened due to habitat destruction and pollution. We characterized the underwater soundscape, along with various ecological parameters, across five marshland habitats of B. splendens , from lentic waterbodies to small canals near a lake in Chiang Rai province (Thailand). All habitats exhibited common traits of low dissolved oxygen and dense herbaceous vegetation. Soundscapes were relatively quiet with Sound Pressure Level (SPL) around 102–105 dB re 1 µPa and most spectral energy below 1,000 Hz. Sound recordings captured diverse biological sounds, including potential fish vocalizations, but primarily insect sounds. Hearing thresholds were determined using auditory evoked potential (AEP) recordings, revealing best hearing range within 100–400 Hz. Males exhibited lower hearing thresholds than females at 400 and 600 Hz. This low-frequency tuning highlights the potential susceptibility of B. splendens to anthropogenic noise activities. This study provides first characterization of the auditory sensitivity and natural soundscape of B. splendens, establishing an important ground for future hearing research in this species. The information provided on the auditory sensory adaptation of B. splendens emphasizes the importance of preserving quiet soundscapes from lentic freshwater ecosystems.