ABR/DPOAE publications

Purpose Present-day cochlear-implant (CI) users can achieve high levels of speech reception in quiet surroundings. Nevertheless, sensitivity to the temporal pitch of sounds is limited, which contributes to deficits in speech reception amid multiple talkers and in appreciation of musical melodies. Short-term, invasive neurophysiological studies in animals have demonstrated limitations in neural phase locking in the tonotopic range of the auditory pathway that is activated by CIs. It remains an open question, however, whether those neural limitations can account for perceptual deficits in those animal species, let alone in human CI users. For that reason, we have evaluated non-invasive recordings of phase locking from cats chronically implanted with a CI. Methods Ten deafened cats (eight female) were implanted with an animal version of a clinical CI array. The electrically evoked frequency following response (eFFRs) was recorded from the scalps of sedated animals at ≥ 10 weeks post-implantation. Stimuli consisted of constant-amplitude electrical pulse trains at rates from ~ 40 to 640 pulses per second. Results Recordings of the eFFR demonstrated robust responses synchronized to electrical pulse trains across all stimulus rates. Analyses of eFFR amplitude and phase transfer functions confirmed that the eFFR, as with its normal-hearing counterpart, originates from multiple subcortical and cortical generators. The slopes of segments of eFFR phase transfer functions revealed stimulus-to-response latencies of generators that dominated the eFFR across restricted ranges of pulse rates. Those rate ranges must coincide with the limits of phase locking by putative generators at successive levels of the auditory neuroaxis and could inform our understanding of the limits to perceptual temporal acuity. Conclusion The eFFR demonstrated here in an animal model provides a valuable non-invasive measure of temporal processing in electric cochlear stimulation that can be related to ongoing perceptual measures in the same animals and is well-suited to evaluate novel modes of auditory prosthesis for enhancing temporal acuity.

For patients with severe and profound hearing loss, cochlear implant (CI), a common and effective modality for restoring hearing, directly stimulates spiral ganglion neurons (SGNs) to generate electrical activity and form auditory perception. However, the postoperative outcome of CI is significantly influenced by the number of surviving SGNs, ​​which is a key focus of preoperative evaluation​​. Existing audiologic function and radiographic tests cannot directly demonstrate the integrity of inner ear primary neurons. In this study, ​​we developed and validated​​ a radionuclide‐labeled anti‐vesicular glutamate transporter 1 (anti‐VGLUT1) antibody‐drug and achieved animal‐level in vivo imaging of cochlear SGNs using nuclear imaging. By screening the public single‐cell sequencing database, it is found that VGLUT1 can serve as a representative cell membrane marker for SGN in the cochlea. The potential of anti‐VGLUT1 conjugated to the long half‐life 177 Lu as a molecular probe to detect the relative number of SGNs in SGN‐injured mouse and pig models is explored. The study provides a novel method for assessing cochlear nerve integrity in vivo by visualizing target antigen expression levels through nuclear imaging. This approach is promising to help CI candidates with preoperative inner ear SGN integrity assessment, contributing to clinical decision‐making.

The role of P2X4, one of the most abundant ionotropic purinergic receptors in the central nervous system, is explored here in the context of auditory function. We observed, by using constitutive and conditional P2X4mCherryIN knock-in adult mouse models, a specific high expression of mCherry-tagged P2X4 in living cochlear outer hair cells (OHCs), from immature postnatal stages to adulthood. This P2X4-mCherry expression, confirmed by immuno-confocal fluorescence microscopy in wild-type mice, was mainly concentrated in the intracellular apical region of the OHCs, in the area of the Hensen’s body, a lysosomal rich region, specifically labeled with the fluorescent dye lysotracker. In addition, the basal cholinergic efferent synaptic region of the OHCs was found to express P2X4 at the cell membrane. Surprisingly, the assessment of the hearing function in constitutive P2X4 knock-out (P2X4KO) mice showed improved auditory brainstem responses with smaller latencies, larger amplitudes and smaller thresholds. These P2X4KO mice, as well as conditional P2X4KO-Myo15-Cre mice, displayed enhanced distortion product otoacoustic emissions (DPOAEs), suggesting an improved electromechanical ‘amplification’ activity by OHCs. These mutant animals showed reduced inhibition of DPOAEs by contralateral noise, consistent with a weaker inhibitory effect of the medial cholinergic olivocochlear efferent circuit (MOC) on OHCs. We concluded that the MOC negative feedback modulation of cochlear micromechanics, in addition to involve Ca 2+ permeable α9/α10 nicotinic receptors, also requires the activation of postsynaptic P2X4 receptors in OHCs. SIGNIFICANCE STATEMENT Our study reveals a specific strong expression of P2X4 in mouse cochlear outer hair cells (OHCs), these cells being essential for generating the distortion products otoacoustic emissions (DPOAES) and tuning the sensitivity and frequency selectivity of the cochlea. Mice lacking P2X4 showed a deficient inhibitory control of their cochlear DPOAEs when activating the medial olivocochlear efferent pathway innervating the OHCs. We propose P2X4 receptors as an important Ca 2+ regulatory component of the micromechanics of OHCs and that genetic defects in these purinergic receptors may potentially lead to hearing disorders such as tinnitus and hyperacusis.

Animals have evolved complex auditory systems to extract acoustic information from natural environmental noise, yet they are challenged by rising levels of novel anthropogenic noise. Songbirds adjust their vocal production in response to increasing noise, but auditory processing of signals in noise remains understudied. Auditory processing characteristics, including auditory filter bandwidth, filter efficiency and critical ratios (level-independent signal-to-noise ratios at threshold), likely influence auditory and behavioral responses to noise. Here, we investigated the effects of noise on auditory processing in three songbird species (black-capped chickadees, tufted titmice and white-breasted nuthatches) that live in mixed-species flocks and rely on heterospecific communication to coordinate mobbing behaviors. We determined masked thresholds and critical ratios from 1 to 4 kHz using auditory evoked potentials. We predicted that nuthatches would have the lowest critical ratios given that they have narrowest filters, followed by titmice and then chickadees. We found that nuthatches had the greatest sensitivity in quiet conditions, but the highest critical ratios, suggesting their auditory sensitivity is highly susceptible to noise. Titmice had the lowest critical ratios, suggesting relatively minor impacts of noise on their auditory processing. This is not consistent with predictions based on auditory filter bandwidth, but is consistent with both recent behavioral findings and predictions made by auditory filter efficiency measures. Detrimental effects of noise were most prevalent in the 2–4 kHz range, frequencies produced in vocalizations. Our results using the critical ratio as a measure of processing in noise suggest that low levels of anthropogenic noise may influence these three species differently.

Purpose Whrn , encoding whirlin, is one of the genes highly relevant to Usher syndrome (USH) that has been known as an autosomal recessive genetic disorder that is characterized with sensorineural hearing loss with retinitis pigmentosa. Although recent studies on the other USH genes, PDZD7 and Ush1 g , showed a possibility of haploinsufficiency effect, the potential contribution of heterozygous Whrn loss to hearing loss remains unclear. Methods To investigate the effect of Whrn haploinsufficiency, we conducted a longitudinal study assessing auditory function in heterozygous Whrn mutant ( Whrn + /− ) mice in which long isoform of Whrn was deleted by replacing exon 1 with Neo cassette without disturbing short isoform. The threshold of auditory brainstem responses (ABRs) was measured on 135 Whrn +/ − mice and littermate 133 wild-type (WT) mice from 1 to 6 months of ages. From those data, the threshold from male and female were separately analyzed to investigate sex-dependent effect. To further investigate underlie mechanisms, hair cell death was investigated using immunohistostaining from 4 to 5 WT, 5 female Whrn + /− , and 7 male Whrn + /− mice at 4–5 months old. Results Hearing threshold was significantly increased with aging in Whrn + /– mice compared to WT controls. Both WT and Whrn + /– mice exhibited sex-dependent variations in hearing sensitivity. Notably, Whrn + /– males showed a progressive hearing loss with age, while Whrn + /– females exhibited elevated hearing thresholds as early as 1–2 month of age compared to WT females. Conclusion These results provide evidence for a haploinsufficiency effect of Whrn on auditory function and highlight its potential role in progressive sensorineural hearing loss.

Tinnitus is a prevalent and distressing medical symptom, and no effective pharmacological treatment currently exists. Despite significant advances, tinnitus remains a scientific enigma. To explore the molecular underpinnings of tinnitus, we developed a noise-induced tinnitus model in mice and utilized metabolomics to identify key differences in metabolic pathways. Our results revealed that oxidative stress-related pathways, including glutathione (GSH) metabolism, were significantly enriched in the auditory cortex of mice exhibiting tinnitus-like behavior. To further explore the role of oxidative stress, we examined the involvement of nuclear factor erythroid 2-related factor 2 (Nrf2) in tinnitus by conducting experiments in Nrf2 knockout (Nrf2-KO) mice. While Nrf2-deficient mice did not develop spontaneous tinnitus or hearing loss, they displayed increased susceptibility to prolonged tinnitus-like behavior after noise exposure. This was accompanied by heightened microglial activation, neuroinflammation, and significant alterations in gut microbiota composition, including greater diversity and dysbiosis. Our findings highlight a novel mechanism underlying tinnitus, emphasizing the role of oxidative stress in the auditory cortex and its connection to noise-induced tinnitus. The deficiency of Nrf2 in mice increases their susceptibility to tinnitus, suggesting that Nrf2 may serve as a promising therapeutic target for preventing noise-induced tinnitus.

Severe to profound sensorineural hearing loss seriously affects the communication and cognitive ability of the patients. Cochlear implantation (CI) is currently the most effective treatment, while it may damage the remaining inner ear function due to its poor biocompatibility and the resultant fibrosis. Herein, a porous methacrylated poly(dimethylsiloxane) (MA‐PDMS)‐coated cochlear electrode is presented for CI and hearing protection. The porous MA‐PDMS is filled with a hybrid hydrogel system made of dexamethasone sodium phosphate (Dex), Ti 3 C 2 T x MXene (MXene), and methacrylate gelatin (GelMA). The coating shows good biocompatibility and drug loading and release capacity in vitro, protective effects on hair cells (HCs) and spiral ganglion neurons (SGNs) of the inner ear, as well as the residual hearing protection and the effective fibrosis reduction in vivo. It is anticipated that this porous electrode drug‐loading coating may provide a valuable reference strategy for the future cochlear electrode transplantation system.

Cell death mediated by the abnormal activation of autophagy has been observed in many neurodegenerative diseases. Dual leucine zipper kinase (DLK), a member of the mitogen‐activated protein kinase cascade, plays a key role in regulating cellular autophagy and the progression of neurodegenerative diseases. However, its role in age‐related hearing loss has not been reported. In this study, we found that DLK, phosphorylated c‐Jun N‐terminal kinase (p‐JNK), and JNK3 expression increased in the cochleae of C57BL/6J mice during aging. The DLK/JNK pathway and autophagy are excessively activated in the House Ear Institute‐Organ of Corti 1 (HEI‐OC1) senescent hair cell line. After DLK was upregulated in HEI‐OC1 cells, autophagy was activated, and cell aging was initiated. Inhibiting the DLK/JNK pathway in senescent HEI‐OC1 cells can reduce autophagy activation and senescence, and inhibiting autophagy activation can also alleviate senescence. The inhibition of DLK or JNK3 in vivo significantly reduced age‐related cochlear structural damage and hearing loss in C57BL/6J mice. The results of the present study showed that DLK/JNK3 may play a key role in cochlear hair cell senescence and age‐related hearing loss through the abnormal activation of autophagy within cochlear hair cells, suggesting that DLK or JNK3 may be potential targets for alleviating age‐related hearing loss.

Background Inflammation is a principal cause of sensorineural hearing loss resulting from cochlear injury. However, current research investigating the mechanisms of sensorineural inflammatory injury remains inadequate. Methods Cochlear inflammation was induced by administering lipopolysaccharide (LPS) into the otic bulla (OB) and posterior semicircular canal (PSCC). Auditory brainstem responses (ABR) were recorded, and cochlear tissue alterations were analyzed using hematoxylin and eosin (HE) staining and immunofluorescence. Levels of cochlear inflammation were quantified using a cytokine array. Additionally, Toll-like receptor 4 (TLR4) knockout mice were employed to evaluate sensorineural neuroprotection. Results LPS injection into the PSCC caused more pronounced and stable cochlear inflammatory damage compared to injection into the OB. LPS exposure led to significant loss of cochlear hair cells, atrophy of the stria vascularis, and spiral ganglion damage. Furthermore, LPS treatment upregulated TLR4 receptor expression, increased the number of Ionized calcium-binding adapter molecule 1 (IBA1) positive cells, and elevated levels of inflammatory cytokines in the cochlea. TLR4 knockout (TLR4-KO) mice demonstrated reduced LPS-induced cochlear sensorineural damage. Conclusion LPS injection into the PSCC induces sensorineural tissue damage in the cochlea and results in sensorineural hearing loss. These findings suggest that TLR4 inhibition can alleviate cochlear inflammation-induced sensorineural hearing loss. TLR4 represents a potential therapeutic target for sensorineural hearing loss.

In utero nicotine exposure from maternal smoking is linked to increased risk of auditory processing deficits. This study investigated the impact of developmental nicotine exposure during the critical period on nicotinic acetylcholine receptor (nAChR) functional expression, glutamatergic synaptic transmission and auditory processing in the mouse auditory brainstem. We assessed nAChR function at a central synapse and the consequences of perinatal nicotine exposure (PNE) on synaptic currents and auditory brainstem responses (ABRs) in mice. Our results indicate developmentally regulated changes in nAChR expression in medial nucleus of the trapezoid body (MNTB) neurons and presynaptic calyx of Held terminals. PNE led to increased ACh‐evoked postsynaptic currents and impaired glutamatergic neurotransmission, underscoring the importance of nAChR activity in early auditory synaptic development. PNE also increased ABR thresholds and reduced ABR peak amplitudes, indicating impaired central auditory processing without cochlear dysfunction. Our study provides new insights into the synaptic disruptions underlying auditory deficits from prenatal nicotine exposure. image Key points In utero nicotine exposure leads to increased risk of sensory processing deficits and elevated expression of nicotinic acetylcholine receptors (nAChRs). nAChRs are essential for auditory processing and are present in the auditory brainstem. Within the medial nucleus of the trapezoid body in the auditory brainstem, the patterning of nicotinic receptor expression during development and how nicotine exposure might affect this are unknown. Nicotinic receptors are expressed postsynaptically before hearing onset and switch to presynaptic expression after hearing onset. Perinatal nicotine exposure disrupts physiological nicotinic receptor patterning and impairs synaptic transmission at the calyx of Held.

Hearing loss often arises from impairments in multiple genes, complicating therapeutic development. MicroRNAs, as master regulators, offer promising targets for complex diseases. We explored miR-96's roles in hair cell (HC) function and noise-induced hearing loss (NIHL), finding that miR-96 -/-, not miR-96 +/- , mice exhibited progressive hearing loss due to gene regulatory network dysregulation from miR-96 loss in HCs not spiral ganglion neurons (SGNs). Viral-mediated delivery of miR-96 into the inner ear partially rescued hearing of miR-96 -/- mice. Tamoxifen-induced depletion of miR-96 in adult UBC CreERT2/+ ; miR-96 fl/fl mice led to hearing loss, with Bach2, Gabra2, Gabra4, and Grk1 upregulation and Tnn, Col11a1, Gjb3, and Hnf4a downregulation. Furthermore, noise trauma reduced miR-96, altering Bach2, Bcl2l1, Slc26a9, Gabrb1, Grk1, Nos2, and Cyp1a1 expression, whereas miR-96 overexpression protected hearing against noise by reversing the expression of Bach2, Bcl2l1, and Cyp1a1. Our findings underscore miR-96's essential role in adult hearing maintenance and NIHL prevention, presenting it as a promising therapeutic target.

Objectives Ferroptosis, a regulated form of cell death, has attracted significant attention in hearing loss research; however, the role of ferroptosis-related genes remains unclear. This study aimed to clarify diagnostic and therapeutic targeting of ferroptosis-related genes in hearing loss. Methods Differentially expressed genes related to hearing loss from the GEO database were intersected with ferroptosis-related genes. The Lasso and SVM-RFE models were applied to reduce the gene set, identifying model genes. Biological functions, pathways, and gene-drug associations related to these model genes were analyzed. Age-related hearing loss (ARHL) genes within the model genes were obtained from a genome-wide association study (GWAS) dataset. Further validation was conducted in HEI-OC1 cells and the cochleae of C57BL/6J mice, including auditory brainstem response (ABR) testing, qRT-PCR, Western blotting, Fe 2+ detection, and immunofluorescence analysis. Results The study identified 20 ferroptosis-related genes associated with hearing loss. Using Lasso and SVM-RFE models, a novel model was constructed, consisting of nine genes ( SCD, ENPP2, PANX2, NEDD4, MEF2C, ABCC5, KLHDC3, CYP4F8 and IFNA2 ). Among these, MEF2C and NEDD4 were found to be associated with ARHL. Conclusion Ferroptosis is a potential pathological mechanism in hearing loss research, and the nine ferroptosis-related genes identified provide promising targets for exploring new diagnostics and treatments for hearing loss. Notably, MEF2C and NEDD4 are associated with ARHL.

Presbycusis or age-related hearing loss (ARHL) affects millions of people worldwide, increasing their risk of cognitive decline and poor quality of life. However, ARHL remains an irreversible condition due to our inability to induce inner-ear hair cell regeneration. Nevertheless, multisession epidural stimulation of the auditory cortex (AC) at the onset of ARHL prevents hearing threshold elevation in naturally aging Wistar rats. Accordingly, we hypothesized that anodal direct current (DC) stimulation of the AC may also compensate for age-related maladaptive, activity-dependent changes. Here, we examined immunocytochemical markers in the AC, including early genes (c-fos and Arc), AMPA receptors (GluR2/3), parvalbumin (PV), and GAD67, along with auditory-evoked potentials (CAEPs) recorded in both auditory and visual (VC) cortices. When comparing 6 and 18.13-month-old rats without AC simulation, we observed loss of c-fos and Arc-positive neurons and decreased GluR2/3 expression, confirming altered AC neuronal network plasticity and activation. In addition, we noted changes in PV and decreased GAD67 immunoreactivity suggesting disrupted inhibition and significantly increased wave amplitudes in CAEPs, altered AC latencies, and decreased VC responses. By contrast, electrically stimulated rats showed no significant variations in early gene markers, GluR2/3, PV, or GAD67 with age, and the amplitudes and latencies of CAEPs recorded in their AC and VC resembled those of young rat. These findings indicate that anodal DC stimulation at the onset of ARHL delays AC aging by minimizing the loss of inhibition and preventing increases in cortical excitability in Wistar rats.

The auditory brainstem response (ABR) is an acoustically evoked EEG potential that is an important diagnostic tool for hearing loss, especially in newborns. The ABR originates from the response sequence of auditory nerve and brainstem nuclei, and a click-evoked ABR typically shows three positive peaks (“waves”) within the first six milliseconds. However, an assignment of the waves of the ABR to specific sources is difficult, and a quantification of contributions to the ABR waves is not available. Here, we exploit the large size and physical separation of the barn owl first-order cochlear nucleus magnocellularis (NM) to estimate single-cell contributions to the ABR. We simultaneously recorded NM neurons’ spikes and the EEG in owls of both sexes, and found that ≳ 5000 spontaneous single-cell spikes are necessary to isolate a significant spike-triggered average (STA) response at the EEG electrode. An average single-neuron contribution to the ABR was predicted by convolving the STA with the cell’s peri-stimulus time histogram. Amplitudes of predicted contributions of single NM cells typically reached 32.9 ± 1.1 nV (mean ± SE, range: 2.5–162.7 nV), or 0.07 ± 0.02 % (median ± SE; range from 0.01% to 1%) of the ABR amplitude. The time of the predicted peak coincided best with the peak of the ABR wave II, independent of the click sound level. Our results suggest that individual neurons’ contributions to an EEG can vary widely, and that wave II of the ABR is shaped by NM units.

Rationale: The GJB2 gene, which encodes connexin 26 (Cx26), is recognized as the leading cause of non-syndromic hereditary hearing loss. In clinical settings, a total of 131 Cx26 mutations have been identified in association with hearing loss. Certain Cx26 mutants display normal structural and functional properties but fail to translocate to the plasma membrane. Enhancing the membrane localization of these mutants may provide a promising strategy for rescuing hearing loss and hair cell degeneration. Methods: This study investigated the membrane localization of Cx26 using in vitro cell lines, cultured cochlear explants, and in vivo murine models. Key proteins involved in the membrane localization of Cx26 were identified and validated through immunoprecipitation-mass spectrometry (IP-MS) and co-immunoprecipitation (Co-IP). Additionally, cell lines and murine models harboring Cx26 mutants were developed to evaluate the effects of Narciclasine on enhancing the membrane localization of these mutants, as well as its potential to rescue hearing loss. Results: The membrane localization of Cx26 was dependent on the integrity of the intracellular transport network consisting of microtubules, actin microfilaments, and the Golgi apparatus. Additionally, SPTBN1 played a significant role in this process. The transmembrane domain 4 (TM4) region exhibited a strong association with the membrane localization of Cx26, and Cx26 mutants located in TM4 region retained in the cytoplasm. Narciclasine promoted cytoskeletal development, thereby enhancing the membrane localization of Cx26 mutants retained in the cytoplasm. This process helped to reconstruct the inner ear gap junction network and rescue hearing loss and hair cell degeneration. Conclusion: These findings present that enhancing the membrane localization of Cx26 mutants can significantly improve auditory function. This strategy offers a potential therapeutic approach for addressing hereditary sensorineural hearing loss associated with GJB2 mutations.

Purpose In the receptor organs of the inner ear, hair cells detect mechanical stimuli such as sounds and accelerations by deflection of their hair bundles. Myosin regulatory light chain (RLC) and non-muscle myosin II (NM2) are expressed at the apical surfaces of hair cells, and NM2 and the phosphorylation of RLC by myosin light chain kinase (MLCK) have earlier been shown to regulate the shapes of hair cells’ apical surfaces in rodents. The aim of our study was to elucidate the function of myosin molecules on hair cell physiology. Methods We investigated the expression of NM2 and RLC in the bullfrog’s saccule by immunostaining. Using NM2 and MLCK inhibitors, we measured the stiffness, spontaneous oscillation, and resting open probability of frog hair bundles. Six to ten saccules from pleural animals were used in each experiment. In addition, we recorded auditory brainstem responses in ten mice after transtympanic injection of an MLCK inhibitor. Results We confirmed the expression of NM2A/B and MYL9 on the apical surfaces of hair cells and of NM2A and MYL12A in hair bundles. We found that NM2 and MLCK inhibitors reduce the stiffness of hair bundles from the bullfrog's saccule. Moreover, MLCK inhibition inhibits the spontaneous oscillation of hair bundles and increases the resting open probability of transduction channels. In addition, MLCK inhibition elevates hearing thresholds in mice. Conclusion We conclude that NM2 and the phosphorylation of RLC modulate the physiological function of hair cells and thereby help to set the normal operating conditions of hair bundles.

Introduction Tinnitus is the perception of non-meaningful sound in the absence of external stimuli. Although tinnitus behavior in animal models is associated with altered central nervous system activity, it is not currently possible to identify tinnitus using neuronal activity alone. In the mouse inferior colliculus (IC), a subpopulation of neurons demonstrates a sustained increase in spontaneous activity after a long-duration sound (LDS). Methods Here, we use the “ LDS test ” to reveal tinnitus-specific differences in sound-evoked plasticity through IC extracellular recordings and the auditory brainstem response (ABR LDS ) in CBA/CaJ mice after sound exposure and behavioral tinnitus assessment. Results Sound-exposed mice showed stronger and shorter tone-evoked responses in the IC compared to unexposed controls, but these differences were not strong predictors of tinnitus. In contrast, in the LDS test, non-tinnitus mice had a significantly stronger suppression in tone-evoked spike rate compared to tinnitus and unexposed control mice. ABR peak amplitudes also revealed robust differences between tinnitus and non-tinnitus mice, with ABR peaks from non-tinnitus mice exhibiting significantly stronger suppression in the LDS test compared to tinnitus and control mice. No significant differences were seen between cohorts in ABR amplitude, latency, wave V:I ratio, wave V:III ratio, I-V intra-peak latency, and I-VI intra-peak latency. We found high-frequency tone stimuli better suited to reveal tinnitus-specific differences for both extracellular IC and ABR recordings. Discussion We successfully used the LDS test to demonstrate that tinnitus-specific differences in sound-evoked plasticity can be shown using both multi-unit near-field recordings in the IC and non-invasive far-field recordings, providing a foundation for future electrophysiological research into the causes and treatment of tinnitus.

Age-related hearing loss (ARHL) is a highly prevalent, burdensome sensorineural hearing loss closely associated with impaired autophagic influx. Our previous studies revealed that neuritin, a neurotrophic factor primarily expressed in the central nervous system, could alleviate drug-induced damages in hair cells (HCs) and spiral ganglion neurons. However, its effects on ARHL and whether these effects are closely related to autophagy remain unclear. Using the Nrn1 knock-in mice and cultured cochlear basilar membrane (CBM) of the neonatal mouse, we show that neuritin could restore aging-associated hearing loss and alleviate senescence-associated damage in the cochlea. Overexpression of neuritin in support cells (SCs) alleviates the loss of cochlear HCs and nerve fibers, reducing the damage to spiral ganglion neurons and the shifts in ABR’s high-frequency threshold. Furthermore, conditional overexpression of neuritin in SCs improves autophagic influx by upregulating the expression of microtubule-associated protein 1 light chain 3 type B (LCB3) protein and downregulating the expression of p21 protein. In cultured neonatal mouse CBM, neuritin administration significantly inhibits D-galactose-induced HC loss, cellular apoptosis, and ROS production and promotes autophagic influx. These effects were weakened when the autophagy inhibitor 3-MA was added. In summary, our results confirm the therapeutic potential of neuritin treatment for ARHL.

Introduction Age-related hearing loss (ARHL) is linked to dementia, with mitochondrial dysfunction playing a key role in its progression. Deficient mitochondrial tRNA modifications impair protein synthesis and energy metabolism, accelerating ARHL. Mitochonic acid 5 (MA-5) has shown promise as a therapeutic candidate by improving mitochondrial function, reducing oxidative stress, and stabilizing membrane potential. Methods In this study, we investigated the effects of MA-5 on ARHL in cyclin-dependent kinase 5 regulatory subunit-associated protein 1 ( Cdk5rap1 ) knockout (KO) mice, which exhibit early-onset ARHL due to abnormalities in mitochondrial transfer RNA (mt-tRNA) modifications. Results MA-5 treatment effectively attenuated ARHL progression in Cdk5rap1 -KO mice by improving auditory brainstem response thresholds and distortion product otoacoustic emissions. It also reduced spiral ganglion and outer hair cell loss, while preserving the cochlear structural integrity by preventing mitochondrial degeneration in spiral ligament fibrocytes. Mechanistically, MA-5 upregulated the expression of silent information regulator sirtuin 1 and promoted the nuclear translocation of yes-associated protein, both of which are involved in regulating mitochondrial function and cellular senescence. Metabolomics analysis further demonstrated that MA-5 restored mitochondrial metabolism, reduced lactate accumulation, and maintained mitochondrial integrity. Conclusion These findings suggest that MA-5 is a viable treatment option for ARHL and other age-related disorders associated with mitochondrial dysfunction.

Introduction Ibrutinib, widely used in leukemia treatment, has been implicated in sensorineural hearing loss; however, its underlying mechanisms remain unclear. Methods This study investigated the impact of ibrutinib on hearing using HEI-OC1 cells, cochlear explants and C57BL/6 J mice. We used RNA-sequences analysis to investigate the potential mechanisms of ibrutinib-induced ototoxicity. Mice received ibrutinib and auditory thresholds were assessed via auditory brainstem response testing; to assess the potential protective effects, we co-administered the caspase inhibitor Z-Val-Ala-Asp (OMe)-fluoromethylketone (Z-VAD-FMK) and monitored hearing. Results Z-VAD-FMK mitigated ibrutinib-induced hearing loss by inhibiting apoptosis in auditory cells. Ibrutinib exposure resulted in cochlear hair cell (HC) damage and subsequent hearing loss by inhibiting the protein kinase B and G protein-coupled receptor 83 (GPR83) pathways. RNA sequencing suggested that GPR83 protects HCs by modulating autophagy. Z-VAD-FMK application and GPR83 overexpression attenuated ibrutinib-induced cochlear HC apoptosis and auditory decline. Conclusion These findings confirm ibrutinib’s ototoxicity and highlight the protective role of GPR83 in ibrutinib-induced hearing loss, supporting future clinical investigations into Z-VAD-FMK and GPR83 as interventions for ibrutinib or other chemotherapeutic drug-induced ototoxicity.