ABR/DPOAE publications

Cisplatin-induced ototoxicity leads to irreversible hearing loss in approximately 50% of treated patients, largely due to the cochlea's exceptionally poor cisplatin clearance compared with other organs. Although sodium thiosulfate (STS), a hydrophilic small molecule, is an established otoprotectant, achieving therapeutically sufficient cochlear concentrations remains challenging because systemic administration is limited by the blood-labyrinth barrier. Here, we report a viscosity-tunable microgel-in-sol system based on hyaluronic acid (HA) that enables sustained, localized delivery of STS to the inner ear via intratympanic injection. The STS-loaded microgel was readily injectable through 31 G needles and provided a six-fold extension in drug release duration compared with free STS solution. However, direct microgel injection caused significant occlusion of the middle ear cavity due to swelling and poor clearance. To overcome this limitation, we developed a microgel-in-sol formulation composed of an HA solution and microgel at a 3:1 volumetric ratio. This formulation exhibited concentration-dependent, lubricant-like viscosity while maintaining effective drug delivery and preserving auditory function, as confirmed by in vivo auditory brainstem response (ABR) measurements. Overall, this microgel-in-sol strategy represents a biocompatible, minimally invasive approach for localized inner-ear drug delivery.

CDC42 is involved in multiple signaling pathways, including actin organization and polarity. We previously reported progressive sensorineural hearing loss (SNHL) in inner ear hair cell (HC)-specific Cdc42-knockout (Atoh1-Cre+/-;Cdc42flox/flox) mice. However, the phenotype was milder than expected, suggesting possible redundancy with other Rho-family GTPases. Thereafter, Takenouchi-Kosaki syndrome (TKS), caused by de novo CDC42 mutations and manifesting as SNHL, was reported, in which the p.Y64C mutation was speculated to be constitutively active. However, the relationship between CDC42 status and hearing phenotypes in TKS remains unclear. Using cell models, mouse models, and patient data, we propose that impaired and/or dysregulated cycling between GDP/inactive and GTP/active forms, through either loss-of-function or constitutive activation, can lead to SNHL. Furthermore, to test redundancy, we generated HC-specific Cdc42;RhoQ double-knockout (Atoh1-Cre+/-;Cdc42flox/flox;RhoQflox/flox) mice, which revealed synergistic roles of CDC42 and RHOQ in cochlear HCs. Supporting this synergy, MDCK cells with CDC42 and RHOQ double knockdown showed greater phospho-cofilin, a key regulator of actin turnover, elevation than single knockdowns.

Objective Cisplatin, a life-saving chemotherapeutic drug, causes ototoxicity. Although sodium thiosulfate is used to prevent ototoxicity in pediatric patients, no other intervention has been approved for clinical use against cisplatin-induced hearing loss. Hence, there is an urgent need to identify drugs that prevent cisplatin ototoxicity. Methods CBA/J mice were treated with cisplatin (3 mg/kg, i.p., daily for 5 days), and MnTBAP (10 mg/kg, i.p., daily for 8 days) was used to inhibit cisplatin-induced ototoxicity. Auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) were recorded before and after treatment to assess hearing loss, while immunohistochemistry with anti-Myosin-VIIa was conducted to examine hair cell loss, with phalloidin to examine spiral ganglion neuron (SGN) loss, and with anti-nitrotyrosine to assess nitrotyrosine levels. Results Cisplatin treatment elevated the nitrotyrosine levels in hair cells and SGNs and increased the loss of these cells in the middle and basal cochlear regions. A negative correlation was observed between cisplatin-induced changes in the hair cell count or SGN density and nitrotyrosine levels. Cisplatin treatment elevated the hearing thresholds, as indicated by the ABRs, and lowered the DPOAE amplitudes, suggesting cisplatin-induced hearing loss. However, MnTBAP cotreatment prevented the cisplatin-induced changes in hearing sensitivity and reversed the morphological changes. Conclusion The otoprotection observed with MnTBAP cotreatment along with the attenuation of cisplatin-induced increase in nitrotyrosine levels in the cochlea indicates its potential as an inhibitor of cochlear nitrative stress and its utility in mitigating cisplatin-induced ototoxicity.

Focused ultrasound (FUS) is a promising noninvasive neuromodulation approach, but whether it can directly activate central auditory neurons in vivo remains unresolved. We applied high-frequency FUS (20 MHz) to the central nucleus of the inferior colliculus (CNIC) in anesthetized guinea pigs while recording electrophysiological responses from the auditory pathway and cochlea. FUS evoked cortical activity through indirect cochlear activation, possibly via skull-mediated mechanical coupling, rather than direct inferior colliculus activation, with ultrasound-evoked compound action potentials predominating in the ipsilateral cochlea. More interestingly, FUS stimulation of the CNIC induced activation of neurons and glial cells in the CNIC and auditory cortex as demonstrated by c-Fos expression, suggesting that FUS stimulation activated the afferent pathway. We also show that FUS engaged the auditory efferent system, likely via medial olivocochlear neurons, producing reduced compound action potential amplitudes, enhanced cochlear microphonics, and persistent effects lasting at least two hours, consistent with long-lasting efferent plasticity. Strikingly, FUS administered before acoustic trauma almost completely prevented noise-induced hearing loss, limiting auditory brainstem response threshold shifts to <10 dB versus ∼60 dB in controls. Gentamicin abolished these physiological and protective effects, implicating medial olivocochlear activation. These findings identify FUS as a potent noninvasive strategy for engaging auditory efferent circuits and protecting against acoustic injury.

Noise-induced hearing loss (NIHL) is a major public health problem caused by damage to cochlear hair cells, synapses, and spiral ganglion neurons (SGNs). Since effective treatments are lacking, we investigated cellular stress responses induced by moderate and loud noise in a mouse model of cochlear synaptopathy. RNA sequencing and spatial transcriptomics revealed that noise exposure elicited a robust but transient upregulation of endoplasmic reticulum chaperones and proteasome subunits in SGNs and their supporting cells. To target this response, we administered TRC051384, a small-molecule activator of the heat shock transcription factor Hsf1, prior to noise exposure. TRC051384 crossed the blood–labyrinth barrier and reached the cochlea, induced heat shock protein gene expression, and restored ubiquitin–proteasome function in SGNs. Notably, TRC051384 treatment enhanced auditory brainstem response threshold recovery, preserved Wave I amplitudes, and maintained ribbon synapse density. Together with the existing literature, these findings identify proteotoxic stress in spiral ganglion neurons as a contributor to noise-induced hearing loss and support pharmacological activation of HSF1 as a promising therapeutic strategy.

Introduction The mitochondrial calcium uniporter (MCU) mediates mitochondrial Ca 2⁺ uptake, but its involvement in cisplatin-induced ototoxicity remains poorly understood. We investigated MCU expression and its association with cisplatin-induced injury in mouse cochlear basilar membranes and HEI-OC1 cells. Methods MCU protein abundance and localization were assessed by Western blotting and immunofluorescence. MCU expression was genetically reduced by lentiviral knockdown, and Ru360 was used as a pharmacological intervention. Apoptosis-related proteins and transcriptomic changes were evaluated. An acute cisplatin-induced ototoxicity model was established in C57BL/6 mice and assessed using auditory brainstem response (ABR) measurements and outer hair cell counts. Results Cisplatin increased MCU expression and reduced SERCA2 expression; the cisplatin-induced increase in MCU was partially reversed by BAPTA-AM and the endoplasmic reticulum stress inhibitor 4-PBA. MCU knockdown did not affect basal cell viability but attenuated cisplatin-induced reductions in viability, TUNEL positivity, and cleaved caspase-3. It was also associated with increased SERCA2 and decreased IP3R, GRP75, and VDAC1 expression. RNA sequencing identified differentially expressed genes enriched in autophagy-related processes and mTOR signaling. MCU knockdown was associated with increased PI3K/AKT/mTOR signaling and changes in Beclin1, LC3B-II, and p62. Ru360 cotreatment partially reproduced the protective phenotype in vitro and was associated with attenuated ABR threshold elevation at selected frequencies and reduced outer hair cell loss in vivo . Discussion These findings support an association between MCU-related signaling, PI3K/AKT/mTOR pathway activation, altered autophagy-related markers, and reduced cisplatin-induced cochlear injury.

Background: Noise-induced hearing loss (NIHL) is a pervasive occupational health challenge, yet the individual susceptibility mechanisms remain unclear. Ferroptosis, an iron-dependent form of programmed cell death, has been implicated in cochlear hair cell damage. This study aims to elucidate the regulatory role of the transcription factor FOXA2 and the deacetylase SIRT1 in ferroptosis and to investigate the association between SIRT1 genetic polymorphisms and NIHL susceptibility in occupational populations. Methods: We employed a multi-level study design combining epidemiological investigation, animal models, and cellular experiments. First, a case–control study was conducted involving 1314 noise-exposed workers (639 cases vs. 675 controls) from a chemical fiber enterprise in Jiangsu Province to analyze the association between SIRT1 single nucleotide polymorphisms (SNPs) and NIHL risk. Second, a C57BL/6J mouse model exposed to 120 dB white noise was established to assess cochlear morphology and protein expression. Third, in HEI-OC1 cochlear hair cells, we performed siRNA-mediated knockdown of Foxa2 and dual-luciferase reporter assays to verify the transcriptional regulation of SIRT1 and its downstream effects on the ferroptosis pathway. Results: Population analysis revealed that the SIRT1 rs12778366 C allele was significantly associated with increased NIHL risk (OR = 1.386, 95% CI: 1.084–1.772, p = 0.009), and this association remained significant after adjustment (p = 0.041). Stratified analysis further revealed a significant gene–environment interaction in workers with >15 years of noise exposure (OR = 2.126, 95% CI: 1.401–3.226, p < 0.001). In vivo, noise exposure led to significant downregulation of Sirt1 and Foxa2 in cochlear tissues, accompanied by elevated ferroptosis markers (Fe2+, MDA) and depleted antioxidant defenses (GSH, xCT, and GPX4). Mechanistically, we demonstrate that FOXA2 transcriptionally activates SIRT1 by binding to its promoter. Knockdown of FOXA2 in vitro suppressed SIRT1 expression, suppressed xCT, a key component of the System Xc−/GPX4 antioxidant axis, and promoted ferroptosis-related cellular changes. Conclusions: This study identifies a novel protective axis where FOXA2 prevents noise-induced ferroptosis in cochlear hair cells by transcriptionally upregulating SIRT1 and maintaining xCT-mediated antioxidant defense. Furthermore, the SIRT1 rs12778366 polymorphism is identified as a candidate variant warranting further investigation in independent cohorts before clinical translation.

Spontaneous calcium (Ca 2+ ) waves play a critical role as internal stimuli in the early developing auditory system before the onset of sensory experiences. However, neither the spatiotemporal control of spontaneous Ca 2+ waves nor their impacts on auditory development are well understood. Here we report that a lateral array of inner supporting cells (ISCs) beneath the inner hair cells displays a spontaneous ultra‐long, ultra‐fast, transient Ca 2+ flash, termed “Ca 2+ lightning”, which triggers a series of simultaneous bursts of Ca 2+ waves in the whole cochlea, before the ear canal opening. The Ca 2+ lightning margins the cochlear ISCs at different developmental stages that correspondingly exhibit different Ca 2+ activities. Triggered by an ATP‐induced high‐level Ca 2+ wave, the Ca 2+ lightning rapidly propagates laterally into neighboring ISCs through the intricate interplay of the T‐type Ca 2+ channel, Anoctamin 1 (Ano1) Ca 2+ ‐activated Cl − channel and Connexin 26 (Cx26). The genetic deletion of Cav3.2, Ano1, or Cx26 abrogates Ca 2+ lightning flashes and dysregulates cell development and functions in peripheral cochleae. We propose that cochlear Ca 2+ lightning flashes orderly with Ca 2+ waves together orchestrate the spatiotemporal maturation processes of the peripheral auditory system before the onset of hearing.

Intratympanic (IT) injection of corticosteroids is a standard clinical treatment for sensorineural hearing loss; however, achieving both biocompatibility and efficient cochlea drug delivery remains a significant challenge. Herein, we engineered a novel drug nanocrystal (NS)-loaded thermo-reversible hydrogel (NS-TG) system of dexamethasone-21-palmitate (DEX-P), a lipophilic prodrug of dexamethasone (DEX), for improved IT delivery. NSs with a mean diameter of 835.0 nm were fabricated using a dual centrifugation process with polyvinyl alcohol as the stabilizer. The NS-TG system, comprising NSs in a 19% (w/v) Poloxamer 407 hydrogel, exhibited rapid gelation (2–3 min) and a 31-fold increase in drug solubility (1.57 ± 0.02 mg/mL) compared to NS alone, through micellar solubilization. In vitro cytotoxicity assays in HEI-OC1 cells revealed that NS-TG is highly biocompatible, maintaining cell viability, whereas the commercial lipid emulsion (Lipothason®) induced significant cytotoxicity. In vivo pharmacokinetic evaluation in mice revealed that IT NS-TG provided superior cochlear drug absorption compared to DEX-SP solutions and DEX-P NS, despite showing lower absorption than the lipid emulsion. These findings suggest that the DEX-P NS-TG system, pending further investigation, could serve as a promising platform for cochlear steroidal delivery, offering an optimal balance between delivery efficiency and local safety for treating inner ear diseases.

Neonatal bilirubin encephalopathy is primarily characterized by central auditory dysfunction and cognitive impairments. However, the precise molecular mechanisms underlying bilirubin-induced neurotoxicity remain poorly understood, hindering the development of effective therapeutic strategies. Using kinase activity prediction tools based on quantitative phosphoproteomics, we identified ROCK2 (Rho-associated protein kinase 2) as a critical kinase regulating the phosphorylation of proteins associated with bilirubin exposure. Molecular docking and MicroScale Thermophoresis assays revealed a strong binding affinity between bilirubin and ROCK2. Interestingly, bilirubin increased ROCK2 protein expression without affecting its mRNA levels, and cycloheximide chase assays revealed enhanced ROCK2 stability, implicating post-translational regulation. While bilirubin did not directly activate ROCK2 kinase activity in vitro, it elevated phosphorylation of its substrate LIMK1, suggesting that ROCK2 accumulation amplifies downstream signaling. In primary rat neurons, ROCK2 inhibitors (Belumosudil and Y-27632) ameliorated bilirubin-induced loss of mitochondrial membrane potential and neuronal cell death. Furthermore, using ROCK2 inhibitors and Rock2+/- mice, we demonstrated that modulation of ROCK2 significantly alleviated bilirubin-induced auditory deficits and cognitive impairments. These behavioral improvements were linked to restored excitatory synaptic transmission in the cochlear nucleus and reduced dendritic damage in hippocampal neurons. These findings position ROCK2 as a promising molecular target for therapeutic intervention in bilirubin encephalopathy.

Optical coherence tomography has allowed in vivo recording of sound-induced vibrations of different regions within the organ of Corti complex (OCC), including the basilar membrane (BM), outer hair cell/Deiters cell (OHC/DC) region, and reticular lamina (RL). In the hook region of the gerbil cochlea, where measurements can be made with a predominantly transverse optical axis, the three regions have different and characteristic motion responses: The OHC/DC region has greater motions than the other two regions at frequencies below the best frequency (sub-BF); the RL region typically has the greatest BF peak and smallest sub-BF motion. The phase of the OHC/DC-region motion increasingly lags BM motion phase as frequency increases; the RL-region motion phase leads BM, but with a relatively small value. All three regions are compressively nonlinear in the BF peak, but only the OHC/DC region shows sub-BF compressive nonlinearity. Here, we describe the strains that arise when the motion transitions between these regions. Large strains (deformations) were observed in the OHC body close to the RL. A region of large strain can be as short as a single 2.7-μm measurement pixel, or it can extend over several pixels, with extensive strains appearing more often at 70 than at 50 dB sound pressure level. Beyond this RL region of large strain, over a distance that can exceed 20 μm, the OHC/DC region displayed nearly spatially unvarying motion; this region vibrated as a relatively rigid body. And beyond this, at sub-BF frequencies, another region of high strain was present, indicating stretching/compressing or bowing/tilting of the DC microtubular stalk.

The neural response of the brainstem to brief sounds, known as the auditory brainstem response (ABR), is widely employed in the laboratory and the clinic to diagnose hearing loss. Current ABR approaches are limited to analyzing the average ABR to hundreds of stimulus trials. Historically, trial-by-trial ABR analysis has not been possible owing to each trial's small signal-to-noise ratio. Here we overcome this limitation and show how to score individual ABR trials. We use the distribution of individual-trial ABR scores to define thresholds, which we call auditory brainstem detection (ABD) thresholds, and to assess suprathreshold hearing. Scores based on individual-trial amplitude and similarity produce lower ABD thresholds than scores based on individual-trial amplitude alone. Our method enables us to rank the suprathreshold hearing of individual subjects. Despite having normal ABR thresholds, some subjects appear to have suprathreshold hearing deficits.

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants linked to adverse health effects. Recent epidemiological data suggest an association between PFAS exposure and hearing loss, but underlying mechanisms remain unclear. This study examined PFAS-induced auditory dysfunction in mice exposed to a mixture of five PFAS compounds (2 mg/L each) in drinking water for seven weeks. Ldlr-/- mice were used due to their susceptibility to metabolic dysfunction, a risk factor for hearing loss. Auditory brainstem responses (ABR) indicated that PFAS exposure significantly elevated hearing thresholds by 18-33 dB across multiple frequencies. Distortion product otoacoustic emissions (DPOAEs) revealed impaired outer hair cell (OHC) function, and immunohistochemical analysis indicated a 20% OHC loss in the basal turn of the cochlea. In addition, PFAS exposure reduced ABR wave-1 amplitudes, and caused a 50% reduction in spiral ganglion cell density, indicating impaired auditory nerve function. Overall, this study provides the first evidence for PFAS-induced high-frequency hearing loss in mice. The findings further indicated that cochlear OHCs and spiral ganglion neurons are potential targets in PFAS-induced hearing loss. Together, these data suggest that PFAS exposure elicits a multifaceted ototoxic response, affecting both sensory and neural elements of the cochlea.

Lipid metabolism is an important biological process that maintains the dynamic balance of several key functions, such as intracellular energy metabolism, signal transduction, and membrane remodeling. However, the role of lipid metabolism in auditory function and the underlying mechanisms remain unclear. Our results reveal that the neomycin exposure disrupts lipid metabolism in auditory system. We find that neomycin-induced hair cells (HC) damage leads to abnormal lipid droplets (LD) accumulation. Further research reveals that decreased YAP expression is a key factor that contributes to abnormal LD accumulation. In both in vivo and in vitro studies, Yap overexpression reduces abnormal LD accumulation and mitigated HC damage. To further investigate its downstream mechanisms, we perform a cross-analysis of Yap -related and lipid metabolism–related genes, identifying that Cox2 is a key downstream target of Yap that contributes to LD accumulation and HC damage. Our work provides clear evidence for the role of lipid metabolism in neomycin-induced hearing loss and elucidates underlying mechanism of Yap/Cox2 pathway. These findings provide new perspectives and avenues for the clinical treatment of sensorineural hearing loss.

Cisplatin (CDDP) is an effective chemotherapeutic agent used to treat solid tumors, but it can cause irreversible hearing loss. Currently, there are no specific preventive measures available for this side effect. G protein-coupled receptor 55 (GPR55) exhibits antioxidant, anti-inflammatory, and anti-apoptotic properties and is implicated in various disease processes. Nevertheless, whether GPR55 plays a role in CDDP-induced hearing loss remains unclear. We explored the effects and mechanisms of O-1602, a GPR55 agonist, on CDDP-induced ototoxicity. Our results showed that GPR55 is present in cochlear hair cells and HEI-OC1 cells, with increased expression following CDDP exposure. Moreover, O-1602-induced activation of GPR55 markedly mitigated the ototoxic effects of CDDP in HEI-OC1 cells, cochlear explants, and mouse models by preventing oxidative stress and apoptosis. In addition, GPR55 protected against CDDP-induced damage via inhibiting the MAPK pathway. Therefore, GPR55 is a potential therapeutic target for preventing CDDP-induced ototoxicity.

Background Ménière’s disease (MD) is a disabling inner-ear disorder. Although the key pathologic alteration of MD is characterized as endolymphatic hydrops (EH), the underlying pathogenic mechanism remains unclear, and no definitive curative treatments are available. Emerging evidence implicates oxidative stress and innate immunity as key contributors to MD pathogenesis. Methods Human vestibular end organs were collected to characterize the reactive oxygen species (ROS) levels and the STING signaling activation, findings that were further corroborated in an LPS-induced EH mouse model. Transfection and transwell co-culture were performed to investigate the feedback loop between sensory epithelial cells and macrophages in vitro. Molecular biology experiments were performed to elucidate the underlying regulatory mechanisms. Additionally, STING and CUL4B deficiency mice were used to explore potential therapeutic targets in vivo. Results The oxidative stress, cytoplasmic dsDNA leakage, and STING activation were elevated in both MD patients and LPS-induced EH mouse model. The dsDNA released from ROS-damaged hair cells activates STING in vestibular macrophages. STING-specific knockout in macrophages alleviates EH, audio-vestibular dysfunction, and interferon-stimulated genes expression in mouse model. The CUL4B-DDB1-ROC1 complex ubiquitinates STING at K370, promoting its degradation and inhibiting activation. Notably, CUL4B deficiency exacerbates LPS-induced EH, audio-vestibular dysfunction, and interferon-stimulated genes (ISG) upregulation, while double conditional knockout reverses these effects. Conclusion Our study demonstrates that STING activation in vestibular macrophages contributes to audio-vestibular dysfunction and modulating this pathway has promising beneficial effects on audio-vestibular function in EH mice model, which is a potential therapeutic strategy for MD.

Noise exposure is a known cause of hearing loss, and only a few effective preventive drugs are available. Therefore, in this study, we aimed to investigate the protective effects of brimonidine on noise‐induced inner ear hearing impairment in mice and explore its underlying mechanisms and long‐term outcomes. Mice were randomly divided into control, noise exposure, and brimonidine groups. A 62‐week follow‐up was conducted after noise exposure. Brimonidine inhibited the noise‐induced increase in inner ear glutamate concentration and downregulated inflammatory factors and immunoglobulins. Brimonidine decreased glutaminase and VGLUT2/3 expression and reduced glutamate synthesis and vesicle transport without affecting its clearance, thereby decreasing glutamate excitotoxicity and protecting synapses and spiral ganglion neurons long term. Mice exposed to noise could temporarily restore their hearing thresholds; however, their auditory function in old age remained significantly worse than those that received brimonidine‐mediated cochlear protection in youth. These findings highlight the importance of enhancing noise protection from an early age.

Noise-induced hearing loss (NIHL) remains highly prevalent in occupational settings, and no pharmacological agent or combination thereof has demonstrated a protective or restorative impact against noise-induced damage in clinic till now. Biomass-derived carbon dots (CDs) are known for their unique biological activities and excellent safety. Marine organisms account for 78% of the planet’s biomass. In this vast and diversified habitat, marine animals make and gather significant amounts of compounds with distinct structural and physiological properties. Here, using eight different marine fauna and flora as carbon sources, safe and green CDs were synthesized through one-pot hydrothermal method. All eight CDs displayed good stability and radical quenching abilities. In ABR testing, the Undaria pinnatifida Suringar-derived CDs (USCDs) exerted the strongest hearing protection abilities under noise exposure in vivo among the eight samples. The structure–activity relationships of marine-derived CDs suggested that improved content of heteroatom or reductive function groups was essential for their radical scavenging and in vivo anti-NIHL activities. The cytoprotective activity for auditory nerve and hair cells in vivo were confirmed by confocal microscopy. Notably, in vitro cell tests demonstrated that USCDs could prevent apoptosis and ferroptosis through ROS scavenging and Fe 2+ -chelating, respectively. Moreover, both in vivo and in vitro experiments demonstrated that USCDs possessed excellent biosafety and blood–labyrinth barrier (BLB) permeability, supporting their potential for systemic administration. These findings broaden the potential applications of CDs in the treatment of inner ear diseases, and provided some insights into the development marine drugs. Graphical Abstract

Age-related hearing loss is a global public health issue that impacts the quality of life in the elderly population. Macrophages are the main immune cell population in the cochlea, yet the role in the development and progression of age-related hearing loss is still unclear. This study analyzed single-cell sequencing data from cochlear tissues of C57BL/6J mice across different ages and identified notable increase in CD74 expression in macrophages with aging. Validation revealed that CD74 levels were elevated in the aged cochlea, while macrophage migration inhibitory factor (MIF) levels decreased. MIF was significantly reduced in both senescent HEI-OC1 cells and supernatant. Notably, the senescent HEI-OC1 supernatant stimulated BV2 cells CD74 expression increased. rCD74 significantly upregulated apoptosis-related genes expression levels in HEI-OC1 cells, while decreasing MIF levels. In the co-culture system of scrambled/CD74 - BV2 cells and HEI-OC1 cells, CD74 - BV2 cells markedly reduced the apoptosis-related genes expression in senescent HEI-OC1 cells. MIF could improve the mitochondrial membrane potential of both groups of HEI-OC1 cells, and decreased the TUNEL positive cells significantly. Our findings using the HEI-OC1 cell model reveal that macrophages secrete CD74 into the microenvironment, where it interacts with MIF, reducing local MIF levels. This interaction weakens MIF’s protective effect on senescent HEI-OC1 cells, promoting apoptosis in these auditory cells. This suggests a potential mechanism whereby elevated CD74 in the aging cochlear microenvironment may contribute to the loss of hair cells in vivo . Targeting macrophage CD74 may offer therapeutic potential for preventing and treating age-related hearing loss.

BACKGROUND: Chronic hearing impairment represents a major global health burden, profoundly diminishing quality of life due to its association with depression and cognitive decline. Recent studies have identified metabolic-dysfunction-associated steatohepatitis (MASH) as an independent systemic risk factor for accelerated hearing loss, implicating a functional liver–inner ear axis. However, the molecular and vascular mechanisms through which MASH-induced systemic inflammation compromises cochlear integrity remain uncertain. METHODS: We investigated the impact of MASH on cochlear pathology and auditory function. MASH was induced in 8-week-old male BALB/c mice by feeding a methionine–choline-deficient (MCD) diet for 4 weeks. After this induction period, the mice were exposed to acoustic trauma and maintained on the same diet for an additional 2 weeks. Systemic and cochlear evaluations were performed to assess the impact of MASH on auditory function and related physiological alterations. RESULTS: The MCD diet induced severe hepatic steatosis and lobular inflammation, accompanied by cochlear stria vascularis (SV) hyperpermeability and inflammation characterized by elevated interleukin (IL)-1β and lipocalin-2 (LCN2), without overt hearing loss or hair cell damage. Following noise exposure, MCD-fed mice demonstrated significantly delayed auditory recovery compared to chow-fed controls. This delay was associated with cochlear synaptopathy (CtBP2 degeneration), exacerbated BLB dysfunction, and ultrastructural alterations in endothelial cells, pericytes, and perivascular macrophages within the stria vascularis. PDGFRβ expression was significantly reduced, while proinflammatory mediators (IL-6, IL-1β, and LCN2) were upregulated, suggesting concurrent vascular injury and inflammatory activation. CONCLUSION: These findings demonstrate that MASH sensitizes the cochlea to noise-induced injury through disruption of the BLB and sustained inflammation, providing a preclinical model and mechanistic insight into the link between MASH and hearing loss.