Auditory Research publications

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.

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.

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.

Objectives. This study aimed to explore the role of the Pcdh15 gene in hearing maintenance and to examine the effects of its deficiency on cochlear structure, cochlear function, and hearing loss in mice.Methods. CRISPR/Cas9 technology was used to generate Pcdh15 knockout (KO) mice. Auditory function was evaluated using hearing tests, while histological approaches were employed to assess morphological changes in cochlear hair cells and spiral ganglion neurons (SGNs). RNA sequencing (RNA-seq) was performed on cochlear tissue from postnatal day 18 (P18) wild-type (WT) and Pcdh15 KO mice to identify differentially expressed genes (DEGs). These DEGs were subjected to functional annotation and pathway analysis, with particular emphasis on oxidative phosphorylation (OXPHOS). Reactive oxygen species (ROS) levels were quantified using flow cytometry and DCFH-DA assays.Results. Pcdh15 KO mice exhibited progressive sensorineural hearing loss, which worsened to profound deafness by P18. Notably, cochlear hair cells and SGNs showed substantial loss and pronounced morphological abnormalities, particularly within the basal high-frequency region. RNA-seq analysis identified 1,359 DEGs, including 1,024 downregulated and 335 upregulated genes. Pathway analysis indicated that Pcdh15 deficiency was associated with inhibition of the OXPHOS pathway, potentially disrupting mitochondrial respiratory chain complexes I, III, IV, and V and thereby impairing energy production and ATP metabolism. In addition, early-stage cochleae from KO mice demonstrated elevated ROS levels and increased oxidative stress, suggesting that redox imbalance may contribute to hearing damage.Conclusion. Pcdh15 plays a critical role in hearing maintenance. Its deficiency is associated with severe hearing loss and marked cochlear abnormalities, which are linked to inhibition of OXPHOS, disruption of energy metabolism, and exacerbation of oxidative stress. Together, these findings provide new insights into the mechanisms underlying hearing loss and suggest potential targets for therapeutic intervention.

Electromotility in mammalian outer hair cells (OHC) is the mechanism underlying cochlear amplification. It is brought about by the piezoelectric-like property of the membrane protein prestin (Slc26a5) that lies in the OHCs lateral plasma membrane. Prestin connects to an underlying cytoskeletal network of circumferential actin filaments that bridge longitudinal spectrin filaments. This network, in turn, lies between the plasma membrane and a closely apposed ER-like tubular array of subsurface cisternae (SSC). Two previous papers examining spectrin knockouts in embryonic hair cells were confined to analyzing the effects on the apical cuticular plate and overlying stereocilia. In this paper, we examine the effects of conditional knockouts of alpha2 spectrin in postnatal OHCs. We find a significant auditory phenotype likely due to the novel disassociation of prestin's gating charge movement from OHC electromotility. In addition, OHCs show enlargement in their SSC and plasma membrane-SSC space with preserved cuticular plates and overlying stereocilia, the latter contrasts with the findings in embryonic knockouts.

Atypical sensory processing is a common feature of autism, yet the neural computations that give rise to these differences, particularly in relation to biological sex and etiological origin, remain unclear. Here we examine predictive auditory processing at the single-neuron level in the inferior colliculus of two adult rat models of autism: a genetic model with a heterozygous Grin2b deletion (Grin2b + /-) and an environmental model based on prenatal valproic acid exposure. We recorded neuronal responses to an auditory oddball paradigm and a cascade control sequence across lemniscal and non-lemniscal IC divisions under high-intensity stimulation, allowing us to derive indices of repetition suppression, prediction error and neuronal mismatch. Using generalized linear mixed-effects models that accounted for animal identity, inferior colliculus division, sex, and rat model, followed by hierarchical group-level comparisons, we identified robust alterations in predictive processing in both autism-like models. These effects varied across inferior colliculus divisions and differed between sexes, revealing distinct phenotype-specific signatures. The results indicate that sex and etiology jointly modulate early auditory computations in autism. More broadly, our findings highlight the translational value of predictive coding frameworks and support the use of complementary animal models to capture neurobiological heterogeneity across the autism spectrum.

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.

Adeno-associated virus (AAV) unequivocally emerges as one of the most powerful and promising delivery vectors for gene therapy targeting hereditary hearing loss. Following AAV transduction in the inner ear, varying degrees of natural immune responses are triggered, primarily characterized by macrophage activation and the secretion of pro-inflammatory factors. Additionally, the production of neutralizing antibodies may affect the efficacy of gene therapy. To evaluate immune dynamics, we injected AAV1 and AAV-ie (capsids with distinct transfection efficiencies) into murine cochleae and analyzed temporal transcriptomic profiles. Our results demonstrate that both capsids induce immune activity but with critical temporal and intensity differences that AAV1 elicits significantly later and milder immune reactions compared to AAV-ie. These findings establish that dynamic cochlear gene expression profiles directly inform the selection of immunologically optimized AAV vectors to minimize adverse responses in future hereditary hearing loss gene therapies.

To investigate auditory acclimatization to high-altitude hypobaric hypoxia, we conducted longitudinal transcriptomic analyses in Wistar rats rapidly transported from 500 m to 3,700 m. Auditory brainstem response (ABR) testing and hematoxylin and eosin staining revealed progressive changes, with hearing impairment at 30 days (D30) followed by acclimatization at 60 days (D60). RNA-seq of cochlear tissues identified 1,329 differentially expressed genes (DEGs) during impairment and 1,441 DEGs during acclimatization. STEM analysis linked these temporal patterns to specific biological processes: peripheral nervous system development (acclimatization) and myotube differentiation (impairment), as annotated by GO/KEGG and Metascape. STEM analysis revealed gene expression profiles that significantly correlated with ABR threshold shifts, encompassing biological processes such as sensory organ morphogenesis and gravity-sensing pathways. Subsequent validation through RT-PCR and immunofluorescence staining confirmed the involvement of key candidate genes, including morphogenesis-associated factors (Aqp1, Rbp4), the mechanosensitive hormone Bglap, and critical transcriptional regulators (Maz, Tfap4, Nf1) in the acclimatization response. This study elucidates key transcriptional mechanisms governing both the initial hearing impairment and subsequent acclimatization processes during high-altitude adaptation.

Dexamethasone-loaded LPNs protect the cochlea from cisplatin.

Background Usher syndrome (USH) is an autosomal recessive disorder characterized by hearing loss, retinitis pigmentosa, and variable vestibular dysfunction. USH2A is one of the causative genes of USH. This study is aimed at exploring the mechanism of hearing loss induced by USH2A gene knockout. Method USH2A knockout (Ush2a −/− ) mice were used, and auditory brainstem response testing was performed on WT, Ush2a −/− , and Ush2a +/− mice. Then, the cochlea tissues were used to carry out immunofluorescence staining, hematoxylin and eosin (H&E) staining, and scanning electron microscopy (SEM). The mRNA expressions were detected by RT‐qPCR. Finally, the differentially expressed genes (DEGs) in cochlear tissues of Ush2a −/− and WT mice were identified by transcriptome sequencing. Results Compared to WT mice, Ush2a −/− and Ush2a +/− mice exhibited moderate‐to‐severe nonprogressive hearing loss, with more pronounced deficits at low (4 kHz) and high (32/24 kHz) frequencies. HE staining and immunofluorescence staining showed that the modiolus, stria vascularis, basilar membrane, and the number of inner hair cells and outer hair cells (OHCs) in USH2A knockout mice have not changed. However, SEM results showed that severe stereociliary collapse was evident in OHCs of the Ush2a −/− group. In addition, through transcriptomic analysis, 3632 upregulated genes and 2921 downregulated genes were obtained in the Ush2a −/− mice. Among these DEGs, the most DEGs associated with hearing loss were Scn2a, Shank2, Bsn, Fcer1g, Prkce, Tgfb1, and Irf7. Conclusion This study demonstrates that USH2A deficiency disrupts auditory function through stereociliary instability and dysregulation of genes critical for synaptic transmission and cytoskeletal dynamics.

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.

Sensorineural hearing loss (SNHL) is significantly more prevalent in individuals with chronic kidney disease (CKD) than in the general population. Although a strong independent association has been observed between kidney dysfunction and the risk of hearing loss, the underlying mechanisms linking these conditions remain poorly understood. This study investigated the pathophysiology of hearing impairment using adriamycin nephropathy (AN), a well-established animal model of CKD. AN was induced in male BALB/c mice using 10 or 12 mg/kg of adriamycin (ADR), resulting in severe kidney injury and concurrent hearing loss. ADR-treated mice exhibited significant glomerular injury, podocyte damage, and elevated renal neutrophil gelatinase-associated lipocalin (NGAL), along with increased serum creatinine and blood urea nitrogen levels. Hearing impairment was evident after 4-8 weeks of ADR treatment, as assessed by auditory brainstem response and distortion-product otoacoustic emissions, and was accompanied by cochlear hair cell loss and ribbon synapse degeneration. AN affected cochlear function by altering ion channel expression in the stria vascularis and inducing blood-labyrinth barrier (BLB) hyperpermeability, along with changes in endothelial cells, pericytes, and perivascular-resident macrophage-like melanocytes. AN significantly increased cochlear NGAL and NLRP3 levels at 4 and 8 weeks following ADR administration. NGAL was highly expressed in the tectorial membrane, cochlear neurons, and organ of Corti, while its receptor, 24p3R, was co-localized with NGAL. These findings demonstrated the role of NGAL and BLB disruption in ADR-induced SNHL, providing novel insights into the mechanistic link between CKD and hearing loss.

The hippocampus is classically linked to memory, yet increasing evidence points to a broader role in perceptual inference and deviance detection. Predictive coding theories propose that perception minimizes mismatches between expected and actual sensory input, expressed in neural signatures such as mismatch negativity (MMN) and P300. Although MMN arises mainly from sensory and prefrontal cortices, the hippocampus is anatomically interconnected with both and may also contribute to prediction error processing. We recorded single- and multi-unit activity and local field potentials (LFPs) from DG and CA1 in urethane-anesthetized rats during an auditory oddball paradigm and a no-repetition control sequence to dissociate prediction error from repetition suppression. Approximately 20% of hippocampal neurons were sound responsive, and a subset showed deviant selectivity. Spiking activity predominantly reflected prediction errors, while LFPs revealed complementary contributions from repetition suppression and prediction error. Early LFP components were enhanced for randomly presented deviants, whereas later components within the P300 latency range were stronger for predictable deviants, indicating temporally distinct phases of error signaling and top-down modulation. These findings identify the hippocampus as an active contributor to auditory deviance detection and support a hierarchical model in which hippocampal circuits participate in predictive sensory processing beyond memory.

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.

Cisplatin (CDDP), a widely used chemotherapeutic agent, is limited by severe ototoxicity side effects. Local drug delivery via the middle ear represents the most effective approach for treating inner ear disease. However, therapeutic efficacy is constrained by poor middle ear retention and limited permeability across the round window membrane (RWM). Quercetin (QU) exhibits potent activity against CDDP-induced cytotoxicity but suffers from delivery challenges. To address this, we developed amino-functionalized mesoporous silica nanoparticles (NH2-MSNs) loaded with QU (QU-N-MSNs), leveraging the permselective properties of the RWM. This system was noninvasively administered to the cochlea via trans-tympanic delivery. The synthesized QU-N-MSNs demonstrated a uniform particle size of approximately 116–124 nm, positive charge, and sustained drug release properties. Compared to free QU, QU-N-MSNs demonstrated significantly enhanced antiapoptotic and cytoprotective activities in vitro. In vivo studies confirmed nanoparticle retention within the inner ear for ≥14 days post administration and efficient RWM penetration. Pretreatment with QU-N-MSNs prior to CDDP exposure in murine models substantially mitigated ototoxicity, as evidenced by reduced hearing threshold shifts across multiple frequencies, preservation of hair cells (HCs) and spiral ganglion neurons (SGNs), and attenuation of mitochondrial-mediated SGN apoptosis. These findings establish QU-N-MSNs as an effective RWM-penetrating delivery platform, offering a promising strategy to enhance hydrophobic drug bioavailability in the inner ear and prevent CDDP-induced ototoxicity.

Cisplatin is a widely used and effective anticancer drug. However, it causes permanent sensorineural hearing loss in over 50% of treated patients. There are no FDA-approved therapies to prevent cisplatin-induced hearing loss (CIHL) in adults, highlighting a critical unmet clinical need. Previous studies suggest that statins, commonly prescribed cholesterol-lowering drugs, are associated with reduced incidence and severity of cisplatin-induced hearing loss. Statins are primarily used to lower cholesterol, but they also exert several pleiotropic effects, making the mechanism(s) underlying this protection unclear. Here we examine whether reduced plasma cholesterol confers protection against CIHL independent of statin treatment. We utilized mice lacking serine protease proprotein convertase subtilisin/kexin type 9 ( Pcsk9 knockout (KO) mice) as a genetic model of reduced plasma cholesterol. We find that Pcsk9 KO mice are protected against cisplatin-induced hearing loss, as reflected by significantly lower ABR and DPOAE threshold shifts relative to wild type (WT) mice following treatment. Histological analyses confirmed preservation of cochlear outer hair cells (OHCs) in Pcsk9 KO mice treated with cisplatin, whereas WT mice showed significant OHC loss in the high-frequency cochlear regions. Finally, hearing loss positively correlated with baseline plasma cholesterol levels. Together our data demonstrate that systemic cholesterol reduction provides significant protection against CIHL, and they suggest that the protective effect of statins against CIHL is mediated by cholesterol reduction.

Background: Age related hearing loss (ARHL) is a sensorineural hearing disease caused by multiple factors and its pathogenesis is still unclear. This work aims to investigate the precise role of AIMP1 in ARHL. Methods: HEI-OC1 cells were treated with 1 mM H2O2 for 2 h to induce cell damage. CCK-8, flow cytometry and TUNEL staining examined cell viability and apoptosis. DCFH-DA fluorescence probe assessed ROS. The levels of MDA, SOD and copper were detected by kits. The expression of proteins related to mitophagy, cuproptosis were examined by western blotting and immunofluorescence. Finally, D-galactose was administered to mice to establish an ARHL model for verifying the functional role of AIMP1 in ARHL. Results: AIMP1 and SIRT1 were down-regulated in H2O2-treated HEI-OC1 cells. AIMP1 overexpression promoted cell viability, reduced ROS and MDA levels, and increased SOD levels in H2O2-treated HEI-OC1 cells. Moreover, the levels of copper and apoptosis were decreased in H2O2-treated HEI-OC1 cells in the presence of AIMP1 overexpression. AIMP1 overexpression caused a down-regulation of cuproptosis-related proteins FDX1, DLAT, DLST, and an up-regulation of mitophagy-related proteins PINK1, Parkin, Mfn2 and Drp1 in H2O2-treated HEI-OC1 cells. Knockdown PINK1 or SIRT1 reversed the influence of AIMP1 overexpression on H2O2 induced HEI-OC1 cell damage. In vivo, AIMP1 overexpression reduced damage of cochlear tissues and partially restored hearing in ARHL mice. Conclusion: AIMP1 up-regulated SIRT1 to promote PINK1/Parkin-mediated mitophagy and inhibit cuproptosis of cochlear hair cells in ARHL mice. Thus, AIMP1 may be a potential target for ARHL treatment.

Diverse biological factors, such as sex and age, confer heterogeneity on sensory processing challenges in autism. These factors result in major difficulties in the processing of contextual information in social and non-social situations. To assess divergence in autistic traits, it is critical to consider sex- and age-related variability. Nevertheless, these differences remain largely elusive. Animal models of autism offer the possibility to examine contextual processing at the single-neuron level. Here, we investigated predictive processing of contextual auditory cues in the auditory midbrain of control and prenatally valproic acid-induced rats, a well-established animal model of autism. The rats were prepubertal and adult female and male animals. We performed single-unit recordings in the inferior colliculus of control and prenatally, or in utero , exposed rats under the classical oddball paradigm and non-repetitive cascade control sequences to study neuronal mismatch. This is the neuronal correlate of mismatch negativity, the brain’s automatic response to interruptions in environmental regularity. When comparing control and exposed rats, our results demonstrated a reduction in neuronal mismatch in rats exposed to valproic acid. However, exposed adult females exhibited an increased neuronal mismatch compared to their control counterparts. With respect to sex distinctions, valproic acid induced sex differences in neuronal mismatch of prepubertal and adult rats that are not observable in control animals. Moreover, we detected an age-dependent refinement in prediction error that is not affected by the drug. But valproic acid altered typical developmental trajectory of neuronal mismatch in both sexes. Such observations support sex- and age-related effects of in utero valproic acid exposure in contextual auditory processing at the neural level of the inferior colliculus. In autism, atypical predictive processing of environmental regularities underlies unusual responses to novel experiences. The present study highlights the importance of sex and age, that confer heterogeneity to these challenges.