Loss of ARHGEF6 Causes Hair Cell Stereocilia Deficits and Hearing Loss in Mice

IQGAP3 deficiency leads to non-syndromic hearing loss via inhibition of CDC42 enzyme activity

BACKGROUND

Genetic factors are important causes of congenital hearing loss. To better understand hereditary hearing loss, we performed in-depth clinical and molecular analysis of families with congenital hearing loss and a new disease-related gene, IQGAP3, was identified in this process. This gene encodes a protein that belongs to the IQGAP family which is well known as a GTPase-activating protein involved in various cellular functions. However, there is no research on the relationship between IQGAP3 and the auditory system.

METHOD

This study was conducted at Guangzhou Women and Children's Medical Center and Nantong University from 2019 to 2023 to confirm the relationship between defective IQGAP3 and hearing loss, and further explore the underlying molecular mechanism. We constructed the iqgap3 knockdown zebrafish model, primary mouse inner progenitor cell model and IQGAP3-knockout HEK293T cell line for this research.

RESULT

We found that IQGAP3 deficiency led to abnormal development of the auditory system and impaired auditory function in zebrafish. In vitro studies showed that loss of this gene's function resulted in a 40.29 % reduction in EdU-positive cells and a 44.25 % decrease in Ki67-positive cells in mouse inner ear progenitor cells, indicating reduced proliferation. This can be linked with inhibition of CDC42 enzymatic activity and the blockade of the Wnt-catenin pathway.

CONCLUSION

We identified IQGAP3 as a novel potential causative gene in hereditary hearing loss. Our findings provide important insights into the molecular basis of hereditary hearing loss.

A novel transcriptomic signature associated with lymphovascular invasion predicts clinical outcomes, tumor microenvironment, and therapeutic response in lung adenocarcinoma

PURPOSE

Since TNM staging has limitations for predicting post-operative outcomes and relapse, more effective prediction tools need to be researched and developed. Lymphovascular invasion, LVI, as a histopathological feature, has been widely shown to have a correlation with poor prognosis and early recurrence of lung adenocarcinoma (LUAD). However, LVI assessment is limited by subjective bias, and therefore its efficacy in practical clinical application needs further clarification. The aim of this study was to formulate a new signature based on LVI-related genes to predict prognosis and recurrence in patients with lung adenocarcinoma.

METHODS

Clinicopathological information, gene sequencing data and whole slide images (WSIs) of LUAD patients were downloaded from the Cancer Genome Atlas (TCGA) databases. LVI statue were evaluated by professional pathologists, and then the differentially expressed genes (LVI DEGs) associated with LVI were screened. The least absolute shrinkage and selection operator (LASSO) and Step Cox regression models were used to construct LVI-associated risk scores (LVRS), including PAQR4, ARGHEF6, CKS1B, CFTR and SEC14L4. The validity of the LVRS score was evaluated on multiple external datasets and our JSSZL cohort dataset. Using LVRS scores and clinical information, nomogram were constructed for use by clinicians. In addition, we further explored the relationship between LVRS score and clinicopathological features, immune infiltration, tumor mutational load, and immunotherapy response, and confirmed the expression of key genes in LVRS score in lung adenocarcinoma tissues using qRT-PCR and immunohistochemistry (IHC) techniques.

RESULTS

Based on the LVRS, patients could be classified into high-LVRS and low-LVRS groups. It was found that OS and PFS were significantly worse in the high-LVRS group than in the low-LVRS group (p < 0.001). By ROC curve analysis, it could be found that the nomogram combining LVRS and clinical information could accurately predict the prognosis of LUAD patients with the area under the curve of 1,3,5-year survival rate could reach 0.754, 0.741 and 0.735. The results of univariate and multivariate analysis showed that LVRS was an independent prognostic factor. At the same time, there were significant differences in the mutation profiles and immune microenvironment between the high-LVRS and low-LVRS groups, with the high-LVRS group having a significantly higher mutation rate than the low-LVRS group and exhibiting immunological "cold" features. By the experimental results, higher expression levels of PAQR4 and CKS1B were found in LUAD tissues, while lower expression levels of ARGHEF6, CFTR and SEC14L4 were observed.

CONCLUSIONS

The LVRS established in this study serves as a valid tool to predict the prognosis and recurrence status of lung adenocarcinoma patients and has a predictive effect on the response to postoperative treatment. The establishment of LVRS may offer some theoretical support to clinical treatment strategies for patients with lung adenocarcinoma following surgical intervention.

Effects of acute exposure to Al2O3-NPs (α and γ) and white noise and their combination on cochlea structure and function in Wistar rats

Hearing loss induced by noise and combinations of factors is a common occupational disease among workers. This study aimed to investigate the impact of acute exposure to white noise and Al2O3 NPs, alone and in combination, on changes in the hearing and structural functions of the cochlea in rats. Thirty-six rats were randomly assigned to one of six groups: Control, acute exposure to white noise, exposure to γ-Al2O3 NPs, exposure to noise plus γ-Al2O3 NPs, exposure to α-Al2O3 NPs, and exposure to the combination of noise plus α-Al2O3 NPs. TTS and PTS were examined using DPOAE, while oxidative index (MDA, GSH-Px), gene expression (NOX3, TGF-ß, CYP1A1), protein expression (ß-Tubulin, Myosin VII), and histopathological changes were examined in the cochlea. The morphology of Al2O3 NPs was examined by TEM. The results of the DPOAE test showed a significant increase in TTS in all groups and an increase in PTS in the groups exposed to noise, γ-Al2O3 NPs, and a combination of noise plus Al2O3 NPs (P < 0.05). In the group exposed to white noise plus Al2O3 NPs, the MDA levels increased, the level of GSH-Px decreased, and the expression percentage of ß-Tubulin and Myosin VII decreased, while the expression of NOX3, TGF-ß, and CYP1A1 (except for the α-Al2O3 NPs group) significantly increased (P < 0.05). Histopathological changes of the cochlea indicated damage to hair and ganglion cells, which was more severe in the combined exposure group. The combined and independent exposure to white noise and Al2O3 NPs damaged hair and ganglion cells for high-frequency perception, affecting the function and structure of the cochlea and leading to TTS and PTS.

Dock4 is required for the maintenance of cochlear hair cells and hearing function

Auditory hair cells (HCs) are the mechanosensory receptors of the cochlea, and HC loss or malfunction can result from genetic defects. Dock4, a member of the Dock180-related protein superfamily, is a guanine nucleotide exchange factor for Rac1, and previous reports have shown that Dock4 mutations are associated with autism spectrum disorder, myelodysplastic syndromes, and tumorigenesis. Here, we found that Dock4 is highly expressed in the cochlear HCs of mice. However, the role of Dock4 in the inner ear has not yet been investigated. Taking advantage of the piggyBac transposon system, Dock4 knockdown (KD) mice were established to explore the role of Dock4 in the cochlea. Compared to wild-type controls, Dock4 KD mice showed significant hearing impairment from postnatal day 60. Dock4 KD mice showed hair bundle deficits and increased oxidative stress, which eventually led to HC apoptosis, late-onset HC loss, and progressive hearing loss. Furthermore, molecular mechanism studies showed that Rac1/β-catenin signaling was significantly downregulated in Dock4 KD cochleae and that this was the cause for the disorganized stereocilia and increased oxidative stress in HCs. Overall, our work demonstrates that the Dock4/Rac1/β-catenin signaling pathway plays a critical role in the maintenance of auditory HCs and hearing function.

The applications of CRISPR/Cas-mediated genome editing in genetic hearing loss

Hearing loss (HL) can be caused by a number of different genetic factors. Non-syndromic HL refers that HL occurs as an isolated symptom in an individual, whereas syndromic HL refers that HL is associated with other symptoms or abnormalities. To date, more than 140 genes have been identified as being associated with non-syndromic HL, and approximately 400 genetic syndromes can include HL as one of the clinical symptoms. However, no gene therapeutic approaches are currently available to restore or improve hearing. Therefore, there is an urgent necessity to elucidate the possible pathogenesis of specific mutations in HL-associated genes and to investigate the promising therapeutic strategies for genetic HL. The development of the CRISPR/Cas system has revolutionized the field of genome engineering, which has become an efficacious and cost-effective tool to foster genetic HL research. Moreover, several in vivo studies have demonstrated the therapeutic efficacy of the CRISPR/Cas-mediated treatments for specific genetic HL. In this review, we briefly introduce the progress in CRISPR/Cas technique as well as the understanding of genetic HL, and then we detail the recent achievements of CRISPR/Cas technique in disease modeling and therapeutic strategies for genetic HL. Furthermore, we discuss the challenges for the application of CRISPR/Cas technique in future clinical treatments.

Transcriptome heterogeneity of congenital cleft palate model in congener New Zealand rabbits induced by dexamethasone

OBJECTIVES

This work aimed to investigate the transcriptome heterogeneity of dexamethasone-induced congenital cleft palate in homozygous New Zealand rabbits and determine the molecular mechanism underlying the occurrence of congenital cleft palate.

METHODS

Dexamethasone (1.0 mg per day) was administered intramuscularly to 20 New Zealand pregnant rabbits from day 14 to day 17 of gestation, and the palatal phenotype of all offspring of each pregnant rabbit was observed. Eight embryos with a 4∶4 ratio of cleft palate to non-cleft palate were selected and divided into the cleft palate group (CP) and non-cleft palate group (NCP). Their palatal tissues were collected for RNA sequencing.

RESULTS

A total of 225 differentially expressed genes (Q<0.05) were found in the CP group compared with the NCP group, of which 120 genes were upregulated and 105 genes were downregulated. The GO and KEGG enrichment analyses of these differentially expressed genes were carried out. The results showed significant enrichment in GO classification, which included heterotrimeric G protein complex, extracellular matrix, transcription factor complex, and basement membrane. Meanwhile, GABA ergic synapse, morphine addiction, retrograde endocannabinoid signaling, glutamate synapse, serotonergic synapse, regulation of actin cytoskeleton, and the Apelin signaling pathway were significantly enriched in the KEGG pathway. Compared with the NCP group, the gene expression levels of ARHGEF6 (P<0.05) and ABI2 (P<0.001) decreased in the CP group, and APC increased (P<0.001); these results were confirmed by real-time polymerase chain reaction.

CONCLUSIONS

Abnormal expression levels of the ARHGEF6, APC, and ABI2 genes involved in the regulation of the actin cytoskeleton in the palatal synapse may be associated with the dexamethasone-induced congenital cleft palate in New Zealand rabbits.

ftr82 is necessary for hair cell morphogenesis and auditory function during zebrafish development

Damages of sensory hair cells (HCs) are mainly responsible for sensorineural hearing loss, while the pathological mechanism remains not fully understood due to the many potential deafness genes unidentified. ftr82, a member of the largely TRIMs family in fish, has been found specifically expressed in the otic vesicle while its function is still unclear. Here, we investigate the roles of ftr82 in HC development and hearing function utilizing the zebrafish model. The results of in situ hybridization illustrate that ftr82 is always restricted to localize in otic vesicles at different stages. The defects of HCs are observed both in ftr82 morphants and mutants, including significantly decreased crista HCs, shortened cilia as well as remarkably reduced functional HCs in neuromasts, which could be successfully rescued by co-injection of exogenous ftr82 mRNA. The behavior assay of startle response indicates that larvae lacking of ftr82 exhibits lower sensitivity to external sound stimuli. Further research reveals that the loss of HCs is mainly caused by cell apoptosis mediated by caspase-3 activation. Our study demonstrates that ftr82 is a crucial hearing-related gene that regulates the HC morphogenesis and auditory function performing, which provides new insight into the rapid identification of the deafness gene.

Gene therapy: an emerging therapy for hair cells regeneration in the cochlea

Sensorineural hearing loss is typically caused by damage to the cochlear hair cells (HCs) due to external stimuli or because of one's genetic factors and the inability to convert sound mechanical energy into nerve impulses. Adult mammalian cochlear HCs cannot regenerate spontaneously; therefore, this type of deafness is usually considered irreversible. Studies on the developmental mechanisms of HC differentiation have revealed that nonsensory cells in the cochlea acquire the ability to differentiate into HCs after the overexpression of specific genes, such as Atoh1, which makes HC regeneration possible. Gene therapy, through in vitro selection and editing of target genes, transforms exogenous gene fragments into target cells and alters the expression of genes in target cells to activate the corresponding differentiation developmental program in target cells. This review summarizes the genes that have been associated with the growth and development of cochlear HCs in recent years and provides an overview of gene therapy approaches in the field of HC regeneration. It concludes with a discussion of the limitations of the current therapeutic approaches to facilitate the early implementation of this therapy in a clinical setting.

Deletion of the Notch ligand Jagged1 during cochlear maturation leads to inner hair cell defects and hearing loss

The mammalian cochlea is an exceptionally well-organized epithelium composed of hair cells, supporting cells, and innervating neurons. Loss or defects in any of these cell types, particularly the specialized sensory hair cells, leads to deafness. The Notch pathway is known to play a critical role in the decision to become either a hair cell or a supporting cell during embryogenesis; however, little is known about how Notch functions later during cochlear maturation. Uniquely amongst Notch ligands, Jagged1 (JAG1) is localized to supporting cells during cell fate acquisition and continues to be expressed into adulthood. Here, we demonstrate that JAG1 in maturing cochlear supporting cells is essential for normal cochlear function. Specifically, we show that deletion of JAG1 during cochlear maturation disrupts the inner hair cell pathway and leads to a type of deafness clinically similar to auditory neuropathy. Common pathologies associated with disruptions in inner hair cell function, including loss of hair cells, synapses, or auditory neurons, were not observed in JAG1 mutant cochleae. Instead, RNA-seq analysis of JAG1-deficient cochleae identified dysregulation of the Rho GTPase pathway, known to be involved in stereocilia development and maintenance. Interestingly, the overexpression of one of the altered genes, Diaph3, is responsible for autosomal dominant auditory neuropathy-1 (AUNA1) in humans and mice, and is associated with defects in the inner hair cell stereocilia. Strikingly, ultrastructural analyses of JAG1-deleted cochleae revealed stereocilia defects in inner hair cells, including fused and elongated bundles, that were similar to those stereocilia defects reported in AUNA1 mice. Taken together, these data indicate a novel role for Notch signaling in normal hearing development through maintaining stereocilia integrity of the inner hair cells during cochlear maturation.

Identification of novel compound heterozygous mutations of the MYO15A gene with autosomal recessive non-syndromic hearing loss

BACKGROUND

The most common inheritance pattern responsible for congenital deafness belongs to autosomal recessive non-syndromic hearing loss (ARNSHL) and mutations of the highly heterogeneous MYO15A locus are present in a large proportion of cases.

METHODS

One Chinese family with ARNSHL was subjected to clinical evaluation and genetic analysis. We used targeted and whole exome sequencing with Sanger sequencing to identify and characterize mutations. Bioinformatics analysis was conducted to evaluate molecular functions.

RESULTS

Three compound heterozygous MYO15A gene variants, including two novel variants, c.6804G > A (p.M2268I), and c.6188_6190delinsGTCA (p.F2063Cfs*60), responsible for deafness were identified. Pathogenicity was assessed by multiple bioinformatics analyses.

CONCLUSION

We identified novel mutations of the MYO15A locus associated with ARNSHL in a Chinese family. The current findings expand the MYO15A pathogenic mutation spectrum to assist with genetic counseling and prenatal diagnosis.

Genetic insights, disease mechanisms, and biological therapeutics for Waardenburg syndrome

Waardenburg syndrome (WS), also known as auditory-pigmentary syndrome, is the most common cause of syndromic hearing loss (HL), which accounts for approximately 2-5% of all patients with congenital hearing loss. WS is classified into four subtypes depending on the clinical phenotypes. Currently, pathogenic mutations of PAX3, MITF, SOX10, EDN3, EDNRB or SNAI2 are associated with different subtypes of WS. Although supportive techniques like hearing aids, cochlear implants, or other assistive listening devices can alleviate the HL symptom, there is no cure for WS to date. Recently major progress has been achieved in preclinical studies of genetic HL in animal models, including gene delivery and stem cell replacement therapies. This review focuses on the current understandings of pathogenic mechanisms and potential biological therapeutic approaches for HL in WS, providing strategies and directions for implementing WS biological therapies, as well as possible problems to be faced, in the future.

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

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

Targeted Next-Generation Sequencing Identified Novel Compound Heterozygous Variants in the PTPRQ Gene Causing Autosomal Recessive Hearing Loss in a Chinese Family

Hearing loss is among the most common congenital sensory impairments. Genetic causes account for more than 50% of the cases of congenital hearing loss. The PTPRQ gene, encoding protein tyrosine phosphatase receptor Q, plays an important role in maintaining the stereocilia structure and function of hair cells. Mutations in the PTPRQ gene have been reported to cause hereditary sensorineural hearing loss. By using next-generation sequencing and Sanger sequencing, we identified a novel compound heterozygous mutation (c.997 G > A and c.6603-3 T > G) of the PTPRQ gene in a Chinese consanguineous family. This is the first report linking these two mutations to recessive hereditary sensorineural hearing loss. These findings contribute to the understanding of the relationship between genotype and hearing phenotype of PTPRQ-related hearing loss, which may be helpful to clinical management and genetic counseling.

A novel missense variant in CEACAM16 gene causes autosomal dominant nonsyndromic hearing loss

Aim

Autosomal dominant non‐syndromic hearing loss is a common sensorineural disorder with extremely high genetic heterogeneity. CEA antigen‐related cell adhesion molecule 16(CEACAM16)is a secreted glycoprotein encoded by the CEACAM16 gene. Mutations in CEACAM16 lead to autosomal dominant non‐syndromic hearing loss in humans, due defects in the tectorial membrane of the inner ear. Here we reported a novel missense variant in CEACAM16 gene causes autosomal dominant non‐syndromic hearing loss.

Material and methods

A four‐generation Chinese family affected by late‐onset and progressive hearing loss was enrolled in this study. The proband was analyzed by targeted next‐generation sequencing and bioinformatic analysis. And in vitro experiments were performed in overexpressed transfected HEK293T cells to investigate the pathogenesis of the mutant protein.

Results

We identified a novel missense variant in the CEACAM16 gene c.763A>G; (p.Arg255Gly) as causing autosomal dominant non‐syndromic hearing loss in the Chinese family. Using Western blot analysis, ELISA, and immunofluorescence we found increased expression level of the secreted mutant CEACAM16 protein, both intracellularly and extracellularly, compared with wild type CEACAM16 protein.

Conclusion

Our study showed that the p.Arg255Gly variant leads to increased secretion of mutant CEACAM16 protein, with potential deleterious effect to the function of the protein. Our findings expand the mutation spectrum of CEACAM16, and further the understanding CEACAM16 function and implications in disease.

Age-Related Hearing Loss: Sensory and Neural Etiology and Their Interdependence

Age-related hearing loss (ARHL) is a common, increasing problem for older adults, affecting about 1 billion people by 2050. We aim to correlate the different reductions of hearing from cochlear hair cells (HCs), spiral ganglion neurons (SGNs), cochlear nuclei (CN), and superior olivary complex (SOC) with the analysis of various reasons for each one on the sensory deficit profiles. Outer HCs show a progressive loss in a basal-to-apical gradient, and inner HCs show a loss in a apex-to-base progression that results in ARHL at high frequencies after 70 years of age. In early neonates, SGNs innervation of cochlear HCs is maintained. Loss of SGNs results in a considerable decrease (~50% or more) of cochlear nuclei in neonates, though the loss is milder in older mice and humans. The dorsal cochlear nuclei (fusiform neurons) project directly to the inferior colliculi while most anterior cochlear nuclei reach the SOC. Reducing the number of neurons in the medial nucleus of the trapezoid body (MNTB) affects the interactions with the lateral superior olive to fine-tune ipsi- and contralateral projections that may remain normal in mice, possibly humans. The inferior colliculi receive direct cochlear fibers and second-order fibers from the superior olivary complex. Loss of the second-order fibers leads to hearing loss in mice and humans. Although ARHL may arise from many complex causes, HC degeneration remains the more significant problem of hearing restoration that would replace the cochlear implant. The review presents recent findings of older humans and mice with hearing loss.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The Rho GTPase Cell Division Cycle 42 Regulates Stereocilia Development in Cochlear Hair Cells

Stereocilia are actin-based cell protrusions on the apical surface of inner ear hair cells, playing a pivotal role in hearing and balancing sensation. The development and maintenance of stereocilia is tightly regulated and deficits in this process usually lead to hearing or balancing disorders. The Rho GTPase cell division cycle 42 (CDC42) is a key regulator of the actin cytoskeleton. It has been reported to localize in the hair cell stereocilia and play important roles in stereocilia maintenance. In the present work, we utilized hair cell-specific Cdc42 knockout mice and CDC42 inhibitor ML141 to explore the role of CDC42 in stereocilia development. Our data show that stereocilia height and width as well as stereocilia resorption are affected in Cdc42-deficient cochlear hair cells when examined at postnatal day 8 (P8). Moreover, ML141 treatment leads to planar cell polarity (PCP) deficits in neonatal hair cells. We also show that overexpression of a constitutively active mutant CDC42 in cochlear hair cells leads to enhanced stereocilia developmental deficits. In conclusion, the present data suggest that CDC42 plays a pivotal role in regulating hair cell stereocilia development.

SMPX Deficiency Causes Stereocilia Degeneration and Progressive Hearing Loss in CBA/CaJ Mice

The small muscle protein, x-linked (SMPX) encodes a small protein containing 88 amino acids. Malfunction of this protein can cause a sex-linked non-syndromic hearing loss, named X-linked deafness 4 (DFNX4). Herein, we reported a point mutation and a frameshift mutation in two Chinese families who developed gradual hearing loss with age. To explore the impaired sites in the hearing system and the mechanism of DFNX4, we established and validated an Smpx null mouse model using CRISPR-Cas9. By analyzing auditory brainstem response (ABR), male Smpx null mice showed a progressive hearing loss starting from high frequency at the 3rd month. Hearing loss in female mice was milder and occurred later compared to male mice, which was very similar to human beings. Through morphological analyses of mice cochleas, we found the hair cell bundles progressively degenerated from the shortest row. Cellular edema occurred at the end phase of stereocilia degeneration, followed by cell death. By transfecting exogenous fluorescent Smpx into living hair cells, Smpx was observed to be expressed in stereocilia. Through noise exposure, it was shown that Smpx might participate in maintaining hair cell bundles. This Smpx knock-out mouse might be used as a suitable model to explore the pathology of DFNX4.

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

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

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

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

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

Promising Applications of Nanoparticles in the Treatment of Hearing Loss

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

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

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

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

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

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

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

Hair Cell Protection from Ototoxic Drugs

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

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

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

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

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

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

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

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

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

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

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

Canonical Wnt Signaling Pathway on Polarity Formation of Utricle Hair Cells

As part of the inner ear, the vestibular system is responsible for sense of balance, which consists of three semicircular canals, the utricle, and the saccule. Increasing evidence has indicated that the noncanonical Wnt/PCP signaling pathway plays a significant role in the development of the polarity of the inner ear. However, the role of canonical Wnt signaling in the polarity of the vestibule is still not completely clear. In this study, we found that canonical Wnt pathway-related genes are expressed in the early stage of development of the utricle and change dynamically. We conditionally knocked out β-catenin, a canonical Wnt signaling core protein, and found that the cilia orientation of hair cells was disordered with reduced number of hair cells in the utricle. Moreover, regulating the canonical Wnt pathway (Licl and IWP2) in vitro also affected hair cell polarity and indicated that Axin2 may be important in this process. In conclusion, our results not only confirm that the regulation of canonical Wnt signaling affects the number of hair cells in the utricle but also provide evidence for its role in polarity development.

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

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

Disruption of the autism-related gene Pak1 causes stereocilia disorganization, hair cell loss, and deafness in mice

Several clinical studies have reported that hearing loss is correlated with autism in children. However, little is known about the underlying mechanism between hearing loss and autism. p21-activated kinases (PAKs) are a family of serine/threonine kinases that can be activated by multiple signaling molecules, particularly the Rho family of small GTPases. Previous studies have shown that Pak1 mutations are associated with autism. In the present study, we take advantage of Pak1 knockout (Pak1^-/-) mice to investigate the role of PAK1 in hearing function. We find that PAK1 is highly expressed in the postnatal mouse cochlea and that PAK1 deficiency leads to hair cell (HC) apoptosis and severe hearing loss. Further investigation indicates that PAK1 deficiency downregulates the phosphorylation of cofilin and ezrin-radixin-moesin and the expression of βII-spectrin, which further decreases the HC synapse density in the basal turn of cochlea and disorganized the HC stereocilia in all three turns of cochlea in Pak1^-/- mice. Overall, our work demonstrates that the autism-related gene Pak1 plays a crucial role in hearing function. As the first candidate gene linking autism and hearing loss, Pak1 may serve as a potential target for the clinical diagnosis of autism-related hearing loss.

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

Background

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

Results

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

Conclusions

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

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

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

Low-Intensity Ultrasound Causes Direct Excitation of Auditory Cortical Neurons

Cochlear implantation is the first-line treatment for severe and profound hearing loss in children and adults. However, deaf patients with cochlear malformations or with cochlear nerve deficiencies are ineligible for cochlear implants. Meanwhile, the limited spatial selectivity and high risk of invasive craniotomy restrict the wide application of auditory brainstem implants. A noninvasive alternative strategy for safe and effective neuronal stimulation is urgently needed to address this issue. Because of its advantage in neural modulation over electrical stimulation, low-intensity ultrasound (US) is considered a safe modality for eliciting neural activity in the central auditory system. Although the neural modulation ability of low-intensity US has been demonstrated in the human primary somatosensory cortex and primary visual cortex, whether low-intensity US can directly activate auditory cortical neurons is still a topic of debate. To clarify the direct effects on auditory neurons, in the present study, we employed low-intensity US to stimulate auditory cortical neurons in vitro. Our data show that both low-frequency (0.8 MHz) and high-frequency (>27 MHz) US stimulation can elicit the inward current and action potentials in cultured neurons. c-Fos staining results indicate that low-intensity US is efficient for stimulating most neurons. Our study suggests that low-intensity US can excite auditory cortical neurons directly, implying that US-induced neural modulation can be a potential approach for activating the auditory cortex of deaf patients.

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

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

Mitochondrial Dysfunction and Sirtuins: Important Targets in Hearing Loss

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

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

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

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

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

CCDC154 Mutant Caused Abnormal Remodeling of the Otic Capsule and Hearing Loss in Mice

Osteopetrosis is a rare inherited bone disease characterized by dysfunction of osteoclasts, causing impaired bone resorption and remodeling, which ultimately leads to increased bone mass and density. Hearing loss is one of the most common complications of osteopetrosis. However, the etiology and pathogenesis of auditory damage still need to be explored. In this study, we found that a spontaneous mutation of coiled-coil domain-containing 154 (CCDC154) gene, a new osteopetrosis-related gene, induced congenital deafness in mice. Homozygous mutant mice showed moderate to severe hearing loss, while heterozygous or wild-type (WT) littermates displayed normal hearing. Pathological observation showed that abnormal bony remodeling of the otic capsule, characterized by increased vascularization and multiple cavitary lesions, was found in homozygous mutant mice. Normal structure of the organ of Corti and no substantial hair cell or spiral ganglion neuron loss was observed in homozygous mutant mice. Our results indicate that mutation of the osteopetrosis-related gene CCDC154 can induce syndromic hereditary deafness in mice. Bony remodeling disorders of the auditory ossicles and otic capsule are involved in the hearing loss caused by CDCC154 mutation.

Autophagy impairment as a key feature for acetaminophen-induced ototoxicity

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

Altered Brain Activity and Functional Connectivity in Unilateral Sudden Sensorineural Hearing Loss

Background

Sudden sensorineural hearing loss (SSNHL) is an otologic emergency and could lead to social difficulties and mental disorders in some patients. Although many studies have analyzed altered brain function in populations with hearing loss, little information is available about patients with idiopathic SSNHL. This study is aimed at investigating brain functional changes in SSNHL via functional magnetic resonance imaging (fMRI).

Methods

Thirty-six patients with SSNHL and thirty well-matched normal hearing individuals underwent resting-state fMRI. Amplitude of low-frequency fluctuation (ALFF), fractional ALFF (fALFF), and functional connectivity (FC) values were calculated.

Results

In the SSNHL patients, ALFF and fALFF were significantly increased in the bilateral putamen but decreased in the right calcarine cortex, right middle temporal gyrus (MTG), and right precentral gyrus. Widespread increases in FC were observed between brain regions, mainly including the bilateral auditory cortex, bilateral visual cortex, left striatum, left angular gyrus (AG), bilateral precuneus, and bilateral limbic lobes in patients with SSNHL. No decreased FC was observed.

Conclusion

SSNHL causes functional alterations in brain regions, mainly in the striatum, auditory cortex, visual cortex, MTG, AG, precuneus, and limbic lobes within the acute period of hearing loss.

Hsp70/Bmi1-FoxO1-SOD Signaling Pathway Contributes to the Protective Effect of Sound Conditioning against Acute Acoustic Trauma in a Rat Model

Sound conditioning (SC) is defined as “toughening” to lower levels of sound over time, which reduces a subsequent noise-induced threshold shift. Although the protective effect of SC in mammals is generally understood, the exact mechanisms involved have not yet been elucidated. To confirm the protective effect of SC against noise exposure (NE) and the stress-related signaling pathway of its rescue, we observed target molecule changes caused by SC of low frequency prior to NE as well as histology analysis in vivo and verified the suggested mechanisms in SGNs in vitro. Further, we investigated the potential role of Hsp70 and Bmi1 in SC by targeting SOD1 and SOD2 which are regulated by the FoxO1 signaling pathway based on mitochondrial function and reactive oxygen species (ROS) levels. Finally, we sought to identify the possible molecular mechanisms associated with the beneficial effects of SC against noise-induced trauma. Data from the rat model were evaluated by western blot, immunofluorescence, and RT-PCR. The results revealed that SC upregulated Hsp70, Bmi1, FoxO1, SOD1, and SOD2 expression in spiral ganglion neurons (SGNs). Moreover, the auditory brainstem responses (ABRs) and electron microscopy revealed that SC could protect against acute acoustic trauma (AAT) based on a significant reduction of hearing impairment and visible reduction in outer hair cell loss as well as ultrastructural changes in OHCs and SGNs. Collectively, these results suggested that the contribution of Bmi1 toward decreased sensitivity to noise-induced trauma following SC was triggered by Hsp70 induction and associated with enhancement of the antioxidant system and decreased mitochondrial superoxide accumulation. This contribution of Bmi1 was achieved by direct targeting of SOD1 and SOD2, which was regulated by FoxO1. Therefore, the Hsp70/Bmi1-FoxO1-SOD signaling pathway might contribute to the protective effect of SC against AAT in a rat model.

Cisplatin-Induced Stria Vascularis Damage Is Associated with Inflammation and Fibrosis

The stria vascularis (SV) generates the endocochlear potential (EP) in the inner ear and is necessary for proper hair cell (HC) mechanotransduction and hearing. Cell junctions are indispensable for the establishment of compositionally distinct fluid compartments in the inner ear. Ototoxic drug cisplatin can damage SV and cause sensorineural hearing loss; however, the underlying mechanisms behind such injury are unclear. In this study, after the intraperitoneal injection of cisplatin (3 mg/kg/day for 7 days) in mice, we determined the auditory function by EP recording and auditory brainstem response (ABR) analysis, observed the ultrastructure of SV by transmission electron microscopy (TEM), and examined the expression and distribution of cell junction proteins by western blot, PCR, and immunofluorescence staining. We discovered that the EP was significantly reduced while ABR thresholds were significantly elevated in cisplatin-treated mice; cisplatin induced ultrastructural changes in marginal cells (MCs), endothelial cells (ECs), pericytes, etc. We found that cisplatin insulted auditory function not only by reducing the expression of zonula occludens protein-1 (ZO-1) in MCs of the SV but also by decreasing the expression of connexin 26 (Cx26) and connexin 43 (Cx43) in MCs and basal cells (BCs). More importantly, cisplatin induced activations of perivascular-resident macrophage-like melanocytes (PVM/Ms) and interleukin-1beta (IL-1β) as well as increased expressions of profibrotic proteins such as laminin and collagen IV in SV. Thus, our results firstly showed that cisplatin induced fibrosis, inflammation, and the complex expression change of cell junctions in SV.

The Influence of Cochlear Implant-Based Electric Stimulation on the Electrophysiological Characteristics of Cultured Spiral Ganglion Neurons

Background

Cochlear implant-based electrical stimulation may be an important reason to induce the residual hearing loss after cochlear implantation. In our previous study, we found that charge-balanced biphasic electrical stimulation inhibited the neurite growth of spiral ganglion neurons (SGNs) and decreased Schwann cell density in vitro. In this study, we want to know whether cochlear implant-based electrical stimulation can induce the change of electrical activity in cultured SGNs.

Methods

Spiral ganglion neuron electrical stimulation in vitro model is established using the devices delivering cochlear implant-based electrical stimulation. After 48 h treatment by 50 μA or 100 μA electrical stimulation, the action potential (AP) and voltage depended calcium current (I Ca) of SGNs are recorded using whole-cell electrophysiological method.

Results

The results show that the I Ca of SGNs is decreased significantly in 50 μA and 100 μA electrical stimulation groups. The reversal potential of I Ca is nearly +80 mV in control SGN, but the reversal potential decreases to +50 mV in 50 μA and 100 μA electrical stimulation groups. Interestingly, the AP amplitude, the AP latency, and the AP duration of SGNs have no statistically significant differences in all three groups.

Conclusion

Our study suggests cochlear implant-based electrical stimulation only significantly inhibit the I Ca of cultured SGNs but has no effect on the firing of AP, and the relation of I Ca inhibition and SGN damage induced by electrical stimulation and its mechanism needs to be further studied.

Cochlear Implantation in a Patient with a Novel POU3F4 Mutation and Incomplete Partition Type-III Malformation

Aims

This study is aimed at (1) analyzing the clinical manifestations and genetic features of a novel POU3F4 mutation in a nonsyndromic X-linked recessive hearing loss family and (2) reporting the outcomes of cochlear implantation in a patient with this mutation.

Methods

A patient who was diagnosed as the IP-III malformation underwent cochlear implantation in our hospital. The genetic analysis was conducted in his family, including the whole-exome sequencing combined with Sanger sequencing and bioinformatic analysis. Clinical features, preoperative auditory and speech performances, and postoperative outcomes of cochlear implant (CI) were assessed on the proband and his family.

Results

A novel variant c.400_401insACTC (p.Q136LfsX58) in the POU3F4 gene was detected in the family, which was cosegregated with the hearing loss. This variant was absent in 200 normal-hearing persons. The phylogenetic analysis and structure modeling of Pou3f4 protein further confirmed that the novel mutation was pathogenic. The proband underwent cochlear implantation on the right ear at four years old and gained greatly auditory and speech improvement. However, the benefits of the CI declined about three and a half years postoperation. Though the right ear had been reimplanted, the outcomes were still worse than before.

Conclusion

A novel frame shift variant c.400_401insACTC (p.Q136LfsX58) in the POU3F4 gene was identified in a Chinese family with X-linked inheritance hearing loss. A patient with this mutation and IP-III malformation could get good benefits from CI. However, the outcomes of the cochlear implantation might decline as the patient grows old.

Targeted Next-Generation Sequencing Identifies Separate Causes of Hearing Loss in One Deaf Family and Variable Clinical Manifestations for the p.R161C Mutation in SOX10

Hearing loss is the most common sensory deficit in humans. Identifying the genetic cause and genotype-phenotype correlation of hearing loss is sometimes challenging due to extensive clinical and genetic heterogeneity. In this study, we applied targeted next-generation sequencing (NGS) to resolve the genetic etiology of hearing loss in a Chinese Han family with multiple affected family members. Targeted sequencing of 415 deafness-related genes identified the heterozygous c.481C>T (p.R161C) mutation in SOX10 and the homozygous c.235delC (p.L79Cfs∗3) mutation in GJB2 as separate pathogenic mutations in distinct affected family members. The SOX10 c.481C>T (p.R161C) mutation has been previously reported in a Caucasian patient with Kallmann syndrome that features congenital hypogonadotropic hypogonadism with anosmia. In contrast, family members carrying the same p.R161C mutation in this study had variable Waardenburg syndrome-associated phenotypes (hearing loss and/or hair hypopigmentation) without olfactory or reproductive anomalies. Our results highlight the importance of applying comprehensive diagnostic approaches such as NGS in molecular diagnosis of hearing loss and show that the p.R161C mutation in SOX10 may be associated with a wide range of variable clinical manifestations.

Atrial Natriuretic Peptide Improves Neurite Outgrowth from Spiral Ganglion Neurons In Vitro through a cGMP-Dependent Manner

The spiral ganglion neurons (SGNs) are the primary afferent neurons in the spiral ganglion (SG), while their degeneration or loss would cause sensorineural hearing loss. As a cardiac-derived hormone, atrial natriuretic peptide (ANP) plays a critical role in cardiovascular homeostasis through binding to its functional receptors (NPR-A and NPR-C). ANP and its receptors are widely expressed in the mammalian nervous system where they could be implicated in the regulation of multiple neural functions. Although previous studies have provided direct evidence for the presence of ANP and its functional receptors in the inner ear, their presence within the cochlear SG and their regulatory roles during auditory neurotransmission and development remain largely unknown. Based on our previous findings, we investigated the expression patterns of ANP and its receptors in the cochlear SG and dissociated SGNs and determined the influence of ANP on neurite outgrowth in vitro by using organotypic SG explants and dissociated SGN cultures from postnatal rats. We have demonstrated that ANP and its receptors are expressed in neurons within the cochlear SG of postnatal rat, while ANP may promote neurite outgrowth of SGNs via the NPR-A/cGMP/PKG pathway in a dose-dependent manner. These results indicate that ANP would play a role in normal neuritogenesis of SGN during cochlear development and represents a potential therapeutic candidate to enhance regeneration and regrowth of SGN neurites.

Differences in Clinical Characteristics and Brain Activity between Patients with Low- and High-Frequency Tinnitus

This study was aimed at delineating and comparing differences in clinical characteristics and brain activity between patients with low- and high-frequency tinnitus (LFT and HFT, respectively) using high-density electroencephalography (EEG). This study enrolled 3217 patients with subjective tinnitus who were divided into LFT (frequency < 4000 Hz) and HFT (≥4000 Hz) groups. Data regarding medical history, Tinnitus Handicap Inventory, tinnitus matching, and hearing threshold were collected from all patients. Twenty tinnitus patients and 20 volunteers were subjected to 256-channel EEG, and neurophysiological differences were evaluated using standardized low-resolution brain electromagnetic tomography (sLORETA) source-localized EEG recordings. Significant differences in sex (p < 0.001), age (p = 0.022), laterality (p < 0.001), intensity (p < 0.001), tinnitus type (p < 0.001), persistent tinnitus (p = 0.04), average threshold (p < 0.001), and hearing loss (p = 0.028) were observed between LFT and HFT groups. The tinnitus pitch only appeared to be correlated with the threshold of the worst hearing loss in the HFT group. Compared with the controls, the LFT group exhibited increased gamma power (p < 0.05), predominantly in the posterior cingulate cortex (PCC, BA31), whereas the HFT group had significantly decreased alpha1 power (p < 0.05) in the angular gyrus (BA39) and auditory association cortex (BA22). Higher gamma linear connectivity between right BA39 and right BA41 was observed in the HFT group relative to controls (t = 3.637, p = 0.027). Significant changes associated with increased gamma in the LFT group and decreased alpha1 in the HFT group indicate that tinnitus pitch is crucial for matching between the tinnitus and control groups. Differences of band frequency energy in brain activity levels may contribute to the clinical characteristics and internal tinnitus “spectrum” differences.

Stem Cell-Based Therapeutic Approaches to Restore Sensorineural Hearing Loss in Mammals

The hair cells that reside in the cochlear sensory epithelium are the fundamental sensory structures responsible for understanding the mechanical sound waves evoked in the environment. The intense damage to these sensory structures may result in permanent hearing loss. The present strategies to rehabilitate the hearing function include either hearing aids or cochlear implants that may recover the hearing capability of deaf patients to a limited extent. Therefore, much attention has been paid on developing regenerative therapies to regenerate/replace the lost hair cells to treat the damaged cochlear sensory epithelium. The stem cell therapy is a promising approach to develop the functional hair cells and neuronal cells from endogenous and exogenous stem cell pool to recover hearing loss. In this review, we specifically discuss the potential of different kinds of stem cells that hold the potential to restore sensorineural hearing loss in mammals and comprehensively explain the current therapeutic applications of stem cells in both the human and mouse inner ear to regenerate/replace the lost hair cells and spiral ganglion neurons.