Therapeutic effect of intraperitoneal dexamethasone on noise-induced permanent threshold shift in mice model.

The purpose of the study was to which investigate whether dexamethasone, which has anti-inflammatory and immune response suppression roles, could treat noise-induced hearing loss caused by damage to hair cells in the cochlea. The experiment used 8-week-old CBA mice exposed to white noise at an intensity of 110 dB SPL for 2 h, with hearing loss confirmed by the auditory brainstem response test. Dexamethasone was administered by intraperitoneal injection for 5 days, and the therapeutic effect was investigated for 3 weeks. The experimental groups were 3 mg/kg of dexamethasone (3 mpk) and 10 mg/kg of dexamethasone (10 mpk), and the control group was a saline-administered group. The results showed that compared to the control group, the hearing threshold value was recovered by 10 dB SPL compared to the saline group from the 14th day in the 3 mpk group. In the 10 mpk group, thresholds were recovered from the 7th day compared to the saline group. This difference was similar at 4 kHz, and in the case of the 10 mpk group, the threshold was recovered by 20 dB SPL compared to the saline group. The study also confirmed the restoration of nerve cell activity and showed a recovery effect of about 20 µV in the amplitude value change in the 10 mpk group. In conclusion, the study suggests that dexamethasone has a therapeutic effect for noise-induced hearing loss by increasing the activity of nerve cells and showing a recovery effect from hair cells damaged by noise.

A nonsense TMEM43 variant leads to disruption of connexin-linked function and autosomal dominant auditory neuropathy spectrum disorder.

Genes that are primarily expressed in cochlear glia-like supporting cells (GLSs) have not been clearly associated with progressive deafness. Herein, we present a deafness locus mapped to chromosome 3p25.1 and an auditory neuropathy spectrum disorder (ANSD) gene, TMEM43, mainly expressed in GLSs. We identify p.(Arg372Ter) of TMEM43 by linkage analysis and exome sequencing in two large Asian families segregating ANSD, which is characterized by inability to discriminate speech despite preserved sensitivity to sound. The knock-in mouse with the p.(Arg372Ter) variant recapitulates a progressive hearing loss with histological abnormalities in GLSs. Mechanistically, TMEM43 interacts with the Connexin26 and Connexin30 gap junction channels, disrupting the passive conductance current in GLSs in a dominant-negative fashion when the p.(Arg372Ter) variant is introduced. Based on these mechanistic insights, cochlear implant was performed on three subjects, and speech discrimination was successfully restored. Our study highlights a pathological role of cochlear GLSs by identifying a deafness gene and its causal relationship with ANSD.

Consensus Statements on the Definition, Classification, and Diagnostic Tests for Tinnitus: A Delphi Study Conducted by the Korean Tinnitus Study Group.

BACKGROUND: Tinnitus is a bothersome condition associated with various symptoms. However, the mechanisms of tinnitus are still uncertain, and a standardized assessment of the diagnostic criteria for tinnitus is required. We aimed to reach a consensus on diagnosing tinnitus with professional experts by conducting a Delphi study with systematic review of the literature. METHODS: Twenty-six experts in managing tinnitus in Korea were recruited, and a two-round modified Delphi study was performed online. The experts evaluated the level of agreement of potential criteria for tinnitus using a scale of 1-9. After the survey, a consensus meeting was held to establish agreement on the results obtained from the Delphi process. Consensus was defined when over 70% of the participants scored 7-9 (agreement) and fewer than 15% scored 1-3 (disagreement). To analyze the responses of the Delphi survey, the content validity ratio and Kendall's coefficient of concordance were evaluated. RESULTS: Consensus was reached for 22 of the 38 statements. For the definition of tinnitus, 10 out of 17 statements reached consensus, with three statements achieving complete agreement including; 1) Tinnitus is a conscious perception of an auditory sensation in the absence of a corresponding external stimulus, 2) Tinnitus can affect one's quality of life, and 3) Tinnitus can be associated with hearing disorders including sensorineural hearing loss, vestibular schwannoma, Meniere's disease, otosclerosis, and others. For the classification of tinnitus, 11 out of 18 statements reached consensus. The participants highly agreed with statements such as; 1) Vascular origin is expected in pulse-synchronous tinnitus, and 2) Tinnitus can be divided into acute or chronic tinnitus. Among three statements on the diagnostic tests for tinnitus only Statement 3, "There are no reliable biomarkers for sensory or emotional factors of tinnitus." reached consensus. All participants agreed to perform pure-tone audiometry and tinnitus questionnaires, including the Tinnitus Handicap Inventory and Tinnitus Questionnaire. CONCLUSION: We used a modified Delphi method to establish a consensus-based definition, a classification, and diagnostic tests for tinnitus. The expert panel reached agreement for several statements, with a high level of consensus. This may provide practical information for clinicians in managing tinnitus.

Tinnitus reduction after active bone-conduction implantation in patients with single-sided deafness: a prospective multicenter study.

PURPOSE: Single-sided deafness (SSD) presents significant challenges for patients, including compromised sound localization, reduced speech recognition, and often, tinnitus. These issues are typically addressed using interventions such as cochlear implantation (CI) and bone conduction implant (BCI). However, evidence regarding the efficacy of BCI in reducing tinnitus in SSD patients remains limited. This study explored the ability of a novel active transcutaneous BCI (Bonebridge BCI602) to alleviate tinnitus in SSD patients. STUDY DESIGN: Prospective cohort multicenter study. SETTING: Tertiary referral hospitals. METHODS: A prospective multicenter study of 30 SSD patients was conducted. The patients were divided into two groups: those with (n = 19) and without (n = 11) tinnitus. Audiometric assessments, subjective questionnaires including the Abbreviated Profile of Hearing Aid Benefit (APHAB) and the Bern Benefit in Single-Sided Deafness (BBSS), and tinnitus evaluations with the Tinnitus Handicap Inventory (THI) and tinnitogram were conducted before and after BCI surgery. RESULTS: THI scores after surgery were significantly reduced in SSD patients with tinnitus. Subjective satisfaction improved in both the tinnitus and non-tinnitus groups; however, the former group exhibited a significantly greater improvement in the APHAB questionnaire score. According to tinnitograms, the loudness of tinnitus decreased, particularly in patients with ipsilateral tinnitus. Patients with residual hearing had greater reductions in their THI scores. However, three patients without residual hearing had a relative worsening of tinnitus after surgery. CONCLUSION: The Bonebridge BCI602 effectively reduced tinnitus in SSD patients, particularly in those with residual hearing. Subjective satisfaction improved in both the tinnitus and non-tinnitus groups. These findings demonstrate the therapeutic potential of BCI for managing SSD and associated tinnitus.

Clinical outcomes of otogenic skull base osteomyelitis.

PURPOSE: Skull base osteomyelitis (SBO) is an uncommon and a potentially life-threatening condition if not promptly recognized and properly treated. The aim of our study was to present a 32-case series of patients diagnosed with SBO at a single center. METHODS: In this retrospective study, we reviewed the data of patients diagnosed with otogenic SBO between January 2011 and January 2020. 32 patients were enrolled in the study. SBO diagnosis was based on a combination of symptoms and physical examination, bone scan, brain magnetic resonance imaging, and pathologic examination findings. The following clinical data were collected during the follow-up period: types of antibiotics used, duration of antibiotic treatment, C-reactive protein level, presence of disease control, duration from the onset of symptoms to diagnosis, and patient survival. RESULTS: The mean follow-up period was 11 (1-110) months. The mean duration of antibiotic treatment was 115 (19-223) days. The mean C-reactive protein levels at the time of diagnosis and at the endpoint of follow-up were 3.05 (0.56-18.31) and 0.21 (0.03-33.61) mg/dL, respectively (P < 0.001). Disease control rate was 34.9% at 1-year and 83.7% at 5-year follow-up. Patient survival rate was 90.6% at 1- and 3-year follow-ups. At the endpoint of follow-up, three patients died. The mean durations from the onset of symptoms to diagnosis were 50 (5-360) and 90 (30-480) days in patients with the controlled disease and in those with the uncontrolled disease, respectively, at the endpoint of follow-up (P = 0.043). CONCLUSION: Comprehensive assessment and aggressive treatment of patients exhibiting symptoms suggestive of SBO would help in the rapid diagnosis of otogenic SBO, resulting in an improvement in prognosis.

Red cell distribution width is associated with hearing impairment in chronic kidney disease population: a retrospective cross-sectional study.

PURPOSE: Previous studies have shown that inflammatory markers are associated with hearing impairment in participants with inflammatory diseases. Therefore, screening for inflammatory status may have value in predicting the risk of hearing loss (HL) in participants with underlying inflammation. Therefore, red cell distribution width (RDW), an indirect indicator of inflammatory status, was used. The aim of the present study was to evaluate the clinical association between RDW and hearing impairment in a Korean population with chronic kidney disease (CKD). METHODS: In this cross sectional study, a total of 461 participants with estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m2 were included. Participants were divided into three tertiles based on their RDW values. The threshold values at 0.5, 1, and 2 kHz were averaged to obtain the Low/Mid-Freq, and the values at 3, 4, and 6 kHz were averaged to obtain the High-Freq. The average hearing threshold (AHT) was calculated as the pure-tone average of the thresholds at 0.5, 1, 2, and 3 kHz. HL was defined as an AHT of > 40 dB. RESULTS: The numbers of participants in the Low, Middle, and High tertiles were 172, 154, and 135, respectively. The AUROCs of RDW and hs-CRP for HL were 0.644 and 0.522, respectively. In the multivariate analysis, the Low/Mid-Freq, High-Freq, and AHT values were lowest in the participants in the Low tertile compared with those in the Middle or High tertiles Multivariate logistic regression analyses showed that participants in the High tertile exhibited 2.32- and 1.78-fold higher odds for HL compared to those of the Low and Middle tertiles, respectively. There were positive associations between RDW and AHT values. CONCLUSION: High RDW was associated with increased odds of hearing impairment in the Korean population with CKD.

Modified U1 snRNA and antisense oligonucleotides rescue splice mutations in SLC26A4 that cause hereditary hearing loss.

One of most important factors for messenger RNA (mRNA) transcription is the spliceosomal component U1 small nuclear RNA (snRNA), which recognizes 5' splicing donor sites at specific regions in pre-mRNA. Mutations in these sites disrupt U1 snRNA binding and cause abnormal splicing. In this study, we investigated mutations at splice sites in SLC26A4 (HGNC 8818), one of the major causative genes of hearing loss, which may result in the synthesis of abnormal pendrin, the channel protein encoded by the gene. Seventeen SLC26A4 variants with mutations in the U1 snRNA binding sites were assessed by minigene splicing assays, and 11 were found to result in abnormal splicing. Interestingly, eight of the 11 pathogenic mutations were intronic, suggesting the importance of conserved sequences at the intronic splice site. The application of modified U1 snRNA effectively rescued the abnormal splicing for most of these mutations. Although three were cryptic mutations, they were rescued by cotransfection of modified U1 snRNA and modified antisense oligonucleotides. Our results demonstrate the important role of snRNA in SLC26A4 mutations, suggesting the therapeutic potential of modified U1 snRNA and antisense oligonucleotides for neutralizing the pathogenic effect of the splice-site mutations that may result in hearing loss.

Effective PEI-mediated delivery of CRISPR-Cas9 complex for targeted gene therapy.

The-state-of-art CRISPR/Cas9 is one of the most powerful among the approaches being developed to rescue fundamental causes of gene-based inheritable diseases. Several strategies for delivering such genome editing materials have been developed, but the safety, efficacy over time, cost of production, and gene size limitations are still under debate and must be addressed to further improve applications. In this study, we evaluated branched forms of the polyethylenimine (PEI) - branched PEI 25 kDa (BPEI-25K) - and found that it could efficiently deliver CRISPR/Cas9 plasmids. Plasmid DNA expressing both guide RNA and Cas9 to target the Slc26a4 locus was successfully delivered into Neuro2a cells and meditated genome editing within the targeted locus. Our results demonstrated that BPEI-25K is a promising non-viral vector to deliver the CRISPR/Cas9 system in vitro to mediate targeted gene therapy, and these findings contribute to an understanding of CRISPR/Cas9 delivery that may enable development of successful in vivo techniques.

Association between sarcopenia and hearing thresholds in postmenopausal women.

Background: Given the association between metabolic disturbance and sarcopenia, sarcopenia may be intrinsically associated with the prevalence of HL. However, few studies describe the association between sarcopenia and HL. The aim of this study was to evaluate the clinical association between sarcopenia and HL in postmenopausal Korean women. Patients and Methods: A total of 4,038 women were ultimately included in this study. All participants were postmenopausal. Participants were divided into two groups based on criteria from the Foundation for the National Institute of Health Sarcopenia Project: a normal group (sarcopenia index ≥ 0.512) and a sarcopenia group (sarcopenia index < 0.512). Low-frequency (Low-Freq), mid-frequency (Mid-Freq), and high-frequency (High-Freq) values were obtained. The average hearing threshold (AHT) was calculated as the pure tone average at the 4 frequencies of 0.5 kHz, 1 kHz, 2 kHz, and 3 kHz. Mild HL was as an AHT of 24 to 40 dB; moderate-to-profound HL was defined as an AHT of 40 dB or greater. Results: Of the 4,038 participants, 272 (6.7%) were allocated to the sarcopenia group, leaving 3,766 (93.3%) in the normal group. The groups differed significantly in terms of having hypertension (775 [20.6%] vs. 108 [39.7%]; P < 0.001) or metabolic syndrome (817 [21.7%] vs. 110 [40.4%]; P < 0.001) in the normal and sarcopenia groups, respectively. Visceral fat area (cm3) in the normal and sarcopenia groups was 99.0 ± 21.9 cm3 and 117.0 ± 21.8 cm3 , respectively (P < 0.001). The hsCRP level was higher in the sarcopenia group than in the normal group. For univariate and multivariate analyses, all 4 hearing thresholds were higher in the sarcopenia group than in the normal group. In addition, linear regression analyses showed Low-Freq, Mid-Freq, and High-Freq to be inversely correlated with the sarcopenia index. The unadjusted OR for mild HL was 2.692 (95% CI, 1.963-3.692; P < 0.001) in the sarcopenia group relative to the normal group, with an adjusted OR of 1.584 (95% CI, 1.131-2.217; P = 0.007). The unadjusted OR for moderate-to-profound HL in the sarcopenia group relative to the normal group was 6.246 (95% CI, 4.530-8.612; P < 0.001); the adjusted OR was 2.667 (95% CI, 1.866-3.812; P < 0.001). Conclusion: Sarcopenia may be associated with HL. It may be beneficial to perform screening audiometry in patients with sarcopenia.

Methionine sulfoxide reductase B3 deficiency causes hearing loss due to stereocilia degeneration and apoptotic cell death in cochlear hair cells.

Methionine sulfoxide reductase B3 (MsrB3) is a protein repair enzyme that specifically reduces methionine-R-sulfoxide to methionine. A recent genetic study showed that the MSRB3 gene is associated with autosomal recessive hearing loss in human deafness DFNB74. However, the precise role of MSRB3 in the auditory system and the pathogenesis of hearing loss have not yet been determined. This work is the first to generate MsrB3 knockout mice to elucidate the possible pathological mechanisms of hearing loss observed in DFNB74 patients. We found that homozygous MsrB3(-/-) mice were profoundly deaf and had largely unaffected vestibular function, whereas heterozygous MsrB3(+/-) mice exhibited normal hearing similar to that of wild-type mice. The MsrB3 protein is expressed in the sensory epithelia of the cochlear and vestibular tissues, beginning at E15.5 and E13.5, respectively. Interestingly, MsrB3 is densely localized at the base of stereocilia on the apical surface of auditory hair cells. MsrB3 deficiency led to progressive degeneration of stereociliary bundles starting at P8, followed by a loss of hair cells, resulting in profound deafness in MsrB3(-/-) mice. The hair cell loss appeared to be mediated by apoptotic cell death, which was measured using TUNEL and caspase 3 immunocytochemistry. Taken together, our data suggest that MsrB3 plays an essential role in maintaining the integrity of hair cells, possibly explaining the pathogenesis of DFNB74 deafness in humans caused by MSRB3 deficiency.

The pathological effects of connexin 26 variants related to hearing loss by in silico and in vitro analysis.

Gap junctions (GJs) are intercellular channels associated with cell-cell communication. Connexin 26 (Cx26) encoded by the GJB2 gene forms GJs of the inner ear, and mutations of GJB2 cause congenital hearing loss that can be syndromic or non-syndromic. It is difficult to predict pathogenic effects using only genetic analysis. Using ionic and biochemical coupling tests, we evaluated the pathogenic effects of Cx26 variants using computational analyses to predict structural abnormalities. For seven out of ten variants, we predicted the variation would result in a loss of GJ function, whereas the others would completely fail to form GJs. Functional studies demonstrated that, although all variants were able to function normally as hetero-oligomeric GJ channels, six variants (p.E47K, p.E47Q, p.H100L, p.H100Y, p.R127L, and p.M195L) did not function normally as homo-oligomeric GJ channels. Interestingly, GJs composed of the Cx26 variant p.R127H were able to function normally, even as homo-oligomeric GJ channels. This study demonstrates the particular location and property of an amino acid are more important mainly than the domain where they belong in the formation and function of GJ, and will provide information that is useful for the accurate diagnosis of hearing loss.

Screening of the SLC17A8 gene as a causative factor for autosomal dominant non-syndromic hearing loss in Koreans.

BACKGROUND: One of the causes of sensorineural hearing loss (SNHL) is degeneration of the inner hair cells in the organ of Corti in the cochlea. The SLC17A8 (solute carrier family 17, member 8) gene encodes vesicular glutamate transporter 3 (VGLUT3), and among its isoforms (VGLUT1-3), only VGLUT3 is expressed selectively in the inner hair cells (IHCs). VGLUT3 transports the neurotransmitter glutamate into the synaptic vesicles of the IHCs. Mutation of the SLC17A8 gene is reported to be associated with DFNA25 (deafness, autosomal dominant 25), an autosomal dominant non-syndromic hearing loss (ADNSHL) in humans. METHODS: In this study, we performed a genetic analysis of 87 unrelated Korean patients with ADNSHL to determine whether the SLC17A8 gene affects hearing ability in the Korean population. RESULTS: We found a novel heterozygous frameshift mutation, 2 non-synonymous variations, and a synonymous variation. The novel frameshift mutation, p.M206Nfs*4, in which methionine is changed to asparagine at amino acid position 206, resulted in a termination codon at amino acid position 209. This alteration is predicted to encode a truncated protein lacking transmembrane domains 5 to 12. This mutation is located in a highly conserved region in VGLUT3 across multiple amino acid alignments in different vertebrate species, but it was not detected in 100 unrelated controls who had normal hearing ability. The results from our study suggest that the p.M206Nfs*4 mutation in the SLC17A8 gene is likely a pathogenic mutation that causes ADNSHL. CONCLUSION: Our findings can facilitate the prediction of the primary cause of ADNSHL in Korean patients.

Pannexin 3 is required for normal progression of skeletal development in vertebrates.

The vertebrate skeletal system has various functions, including support, movement, protection, and the production of blood cells. The development of cartilage and bones, the core components of the skeletal system, is mediated by systematic inter- and intracellular communication among multiple signaling pathways in differentiating progenitors and the surrounding tissues. Recently, Pannexin (Panx) 3 has been shown to play important roles in bone development in vitro by mediating multiple signaling pathways, although its roles in vivo have not been explored. In this study, we generated and analyzed Panx3 knockout mice and examined the skeletal phenotypes of panx3 morphant zebrafish. Panx3(-/-) embryos exhibited delays in hypertrophic chondrocyte differentiation and osteoblast differentiation as well as the initiation of mineralization, resulting in shortened long bones in adulthood. The abnormal progression of hypertrophic chondrogenesis appeared to be associated with the sustained proliferation of chondrocytes, which resulted from increased intracellular cAMP levels. Similarly, osteoblast differentiation and mineralization were delayed in panx3 morphant zebrafish. Taken together, our results provide evidence of the crucial roles of Panx3 in vertebrate skeletal development in vivo.

Dexamethasone Is One of the Factors Minimizing the Inner Ear Damage from Electrode Insertion in Cochlear Implantation.

The aim of this study was to investigate the efficacy of preoperative and intraoperative steroid administration for inner ear protection in cochlear implantation (CI). Nineteen subjects who underwent CI were included in the study, and 10 subjects were enrolled as controls (steroid-administered group, n = 19; control group, n = 10). Dexamethasone (dexamethasone sodium phosphate, 5 mg/ml) was systemically administered preoperatively (1 ml) and topically applied during CI (0.5 ml). The extent of hearing preservation (HP) after CI and the change in the bithermal caloric response were evaluated. Hearing level was calculated using mean thresholds [(250 Hz + 500 Hz + 1,000 Hz + 2,000 Hz)/4]. Preoperative hearing thresholds were similar in the steroid-administered and control groups (100.92 ± 12.60 vs. 103.29 ± 14.39 dB, p = 0.650). The mean thresholds significantly increased in both groups after surgery (108.46 ± 14.08 dB, p = 0.006, for the steroid-administered group; 117.50 ± 6.34 dB, p = 0.027, for the control group), and the difference between the groups was also significant (p = 0.027). The postoperative shift in the hearing thresholds at frequencies of 500 and 1,000 Hz was significant in the steroid-administered group and that at the frequencies of 500, 1,000 and 2,000 Hz was significant in the control group. However, the extent of the shift in hearing threshold levels at each frequency was not significantly different between the groups. Preservation of hearing thresholds was compared between the groups, and there were significantly more subjects with complete and partial HP in the steroid-administered group than in the control group (p = 0.008). The preoperative caloric response was maintained after CI in the steroid-administered group. This study suggests that the perioperative use of a steroid could minimize the inner ear damage after CI.

Visceral Fat Area Determined Using Bioimpedance Analysis Is Associated with Hearing Loss.

BACKGROUND: Visceral fat area (VFA) using bioimpedance analysis (BIA) as a simple analyzer can be used to assess VFA, which may be associated with HL. The aim of the present study was to evaluate the clinical relevance and usefulness of VFA using BIA as a predictor of HL. PATIENTS AND METHODS: In total, 18,415 patients were recruited into our study. VFAs were measured using multi-frequency BIA. VFAs were normalized by body mass index (BMI). Participants were divided into 3 tertiles based on their VFA/BMI for both sexes. For both ears of each participant, the low-frequency (Low-Freq), mid-frequency (Mid-Freq), and high-frequency (High-Freq) values were obtained calculating the pure tone averages at 0.5 and 1 kHz, 2 and 3 kHz, and 4 and 6 kHz, respectively. The average hearing threshold (AHT) was calculated as the pure tone average at the 4 frequencies (i.e., 0.5, 1, 2, and 3 kHz). HL was defined as AHT >40 dB. RESULTS: The VFA/BMI had the greatest AUROC among VFA, BMI, and VFA/BMI in both sexes in this study. In both univariate and multivariate analyses, VFA/BMI tertiles were associated with all 4 hearing thresholds (i.e., Low-Freq, Mid-Freq, High-Freq, and AHT). The 4 hearing thresholds were positively correlated with VFA/BMI as a continuous variable. The odds ratio for HL increased as the VFA/BMI tertile increased. CONCLUSION: VFA/BMI was associated with hearing impairment in the Asian population. The participants with high VFA/BMI should be closely monitored for hearing impairment.

A New Trans-Tympanic Microphone Approach for Fully Implantable Hearing Devices.

Fully implantable hearing devices (FIHDs) have been developed as a new technology to overcome the disadvantages of conventional acoustic hearing aids. The implantable microphones currently used in FIHDs, however, have difficulty achieving high sensitivity to environmental sounds, low sensitivity to body noise, and ease of implantation. In general, implantable microphones may be placed under the skin in the temporal bone region of the skull. In this situation, body noise picked up during mastication and touching can be significant, and the layer of skin and hair can both attenuate and distort sounds. The new approach presently proposed is a microphone implanted at the tympanic membrane. This method increases the microphone's sensitivity by utilizing the pinna's directionally dependent sound collection capabilities and the natural resonances of the ear canal. The sensitivity and insertion loss of this microphone were measured in human cadaveric specimens in the 0.1 to 16 kHz frequency range. In addition, the maximum stable gain due to feedback between the trans-tympanic microphone and a round-window-drive transducer, was measured. The results confirmed in situ high-performance capabilities of the proposed trans-tympanic microphone.

Identification of pathogenic mechanisms of COCH mutations, abolished cochlin secretion, and intracellular aggregate formation: genotype-phenotype correlations in DFNA9 deafness and vestibular disorder.

Mutations in COCH (coagulation factor C homology) cause autosomal-dominant nonsyndromic hearing loss with variable degrees of clinical onset and vestibular malfunction. We selected eight uncharacterized mutations and performed immunocytochemical and Western blot analyses to track cochlin through the secretory pathway. We then performed a comprehensive analysis of clinical information from DFNA9 patients with all 21 known COCH mutations in conjunction with cellular and molecular findings to identify genotype-phenotype correlations. Our studies revealed that five mutants were not secreted into the media: two von Willebrand factor A (vWFA) domain mutants, which were not transported from the endoplasmic reticulum to Golgi complex and formed high-molecular-weight aggregates in cell lysates, and three LCCL domain mutants, which were detected as intracellular dimeric cochlins. Mutant cochlins that were not secreted and accumulated in cells result in earlier age of onset of hearing defects. In addition, individuals with LCCL domain mutations show accompanying vestibular dysfunction, whereas those with vWFA domain mutations exhibit predominantly hearing loss. This is the first report showing failure of mutant cochlin transport through the secretory pathway, abolishment of cochlin secretion, and formation and retention of dimers and large multimeric intracellular aggregates, and high correlation with earlier onset and progression of hearing loss in individuals with these DFNA9-causing mutations.

Evaluation of the pathogenicity of GJB3 and GJB6 variants associated with nonsyndromic hearing loss.

A number of genes responsible for hearing loss are related to ion recycling and homeostasis in the inner ear. Connexins (Cx26 encoded by GJB2, Cx31 encoded by GJB3 and Cx30 encoded by GJB6) are core components of gap junctions in the inner ear. Gap junctions are intercellular communication channels and important factors that are associated with hearing loss. To date, a molecular genetics study of GJB3 and GJB6 as a causative gene for hearing loss has not been performed in Korea. This study was therefore performed to elucidate the genetic characteristics of Korean patients with nonsyndromic sensorineural hearing loss and to determine the pathological mechanism of hearing loss by analyzing the intercellular communication function of Cx30 and Cx31 variants. Sequencing analysis of the GJB3 and GJB6 genes in our population revealed a total of nine variants, including four novel variants in the two genes. Three of the novel variants (Cx31-p.V27M, Cx31-p.V43M and Cx-30-p.I248V) and two previously reported variants (Cx31-p.V84I and Cx30-p.A40V) were selected for functional studies using a pathogenicity prediction program and assessed for whether the mutations were located in a conserved region of the protein. The results of biochemical and ionic coupling tests showed that both the Cx31-p.V27M and Cx31-p.V84I variants did not function normally when each was expressed as a heterozygote with the wild-type Cx31. This study demonstrated that two variants of Cx31 were pathogenic mutations with deleterious effect. This information will be valuable in understanding the pathogenic role of GJB3 and GJB6 mutations associated with hearing loss.

Functional mapping of the auditory tract in rodent tinnitus model using manganese-enhanced magnetic resonance imaging.

Animal models of salicylate-induced tinnitus have demonstrated that salicylate modulates neuronal activity in several brain structures leading to neuronal hyperactivity in auditory and non-auditory brain areas. In addition, these animal tinnitus models indicate that tinnitus can be a perceptual consequence of altered spontaneous neural activity along the auditory pathway. Peripheral and/or central effects of salicylate can account for neuronal activity changes in salicylate-induced tinnitus. Because of this ambiguity, an in vivo imaging study would be able to address the peripheral and/or central involvement of salicylate-induced tinnitus. Therefore, in the present study, we developed a novel manganese-enhanced magnetic resonance imaging (MEMRI) method to map the in vivo functional auditory tract in a salicylate-induced tinnitus animal model by administrating manganese through the round window. We found that acute salicylate-induced tinnitus resulted in higher manganese uptake in the cochlea and in the central auditory structures. Furthermore, serial MRI scans demonstrated that the manganese signal increased in an anterograde fashion from the cochlea to the cochlear nucleus. Therefore, our in vivo MEMRI data suggest that acute salicylate-induced tinnitus is associated with higher spontaneous neural activity both in peripheral and central auditory pathways.

Alpha-lipoic acid protects against cisplatin-induced ototoxicity via the regulation of MAPKs and proinflammatory cytokines.

Cisplatin is an effective antineoplastic drug that is widely used to treat various cancers; however, it causes side effects such as ototoxicity via the induction of apoptosis of hair cells in the cochlea. Alpha-lipoic acid (ALA) has been reported to exert a protective effect against both antibiotic-induced and cisplatin-induced hearing loss. Therefore, this study was conducted to (1) elucidate the mechanism of the protective effects of ALA against cisplatin-induced ototoxicity using in vitro and ex vivo culture systems of HEI-OC1 auditory cells and rat cochlear explants and (2) to gain additional insight into the apoptotic mechanism of cisplatin-induced ototoxicity. ALA pretreatment significantly reduced apoptotic cell death of the inner and outer hair cells in cisplatin-treated organ of Corti explants and attenuated ototoxicity via marked inhibition of the increase in the expression of IL-1ß and IL-6, the phosphorylation of ERK and p38, the degradation of IκBα, the increase in intracellular levels of ROS, and the activation of caspase-3 in cisplatin-treated HEI-OC1 cells. This study represents the first histological evaluation of the organ of Corti following treatment with ALA, and these results indicate that the protective effects of ALA against cisplatin-induced ototoxicity are mediated via the regulation of MAPKs and proinflammatory cytokines.