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Gan NS, Oziębło D, Skarżyński H, Ołdak M. Monogenic Causes of Low-Frequency Non-Syndromic Hearing Loss. Audiol Neurootol 2023; 28:327-337. [PMID: 37121227 DOI: 10.1159/000529464] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 01/23/2023] [Indexed: 05/02/2023] Open
Abstract
BACKGROUND Low-frequency non-syndromic hearing loss (LFNSHL) is a rare form of hearing loss (HL). It is defined as HL at low frequencies (≤2,000 Hz) resulting in a characteristic ascending audiogram. LFNSHL is usually diagnosed postlingually and is progressive, leading to HL affecting other frequencies as well. Sometimes it occurs with tinnitus. Around half of the diagnosed prelingual HL cases have a genetic cause and it is usually inherited in an autosomal recessive mode. Postlingual HL caused by genetic changes generally has an autosomal dominant pattern of inheritance and its incidence remains unknown. SUMMARY To date, only a handful of genes have been found as causing LFNSHL: well-established WFS1 and, reported in some cases, DIAPH1, MYO7A, TNC, and CCDC50 (respectively, responsible for DFNA6/14/38, DFNA1, DFNA11, DFNA56, and DFNA44). In this review, we set out audiological phenotypes, causative genetic changes, and molecular mechanisms leading to the development of LFNSHL. KEY MESSAGES LFNSHL is most commonly caused by pathogenic variants in the WFS1 gene, but it is also important to consider changes in other HL genes, which may result in similar audiological phenotype.
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Affiliation(s)
- Nina Sara Gan
- Department of Genetics, Institute of Physiology and Pathology of Hearing, Warsaw, Poland
| | - Dominika Oziębło
- Department of Genetics, Institute of Physiology and Pathology of Hearing, Warsaw, Poland
| | - Henryk Skarżyński
- Oto-Rhino-Laryngology Surgery Clinic, Institute of Physiology and Pathology of Hearing, Warsaw, Poland
| | - Monika Ołdak
- Department of Genetics, Institute of Physiology and Pathology of Hearing, Warsaw, Poland
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2
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Kim SY, Kim BJ, Oh DY, Han JH, Yi N, Kim NJ, Park MK, Keum C, Seo GH, Choi BY. Improving genetic diagnosis by disease-specific, ACMG/AMP variant interpretation guidelines for hearing loss. Sci Rep 2022; 12:12457. [PMID: 35864128 PMCID: PMC9304357 DOI: 10.1038/s41598-022-16661-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 07/13/2022] [Indexed: 12/29/2022] Open
Abstract
The 2018 Hearing Loss Expert Panel (HL-EP)-specific guidelines specified from the universal 2015 ACMG/AMP guidelines are proposed to be used in genetic HL, which prompted this study. A genetic HL cohort comprising 135 unrelated probands with available exome sequencing data was established. Overall, 169 variants were prioritized as candidates and interpreted using the 2015 ACMG/AMP and 2018 HL-EP guidelines. Changes in rule application and variant classification between the guidelines were compared. The concordance rate of variant classification of each variant between the guidelines was 71.60%, with significant difference. The proportion of pathogenic variants increased from 13.02% (2015) to 29.59% (2018). Variant classifications of autosomal recessive (AR) variants that previously belonged to VUS or likely pathogenic in the 2015 guidelines were changed toward pathogenic in the 2018 guidelines more frequently than those of autosomal dominant variants (29.17% vs. 6.38%, P = 0.005). Stratification of the PM3 and PP1 rules in the 2018 guidelines led to more substantial escalation than that in the 2015 guidelines. We compared the disease-specific guidelines (2018) with the universal guidelines (2015) using real-world data. Owing to the sophistication of case-level data, the HL-specific guidelines have more explicitly classified AR variants toward "likely pathogenic" or "pathogenic", serving as potential references for other recessive genetic diseases.
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Affiliation(s)
- So Young Kim
- grid.410886.30000 0004 0647 3511Department of Otorhinolaryngology-Head and Neck Surgery, CHA Bundang Medical Center, CHA University, Seongnam, South Korea
| | - Bong Jik Kim
- grid.254230.20000 0001 0722 6377Department of Otolaryngology-Head and Neck Surgery, Chungnam National University Sejong Hospital, Chungnam National University College of Medicine, Daejeon, South Korea
| | - Doo Yi Oh
- grid.412480.b0000 0004 0647 3378Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Jin Hee Han
- grid.412480.b0000 0004 0647 3378Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Nayoung Yi
- grid.254230.20000 0001 0722 6377Department of Otolaryngology-Head and Neck Surgery, Chungnam National University Sejong Hospital, Chungnam National University College of Medicine, Daejeon, South Korea ,grid.412480.b0000 0004 0647 3378Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Namju Justin Kim
- grid.412480.b0000 0004 0647 3378Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Bundang Hospital, Seongnam, South Korea ,grid.152326.10000 0001 2264 7217Department of Biological Sciences, Vanderbilt University, Nashville, USA
| | - Moo Kyun Park
- grid.31501.360000 0004 0470 5905Department of Otorhinolaryngology, Seoul National University College of Medicine, Seoul, South Korea
| | | | | | - Byung Yoon Choi
- grid.412480.b0000 0004 0647 3378Department of Otorhinolaryngology-Head and Neck Surgery, Seoul National University Bundang Hospital, Seongnam, South Korea
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3
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Kim YS, Kim Y, Lee SJ, Han JH, Yi N, Yoo HS, Carandang M, Lee SY, Kim BJ, Choi BY. Efficacy of cochlear implants in children with borderline hearing who have already achieved significant language development with hearing aids. PLoS One 2022; 17:e0267898. [PMID: 35648744 PMCID: PMC9159549 DOI: 10.1371/journal.pone.0267898] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 04/18/2022] [Indexed: 11/30/2022] Open
Abstract
There are still debates about timing and effectiveness of cochlear implants (CI) in pediatric subjects with significant residual hearing who do not belong to traditional indication of CI. In this study, we aimed to investigate the outcomes of CI, specifically on improvement of pronunciation, among hearing-impaired children already with a substantial degree of language skills as evaluated by Categories of Auditory Perception (CAP) scores or sentence score. Our cohort comprised pediatric CI recipients from July 2018 through October 2020. Among them, cases with CAP scores of 5 or 6 preoperatively were defined as "borderline cases". We investigated prevalence and etiologies, and compared speech evaluation data preoperatively and postoperatively at three time points (3, 6 and 9-12 months after implantation). Among 86 pediatric CI recipients, 13 subjects (15.12%) had language development that reached CAP scores of 5 or 6 before implantation. Postoperative speech evaluation data 6 months after implantation revealed significant improvement of pronunciation (Urimal Test of Articulation and Phonation scores: UTAP), Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS) and word perception scores, but not of CAP and sentence perception scores. Notably, the significant improvement of pronunciation based on UTAP scores outstripped that of other speech parameters and this continued steadily up to one-year postoperatively. The result of the study serves as evidence for what to expect from cochlear implantation in hearing-impaired children who have already achieved a substantial degree of language development in terms of CAP scores or sentence perception scores, preoperatively.
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Affiliation(s)
- Young Seok Kim
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Yehree Kim
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Seung Jae Lee
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Jin Hee Han
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Nayoung Yi
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
| | - Hyo Soon Yoo
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
- Department of Otorhinolaryngology, Seoul National University Hospital, Seoul, South Korea
| | - Marge Carandang
- Department of Otorhinolaryngology-Head and Neck Surgery, East Avenue Medical Center, Metro Manila, Philippines
| | - Sang-Yeon Lee
- Department of Otorhinolaryngology, Seoul National University Hospital, Seoul, South Korea
| | - Bong Jik Kim
- Department of Otorhinolaryngology, Chungnam National University Sejong Hospital, College of Medicine, Chungnam National University, Daejeon, Korea
| | - Byung Yoon Choi
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea
- Sensory Organ Research Institute, Seoul National University Medical Research Center, Seoul, South Korea
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4
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Chiereghin C, Robusto M, Massa V, Castorina P, Ambrosetti U, Asselta R, Soldà G. Role of Cytoskeletal Diaphanous-Related Formins in Hearing Loss. Cells 2022; 11:cells11111726. [PMID: 35681420 PMCID: PMC9179844 DOI: 10.3390/cells11111726] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 05/16/2022] [Accepted: 05/18/2022] [Indexed: 02/04/2023] Open
Abstract
Hearing relies on the proper functioning of auditory hair cells and on actin-based cytoskeletal structures. Diaphanous-related formins (DRFs) are evolutionarily conserved cytoskeletal proteins that regulate the nucleation of linear unbranched actin filaments. They play key roles during metazoan development, and they seem particularly pivotal for the correct physiology of the reproductive and auditory systems. Indeed, in Drosophila melanogaster, a single diaphanous (dia) gene is present, and mutants show sterility and impaired response to sound. Vertebrates, instead, have three orthologs of the diaphanous gene: DIAPH1, DIAPH2, and DIAPH3. In humans, defects in DIAPH1 and DIAPH3 have been associated with different types of hearing loss. In particular, heterozygous mutations in DIAPH1 are responsible for autosomal dominant deafness with or without thrombocytopenia (DFNA1, MIM #124900), whereas regulatory mutations inducing the overexpression of DIAPH3 cause autosomal dominant auditory neuropathy 1 (AUNA1, MIM #609129). Here, we provide an overview of the expression and function of DRFs in normal hearing and deafness.
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Affiliation(s)
- Chiara Chiereghin
- IRCCS Humanitas Research Hospital, Via Manzoni 56, 20089 Milan, Italy; (C.C.); (R.A.)
| | - Michela Robusto
- Experimental Therapeutics Program, IFOM ETS—The AIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milan, Italy;
| | - Valentina Massa
- Dipartimento di Scienze della Salute, Università degli Studi di Milano, Via Di Rudinì 8, 20146 Milan, Italy;
| | | | - Umberto Ambrosetti
- Dipartimento di Scienze Cliniche e di Comunità, Università degli Studi di Milano and Fondazione IRCCS Cà Granda Ospedale Maggiore Policlinico, UO Audiologia, Via F. Sforza 35, 20122 Milan, Italy;
| | - Rosanna Asselta
- IRCCS Humanitas Research Hospital, Via Manzoni 56, 20089 Milan, Italy; (C.C.); (R.A.)
- Department of Biomedical Sciences, Humanitas University, Via Rita Levi Montalcini 4, 20072 Milan, Italy
| | - Giulia Soldà
- IRCCS Humanitas Research Hospital, Via Manzoni 56, 20089 Milan, Italy; (C.C.); (R.A.)
- Department of Biomedical Sciences, Humanitas University, Via Rita Levi Montalcini 4, 20072 Milan, Italy
- Correspondence:
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5
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Kim BJ, Miyoshi T, Chaudhry T, Friedman TB, Choi BY, Ueyama T. Late‐onset hearing loss case associated with a heterozygous truncating variant of
DIAPH1. Clin Genet 2022; 101:466-471. [PMID: 35060117 PMCID: PMC8981108 DOI: 10.1111/cge.14115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 01/18/2022] [Accepted: 01/19/2022] [Indexed: 11/29/2022]
Abstract
Diaphanous-related formin 1 (DIAPH1) is a formin homology F-actin elongating protein encoded by DIAPH1. Homozygous recessive variants resulting in the loss of DIAPH1 function cause seizures, cortical blindness, and microcephaly syndrome (SCBMS), but hearing loss has not been reported. In contrast, dominant variants of human DIAPH1 are associated with DFNA1 non-syndromic sensorineural hearing loss. The deafness phenotype is due partly to abnormal F-actin elongation activity caused by disruption of the DIAPH1 autoinhibitory mechanism. We report an elderly female heterozygous for the c.3145C>T: p.R1049X variant who showed late-onset sensorineural hearing loss in her fifth decade. p.R1049X lacks F-actin elongation activity because this variant truncates one-third of the FH2 domain, which is vital for DIAPH1 dimerization and processive F-actin elongation activity. Concordantly, no increase of F-actin or processive F-actin elongation activity was observed after overexpression of p.R1049X DIAPH1 in HeLa cells or by single-molecule microscopy using Xenopus XTC cells. However, overexpression of the p.R1049X variant impairs formation of cell-cell junctions and mitosis. We speculate that late-onset hearing loss is a long-term consequence of heterozygosity for the recessive p.R1049X variant, a phenotype that may have been overlooked among carriers of other recessive alleles of DIAPH1.
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Affiliation(s)
- Bong Jik Kim
- Department of Otolaryngology–Head and Neck Surgery Chungnam National University College of Medicine, Chungnam National University Sejong Hospital Sejong Republic of Korea
| | - Takushi Miyoshi
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health Bethesda MD USA
- Department of Otolaryngology ‐ Head and Neck Surgery Graduate School of Medicine, Kyoto University Kyoto Japan
| | - Taimur Chaudhry
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health Bethesda MD USA
| | - Thomas B. Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health Bethesda MD USA
| | - Byung Yoon Choi
- Department of Otorhinolaryngology Seoul National University Bundang Hospital Seongnam Republic of Korea
| | - Takehiko Ueyama
- Laboratory of Molecular Pharmacology, Biosignal Research Center, Kobe University Kobe Japan
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6
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Abstract
Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insufficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging-related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.
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Affiliation(s)
| | - Miguel A. Alonso
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, 28049 Madrid, Spain;
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7
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Lakha R, Montero AM, Jabeen T, Costeas CC, Ma J, Vizcarra CL. Variable Autoinhibition among Deafness-Associated Variants of Diaphanous 1 (DIAPH1). Biochemistry 2021; 60:2320-2329. [PMID: 34279089 DOI: 10.1021/acs.biochem.1c00170] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
One of the earliest mapped human deafness genes, DIAPH1, encodes the formin DIAPH1. To date, at least three distinct mutations in the C-terminal domains and two additional mutations in the N-terminal region are associated with autosomal dominant hearing loss. The underlying molecular mechanisms are not known, and the role of formins in the inner ear is not well understood. In this study, we use biochemical assays to test the hypotheses that autoinhibition and/or actin assembly activities are disrupted by DFNA1 mutations. Our results indicate that C-terminal mutant forms of DIAPH1 are functional in vitro and promote actin filament assembly. Similarly, N-terminal mutants are well-folded and have quaternary structures and thermal stabilities similar to those of the wild-type (WT) protein. The strength of the autoinhibitory interactions varies widely among mutants, with the ttaa, A265S, and I530S mutations having an affinity similar to that of WT and the 1213x and Δag mutations completely abolishing autoinhibition. These data indicate that, in some cases, hearing loss may be linked to weakened inhibition of actin assembly.
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Affiliation(s)
- Rabina Lakha
- Department of Chemistry, Barnard College, New York, New York 10027, United States
| | - Angela M Montero
- Department of Chemistry, Barnard College, New York, New York 10027, United States
| | - Tayyaba Jabeen
- Department of Chemistry, Barnard College, New York, New York 10027, United States
| | - Christina C Costeas
- Department of Chemistry, Barnard College, New York, New York 10027, United States
| | - Jia Ma
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Christina L Vizcarra
- Department of Chemistry, Barnard College, New York, New York 10027, United States
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8
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Miyoshi T, Belyantseva IA, Kitajiri SI, Miyajima H, Nishio SY, Usami SI, Kim BJ, Choi BY, Omori K, Shroff H, Friedman TB. Human deafness-associated variants alter the dynamics of key molecules in hair cell stereocilia F-actin cores. Hum Genet 2021; 141:363-382. [PMID: 34232383 DOI: 10.1007/s00439-021-02304-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 06/15/2021] [Indexed: 12/16/2022]
Abstract
Stereocilia protrude up to 100 µm from the apical surface of vertebrate inner ear hair cells and are packed with cross-linked filamentous actin (F-actin). They function as mechanical switches to convert sound vibration into electrochemical neuronal signals transmitted to the brain. Several genes encode molecular components of stereocilia including actin monomers, actin regulatory and bundling proteins, motor proteins and the proteins of the mechanotransduction complex. A stereocilium F-actin core is a dynamic system, which is continuously being remodeled while maintaining an outwardly stable architecture under the regulation of F-actin barbed-end cappers, severing proteins and crosslinkers. The F-actin cores of stereocilia also provide a pathway for motor proteins to transport cargos including components of tip-link densities, scaffolding proteins and actin regulatory proteins. Deficiencies and mutations of stereocilia components that disturb this "dynamic equilibrium" in stereocilia can induce morphological changes and disrupt mechanotransduction causing sensorineural hearing loss, best studied in mouse and zebrafish models. Currently, at least 23 genes, associated with human syndromic and nonsyndromic hearing loss, encode proteins involved in the development and maintenance of stereocilia F-actin cores. However, it is challenging to predict how variants associated with sensorineural hearing loss segregating in families affect protein function. Here, we review the functions of several molecular components of stereocilia F-actin cores and provide new data from our experimental approach to directly evaluate the pathogenicity and functional impact of reported and novel variants of DIAPH1 in autosomal-dominant DFNA1 hearing loss using single-molecule fluorescence microscopy.
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Affiliation(s)
- Takushi Miyoshi
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Porter Neuroscience Research Center, Room 1F-143A, Bethesda, MD, 20892, USA. .,Department of Otolaryngology-Head and Neck Surgery, Graduate School of Medicine, Kyoto University, Kyoto, 606-8507, Japan.
| | - Inna A Belyantseva
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Porter Neuroscience Research Center, Room 1F-143A, Bethesda, MD, 20892, USA
| | - Shin-Ichiro Kitajiri
- Department of Hearing Implant Sciences, Shinshu University School of Medicine, 390-8621, Matsumoto, Japan
| | - Hiroki Miyajima
- Department of Otolaryngology, Shinshu University School of Medicine, Matsumoto, 390-8621, Japan.,Department of Otolaryngology, Aizawa Hospital, Matsumoto, 390-8510, Japan
| | - Shin-Ya Nishio
- Department of Hearing Implant Sciences, Shinshu University School of Medicine, 390-8621, Matsumoto, Japan
| | - Shin-Ichi Usami
- Department of Hearing Implant Sciences, Shinshu University School of Medicine, 390-8621, Matsumoto, Japan
| | - Bong Jik Kim
- Department of Otolaryngology-Head and Neck Surgery, Chungnam National University College of Medicine, Chungnam National University Sejong Hospital, Sejong, 30099, South Korea.,Brain Research Institute, Chungnam National University College of Medicine, Daejeon, 35015, South Korea
| | - Byung Yoon Choi
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seongnam, 13620, South Korea
| | - Koichi Omori
- Department of Otolaryngology-Head and Neck Surgery, Graduate School of Medicine, Kyoto University, Kyoto, 606-8507, Japan
| | - Hari Shroff
- Laboratory of High Resolution Optical Imaging, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Porter Neuroscience Research Center, Room 1F-143A, Bethesda, MD, 20892, USA
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The integrity of cochlear hair cells is established and maintained through the localization of Dia1 at apical junctional complexes and stereocilia. Cell Death Dis 2020; 11:536. [PMID: 32678080 PMCID: PMC7366933 DOI: 10.1038/s41419-020-02743-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 07/01/2020] [Accepted: 07/03/2020] [Indexed: 02/07/2023]
Abstract
Dia1, which belongs to the diaphanous-related formin family, influences a variety of cellular processes through straight actin elongation activity. Recently, novel DIA1 mutants such as p.R1213X (p.R1204X) and p.A265S, have been reported to cause an autosomal dominant sensorineural hearing loss (DFNA1). Additionally, active DIA1 mutants induce progressive hearing loss in a gain-of-function manner. However, the subcellular localization and pathological function of DIA1(R1213X/R1204X) remains unknown. In the present study, we demonstrated the localization of endogenous Dia1 and the constitutively active DIA1 mutant in the cochlea, using transgenic mice expressing FLAG-tagged DIA1(R1204X) (DIA1-TG). Endogenous Dia1 and the DIA1 mutant were regionally expressed at the organ of Corti and the spiral ganglion from early life; alongside cochlear maturation, they became localized at the apical junctional complexes (AJCs) between hair cells (HCs) and supporting cells (SCs). To investigate HC vulnerability in the DIA1-TG mice, we exposed 4-week-old mice to moderate noise, which induced temporary threshold shifts with cochlear synaptopathy and ultrastructural changes in stereocilia 4 weeks post noise exposure. Furthermore, we established a knock-in (KI) mouse line expressing AcGFP-tagged DIA1(R1213X) (DIA1-KI) and confirmed mutant localization at AJCs and the tips of stereocilia in HCs. In MDCKAcGFP-DIA1(R1213X) cells with stable expression of AcGFP-DIA1(R1213X), AcGFP-DIA1(R1213X) revealed marked localization at microvilli on the apical surface of cells and decreased localization at cell-cell junctions. The DIA1-TG mice demonstrated hazy and ruffled circumferential actin belts at AJCs and abnormal stereocilia accompanied with HC loss at 5 months of age. In conclusion, Dia1 plays a pivotal role in the development and maintenance of AJCs and stereocilia, ensuring cochlear and HC integrity. Subclinical/latent vulnerability of HCs may be the cause of progressive hearing loss in DFNA1 patients, thus suggesting new therapeutic targets for preventing HC degeneration and progressive hearing loss associated with DFNA1.
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