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Holt JR, Fettiplace R, Müller U. Sensory transduction in auditory hair cells-PIEZOs can't touch this. J Gen Physiol 2024; 156:e202413585. [PMID: 38727631 PMCID: PMC11090049 DOI: 10.1085/jgp.202413585] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/15/2024] Open
Abstract
In this Viewpoint, Holt, Fettiplace, and Müller weigh the evidence supporting a role for PIEZO and TMC channels in mechanosensory transduction in inner ear hair cells.
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Affiliation(s)
- Jeffrey R. Holt
- Departments of Otolaryngology and Neurology, Boston Children’s Hospital and Harvard Medical School, Boston, MA, USA
| | - Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Ulrich Müller
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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Kindig K, Stepanyan R, Kindt KS, McDermott BM. Asymmetric mechanotransduction by hair cells of the zebrafish lateral line. Curr Biol 2023; 33:1295-1307.e3. [PMID: 36905930 DOI: 10.1016/j.cub.2023.02.033] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 11/22/2022] [Accepted: 02/09/2023] [Indexed: 03/12/2023]
Abstract
In the lateral line system, water motion is detected by neuromast organs, fundamental units that are arrayed on a fish's surface. Each neuromast contains hair cells, specialized mechanoreceptors that convert mechanical stimuli, in the form of water movement, into electrical signals. The orientation of hair cells' mechanosensitive structures ensures that the opening of mechanically gated channels is maximal when deflected in a single direction. In each neuromast organ, hair cells have two opposing orientations, enabling bi-directional detection of water movement. Interestingly, Tmc2b and Tmc2a proteins, which constitute the mechanotransduction channels in neuromasts, distribute asymmetrically so that Tmc2a is expressed in hair cells of only one orientation. Here, using both in vivo recording of extracellular potentials and calcium imaging of neuromasts, we demonstrate that hair cells of one orientation have larger mechanosensitive responses. The associated afferent neuron processes that innervate neuromast hair cells faithfully preserve this functional difference. Moreover, Emx2, a transcription factor required for the formation of hair cells with opposing orientations, is necessary to establish this functional asymmetry within neuromasts. Remarkably, loss of Tmc2a does not impact hair cell orientation but abolishes the functional asymmetry as measured by recording extracellular potentials and calcium imaging. Overall, our work indicates that oppositely oriented hair cells within a neuromast employ different proteins to alter mechanotransduction to sense the direction of water motion.
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Affiliation(s)
- Kayla Kindig
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ruben Stepanyan
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
| | - Katie S Kindt
- Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, Bethesda, MD 20892, USA.
| | - Brian M McDermott
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA; Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
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The conductance and organization of the TMC1-containing mechanotransducer channel complex in auditory hair cells. Proc Natl Acad Sci U S A 2022; 119:e2210849119. [PMID: 36191207 PMCID: PMC9564823 DOI: 10.1073/pnas.2210849119] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We studied the role of TMC1 as the central component of the hair cell mechanotransducer (MET) channel by characterizing transduction in mice harboring mutations in the pore region. All Tmc1 mutations reduced the Ca2+ influx into the hair bundle. Two mutations (Tmc1 p.D528N or Tmc1 p.E520Q) also decreased channel conductance and two (Tmc1 p. D569N or Tmc1 p.W554L) lowered expression. These mutations endorse TMC1 as the pore of the MET channel. The MET channel also contains accessory subunits, LHFPL5 and TMIE. MET currents were small in Lhfpl5 or Tmie knockout mice. Nevertheless, MET channels could still be activated by hair bundle displacement; single-channel conductance was unaffected in Lhfpl5−/− but reduced in Tmie−/−, suggesting TMIE likely contributes to the pore. Transmembrane channel-like protein 1 (TMC1) is thought to form the ion-conducting pore of the mechanoelectrical transducer (MET) channel in auditory hair cells. Using single-channel analysis and ionic permeability measurements, we characterized six missense mutations in the purported pore region of mouse TMC1. All mutations reduced the Ca2+ permeability of the MET channel, triggering hair cell apoptosis and deafness. In addition, Tmc1 p.E520Q and Tmc1 p.D528N reduced channel conductance, whereas Tmc1 p.W554L and Tmc1 p.D569N lowered channel expression without affecting the conductance. Tmc1 p.M412K and Tmc1 p.T416K reduced only the Ca2+ permeability. The consequences of these mutations endorse TMC1 as the pore of the MET channel. The accessory subunits, LHFPL5 and TMIE, are thought to be involved in targeting TMC1 to the tips of the stereocilia. We found sufficient expression of TMC1 in outer hair cells of Lhfpl5 and Tmie knockout mice to determine the properties of the channels, which could still be gated by hair bundle displacement. Single-channel conductance was unaffected in Lhfpl5−/− but was reduced in Tmie−/−, implying TMIE very likely contributes to the pore. Both the working range and half-saturation point of the residual MET current in Lhfpl5−/− were substantially increased, suggesting that LHFPL5 is part of the mechanical coupling between the tip-link and the MET channel. Based on counts of numbers of stereocilia per bundle, we estimate that each PCDH15 and LHFPL5 monomer may contact two channels irrespective of location.
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Liang X, Qiu X, Dionne G, Cunningham CL, Pucak ML, Peng G, Kim YH, Lauer A, Shapiro L, Müller U. CIB2 and CIB3 are auxiliary subunits of the mechanotransduction channel of hair cells. Neuron 2021; 109:2131-2149.e15. [PMID: 34089643 PMCID: PMC8374959 DOI: 10.1016/j.neuron.2021.05.007] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 01/17/2021] [Accepted: 05/07/2021] [Indexed: 12/25/2022]
Abstract
CIB2 is a Ca2+- and Mg2+-binding protein essential for mechanoelectrical transduction (MET) by cochlear hair cells, but not by vestibular hair cells that co-express CIB2 and CIB3. Here, we show that in cochlear hair cells, CIB3 can functionally substitute for CIB2. Using X-ray crystallography, we demonstrate that CIB2 and CIB3 are structurally similar to KChIP proteins, auxiliary subunits of voltage-gated Kv4 channels. CIB2 and CIB3 bind to TMC1/2 through a domain in TMC1/2 flanked by transmembrane domains 2 and 3. The co-crystal structure of the CIB-binding domain in TMC1 with CIB3 reveals that interactions are mediated through a conserved CIB hydrophobic groove, similar to KChIP1 binding of Kv4. Functional studies in mice show that CIB2 regulates TMC1/2 localization and function in hair cells, processes that are affected by deafness-causing CIB2 mutations. We conclude that CIB2 and CIB3 are MET channel auxiliary subunits with striking similarity to Kv4 channel auxiliary subunits.
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Affiliation(s)
- Xiaoping Liang
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Xufeng Qiu
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Gilman Dionne
- Department of Biochemistry and Molecular Biophysics, Zuckerman Mind Brain, Department of Systems Biology, Columbia University, New York, NY 10032, USA
| | - Christopher L Cunningham
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Michele L Pucak
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Guihong Peng
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ye-Hyun Kim
- Department of Otolaryngology-HNS, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Amanda Lauer
- Department of Otolaryngology-HNS, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Lawrence Shapiro
- Department of Biochemistry and Molecular Biophysics, Zuckerman Mind Brain, Department of Systems Biology, Columbia University, New York, NY 10032, USA.
| | - Ulrich Müller
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Liu S, Wang S, Zou L, Xiong W. Mechanisms in cochlear hair cell mechano-electrical transduction for acquisition of sound frequency and intensity. Cell Mol Life Sci 2021; 78:5083-5094. [PMID: 33871677 PMCID: PMC11072359 DOI: 10.1007/s00018-021-03840-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 03/30/2021] [Accepted: 04/09/2021] [Indexed: 10/21/2022]
Abstract
Sound signals are acquired and digitized in the cochlea by the hair cells that further transmit the coded information to the central auditory pathways. Any defect in hair cell function may induce problems in the auditory system and hearing-based brain function. In the past 2 decades, our understanding of auditory transduction has been substantially deepened because of advances in molecular, structural, and functional studies. Results from these experiments can be perfectly embedded in the previously established profile from anatomical, histological, genetic, and biophysical research. This review aims to summarize the progress on the molecular and cellular mechanisms of the mechano-electrical transduction (MET) channel in the cochlear hair cells, which is involved in the acquisition of sound frequency and intensity-the two major parameters of an acoustic cue. We also discuss recent studies on TMC1, the molecule likely to form the MET channel pore.
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Affiliation(s)
- Shuang Liu
- School of Life Sciences, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China
- IDG/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China
| | - Shufeng Wang
- School of Life Sciences, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China
- IDG/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China
| | - Linzhi Zou
- School of Life Sciences, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China
- IDG/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China
| | - Wei Xiong
- School of Life Sciences, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China.
- IDG/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, 1 Qinghuayuan, Beijing, 100084, China.
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Abstract
Sound-induced mechanical stimuli are detected by elaborate mechanosensory transduction (MT) machinery in highly specialized hair cells of the inner ear. Genetic studies of inherited deafness in the past decades have uncovered several molecular constituents of the MT complex, and intense debate has surrounded the molecular identity of the pore-forming subunits. How the MT components function in concert in response to physical stimulation is not fully understood. In this review, we summarize and discuss multiple lines of evidence supporting the hypothesis that transmembrane channel-like 1 is a long-sought MT channel subunit. We also review specific roles of other components of the MT complex, including protocadherin 15, cadherin 23, lipoma HMGIC fusion partner-like 5, transmembrane inner ear, calcium and integrin-binding family member 2, and ankyrins. Based on these recent advances, we propose a unifying theory of hair cell MT that may reconcile most of the functional discoveries obtained to date. Finally, we discuss key questions that need to be addressed for a comprehensive understanding of hair cell MT at molecular and atomic levels.
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Affiliation(s)
- Wang Zheng
- Departments of Otolaryngology and Neurology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA;
| | - Jeffrey R Holt
- Departments of Otolaryngology and Neurology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA;
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Li S, Yan Z. Mechanotransduction Ion Channels in Hearing and Touch. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1349:371-385. [DOI: 10.1007/978-981-16-4254-8_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Bonet IJM, Araldi D, Bogen O, Levine JD. Involvement of TACAN, a Mechanotransducing Ion Channel, in Inflammatory But Not Neuropathic Hyperalgesia in the Rat. THE JOURNAL OF PAIN 2020; 22:498-508. [PMID: 33232830 DOI: 10.1016/j.jpain.2020.11.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 11/09/2020] [Accepted: 11/13/2020] [Indexed: 12/15/2022]
Abstract
TACAN (Tmem120A), a mechanotransducing ion channel highly expressed in a subset of nociceptors, has recently been shown to contribute to detection of noxious mechanical stimulation. In the present study we evaluated its role in sensitization to mechanical stimuli associated with preclinical models of inflammatory and chemotherapy-induced neuropathic pain (CIPN). Intrathecal administration of an oligodeoxynucleotide antisense (AS-ODN) to TACAN mRNA attenuated TACAN protein expression in rat dorsal root ganglia (DRG). While TACAN AS-ODN produced only a modest increase in mechanical nociceptive threshold, it markedly reduced mechanical hyperalgesia produced by intradermal administration of prostaglandin E2, tumor necrosis factor alpha, and low molecular weight hyaluronan, and systemic administration of lipopolysaccharide, compatible with a prominent role of TACAN in mechanical hyperalgesia produced by inflammation. In contrast, TACAN AS-ODN had no effect on mechanical hyperalgesia associated with CIPN produced by oxaliplatin or paclitaxel. Our results provide evidence that TACAN plays a role in mechanical hyperalgesia induced by pronociceptive inflammatory mediators, but not CIPN, compatible with multiple mechanisms mediating mechanical nociception, and sensitization to mechanical stimuli in preclinical models of inflammatory versus CIPN. PERSPECTIVE: We evaluated the role of TACAN, a mechanotransducing ion channel in nociceptors, in preclinical models of inflammatory and CIPN. Attenuation of TACAN expression reduced hyperalgesia produced by inflammatory mediators but had not chemotherapeutic agents. Our findings support the presence of multiple mechanotransducers in nociceptors.
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Affiliation(s)
- Ivan J M Bonet
- Departments of Medicine and Oral & Maxillofacial Surgery, and Division of Neuroscience, UCSF Pain and Addiction Research Center, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, California
| | - Dionéia Araldi
- Departments of Medicine and Oral & Maxillofacial Surgery, and Division of Neuroscience, UCSF Pain and Addiction Research Center, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, California
| | - Oliver Bogen
- Departments of Medicine and Oral & Maxillofacial Surgery, and Division of Neuroscience, UCSF Pain and Addiction Research Center, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, California
| | - Jon D Levine
- Departments of Medicine and Oral & Maxillofacial Surgery, and Division of Neuroscience, UCSF Pain and Addiction Research Center, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, California.
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Cunningham CL, Qiu X, Wu Z, Zhao B, Peng G, Kim YH, Lauer A, Müller U. TMIE Defines Pore and Gating Properties of the Mechanotransduction Channel of Mammalian Cochlear Hair Cells. Neuron 2020; 107:126-143.e8. [PMID: 32343945 PMCID: PMC7351599 DOI: 10.1016/j.neuron.2020.03.033] [Citation(s) in RCA: 65] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 02/24/2020] [Accepted: 03/30/2020] [Indexed: 12/29/2022]
Abstract
TMC1 and TMC2 (TMC1/2) have been proposed to form the pore of the mechanotransduction channel of cochlear hair cells. Here, we show that TMC1/2 cannot form mechanotransduction channels in cochlear hair cells without TMIE. TMIE binds to TMC1/2, and a TMIE mutation that perturbs TMC1/2 binding abolishes mechanotransduction. N-terminal TMIE deletions affect the response of the mechanotransduction channel to mechanical force. Similar to mechanically gated TREK channels, the C-terminal cytoplasmic TMIE domain contains charged amino acids that mediate binding to phospholipids, including PIP2. TMIE point mutations in the C terminus that are linked to deafness disrupt phospholipid binding, sensitize the channel to PIP2 depletion from hair cells, and alter the channel's unitary conductance and ion selectivity. We conclude that TMIE is a subunit of the cochlear mechanotransduction channel and that channel function is regulated by a phospholipid-sensing domain in TMIE with similarity to those in other mechanically gated ion channels.
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Affiliation(s)
- Christopher L Cunningham
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Xufeng Qiu
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Zizhen Wu
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Bo Zhao
- Department of Otolaryngology - Head & Neck Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Guihong Peng
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ye-Hyun Kim
- Department of Otolaryngology - HNS, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Amanda Lauer
- Department of Otolaryngology - HNS, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ulrich Müller
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Sarmadi A, Nasrniya S, Soleimani Farsani M, Narrei S, Nouri Z, Sepehrnejad M, Nilforoush MH, Abtahi H, Tabatabaiefar MA. A novel pathogenic variant in the LRTOMT gene causes autosomal recessive non-syndromic hearing loss in an Iranian family. BMC MEDICAL GENETICS 2020; 21:127. [PMID: 32517708 PMCID: PMC7285524 DOI: 10.1186/s12881-020-01061-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2020] [Accepted: 06/02/2020] [Indexed: 02/07/2023]
Abstract
Background Hearing loss (HL) is the most common sensorineural disorder with high phenotypic and genotypic heterogeneity, which negatively affects life quality. Autosomal recessive non-syndromic hearing loss (ARNSHL) constitutes a major share of HL cases. In the present study, Whole exome sequencing (WES) was applied to investigate the underlying etiology of HL in an Iranian patient with ARNSHL. Methods A proband from an Iranian consanguineous family was examined via WES, following GJB2 sequencing. WES was utilized to find possible genetic etiology of the disease. Various Bioinformatics tools were used to assess the pathogenicity of the variants. Co-segregation analysis of the candidate variant was carried out. Interpretation of variants was performed according to the American College of Medical Genetics and Genomics (ACMG) guidelines. Results WES results showed a novel frameshift (16 bp deletion) variant (p.Ala170Alafs*20) in the LRTOMT gene. This variant, which resides in exon 6, was found to be co-segregating in the family. It fulfils the criteria set by the ACMG guidelines of being pathogenic. Conclusion Here, we report successful application of WES to identify the molecular pathogenesis of ARNSHL, which is a genetically heterogeneous disorder, in a patient with ARNSHL.
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Affiliation(s)
- Akram Sarmadi
- Department of Genetics and Molecular Biology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.,Genetics Department, Erythron Pathobiology and Genetics lab, Isfahan, Iran
| | - Samane Nasrniya
- Department of Genetics and Molecular Biology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran
| | - Maryam Soleimani Farsani
- Department of Biotechnology, Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan, Iran
| | - Sina Narrei
- Genetics Department, Erythron Pathobiology and Genetics lab, Isfahan, Iran
| | - Zahra Nouri
- Department of Medical Biotechnology, School of Advanced Technologies in Medicine, Tehran University of Medical Sciences, Tehran, Iran
| | - Mahsa Sepehrnejad
- Department of Otolaryngology, Al-Zahra Hospital, Isfahan University of Medical Sciences, Isfahan, Iran
| | | | - Hamidreza Abtahi
- Department of Otolaryngology, Al-Zahra Hospital, Isfahan University of Medical Sciences, Isfahan, Iran
| | - Mohammad Amin Tabatabaiefar
- Department of Genetics and Molecular Biology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. .,Pediatric Inherited Diseases Research Center, Research Institute for Primordial Prevention of Noncommunicable Disease, Isfahan University of Medical Sciences, Isfahan, Iran. .,GenTArget Corp (GTAC), Deputy of Research and Technology, Isfahan University of Medical Sciences, Isfahan, Iran.
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Disruption of tmc1/2a/2b Genes in Zebrafish Reveals Subunit Requirements in Subtypes of Inner Ear Hair Cells. J Neurosci 2020; 40:4457-4468. [PMID: 32371604 DOI: 10.1523/jneurosci.0163-20.2020] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 04/14/2020] [Accepted: 04/16/2020] [Indexed: 01/11/2023] Open
Abstract
Detection of sound and head movement requires mechanoelectrical transduction (MET) channels at tips of hair-cell stereocilia. In vertebrates, the transmembrane channel-like (TMC) proteins TMC1 and TMC2 fulfill critical roles in MET, and substantial evidence implicates these TMCs as subunits of the MET channel. To identify developmental and functional roles of this Tmc subfamily in the zebrafish inner ear, we tested the effects of truncating mutations in tmc1, tmc2a, and tmc2b on in vivo mechanosensation at the onset of hearing and balance, before gender differentiation. We find that tmc1/2a/2b triple-mutant larvae cannot detect sound or orient with respect to gravity. They lack acoustic-evoked behavioral responses, vestibular-induced eye movements, and hair-cell activity as assessed with FM dye labeling and microphonic potentials. Despite complete loss of hair-cell function, tmc triple-mutant larvae retain normal gross morphology of hair bundles and proper trafficking of known MET components Protocadherin 15a (Pcdh15a), Lipoma HMGIC fusion partner-like 5 (Lhfpl5), and Transmembrane inner ear protein (Tmie). Transgenic, hair cell-specific expression of Tmc2b-mEGFP rescues the behavioral and physiological deficits in tmc triple mutants. Results from tmc single and double mutants evince a principle role for Tmc2a and Tmc2b in hearing and balance, respectively, whereas Tmc1 has lower overall impact. Our experiments reveal that, in developing cristae, hair cells stratify into an upper, Tmc2a-dependent layer of teardrop-shaped cells and a lower, Tmc1/2b-dependent tier of gourd-shaped cells. Collectively, our genetic evidence indicates that auditory/vestibular end organs and subsets of hair cells therein rely on distinct combinations of Tmc1/2a/2b.SIGNIFICANCE STATEMENT We assessed the effects of tmc1/2a/2b truncation mutations on mechanoelectrical transduction (MET) in the inner-ear hair cells of larval zebrafish. tmc triple mutants lacked behavioral responses to sound and head movements, while further assays demonstrated no observable mechanosensitivity in the tmc1/2a/2b triple mutant inner ear. Examination of tmc double mutants revealed major contributions from Tmc2a and Tmc2b to macular function; however, Tmc1 had less overall impact. FM labeling of lateral cristae in tmc double mutants revealed the presence of two distinct cell types, an upper layer of teardrop-shaped cells that rely on Tmc2a, and a lower layer of gourd-shaped cells that rely on Tmc1/2b.
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Goldring AC, Beurg M, Fettiplace R. The contribution of TMC1 to adaptation of mechanoelectrical transduction channels in cochlear outer hair cells. J Physiol 2019; 597:5949-5961. [PMID: 31633194 PMCID: PMC6910908 DOI: 10.1113/jp278799] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2019] [Accepted: 10/17/2019] [Indexed: 01/23/2023] Open
Abstract
KEY POINTS Hair cell mechanoelectrical transducer channels are opened by deflections of the hair bundle about a resting position set by incompletely understood adaptation mechanisms. We used three characteristics to define adaptation in hair cell mutants of transmembrane channel-like proteins, TMC1 and TMC2, which are considered to be channel constituents. The results obtained demonstrate that the three characteristics are not equivalent, and raise doubts about simple models in which intracellular Ca2+ regulates adaptation. Adaptation is faster and more effective in TMC1-containing than in TMC2-containing transducer channels. This result ties adaptation to the channel complex, and suggests that TMC1 is a better isoform for use in cochlear hair cells. We describe a TMC1 point mutation, D569N, that reduces the resting open probability and Ca2+ permeability of the transducer channels, comprising properties that may contribute to the deafness phenotype. ABSTRACT Recordings of mechanoelectrical transducer (MET) currents in cochlear hair cells were made in mice with mutations of transmembrane channel-like (TMC) protein to examine the effects on fast transducer adaptation. Adaptation was faster and more complete in Tmc2-/- than in Tmc1-/- , although this disparity was not explained by differences in Ca2+ permeability or Ca2+ influx between the two isoforms, with TMC2 having the larger permeability. We made a mouse mutation, Tmc1 p.D569N, homologous to a human DFNA36 deafness mutation, which also had MET channels with lower Ca2+ -permeability but showed better fast adaptation than wild-type Tmc1+/+ channels. Consistent with the more effective adaptation in Tmc1 p.D569N, the resting probability of MET channel opening was smaller. The three TMC variants studied have comparable single-channel conductances, although the lack of correlation between channel Ca2+ permeability and adaptation opposes the hypothesis that adaptation is controlled simply by Ca2+ influx through the channels. During the first postnatal week of mouse development, the MET currents amplitude grew, and transducer adaptation became faster and more effective. We attribute changes in adaptation partly to a developmental switch from TMC2- to TMC1- containing channels and partly to an increase in channel expression. More complete and faster adaptation, coupled with larger MET currents, may account for the sole use of TMC1 in the adult cochlear hair cells.
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Affiliation(s)
- Adam C Goldring
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Maryline Beurg
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
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Liu S, Wang S, Zou L, Li J, Song C, Chen J, Hu Q, Liu L, Huang P, Xiong W. TMC1 is an essential component of a leak channel that modulates tonotopy and excitability of auditory hair cells in mice. eLife 2019; 8:47441. [PMID: 31661074 PMCID: PMC6853638 DOI: 10.7554/elife.47441] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 10/24/2019] [Indexed: 11/13/2022] Open
Abstract
Hearing sensation relies on the mechano-electrical transducer (MET) channel of cochlear hair cells, in which transmembrane channel-like 1 (TMC1) and transmembrane channel-like 2 (TMC2) have been proposed to be the pore-forming subunits in mammals. TMCs were also found to regulate biological processes other than MET in invertebrates, ranging from sensations to motor function. However, whether TMCs have a non-MET role remains elusive in mammals. Here, we report that in mouse hair cells, TMC1, but not TMC2, provides a background leak conductance, with properties distinct from those of the MET channels. By cysteine substitutions in TMC1, we characterized four amino acids that are required for the leak conductance. The leak conductance is graded in a frequency-dependent manner along the length of the cochlea and is indispensable for action potential firing. Taken together, our results show that TMC1 confers a background leak conductance in cochlear hair cells, which may be critical for the acquisition of sound-frequency and -intensity.
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Affiliation(s)
- Shuang Liu
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Shufeng Wang
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Linzhi Zou
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Jie Li
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Chenmeng Song
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Jiaofeng Chen
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Qun Hu
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Lian Liu
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
| | - Pingbo Huang
- Department of Chemical and Biological Engineering, Hong Kong University of Science and Technology, Hong Kong, China.,State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China.,Division of Life Science, Hong Kong University of Science and Technology, Hong Kong, China
| | - Wei Xiong
- School of Life Sciences, Tsinghua University, Beijing, China.,IDG/McGovern Institute for Brain Research at Tsinghua University, Beijing, China
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14
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Corey DP, Akyuz N, Holt JR. Function and Dysfunction of TMC Channels in Inner Ear Hair Cells. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033506. [PMID: 30291150 DOI: 10.1101/cshperspect.a033506] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The TMC1 channel was identified as a protein essential for hearing in mouse and human, and recognized as one of a family of eight such proteins in mammals. The TMC family is part of a superfamily of seven branches, which includes the TMEM16s. Vertebrate hair cells express both TMC1 and TMC2. They are located at the tips of stereocilia and are required for hair cell mechanotransduction. TMC1 assembles as a dimer and its similarity to the TMEM16s has enabled a predicted tertiary structure with an ion conduction pore in each subunit of the dimer. Cysteine mutagenesis of the pore supports the role of TMC1 and TMC2 as the core channel proteins of a larger mechanotransduction complex that includes PCDH15 and LHFPL5, and perhaps TMIE, CIB2 and others.
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Affiliation(s)
- David P Corey
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
| | - Nurunisa Akyuz
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
| | - Jeffrey R Holt
- Departments of Otolaryngology and Neurology, F.M. Kirby Neurobiology Center, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115
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15
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A Tmc1 mutation reduces calcium permeability and expression of mechanoelectrical transduction channels in cochlear hair cells. Proc Natl Acad Sci U S A 2019; 116:20743-20749. [PMID: 31548403 PMCID: PMC6789967 DOI: 10.1073/pnas.1908058116] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cochlear hair cells transduce sound into electrical signals by activation of mechanically sensitive ion channels thought to be formed by TMC1. We generated a single aspartate/asparagine substitution in mouse TMC1 which is homologous to a human genetic deafness mutation. The main consequence was reduction in the Ca2+ permeability of the mechanically sensitive channel with little change in its unitary conductance. Nevertheless, there was a much reduced expression of the ion channel, which led within 4 wk to death of the outer hair cells culminating in deafness. The mouse mutant accounts for the human deafness and implies that TMC1, in addition to forming the mechanically sensitive ion channel, regulates its own expression. Mechanoelectrical transducer (MET) currents were recorded from cochlear hair cells in mice with mutations of transmembrane channel-like protein TMC1 to study the effects on MET channel properties. We characterized a Tmc1 mouse with a single-amino-acid mutation (D569N), homologous to a dominant human deafness mutation. Measurements were made in both Tmc2 wild-type and Tmc2 knockout mice. By 30 d, Tmc1 pD569N heterozygote mice were profoundly deaf, and there was substantial loss of outer hair cells (OHCs). MET current in OHCs of Tmc1 pD569N mutants developed over the first neonatal week to attain a maximum amplitude one-third the size of that in Tmc1 wild-type mice, similar at apex and base, and lacking the tonotopic size gradient seen in wild type. The MET-channel Ca2+ permeability was reduced 3-fold in Tmc1 pD569N homozygotes, intermediate deficits being seen in heterozygotes. Reduced Ca2+ permeability resembled that of the Tmc1 pM412K Beethoven mutant, a previously studied semidominant mouse mutation. The MET channel unitary conductance, assayed by single-channel recordings and by measurements of current noise, was unaffected in mutant apical OHCs. We show that, in contrast to the Tmc1 M412K mutant, there was reduced expression of the TMC1 D569N channel at the transduction site assessed by immunolabeling, despite the persistence of tip links. The reduction in MET channel Ca2+ permeability seen in both mutants may be the proximate cause of hair-cell apoptosis, but changes in bundle shape and protein expression in Tmc1 D569N suggest another role for TMC1 apart from forming the channel.
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16
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Heil P, Peterson AJ. Nelson's notch in the rate-level functions of auditory-nerve fibers might be caused by PIEZO2-mediated reverse-polarity currents in hair cells. Hear Res 2019; 381:107783. [DOI: 10.1016/j.heares.2019.107783] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 07/17/2019] [Accepted: 08/06/2019] [Indexed: 11/30/2022]
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17
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Cunningham CL, Müller U. Molecular Structure of the Hair Cell Mechanoelectrical Transduction Complex. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033167. [PMID: 30082452 DOI: 10.1101/cshperspect.a033167] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Cochlear hair cells employ mechanically gated ion channels located in stereocilia that open in response to sound wave-induced motion of the basilar membrane, converting mechanical stimulation to graded changes in hair cell membrane potential. Membrane potential changes in hair cells cause neurotransmitter release from hair cells that initiate electrical signals in the nerve terminals of afferent fibers from spiral ganglion neurons. These signals are then propagated within the central nervous system (CNS) to mediate the sensation of hearing. Recent studies show that the mechanoelectrical transduction (MET) machinery of hair cells is formed by an ensemble of proteins. Candidate components forming the MET channel have been identified, but none alone fulfills all criteria necessary to define them as pore-forming subunits of the MET channel. We will review here recent findings on the identification and function of proteins that are components of the MET machinery in hair cells and consider remaining open questions.
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Affiliation(s)
- Christopher L Cunningham
- The Solomon Snyder Department of Neuroscience, Johns Hopkins University, Baltimore, Maryland 21205
| | - Ulrich Müller
- The Solomon Snyder Department of Neuroscience, Johns Hopkins University, Baltimore, Maryland 21205
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18
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Asai Y, Pan B, Nist-Lund C, Galvin A, Lukashkin AN, Lukashkina VA, Chen T, Zhou W, Zhu H, Russell IJ, Holt JR, Géléoc GSG. Transgenic Tmc2 expression preserves inner ear hair cells and vestibular function in mice lacking Tmc1. Sci Rep 2018; 8:12124. [PMID: 30108254 PMCID: PMC6092434 DOI: 10.1038/s41598-018-28958-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 07/03/2018] [Indexed: 01/18/2023] Open
Abstract
Recent work has demonstrated that transmembrane channel-like 1 protein (TMC1) is an essential component of the sensory transduction complex in hair cells of the inner ear. A closely related homolog, TMC2, is expressed transiently in the neonatal mouse cochlea and can enable sensory transduction in Tmc1-null mice during the first postnatal week. Both TMC1 and TMC2 are expressed at adult stages in mouse vestibular hair cells. The extent to which TMC1 and TMC2 can substitute for each other is unknown. Several biophysical differences between TMC1 and TMC2 suggest these proteins perform similar but not identical functions. To investigate these differences, and whether TMC2 can substitute for TMC1 in mature hair cells, we generated a knock-in mouse model allowing Cre-inducible expression of Tmc2. We assayed for changes in hair cell sensory transduction and auditory and vestibular function in Tmc2 knockin mice (Tm[Tmc2]) in the presence or absence of endogenous Tmc1, Tmc2 or both. Our results show that expression of Tm[TMC2] restores sensory transduction in vestibular hair cells and transiently in cochlear hair cells in the absence of TMC1. The cellular rescue leads to recovery of balance but not auditory function. We conclude that TMC1 provides some additional necessary function, not provided by TMC2.
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Affiliation(s)
- Yukako Asai
- Department of Otolaryngology and Communication Enhancement, F.M. Kirby Center for Neurobiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Bifeng Pan
- Department of Otolaryngology and Communication Enhancement, F.M. Kirby Center for Neurobiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Carl Nist-Lund
- Department of Otolaryngology and Communication Enhancement, F.M. Kirby Center for Neurobiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Alice Galvin
- Department of Otolaryngology and Communication Enhancement, F.M. Kirby Center for Neurobiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Andrei N Lukashkin
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK
| | - Victoria A Lukashkina
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK
| | - Tianwen Chen
- Department of Otolaryngology and Communicative Sciences, University of Mississippi Medical Center, Oxford, MS, USA
| | - Wu Zhou
- Department of Otolaryngology and Communicative Sciences, University of Mississippi Medical Center, Oxford, MS, USA
| | - Hong Zhu
- Department of Otolaryngology and Communicative Sciences, University of Mississippi Medical Center, Oxford, MS, USA
| | - Ian J Russell
- Sensory Neuroscience Research Group, School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK
| | - Jeffrey R Holt
- Department of Otolaryngology and Communication Enhancement, F.M. Kirby Center for Neurobiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
- Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Gwenaelle S G Géléoc
- Department of Otolaryngology and Communication Enhancement, F.M. Kirby Center for Neurobiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
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19
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GsMTx4-D provides protection to the D2.mdx mouse. Neuromuscul Disord 2018; 28:868-877. [PMID: 30174173 DOI: 10.1016/j.nmd.2018.07.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 07/02/2018] [Accepted: 07/17/2018] [Indexed: 12/23/2022]
Abstract
Duchenne muscular dystrophy is a life-limiting muscle disease that has no current effective therapy. Despite mounting evidence that dysregulation of mechanosensitive ion channels is a significant contributor to dystrophy pathogenesis, effective pharmacologic strategies targeting these channels are lacking. GsMTx4, and its enantiomer GsMTx4-D, are peptide inhibitors of mechanosensitive channels with identical activity. In previous studies, acute in vitro application of GsMTx4 to dystrophic murine muscle effectively reduced the excess MSC dependent calcium influx linked to contraction-induced muscle damage. Here we sought to determine if in vivo treatment with GsMTx4-D proffered benefit in the D2.mdx mouse. GsMTx4-D showed a 1-week half-life when administered by subcutaneous injection over four weeks. Informed by these results, D2.mdx mice were then treated by a subcutaneous injection regimen of GsMTx4-D for six weeks followed by determination of muscle mass, muscle susceptibility to eccentric contraction injury and multiple histological indicators of disease progression. The mice showed a reduction in the loss of muscle mass and a decrease in susceptibility to contraction induced injury. These protective effects were realized without reduction in fibrosis, supporting a model where GsMTx4-D acts directly on muscle cells. We propose GsMTx4-D represents a promising new therapy to slow disease progression and may complement other therapies such as anti-inflammatory agents and gene-replacement strategies.
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20
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Variable number of TMC1-dependent mechanotransducer channels underlie tonotopic conductance gradients in the cochlea. Nat Commun 2018; 9:2185. [PMID: 29872055 PMCID: PMC5988745 DOI: 10.1038/s41467-018-04589-8] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Accepted: 04/16/2018] [Indexed: 11/25/2022] Open
Abstract
Functional mechanoelectrical transduction (MET) channels of cochlear hair cells require the presence of transmembrane channel-like protein isoforms TMC1 or TMC2. We show that TMCs are required for normal stereociliary bundle development and distinctively influence channel properties. TMC1-dependent channels have larger single-channel conductance and in outer hair cells (OHCs) support a tonotopic apex-to-base conductance gradient. Each MET channel complex exhibits multiple conductance states in ~50 pS increments, basal MET channels having more large-conductance levels. Using mice expressing fluorescently tagged TMCs, we show a three-fold increase in number of TMC1 molecules per stereocilium tip from cochlear apex to base, mirroring the channel conductance gradient in OHCs. Single-molecule photobleaching indicates the number of TMC1 molecules per MET complex changes from ~8 at the apex to ~20 at base. The results suggest there are varying numbers of channels per MET complex, each requiring multiple TMC1 molecules, and together operating in a coordinated or cooperative manner. Mechanoelectrical transduction channel (MET) current found in stereocilia of hair cells matures over the first postnatal week. Here the authors look at the contribution of transmembrane channel-like protein 1 and 2 (TMC1 and TMC2) to MET current during development of tonotopic gradients.
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21
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Qiu X, Müller U. Mechanically Gated Ion Channels in Mammalian Hair Cells. Front Cell Neurosci 2018; 12:100. [PMID: 29755320 PMCID: PMC5932396 DOI: 10.3389/fncel.2018.00100] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 03/26/2018] [Indexed: 01/05/2023] Open
Abstract
Hair cells in the inner ear convert mechanical stimuli provided by sound waves and head movements into electrical signal. Several mechanically evoked ionic currents with different properties have been recorded in hair cells. The search for the proteins that form the underlying ion channels is still in progress. The mechanoelectrical transduction (MET) channel near the tips of stereociliary in hair cells, which is responsible for sensory transduction, has been studied most extensively. Several components of the sensory mechanotransduction machinery in stereocilia have been identified, including the multi-transmembrane proteins tetraspan membrane protein in hair cell stereocilia (TMHS)/LHFPL5, transmembrane inner ear (TMIE) and transmembrane channel-like proteins 1 and 2 (TMC1/2). However, there remains considerable uncertainty regarding the molecules that form the channel pore. In addition to the sensory MET channel, hair cells express the mechanically gated ion channel PIEZO2, which is localized near the base of stereocilia and not essential for sensory transduction. The function of PIEZO2 in hair cells is not entirely clear but it might have a role in damage sensing and repair processes. Additional stretch-activated channels of unknown molecular identity and function have been found to localize at the basolateral membrane of hair cells. Here, we review current knowledge regarding the different mechanically gated ion channels in hair cells and discuss open questions concerning their molecular composition and function.
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Affiliation(s)
- Xufeng Qiu
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Ulrich Müller
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
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22
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Morgan CP, Zhao H, LeMasurier M, Xiong W, Pan B, Kazmierczak P, Avenarius MR, Bateschell M, Larisch R, Ricci AJ, Müller U, Barr-Gillespie PG. TRPV6, TRPM6 and TRPM7 Do Not Contribute to Hair-Cell Mechanotransduction. Front Cell Neurosci 2018; 12:41. [PMID: 29515374 PMCID: PMC5826258 DOI: 10.3389/fncel.2018.00041] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 02/01/2018] [Indexed: 12/02/2022] Open
Abstract
Hair cells of the inner ear transduce mechanical stimuli like sound or head movements into electrical signals, which are propagated to the central nervous system. The hair-cell mechanotransduction channel remains unidentified. We tested whether three transient receptor channel (TRP) family members, TRPV6, TRPM6 and TRPM7, were necessary for transduction. TRPV6 interacted with USH1C (harmonin), a scaffolding protein that participates in transduction. Using a cysteine-substitution knock-in mouse line and methanethiosulfonate (MTS) reagents selective for this allele, we found that inhibition of TRPV6 had no effect on transduction in mouse cochlear hair cells. TRPM6 and TRPM7 each interacted with the tip-link component PCDH15 in cultured eukaryotic cells, which suggested they might be part of the transduction complex. Cochlear hair cell transduction was not affected by manipulations of Mg2+, however, which normally perturbs TRPM6 and TRPM7. To definitively examine the role of these two channels in transduction, we showed that deletion of either or both of their genes selectively in hair cells had no effect on auditory function. We suggest that TRPV6, TRPM6 and TRPM7 are unlikely to be the pore-forming subunit of the hair-cell transduction channel.
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Affiliation(s)
- Clive P. Morgan
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Hongyu Zhao
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Meredith LeMasurier
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Wei Xiong
- Department of Neuroscience, Scripps Research Institute, La Jolla, CA, United States
| | - Bifeng Pan
- Department of Otolaryngology, Stanford University, Stanford, CA, United States
| | - Piotr Kazmierczak
- Department of Neuroscience, Scripps Research Institute, La Jolla, CA, United States
| | - Matthew R. Avenarius
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Michael Bateschell
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Ruby Larisch
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
| | - Anthony J. Ricci
- Department of Otolaryngology, Stanford University, Stanford, CA, United States
| | - Ulrich Müller
- Department of Neuroscience, Scripps Research Institute, La Jolla, CA, United States
| | - Peter G. Barr-Gillespie
- Oregon Hearing Research Center & Vollum Institute, Oregon Health & Science University, Portland, OR, United States
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23
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Chou SW, Chen Z, Zhu S, Davis RW, Hu J, Liu L, Fernando CA, Kindig K, Brown WC, Stepanyan R, McDermott BM. A molecular basis for water motion detection by the mechanosensory lateral line of zebrafish. Nat Commun 2017; 8:2234. [PMID: 29269857 PMCID: PMC5740173 DOI: 10.1038/s41467-017-01604-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 09/29/2017] [Indexed: 11/16/2022] Open
Abstract
Detection of water motion by the lateral line relies on mechanotransduction complexes at stereocilia tips. This sensory system is comprised of neuromasts, patches of hair cells with stereociliary bundles arranged with morphological mirror symmetry that are mechanically responsive to two opposing directions. Here, we find that transmembrane channel-like 2b (Tmc2b) is differentially required for mechanotransduction in the zebrafish lateral line. Despite similarities in neuromast hair cell morphology, three classes of these cells can be distinguished by their Tmc2b reliance. We map mechanosensitivity along the lateral line using imaging and electrophysiology to determine that a hair cell's Tmc2b dependence is governed by neuromast topological position and hair bundle orientation. Overall, water flow is detected by molecular machinery that can vary between hair cells of different neuromasts. Moreover, hair cells within the same neuromast can break morphologic symmetry of the sensory organ at the stereocilia tips.
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Affiliation(s)
- Shih-Wei Chou
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Zongwei Chen
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Shaoyuan Zhu
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Robin W Davis
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Jiaqi Hu
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Li Liu
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Carol A Fernando
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Kayla Kindig
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - William C Brown
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Ruben Stepanyan
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
- Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Brian M McDermott
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.
- Department of Biology, Case Western Reserve University, Cleveland, OH, 44106, USA.
- Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.
- Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.
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24
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Lipid bilayer mediates ion-channel cooperativity in a model of hair-cell mechanotransduction. Proc Natl Acad Sci U S A 2017; 114:E11010-E11019. [PMID: 29217640 DOI: 10.1073/pnas.1713135114] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mechanoelectrical transduction in the inner ear is a biophysical process underlying the senses of hearing and balance. The key players involved in this process are mechanosensitive ion channels. They are located in the stereocilia of hair cells and opened by the tension in specialized molecular springs, the tip links, connecting adjacent stereocilia. When channels open, the tip links relax, reducing the hair-bundle stiffness. This gating compliance makes hair cells especially sensitive to small stimuli. The classical explanation for the gating compliance is that the conformational rearrangement of a single channel directly shortens the tip link. However, to reconcile theoretical models based on this mechanism with experimental data, an unrealistically large structural change of the channel is required. Experimental evidence indicates that each tip link is a dimeric molecule, associated on average with two channels at its lower end. It also indicates that the lipid bilayer modulates channel gating, although it is not clear how. Here, we design and analyze a model of mechanotransduction where each tip link attaches to two channels, mobile within the membrane. Their states and positions are coupled by membrane-mediated elastic forces arising from the interaction between the channels' hydrophobic cores and that of the lipid bilayer. This coupling induces cooperative opening and closing of the channels. The model reproduces the main properties of hair-cell mechanotransduction using only realistic parameters constrained by experimental evidence. This work provides an insight into the fundamental role that membrane-mediated ion-channel cooperativity can play in sensory physiology.
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25
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Tompkins N, Spinelli KJ, Choi D, Barr-Gillespie PG. A Model for Link Pruning to Establish Correctly Polarized and Oriented Tip Links in Hair Bundles. Biophys J 2017; 113:1868-1881. [PMID: 29045880 DOI: 10.1016/j.bpj.2017.08.029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 08/14/2017] [Accepted: 08/21/2017] [Indexed: 10/18/2022] Open
Abstract
Tip links are thought to gate the mechanically sensitive transduction channels of hair cells, but how they form during development and regeneration remains mysterious. In particular, it is unclear how tip links are strung between stereocilia so that they are oriented parallel to a single axis; why their polarity is uniform despite their constituent molecules' intrinsic asymmetry; and why only a single tip link is present at each tip-link position. We present here a series of simple rules that reasonably explain why these phenomena occur. In particular, our model relies on each of the two ends of the tip link having distinct Ca2+-dependent stability and being connected to different motor complexes. A simulation employing these rules allowed us to explore the parameter space for the model, demonstrating the importance of the feedback between transduction channels and angled links, links that are 60° off-axis with respect to mature tip links. We tested this key aspect of the model by examining angled links in chick cochlea hair cells. As implied by the assumptions used to generate the model, we found that angled links were stabilized if there was no tip link at the tip of the upper stereocilium, and appeared when transduction channels were blocked. The model thus plausibly explains how tip-link formation and pruning can occur.
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Affiliation(s)
- Nathan Tompkins
- Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, Oregon
| | - Kateri J Spinelli
- Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, Oregon
| | - Dongseok Choi
- School of Public Health, Oregon Health and Science University, Portland, Oregon; Graduate School of Dentistry, Kyung Hee University, Seoul, South Korea
| | - Peter G Barr-Gillespie
- Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, Oregon.
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Beurg M, Fettiplace R. PIEZO2 as the anomalous mechanotransducer channel in auditory hair cells. J Physiol 2017; 595:7039-7048. [PMID: 28983916 PMCID: PMC5709317 DOI: 10.1113/jp274996] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Accepted: 09/01/2017] [Indexed: 12/24/2022] Open
Abstract
Throughout postnatal maturation of the mouse inner ear, cochlear hair cells display at least two types of mechanically gated ion channel: normal mechanotransducer (MT) channels at the tips of the stereocilia, activated by tension in interciliary tip links, and anomalous mechanosensitive (MS) channels on the top surface of the cells. The anomalous MS channels are responsible for the reverse‐polarity current that appears in mutants in which normal transduction is lost. They are also seen in wild‐type hair cells around birth, appearing 2 days earlier than normal MT channels, and being down‐regulated with the emergence of the normal channels. We review the evidence that the normal and anomalous channels are distinct channel types, which includes differences in localization, susceptibility to pharmacological agents, single‐channel conductance and Ca2+ permeability. The dichotomy is reinforced by the observation that the anomalous current is absent in cochlear cells of Piezo2‐null mice, even though the normal MT current persists. The anomalous current is suppressed by high intracellular Ca2+, suggesting that influx of the divalent ion via more Ca2+‐permeable normal MT channels inhibits the anomalous channels, thus explaining the temporal relationship between the two. Piezo2‐null mice have largely normal hearing, exhibiting up to 20 dB elevation in threshold in the acoustic brainstem response, so raising questions about the significance of PIEZO2 in the cochlea. Since the anomalous current declines with postnatal age, PIEZO2 may contribute to hair cell development, but it does not underlie the normal MT current. Its role in the development of hearing is not understood.
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Affiliation(s)
- Maryline Beurg
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, 53706, USA
| | - Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, 53706, USA
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Mahendrasingam S, Fettiplace R, Alagramam KN, Cross E, Furness DN. Spatiotemporal changes in the distribution of LHFPL5 in mice cochlear hair bundles during development and in the absence of PCDH15. PLoS One 2017; 12:e0185285. [PMID: 29069081 PMCID: PMC5656302 DOI: 10.1371/journal.pone.0185285] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2017] [Accepted: 09/08/2017] [Indexed: 11/18/2022] Open
Abstract
Mechanosensory transduction by vertebrate hair cells depends on a protein complex at the tips of shorter stereocilia associated with mechanoelectrical transduction channels activated by tip links in the hair bundle. In mammalian hair cells, this complex includes transmembrane channel-like protein subunit 1 (TMC1), lipoma HMGIC fusion partner-like 5 protein (LHFPL5) and protocadherin 15 (PCDH15), a lower-end component of the tip link. TMC1 interacts with LHFPL5 and PCDH15 but how the complex develops to maturity, and the relationships between these proteins, remains uncertain. Here we evaluate the spatiotemporal development of LHFPL5 distributions in mouse cochlear hair bundles by immunofluorescence and immunogold transmission electron microscopy, from postnatal day 0 (P0) through P21 in wild type and PCDH15-deficient mice. At P0, hair bundles contain many short microvilli-like processes which we term unranked stereocilia, and a subset of lengthening rows, adjacent to a kinocilium. LHFPL5 is distributed throughout the bundle, including on stereocilia tips and the kinocilium. At P3, 4-to-6 rows of ranked stereocilia are evident, total LHFPL5 expression peaks, and LHFPL5 is localised to ranked stereocilia tips of all rows and to lower shaft/ankle links. By P12, the bundle has a mature pattern with 3 ranked rows but virtually no unranked stereocilia or kinocilium; LHFPL5 expression has declined and become restricted to the tips of shorter stereocilia. Throughout development from P0, expression of LHFPL5 is greater overall on apical than basal bundles, but there is, on average, an equal amount of labelling per labelled tip. In P3 mice lacking PCDH15, LHFPL5 labelling is not at the tips but is primarily on unranked stereocilia and lower lateral links. These data show that LHFPL5 is already present in the MET apparatus at P0 but requires PCDH15 at P3 to remain there. Shaft/ankle link localisation suggests it interacts with link proteins other than PCDH15.
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Affiliation(s)
| | - Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, WI, United States of America
| | - Kumar N. Alagramam
- Otolaryngology Head and Neck Surgery, University Hospital Cleveland Medical Center, Case Western Reserve University, Cleveland, Ohio, OH, United States of America
| | - Ellen Cross
- School of Life Sciences, Keele University, Keele, Staffordshire, United Kingdom
| | - David N. Furness
- School of Life Sciences, Keele University, Keele, Staffordshire, United Kingdom
- * E-mail:
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Corns LF, Jeng JY, Richardson GP, Kros CJ, Marcotti W. TMC2 Modifies Permeation Properties of the Mechanoelectrical Transducer Channel in Early Postnatal Mouse Cochlear Outer Hair Cells. Front Mol Neurosci 2017; 10:326. [PMID: 29093662 PMCID: PMC5651230 DOI: 10.3389/fnmol.2017.00326] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 09/27/2017] [Indexed: 01/11/2023] Open
Abstract
The ability of cochlear hair cells to convert sound into receptor potentials relies on the mechanoelectrical transducer (MET) channels present in their stereociliary bundles. There is strong evidence implying that transmembrane channel-like protein (TMC) 1 contributes to the pore-forming subunit of the mature MET channel, yet its expression is delayed (~>P5 in apical outer hair cells, OHCs) compared to the onset of mechanotransduction (~P1). Instead, the temporal expression of TMC2 coincides with this onset, indicating that it could be part of the immature MET channel. We investigated MET channel properties from OHCs of homo- and heterozygous Tmc2 knockout mice. In the presence of TMC2, the MET channel blocker dihydrostreptomycin (DHS) had a lower affinity for the channel, when the aminoglycoside was applied extracellularly or intracellularly, with the latter effect being more pronounced. In Tmc2 knockout mice OHCs were protected from aminoglycoside ototoxicity during the first postnatal week, most likely due to their small MET current and the lower saturation level for aminoglycoside entry into the individual MET channels. DHS entry through the MET channels of Tmc2 knockout OHCs was lower during the first than in the second postnatal week, suggestive of a developmental change in the channel pore properties independent of TMC2. However, the ability of TMC2 to modify the MET channel properties strongly suggests it contributes to the pore-forming subunit of the neonatal channel. Nevertheless, we found that TMC2, different from TMC1, is not necessary for OHC development. While TMC2 is required for mechanotransduction in mature vestibular hair cells, its expression in the immature cochlea may be an evolutionary remnant.
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Affiliation(s)
- Laura F. Corns
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Jing-Yi Jeng
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Guy P. Richardson
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - Corné J. Kros
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - Walter Marcotti
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
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29
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Fettiplace R. Hair Cell Transduction, Tuning, and Synaptic Transmission in the Mammalian Cochlea. Compr Physiol 2017; 7:1197-1227. [PMID: 28915323 DOI: 10.1002/cphy.c160049] [Citation(s) in RCA: 191] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via submicrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower end of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell's characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses. © 2017 American Physiological Society. Compr Physiol 7:1197-1227, 2017.
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Affiliation(s)
- Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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Suchyna TM. Piezo channels and GsMTx4: Two milestones in our understanding of excitatory mechanosensitive channels and their role in pathology. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2017; 130:244-253. [PMID: 28778608 DOI: 10.1016/j.pbiomolbio.2017.07.011] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 07/17/2017] [Accepted: 07/21/2017] [Indexed: 12/19/2022]
Abstract
Discovery of Piezo channels and the reporting of their sensitivity to the inhibitor GsMTx4 were important milestones in the study of non-selective cationic mechanosensitive channels (MSCs) in normal physiology and pathogenesis. GsMTx4 had been used for years to investigate the functional role of cationic MSCs, especially in muscle tissue, but with little understanding of its target or inhibitory mechanism. The sensitivity of Piezo channels to bilayer stress and its robust mechanosensitivity when expressed in heterologous systems were keys to determining GsMTx4's mechanism of action. However, questions remain regarding Piezo's role in muscle function due to the non-selective nature of GsMTx4 inhibition toward membrane mechanoenzymes and the implication of MCS channel types by genetic knockdown. Evidence supporting Piezo like activity, at least in the developmental stages of muscle, is presented. While the MSC targets of GsMTx4 in muscle pathology are unclear, its muscle protective effects are clearly demonstrated in two recent in situ studies on normal cardiomyocytes and dystrophic skeletal muscle. The muscle protective function may be due to the combined effect of GsMTx4's inhibitory action on cationic MSCs like Piezo and TRP, and its potentiation of repolarizing K+ selective MSCs like K2P and SAKCa. Paradoxically, the potent in vitro action of GsMTx4 on many physiological functions seems to conflict with its lack of in situ side-effects on normal animal physiology. Future investigations into cytoskeletal control of sarcolemma mechanics and the suspected inclusion of MSCs in membrane micro/nano sized domains with distinct mechanical properties will aide our understanding of this dichotomy.
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Affiliation(s)
- Thomas M Suchyna
- University of Buffalo, Dept. of Physiology and Biophysics, Buffalo, NY, USA.
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31
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Molecular Identity of the Mechanotransduction Channel in Hair Cells: Not Quiet There Yet. J Neurosci 2017; 36:10927-10934. [PMID: 27798175 DOI: 10.1523/jneurosci.1149-16.2016] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 05/23/2016] [Indexed: 12/31/2022] Open
Abstract
Hair cells in the mammalian cochlea are specialized mechanosensory cells that convert sound-induced vibrations into electrochemical signals. The molecular composition of the mechanotransduction channel underlying auditory perception has been difficult to define. The study of genes that are linked to inherited forms of deafness has recently provided tantalizing clues. Current findings indicate that the mechanotransduction channel in hair cells is a complex molecular machine. Four different proteins (TMHS/LHFPL5, TMIE, TMC1, and TMC2) have so far been linked to the transduction channel, but which proteins contribute to the channel pore still needs to be determined. Current evidence also suggests that the channel complex may contain additional, yet to be identified components.
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Fettiplace R. Is TMC1 the Hair Cell Mechanotransducer Channel? Biophys J 2017; 111:3-9. [PMID: 27410728 PMCID: PMC4945579 DOI: 10.1016/j.bpj.2016.05.032] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Revised: 05/06/2016] [Accepted: 05/19/2016] [Indexed: 10/26/2022] Open
Abstract
Transmembrane channel-like protein isoform-1 (TMC1) has emerged over the past five years as a prime contender for the mechano-electrical transducer (MET) channel in hair cells of the inner ear. TMC1 is thought to have a six-transmembrane domain structure reminiscent of some other ion-channel subunits, and is targeted to the tips of the stereocilia in the sensory hair bundle, where the MET channel is located. Moreover, there are TMC1 mutations linked to human deafness causing loss of conventional MET currents, hair cell degeneration, and deafness in mice. Finally, mutations of Tmc1 can alter the conductance and Ca(2+) selectivity of the MET channels. For several reasons though, it is unclear that TMC1 is indeed the MET channel pore: 1) in other animals or tissues, mutations of TMC family members do not directly affect cellular mechanosensitivity; 2) there are residual manifestations of mechanosensitivity in hair cells of mouse Tmc1:Tmc2 double knockouts; 3) there is so far no evidence that expression of mammalian Tmc1 generates a mechanically sensitive ion channel in the plasma membrane when expressed in heterologous cells; and 4) there are other proteins, such as TMIE and LHFPL5, which behave similarly to TMC1, their mutation also leading to loss of MET current and deafness. This review will present these disparate lines of evidence and describes recent work that addresses the role of TMC1.
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Affiliation(s)
- Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
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33
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Scholz N, Monk KR, Kittel RJ, Langenhan T. Adhesion GPCRs as a Putative Class of Metabotropic Mechanosensors. Handb Exp Pharmacol 2017; 234:221-247. [PMID: 27832490 DOI: 10.1007/978-3-319-41523-9_10] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Adhesion GPCRs as mechanosensors. Different aGPCR homologs and their cognate ligands have been described in settings, which suggest that they function in a mechanosensory capacity. For details, see text G protein-coupled receptors (GPCRs) constitute the most versatile superfamily of biosensors. This group of receptors is formed by hundreds of GPCRs, each of which is tuned to the perception of a specific set of stimuli a cell may encounter emanating from the outside world or from internal sources. Most GPCRs are receptive for chemical compounds such as peptides, proteins, lipids, nucleotides, sugars, and other organic compounds, and this capacity is utilized in several sensory organs to initiate visual, olfactory, gustatory, or endocrine signals. In contrast, GPCRs have only anecdotally been implicated in the perception of mechanical stimuli. Recent studies, however, show that the family of adhesion GPCRs (aGPCRs), which represents a large panel of over 30 homologs within the GPCR superfamily, displays molecular design and expression patterns that are compatible with receptivity toward mechanical cues (Fig. 1). Here, we review physiological and molecular principles of established mechanosensors, discuss their relevance for current research of the mechanosensory function of aGPCRs, and survey the current state of knowledge on aGPCRs as mechanosensing molecules.
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Affiliation(s)
- Nicole Scholz
- Department of Neurophysiology, Institute of Physiology, University of Würzburg, Röntgenring 9, Würzburg, 97070, Germany.
| | - Kelly R Monk
- Department of Developmental Biology, Hope Center for Neurologic Disorders, Washington University School of Medicine, St. Louis, 63110, MO, USA
| | - Robert J Kittel
- Department of Neurophysiology, Institute of Physiology, University of Würzburg, Röntgenring 9, Würzburg, 97070, Germany
| | - Tobias Langenhan
- Department of Neurophysiology, Institute of Physiology, University of Würzburg, Röntgenring 9, Würzburg, 97070, Germany.
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Erickson T, Morgan CP, Olt J, Hardy K, Busch-Nentwich E, Maeda R, Clemens R, Krey JF, Nechiporuk A, Barr-Gillespie PG, Marcotti W, Nicolson T. Integration of Tmc1/2 into the mechanotransduction complex in zebrafish hair cells is regulated by Transmembrane O-methyltransferase (Tomt). eLife 2017; 6:e28474. [PMID: 28534737 PMCID: PMC5462536 DOI: 10.7554/elife.28474] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Accepted: 05/20/2017] [Indexed: 01/18/2023] Open
Abstract
Transmembrane O-methyltransferase (TOMT/LRTOMT) is responsible for non-syndromic deafness DFNB63. However, the specific defects that lead to hearing loss have not been described. Using a zebrafish model of DFNB63, we show that the auditory and vestibular phenotypes are due to a lack of mechanotransduction (MET) in Tomt-deficient hair cells. GFP-tagged Tomt is enriched in the Golgi of hair cells, suggesting that Tomt might regulate the trafficking of other MET components to the hair bundle. We found that Tmc1/2 proteins are specifically excluded from the hair bundle in tomt mutants, whereas other MET complex proteins can still localize to the bundle. Furthermore, mouse TOMT and TMC1 can directly interact in HEK 293 cells, and this interaction is modulated by His183 in TOMT. Thus, we propose a model of MET complex assembly where Tomt and the Tmcs interact within the secretory pathway to traffic Tmc proteins to the hair bundle.
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Affiliation(s)
- Timothy Erickson
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
| | - Clive P Morgan
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
| | - Jennifer Olt
- Department of Biomedical Science, University of Sheffield, Sheffield, United States
| | - Katherine Hardy
- Department of Biomedical Science, University of Sheffield, Sheffield, United States
| | | | - Reo Maeda
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
| | - Rachel Clemens
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
| | - Jocelyn F Krey
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
| | - Alex Nechiporuk
- Department of Cell, Developmental and Cancer Biology, Oregon Health and Science University, Portland, United States
| | - Peter G Barr-Gillespie
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
| | - Walter Marcotti
- Department of Biomedical Science, University of Sheffield, Sheffield, United States
| | - Teresa Nicolson
- Oregon Hearing Research Center and the Vollum Institute, Oregon Health and Science University, Portland, United States
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35
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36
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Mechanosensory hair cells express two molecularly distinct mechanotransduction channels. Nat Neurosci 2016; 20:24-33. [PMID: 27893727 PMCID: PMC5191906 DOI: 10.1038/nn.4449] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 10/27/2016] [Indexed: 12/26/2022]
Abstract
Auditory hair cells contain mechanotransduction channels that rapidly open in response to sound-induced vibrations. Surprisingly, we report here that auditory hair cells contain two molecularly distinct mechanotransduction channels. One ion channel is activated by sound and is responsible for sensory transduction. This sensory transduction channel is expressed in hair-cell stereocilia and previous studies show that its activity is affected by mutations in the genes encoding the transmembrane proteins TMHS/LHFPL5, TMIE and TMC1/2. We show here that the second ion channel is expressed at the apical surface of hair cells and contains the Piezo2 protein. The activity of the Piezo2-dependent channel is controlled by the intracellular Ca2+ concentration and can be recorded following disruption of the sensory transduction machinery or more generally by disruption of the sensory epithelium. We thus conclude that hair cells express two molecularly and functionally distinct mechanotransduction channels with different subcellular distribution.
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37
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Corns LF, Marcotti W. Piezo1 haploinsufficiency does not alter mechanotransduction in mouse cochlear outer hair cells. Physiol Rep 2016; 4:4/3/e12701. [PMID: 26869684 PMCID: PMC4758935 DOI: 10.14814/phy2.12701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The mechanoelectrical transducer (MET) channels located at the stereocilia tip of cochlear hair cells are crucial to convert the mechanical energy of sound into receptor potentials, but the identity of its pore-forming subunits remains uncertain. Piezo1, which has been identified in the transcriptome of mammalian cochlear hair cells, encodes a transmembrane protein that forms mechanosensitive channels in other tissues. We investigated the properties of the MET channel in outer hair cells (OHCs) of Piezo1 mice (postnatal day 6-9). The MET current was elicited by deflecting the hair bundle of OHCs using sinewave and step stimuli from a piezo-driven fluid jet. Apical and basal OHCs were investigated because the properties of the MET channel vary along the cochlea. We found that the maximal MET current amplitude and the resting open probability of the MET channel in OHCs were similar between Piezo1(+/-) haploinsufficient mice and wild-type littermates. The sensitivity to block by the permeant MET channel blocker dihydrostreptomycin was also similar between the two genotypes. Finally, the anomalous mechano-gated current, which is activated by sheer force and which is tip-link independent, was unaffected in OHCs from Piezo1(+/-) haploinsufficient mice. Our results suggest that Piezo1 is unlikely to be a component of the MET channel complex in mammalian cochlear OHCs.
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Affiliation(s)
- Laura F Corns
- Department of Biomedical Science, University of Sheffield, Sheffield, UK
| | - Walter Marcotti
- Department of Biomedical Science, University of Sheffield, Sheffield, UK
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38
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Adaptation Independent Modulation of Auditory Hair Cell Mechanotransduction Channel Open Probability Implicates a Role for the Lipid Bilayer. J Neurosci 2016; 36:2945-56. [PMID: 26961949 DOI: 10.1523/jneurosci.3011-15.2016] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The auditory system is able to detect movement down to atomic dimensions. This sensitivity comes in part from mechanisms associated with gating of hair cell mechanoelectric transduction (MET) channels. MET channels, located at the tops of stereocilia, are poised to detect tension induced by hair bundle deflection. Hair bundle deflection generates a force by pulling on tip-link proteins connecting adjacent stereocilia. The resting open probability (P(open)) of MET channels determines the linearity and sensitivity to mechanical stimulation. Classically, P(open) is regulated by a calcium-sensitive adaptation mechanism in which lowering extracellular calcium or depolarization increases P(open). Recent data demonstrated that the fast component of adaptation is independent of both calcium and voltage, thus requiring an alternative explanation for the sensitivity of P(open) to calcium and voltage. Using rat auditory hair cells, we characterize a mechanism, separate from fast adaptation, whereby divalent ions interacting with the local lipid environment modulate resting P(open). The specificity of this effect for different divalent ions suggests binding sites that are not an EF-hand or calmodulin model. GsMTx4, a lipid-mediated modifier of cationic stretch-activated channels, eliminated the voltage and divalent sensitivity with minimal effects on adaptation. We hypothesize that the dual mechanisms (lipid modulation and adaptation) extend the dynamic range of the system while maintaining adaptation kinetics at their maximal rates.
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39
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TMC-1 Mediates Alkaline Sensation in C. elegans through Nociceptive Neurons. Neuron 2016; 91:146-54. [PMID: 27321925 DOI: 10.1016/j.neuron.2016.05.023] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2015] [Revised: 04/03/2016] [Accepted: 05/04/2016] [Indexed: 11/22/2022]
Abstract
Noxious pH triggers pungent taste and nocifensive behavior. While the mechanisms underlying acidic pH sensation have been extensively characterized, little is known about how animals sense alkaline pH in the environment. TMC genes encode a family of evolutionarily conserved membrane proteins whose functions are largely unknown. Here, we characterize C. elegans TMC-1, which was suggested to form a Na(+)-sensitive channel mediating salt chemosensation. Interestingly, we find that TMC-1 is required for worms to avoid noxious alkaline environment. Alkaline pH evokes an inward current in nociceptive neurons, which is primarily mediated by TMC-1 and to a lesser extent by the TRP channel OSM-9. However, unlike OSM-9, which is sensitive to both acidic and alkaline pH, TMC-1 is only required for alkali-activated current, revealing a specificity for alkaline sensation. Ectopic expression of TMC-1 confers alkaline sensitivity to alkali-insensitive cells. Our results identify an unexpected role for TMCs in alkaline sensation and nociception.
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40
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Transmembrane channel-like (tmc) gene regulates Drosophila larval locomotion. Proc Natl Acad Sci U S A 2016; 113:7243-8. [PMID: 27298354 DOI: 10.1073/pnas.1606537113] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Drosophila larval locomotion, which entails rhythmic body contractions, is controlled by sensory feedback from proprioceptors. The molecular mechanisms mediating this feedback are little understood. By using genetic knock-in and immunostaining, we found that the Drosophila melanogaster transmembrane channel-like (tmc) gene is expressed in the larval class I and class II dendritic arborization (da) neurons and bipolar dendrite (bd) neurons, both of which are known to provide sensory feedback for larval locomotion. Larvae with knockdown or loss of tmc function displayed reduced crawling speeds, increased head cast frequencies, and enhanced backward locomotion. Expressing Drosophila TMC or mammalian TMC1 and/or TMC2 in the tmc-positive neurons rescued these mutant phenotypes. Bending of the larval body activated the tmc-positive neurons, and in tmc mutants this bending response was impaired. This implicates TMC's roles in Drosophila proprioception and the sensory control of larval locomotion. It also provides evidence for a functional conservation between Drosophila and mammalian TMCs.
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41
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Beurg M, Goldring AC, Fettiplace R. The effects of Tmc1 Beethoven mutation on mechanotransducer channel function in cochlear hair cells. ACTA ACUST UNITED AC 2016; 146:233-43. [PMID: 26324676 PMCID: PMC4555472 DOI: 10.1085/jgp.201511458] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Analyses of the Tmc1 Beethoven mouse mutant indicate that hair cell mechanotransducer channel adaptation in mammals is mainly regulated by changes in intracellular Ca2+. Sound stimuli are converted into electrical signals via gating of mechano-electrical transducer (MT) channels in the hair cell stereociliary bundle. The molecular composition of the MT channel is still not fully established, although transmembrane channel–like protein isoform 1 (TMC1) may be one component. We found that in outer hair cells of Beethoven mice containing a M412K point mutation in TMC1, MT channels had a similar unitary conductance to that of wild-type channels but a reduced selectivity for Ca2+. The Ca2+-dependent adaptation that adjusts the operating range of the channel was also impaired in Beethoven mutants, with reduced shifts in the relationship between MT current and hair bundle displacement for adapting steps or after lowering extracellular Ca2+; these effects may be attributed to the channel’s reduced Ca2+ permeability. Moreover, the density of stereociliary CaATPase pumps for Ca2+ extrusion was decreased in the mutant. The results suggest that a major component of channel adaptation is regulated by changes in intracellular Ca2+. Consistent with this idea, the adaptive shift in the current–displacement relationship when hair bundles were bathed in endolymph-like Ca2+ saline was usually abolished by raising the intracellular Ca2+ concentration.
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Affiliation(s)
- Maryline Beurg
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706
| | - Adam C Goldring
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706
| | - Robert Fettiplace
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706
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Tmc1 Point Mutation Affects Ca2+ Sensitivity and Block by Dihydrostreptomycin of the Mechanoelectrical Transducer Current of Mouse Outer Hair Cells. J Neurosci 2016; 36:336-49. [PMID: 26758827 DOI: 10.1523/jneurosci.2439-15.2016] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
UNLABELLED The transduction of sound into electrical signals depends on mechanically sensitive ion channels in the stereociliary bundle. The molecular composition of this mechanoelectrical transducer (MET) channel is not yet known. Transmembrane channel-like protein isoforms 1 (TMC1) and 2 (TMC2) have been proposed to form part of the MET channel, although their exact roles are still unclear. Using Beethoven (Tmc1(Bth/Bth)) mice, which have an M412K point mutation in TMC1 that adds a positive charge, we found that Ca(2+) permeability and conductance of the MET channel of outer hair cells (OHCs) were reduced. Tmc1(Bth/Bth) OHCs were also less sensitive to block by the permeant MET channel blocker dihydrostreptomycin, whether applied extracellularly or intracellularly. These findings suggest that the amino acid that is mutated in Bth is situated at or near the negatively charged binding site for dihydrostreptomycin within the permeation pore of the channel. We also found that the Ca(2+) dependence of the operating range of the MET channel was altered by the M412K mutation. Depolarization did not increase the resting open probability of the MET current of Tmc1(Bth/Bth) OHCs, whereas raising the intracellular concentration of the Ca(2+) chelator BAPTA caused smaller increases in resting open probability in Bth mutant OHCs than in wild-type control cells. We propose that these observations can be explained by the reduced Ca(2+) permeability of the mutated MET channel indirectly causing the Ca(2+) sensor for adaptation, at or near the intracellular face of the MET channel, to become more sensitive to Ca(2+) influx as a compensatory mechanism. SIGNIFICANCE STATEMENT In the auditory system, the hair cells convert sound-induced mechanical movement of the hair bundles atop these cells into electrical signals through the opening of mechanically gated ion channels at the tips of the bundles. Although the nature of these mechanoelectrical transducer (MET) channels is still unclear, recent studies implicate transmembrane channel-like protein isoform 1 (TMC1) channels in the mammalian cochlea. Using a mutant mouse model (Beethoven) for progressive hearing loss in humans (DFNA36), which harbors a point mutation in the Tmc1 gene, we show that this mutation affects the MET channel pore, reducing its Ca(2+) permeability and its affinity for the permeant blocker dihydrostreptomycin. A number of phenomena that we ascribe to Ca(2+)-dependent adaptation appear stronger, in compensation for the reduced Ca(2+) entry.
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Development and localization of reverse-polarity mechanotransducer channels in cochlear hair cells. Proc Natl Acad Sci U S A 2016; 113:6767-72. [PMID: 27162344 DOI: 10.1073/pnas.1601067113] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cochlear hair cells normally detect positive deflections of their hair bundles, rotating toward their tallest edge, which opens mechanotransducer (MT) channels by increased tension in interciliary tip links. After tip-link destruction, the normal polarity of MT current is replaced by a mechanically sensitive current evoked by negative bundle deflections. The "reverse-polarity" current was investigated in cochlear hair cells after tip-link destruction with BAPTA, in transmembrane channel-like protein isoforms 1/2 (Tmc1:Tmc2) double mutants, and during perinatal development. This current is a natural adjunct of embryonic development, present in all wild-type hair cells but declining after birth with emergence of the normal-polarity current. Evidence indicated the reverse-polarity current seen developmentally was a manifestation of the same ion channel as that evident under abnormal conditions in Tmc mutants or after tip-link destruction. In all cases, sinusoidal fluid-jet stimuli from different orientations suggested the underlying channels were opened not directly by deflections of the hair bundle but by deformation of the apical plasma membrane. Cell-attached patch recording on the hair-cell apical membrane revealed, after BAPTA treatment or during perinatal development, 90-pS stretch-activated cation channels that could be blocked by Ca(2+) and by FM1-43. High-speed Ca(2+) imaging, using swept-field confocal microscopy, showed the Ca(2+) influx through the reverse-polarity channels was not localized to the hair bundle, but distributed across the apical plasma membrane. These reverse-polarity channels, which we propose to be renamed "unconventional" mechanically sensitive channels, have some properties similar to the normal MT channels, but the relationship between the two types is still not well defined.
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Abstract
Mechanotransduction, the conversion of physical forces into biochemical signals, is essential for various physiological processes such as the conscious sensations of touch and hearing, and the unconscious sensation of blood flow. Mechanically activated (MA) ion channels have been proposed as sensors of physical force, but the identity of these channels and an understanding of how mechanical force is transduced has remained elusive. A number of recent studies on previously known ion channels along with the identification of novel MA ion channels have greatly transformed our understanding of touch and hearing in both vertebrates and invertebrates. Here, we present an updated review of eukaryotic ion channel families that have been implicated in mechanotransduction processes and evaluate the qualifications of the candidate genes according to specified criteria. We then discuss the proposed gating models for MA ion channels and highlight recent structural studies of mechanosensitive potassium channels.
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Affiliation(s)
- Sanjeev S Ranade
- Howard Hughes Medical Institute, Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Ruhma Syeda
- Howard Hughes Medical Institute, Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Ardem Patapoutian
- Howard Hughes Medical Institute, Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA.
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Pepermans E, Petit C. The tip-link molecular complex of the auditory mechano-electrical transduction machinery. Hear Res 2015; 330:10-7. [DOI: 10.1016/j.heares.2015.05.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 04/30/2015] [Accepted: 05/08/2015] [Indexed: 12/11/2022]
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Abstract
Recent papers suggest that TMC1 and TMC2 constitute the ion channels mediating hearing and balance. Kurima et al. (2015) now show these proteins are expressed in the right place and at the right time, bringing us closer to definitive identification.
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47
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Zhao B, Müller U. The elusive mechanotransduction machinery of hair cells. Curr Opin Neurobiol 2015; 34:172-9. [PMID: 26342686 DOI: 10.1016/j.conb.2015.08.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Revised: 08/06/2015] [Accepted: 08/18/2015] [Indexed: 11/18/2022]
Abstract
Hair cells in the mammalian cochlea are specialized sensory cells that convert mechanical signals evoked by sound waves into electrochemical signals. Several integral membrane proteins have recently been identified that are closely linked to the mechanotransduction process. Efforts are under way to determine the extent to which they are subunits of the long thought-after mechanotransduction channel. Recent findings also suggest that mechanotransduction may have a role in fine tuning the length of the stereocilia and thus in the regulation of morphological features of hair cells that are inherently linked to the mechanotransduction process.
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Affiliation(s)
- Bo Zhao
- Department of Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Ulrich Müller
- Department of Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, United States.
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Kurima K, Ebrahim S, Pan B, Sedlacek M, Sengupta P, Millis BA, Cui R, Nakanishi H, Fujikawa T, Kawashima Y, Choi BY, Monahan K, Holt JR, Griffith AJ, Kachar B. TMC1 and TMC2 Localize at the Site of Mechanotransduction in Mammalian Inner Ear Hair Cell Stereocilia. Cell Rep 2015; 12:1606-17. [PMID: 26321635 DOI: 10.1016/j.celrep.2015.07.058] [Citation(s) in RCA: 130] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 06/11/2015] [Accepted: 07/28/2015] [Indexed: 02/06/2023] Open
Abstract
Mechanosensitive ion channels at stereocilia tips mediate mechanoelectrical transduction (MET) in inner ear sensory hair cells. Transmembrane channel-like 1 and 2 (TMC1 and TMC2) are essential for MET and are hypothesized to be components of the MET complex, but evidence for their predicted spatiotemporal localization in stereocilia is lacking. Here, we determine the stereocilia localization of the TMC proteins in mice expressing TMC1-mCherry and TMC2-AcGFP. Functionality of the tagged proteins was verified by transgenic rescue of MET currents and hearing in Tmc1(Δ/Δ);Tmc2(Δ/Δ) mice. TMC1-mCherry and TMC2-AcGFP localize along the length of immature stereocilia. However, as hair cells develop, the two proteins localize predominantly to stereocilia tips. Both TMCs are absent from the tips of the tallest stereocilia, where MET activity is not detectable. This distribution was confirmed for the endogenous proteins by immunofluorescence. These data are consistent with TMC1 and TMC2 being components of the stereocilia MET channel complex.
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Affiliation(s)
- Kiyoto Kurima
- Molecular Biology and Genetics Section, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Seham Ebrahim
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Bifeng Pan
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | - Miloslav Sedlacek
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Prabuddha Sengupta
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA
| | - Bryan A Millis
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Runjia Cui
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Hiroshi Nakanishi
- Molecular Biology and Genetics Section, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Taro Fujikawa
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Yoshiyuki Kawashima
- Molecular Biology and Genetics Section, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Byung Yoon Choi
- Molecular Biology and Genetics Section, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Kelly Monahan
- Molecular Biology and Genetics Section, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA
| | - Jeffrey R Holt
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | - Andrew J Griffith
- Molecular Biology and Genetics Section, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA,.
| | - Bechara Kachar
- Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, USA,.
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Pan B, Holt JR. The molecules that mediate sensory transduction in the mammalian inner ear. Curr Opin Neurobiol 2015. [PMID: 26218316 DOI: 10.1016/j.conb.2015.06.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Years of searching and researching have finally yielded a few leads in the quest to identify molecules required for mechanosensory transduction in the mammalian inner ear. Studies of human and mouse genetics have raised the profile of several molecules that are crucial for the function sensory hair cells. Follow up studies have begun to define the molecular function and biochemical interactions of several key proteins. These studies have exposed a sensory transduction apparatus that is more complex than originally envisioned and have reinvigorated the search for additional molecular components required for normal inner ear function.
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Affiliation(s)
- Bifeng Pan
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, United States
| | - Jeffrey R Holt
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, United States.
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50
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How many proteins does it take to gate hair cell mechanotransduction? Proc Natl Acad Sci U S A 2015; 112:1254-5. [PMID: 25617369 DOI: 10.1073/pnas.1424987112] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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