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Scharr AL, Ó Maoiléidigh D, Ricci AJ. Coupling between the Stereocilia of Rat Sensory Inner-Hair-Cell Hair Bundles Is Weak, Shaping Their Sensitivity to Stimulation. J Neurosci 2023; 43:2053-2074. [PMID: 36746628 PMCID: PMC10039747 DOI: 10.1523/jneurosci.1588-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 01/16/2023] [Accepted: 01/31/2023] [Indexed: 02/08/2023] Open
Abstract
The hair bundle is the universal mechanosensory organelle of auditory, vestibular, and lateral-line systems. A bundle comprises mechanically coupled stereocilia, whose displacements in response to stimulation activate a receptor current. The similarity of stereociliary displacements within a bundle regulates fundamental properties of the receptor current like its speed, magnitude, and sensitivity. However, the dynamics of individual stereocilia from the mammalian cochlea in response to a known bundle stimulus has not been quantified. We developed a novel high-speed system, which dynamically stimulates and tracks individual inner-hair-cell stereocilia from male and female rats. Stimulating two to three of the tallest stereocilia within a bundle (nonuniform stimulation) caused dissimilar stereociliary displacements. Stereocilia farther from the stimulator moved less, but with little delay, implying that there is little slack in the system. Along the axis of mechanical sensitivity, stereocilium displacements peaked and reversed direction in response to a step stimulus. A viscoelastic model explained the observed displacement dynamics, which implies that coupling between the tallest stereocilia is effectively viscoelastic. Coupling elements between the tallest inner-hair-cell stereocilia were two to three times stronger than elements anchoring stereocilia to the surface of the cell but were 100-10,000 times weaker than those of a well-studied noncochlear hair bundle. Coupling was too weak to ensure that stereocilia move similarly in response to nonuniform stimulation at auditory frequencies. Our results imply that more uniform stimulation across the tallest stereocilia of an inner-hair-cell bundle in vivo is required to ensure stereociliary displacement similarity, increasing the speed, sensitivity, and magnitude of the receptor current.SIGNIFICANCE STATEMENT Generation of the receptor current of the hair cell is the first step in electrically encoding auditory information in the hearing organs of all vertebrates. The receptor current is shaped by mechanical coupling between stereocilia in the hair bundle of each hair cell. Here, we provide foundational information on the mechanical coupling between stereocilia of cochlear inner-hair cells. In contrast to other types of hair cell, coupling between inner-hair-cell stereocilia is weak, causing slower, smaller, and less sensitive receptor currents in response to stimulation of few, rather than many, stereocilia. Our results imply that inner-hair cells need many stereocilia to be stimulated in vivo to ensure fast, large, and sensitive receptor currents.
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Affiliation(s)
| | | | - Anthony J Ricci
- Department of Otolaryngology
- Neuroscience Graduate Program
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305
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Miller KK, Atkinson P, Mendoza KR, Ó Maoiléidigh D, Grillet N. Dimensions of a Living Cochlear Hair Bundle. Front Cell Dev Biol 2021; 9:742529. [PMID: 34900993 PMCID: PMC8657763 DOI: 10.3389/fcell.2021.742529] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Accepted: 10/13/2021] [Indexed: 11/23/2022] Open
Abstract
The hair bundle is the mechanosensory organelle of hair cells that detects mechanical stimuli caused by sounds, head motions, and fluid flows. Each hair bundle is an assembly of cellular-protrusions called stereocilia, which differ in height to form a staircase. Stereocilia have different heights, widths, and separations in different species, sensory organs, positions within an organ, hair-cell types, and even within a single hair bundle. The dimensions of the stereociliary assembly dictate how the hair bundle responds to stimuli. These hair-bundle properties have been measured previously only to a limited degree. In particular, mammalian data are either incomplete, lack control for age or position within an organ, or have artifacts owing to fixation or dehydration. Here, we provide a complete set of measurements for postnatal day (P) 11 C57BL/6J mouse apical inner hair cells (IHCs) obtained from living tissue, tissue mildly-fixed for fluorescent imaging, or tissue strongly fixed and dehydrated for scanning electronic microscopy (SEM). We found that hair bundles mildly-fixed for fluorescence had the same dimensions as living hair bundles, whereas SEM-prepared hair bundles shrank uniformly in stereociliary heights, widths, and separations. By determining the shrinkage factors, we imputed live dimensions from SEM that were too small to observe optically. Accordingly, we created the first complete blueprint of a living IHC hair bundle. We show that SEM-prepared measurements strongly affect calculations of a bundle’s mechanical properties – overestimating stereociliary deflection stiffness and underestimating the fluid coupling between stereocilia. The methods of measurement, the data, and the consequences we describe illustrate the high levels of accuracy and precision required to understand hair-bundle mechanotransduction.
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Affiliation(s)
- Katharine K Miller
- Department of Otolaryngology-Head and Neck Surgery, School of Medicine, Stanford University, Stanford, CA, United States
| | - Patrick Atkinson
- Department of Otolaryngology-Head and Neck Surgery, School of Medicine, Stanford University, Stanford, CA, United States
| | - Kyssia Ruth Mendoza
- Department of Otolaryngology-Head and Neck Surgery, School of Medicine, Stanford University, Stanford, CA, United States
| | - Dáibhid Ó Maoiléidigh
- Department of Otolaryngology-Head and Neck Surgery, School of Medicine, Stanford University, Stanford, CA, United States
| | - Nicolas Grillet
- Department of Otolaryngology-Head and Neck Surgery, School of Medicine, Stanford University, Stanford, CA, United States
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3
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Cheatham MA. Spontaneous otoacoustic emissions are biomarkers for mice with tectorial membrane defects. Hear Res 2021; 409:108314. [PMID: 34332206 DOI: 10.1016/j.heares.2021.108314] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 06/22/2021] [Accepted: 07/12/2021] [Indexed: 01/12/2023]
Abstract
Cochlear function depends on the operation of a coupled feedback loop, incorporating outer hair cells (OHCs), and structured to assure that inner hair cells (IHCs) convey frequency specific acoustic information to the brain, even at very low sound levels. Although our knowledge of OHC function and its contribution to cochlear amplification has expanded, the importance of the tectorial membrane (TM) to the processing of mechanical inputs has not been fully elucidated. In addition, there are a surprising number of genetic mutations that affect TM structure and that produce hearing loss in humans. By synthesizing old and new results obtained on several mouse mutants, we learned that animals with abnormal TMs are prone to generate spontaneous otoacoustic emissions (SOAE), which are uncommon in most wildtype laboratory animals. Because SOAEs are not produced in TM mutants or in humans when threshold shifts exceed approximately 25 dB, some degree of cochlear amplification is required. However, amplification by itself is not sufficient because normal mice are rarely spontaneous emitters. Since SOAEs reflect active cochlear operation, TM mutants are valuable for studying the oscillatory nature of the amplification process and the structures associated with its stabilization. Inasmuch as the mouse models were selected to mirror human auditory disorders, using SOAEs as a noninvasive clinical tool may assist the classification of individuals with genetic defects that influence the active mechanisms responsible for sensitivity and frequency selectivity, the hallmarks of mammalian hearing.
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Affiliation(s)
- Mary Ann Cheatham
- The Knowles Hearing Center, Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, 2-240 Frances Searle Building, 2240 Campus Drive, Evanston, IL 60208, USA.
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4
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Peng Z, Resnick A, Young YN. Primary cilium: a paradigm for integrating mathematical modeling with experiments and numerical simulations in mechanobiology. MATHEMATICAL BIOSCIENCES AND ENGINEERING : MBE 2021; 18:1215-1237. [PMID: 33757184 PMCID: PMC8552149 DOI: 10.3934/mbe.2021066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Primary cilia are non-motile, solitary (one per cell) microtubule-based organelles that emerge from the mother centriole after cells have exited the mitotic cycle. Identified as a mechanosensing organelle that responds to both mechanical and chemical stimuli, the primary cilium provides a fertile ground for integrative investigations of mathematical modeling, numerical simulations, and experiments. Recent experimental findings revealed considerable complexity to the underlying mechanosensory mechanisms that transmit extracellular stimuli to intracellular signaling many of which include primary cilia. In this invited review, we provide a brief survey of experimental findings on primary cilia and how these results lead to various mathematical models of the mechanics of the primary cilium bent under an external forcing such as a fluid flow or a trap. Mathematical modeling of the primary cilium as a fluid-structure interaction problem highlights the importance of basal anchorage and the anisotropic moduli of the microtubules. As theoretical modeling and numerical simulations progress, along with improved state-of-the-art experiments on primary cilia, we hope that details of ciliary regulated mechano-chemical signaling dynamics in cellular physiology will be understood in the near future.
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Affiliation(s)
- Zhangli Peng
- Department of Bioengineering, University of Illinois at Chicago, 851 S. Morgan St., Chicago, IL 60607, USA
| | - Andrew Resnick
- Department of Physics, Center for Gene Regulation in Health and Disease, Cleveland State University, Cleveland, OH 44115, USA
| | - Y.-N. Young
- Department of Mathematical Sciences, New Jersey Institute of Technology, University Heights, Newark, NJ 07102, USA
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5
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Cartagena-Rivera AX, Le Gal S, Richards K, Verpy E, Chadwick RS. Cochlear outer hair cell horizontal top connectors mediate mature stereocilia bundle mechanics. SCIENCE ADVANCES 2019; 5:eaat9934. [PMID: 30801007 PMCID: PMC6382404 DOI: 10.1126/sciadv.aat9934] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Accepted: 01/10/2019] [Indexed: 05/23/2023]
Abstract
Outer hair cell (OHC) stereocilia bundle deflection opens mechanoelectrical transduction channels at the tips of the stereocilia from the middle and short rows, while bundle cohesion is maintained owing to the presence of horizontal top connectors. Here, we used a quantitative noncontact atomic force microscopy method to investigate stereocilia bundle stiffness and damping, when stimulated at acoustic frequencies and nanometer distances from the bundle. Stereocilia bundle mechanics were determined in stereocilin-deficient mice lacking top connectors and with detached tectorial membrane (Strc -/-/Tecta -/- double knockout) and heterozygous littermate controls (Strc +/-/Tecta -/-). A substantial decrease in bundle stiffness and damping by ~60 and ~74% on postnatal days P13 to P15 was observed when top connectors were absent. Additionally, we followed bundle mechanics during OHC top connectors development between P9 and P15 and quantified the observed increase in OHC bundle stiffness and damping in Strc +/-/Tecta -/- mice while no significant change was detected in Strc -/-/Tecta -/- animals.
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Affiliation(s)
- Alexander X. Cartagena-Rivera
- Section on Auditory Mechanics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
| | - Sébastien Le Gal
- Unité de Génétique et Physiologie de l’Audition, Institut Pasteur, 75015 Paris, France
- UMRS 1120, Institut National de la Santé et de la Recherche Médicale (INSERM), 75015 Paris, France
- Sorbonne Universités, Université Pierre et Marie Curie Paris 06, Complexité du Vivant, 75005 Paris, France
| | - Kerianne Richards
- Genomics and Computational Biology Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
| | - Elisabeth Verpy
- Unité de Génétique et Physiologie de l’Audition, Institut Pasteur, 75015 Paris, France
- UMRS 1120, Institut National de la Santé et de la Recherche Médicale (INSERM), 75015 Paris, France
- Sorbonne Universités, Université Pierre et Marie Curie Paris 06, Complexité du Vivant, 75005 Paris, France
| | - Richard S. Chadwick
- Section on Auditory Mechanics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
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Araya-Secchi R, Neel BL, Sotomayor M. An elastic element in the protocadherin-15 tip link of the inner ear. Nat Commun 2016; 7:13458. [PMID: 27857071 PMCID: PMC5120219 DOI: 10.1038/ncomms13458] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2016] [Accepted: 10/03/2016] [Indexed: 01/16/2023] Open
Abstract
Tip link filaments convey force and gate inner-ear hair-cell transduction channels to mediate perception of sound and head movements. Cadherin-23 and protocadherin-15 form tip links through a calcium-dependent interaction of their extracellular domains made of multiple extracellular cadherin (EC) repeats. These repeats are structurally similar, but not identical in sequence, often featuring linkers with conserved calcium-binding sites that confer mechanical strength to them. Here we present the X-ray crystal structures of human protocadherin-15 EC8-EC10 and mouse EC9-EC10, which show an EC8-9 canonical-like calcium-binding linker, and an EC9-10 calcium-free linker that alters the linear arrangement of EC repeats. Molecular dynamics simulations and small-angle X-ray scattering experiments support this non-linear conformation. Simulations also suggest that unbending of EC9-10 confers some elasticity to otherwise rigid tip links. The new structure provides a first view of protocadherin-15's non-canonical EC linkers and suggests how they may function in inner-ear mechanotransduction, with implications for other cadherins.
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Affiliation(s)
- Raul Araya-Secchi
- Department of Chemistry and Biochemistry, The Ohio State University, 484 W 12th Avenue, Columbus, Ohio 43210, USA
| | - Brandon L. Neel
- Department of Chemistry and Biochemistry, The Ohio State University, 484 W 12th Avenue, Columbus, Ohio 43210, USA
| | - Marcos Sotomayor
- Department of Chemistry and Biochemistry, The Ohio State University, 484 W 12th Avenue, Columbus, Ohio 43210, USA
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7
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Parker A, Chessum L, Mburu P, Sanderson J, Bowl MR. Light and Electron Microscopy Methods for Examination of Cochlear Morphology in Mouse Models of Deafness. ACTA ACUST UNITED AC 2016; 6:272-306. [PMID: 27584554 DOI: 10.1002/cpmo.10] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Mice are an invaluable model organism for the study of auditory function. Even though there are differences in size and frequency response, the anatomy and physiology of the mouse and human ear are remarkably similar. In addition, the tools available for genetic manipulation in the mouse have enabled the generation of models carrying mutations in orthologous human deafness-causing genes, helping to validate these lesions and assess their functional consequence. Reciprocally, novel gene mutations discovered to cause auditory deficits in the mouse highlight potential new loci for human hearing loss, and expand our basic knowledge of the mechanisms and pathways important for the function of the mammalian ear. Microscopy and imaging are invaluable techniques that allow detailed characterization of cochlear pathologies associated with particular gene mutations. However, the highly organized, delicate, and intricate structures responsible for transduction of sound waves into nerve impulses are encapsulated in one of the hardest bones in the body - the temporal bone. This makes sample preparation without damage to the soft tissue, be it from dissection or processing, somewhat challenging. Fortunately, there are numerous methods for achieving high-quality images of the mouse cochlea. Reported in this article are a selection of sample preparation and imaging techniques that can be used routinely to assess cochlear morphology. Several protocols are also described for immunodetection of proteins in the cochlea. In addition, the advantages and disadvantages between different imaging platforms and their suitability for different types of microscopic examination are highlighted. © 2016 by John Wiley & Sons, Inc.
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Affiliation(s)
- Andrew Parker
- Mammalian Genetics Unit, MRC Harwell, Oxfordshire, United Kingdom
| | - Lauren Chessum
- Mammalian Genetics Unit, MRC Harwell, Oxfordshire, United Kingdom
| | - Philomena Mburu
- Mammalian Genetics Unit, MRC Harwell, Oxfordshire, United Kingdom
| | - Jeremy Sanderson
- Mammalian Genetics Unit, MRC Harwell, Oxfordshire, United Kingdom
| | - Michael R Bowl
- Mammalian Genetics Unit, MRC Harwell, Oxfordshire, United Kingdom
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8
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Mak SY, Li Z, Frere A, Chan TC, Shum HC. Musical interfaces: visualization and reconstruction of music with a microfluidic two-phase flow. Sci Rep 2014; 4:6675. [PMID: 25327509 PMCID: PMC4202207 DOI: 10.1038/srep06675] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 09/24/2014] [Indexed: 01/01/2023] Open
Abstract
Detection of sound wave in fluids can hardly be realized because of the lack of approaches to visualize the very minute sound-induced fluid motion. In this paper, we demonstrate the first direct visualization of music in the form of ripples at a microfluidic aqueous-aqueous interface with an ultra-low interfacial tension. The interfaces respond to sound of different frequency and amplitude robustly with sufficiently precise time resolution for the recording of musical notes and even subsequent reconstruction with high fidelity. Our work shows the possibility of sensing and transmitting vibrations as tiny as those induced by sound. This robust control of the interfacial dynamics enables a platform for investigating the mechanical properties of microstructures and for studying frequency-dependent phenomena, for example, in biological systems.
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Affiliation(s)
- Sze Yi Mak
- 1] HKU-Shenzhen Institute of Research and Innovation, Shenzhen, Guangdong, China [2] Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
| | - Zida Li
- Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
| | - Arnaud Frere
- Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
| | - Tat Chuen Chan
- Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
| | - Ho Cheung Shum
- 1] HKU-Shenzhen Institute of Research and Innovation, Shenzhen, Guangdong, China [2] Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong
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9
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Abstract
To enhance weak sounds while compressing the dynamic intensity range, auditory sensory cells amplify sound-induced vibrations in a nonlinear, intensity-dependent manner. In the course of this process, instantaneous waveform distortion is produced, with two conspicuous kinds of interwoven consequences, the introduction of new sound frequencies absent from the original stimuli, which are audible and detectable in the ear canal as otoacoustic emissions, and the possibility for an interfering sound to suppress the response to a probe tone, thereby enhancing contrast among frequency components. We review how the diverse manifestations of auditory nonlinearity originate in the gating principle of their mechanoelectrical transduction channels; how they depend on the coordinated opening of these ion channels ensured by connecting elements; and their links to the dynamic behavior of auditory sensory cells. This paper also reviews how the complex properties of waves traveling through the cochlea shape the manifestations of auditory nonlinearity. Examination methods based on the detection of distortions open noninvasive windows on the modes of activity of mechanosensitive structures in auditory sensory cells and on the distribution of sites of nonlinearity along the cochlear tonotopic axis, helpful for deciphering cochlear molecular physiology in hearing-impaired animal models. Otoacoustic emissions enable fast tests of peripheral sound processing in patients. The study of auditory distortions also contributes to the understanding of the perception of complex sounds.
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Affiliation(s)
- Paul Avan
- Laboratory of Neurosensory Biophysics, University of Auvergne, School of Medicine, Clermont-Ferrand, France; Institut National de la Santé et de la Recherche Médicale (INSERM), UMR 1107, Clermont-Ferrand, France; Centre Jean Perrin, Clermont-Ferrand, France; Department of Otolaryngology, County Hospital, Krems an der Donau, Austria; Laboratory of Genetics and Physiology of Hearing, Department of Neuroscience, Institut Pasteur, Paris, France; Collège de France, Genetics and Cell Physiology, Paris, France
| | - Béla Büki
- Laboratory of Neurosensory Biophysics, University of Auvergne, School of Medicine, Clermont-Ferrand, France; Institut National de la Santé et de la Recherche Médicale (INSERM), UMR 1107, Clermont-Ferrand, France; Centre Jean Perrin, Clermont-Ferrand, France; Department of Otolaryngology, County Hospital, Krems an der Donau, Austria; Laboratory of Genetics and Physiology of Hearing, Department of Neuroscience, Institut Pasteur, Paris, France; Collège de France, Genetics and Cell Physiology, Paris, France
| | - Christine Petit
- Laboratory of Neurosensory Biophysics, University of Auvergne, School of Medicine, Clermont-Ferrand, France; Institut National de la Santé et de la Recherche Médicale (INSERM), UMR 1107, Clermont-Ferrand, France; Centre Jean Perrin, Clermont-Ferrand, France; Department of Otolaryngology, County Hospital, Krems an der Donau, Austria; Laboratory of Genetics and Physiology of Hearing, Department of Neuroscience, Institut Pasteur, Paris, France; Collège de France, Genetics and Cell Physiology, Paris, France
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10
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Indzhykulian AA, Stepanyan R, Nelina A, Spinelli KJ, Ahmed ZM, Belyantseva IA, Friedman TB, Barr-Gillespie PG, Frolenkov GI. Molecular remodeling of tip links underlies mechanosensory regeneration in auditory hair cells. PLoS Biol 2013; 11:e1001583. [PMID: 23776407 PMCID: PMC3679001 DOI: 10.1371/journal.pbio.1001583] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 05/02/2013] [Indexed: 11/18/2022] Open
Abstract
Sound detection by inner ear hair cells requires tip links that interconnect mechanosensory stereocilia and convey force to yet unidentified transduction channels. Current models postulate a static composition of the tip link, with protocadherin 15 (PCDH15) at the lower and cadherin 23 (CDH23) at the upper end of the link. In terminally differentiated mammalian auditory hair cells, tip links are subjected to sound-induced forces throughout an organism's life. Although hair cells can regenerate disrupted tip links and restore hearing, the molecular details of this process are unknown. We developed a novel implementation of backscatter electron scanning microscopy to visualize simultaneously immuno-gold particles and stereocilia links, both of only a few nanometers in diameter. We show that functional, mechanotransduction-mediating tip links have at least two molecular compositions, containing either PCDH15/CDH23 or PCDH15/PCDH15. During regeneration, shorter tip links containing nearly equal amounts of PCDH15 at both ends appear first. Whole-cell patch-clamp recordings demonstrate that these transient PCDH15/PCDH15 links mediate mechanotransduction currents of normal amplitude but abnormal Ca(2+)-dependent decay (adaptation). The mature PCDH15/CDH23 tip link composition is re-established later, concomitant with complete recovery of adaptation. Thus, our findings provide a molecular mechanism for regeneration and maintenance of mechanosensory function in postmitotic auditory hair cells and could help identify elusive components of the mechanotransduction machinery.
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Affiliation(s)
- Artur A. Indzhykulian
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Ruben Stepanyan
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Anastasiia Nelina
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Kateri J. Spinelli
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Zubair M. Ahmed
- Division of Pediatric Ophthalmology, Cincinnati Children's Research Foundation, Cincinnati, Ohio, United States of America
| | - Inna A. Belyantseva
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland, United States of America
| | - Thomas B. Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland, United States of America
| | - Peter G. Barr-Gillespie
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Gregory I. Frolenkov
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail:
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11
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Hakizimana P, Brownell WE, Jacob S, Fridberger A. Sound-induced length changes in outer hair cell stereocilia. Nat Commun 2013; 3:1094. [PMID: 23033070 PMCID: PMC3594849 DOI: 10.1038/ncomms2100] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 08/30/2012] [Indexed: 11/09/2022] Open
Abstract
Hearing relies on mechanical stimulation of stereocilia bundles on the sensory cells of the inner ear. When sound hits the ear, these stereocilia pivot about a neck-like taper near their base. More than three decades of research have established that sideways deflection of stereocilia is essential for converting mechanical stimuli into electrical signals. Here we show that mammalian outer hair cell stereocilia not only move sideways but also change length during sound stimulation. Currents that enter stereocilia through mechanically sensitive ion channels control the magnitude of both length changes and bundle deflections in a reciprocal manner: the smaller the length change, the larger is the bundle deflection. Thus, the transduction current is important for maintaining the resting mechanical properties of stereocilia. Hair cell stimulation is most effective when bundles are in a state that ensures minimal length change.
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Affiliation(s)
- Pierre Hakizimana
- Department of Clinical Science, Intervention and Technology, Karolinska Institutet, M1 Karolinska University Hospital, SE-17176 Stockholm, Sweden
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12
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A mouse model for human deafness DFNB22 reveals that hearing impairment is due to a loss of inner hair cell stimulation. Proc Natl Acad Sci U S A 2012; 109:19351-6. [PMID: 23129639 DOI: 10.1073/pnas.1210159109] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The gene causative for the human nonsyndromic recessive form of deafness DFNB22 encodes otoancorin, a 120-kDa inner ear-specific protein that is expressed on the surface of the spiral limbus in the cochlea. Gene targeting in ES cells was used to create an EGFP knock-in, otoancorin KO (Otoa(EGFP/EGFP)) mouse. In the Otoa(EGFP/EGFP) mouse, the tectorial membrane (TM), a ribbon-like strip of ECM that is normally anchored by one edge to the spiral limbus and lies over the organ of Corti, retains its general form, and remains in close proximity to the organ of Corti, but is detached from the limbal surface. Measurements of cochlear microphonic potentials, distortion product otoacoustic emissions, and basilar membrane motion indicate that the TM remains functionally attached to the electromotile, sensorimotor outer hair cells of the organ of Corti, and that the amplification and frequency tuning of the basilar membrane responses to sounds are almost normal. The compound action potential masker tuning curves, a measure of the tuning of the sensory inner hair cells, are also sharply tuned, but the thresholds of the compound action potentials, a measure of inner hair cell sensitivity, are significantly elevated. These results indicate that the hearing loss in patients with Otoa mutations is caused by a defect in inner hair cell stimulation, and reveal the limbal attachment of the TM plays a critical role in this process.
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13
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Guinan JJ. How are inner hair cells stimulated? Evidence for multiple mechanical drives. Hear Res 2012; 292:35-50. [PMID: 22959529 DOI: 10.1016/j.heares.2012.08.005] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 07/24/2012] [Accepted: 08/01/2012] [Indexed: 11/30/2022]
Abstract
Recent studies indicate that the gap over outer hair cells (OHCs) between the reticular lamina (RL) and the tectorial membrane (TM) varies cyclically during low-frequency sounds. Variation in the RL-TM gap produces radial fluid flow in the gap that can drive inner hair cell (IHC) stereocilia. Analysis of RL-TM gap changes reveals three IHC drives in addition to classic SHEAR. For upward basilar-membrane (BM) motion, IHC stereocilia are deflected in the excitatory direction by SHEAR and OHC-MOTILITY, but in the inhibitory direction by TM-PUSH and CILIA-SLANT. Upward BM motion causes OHC somatic contraction which tilts the RL, compresses the RL-TM gap over IHCs and expands the RL-TM gap over OHCs, thereby producing an outward (away from the IHCs) radial fluid flow which is the OHC-MOTILITY drive. For upward BM motion, the force that moves the TM upward also compresses the RL-TM gap over OHCs causing inward radial flow past IHCs which is the TM-PUSH drive. Motions that produce large tilting of OHC stereocilia squeeze the supra-OHC RL-TM gap and caused inward radial flow past IHCs which is the CILIA-SLANT drive. Combinations of these drives explain: (1) the reversal at high sound levels of auditory nerve (AN) initial peak (ANIP) responses to clicks, and medial olivocochlear (MOC) inhibition of ANIP responses below, but not above, the ANIP reversal, (2) dips and phase reversals in AN responses to tones in cats and chinchillas, (3) hypersensitivity and phase reversals in tuning-curve tails after OHC ablation, and (4) MOC inhibition of tail-frequency AN responses. The OHC-MOTILITY drive provides another mechanism, in addition to BM motion amplification, that uses active processes to enhance the output of the cochlea. The ability of these IHC drives to explain previously anomalous data provides strong, although indirect, evidence that these drives are significant and presents a new view of how the cochlea works at frequencies below 3 kHz.
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Affiliation(s)
- John J Guinan
- Eaton-Peabody Laboratory of Auditory Physiology, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA.
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Gavara N, Manoussaki D, Chadwick RS. Auditory mechanics of the tectorial membrane and the cochlear spiral. Curr Opin Otolaryngol Head Neck Surg 2011; 19:382-7. [PMID: 21785353 PMCID: PMC3327783 DOI: 10.1097/moo.0b013e32834a5bc9] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW This review is timely and relevant because new experimental and theoretical findings suggest that cochlear mechanics from the nanoscale to the macroscale are affected by the mechanical properties of the tectorial membrane and the cochlea's spiral shape. RECENT FINDINGS Main tectorial membrane themes addressed in this review are composition and morphology, nanoscale mechanical interactions with the outer hair cell bundle, macroscale longitudinal coupling, fluid interaction with inner hair cell bundles, and macroscale dynamics and waves. Main cochlear spiral themes are macroscale, low-frequency energy focusing and microscale organ of Corti shear gain. SUMMARY Recent experimental and theoretical findings reveal exquisite sensitivity of cochlear mechanical performance to tectorial membrane structural organization, mechanics, and its positioning with respect to hair bundles. The cochlear spiral geometry is a major determinant of low-frequency hearing. These findings suggest a number of important research directions.
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Affiliation(s)
- Núria Gavara
- Auditory Mechanics Section, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, USA
| | - Daphne Manoussaki
- Department of Sciences, Technical University of Crete, Hania, Greece
| | - Richard S. Chadwick
- Auditory Mechanics Section, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, USA
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