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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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2
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Lanthier F, Laforge J, Pflieger JF. Influence of the vestibular system on the neonatal motor behaviors in the gray short-tailed opossum ( Monodelphis domestica). IBRO Neurosci Rep 2023; 15:42-49. [PMID: 37415730 PMCID: PMC10320520 DOI: 10.1016/j.ibneur.2023.06.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Accepted: 06/15/2023] [Indexed: 07/08/2023] Open
Abstract
Marsupials are born very immature yet must be sufficiently autonomous to crawl on the mother's belly, find a teat and attach to it to pursue their development. Sensory inputs are necessary to guide the newborn to a teat and induce attachment. The vestibular system, which perceives gravity and head movements, is one of the senses proposed to guide newborns towards the teats but there are conflicting observations about its functionality at birth (postnatal day (P) 0). To test if the vestibular system of opossum newborns is functional and can influence locomotion, we used two approaches. First, we stimulated the vestibular apparatus in in vitro preparations from opossums aged from P1 to P12 and recorded motor responses: at all ages studied, mechanical pressures applied on the vestibular organs induced spinal roots activity whereas head tilts did not induce forelimb muscle contractions. Second, using immunofluorescence, we assessed the presence of Piezo2, a protein involved in mechanotransduction in vestibular hair cells. Piezo2 labeling was scant in the utricular macula at birth, but observed in all vestibular organs at P7, its intensity increasing up to P14; it seemed to stay the same at P21. Our results indicate that neural pathways from the labyrinth to the spinal cord are already in place around birth but that the vestibular organs are too immature to influence motor activity before the end of the second postnatal week in the opossum. It may be the rule in marsupial species that the vestibular system becomes functional only after birth.
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Affiliation(s)
| | | | - Jean-François Pflieger
- Correspondence to: Département de Sciences biologiques, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, QC H3C 3J7, Canada.
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3
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Signatures of cochlear processing in neuronal coding of auditory information. Mol Cell Neurosci 2022; 120:103732. [PMID: 35489636 DOI: 10.1016/j.mcn.2022.103732] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2021] [Revised: 04/19/2022] [Accepted: 04/21/2022] [Indexed: 11/22/2022] Open
Abstract
The vertebrate ear is endowed with remarkable perceptual capabilities. The faintest sounds produce vibrations of magnitudes comparable to those generated by thermal noise and can nonetheless be detected through efficient amplification of small acoustic stimuli. Two mechanisms have been proposed to underlie such sound amplification in the mammalian cochlea: somatic electromotility and active hair-bundle motility. These biomechanical mechanisms may work in concert to tune auditory sensitivity. In addition to amplitude sensitivity, the hearing system shows exceptional frequency discrimination allowing mammals to distinguish complex sounds with great accuracy. For instance, although the wide hearing range of humans encompasses frequencies from 20 Hz to 20 kHz, our frequency resolution extends to one-thirtieth of the interval between successive keys on a piano. In this article, we review the different cochlear mechanisms underlying sound encoding in the auditory system, with a particular focus on the frequency decomposition of sounds. The relation between peak frequency of activation and location along the cochlea - known as tonotopy - arises from multiple gradients in biophysical properties of the sensory epithelium. Tonotopic mapping represents a major organizational principle both in the peripheral hearing system and in higher processing levels and permits the spectral decomposition of complex tones. The ribbon synapses connecting sensory hair cells to auditory afferents and the downstream spiral ganglion neurons are also tuned to process periodic stimuli according to their preferred frequency. Though sensory hair cells and neurons necessarily filter signals beyond a few kHz, many animals can hear well beyond this range. We finally describe how the cochlear structure shapes the neural code for further processing in order to send meaningful information to the brain. Both the phase-locked response of auditory nerve fibers and tonotopy are key to decode sound frequency information and place specific constraints on the downstream neuronal network.
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Mechanotransduction in mammalian sensory hair cells. Mol Cell Neurosci 2022; 120:103706. [PMID: 35218890 PMCID: PMC9177625 DOI: 10.1016/j.mcn.2022.103706] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Revised: 02/14/2022] [Accepted: 02/18/2022] [Indexed: 11/23/2022] Open
Abstract
In the inner ear, the auditory and vestibular systems detect and translate sensory information regarding sound and balance. The sensory cells that transform mechanical input into an electrical signal in these systems are called hair cells. A specialized organelle on the apical surface of the hair cells called the hair bundle detects the mechanical signals. Displacement of the hair bundle causes mechanotransduction channels to open. The morphology and organization of the hair bundle, as well as the properties and characteristics of the mechanotransduction process, differ between the different hair cell types in the auditory and vestibular systems. These differences likely contribute to maximizing the transduction of specific signals in each system. This review will discuss the molecules essential for mechanotransduction and the properties of the mechanotransduction process, focusing our attention on recent data and differences between the auditory and vestibular systems.
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Li J, Liu S, Song C, Hu Q, Zhao Z, Deng T, Wang Y, Zhu T, Zou L, Wang S, Chen J, Liu L, Hou H, Yuan K, Zheng H, Liu Z, Chen X, Sun W, Xiao B, Xiong W. PIEZO2 mediates ultrasonic hearing via cochlear outer hair cells in mice. Proc Natl Acad Sci U S A 2021; 118:e2101207118. [PMID: 34244441 PMCID: PMC8285978 DOI: 10.1073/pnas.2101207118] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Ultrasonic hearing and vocalization are the physiological mechanisms controlling echolocation used in hunting and navigation by microbats and bottleneck dolphins and for social communication by mice and rats. The molecular and cellular basis for ultrasonic hearing is as yet unknown. Here, we show that knockout of the mechanosensitive ion channel PIEZO2 in cochlea disrupts ultrasonic- but not low-frequency hearing in mice, as shown by audiometry and acoustically associative freezing behavior. Deletion of Piezo2 in outer hair cells (OHCs) specifically abolishes associative learning in mice during hearing exposure at ultrasonic frequencies. Ex vivo cochlear Ca2+ imaging has revealed that ultrasonic transduction requires both PIEZO2 and the hair-cell mechanotransduction channel. The present study demonstrates that OHCs serve as effector cells, combining with PIEZO2 as an essential molecule for ultrasonic hearing in mice.
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Affiliation(s)
- Jie Li
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Shuang Liu
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Chenmeng Song
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Qun Hu
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Zhikai Zhao
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Tuantuan Deng
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
- School of Pharmaceutical Sciences, Tsinghua University, Beijing, China 100084
- Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing, China 100084
| | - Yi Wang
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Tong Zhu
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Linzhi Zou
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Shufeng Wang
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Jiaofeng Chen
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Lian Liu
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Hanqing Hou
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
| | - Kexin Yuan
- School of Life Sciences, Tsinghua University, Beijing, China 100084
- Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China 100084
| | - Hairong Zheng
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Key Laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China 440305
| | - Zhiyong Liu
- Institute of Neuroscience, CAS (Chinese Academy of Sciences) Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China 200031
| | - Xiaowei Chen
- Brain Research Center and State Key Laboratory of Trauma, Burns, and Combined Injury, Third Military Medical University, Chongqing, China 400038
- CAS (Chinese Academy of Sciences) Center for Excellence in Brain Science and Intelligence Technology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China 200031
| | - Wenzhi Sun
- Chinese Institute for Brain Research, Beijing, China 102206
- School of Basic Medical Sciences, Capital Medical University, Beijing, China 100069
| | - Bailong Xiao
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
- School of Pharmaceutical Sciences, Tsinghua University, Beijing, China 100084
- Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing, China 100084
| | - Wei Xiong
- School of Life Sciences, Tsinghua University, Beijing, China 100084;
- IDG (International Data Group)/McGovern Institute for Brain Research at Tsinghua University, Tsinghua University, Beijing, China 100084
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6
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Richardson GP, Petit C. Hair-Bundle Links: Genetics as the Gateway to Function. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033142. [PMID: 30617060 DOI: 10.1101/cshperspect.a033142] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Up to five distinct cell-surface specializations interconnect the stereocilia and the kinocilium of the mature hair bundle in some species: kinocilial links, tip links, top connectors, shaft connectors, and ankle links. In developing hair bundles, transient lateral links are prominent. Mutations in genes encoding proteins associated with these links cause Usher deafness/blindness syndrome or nonsyndromic (isolated) forms of human hereditary deafness, and mice with constitutive or conditional alleles of these genes have provided considerable insight into the molecular composition and function of the different links. We describe the structure of these links and review evidence showing CDH23 and PCDH15 are components of the tip, kinocilial, and transient-lateral links, that stereocilin (STRC) and protein tyrosine phosphatase (PTPRQ) are associated with top and shaft connectors, respectively, and that USH2A and ADGRV1 are associated with the ankle links. Whereas tip links are required for mechanoelectrical transduction, all link proteins play key roles in the normal development and/or the maintenance of hair bundle structure and function. Recent crystallographic and single-particle analyses of PCDH15 and CDH23 provide insight as to how the structure of tip link may contribute to the elastic element predicted to lie in series with the hair cell's mechanoelectrical transducer channel.
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Affiliation(s)
- Guy P Richardson
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
| | - Christine Petit
- Institut Pasteur, 75724 Paris Cedex 15, France.,Collège de France, 75231 Paris Cedex 05, France
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7
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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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8
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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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9
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Bortolozzi M, Mammano F. PMCA2 pump mutations and hereditary deafness. Neurosci Lett 2019; 663:18-24. [PMID: 29452611 DOI: 10.1016/j.neulet.2017.09.059] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Revised: 09/25/2017] [Accepted: 09/28/2017] [Indexed: 01/21/2023]
Abstract
Hair cells of the inner ear detect sound stimuli, inertial or gravitational forces by deflection of their apical stereocilia. A small number of stereociliary cation-selective mechanotransduction (MET) channels admit K+ and Ca2+ ions into the cytoplasm promoting hair cell membrane depolarization and, consequently, neurotransmitter release at the cell basolateral pole. Ca2+ influx into the stereocilia compartment is counteracted by the unusual w/a splicing variant of plasma-membrane calcium-pump isoform 2 (PMCA2) which, unlike other PMCA2 variants, increases only marginally its activity in response to a rapid variation of the cytoplasmic free Ca2+ concentration ([Ca2+]c). Missense mutations of PMCA2w/a cause deafness and loss of balance in humans. Mouse models in which the pump is genetically ablated or mutated show hearing and balance impairment, which correlates with defects in homeostatic regulation of stereociliary [Ca2+]c, decreased sensitivity of mechanotransduction channels to hair bundle displacement and progressive degeneration of the organ of Corti. These results highlight a critical role played by the PMCA2w/a pump in the control of hair cell function and survival, and provide mechanistic insight into the etiology of deafness and vestibular disorders.
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Affiliation(s)
- Mario Bortolozzi
- University of Padua, Department of Physics and Astronomy "G. Galilei", Padua, Italy; Venetian Institute of Molecular Medicine (VIMM), Padua, Italy; CNR Institute of Protein Biochemistry, Naples, Italy.
| | - Fabio Mammano
- University of Padua, Department of Physics and Astronomy "G. Galilei", Padua, Italy; Venetian Institute of Molecular Medicine (VIMM), Padua, Italy; CNR Institute of Cell Biology and Neurobiology, Monterotondo Scalo, Rome, Italy
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10
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Jaiganesh A, Narui Y, Araya-Secchi R, Sotomayor M. Beyond Cell-Cell Adhesion: Sensational Cadherins for Hearing and Balance. Cold Spring Harb Perspect Biol 2018; 10:a029280. [PMID: 28847902 PMCID: PMC6008173 DOI: 10.1101/cshperspect.a029280] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cadherins form a large family of proteins often involved in calcium-dependent cellular adhesion. Although classical members of the family can provide a physical bond between cells, a subset of special cadherins use their extracellular domains to interlink apical specializations of single epithelial sensory cells. Two of these cadherins, cadherin-23 (CDH23) and protocadherin-15 (PCDH15), form extracellular "tip link" filaments that connect apical bundles of stereocilia on hair cells essential for inner-ear mechanotransduction. As these bundles deflect in response to mechanical stimuli from sound or head movements, tip links gate hair-cell mechanosensitive channels to initiate sensory perception. Here, we review the unusual and diverse structural properties of these tip-link cadherins and the functional significance of their deafness-related missense mutations. Based on the structural features of CDH23 and PCDH15, we discuss the elasticity of tip links and models that bridge the gap between the nanomechanics of cadherins and the micromechanics of hair-cell bundles during inner-ear mechanotransduction.
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Affiliation(s)
- Avinash Jaiganesh
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210
| | - Yoshie Narui
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210
| | - Raul Araya-Secchi
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210
| | - Marcos Sotomayor
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210
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11
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Cooper NP, Vavakou A, van der Heijden M. Vibration hotspots reveal longitudinal funneling of sound-evoked motion in the mammalian cochlea. Nat Commun 2018; 9:3054. [PMID: 30076297 PMCID: PMC6076242 DOI: 10.1038/s41467-018-05483-z] [Citation(s) in RCA: 78] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 07/09/2018] [Indexed: 12/03/2022] Open
Abstract
The micromechanical mechanisms that underpin tuning and dynamic range compression in the mammalian inner ear are fundamental to hearing, but poorly understood. Here, we present new, high-resolution optical measurements that directly map sound-evoked vibrations on to anatomical structures in the intact, living gerbil cochlea. The largest vibrations occur in a tightly delineated hotspot centering near the interface between the Deiters' and outer hair cells. Hotspot vibrations are less sharply tuned, but more nonlinear, than basilar membrane vibrations, and behave non-monotonically (exhibiting hyper-compression) near their characteristic frequency. Amplitude and phase differences between hotspot and basilar membrane responses depend on both frequency and measurement angle, and indicate that hotspot vibrations involve longitudinal motion. We hypothesize that structural coupling between the Deiters' and outer hair cells funnels sound-evoked motion into the hotspot region, under the control of the outer hair cells, to optimize cochlear tuning and compression.
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Affiliation(s)
- Nigel P Cooper
- Department of Neuroscience, Erasmus MC, Room Ee 1285, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands
| | - Anna Vavakou
- Department of Neuroscience, Erasmus MC, Room Ee 1285, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands
| | - Marcel van der Heijden
- Department of Neuroscience, Erasmus MC, Room Ee 1285, P.O. Box 2040, 3000 CA, Rotterdam, The Netherlands.
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12
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Abstract
Sensory hair cells are specialized secondary sensory cells that mediate our senses of hearing, balance, linear acceleration, and angular acceleration (head rotation). In addition, hair cells in fish and amphibians mediate sensitivity to water movement through the lateral line system, and closely related electroreceptive cells mediate sensitivity to low-voltage electric fields in the aquatic environment of many fish species and several species of amphibian. Sensory hair cells share many structural and functional features across all vertebrate groups, while at the same time they are specialized for employment in a wide variety of sensory tasks. The complexity of hair cell structure is large, and the diversity of hair cell applications in sensory systems exceeds that seen for most, if not all, sensory cell types. The intent of this review is to summarize the more significant structural features and some of the more interesting and important physiological mechanisms that have been elucidated thus far. Outside vertebrates, hair cells are only known to exist in the coronal organ of tunicates. Electrical resonance, electromotility, and their exquisite mechanical sensitivity all contribute to the attractiveness of hair cells as a research subject.
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13
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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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14
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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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15
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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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In vivo genetic manipulation of inner ear connexin expression by bovine adeno-associated viral vectors. Sci Rep 2017; 7:6567. [PMID: 28779115 PMCID: PMC5544751 DOI: 10.1038/s41598-017-06759-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 06/19/2017] [Indexed: 01/03/2023] Open
Abstract
We have previously shown that in vitro transduction with bovine adeno–associated viral (BAAV) vectors restores connexin expression and rescues gap junction coupling in cochlear organotypic cultures from connexin–deficient mice that are models DFNB1 nonsyndromic hearing loss and deafness. The aims of this study were to manipulate inner ear connexin expression in vivo using BAAV vectors, and to identify the optimal route of vector delivery. Injection of a BAAV vector encoding a bacterial Cre recombinase via canalostomy in adult mice with floxed connexin 26 (Cx26) alleles promoted Cre/LoxP recombination, resulting in decreased Cx26 expression, decreased endocochlear potential, increased hearing thresholds, and extensive loss of outer hair cells. Injection of a BAAV vector encoding GFP-tagged Cx30 via canalostomy in P4 mice lacking connexin 30 (Cx30) promoted formation of Cx30 gap junctions at points of contacts between adjacent non-sensory cells of the cochlear sensory epithelium. Levels of exogenous Cx30 decayed over time, but were still detectable four weeks after canalostomy. Our results suggest that persistence of BAAV-mediated gene replacement in the cochlea is limited by the extensive remodeling of the organ of Corti throughout postnatal development and associated loss of non-sensory cells.
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Are TMCs the Mechanotransduction Channels of Vertebrate Hair Cells? J Neurosci 2017; 36:10921-10926. [PMID: 27798174 DOI: 10.1523/jneurosci.1148-16.2016] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 06/13/2016] [Indexed: 11/21/2022] Open
Abstract
Sensory transduction in vertebrate hair cells and the molecules that mediate it have long been of great interest. Some components of the mechanotransduction apparatus have been identified, most as deafness gene products. Although prior candidates for the mechanotransduction channel have been proposed, each has faded with new evidence. Now, two strong candidates, TMC1 and TMC2 (transmembrane channel-like), have emerged from discovery of deafness genes in humans and mice. They are expressed at the right time during development: exactly at the onset of mechanosensitivity. They are expressed in the right place: in hair cells but not surrounding cells. Fluorescently tagged TMCs localize to the tips of stereocilia, the site of the transduction channels. TMCs bind other proteins essential for mechanosensation, suggesting a larger transduction complex. Although TMC1 and TMC2 can substitute for each other, genetic deletion of both renders mouse hair cells mechanically insensitive. Finally, the conductance and Ca2+ selectivity of the transduction channels depend on the TMC proteins, differing when hair cells express one or the other TMC, and differing if TMC1 harbors a point mutation. Some contrary evidence has emerged: a current activated in hair cells by negative pressure, with some similarity to the transduction current, persists in TMC knock-outs. But it is not clear that this anomalous current is carried by the same proteins. Further evidence is desired, such as production of a mechanically gated conductance by pure TMCs. But the great majority of evidence is consistent with these TMCs as pore-forming subunits of the long-sought hair-cell transduction channel.
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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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CIB2 interacts with TMC1 and TMC2 and is essential for mechanotransduction in auditory hair cells. Nat Commun 2017; 8:43. [PMID: 28663585 PMCID: PMC5491523 DOI: 10.1038/s41467-017-00061-1] [Citation(s) in RCA: 98] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 05/02/2017] [Indexed: 11/24/2022] Open
Abstract
Inner ear hair cells detect sound through deflection of stereocilia, the microvilli-like projections that are arranged in rows of graded heights. Calcium and integrin-binding protein 2 is essential for hearing and localizes to stereocilia, but its exact function is unknown. Here, we have characterized two mutant mouse lines, one lacking calcium and integrin-binding protein 2 and one carrying a human deafness-related Cib2 mutation, and show that both are deaf and exhibit no mechanotransduction in auditory hair cells, despite the presence of tip links that gate the mechanotransducer channels. In addition, mechanotransducing shorter row stereocilia overgrow in hair cell bundles of both Cib2 mutants. Furthermore, we report that calcium and integrin-binding protein 2 binds to the components of the hair cell mechanotransduction complex, TMC1 and TMC2, and these interactions are disrupted by deafness-causing Cib2 mutations. We conclude that calcium and integrin-binding protein 2 is required for normal operation of the mechanotransducer channels and is involved in limiting the growth of transducing stereocilia. Inner ear hair cells detect sound through deflection of stereocilia that harbor mechanically-gated channels. Here the authors show that protein responsible for Usher syndrome, CIB2, interacts with these channels and is essential for their function and hearing in mice.
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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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21
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Cunningham CL, Wu Z, Jafari A, Zhao B, Schrode K, Harkins-Perry S, Lauer A, Müller U. The murine catecholamine methyltransferase mTOMT is essential for mechanotransduction by cochlear hair cells. eLife 2017; 6. [PMID: 28504928 PMCID: PMC5462538 DOI: 10.7554/elife.24318] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 05/14/2017] [Indexed: 12/26/2022] Open
Abstract
Hair cells of the cochlea are mechanosensors for the perception of sound. Mutations in the LRTOMT gene, which encodes a protein with homology to the catecholamine methyltransferase COMT that is linked to schizophrenia, cause deafness. Here, we show that Tomt/Comt2, the murine ortholog of LRTOMT, has an unexpected function in the regulation of mechanotransduction by hair cells. The role of mTOMT in hair cells is independent of mTOMT methyltransferase function and mCOMT cannot substitute for mTOMT function. Instead, mTOMT binds to putative components of the mechanotransduction channel in hair cells and is essential for the transport of some of these components into the mechanically sensitive stereocilia of hair cells. Our studies thus suggest functional diversification between mCOMT and mTOMT, where mTOMT is critical for the assembly of the mechanotransduction machinery of hair cells. Defects in this process are likely mechanistically linked to deafness caused by mutations in LRTOMT/Tomt. DOI:http://dx.doi.org/10.7554/eLife.24318.001
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Affiliation(s)
- Christopher L Cunningham
- The Solomon Snyder Department of Neuroscience, Johns Hopkins University, Baltimore, United States
| | - Zizhen Wu
- The Solomon Snyder Department of Neuroscience, Johns Hopkins University, Baltimore, United States
| | - Aria Jafari
- Department of Surgery, University of California, San Diego, San Diego, United States
| | - Bo Zhao
- Department of Otolaryngology Head and Neck Surgery, Indiana University School of Medicine, Indianapolis, United States
| | - Kat Schrode
- Department of Otolaryngology, Johns Hopkins University, Baltimore, United States
| | - Sarah Harkins-Perry
- Department of Molecular and Cellular Biology, The Scripps Research Institute, La Jolla, United States
| | - Amanda Lauer
- Department of Otolaryngology, Johns Hopkins University, Baltimore, United States
| | - Ulrich Müller
- The Solomon Snyder Department of Neuroscience, Johns Hopkins University, Baltimore, United States
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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: 81] [Impact Index Per Article: 10.1] [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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Stretching out the early steps in hearing. Proc Natl Acad Sci U S A 2016; 113:6594-5. [DOI: 10.1073/pnas.1606666113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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