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Effertz T, Moser T, Oliver D. Recent advances in cochlear hair cell nanophysiology: subcellular compartmentalization of electrical signaling in compact sensory cells. Fac Rev 2021; 9:24. [PMID: 33659956 PMCID: PMC7886071 DOI: 10.12703/r/9-24] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In recent years, genetics, physiology, and structural biology have advanced into the molecular details of the sensory physiology of auditory hair cells. Inner hair cells (IHCs) and outer hair cells (OHCs) mediate two key functions: active amplification and non-linear compression of cochlear vibrations by OHCs and sound encoding by IHCs at their afferent synapses with the spiral ganglion neurons. OHCs and IHCs share some molecular physiology, e.g. mechanotransduction at the apical hair bundles, ribbon-type presynaptic active zones, and ionic conductances in the basolateral membrane. Unique features enabling their specific function include prestin-based electromotility of OHCs and indefatigable transmitter release at the highest known rates by ribbon-type IHC active zones. Despite their compact morphology, the molecular machineries that either generate electrical signals or are driven by these signals are essentially all segregated into local subcellular structures. This review provides a brief account on recent insights into the molecular physiology of cochlear hair cells with a specific focus on organization into membrane domains.
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Affiliation(s)
- Thomas Effertz
- InnerEarLab, Department of Otorhinolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany
- Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
- Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, 37075 Göttingen, Germany
| | - Dominik Oliver
- Institute for Physiology and Pathophysiology, Philipps University, Deutschhausstraße 2, 35037 Marburg, Germany
- Center for Mind, Brain and Behavior (CMBB), Universities of Marburg and Giessen, Germany
- DFG Research Training Group, Membrane Plasticity in Tissue Development and Remodelling, GRK 2213, Philipps University, Marburg, Germany
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Age-related hearing loss pertaining to potassium ion channels in the cochlea and auditory pathway. Pflugers Arch 2020; 473:823-840. [PMID: 33336302 PMCID: PMC8076138 DOI: 10.1007/s00424-020-02496-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 10/27/2020] [Accepted: 11/10/2020] [Indexed: 12/12/2022]
Abstract
Age-related hearing loss (ARHL) is the most prevalent sensory deficit in the elderly and constitutes the third highest risk factor for dementia. Lifetime noise exposure, genetic predispositions for degeneration, and metabolic stress are assumed to be the major causes of ARHL. Both noise-induced and hereditary progressive hearing have been linked to decreased cell surface expression and impaired conductance of the potassium ion channel KV7.4 (KCNQ4) in outer hair cells, inspiring future therapies to maintain or prevent the decline of potassium ion channel surface expression to reduce ARHL. In concert with KV7.4 in outer hair cells, KV7.1 (KCNQ1) in the stria vascularis, calcium-activated potassium channels BK (KCNMA1) and SK2 (KCNN2) in hair cells and efferent fiber synapses, and KV3.1 (KCNC1) in the spiral ganglia and ascending auditory circuits share an upregulated expression or subcellular targeting during final differentiation at hearing onset. They also share a distinctive fragility for noise exposure and age-dependent shortfalls in energy supply required for sustained surface expression. Here, we review and discuss the possible contribution of select potassium ion channels in the cochlea and auditory pathway to ARHL. We postulate genes, proteins, or modulators that contribute to sustained ion currents or proper surface expressions of potassium channels under challenging conditions as key for future therapies of ARHL.
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Möhrle D, Reimann K, Wolter S, Wolters M, Varakina K, Mergia E, Eichert N, Geisler HS, Sandner P, Ruth P, Friebe A, Feil R, Zimmermann U, Koesling D, Knipper M, Rüttiger L. NO-Sensitive Guanylate Cyclase Isoforms NO-GC1 and NO-GC2 Contribute to Noise-Induced Inner Hair Cell Synaptopathy. Mol Pharmacol 2017; 92:375-388. [DOI: 10.1124/mol.117.108548] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 07/18/2017] [Indexed: 12/21/2022] Open
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Pyott SJ, Duncan RK. BK Channels in the Vertebrate Inner Ear. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2016; 128:369-99. [PMID: 27238269 DOI: 10.1016/bs.irn.2016.03.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The perception of complex acoustic stimuli begins with the deconstruction of sound into its frequency components. This spectral processing occurs first and foremost in the inner ear. In vertebrates, two very different strategies of frequency analysis have evolved. In nonmammalian vertebrates, the sensory hair cells of the inner ear are intrinsically electrically tuned to a narrow band of acoustic frequencies. This electrical tuning relies on the interplay between BK channels and voltage-gated calcium channels. Systematic variations in BK channel density and kinetics establish a gradient in electrical resonance that enables the coding of a broad range of acoustic frequencies. In contrast, mammalian hair cells are extrinsically tuned by mechanical properties of the cochlear duct. Even so, mammalian hair cells also express BK channels. These BK channels play critical roles in various aspects of mammalian auditory signaling, from developmental maturation to protection against acoustic trauma. This review summarizes the anatomical localization, biophysical properties, and functional contributions of BK channels in vertebrate inner ears. Areas of future research, based on an updated understanding of the biology of both BK channels and the inner ear, are also highlighted. Investigation of BK channels in the inner ear continues to provide fertile research grounds for examining both BK channel biophysics and the molecular mechanisms underlying signal processing in the auditory periphery.
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Affiliation(s)
- S J Pyott
- University Medical Center Groningen, Groningen, The Netherlands.
| | - R K Duncan
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
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More similar than you think: Frog metamorphosis as a model of human perinatal endocrinology. Dev Biol 2015; 408:188-95. [DOI: 10.1016/j.ydbio.2015.02.018] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 02/05/2015] [Accepted: 02/20/2015] [Indexed: 11/21/2022]
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Sundaresan S, Balasubbu S, Mustapha M. Thyroid hormone is required for the pruning of afferent type II spiral ganglion neurons in the mouse cochlea. Neuroscience 2015; 312:165-78. [PMID: 26592716 DOI: 10.1016/j.neuroscience.2015.11.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Revised: 11/09/2015] [Accepted: 11/10/2015] [Indexed: 12/13/2022]
Abstract
Afferent connections to the sensory inner (IHCs) and outer hair cells (OHCs) in the cochlea refine and functionally mature during the thyroid hormone (TH)-critical period of inner ear development that occurs perinatally in rodents. In this study, we investigated the effects of hypothyroidism on afferent type II innervation to outer hair cells using the Snell dwarf mouse (Pit1(dw)). Using a transgenic approach to specifically label type II spiral ganglion neurons (SGNs), we found that lack of TH causes persistence of excess type II SGN connections to the OHCs, as well as continued expression of the hair cell functional marker, otoferlin (OTOF), in the OHCs beyond the maturation period. We also observed a concurrent delay in efferent attachment to the OHCs. Supplementing with TH during the early postnatal period from postnatal day (P) 3 to P4 reversed the defect in type II SGN pruning but did not alter OTOF expression. Our results show that hypothyroidism causes a defect in the large-scale pruning of afferent type II SGNs in the cochlea, and a delay in efferent attachment and the maturation of OTOF expression. Our data suggest that the state of maturation of hair cells, as determined by OTOF expression, may not regulate the pruning of their afferent innervation.
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Affiliation(s)
- S Sundaresan
- Department of Otolaryngology-Head & Neck Surgery, 300 Pasteur Drive, Stanford University, Stanford, CA 94035, United States
| | - S Balasubbu
- Department of Otolaryngology-Head & Neck Surgery, 300 Pasteur Drive, Stanford University, Stanford, CA 94035, United States
| | - M Mustapha
- Department of Otolaryngology-Head & Neck Surgery, 300 Pasteur Drive, Stanford University, Stanford, CA 94035, United States.
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Choi J, Suzuki KIT, Sakuma T, Shewade L, Yamamoto T, Buchholz DR. Unliganded thyroid hormone receptor α regulates developmental timing via gene repression in Xenopus tropicalis. Endocrinology 2015; 156:735-44. [PMID: 25456067 PMCID: PMC4298327 DOI: 10.1210/en.2014-1554] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Thyroid hormone (TH) receptor (TR) expression begins early in development in all vertebrates when circulating TH levels are absent or minimal, yet few developmental roles for unliganded TRs have been established. Unliganded TRs are expected to repress TH-response genes, increase tissue responsivity to TH, and regulate the timing of developmental events. Here we examined the role of unliganded TRα in gene repression and development in Xenopus tropicalis. We used transcription activator-like effector nuclease gene disruption technology to generate founder animals with mutations in the TRα gene and bred them to produce F1 offspring with a normal phenotype and a mutant phenotype, characterized by precocious hind limb development. Offspring with a normal phenotype had zero or one disrupted TRα alleles, and tadpoles with the mutant hind limb phenotype had two truncated TRα alleles with frame shift mutations between the two zinc fingers followed by 40-50 mutant amino acids and then an out-of-frame stop codon. We examined TH-response gene expression and early larval development with and without exogenous TH in F1 offspring. As hypothesized, mutant phenotype tadpoles had increased expression of TH-response genes in the absence of TH and impaired induction of these same genes after exogenous TH treatment, compared with normal phenotype animals. Also, mutant hind limb phenotype animals had reduced hind limb and gill responsivity to exogenous TH. Similar results in methimazole-treated tadpoles showed that increased TH-response gene expression and precocious development were not due to early production of TH. These results indicate that unliganded TRα delays developmental progression by repressing TH-response genes.
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Affiliation(s)
- Jinyoung Choi
- Department of Biological Sciences (J.C., L.S., D.R.B.), University of Cincinnati, Cincinnati, Ohio 45221; and Department of Mathematical and Life Sciences (K.T.S., T.S., T.Y.), Graduate School of Science, Hiroshima University, Hiroshima 739-8526, Japan
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Dettling J, Franz C, Zimmermann U, Lee SC, Bress A, Brandt N, Feil R, Pfister M, Engel J, Flamant F, Rüttiger L, Knipper M. Autonomous functions of murine thyroid hormone receptor TRα and TRβ in cochlear hair cells. Mol Cell Endocrinol 2014; 382:26-37. [PMID: 24012852 DOI: 10.1016/j.mce.2013.08.025] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 08/22/2013] [Accepted: 08/29/2013] [Indexed: 11/18/2022]
Abstract
Thyroid hormone acts on gene transcription by binding to its nuclear receptors TRα1 and TRβ. Whereas global deletion of TRβ causes deafness, global TRα-deficient mice have normal hearing thresholds. Since the individual roles of the two receptors in cochlear hair cells are still unclear, we generated mice with a hair cell-specific mutation of TRα1 or deletion of TRβ using the Cre-loxP system. Hair cell-specific TRβ mutant mice showed normal hearing thresholds but delayed BK channel expression in inner hair cells, slightly stronger outer hair cell function, and slightly reduced amplitudes of auditory brainstem responses. In contrast, hair cell-specific TRα mutant mice showed normal timing of BK channel expression, slightly reduced outer hair cell function, and slightly enhanced amplitudes of auditory brainstem responses. Our data demonstrate that TRβ-related deafness originates outside of hair cells and that TRα and TRβ play opposing, non-redundant roles in hair cells. A role for thyroid hormone receptors in controlling key regulators that shape signal transduction during development is discussed. Thyroid hormone may act through different thyroid hormone receptor activities to permanently alter the sensitivity of auditory neurotransmission.
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Affiliation(s)
- Juliane Dettling
- Molecular Physiology of Hearing, Hearing Research Centre Tübingen (THRC), Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Christoph Franz
- Molecular Physiology of Hearing, Hearing Research Centre Tübingen (THRC), Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Ulrike Zimmermann
- Molecular Physiology of Hearing, Hearing Research Centre Tübingen (THRC), Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Sze Chim Lee
- Molecular Physiology of Hearing, Hearing Research Centre Tübingen (THRC), Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Andreas Bress
- Molecular Genetics, THRC, Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Niels Brandt
- Department of Biophysics, Saarland University, 66421 Homburg/Saar, Germany
| | - Robert Feil
- Department of Signal Transduction & Transgenic Models, Interfaculty Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany
| | - Markus Pfister
- Molecular Genetics, THRC, Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Jutta Engel
- Department of Biophysics, Saarland University, 66421 Homburg/Saar, Germany
| | - Frédéric Flamant
- Institut de Génomique Fonctionnelle, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon cedex 07, Lyon, France
| | - Lukas Rüttiger
- Molecular Physiology of Hearing, Hearing Research Centre Tübingen (THRC), Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany
| | - Marlies Knipper
- Molecular Physiology of Hearing, Hearing Research Centre Tübingen (THRC), Department of Otolaryngology, University of Tübingen, Elfriede-Aulhorn-Str. 5, 72076 Tübingen, Germany.
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Thyroid hormone receptor activity in the absence of ligand: Physiological and developmental implications. Biochim Biophys Acta Gen Subj 2013; 1830:3893-9. [DOI: 10.1016/j.bbagen.2012.04.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 04/11/2012] [Accepted: 04/16/2012] [Indexed: 12/24/2022]
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Abstract
The senses are our window to the world, our interface with the habitat in which we live in and the basis for our communication with each other. Although sensory systems are not generally viewed as major targets of endocrine regulation, sensory development is profoundly influenced by thyroid hormone (T(3)) signalling. In this article, we discuss this developmental role of T(3) and highlight the auditory system as the best-studied example of the interplay between systemic and local tissue mechanisms by which T(3) stimulates the onset of sensory function. Several genes that mediate the action of T(3) are known to promote sensory development in mice, including genes that encode T(3) receptors and deiodinase enzymes that amplify or deplete levels of T(3). We also discuss the current knowledge of sensory defects in human genetic disorders in which T(3) signalling is impaired. As sensory input provides the only means of acquiring information from the environment, the stimulation of sensory development is one of the most fundamental functions of T(3) signalling.
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Affiliation(s)
- Lily Ng
- National Institute of Diabetes and Digestive and Kidney Disease, Laboratory of Endocrinology and Receptor Biology, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA
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Defourny J, Lallemend F, Malgrange B. Structure and development of cochlear afferent innervation in mammals. Am J Physiol Cell Physiol 2011; 301:C750-61. [PMID: 21753183 DOI: 10.1152/ajpcell.00516.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In mammals, sensorineural deafness results from damage to the auditory receptors of the inner ear, the nerve pathways to the brain or the cortical area that receives sound information. In this review, we first focused on the cellular and molecular events taking part to spiral ganglion axon growth, extension to the organ of Corti, and refinement. In the second half, we considered the functional maturation of synaptic contacts between sensory hair cells and their afferent projections. A better understanding of all these processes could open insights into novel therapeutic strategies aimed to re-establish primary connections from sound transducers to the ascending auditory nerve pathways.
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Mazurek B, Fuchs J, Stute K, Angerstein M, Amarjargal N, Olze H, Gross J. Decrease of prestin expression by increased potassium concentration in organotypic cultures of the organ of Corti of newborn rats. Neurosci Lett 2011; 499:52-6. [PMID: 21624428 DOI: 10.1016/j.neulet.2011.05.031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 05/13/2011] [Indexed: 11/19/2022]
Abstract
Prestin is the motor protein of the outer hair cells of the organ of Corti and a key factor in ensuring a high sensitivity level of mammalian hearing. In the present study, we examined the effects of increased extracellular potassium (K(+)) concentration on the expression of prestin mRNA and the transcription factors Gata-3 and Carf in the organotypic culture of the organ of Corti of newborn rats. Mannitol and NaCl were used to analyze possible effects of hyperosmotic stress or ion-specific changes, respectively. An increase in prestin expression by a factor of 1.5-2.0 was seen in cultures grown in the presence of 5mM K(+). Potassium concentration of 35 and 55 mM induced a parallel decrease in prestin and Carf expression, but Gata-3 expression increased. Mannitol had no effect on gene expression whereas increased NaCl concentrations decreased prestin, but not Carf expression. The data suggest that chronic depolarization might decrease the prestin expression and possibly contribute to hearing loss and tinnitus.
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Affiliation(s)
- Birgit Mazurek
- Molecular Biology Research Laboratory, Department of Otorhinolaryngology CCM, Charité - Universitätsmedizin Berlin, Berlin, Germany
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Wersinger E, McLean WJ, Fuchs PA, Pyott SJ. BK channels mediate cholinergic inhibition of high frequency cochlear hair cells. PLoS One 2010; 5:e13836. [PMID: 21079807 PMCID: PMC2973960 DOI: 10.1371/journal.pone.0013836] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Accepted: 10/07/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Outer hair cells are the specialized sensory cells that empower the mammalian hearing organ, the cochlea, with its remarkable sensitivity and frequency selectivity. Sound-evoked receptor potentials in outer hair cells are shaped by both voltage-gated K(+) channels that control the membrane potential and also ligand-gated K(+) channels involved in the cholinergic efferent modulation of the membrane potential. The objectives of this study were to investigate the tonotopic contribution of BK channels to voltage- and ligand-gated currents in mature outer hair cells from the rat cochlea. METHODOLOGY/PRINCIPAL Findings In this work we used patch clamp electrophysiology and immunofluorescence in tonotopically defined segments of the rat cochlea to determine the contribution of BK channels to voltage- and ligand-gated currents in outer hair cells. Although voltage and ligand-gated currents have been investigated previously in hair cells from the rat cochlea, little is known about their tonotopic distribution or potential contribution to efferent inhibition. We found that apical (low frequency) outer hair cells had no BK channel immunoreactivity and little or no BK current. In marked contrast, basal (high frequency) outer hair cells had abundant BK channel immunoreactivity and BK currents contributed significantly to both voltage-gated and ACh-evoked K(+) currents. CONCLUSIONS/SIGNIFICANCE Our findings suggest that basal (high frequency) outer hair cells may employ an alternative mechanism of efferent inhibition mediated by BK channels instead of SK2 channels. Thus, efferent synapses may use different mechanisms of action both developmentally and tonotopically to support high frequency audition. High frequency audition has required various functional specializations of the mammalian cochlea, and as shown in our work, may include the utilization of BK channels at efferent synapses. This mechanism of efferent inhibition may be related to the unique acetylcholine receptors that have evolved in mammalian hair cells compared to those of other vertebrates.
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Affiliation(s)
- Eric Wersinger
- Department of Otolaryngology Head and Neck Surgery, Center for Hearing and Balance, and Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Will J. McLean
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, United States of America
| | - Paul A. Fuchs
- Department of Otolaryngology Head and Neck Surgery, Center for Hearing and Balance, and Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Sonja J. Pyott
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, United States of America
- * E-mail:
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Schreiber AM, Wang X, Tan Y, Sievers Q, Sievers B, Lee M, Burrall K. Thyroid hormone mediates otolith growth and development during flatfish metamorphosis. Gen Comp Endocrinol 2010; 169:130-7. [PMID: 20736011 DOI: 10.1016/j.ygcen.2010.08.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 08/03/2010] [Accepted: 08/16/2010] [Indexed: 11/15/2022]
Abstract
Flatfish begin life as bilaterally symmetrical larvae that swim up-right, then abruptly metamorphose into asymmetrically shaped juveniles with lateralized swimming postures. Flatfish metamorphosis is mediated entirely by thyroid hormone (TH). Changes in flatfish swim posture are thought to be regulated via vestibular remodeling, although the influence of TH on teleost inner ear development remains unclear. This study addresses the role of TH on the development of the three otolith end-organs (sacculus, utricle, and lagena) during southern flounder (Paralichthys lethostigma) metamorphosis. Compared with pre-metamorphosis, growth rates of the sacculus and utricle otoliths increase dramatically during metamorphosis in a manner that is uncoupled from general somatic growth. Treatment of P. lethostigma larvae with methimazol (a pharmacological inhibitor of endogenous TH production) inhibits growth of the sacculus and utricle, whereas treatment with TH dramatically accelerates their growth. In contrast with the sacculus and utricle otoliths that begin to form and mineralize during embryogenesis, a non-mineralized lagena otolith is first visible 10-12 days after hatching. The lagena grows during pre- and pro-metamorphosis, then abruptly mineralizes during metamorphic climax. Mineralization of the lagena, but not growth, can be induced with TH treatment, whereas treatment with methimazol completely inhibits lagena mineralization without inhibiting its growth. These findings suggest that during southern flounder metamorphosis TH exerts differential effects on growth and development among the three types of otolith.
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Affiliation(s)
- A M Schreiber
- Carnegie Institution, Department of Embryology, Baltimore, MD 21210, USA.
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Reduced electromotility of outer hair cells associated with connexin-related forms of deafness: an in silico study of a cochlear network mechanism. J Assoc Res Otolaryngol 2010; 11:559-71. [PMID: 20635191 DOI: 10.1007/s10162-010-0226-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 06/23/2010] [Indexed: 10/19/2022] Open
Abstract
Mutations in the GJB2 gene encoding for the connexin 26 (Cx26) protein are the most common source of nonsyndromic forms of deafness. Cx26 is a building block of gap junctions (GJs) which establish electrical connectivity in distinct cochlear compartments by allowing intercellular ionic (and metabolic) exchange. Animal models of the Cx26 deficiency in the organ of Corti seem to suggest that the hearing loss and the degeneration of outer hair cells (OHCs) and inner hair cells is due to failed K(+) and metabolite homeostasis. However, OHCs can develop normally in some mutants, suggesting that the hair cells death is not the universal mechanism. In search for alternatives, we have developed an in silico large scale three-dimensional model of electrical current flow in the cochlea in the small signal, linearised, regime. The effect of mutations was analysed by varying the magnitude of resistive components representing the GJ network in the organ of Corti. The simulations indeed show that reduced GJ conductivity increases the attenuation of the OHC transmembrane potential at frequencies above 5 kHz from 6.1 dB/decade in the wild-type to 14.2 dB/decade. As a consequence of increased GJ electrical filtering, the OHC transmembrane potential is reduced by up to 35 dB at frequencies >10 kHz. OHC electromotility, driven by this potential, is crucial for sound amplification, cochlear sensitivity and frequency selectivity. Therefore, we conclude that reduced OHC electromotility may represent an additional mechanism underlying deafness in the presence of Cx26 mutations and may explain lowered OHC functionality in particular reported Cx26 mutants.
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Herde MK, Friauf E, Rust MB. Developmental expression of the actin depolymerizing factor ADF in the mouse inner ear and spiral ganglia. J Comp Neurol 2010; 518:1724-41. [PMID: 20235171 DOI: 10.1002/cne.22298] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Hair cells, the inner ear's sensory cells, are characterized by tens to hundreds of actin-rich stereocilia that form the hair bundle apparatus necessary for mechanoelectrical transduction. Both the number and length of actin filaments are precisely regulated in stereocilia. Proper cochlear and vestibular function also depends on actin filaments in nonsensory supporting cells. The formation of actin filaments is a dynamic, treadmill-like process in which actin-binding proteins play crucial roles. However, little is known about the presence and function of actin binding molecules in the inner ear, which set up, and maintain, actin-rich structures and regulate actin turnover. Here we examined the expression and subcellular location of the actin filament depolymerizing factor (ADF) in the cochlea and vestibular organs. By means of immunocytochemistry and confocal microscopy, we analyzed whole-mount preparations and cross-sections in fetal and postnatal mice (E15-P26). We found a transient ADF expression in immature hair cells of the organ of Corti, the utricle, and the saccule. Interestingly, the stereocilia were not labeled. By P26, ADF expression was restricted to supporting cells. In addition, we localized ADF in presynaptic terminals of medio-olivocochlear projections after hearing onset. A small population of spiral ganglion neurons strongly expressed ADF. Based on their relative number, peripheral location within the ganglion, smaller soma size, and coexpression of neurofilament 200, we identified these cells as Type II spiral ganglion neurons. The developmentally regulated ADF expression suggests a temporally restricted function in the stereocilia and, thus, a hitherto undescribed role of ADF.
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Affiliation(s)
- Michel K Herde
- Neurobiology/Neurophysiology Group, Department of Biology, University of Kaiserslautern, 67663 Kaiserslautern, Germany
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Abstract
PURPOSE OF REVIEW Normal cochlear function depends on maintaining the correct ionic environment for the sensory hair cells. Here we review recent literature on the cellular distribution of potassium transport-related molecules in the cochlea. RECENT FINDINGS Transgenic animal models have identified novel molecules essential for normal hearing and support the idea that potassium is recycled in the cochlea. The findings indicate that extracellular potassium released by outer hair cells into the space of Nuel is taken up by supporting cells, that the gap junction system in the organ of Corti is involved in potassium handling in the cochlea, that the gap junction system in stria vascularis is essential for the generation of the endocochlear potential, and that computational models can assist in the interpretation of the systems biology of hearing and integrate the molecular, electrical, and mechanical networks of the cochlear partition. Such models suggest that outer hair cell electromotility can amplify over a much broader frequency range than expected from isolated cell studies. SUMMARY These new findings clarify the role of endolymphatic potassium in normal cochlear function. They also help current understanding of the mechanisms of certain forms of hereditary hearing loss.
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Wangemann P, Kim HM, Billings S, Nakaya K, Li X, Singh R, Sharlin DS, Forrest D, Marcus DC, Fong P. Developmental delays consistent with cochlear hypothyroidism contribute to failure to develop hearing in mice lacking Slc26a4/pendrin expression. Am J Physiol Renal Physiol 2009; 297:F1435-47. [PMID: 19692489 PMCID: PMC2781347 DOI: 10.1152/ajprenal.00011.2009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Accepted: 08/13/2009] [Indexed: 02/08/2023] Open
Abstract
Mutations of SLC26A4 cause an enlarged vestibular aqueduct, nonsyndromic deafness, and deafness as part of Pendred syndrome. SLC26A4 encodes pendrin, an anion exchanger located in the cochlea, thyroid, and kidney. The goal of the present study was to determine whether developmental delays, possibly mediated by systemic or local hypothyroidism, contribute to the failure to develop hearing in mice lacking Slc26a4 (Slc26a4(-/-)). We evaluated thyroid function by voltage and pH measurements, by array-assisted gene expression analysis, and by determination of plasma thyroxine levels. Cochlear development was evaluated for signs of hypothyroidism by microscopy, in situ hybridization, and quantitative RT-PCR. No differences in plasma thyroxine levels were found in Slc26a4(-/-) and sex-matched Slc26a4(+/-) littermates between postnatal day 5 (P5) and P90. In adult Slc26a4(-/-) mice, the transepithelial potential and the pH of thyroid follicles were reduced. No differences in the expression of genes that participate in thyroid hormone synthesis or ion transport were observed at P15, when plasma thyroxine levels peaked. Scala media of the cochlea was 10-fold enlarged, bulging into and thereby displacing fibrocytes, which express Dio2 to generate a cochlear thyroid hormone peak at P7. Cochlear development, including tunnel opening, arrival of efferent innervation at outer hair cells, endochondral and intramembraneous ossification, and developmental changes in the expression of Dio2, Dio3, and Tectb were delayed by 1-4 days. These data suggest that pendrin functions as a HCO3- transporter in the thyroid, that Slc26a4(-/-) mice are systemically euthyroid, and that delays in cochlear development, possibly due to local hypothyroidism, lead to the failure to develop hearing.
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Affiliation(s)
- Philine Wangemann
- Anatomy and Physiology Department, Kansas State University, Manhattan, KS 66506, USA.
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19
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Abstract
Thyroid hormone receptor beta (TRbeta) dysfunction leads to deafness in humans and mice. Deafness in TRbeta(-/-) mutant mice has been attributed to TRbeta-mediated control of voltage- and Ca(2+)-activated K(+) (BK) channel expression in inner hair cells (IHCs). However, normal hearing in young constitutive BKalpha(-/-) mutants contradicts this hypothesis. Here, we show that mice with hair cell-specific deletion of TRbeta after postnatal day 11 (P11) have a delay in BKalpha expression but normal hearing, indicating that the origin of hearing loss in TRbeta(-/-) mutant mice manifested before P11. Analyzing the phenotype of IHCs in constitutive TRbeta(-/-) mice, we found normal Ca(2+) current amplitudes, exocytosis, and shape of compound action potential waveforms. In contrast, reduced distortion product otoacoustic emissions and cochlear microphonics associated with an abnormal structure of the tectorial membrane and enhanced tectorin levels suggest that disturbed mechanical performance is the primary cause of deafness resulting from TRbeta deficiency.
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Friauf E, Wenz M, Oberhofer M, Nothwang HG, Balakrishnan V, Knipper M, Löhrke S. Hypothyroidism impairs chloride homeostasis and onset of inhibitory neurotransmission in developing auditory brainstem and hippocampal neurons. Eur J Neurosci 2008; 28:2371-80. [PMID: 19087168 DOI: 10.1111/j.1460-9568.2008.06528.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
Abstract
Thyroid hormone (TH) deficiency during perinatal life causes a multitude of functional and morphological deficits in the brain. In rats and mice, TH dependency of neural maturation is particularly evident during the first 1-2 weeks of postnatal development. During the same period, synaptic transmission via the inhibitory transmitters glycine and GABA changes from excitatory depolarizing effects to inhibitory hyperpolarizing ones in most neurons [depolarizing-hyperpolarizing (D/H) shift]. The D/H shift is caused by the activation of the K(+)-Cl(-) co-transporter KCC2 which extrudes Cl(-) from the cytosol, thus generating an inward-directed electrochemical Cl(-) gradient. Here we analyzed whether the D/H shift and, consequently, the onset of inhibitory neurotransmission are influenced by TH. Gramicidin perforated-patch recordings from auditory brainstem neurons of experimentally hypothyroid rats revealed depolarizing glycine effects until postnatal day (P)11, i.e. almost 1 week longer than in control rats, in which the D/H shift occurred at approximately P5-6. Likewise, until P12-13 the equilibrium potential E(Gly) in hypothyroids was more positive than the membrane resting potential. Normal E(Gly) could be restored upon TH substitution in P11-12 hypothyroids. These data demonstrate a disturbed Cl(-) homeostasis following TH deficiency and point to a delayed onset of synaptic inhibition. Interestingly, immunohistochemistry demonstrated an unchanged KCC2 distribution in hypothyroids, implying that TH deficiency did not affect KCC2 gene expression but may have impaired the functional status of KCC2. Hippocampal neurons of hypothyroid P16-17 rats also demonstrated an impaired Cl(-) homeostasis, indicating that TH may have promoted the D/H shift and maturation of synaptic inhibition throughout the brain.
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Affiliation(s)
- Eckhard Friauf
- Animal Physiology Group, Department of Biology, University of Kaiserslautern, POB 3049, D-67653 Kaiserslautern, Germany.
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21
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State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology. Histochem Cell Biol 2008; 130:1205-51. [PMID: 18985372 DOI: 10.1007/s00418-008-0535-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/21/2008] [Indexed: 10/25/2022]
Abstract
Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.
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22
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Song L, McGee J, Walsh EJ. The influence of thyroid hormone deficiency on the development of cochlear nonlinearities. J Assoc Res Otolaryngol 2008; 9:464-76. [PMID: 18855071 DOI: 10.1007/s10162-008-0140-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2007] [Accepted: 09/11/2008] [Indexed: 11/24/2022] Open
Abstract
It is well known that failure to treat severe congenital hypothyroidism leads to profound auditory disability, and it has been suggested that an intracochlear defect, or defects, associated with the condition diminishes the efficacy of an active, physiologically vulnerable nonlinear transduction process commonly referred to as cochlear amplification. We address this question directly by tracking the development of threshold-frequency (tuning) curves and two-tone suppression in hypothyroid, Tshr mutant mice born to hypothyroid dams and comparing those findings with findings observed in euthyroid mice. Like sharp tuning, two-tone suppression is a product of transduction nonlinearity and is a useful indicator of the functional status of cochlear amplification. In contrast to euthyroid mice that acquire sharp tuning, normal two-tone suppression, and adultlike sensitivity by the end of the third postnatal week, as shown in earlier studies, hypothyroid mice remained grossly insensitive to sound throughout life. In addition, tuning was generally broad in hypothyroid mice, tuning curve "tips" were frequently missing, and two-tone suppression was rarely observed. However, unlike tip thresholds, tuning curve "tail" thresholds, a feature that reflects the functional status of passive elements of transduction, acquired normal values over a roughly 2-month postnatal time period. These observations collectively suggest that active transduction micromechanics, at least in the frequency region studied here, are profoundly affected by thyroid hormone and support speculation that abnormal outer hair cell function may be the cause of the primary, enduring peripheral auditory defect associated with profound, congenital hypothyroidism in the Tshr mutant mouse.
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Affiliation(s)
- Lei Song
- Developmental Auditory Physiology Laboratory, Boys Town National Research Hospital, 555 North 30th Street, Omaha, NE 68131, USA
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23
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Xia A, Wooltorton JRA, Palmer DJ, Ng P, Pereira FA, Eatock RA, Oghalai JS. Functional prestin transduction of immature outer hair cells from normal and prestin-null mice. J Assoc Res Otolaryngol 2008; 9:307-20. [PMID: 18506528 DOI: 10.1007/s10162-008-0121-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2007] [Accepted: 04/04/2008] [Indexed: 10/22/2022] Open
Abstract
Prestin is a membrane protein in the outer hair cell (OHC) that has been shown to be essential for electromotility. OHCs from prestin-null mice do not express prestin, do not have a nonlinear capacitance (the electrical signature of electromotility), and are smaller in size than wild-type OHCs. We sought to determine whether prestin-null OHCs can be transduced to incorporate functional prestin protein in a normal fashion. A recombinant helper-dependent adenovirus expressing prestin and green fluorescent protein (HDAd-prestin-GFP) was created and tested in human embryonic kidney cells (HEK cells). Transduced HEK cells demonstrated membrane expression of prestin and nonlinear capacitance. HDAd-prestin-GFP was then applied to cochlear sensory epithelium explants harvested from wild-type and prestin-null mice at postnatal days 2-3, the age at which native prestin is just beginning to become functional in wild-type mice. At postnatal days 4-5, we investigated transduced OHCs for (1) their prestin expression pattern as revealed by immunofluorescence; (2) their cell surface area as measured by linear capacitance; and (3) their prestin function as indicated by nonlinear capacitance. HDAd-prestin-GFP efficiently transduced OHCs of both genotypes and prestin protein localized to the plasma membrane. Whole-cell voltage clamp studies revealed a nonlinear capacitance in transduced wild-type and prestin-null OHCs, but not in non-transduced cells of either genotype. Prestin transduction did not increase the linear capacitance (cell surface area) for either genotype. In peak nonlinear capacitance, voltage at peak nonlinear capacitance, charge density of the nonlinear capacitance, and shape of the voltage-capacitance curves, the transduced cells of the two genotypes resembled each other and previously reported data from adult wild-type mouse OHCs. Thus, prestin introduced into prestin-deficient OHCs segregates normally to the cell membrane and generates a normal nonlinear capacitance, indicative of normal prestin function.
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Affiliation(s)
- Anping Xia
- Bobby R. Alford Department of Otolaryngology, Head and Neck Surgery, Baylor College of Medicine, One Baylor Plaza, NA102, Houston, TX 77030, USA
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Collin RW, Kalay E, Tariq M, Peters T, van der Zwaag B, Venselaar H, Oostrik J, Lee K, Ahmed ZM, Çaylan R, Li Y, Spierenburg HA, Eyupoglu E, Heister A, Riazuddin S, Bahat E, Ansar M, Arslan S, Wollnik B, Brunner HG, Cremers CW, Karaguzel A, Ahmad W, Cremers FP, Vriend G, Friedman TB, Riazuddin S, Leal SM, Kremer H. Mutations of ESRRB encoding estrogen-related receptor beta cause autosomal-recessive nonsyndromic hearing impairment DFNB35. Am J Hum Genet 2008; 82:125-38. [PMID: 18179891 PMCID: PMC2253958 DOI: 10.1016/j.ajhg.2007.09.008] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Revised: 09/20/2007] [Accepted: 09/21/2007] [Indexed: 01/09/2023] Open
Abstract
In a large consanguineous family of Turkish origin, genome-wide homozygosity mapping revealed a locus for recessive nonsyndromic hearing impairment on chromosome 14q24.3-q34.12. Fine mapping with microsatellite markers defined the critical linkage interval to a 18.7 cM region flanked by markers D14S53 and D14S1015. This region partially overlapped with the DFNB35 locus. Mutation analysis of ESRRB, a candidate gene in the overlapping region, revealed a homozygous 7 bp duplication in exon 8 in all affected individuals. This duplication results in a frame shift and premature stop codon. Sequence analysis of the ESRRB gene in the affected individuals of the original DFNB35 family and in three other DFNB35-linked consanguineous families from Pakistan revealed four missense mutations. ESRRB encodes the estrogen-related receptor beta protein, and one of the substitutions (p.A110V) is located in the DNA-binding domain of ESRRB, whereas the other three are substitutions (p.L320P, p.V342L, and p.L347P) located within the ligand-binding domain. Molecular modeling of this nuclear receptor showed that the missense mutations are likely to affect the structure and stability of these domains. RNA in situ hybridization in mice revealed that Esrrb is expressed during inner-ear development, whereas immunohistochemical analysis showed that ESRRB is present postnatally in the cochlea. Our data indicate that ESRRB is essential for inner-ear development and function. To our knowledge, this is the first report of pathogenic mutations of an estrogen-related receptor gene.
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Alonso M, Goodwin C, Liao X, Page D, Refetoff S, Weiss RE. Effects of maternal levels of thyroid hormone (TH) on the hypothalamus-pituitary-thyroid set point: studies in TH receptor beta knockout mice. Endocrinology 2007; 148:5305-12. [PMID: 17690164 DOI: 10.1210/en.2007-0677] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A level of thyroid hormone (TH) in agreement with the tissue requirements is essential for vertebrate embryogenesis and fetal maturation. In this study we evaluate the immediate and long-term effects of incongruent intrauterine TH levels between mother and fetus using the TH receptor (TR) beta(-/-) knockout mouse as a model. We took advantage of the fact that the TRbeta(-/-) females have elevated serum TH but are not thyrotoxic due to resistance to TH. We used crosses between heterozygotes with wild-type phenotype (TRbeta(+/-)) males and TRbeta(-/-) females, with a hyperiodothyroninemic (high T(4) and T(3) levels) intrauterine environment (TH congruent with the TRbeta(-/-) fetus and excessive for the TRbeta(+/-) fetus), and reciprocal crosses between TRbeta(-/-) males and TRbeta(+/-) females, providing a euiodothyroninemic intrauterine environment. We found that TRbeta(-/-) dams had reduced litter sizes and pups with lower birth weight but preserved the mendelian TRbeta(-/-) to TRbeta(+/-) ratio at birth, indicating that the incongruous TH levels did not decrease intrauterine survival of a specific genotype. The results of studies in newborns demonstrate that TRbeta(+/-) pups born to TRbeta(-/-) dams have persistent suppression of serum TSH without a peak. On the other hand, TRbeta(-/-) pups born to TRbeta(+/-) dams have lower serum TSH at birth and a tendency to peak higher, compared with TRbeta(-/-) pups born to TRbeta(-/-) dams. The studies in the adult progeny demonstrate that TRbeta(+/-) mice born to TRbeta(-/-) dams and, thus, exposed to higher intrauterine TH levels, have greater resistance to TH at the level of the pituitary when stimulated with TRH. On the other hand, TRbeta(-/-) mice born to TRbeta(+/-) dams and, thus, deprived of TH in uterine life, were more sensitive to TH when similarly stimulated with TRH. Thus, TH exposure in utero has an effect on the regulatory set point of the hypothalamus-pituitary-thyroid axis, which can be seen early in life and persists into adulthood.
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Affiliation(s)
- Manuela Alonso
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
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26
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Abstract
The progress in discerning the structure and function of cells and tissues in health and disease has been achieved to a large extent by the continued development of new reagents for histochemistry, the improvement of existing techniques and new imaging techniques. This review will highlight some advancements made in these fields.
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27
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Affiliation(s)
- M Knipper
- Molekulare Neurobiologie, Hörforschungszentrum Tübingen, Universitäts-Hals-Nasen-Ohren-Klinik, 72076, Tübingen.
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