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Wang Y, Jin Y, Zhang Q, Xiong Y, Gu X, Zeng S, Chen W. Research progress in delineating the pathological mechanisms of GJB2-related hearing loss. Front Cell Neurosci 2023; 17:1208406. [PMID: 37333892 PMCID: PMC10272732 DOI: 10.3389/fncel.2023.1208406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 05/15/2023] [Indexed: 06/20/2023] Open
Abstract
Hearing loss is the most common congenital sensory impairment. Mutations or deficiencies of the GJB2 gene are the most common genetic cause of congenital non-syndromic deafness. Pathological changes such as decreased potential in the cochlea, active cochlear amplification disorders, cochlear developmental disorders and macrophage activation have been observed in various GJB2 transgenic mouse models. In the past, researchers generally believed that the pathological mechanisms underlying GJB2-related hearing loss comprised a K+ circulation defect and abnormal ATP-Ca2+ signals. However, recent studies have shown that K+ circulation is rarely associated with the pathological process of GJB2-related hearing loss, while cochlear developmental disorders and oxidative stress play an important, even critical, role in the occurrence of GJB2-related hearing loss. Nevertheless, these research has not been systematically summarized. In this review, we summarize the pathological mechanisms of GJB2-related hearing loss, including aspects of K+ circulation, developmental disorders of the organ of Corti, nutrition delivery, oxidative stress and ATP-Ca2+ signals. Clarifying the pathological mechanism of GJB2-related hearing loss can help develop new prevention and treatment strategies.
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Affiliation(s)
- Yujun Wang
- Department of Intensive Care Unit, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yuan Jin
- Department of Otorhinolaryngology–Head and Neck Surgery, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Qiong Zhang
- Department of Otorhinolaryngology–Head and Neck Surgery, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Ying Xiong
- Department of Otorhinolaryngology–Head and Neck Surgery, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Xiang Gu
- Department of Otorhinolaryngology–Head and Neck Surgery, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Shan Zeng
- Department of Otorhinolaryngology–Head and Neck Surgery, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Wei Chen
- Department of Otorhinolaryngology–Head and Neck Surgery, The Central Hospital of Wuhan, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
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2
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Liu LM, Liang C, Chen J, Fang S, Zhao HB. Cx26 heterozygous mutations cause hyperacusis-like hearing oversensitivity and increase susceptibility to noise. Sci Adv 2023; 9:eadf4144. [PMID: 36753545 PMCID: PMC9908021 DOI: 10.1126/sciadv.adf4144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 01/10/2023] [Indexed: 06/18/2023]
Abstract
Gap junction gene GJB2 (Cx26) mutations cause >50% of nonsyndromic hearing loss. Its recessive hetero-mutation carriers, who have no deafness, occupy ~10 to 20% of the general population. Here, we report an unexpected finding that these heterozygote carriers have hearing oversensitivity, and active cochlear amplification increased. Mouse models show that Cx26 hetero-deletion reduced endocochlear potential generation in the cochlear lateral wall and caused outer hair cell electromotor protein prestin compensatively up-regulated to increase active cochlear amplification and hearing sensitivity. The increase of active cochlear amplification also increased sensitivity to noise; exposure to daily-level noise could cause Cx26+/- mice permanent hearing threshold shift, leading to hearing loss. This study demonstrates that Cx26 recessive heterozygous mutations are not "harmless" for hearing as previously considered and can cause hyperacusis-like hearing oversensitivity. The data also indicate that GJB2 hetero-mutation carriers are vulnerable to noise and should avoid noise exposure in daily life.
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Affiliation(s)
- Li-Man Liu
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
- Department of Surgery–Otolaryngology, Yale University Medical School, 310 Cedar Street, New Haven, CT 06510, USA
| | - Chun Liang
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
- Hearing Function Testing Center, Shenzhen Maternity and Child Healthcare Hospital, 3012 Fuqiang Road, Shenzhen 518017, China
| | - Jin Chen
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
| | - Shu Fang
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
| | - Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
- Department of Surgery–Otolaryngology, Yale University Medical School, 310 Cedar Street, New Haven, CT 06510, USA
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3
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Zhao HB, Liu LM, Yu N, Zhu Y, Mei L, Chen J, Liang C. Efferent neurons control hearing sensitivity and protect hearing from noise through the regulation of gap junctions between cochlear supporting cells. J Neurophysiol 2022; 127:313-327. [PMID: 34907797 PMCID: PMC8759971 DOI: 10.1152/jn.00468.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
It is critical for hearing that the descending cochlear efferent system provides a negative feedback to hair cells to regulate hearing sensitivity and protect hearing from noise. The medial olivocochlear (MOC) efferent nerves project to outer hair cells (OHCs) to regulate OHC electromotility, which is an active cochlear amplifier and can increase hearing sensitivity. Here, we report that the MOC efferent nerves also could innervate supporting cells (SCs) in the vicinity of OHCs to regulate hearing sensitivity. MOC nerve fibers are cholinergic, and acetylcholine (ACh) is a primary neurotransmitter. Immunofluorescent staining showed that MOC nerve endings, presynaptic vesicular acetylcholine transporters (VAChTs), and postsynaptic ACh receptors were visible at SCs and in the SC area. Application of ACh in SCs could evoke a typical inward current and reduce gap junctions (GJs) between them, which consequently enhanced the direct effect of ACh on OHCs to shift but not eliminate OHC electromotility. This indirect, GJ-mediated inhibition had a long-lasting influence. In vivo experiments further demonstrated that deficiency of this GJ-mediated efferent pathway decreased the regulation of active cochlear amplification and compromised the protection against noise. In particular, distortion product otoacoustic emission (DPOAE) showed a delayed reduction after noise exposure. Our findings reveal a new pathway for the MOC efferent system via innervating SCs to control active cochlear amplification and hearing sensitivity. These data also suggest that this SC GJ-mediated efferent pathway may play a critical role in long-term efferent inhibition and is required for protection of hearing from noise trauma.NEW & NOTEWORTHY The cochlear efferent system provides a negative feedback to control hair cell activity and hearing sensitivity and plays a critical role in noise protection. We reveal a new efferent control pathway in which medial olivocochlear efferent fibers have innervations with cochlear supporting cells to control their gap junctions, therefore regulating outer hair cell electromotility and hearing sensitivity. This supporting cell gap junction-mediated efferent control pathway is required for the protection of hearing from noise.
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4
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He W, Ren T. The origin of mechanical harmonic distortion within the organ of Corti in living gerbil cochleae. Commun Biol 2021; 4:1008. [PMID: 34433876 PMCID: PMC8387486 DOI: 10.1038/s42003-021-02540-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 08/11/2021] [Indexed: 11/09/2022] Open
Abstract
Although auditory harmonic distortion has been demonstrated psychophysically in humans and electrophysiologically in experimental animals, the cellular origin of the mechanical harmonic distortion remains unclear. To demonstrate the outer hair cell-generated harmonics within the organ of Corti, we measured sub-nanometer vibrations of the reticular lamina from the apical ends of the outer hair cells in living gerbil cochleae using a custom-built heterodyne low-coherence interferometer. The harmonics in the reticular lamina vibration are significantly larger and have broader spectra and shorter latencies than those in the basilar membrane vibration. The latency of the second harmonic is significantly greater than that of the fundamental at low stimulus frequencies. These data indicate that the mechanical harmonics are generated by the outer hair cells over a broad cochlear region and propagate from the generation sites to their own best-frequency locations.
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Affiliation(s)
- Wenxuan He
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, OR, USA
| | - Tianying Ren
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, OR, USA.
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5
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Chen Z, Zhu S, Kindig K, Wang S, Chou SW, Davis RW, Dercoli MR, Weaver H, Stepanyan R, McDermott BM. Tmc proteins are essential for zebrafish hearing where Tmc1 is not obligatory. Hum Mol Genet 2021; 29:2004-2021. [PMID: 32167554 DOI: 10.1093/hmg/ddaa045] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Accepted: 02/13/2020] [Indexed: 12/19/2022] Open
Abstract
Perception of sound is initiated by mechanically gated ion channels at the tips of stereocilia. Mature mammalian auditory hair cells require transmembrane channel-like 1 (TMC1) for mechanotransduction, and mutations of the cognate genetic sequences result in dominant or recessive heritable deafness forms in humans and mice. In contrast, zebrafish lateral line hair cells, which detect water motion, require Tmc2a and Tmc2b. Here, we use standard and multiplex genome editing in conjunction with functional and behavioral assays to determine the reliance of zebrafish hearing and vestibular organs on Tmc proteins. Surprisingly, our approach using multiple mutant alleles demonstrates that hearing in zebrafish is not dependent on Tmc1, nor is it fully dependent on Tmc2a and Tmc2b. Hearing however is absent in triple-mutant zebrafish that lack Tmc1, Tmc2a and Tmc2b. These outcomes reveal a striking resemblance of Tmc protein reliance in the vestibular sensory epithelia of mammals to the maculae of zebrafish. Moreover, our findings disclose a logic of Tmc use where hearing depends on a complement of Tmc proteins beyond those employed to sense water motion.
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Affiliation(s)
- Zongwei Chen
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Shaoyuan Zhu
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Kayla Kindig
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Shengxuan Wang
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Shih-Wei Chou
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Robin Woods Davis
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Michael R Dercoli
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Hannah Weaver
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ruben Stepanyan
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Brian M McDermott
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA.,Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.,Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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Fukunaga I, Oe Y, Danzaki K, Ohta S, Chen C, Shirai K, Kawano A, Ikeda K, Kamiya K. Modeling gap junction beta 2 gene-related deafness with human iPSC. Hum Mol Genet 2021; 30:1429-1442. [PMID: 33997905 DOI: 10.1093/hmg/ddab097] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 03/29/2021] [Accepted: 03/31/2021] [Indexed: 02/06/2023] Open
Abstract
There are >120 forms of non-syndromic deafness associated with identified genetic loci. In particular, mutation of the gap junction beta 2 gene (GJB2), which encodes connexin (CX)26 protein, is the most frequent cause of hereditary deafness worldwide. We previously described an induction method to develop functional CX26 gap junction-forming cells from mouse-induced pluripotent stem cells (iPSCs) and generated in vitro models for GJB2-related deafness. However, functional CX26 gap junction-forming cells derived from human iPSCs or embryonic stem cells (ESCs) have not yet been reported. In this study, we generated human iPSC-derived functional CX26 gap junction-forming cells (iCX26GJCs), which have the characteristics of cochlear supporting cells. These iCX26GJCs had gap junction plaque-like formations at cell-cell borders and co-expressed several markers that are expressed in cochlear supporting cells. Furthermore, we generated iCX26GJCs derived from iPSCs from two patients with the most common GJB2 mutation in Asia, and these cells reproduced the pathology of GJB2-related deafness. These in vitro models may be useful for establishing optimal therapies and drug screening for various mutations in GJB2-related deafness.
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Affiliation(s)
- Ichiro Fukunaga
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
| | - Yoko Oe
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
| | - Keiko Danzaki
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
| | - Sayaka Ohta
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
| | - Cheng Chen
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
| | - Kyoko Shirai
- Department of Otolaryngology, Head and Neck Surgery, Tokyo Medical University, Tokyo 1600023, Japan
| | - Atsushi Kawano
- Department of Otolaryngology, Head and Neck Surgery, Tokyo Medical University, Tokyo 1600023, Japan
| | - Katsuhisa Ikeda
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
| | - Kazusaku Kamiya
- Department of Otorhinolaryngology, Juntendo University Faculty of Medicine, Tokyo 1138421, Japan
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7
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Nankali A, Wang Y, Strimbu CE, Olson ES, Grosh K. A role for tectorial membrane mechanics in activating the cochlear amplifier. Sci Rep 2020; 10:17620. [PMID: 33077807 PMCID: PMC7573614 DOI: 10.1038/s41598-020-73873-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Accepted: 09/21/2020] [Indexed: 12/02/2022] Open
Abstract
The mechanical and electrical responses of the mammalian cochlea to acoustic stimuli are nonlinear and highly tuned in frequency. This is due to the electromechanical properties of cochlear outer hair cells (OHCs). At each location along the cochlear spiral, the OHCs mediate an active process in which the sensory tissue motion is enhanced at frequencies close to the most sensitive frequency (called the characteristic frequency, CF). Previous experimental results showed an approximate 0.3 cycle phase shift in the OHC-generated extracellular voltage relative the basilar membrane displacement, which was initiated at a frequency approximately one-half octave lower than the CF. Findings in the present paper reinforce that result. This shift is significant because it brings the phase of the OHC-derived electromotile force near to that of the basilar membrane velocity at frequencies above the shift, thereby enabling the transfer of electrical to mechanical power at the basilar membrane. In order to seek a candidate physical mechanism for this phenomenon, we used a comprehensive electromechanical mathematical model of the cochlear response to sound. The model predicts the phase shift in the extracellular voltage referenced to the basilar membrane at a frequency approximately one-half octave below CF, in accordance with the experimental data. In the model, this feature arises from a minimum in the radial impedance of the tectorial membrane and its limbal attachment. These experimental and theoretical results are consistent with the hypothesis that a tectorial membrane resonance introduces the correct phasing between mechanical and electrical responses for power generation, effectively turning on the cochlear amplifier.
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Affiliation(s)
- Amir Nankali
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Yi Wang
- Biomedical Engineering, Columbia University, New York, NY, USA
| | | | - Elizabeth S Olson
- Otolaryngology, Head and Neck Surgery, Columbia University, New York, NY, USA.,Biomedical Engineering, Columbia University, New York, NY, USA
| | - Karl Grosh
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA. .,Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
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Abstract
It has been demonstrated that isolated auditory sensory cells, outer hair cells, can generate distortion products at low frequencies. It remains unknown, however, whether or not motile outer hair cells are able to generate two-tone distortion at high frequencies in living cochleae under the mechanical loads caused by surounding tissues and fluids. By measuring sub-nanometer vibration directly from the apical ends of outer hair cells using a custom-built heterodyne low-coherence interferometer, here we show outer hair cell-generated two-tone distortion in reticular lamina motion in the living cochlea. Reticular-lamina distortion is significantly greater and occurs at a broader frequency range than that of the basilar membrane. Contrary to expectations, our results indicate that motile outer hair cells are capable of generating two-tone distortion in vivo not only at the locations tuned to primary tones but also at a broad region basal to these locations. Ren et al. used an in house heterodyne low-coherence interferometer to measure sub-nanometer vibrations, a proxy for distortion products, in living cochleae of gerbils. They were able to locate the generation source of the outer hair cell in the reticular lamina versus the basilar membrane in vivo.
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10
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Fukunaga I, Fujimoto A, Hatakeyama K, Kurebayashi N, Ikeda K, Kamiya K. Generation of Functional CX26–Gap‐Junction‐Plaque‐Forming Cells with Spontaneous Ca
2+
Transients via a Gap Junction Characteristic of Developing Cochlea. ACTA ACUST UNITED AC 2019; 51:e100. [DOI: 10.1002/cpsc.100] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Ichiro Fukunaga
- Department of OtorhinolaryngologyJuntendo University Faculty of Medicine Tokyo Japan
| | - Ayumi Fujimoto
- Department of OtorhinolaryngologyJuntendo University Faculty of Medicine Tokyo Japan
| | - Kaori Hatakeyama
- Department of OtorhinolaryngologyJuntendo University Faculty of Medicine Tokyo Japan
| | - Nagomi Kurebayashi
- Department of Cellular and Molecular PharmacologyJuntendo University Graduate School of Medicine Tokyo Japan
| | - Katsuhisa Ikeda
- Department of OtorhinolaryngologyJuntendo University Faculty of Medicine Tokyo Japan
| | - Kazusaku Kamiya
- Department of OtorhinolaryngologyJuntendo University Faculty of Medicine Tokyo Japan
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Chen S, Xie L, Xu K, Cao HY, Wu X, Xu XX, Sun Y, Kong WJ. Developmental abnormalities in supporting cell phalangeal processes and cytoskeleton in the Gjb2 knockdown mouse model. Dis Model Mech 2018; 11:dmm.033019. [PMID: 29361521 PMCID: PMC5894950 DOI: 10.1242/dmm.033019] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 01/15/2018] [Indexed: 12/30/2022] Open
Abstract
Mutations in the GJB2 gene [which encodes connexin 26 (Cx26)] are the most common causes of hereditary hearing loss in humans, and previous studies showed postnatal development arrest of the organ of Corti in different Cx26-null mouse models. To explore the pathological changes and the mechanism behind the cochlear abnormalities in these mice further, we established transgenic mouse models by conditional knockdown of cochlear Cx26 at postnatal day (P) 0 and P8. Auditory brainstem responses were recorded and the morphological features in the organ of Corti were analyzed 18 days after Cx26 knockdown. Mice in the P0 knockdown group displayed severe hearing loss at all frequencies, whereas mice in the P8 knockdown group showed nearly normal hearing. In the P8 knockdown group, the organ of Corti displayed normal architecture, and no ultrastructural changes were observed. In the P0 knockdown group, the phalangeal processes of Deiter's cells did not develop into finger-like structures, and the formation of microtubules in the pillar cells was significantly reduced; moreover, the amount of acetylated α-tubulin was reduced in pillar cells. Our results indicate that Gjb2 participates in postnatal development of the cytoskeleton in pillar cells during structural maturation of the organ of Corti. In P0 knockdown mice, the reduction in microtubules in pillar cells might be responsible for the failure of the tunnel of Corti to open, and the malformed phalangeal processes might negatively affect the supporting framework of the organ of Corti, which would be a new mechanism of Gjb2-related hearing loss. Summary: A reduction in connexin 26 before opening of the tunnel of Corti impedes microtubule formation in supporting cells, and this may lead to cochlear developmental abnormalities and deafness in the Gjb2 knockdown mouse model.
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Affiliation(s)
- Sen Chen
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Le Xie
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Kai Xu
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Hai-Yan Cao
- Department of Ultrasound, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Xia Wu
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Xiao-Xiang Xu
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Yu Sun
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China .,Institute of Otorhinolaryngology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
| | - Wei-Jia Kong
- Department of Otorhinolaryngology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China .,Institute of Otorhinolaryngology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China
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12
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Sinha S, Sachar HS, Das S. Effect of Plasma Membrane Semipermeability in Making the Membrane Electric Double Layer Capacitances Significant. Langmuir 2018; 34:1760-1766. [PMID: 29294274 DOI: 10.1021/acs.langmuir.7b02939] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Electric double layers (or EDLs) formed at the membrane-electrolyte interface (MEI) and membrane-cytosol interface (MCI) of a charged lipid bilayer plasma membrane develop finitely large capacitances. However, these EDL capacitances are often much larger than the intrinsic capacitance of the membrane, and all of these capacitances are in series. Consequently, the effect of these EDL capacitances in dictating the overall membrane-EDL effective capacitance Ceff becomes negligible. In this paper, we challenge this conventional notion pertaining to the membrane-EDL capacitances. We demonstrate that, on the basis of the system parameters, the EDL capacitance for both the permeable and semipermeable membranes can be small enough to influence Ceff. For the semipermeable membranes, however, this lowering of the EDL capacitance can be much larger, ensuring a reduction of Ceff by more than 20-25%. Furthermore, for the semipermeable membranes, the reduction in Ceff is witnessed over a much larger range of system parameters. We attribute such an occurrence to the highly nonintuitive electrostatic potential distribution associated with the recently discovered phenomena of charge-inversion-like electrostatics and the attainment of a positive zeta potential at the MCI for charged semipermeable membranes. We anticipate that our findings will impact the quantification and the identification of a large number of biophysical phenomena that are probed by measuring the plasma membrane capacitance.
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Affiliation(s)
- Shayandev Sinha
- Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States
| | - Harnoor Singh Sachar
- Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States
| | - Siddhartha Das
- Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States
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13
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Abitbol JM, Kelly JJ, Barr KJ, Allman BL, Laird DW. Mice harbouring an oculodentodigital dysplasia-linked Cx43 G60S mutation have severe hearing loss. J Cell Sci 2018; 131:jcs.214635. [DOI: 10.1242/jcs.214635] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Accepted: 03/27/2018] [Indexed: 01/22/2023] Open
Abstract
Given the importance of connexin43 (Cx43) function in the central nervous system and sensory organ processing we proposed that it would also be crucial in auditory function. To that end, hearing was examined in two mouse models of oculodentodigital dysplasia that globally express GJA1 (Cx43) mutations resulting in mild or severe loss of Cx43 function. Although Cx43I130T/+ mutant mice with ∼50% Cx43 channel function did not have any hearing loss, Cx43G60S/+ mutant mice with ∼20% Cx43 channel function had severe hearing loss. There was no evidence of inner ear sensory hair cell loss, suggesting that the Cx43-linked hearing loss lies downstream in the auditory pathway. Since evidence suggests that Cx26 function is essential for hearing and may be protective against noise-induced hearing loss, we challenged Cx43I130T/+ mice with a loud noise and found that they had similar susceptibility to noise-induced hearing loss as controls suggesting that decreased Cx43 function does not sensitize the mice for environmentally-induced hearing loss. Taken together, this study suggests that Cx43 plays an important role in baseline hearing and is essential for auditory processing.
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Affiliation(s)
| | - John J. Kelly
- University of Western Ontario, London, Ontario, Canada
| | - Kevin J. Barr
- University of Western Ontario, London, Ontario, Canada
| | | | - Dale W. Laird
- University of Western Ontario, London, Ontario, Canada
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14
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Abstract
The first major recognition of drug-induced hearing loss can be traced back more than seven decades to the development of streptomycin as an antimicrobial agent. Since then at least 130 therapeutic drugs have been recognized as having ototoxic side-effects. Two important classes of ototoxic drugs are the aminoglycoside antibiotics and the platinum-based antineoplastic agents. These drugs save the lives of millions of people worldwide, but they also cause irreparable hearing loss. In the inner ear, sensory hair cells (HCs) and spiral ganglion neurons (SGNs) are important cellular targets of these drugs, and most mechanistic studies have focused on the cell-autonomous responses of these cell types in response to ototoxic stress. Despite several decades of studies on ototoxicity, important unanswered questions remain, including the cellular and molecular mechanisms that determine whether HCs and SGNs will live or die when confronted with ototoxic challenge. Emerging evidence indicates that other cell types in the inner ear can act as mediators of survival or death of sensory cells and SGNs. For example, glia-like supporting cells (SCs) can promote survival of both HCs and SGNs. Alternatively, SCs can act to promote HC death and inhibit neural fiber expansion. Similarly, tissue resident macrophages activate either pro-survival or pro-death signaling that can influence HC survival after exposure to ototoxic agents. Together these data indicate that autonomous responses that occur within a stressed HC or SGN are not the only (and possibly not the primary) determinants of whether the stressed cell ultimately lives or dies. Instead non-cell-autonomous responses are emerging as significant determinants of HC and SGN survival vs. death in the face of ototoxic stress. The goal of this review is to summarize the current evidence on non-cell-autonomous responses to ototoxic stress and to discuss ways in which this knowledge may advance the development of therapies to reduce hearing loss caused by these drugs.
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Affiliation(s)
- Shimon P Francis
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesda, MD, United States
| | - Lisa L Cunningham
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesda, MD, United States
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15
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Mei L, Chen J, Zong L, Zhu Y, Liang C, Jones RO, Zhao HB. A deafness mechanism of digenic Cx26 (GJB2) and Cx30 (GJB6) mutations: Reduction of endocochlear potential by impairment of heterogeneous gap junctional function in the cochlear lateral wall. Neurobiol Dis 2017; 108:195-203. [PMID: 28823936 DOI: 10.1016/j.nbd.2017.08.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2017] [Revised: 07/12/2017] [Accepted: 08/16/2017] [Indexed: 12/19/2022] Open
Abstract
Digenic Connexin26 (Cx26, GJB2) and Cx30 (GJB6) heterozygous mutations are the second most frequent cause of recessive deafness in humans. However, the underlying deafness mechanism remains unclear. In this study, we created different double Cx26 and Cx30 heterozygous (Cx26+/-/Cx30+/-) mouse models to investigate the underlying pathological changes and deafness mechanism. We found that double Cx26+/-/Cx30+/- heterozygous mice had hearing loss. Endocochlear potential (EP), which is a driving force for hair cells producing auditory receptor current, was reduced. However, unlike Cx26 homozygous knockout (Cx26-/-) mice, the cochlea in Cx26+/-/Cx30+/- mice displayed normal development and had no apparent hair cell degeneration. Gap junctions (GJs) in the cochlea form two independent networks: the epithelial cell GJ network in the organ of Corti and the connective tissue GJ network in the cochlear lateral wall. We further found that double heterozygous deletion of Cx26 and Cx30 in the epithelial cells did not reduce EP and had normal hearing, suggesting that Cx26+/-/Cx30+/- may mainly impair gap junctional functions in the cochlear lateral wall and lead to EP reduction and hearing loss. Most of Cx26 and Cx30 in the cochlear lateral wall co-expressed in the same gap junctional plaques. Moreover, sole Cx26+/- or Cx30+/- heterozygous mice had no hearing loss. These data further suggest that digenic Cx26 and Cx30 mutations may impair heterozygous coupling of Cx26 and Cx30 in the cochlear lateral wall to reduce EP, thereby leading to hearing loss.
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Affiliation(s)
- Ling Mei
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA; Department of Otolaryngology, Xinhua Hospital, Shanghai Jiao Tong University Medical School, Shanghai 200092, PR China
| | - Jin Chen
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA; Department of Otolaryngology, Tongji Hospital, Huazhong University of Science & Technology, 1095 Jiefang Avenue, Wuhan 430030, PR China
| | - Liang Zong
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA; Department of Otolaryngology, Chinese PLA General Hospital, 28 Fuxing Road, Beijing 100853, PR China
| | - Yan Zhu
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
| | - Chun Liang
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
| | - Raleigh O Jones
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA
| | - Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA.
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16
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Zhao HB. Hypothesis of K +-Recycling Defect Is Not a Primary Deafness Mechanism for Cx26 ( GJB2) Deficiency. Front Mol Neurosci 2017; 10:162. [PMID: 28603488 PMCID: PMC5445178 DOI: 10.3389/fnmol.2017.00162] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 05/10/2017] [Indexed: 12/20/2022] Open
Abstract
K+-recycling defect is a long-standing hypothesis for deafness mechanism of Connexin26 (Cx26, GJB2) mutations, which cause the most common hereditary deafness and are responsible for >50% of nonsyndromic hearing loss. The hypothesis states that Cx26 deficiency may disrupt inner ear gap junctions and compromise sinking and recycling of expelled K+ ions after hair cell excitation, causing accumulation of K+-ions in the extracellular space around hair cells producing K+-toxicity, which eventually induces hair cell degeneration and hearing loss. However, this hypothesis has never been directly evidenced, even though it has been widely referred to. Recently, more and more experiments demonstrate that this hypothesis may not be a deafness mechanism underlying Cx26 deficiency. In this review article, we summarized recent advances on the K+-recycling and mechanisms underlying Cx26 deficiency induced hearing loss. The mechanisms underlying K+-sinking, which is the first step for K+-recycling in the cochlea, and Cx26 deficiency induced cochlear developmental disorders, which are responsible for Cx26 deficiency induced congenital deafness and associated with disruption of permeability of inner ear gap junctional channels to miRNAs, are also summarized and discussed.
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Affiliation(s)
- Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical CenterLexington, KY, United States
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17
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Zong L, Chen J, Zhu Y, Zhao HB. Progressive age-dependence and frequency difference in the effect of gap junctions on active cochlear amplification and hearing. Biochem Biophys Res Commun 2017; 489:223-227. [PMID: 28552523 DOI: 10.1016/j.bbrc.2017.05.137] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Accepted: 05/24/2017] [Indexed: 10/19/2022]
Abstract
Mutations of Connexin 26 (Cx26, GJB2), which is a predominant gap junction isoform in the cochlea, can induce high incidence of nonsyndromic hearing loss. We previously found that targeted-deletion of Cx26 in supporting Deiters cells and outer pillar cells in the cochlea can influence outer hair cell (OHC) electromotility and reduce active cochlear amplification leading to hearing loss, even though there are no gap junction connexin expressions in the auditory sensory hair cells. Here, we further report that hearing loss and the reduction of active amplification in the Cx26 targeted-deletion mice are progressive and different at high and low frequency regions, first occurring in the high frequency region and then progressively extending to the middle and low frequency regions with mouse age increased. The speed of hearing loss extending was fast in the basal high frequency region and slow in the apical low frequency region, showing a logarithmic function with mouse age. Before postnatal day 25, there were no significant hearing loss and the reduction of active cochlear amplification in the low frequency region. Hearing loss and the reduction of active cochlear amplification also had frequency difference, severe and large in the high frequency regions. These new data indicate that the effect of gap junction on active cochlear amplification is progressive, but, consistent with our previous report, exists in both high and low frequency regions in adulthood. These new data also suggest that cochlear gap junctions may have an important role in age-related hearing loss.
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Affiliation(s)
- Liang Zong
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States; Department of Otolaryngology, Chinese PLA General Hospital, 28 Fuxing Road, Beijing, 100853, PR China
| | - Jin Chen
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States; Department of Otolaryngology, Tongji Hospital, Huazhong University of Science & Technology, 1095 Jiefang Avenue, Wuhan 430030, PR China
| | - Yan Zhu
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - Hong-Bo Zhao
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States.
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18
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Wingard JC, Zhao HB. Cellular and Deafness Mechanisms Underlying Connexin Mutation-Induced Hearing Loss - A Common Hereditary Deafness. Front Cell Neurosci 2015; 9:202. [PMID: 26074771 PMCID: PMC4448512 DOI: 10.3389/fncel.2015.00202] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2015] [Accepted: 05/11/2015] [Indexed: 11/30/2022] Open
Abstract
Hearing loss due to mutations in the connexin gene family, which encodes gap junctional proteins, is a common form of hereditary deafness. In particular, connexin 26 (Cx26, GJB2) mutations are responsible for ~50% of non-syndromic hearing loss, which is the highest incidence of genetic disease. In the clinic, Cx26 mutations cause various auditory phenotypes ranging from profound congenital deafness at birth to mild, progressive hearing loss in late childhood. Recent experiments demonstrate that congenital deafness mainly results from cochlear developmental disorders rather than hair cell degeneration and endocochlear potential reduction, while late-onset hearing loss results from reduction of active cochlear amplification, even though cochlear hair cells have no connexin expression. However, there is no apparent, demonstrable relationship between specific changes in connexin (channel) functions and the phenotypes of mutation-induced hearing loss. Moreover, new experiments further demonstrate that the hypothesized K+-recycling disruption is not a principal deafness mechanism for connexin deficiency induced hearing loss. Cx30 (GJB6), Cx29 (GJC3), Cx31 (GJB3), and Cx43 (GJA1) mutations can also cause hearing loss with distinct pathological changes in the cochlea. These new studies provide invaluable information about deafness mechanisms underlying connexin mutation-induced hearing loss and also provide important information for developing new protective and therapeutic strategies for this common deafness. However, the detailed cellular mechanisms underlying these pathological changes remain unclear. Also, little is known about specific mutation-induced pathological changes in vivo and little information is available for humans. Such further studies are urgently required.
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Affiliation(s)
- Jeffrey C Wingard
- Department of Otolaryngology, University of Kentucky Medical Center , Lexington, KY , USA
| | - Hong-Bo Zhao
- Department of Otolaryngology, University of Kentucky Medical Center , Lexington, KY , USA
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19
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Wei K, Glaser JI, Deng L, Thompson CK, Stevenson IH, Wang Q, Hornby TG, Heckman CJ, Kording KP. Serotonin affects movement gain control in the spinal cord. J Neurosci 2014; 34:12690-700. [PMID: 25232107 DOI: 10.1523/JNEUROSCI.1855-14.2014] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
A fundamental challenge for the nervous system is to encode signals spanning many orders of magnitude with neurons of limited bandwidth. To meet this challenge, perceptual systems use gain control. However, whether the motor system uses an analogous mechanism is essentially unknown. Neuromodulators, such as serotonin, are prime candidates for gain control signals during force production. Serotonergic neurons project diffusely to motor pools, and, therefore, force production by one muscle should change the gain of others. Here we present behavioral and pharmaceutical evidence that serotonin modulates the input-output gain of motoneurons in humans. By selectively changing the efficacy of serotonin with drugs, we systematically modulated the amplitude of spinal reflexes. More importantly, force production in different limbs interacts systematically, as predicted by a spinal gain control mechanism. Psychophysics and pharmacology suggest that the motor system adopts gain control mechanisms, and serotonin is a primary driver for their implementation in force production.
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20
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Zhu Y, Chen J, Liang C, Zong L, Chen J, Jones RO, Zhao HB. Connexin26 (GJB2) deficiency reduces active cochlear amplification leading to late-onset hearing loss. Neuroscience 2014; 284:719-729. [PMID: 25451287 DOI: 10.1016/j.neuroscience.2014.10.061] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2014] [Revised: 10/21/2014] [Accepted: 10/26/2014] [Indexed: 12/21/2022]
Abstract
Connexin26 (Cx26, GJB2) mutations account for >50% of nonsyndromic hearing loss. The deafness is not always congenital. A large group of these patients (∼30%) demonstrate a late-onset hearing loss, starting in childhood. They have normal hearing early in life and are therefore good candidates for applying protective and therapeutic interventions. However, the underlying deafness mechanism is unclear. In this study, we used a time-controlled, inducible gene knockout technique to knockout Cx26 expression in the cochlea after birth. We found that deletion of Cx26 after postnatal day 5 (P5) in mice could lead to late-onset hearing loss. Similar to clinical observations, the mice demonstrated progressive, mild to moderate hearing loss. The hearing loss initiated at high frequencies and then extended to the middle- and low-frequency range. The cochlea showed normal development and had no apparent hair cell loss. However, distortion product otoacoustic emission (DPOAE) was reduced. The reduction was also progressive and large at high-frequencies. Consistent with DPOAE reduction, we found that outer hair cell electromotility-associated nonlinear capacitance was shifted to the right and the slope of voltage dependence was reduced. The endocochlear potential was reduced in Cx26 conditional knockout (cKO) mice but the reduction was not associated with progressive hearing loss. These data suggest that Cx26 deficiency may impair active cochlear amplification leading to late-onset hearing loss. Our study also helps develop newer protective and therapeutic interventions to this common nonsyndromic hearing loss.
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Affiliation(s)
- Y Zhu
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - J Chen
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - C Liang
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - L Zong
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - J Chen
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - R O Jones
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States
| | - H-B Zhao
- Dept. of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, United States.
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21
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Tateno T, Nishikawa J, Tsuchioka N, Shintaku H, Kawano S. A hardware model of the auditory periphery to transduce acoustic signals into neural activity. Front Neuroeng 2013; 6:12. [PMID: 24324432 PMCID: PMC3840400 DOI: 10.3389/fneng.2013.00012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 10/28/2013] [Indexed: 11/13/2022]
Abstract
To improve the performance of cochlear implants, we have integrated a microdevice into a model of the auditory periphery with the goal of creating a microprocessor. We constructed an artificial peripheral auditory system using a hybrid model in which polyvinylidene difluoride was used as a piezoelectric sensor to convert mechanical stimuli into electric signals. To produce frequency selectivity, the slit on a stainless steel base plate was designed such that the local resonance frequency of the membrane over the slit reflected the transfer function. In the acoustic sensor, electric signals were generated based on the piezoelectric effect from local stress in the membrane. The electrodes on the resonating plate produced relatively large electric output signals. The signals were fed into a computer model that mimicked some functions of inner hair cells, inner hair cell–auditory nerve synapses, and auditory nerve fibers. In general, the responses of the model to pure-tone burst and complex stimuli accurately represented the discharge rates of high-spontaneous-rate auditory nerve fibers across a range of frequencies greater than 1 kHz and middle to high sound pressure levels. Thus, the model provides a tool to understand information processing in the peripheral auditory system and a basic design for connecting artificial acoustic sensors to the peripheral auditory nervous system. Finally, we discuss the need for stimulus control with an appropriate model of the auditory periphery based on auditory brainstem responses that were electrically evoked by different temporal pulse patterns with the same pulse number.
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Affiliation(s)
- Takashi Tateno
- Special Research Promotion Group, Graduate School of Frontier Biosciences, Osaka University Osaka, Japan ; Biomedical Systems Engineering, Bioengineering and Bioinformatics, Graduate School of Information Science and Technology, Hokkaido University Sapporo, Japan
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22
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Zhu Y, Liang C, Chen J, Zong L, Chen GD, Zhao HB. Active cochlear amplification is dependent on supporting cell gap junctions. Nat Commun 2013; 4:1786. [PMID: 23653198 DOI: 10.1038/ncomms2806] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Accepted: 03/25/2013] [Indexed: 01/01/2023] Open
Abstract
Mammalian hearing relies upon active cochlear mechanics, which arises from outer hair
cell (OHC) electromotility and hair bundle movement, to amplify acoustic stimulations increasing
hearing sensitivity and frequency selectivity. Here we describe the novel finding that gap junctions
between cochlear supporting cells also have a critical role in active cochlear amplification
in vivo. We find that targeted-deletion of connexin26 (Cx26) in Deiters cells (DCs)
and outer pillar cells (OPCs), which constrain OHCs standing on the basilar membrane, causes a
leftward shift in OHC electromotility towards hyperpolarization, and reduces active cochlear
amplification with hearing loss. Coincident with large reduction in distortion product otoacoustic
emission (DPOAE) and severe hearing loss at high frequencies, the shift is larger in shorter OHCs.
Our study demonstrates that active cochlear amplification in vivo is dependent on
supporting cell gap junctions. These new findings also show that Cx26 deficiency can reduce active
cochlear amplification to induce hearing loss.
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23
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Liang C, Zhu Y, Zong L, Lu GJ, Zhao HB. Cell degeneration is not a primary causer for Connexin26 (GJB2) deficiency associated hearing loss. Neurosci Lett 2012; 528:36-41. [PMID: 22975134 DOI: 10.1016/j.neulet.2012.08.085] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 08/06/2012] [Accepted: 08/14/2012] [Indexed: 11/16/2022]
Abstract
Connexin26 (Cx26, GJB2) mutations can induce congenital deafness and are responsible for ∼50% of nonsyndromic hearing loss in children. Mouse models show that Cx26 deficiency induces cochlear development disorder, hair cell loss, and spiral ganglion (SG) neuron degeneration. Hair cell loss and cell degeneration have been considered as a primary causer responsible for Cx26 deficiency associated hearing loss. In this study, by coincidental examination of cochlear postnatal development with recording of auditory brainstem response (ABR) and hair cell function, we found that occurrence of hearing loss in Cx26 knockout (KO) mice was ahead of hair cell loss and cochlear cell degeneration. ABR was absent at the whole-frequency range (8-40 kHz) after birth. However, cochlear cells including SG neurons had no significant degeneration throughout postnatal development. Severe cochlear hair cell loss and SG neuron degeneration were only visible in middle and basal turns, i.e., in middle and high frequency regions, in the adult Cx26 KO mouse cochlea. Functional tests show that hair cells in Cx26 KO mice functioned normally; outer hair cells retained electromotility. These data suggest that cell degeneration is not a primary causer of Cx26 deficiency associated hearing loss. Some mechanisms other than cell degeneration, such as cochlear development disorders, may play an essential role in this common hereditary deafness.
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Affiliation(s)
- Chun Liang
- Department of Otolaryngology, University of Kentucky Medical School, Lexington, KY 40536, USA
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24
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Zhu Y, Zhao HB. ATP activates P2X receptors to mediate gap junctional coupling in the cochlea. Biochem Biophys Res Commun 2012; 426:528-32. [PMID: 22982314 DOI: 10.1016/j.bbrc.2012.08.119] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 08/24/2012] [Indexed: 10/27/2022]
Abstract
ATP is an important extracellular signaling molecule and can activate both ionotropic (P2X) and metabotropic purinergic (P2Y) receptors to influence cellular function in many aspects. Gap junction is an intercellular channel and plays a critical role in hearing. Here, we report that stimulation of ATP reduced gap junctional coupling between cochlear supporting cells. This uncoupling effect could be evoked by nanomolar physiological levels of ATP. A P2X receptor agonist benzoylbenzoyl-ATP (BzATP) but not a P2Y receptor agonist UTP stimulated this uncoupling effect. Application of P2X receptor antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 50μM) or oxidized ATP (oATP, 0.1mM) eliminated this uncoupling effect. We further found that ATP activated P2X receptors in the cochlear supporting cells allowing Ca(2+) influxing, thereby increasing intracellular Ca(2+) concentration to mediate gap junctions. These data suggest that ATP can mediate cochlear gap junctions at the physiological level by the activation of P2X receptors rather than P2Y receptors. This P2X receptor-mediated purinergic control on the cochlear gap junctions may play an important role in the regulation of K(+)-recycling for ionic homeostasis in the cochlea and the reduction of hearing sensitivity under noise stress for protection.
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Affiliation(s)
- Yan Zhu
- Dept. of Otolaryngology, University of Kentucky Medical Center, Lexington, KY 40536 0293, United States
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25
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Liu CC, Gao SS, Yuan T, Steele C, Puria S, Oghalai JS. Biophysical mechanisms underlying outer hair cell loss associated with a shortened tectorial membrane. J Assoc Res Otolaryngol 2011; 12:577-94. [PMID: 21567249 PMCID: PMC3173552 DOI: 10.1007/s10162-011-0269-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2011] [Accepted: 04/17/2011] [Indexed: 01/09/2023] Open
Abstract
The tectorial membrane (TM) connects to the stereociliary bundles of outer hair cells (OHCs). Humans with an autosomal dominant C1509G mutation in alpha-tectorin, a protein constituent of the TM, are born with a partial hearing loss that worsens over time. The Tecta(C1509/+) transgenic mouse with the same point mutation has partial hearing loss secondary to a shortened TM that only contacts the first row of OHCs. As well, Tecta(C1509G/+) mice have increased expression of the OHC electromotility protein, prestin. We sought to determine whether these changes impact OHC survival. Distortion product otoacoustic emission thresholds in a quiet environment did not change to 6 months of age. However, noise exposure produced acute threshold shifts that fully recovered in Tecta (+/+) mice but only partially recovered in Tecta(C1509G/+) mice. While Tecta(+/+) mice lost OHCs primarily at the base and within all three rows, Tecta(C1509G/+) mice lost most of their OHCs in a more apical region of the cochlea and nearly completely within the first row. In order to estimate the impact of a shorter TM on the forces faced by the stereocilia within the first OHC row, both the wild type and the heterozygous conditions were simulated in a computational model. These analyses predicted that the shear force on the stereocilia is ~50% higher in the heterozygous condition. We then measured electrically induced movements of the reticular lamina in situ and found that while they decreased to the noise floor in prestin null mice, they were increased by 4.58 dB in Tecta(C1509G/+) mice compared to Tecta(+/+) mice. The increased movements were associated with a fourfold increase in OHC death as measured by vital dye staining. Together, these findings indicate that uncoupling the TM from some OHCs leads to partial hearing loss and places the remaining coupled OHCs at higher risk. Both the mechanics of the malformed TM and the increased prestin-related movements of the organ of Corti contribute to this higher risk profile.
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Affiliation(s)
- Christopher C. Liu
- The Bobby R. Alford Department of Otolaryngology–Head and Neck Surgery, Baylor College of Medicine, Houston, TX 77030 USA
| | - Simon S. Gao
- Department of Bioengineering, Rice University, Houston, TX 77005 USA
| | - Tao Yuan
- The Bobby R. Alford Department of Otolaryngology–Head and Neck Surgery, Baylor College of Medicine, Houston, TX 77030 USA
| | - Charles Steele
- Department of Mechanical Engineering, Stanford University, Stanford, CA 94304-5739 USA
| | - Sunil Puria
- Department of Mechanical Engineering, Stanford University, Stanford, CA 94304-5739 USA
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, 801 Welch Road, Stanford, CA 94305-5739 USA
| | - John S. Oghalai
- Department of Bioengineering, Rice University, Houston, TX 77005 USA
- Department of Otolaryngology–Head and Neck Surgery, Stanford University, 801 Welch Road, Stanford, CA 94305-5739 USA
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26
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Wang J, Tymczyszyn N, Yu Z, Yin S, Bance M, Robertson GS. Overexpression of X-linked inhibitor of apoptosis protein protects against noise-induced hearing loss in mice. Gene Ther 2011; 18:560-8. [PMID: 21228883 DOI: 10.1038/gt.2010.172] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Apoptosis is responsible for cochlear cell death induced by noise. Here, we show that transgenic (TG) mice that overexpress X-linked inhibitor of apoptosis protein (XIAP) under control of the ubiquitin promoter display reduced hearing loss and cochlear damage induced by acoustic overstimulation (125 dB sound pressure level, 6 h) compared with wild-type (WT) littermates. Hearing status was evaluated using the auditory brainstem response (ABR), whereas cochlear damage was assessed by counts of surviving hair cells (HCs) and spiral ganglion neurons (SGNs) as well as their fibers to HCs. Significantly smaller threshold shifts were found for TG mice than WT littermates. Correspondingly, the TG mice also showed a reduced loss of HCs, SGNs and their fibers to HCs. HC loss was limited to the basal end of the cochlea that detects high frequency sound. In contrast, the ABRs demonstrated a loss of hearing sensitivity across the entire frequency range tested (2-32 kHz) indicating that the hearing loss could not be fully attributed to HC loss alone. The TG mice displayed superior hearing sensitivity over this whole range, suggesting that XIAP overexpression reduces noise-induced hearing loss not only by protecting HCs but also other components of the cochlea.
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Affiliation(s)
- J Wang
- School of Human Communication Disorder, Dalhousie University, Halifax, Nova Scotia, Canada.
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27
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Ashmore J, Avan P, Brownell WE, Dallos P, Dierkes K, Fettiplace R, Grosh K, Hackney CM, Hudspeth AJ, Jülicher F, Lindner B, Martin P, Meaud J, Petit C, Santos-Sacchi J, Sacchi JR, Canlon B. The remarkable cochlear amplifier. Hear Res 2010; 266:1-17. [PMID: 20541061 DOI: 10.1016/j.heares.2010.05.001] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Accepted: 05/06/2010] [Indexed: 11/26/2022]
Abstract
This composite article is intended to give the experts in the field of cochlear mechanics an opportunity to voice their personal opinion on the one mechanism they believe dominates cochlear amplification in mammals. A collection of these ideas are presented here for the auditory community and others interested in the cochlear amplifier. Each expert has given their own personal view on the topic and at the end of their commentary they have suggested several experiments that would be required for the decisive mechanism underlying the cochlear amplifier. These experiments are presently lacking but if successfully performed would have an enormous impact on our understanding of the cochlear amplifier.
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28
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Abstract
Outer hair cell (OHC) or prestin-based electromotility is an active cochlear amplifier in the mammalian inner ear that can increase hearing sensitivity and frequency selectivity. In situ, Deiters supporting cells are well-coupled by gap junctions and constrain OHCs standing on the basilar membrane. Here, we report that both electrical and mechanical stimulations in Deiters cells (DCs) can modulate OHC electromotility. There was no direct electrical conductance between the DCs and the OHCs. However, depolarization in DCs reduced OHC electromotility associated nonlinear capacitance (NLC) and distortion products. Increase in the turgor pressure of DCs also shifted OHC NLC to the negative voltage direction. Destruction of the cytoskeleton in DCs or dissociation of the mechanical-coupling between DCs and OHCs abolished these effects, indicating the modulation through the cytoskeleton activation and DC-OHC mechanical coupling rather than via electric field potentials. We also found that changes in gap junctional coupling between DCs induced large membrane potential and current changes in the DCs and shifted OHC NLC. Uncoupling of gap junctions between DCs shifted NLC to the negative direction. These data indicate that DCs not only provide a physical scaffold to support OHCs but also can directly modulate OHC electromotility through the DC-OHC mechanical coupling. Our findings reveal a new mechanism of cochlear supporting cells and gap junctional coupling to modulate OHC electromotility and eventually hearing sensitivity in the inner ear.
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Affiliation(s)
- Ning Yu
- Department of Surgery – Otolaryngology, University of Kentucky Medical Center, Lexington, Kentucky, United States of America
| | - Hong-Bo Zhao
- Department of Surgery – Otolaryngology, University of Kentucky Medical Center, Lexington, Kentucky, United States of America
- * E-mail:
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29
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Rabbitt RD, Clifford S, Breneman KD, Farrell B, Brownell WE. Power efficiency of outer hair cell somatic electromotility. PLoS Comput Biol 2009; 5:e1000444. [PMID: 19629162 PMCID: PMC2705677 DOI: 10.1371/journal.pcbi.1000444] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2009] [Accepted: 06/23/2009] [Indexed: 11/18/2022] Open
Abstract
Cochlear outer hair cells (OHCs) are fast biological motors that serve to enhance the vibration of the organ of Corti and increase the sensitivity of the inner ear to sound. Exactly how OHCs produce useful mechanical power at auditory frequencies, given their intrinsic biophysical properties, has been a subject of considerable debate. To address this we formulated a mathematical model of the OHC based on first principles and analyzed the power conversion efficiency in the frequency domain. The model includes a mixture-composite constitutive model of the active lateral wall and spatially distributed electro-mechanical fields. The analysis predicts that: 1) the peak power efficiency is likely to be tuned to a specific frequency, dependent upon OHC length, and this tuning may contribute to the place principle and frequency selectivity in the cochlea; 2) the OHC power output can be detuned and attenuated by increasing the basal conductance of the cell, a parameter likely controlled by the brain via the efferent system; and 3) power output efficiency is limited by mechanical properties of the load, thus suggesting that impedance of the organ of Corti may be matched regionally to the OHC. The high power efficiency, tuning, and efferent control of outer hair cells are the direct result of biophysical properties of the cells, thus providing the physical basis for the remarkable sensitivity and selectivity of hearing.
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Affiliation(s)
- Richard D. Rabbitt
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America
- Marine Biological Laboratory, Woods Hole, Massachusetts, United States of America
| | - Sarah Clifford
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America
| | - Kathryn D. Breneman
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America
| | - Brenda Farrell
- Department of Otolaryngology, Head and Neck Surgery, Baylor College of Medicine, Houston, Texas, United States of America
| | - William E. Brownell
- Department of Otolaryngology, Head and Neck Surgery, Baylor College of Medicine, Houston, Texas, United States of America
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30
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Abstract
The gap junction in vertebrates is encoded by the connexin gene family. Recently, a new gene family termed pannexin (Panx) has been identified in vertebrates and found to encode gap junctional proteins as well. To date, three pannexin isoforms (Panx1, 2, and 3) have been cloned from mouse and human genomes. In this study, expression of pannexins in the mouse and rat cochlea was investigated. Polymerase chain reaction and Western blot analysis showed that all three pannexin isoforms were expressed in the cochlea. Immunofluorescent staining showed that Panx1 expression was extensive. In the organ of Corti, Panx1 labeling was found in supporting cells, including pillar cells, Hensen cells, Claudius cells, and Boettcher cells. Both surface plaque-like punctate labeling and diffuse-cytoplasmic labeling were visible. However, the labeling was weak and rare in Deiters cells. No labeling was found in the hair cells. Intense labeling for Panx1 was also observed in the interdental cells in the spiral limbus, the inner and outer sulcus cells, and the type II fibrocytes in the spiral prominence and central region in the cochlear lateral wall. In addition, Panx1 labeling was detectable in Reissner's membrane and strial blood vessel cells. Panx2 labeling was restricted to the basal cells in the stria vascularis and was also detectable in the spiral ganglion neurons. However, no overlapping labeling for Panx1 and Panx2 was observed. Finally, Panx3 labeling was exclusively observed in the cochlear bone. Thus, Panx1, 2, and 3 are abundantly expressed in the mammalian cochlea and demonstrate distinct cellular distributions. Like connexins, they may play an important role in hearing.
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Affiliation(s)
- Xiao-Hui Wang
- Department of Surgery-Otolaryngology, University of Kentucky Medical Center, Lexington, Kentucky 40536, USA
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Yu N, Zhu ML, Johnson B, Liu YP, Jones RO, Zhao HB. Prestin up-regulation in chronic salicylate (aspirin) administration: an implication of functional dependence of prestin expression. Cell Mol Life Sci 2008; 65:2407-18. [PMID: 18560754 DOI: 10.1007/s00018-008-8195-y] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Salicylate (aspirin) can reversibly eliminate outer hair cell (OHC) electromotility to induce hearing loss. Prestin is the OHC electromotility motor protein. Here we report that, consistency with increase in distortion product otoacoustic emission, long-term administration of salicylate can increase prestin expression and OHC electromotility. The prestin expression at the mRNA and protein levels was increased by three- to four-fold. In contrast to the acute inhibition, the OHC electromotility associated charge density was also increased by 18%. This incremental increase was reversible. After cessation of salicylate administration, the prestin expression returned to normal. We also found that long-term administration of salicylate did not alter cyclooxygenase (Cox) II expression but down-regulated NF-kappaB and increased nuclear transcription factors c-fos and egr-1. The data suggest that prestin expression in vivo is dynamically up-regulated to increase OHC electromotility in long-term administration of salicylate via the Cox-II-independent pathways.
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32
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Chen GD, Tanaka C, Henderson D. Relation between outer hair cell loss and hearing loss in rats exposed to styrene. Hear Res 2008; 243:28-34. [PMID: 18586423 DOI: 10.1016/j.heares.2008.05.008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2008] [Revised: 04/24/2008] [Accepted: 05/08/2008] [Indexed: 11/19/2022]
Abstract
The relationship between outer hair cell (OHC) loss and cochlear sensitivity is still unclear, because in many animal models there exist surviving but dysfunctional OHCs and also injured/dead inner hair cells (IHC). Styrene is an ototoxic agent, which targets and destroys OHCs starting from the third row to the second and first rows depending on the exposure level. The remaining cells may be less affected. In this experiment, rats were exposed to styrene by gavage at different doses (200-800 mg/kg/day) for varying periods (5 days/week for 3-12 weeks). An interesting finding was that the cochlear sensitivity was not affected in a few rats with all OHCs in the third row being destroyed by styrene. A further loss of OHCs was usually accompanied with a linear input/output (I/O) function of cochlear compound action potentials (CAP), indicating the loss of cochlear amplification. However, normal CAP amplitudes at the highest stimulation level of 90 dB SPL were often observed when all OHCs were destroyed, indicating normal function of the remaining IHCs. The OHC-loss/hearing-loss relation appeared to be a sigmoid-type function. Initially, styrene-induced OHC losses (<33%) did not result in a significant threshold shift. Then CAP threshold shift increased dramatically with OHC loss from 33% to 66%. Then, CAP threshold changed less with OHC loss. The data suggest a tri-modal relationship between OHC loss and cochlear amplification. That is, under the condition that all surviving OHCs are ideally functioning, the cochlear amplifier is not affected until 33% of OHCs are absent, then the gain of the amplifier decreases proportionally with the OHC loss, and at last the amplifier may fail completely when more than 67% of OHCs are lost.
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Affiliation(s)
- Guang-Di Chen
- Center for Hearing and Deafness, SUNY at Buffalo, Buffalo, NY 14214, USA.
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Yu N, Zhao HB. ATP activates P2x receptors and requires extracellular Ca(++) participation to modify outer hair cell nonlinear capacitance. Pflugers Arch 2008; 457:453-61. [PMID: 18491132 DOI: 10.1007/s00424-008-0522-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2007] [Accepted: 04/18/2008] [Indexed: 01/22/2023]
Abstract
Intracochlear ATP is an important mediator in regulating hearing function. ATP can activate ionotropic purinergic (P2x) and metabotropic purinergic (P2y) receptors to influence cell functions. In this paper, we report that ATP can activate P2x receptors directly to modify outer hair cell (OHC) electromotility, which is an active cochlear amplifier determining hearing sensitivity and frequency selectivity in mammals. We found that ATP, but not UTP, a P2y receptor agonist, reduced the OHC electromotility-associated nonlinear capacitance (NLC) and shifted its voltage dependence to the right (depolarizing) direction. Blockage of the activation of P2x receptors by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), suramin, and 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS) could block the ATP effect. This modification also required extracellular Ca(++) participation. Removal of extracellular Ca(++) abolished the ATP effect. However, chelation of intracellular Ca(++) concentration by a fast calcium-chelating reagent 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA, 10 mM) did not affect the effect of ATP on NLC. The effect is also independent of K(+) ions. Substitution of Cs(+) for intracellular or extracellular K(+) did not affect the ATP effect. Our findings indicate that ATP activates P2x receptors instead of P2y receptors to modify OHC electromotility. Extracellular Ca(++) is required for this modification.
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34
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Schumacher KR, Popel AS, Anvari B, Brownell WE, Spector AA. Modeling the Mechanics of Tethers Pulled From the Cochlear Outer Hair Cell Membrane. J Biomech Eng 2008; 130:031007. [DOI: 10.1115/1.2907758] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cell membrane tethers are formed naturally (e.g., in leukocyte rolling) and experimentally to probe membrane properties. In cochlear outer hair cells, the plasma membrane is part of the trilayer lateral wall, where the membrane is attached to the cytoskeleton by a system of radial pillars. The mechanics of these cells is important to the sound amplification and frequency selectivity of the ear. We present a modeling study to simulate the membrane deflection, bending, and interaction with the cytoskeleton in the outer hair cell tether pulling experiment. In our analysis, three regions of the membrane are considered: the body of a cylindrical tether, the area where the membrane is attached and interacts with the cytoskeleton, and the transition region between the two. By using a computational method, we found the shape of the membrane in all three regions over a range of tether lengths and forces observed in experiments. We also analyze the effects of biophysical properties of the membrane, including the bending modulus and the forces of the membrane adhesion to the cytoskeleton. The model’s results provide a better understanding of the mechanics of tethers pulled from cell membranes.
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Affiliation(s)
| | - Aleksander S. Popel
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205
| | - Bahman Anvari
- Department of Bioengineering, University of California-Riverside, Riverside, CA 92521
| | - William E. Brownell
- Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, TX 77030
| | - Alexander A. Spector
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205
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35
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Abstract
Normal hearing depends on sound amplification within the mammalian cochlea. The amplification, without which the auditory system is effectively deaf, can be traced to the correct functioning of a group of motile sensory hair cells, the outer hair cells of the cochlea. Acting like motor cells, outer hair cells produce forces that are driven by graded changes in membrane potential. The forces depend on the presence of a motor protein in the lateral membrane of the cells. This protein, known as prestin, is a member of a transporter superfamily SLC26. The functional and structural properties of prestin are described in this review. Whether outer hair cell motility might account for sound amplification at all frequencies is also a critical question and is reviewed here.
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Affiliation(s)
- Jonathan Ashmore
- Department of Physiology and UCL Ear Institute, University College London, London, United Kingdom.
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36
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Abstract
Outer hair cells (OHCs) play an important role in cochlear amplification via their length changes (electromotility). A noise-induced cochlear amplification loss leading to a permanent threshold shift (PTS) was observed without a significant hair cell loss in rats [Chen, G.D., Liu, Y., 2005. Mechanisms of noise-induced hearing loss potentiation by hypoxia. Hear. Res. 200, 1-9.]. Since motor proteins are inserted in the OHC lateral membrane, any change in the OHC plasma membrane may result in a loss of OHC electromotility, leading to a loss of cochlear amplification. In this study, the lateral diffusion in the OHC plasma membrane was determined in vitro in guinea pigs by fluorescent recovery after photobleaching (FRAP) after an in vivo noise exposure. The lateral diffusion in the OHC plasma membrane demonstrated a length-dependence, which increased as OHC length increased. A reduction in the lateral diffusion was observed in those OHCs with lengths of 50-70 microm after exposure to an 8-kHz octave band noise at 110 dB SPL for 3h. This membrane fluidity change was associated with the selective PTS at frequencies around 8 kHz. The reduction of the lateral diffusion in the OHC lateral wall indicated that noise could impair the micromechanics of the OHC lateral wall and might consequently impair OHC electromotility to induce threshold shift.
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Affiliation(s)
- Guang-Di Chen
- Center for Hearing and Deafness, 137 Cary Hall, 3435 Main Street, SUNY at Buffalo, Buffalo, NY 14214, USA.
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37
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Abstract
Connexin26 (Cx26) and Cx30 are predominant isoforms of gap junction channels in the cochlea and play a critical role in hearing. In this study, the cellular distributions of Cx26 and Cx30 in the cochlear sensory epithelium of guinea pigs were examined by immunofluorescent staining and confocal microscopy in whole mounts of the cochlear sensory epithelium and dissociated cell preparations. The expression of Cx26 and Cx30 demonstrated a longitudinal gradient distribution in the epithelium and was reduced threefold from the cochlear apex to base. The reduction was more pronounced in the Deiters cells and pillar cells than in the Hensen cells. Cx26 was expressed in all types of supporting cells, but little Cx30 labeling was seen in the Hensen cells. Cx26 expression in the Hensen cells was concentrated mainly in the second and third rows, forming a distinct band along the sensory epithelium at its outer region. In the dissociated Deiters cells and pillar cells, Cx30 showed dense labeling at the cell bodies and processes in the reticular lamina. Cx26 labeling largely overlapped that of Cx30 in these regions. Cx26 and Cx30 were also coexpressed in the gap junctional plaques between Claudius cells. Neither Cx26 nor Cx30 labeling was seen in the hair cells and spiral ganglion neurons. These observations demonstrate that Cx26 and Cx30 have a longitudinal gradient distribution and distinct cellular expression in the auditory sensory epithelium. This further supports our previous reports that Cx26 and Cx30 can solely and concertedly perform different functions in the cochlea.
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Affiliation(s)
- Hong-Bo Zhao
- Department of Surgery-Otolaryngology, University of Kentucky Medical Center, Lexington, Kentucky 40536, USA.
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38
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Kennedy HJ, Evans MG, Crawford AC, Fettiplace R. Depolarization of cochlear outer hair cells evokes active hair bundle motion by two mechanisms. J Neurosci 2006; 26:2757-66. [PMID: 16525055 PMCID: PMC6675159 DOI: 10.1523/jneurosci.3808-05.2006] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
There is current debate about the origin of mechanical amplification whereby outer hair cells generate force to augment the sensitivity and frequency selectivity of the mammalian cochlea. To distinguish contributions to force production from the mechanotransducer (MET) channels and somatic motility, we have measured hair bundle motion during depolarization of individual outer hair cells in isolated rat cochleas. Depolarization evoked rapid positive bundle deflections that were reduced by perfusion with the MET channel blocker dihydrostreptomycin, with no effect on the nonlinear capacitance that is a manifestation of prestin-driven somatic motility. However, the movements were also diminished by Na salicylate and depended on the intracellular anion, properties implying involvement of the prestin motor. Furthermore, depolarization of one outer hair cell caused motion of neighboring hair bundles, indicating overall motion of the reticular lamina. Depolarization of solitary outer hair cells caused cell-length changes whose voltage-activation range depended on the intracellular anion but were insensitive to dihydrostreptomycin. These results imply that both the MET channels and the somatic motor participate in hair bundle motion evoked by depolarization. It is conceivable that the two processes can interact, a signal from the MET channels being capable of modulating the activity of the prestin motor.
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MESH Headings
- Age Factors
- Animals
- Animals, Newborn
- Anions/metabolism
- Calcium/pharmacology
- Cell Movement/drug effects
- Cell Movement/physiology
- Cell Movement/radiation effects
- Cochlea/cytology
- Diagnostic Imaging/methods
- Dihydrostreptomycin Sulfate/pharmacology
- Dose-Response Relationship, Radiation
- Hair Cells, Auditory, Outer/cytology
- Hair Cells, Auditory, Outer/drug effects
- Hair Cells, Auditory, Outer/physiology
- Hair Cells, Auditory, Outer/radiation effects
- Intracellular Space/metabolism
- Mechanotransduction, Cellular/physiology
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Membrane Potentials/radiation effects
- Patch-Clamp Techniques/methods
- Physical Stimulation/methods
- Rats
- Rats, Sprague-Dawley
- Sodium Salicylate/pharmacology
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39
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Abstract
Gap junctions play a critical role in hearing and mutations in connexin genes cause a high incidence of human deafness. Pathogenesis mainly occurs in the cochlea, where gap junctions form extensive networks between non-sensory cells that can be divided into two independent gap junction systems, the epithelial cell gap junction system and the connective tissue cell gap junction system. At least four different connexins have been reported to be present in the mammalian inner ear, and gap junctions are thought to provide a route for recycling potassium ions that pass through the sensory cells during the mechanosensory transduction process back to the endolymph. Here we review the cochlear gap junction networks and their hypothesized role in potassium ion recycling mechanism, pharmacological and physiological gating of cochlear connexins, animal models harboring connexin mutations and functional studies of mutant channels that cause human deafness. These studies elucidate gap junction functions in the cochlea and also provide insight for understanding the pathogenesis of this common hereditary deafness induced by connexin mutations.
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Affiliation(s)
- H.-B. Zhao
- Department of Surgery-Otolaryngology, University of Kentucky Medical Center, Lexington, KY, USA
| | - T. Kikuchi
- Department of Otolaryngology-Head and Neck Surgery, Tohoku University Graduate School of Medicine, Sendai, Japan
| | - A. Ngezahayo
- Institute of Biophysics, University of Hannover, Hannover, Germany
| | - T.W. White
- Department of Physiology and Biophysics, State University of New York, Stony Brook, NY, USA
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40
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Abstract
Connexin gap junctions play an important role in hearing function, but the mechanism by which this contribution occurs is unknown. Connexins in the cochlea are expressed only in supporting cells; no connexin expression occurs in auditory sensory hair cells. A gap junctional channel is formed by two hemichannels. Here, we show that connexin hemichannels in the cochlea can release ATP at levels that account for the submicromolar concentrations measured in the cochlear fluids in vivo. The release could be increased 3- to 5-fold by a reduction of extracellular Ca2+ or an increase in membrane stress, and blocked by gap junctional blockers. We also demonstrated that extracellular ATP at submicromolar levels apparently affected outer hair cell (OHC) electromotility, which is an active cochlear amplifier determining cochlear sensitivity to sound stimulation in mammals. ATP reduced OHC electromotility and the slope factor of the voltage dependence and shifted the operating point to reduce the active amplifier gain. ATP also reduced the generation of distortion products. Immunofluorescent staining showed that purinergic receptors P2x2 and P2x7 were distributed on the OHC surface. Blockage of P2 receptors eliminated the effect of ATP on the OHC electromotility. The data revealed that there is a hemichannel-mediated, purinergic intercellular signaling pathway between supporting cells and hair cells in the cochlea to control hearing sensitivity. The data also demonstrated a potential source of ATP in the cochlea.
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Affiliation(s)
- Hong-Bo Zhao
- Department of Surgery-Otolaryngology, University of Kentucky Medical Center, Lexington, KY 40536-0293, USA.
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41
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Liao Z, Popel AS, Brownell WE, Spector AA. Effect of voltage-dependent membrane properties on active force generation in cochlear outer hair cell. J Acoust Soc Am 2005; 118:3737-46. [PMID: 16419818 DOI: 10.1121/1.2118387] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
A computational model is proposed to analyze the active force production in an individual outer hair cell (OHC) under high-frequency conditions. The model takes into account important biophysical properties of the cell as well as constraints imposed by the surrounding environment. The biophysical properties include the elastic, piezoelectric, and viscous characteristics of the cell wall. The effect of the environment is associated with the stiffness of the constraint and the drag forces acting on the cell due to the interaction with the external and internal viscous fluids. The study concentrated on a combined effect of the transmembrane potential, frequency, and stiffness of the constraints. The effect of the voltage-dependent stiffness of the cell was particularly investigated and it was found to be twofold. First, it results in higher sensitivity and nonlinearity of the OHC active force production in the physiological range. Second, it determines smaller active forces in the hyperpolarization range. The resonant properties of the active force as functions of voltage and the constraint stiffness were also analyzed. The obtained results can be important for a better understanding of the OHC active force production and the contribution of cell electromotility to the cochlear amplification, sensitivity, and nonlinearity.
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Affiliation(s)
- Zhijie Liao
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21205, USA.
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42
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Abstract
Mammalian hearing owes its remarkable sensitivity and frequency selectivity to a local mechanical feedback process within the cochlea. Cochlear outer hair cells (OHCs) function as the key elements in the feedback loop in which the fast somatic motility of OHCs is thought to be the source of cochlear amplification. An alternative view is that amplification arises from active hair-bundle movement, similar to that seen in nonmammalian hair cells. We measured voltage-evoked hair-bundle motions in the gerbil cochlea to determine if such movements were also present in mammalian OHCs. The OHCs showed bundle movement with peak responses of up to 830 nm. The movement was insensitive to manipulations that would normally block mechanotransduction in the stereocilia, and it was absent in neonatal OHCs and prestin-knockout OHCs. These findings suggest that the bundle movement originated in somatic motility and that somatic motility has a central role in cochlear amplification in mammals.
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Affiliation(s)
- Shuping Jia
- Hair Cell Biophysics Laboratory, Department of Biomedical Sciences, Creighton University School of Medicine, 2500 California Plaza, Omaha, Nebraska 68175, USA
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43
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Abstract
Abstract A gap junction is composed of two hemichannels and possesses a relatively large pore size ( approximately 10-15 A), allowing passage of ions and molecules up to 1 kDa. Here, we report that connexin hemichannels and gap junctions in the guinea pig cochlea had significant charge selectivity among permeating molecules. In coincubation with anionic and cationic fluorescent dyes, hemichannel permeability in isolated cochlear supporting cells showed significant charge selectivity; 31% of cells had only cationic dye influx and 6% of cells had only anionic dye influx. Charge-selective influx contrary to dye size was also found, indicating charge as a dominant determinant in permeability. The cell-cell gap junctional permeability was consistent with hemichannel permeability and also showed strong charge selectivity; the permeation of anionic dyes was slower than that of cationic probes in the cochlear sensory epithelium. With a combination of immunofluorescent staining for connexin26 (Cx26) and Cx30, which are the predominant connexin isoforms in the cochlea, Cx26 was demonstrated to correlate with anionic permeability. The data indicated that cochlear gap junctions have strong charge selectivity in molecular permeability and metabolic communication. Cx26 mutation may induce specific, irreparable impairment in intercellular signalling and energy and nutrient supplies in the cochlea, causing cell degeneration and hearing loss, given that many important cell-signalling and nutrient and energy molecules (e.g. IP3, ATP, cAMP and cGMP) are anions.
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Affiliation(s)
- Hong-Bo Zhao
- Department of Surgery--Otolaryngology, University of Kentucky Medical Center, Lexington, Kentucky, 40536, USA.
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44
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Huang ZW, Luo Y, Wu Z, Tao Z, Jones RO, Zhao HB. Paradoxical Enhancement of Active Cochlear Mechanics in Long-Term Administration of Salicylate. J Neurophysiol 2005; 93:2053-61. [PMID: 15590729 DOI: 10.1152/jn.00959.2004] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Aspirin (salicylate) is a common drug and frequently used long term in the clinic. It has been well documented that salicylate can cause reversible hearing loss and tinnitus and diminish outer hair cell (OHC) electromotility, which is capable of actively boosting the basilar membrane vibration and producing acoustic emission. However, aspirin's ototoxic mechanisms still remain largely unclear. In this experiment, the effects of long-term salicylate administration on cochlear hearing functions were investigated by measuring distortion product otoacoustic emissions (DPOAEs) in awake guinea pigs. A single injection of sodium salicylate (200 mg/kg) could reduce the amplitude of the cubic distortion product of 2 f1- f2 within 2 h. The reduction was significant at 20–50 dB SPL stimulus levels and recovered after 8 h. However, following daily injections of sodium salicylate (200 mg/kg, b.i.d.), the distortion product of 2 f1- f2 progressively increased. After injection for 14 days, the distortion product increased about 2–3.5 dB SPL. The increase rate was about 0.2 dB SPL/day. The DP-I/O function remained nonlinear. The increase was greater at 40–70 dB SPL primary sound intensities and reversible. After cessation of salicylate treatment for 4 wk, the increased distortion product returned to the initial normal levels. The rate of recovery was 0.1 dB SPL/day. In the control animals with saline injection, there was no change in DPOAEs. The data revealed that long-term administration of salicylate could paradoxically enhance active cochlear mechanics. The data also suggested that salicylate-induced tinnitus might be generated at the OHC level.
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Affiliation(s)
- Zhi-Wu Huang
- Department of Otolaryngology, People's Hospital, Faculty of Medicine, Wuhan University, Wuhan, China
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Santos-Sacchi J. Determination of cell capacitance using the exact empirical solution of partial differential Y/partial differential Cm and its phase angle. Biophys J 2005; 87:714-27. [PMID: 15240504 PMCID: PMC1304394 DOI: 10.1529/biophysj.103.033993] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Measures of membrane capacitance offer insight into a variety of cellular processes. Unfortunately, popular methodologies rely on model simplifications that sensitize them to interference from inevitable changes in resistive components of the traditional cell-clamp model. Here I report on a novel method to measure membrane capacitance that disposes of the usual simplifications and assumptions, yet is immune to such interference and works on the millisecond timescale. It is based on the exact empirical determination of the elusive partial derivative, partial differential Y/partial differential C(m), which heretofore had been approximated. Furthermore, I illustrate how this method extends to the vesicle fusion problem by permitting the determination of partial differential Y(v)/partial differential C(v), thereby providing estimates of fusion pore conductance and vesicle capacitance. Finally, I provide simulation examples and physiological examples of how the method can be used to study processes that are routinely interrogated by measures of membrane capacitance.
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Affiliation(s)
- Joseph Santos-Sacchi
- Otolaryngology and Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
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Abstract
Our results demonstrate high-frequency electrical resonances in outer hair cells (OHCs) exhibiting features analogous to classical piezoelectric transducers. The fundamental (first) resonance frequency averaged f(n) approximately 13 kHz (Q approximately 1.7). Higher-order resonances were also observed. To obtain these results, OHCs were positioned in a custom microchamber and subjected to stimulating electric fields along the axis of the cell (1-100 kHz, 4-16 mV/80 microm). Electrodes embedded in the side walls of the microchamber were used in a voltage-divider configuration to estimate the electrical admittance of the top portion of the cell-loaded chamber (containing the electromotile lateral wall) relative to the lower portion (containing the basal plasma membrane). This ratio exhibited resonance-like electrical tuning. Resonance was also detected independently using a secondary 1-MHz radio-frequency interrogation signal applied transversely across the cell diameter. The radio-frequency interrogation revealed changes in the transverse electric impedance modulated by the axial stimulus. Modulation of the transverse electric impedance was particularly pronounced near the resonant frequencies. OHCs used in our study were isolated from the apical region of the guinea pig cochlea, a region that responds exclusively to low-frequency acoustic stimuli. In this sense, electrical resonances we observed in vitro were at least an order of magnitude higher (ultrasonic) than the best physiological frequency of the same OHCs under acoustic stimuli in vivo. These resonance data further support the piezoelectric theory of OHC function, and implicate piezoelectricity in the broad-band electromechanical behavior of OHCs underlying mammalian cochlear function.
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Affiliation(s)
- R D Rabbitt
- Department of Bioengineering, University of Utah, 506 BPRB 20 South, 2030 East Salt Lake City, UT 84112, USA.
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Abstract
Stretching or compressing an outer hair cell alters its membrane potential and, conversely, changing the electrical potential alters its length. This bi-directional energy conversion takes place in the cell's lateral wall and resembles the direct and converse piezoelectric effects both qualitatively and quantitatively. A piezoelectric model of the lateral wall has been developed that is based on the electrical and material parameters of the lateral wall. An equivalent circuit for the outer hair cell that includes piezoelectricity shows a greater admittance at high frequencies than one containing only membrane resistance and capacitance. The model also predicts resonance at ultrasonic frequencies that is inversely proportional to cell length. These features suggest all mammals use outer hair cell piezoelectricity to support the high-frequency receptor potentials that drive electromotility. It is also possible that members of some mammalian orders use outer hair cell piezoelectric resonance in detecting species-specific vocalizations.
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Affiliation(s)
- Erik K Weitzel
- Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, Texas 77030, USA
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48
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Abstract
In the present paper, referring to known characteristics of the outer hair cells functioning in the cochlea of the inner ear, a functional model of the outer hair cells is constructed. It consists of a linear feed-forward circuit and a non-linear positive feedback circuit. The feed-forward circuit reflects the contribution of local basilar and tectorial membrane areas and passive outer hair cells' physical parameters to the forming of low-selectivity resonance characteristics. The non-linear positive feedback circuit reflects the non-linear outer hair cell signal transduction processes and the active role of efferents from the medial superior olive in altering circuit sensitivity and selectivity. Referring to an analytical description of the circuit model and computer simulation results, an explanation is given over the biological meaning of the outer hair cells' non-linearities in signal transduction processes and the role of the non-linearities in achieving the following: signal compression, the dependency of circuit sensitivity and frequency selectivity upon the input signal amplitude, the compatibility of high-frequency selectivity and short transient response of the biological filtering circuits.
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Affiliation(s)
- Antanas Stasiunas
- Department of Applied Electronics, Kaunas University of Technology, LT-3031 Kaunas, Lithuania
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Abstract
The amplification of acoustic stimuli is a feature of hair cells that evolved early on in vertebrates. Though standard stereocilia mechanisms to promote such amplification may persist in the mammal, an additional mechanism evolved to enhance high frequency sensation. Only in mammals, a special cell type, the outer hair cell, arose that possesses a remarkably fast somatic mechanical response, which probably endows the passive cochlea with a boost in sensitivity by a factor of 100 (40dB), at least. Experiments conducted over the past few years have shed light on many aspects of outer hair cell electromotility, including the molecular identification of the motor, the effects of a knockout, and underlying mechanisms of action. A review of this remarkable progress is attempted.
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Affiliation(s)
- Joseph Santos-Sacchi
- Yale University School of Medicine, Otolaryngology and Neurobiology, BML 244 333 Cedar Street, New Haven, CT 06510, USA.
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Abstract
Outer hair cells underlie high frequency cochlear amplification in mammals. Fast somatic motility can be driven by voltage-dependent conformational changes in the motor protein, prestin, which resides exclusively within lateral plasma membrane of the cell. Yet, how a voltage-driven motor could contribute to high frequency amplification, despite the low-pass membrane filter of the cell, remains an enigma. The recent identification of prestin's Cl- sensitivity revealed an alternative mechanism in which intracellular Cl- fluctuations near prestin could influence the motor. We report the existence of a stretch-sensitive conductance within the lateral membrane that passes anions and cations and is gated at acoustic rates. The resultant intracellular Cl- oscillations near prestin may drive motor protein transitions, as evidenced by pronounced shifts in prestin's state-probability function along the voltage axis. The sensitivity of prestin's state probability to intracellular Cl- levels betokens a more complicated role for Cl- than a simple extrinsic voltage sensor. Instead, we suggest an allosteric modulation of prestin by Cl- and other anions. Finally, we hypothesize that prestin sensitivity to anion flux through the mechanically activated lateral membrane can provide a driving force that circumvents the membrane's low-pass filter, thus permitting amplification at high acoustic frequencies.
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Affiliation(s)
- Volodymyr Rybalchenko
- Department of Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA
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