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Cai W, Grosh K. Rate Dependent Cochlear Outer Hair Cell Force Generation: Models and Parameter Estimation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.13.571371. [PMID: 38168239 PMCID: PMC10760109 DOI: 10.1101/2023.12.13.571371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The outer hair cells (OHCs) of the mammalian cochlea are the mediators of an active, nonlinear electromechanical process necessary for sensitive, frequency specific hearing. The membrane protein prestin conveys to the OHC a piezoelectric-like behavior hypothesized to actuate a high frequency, cycle-by-cycle conversion of electrical to mechanical energy to boost cochlear responses to low-level sound. This hypothesis has been debated for decades, and we address two key remaining issues: the influence of the rate dependence of conformal changes in prestin and the OHC transmembrane impedance. We develop a theoretical electromechanical model of the OHC that explicitly includes rate dependence of conformal transitions, viscoelasticity, and piezoelectricity. Using this theory, we show the influence of rate dependence and viscoelasticity on electromechanical force generation. Further, we stress the importance of using the correct mechanical boundary conditions when estimating the transmembrane capacitance. Finally, a set of experiments is described to uniquely estimate the constitutive properties of the OHC from whole-cell measurements.
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2
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Kuwabara MF, Haddad BG, Lenz-Schwab D, Hartmann J, Longo P, Huckschlag BM, Fuß A, Questino A, Berger TK, Machtens JP, Oliver D. Elevator-like movements of prestin mediate outer hair cell electromotility. Nat Commun 2023; 14:7145. [PMID: 37932294 PMCID: PMC10628124 DOI: 10.1038/s41467-023-42489-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Accepted: 10/12/2023] [Indexed: 11/08/2023] Open
Abstract
The outstanding acuity of the mammalian ear relies on cochlear amplification, an active mechanism based on the electromotility (eM) of outer hair cells. eM is a piezoelectric mechanism generated by little-understood, voltage-induced conformational changes of the anion transporter homolog prestin (SLC26A5). We used a combination of molecular dynamics (MD) simulations and biophysical approaches to identify the structural dynamics of prestin that mediate eM. MD simulations showed that prestin samples a vast conformational landscape with expanded (ES) and compact (CS) states beyond previously reported prestin structures. Transition from CS to ES is dominated by the translational-rotational movement of prestin's transport domain, akin to elevator-type substrate translocation by related solute carriers. Reversible transition between CS and ES states was supported experimentally by cysteine accessibility scanning, cysteine cross-linking between transport and scaffold domains, and voltage-clamp fluorometry (VCF). Our data demonstrate that prestin's piezoelectric dynamics recapitulate essential steps of a structurally conserved ion transport cycle.
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Affiliation(s)
- Makoto F Kuwabara
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Bassam G Haddad
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany
| | - Dominik Lenz-Schwab
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Julia Hartmann
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Piersilvio Longo
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany
| | - Britt-Marie Huckschlag
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Anneke Fuß
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Annalisa Questino
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Thomas K Berger
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany
| | - Jan-Philipp Machtens
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany.
- Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany.
| | - Dominik Oliver
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, 35037, Marburg, Germany.
- DFG Research Training Group, Membrane Plasticity in Tissue Development and Remodeling, GRK 2213, Philipps University, Marburg, Germany.
- Center for Mind, Brain and Behavior (CMBB), Universities of Marburg and Giessen, Marburg, Germany.
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Zhang Y, Lin G, Xue N, Wang Y, Du T, Liu H, Xiong W, Shang W, Wu H, Song L. Differential outcomes of high-fat diet on age-related rescaling of cochlear frequency place coding. FASEB J 2023; 37:e23167. [PMID: 37651093 DOI: 10.1096/fj.202300457rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 08/01/2023] [Accepted: 08/14/2023] [Indexed: 09/01/2023]
Abstract
Auditory frequency coding is place-specific, which depends on the mechanical coupling of the basilar membrane-outer hair cell (OHC)-tectorial membrane network. Prestin-based OHC electromotility improves cochlear frequency selectivity and sensitivity. Cochlear amplification determines the frequency coding wherein discrete sound frequencies find a 'best' place along the cochlear length. Loss of OHC is the leading cause of age-related hearing loss (ARHL) and is the most common cause of sensorineural hearing loss and compromised speech perception. Lipid interaction with Prestin impacts OHC function. It has been established that high-fat diet (HFD) is associated with ARHL. To determine whether genetic background and metabolism preserve cochlear frequency place coding, we examined the effect of HFD in C57BL/6J (B6) and CBA/CaJ (CBA) on ARHL.We found a significant rescuing effect on ARHL in aged B6 HFD cohort. Prestin levels and cell sizes were better maintained in the experimental B6-HFD group. We also found that distortion product otoacoustic emission (DPOAE) group delay measurement was preserved, which suggested stable frequency place coding. In contrast, the response to HFD in the CBA cohort was modest with no appreciable benefit to hearing threshold. Notably, group delay was shortened with age along with the control. In addition, the frequency dependent OHC nonlinear capacitance gradient was most pronounced at young age but decreased with age. Cochlear RNA-seq analysis revealed differential TRPV1 expression and lipid homeostasis. Activation of TRPV1 and downregulation of arachidonic acid led to downregulation of inflammatory response in B6 HFD, which protects the cochlea from ARHL. The genetic background and metabolic state-derived changes in OHC morphology and function collectively contribute to a redefined cochlear frequency place coding and improved age-related pitch perception.
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Affiliation(s)
- Yu Zhang
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Guotong Lin
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Na Xue
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Yi Wang
- School of Life Sciences, Tsinghua University, Beijing, China
| | - Tingting Du
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Huihui Liu
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Wei Xiong
- Chinese Institute for Brain Research, Beijing, China
| | - Wei Shang
- Navy Clinical Medical School, Anhui Medical University, Hefei, China
- In Vitro Fertility (IVF) Center Department of Obstetrics and Gynecology, the Sixth Medical Center of PLA General Hospital, Beijing, China
- Department of Obstetrics and Gynecology, Chinese PLA General Hospital, Beijing, China
| | - Hao Wu
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Lei Song
- Department of Otolaryngology, Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
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Tan WJT, Santos-Sacchi J, Tonello J, Shanker A, Ivanova AV. Pharmacological Modulation of Energy and Metabolic Pathways Protects Hearing in the Fus1/Tusc2 Knockout Model of Mitochondrial Dysfunction and Oxidative Stress. Antioxidants (Basel) 2023; 12:1225. [PMID: 37371955 DOI: 10.3390/antiox12061225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 05/23/2023] [Accepted: 05/31/2023] [Indexed: 06/29/2023] Open
Abstract
Tightly regulated and robust mitochondrial activities are critical for normal hearing. Previously, we demonstrated that Fus1/Tusc2 KO mice with mitochondrial dysfunction exhibit premature hearing loss. Molecular analysis of the cochlea revealed hyperactivation of the mTOR pathway, oxidative stress, and altered mitochondrial morphology and quantity, suggesting compromised energy sensing and production. Here, we investigated whether the pharmacological modulation of metabolic pathways using rapamycin (RAPA) or 2-deoxy-D-glucose (2-DG) supplementation can protect against hearing loss in female Fus1 KO mice. Additionally, we aimed to identify mitochondria- and Fus1/Tusc2-dependent molecular pathways and processes critical for hearing. We found that inhibiting mTOR or activating alternative mitochondrial energetic pathways to glycolysis protected hearing in the mice. Comparative gene expression analysis revealed the dysregulation of critical biological processes in the KO cochlea, including mitochondrial metabolism, neural and immune responses, and the cochlear hypothalamic-pituitary-adrenal axis signaling system. RAPA and 2-DG mostly normalized these processes, although some genes showed a drug-specific response or no response at all. Interestingly, both drugs resulted in a pronounced upregulation of critical hearing-related genes not altered in the non-treated KO cochlea, including cytoskeletal and motor proteins and calcium-linked transporters and voltage-gated channels. These findings suggest that the pharmacological modulation of mitochondrial metabolism and bioenergetics may restore and activate processes critical for hearing, thereby protecting against hearing loss.
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Affiliation(s)
- Winston J T Tan
- Department of Physiology, Faculty of Medical and Health Sciences, The University of Auckland, Auckland 1023, New Zealand
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT 06510, USA
| | - Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT 06510, USA
| | - Jane Tonello
- School of Medicine, Meharry Medical College, Nashville, TN 37208, USA
| | - Anil Shanker
- School of Medicine, Meharry Medical College, Nashville, TN 37208, USA
| | - Alla V Ivanova
- School of Graduate Studies and Research, Meharry Medical College, Nashville, TN 37208, USA
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Capshaw G, Brown AD, Peña JL, Carr CE, Christensen-Dalsgaard J, Tollin DJ, Womack MC, McCullagh EA. The continued importance of comparative auditory research to modern scientific discovery. Hear Res 2023; 433:108766. [PMID: 37084504 PMCID: PMC10321136 DOI: 10.1016/j.heares.2023.108766] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 03/23/2023] [Accepted: 04/05/2023] [Indexed: 04/23/2023]
Abstract
A rich history of comparative research in the auditory field has afforded a synthetic view of sound information processing by ears and brains. Some organisms have proven to be powerful models for human hearing due to fundamental similarities (e.g., well-matched hearing ranges), while others feature intriguing differences (e.g., atympanic ears) that invite further study. Work across diverse "non-traditional" organisms, from small mammals to avians to amphibians and beyond, continues to propel auditory science forward, netting a variety of biomedical and technological advances along the way. In this brief review, limited primarily to tetrapod vertebrates, we discuss the continued importance of comparative studies in hearing research from the periphery to central nervous system with a focus on outstanding questions such as mechanisms for sound capture, peripheral and central processing of directional/spatial information, and non-canonical auditory processing, including efferent and hormonal effects.
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Affiliation(s)
- Grace Capshaw
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, MD 21218, USA.
| | - Andrew D Brown
- Department of Speech and Hearing Sciences, University of Washington, Seattle, WA 98105, USA
| | - José L Peña
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Catherine E Carr
- Department of Biology, University of Maryland, College Park, MD 20742, USA
| | | | - Daniel J Tollin
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA; Department of Otolaryngology, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Molly C Womack
- Department of Biology, Utah State University, Logan, UT 84322, USA.
| | - Elizabeth A McCullagh
- Department of Integrative Biology, Oklahoma State University, Stillwater, OK 74078, USA.
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6
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Tan WJT, Song L. Role of mitochondrial dysfunction and oxidative stress in sensorineural hearing loss. Hear Res 2023; 434:108783. [PMID: 37167889 DOI: 10.1016/j.heares.2023.108783] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 04/19/2023] [Accepted: 04/28/2023] [Indexed: 05/13/2023]
Abstract
Sensorineural hearing loss (SNHL) can either be genetically inherited or acquired as a result of aging, noise exposure, or ototoxic drugs. Although the precise pathophysiological mechanisms underlying SNHL remain unclear, an overwhelming body of evidence implicates mitochondrial dysfunction and oxidative stress playing a central etiological role. With its high metabolic demands, the cochlea, particularly the sensory hair cells, stria vascularis, and spiral ganglion neurons, is vulnerable to the damaging effects of mitochondrial reactive oxygen species (ROS). Mitochondrial dysfunction and consequent oxidative stress in cochlear cells can be caused by inherited mitochondrial DNA (mtDNA) mutations (hereditary hearing loss and aminoglycoside-induced ototoxicity), accumulation of acquired mtDNA mutations with age (age-related hearing loss), mitochondrial overdrive and calcium dysregulation (noise-induced hearing loss and cisplatin-induced ototoxicity), or accumulation of ototoxic drugs within hair cell mitochondria (drug-induced hearing loss). In this review, we provide an overview of our current knowledge on the role of mitochondrial dysfunction and oxidative stress in the development of SNHL caused by genetic mutations, aging, exposure to excessive noise, and ototoxic drugs. We also explore the advancements in antioxidant therapies for the different forms of acquired SNHL that are being evaluated in preclinical and clinical studies.
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Affiliation(s)
- Winston J T Tan
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, 06510, USA; Department of Physiology, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, 1023, New Zealand.
| | - Lei Song
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, 06510, USA; Department of Otolaryngology - Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200125, China; Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, 200125, China.
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7
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Santos-Sacchi J, Bai JP, Navaratnam D. Megahertz Sampling of Prestin (SLC26a5) Voltage-Sensor Charge Movements in Outer Hair Cell Membranes Reveals Ultrasonic Activity that May Support Electromotility and Cochlear Amplification. J Neurosci 2023; 43:2460-2468. [PMID: 36868859 PMCID: PMC10082455 DOI: 10.1523/jneurosci.2033-22.2023] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 02/21/2023] [Accepted: 02/26/2023] [Indexed: 03/05/2023] Open
Abstract
Charged moieties in the outer hair cell (OHC) membrane motor protein, prestin, are driven by transmembrane voltage to power OHC electromotility (eM) and cochlear amplification (CA), an enhancement of mammalian hearing. Consequently, the speed of prestin's conformational switching constrains its dynamic influence on micromechanics of the cell and the organ of Corti. Corresponding voltage-sensor charge movements in prestin, classically assessed as a voltage-dependent, nonlinear membrane capacitance (NLC), have been used to gauge its frequency response, but have been validly measured only out to 30 kHz. Thus, controversy exists concerning the effectiveness of eM in supporting CA at ultrasonic frequencies where some mammals can hear. Using megahertz sampling of guinea pig (either sex) prestin charge movements, we extend interrogations of NLC into the ultrasonic range (up to 120 kHz) and find an order of magnitude larger response at 80 kHz than previously predicted, indicating that an influence of eM at ultrasonic frequencies is likely, in line with recent in vivo results (Levic et al., 2022). Given wider bandwidth interrogations, we also validate kinetic model predictions of prestin by directly observing its characteristic cut-off frequency under voltage-clamp as the intersection frequency (Fis), near 19 kHz, of the real and imaginary components of complex NLC (cNLC). The frequency response of prestin displacement current noise determined from either the Nyquist relation or stationary measures aligns with this cut-off. We conclude that voltage stimulation accurately assesses the spectral limits of prestin activity, and that voltage-dependent conformational switching is physiologically significant in the ultrasonic range.SIGNIFICANCE STATEMENT The motor protein prestin powers outer hair cell (OHC) electromotility (eM) and cochlear amplification (CA), an enhancement of high-frequency mammalian hearing. The ability of prestin to work at very high frequencies depends on its membrane voltage-driven conformation switching. Using megahertz sampling, we extend measures of prestin charge movement into the ultrasonic range and find response magnitude at 80 kHz an order of magnitude larger than previously estimated, despite confirmation of previous low pass characteristic frequency cut-offs. The frequency response of prestin noise garnered by the admittance-based Nyquist relation or stationary noise measures confirms this characteristic cut-off frequency. Our data indicate that voltage perturbation provides accurate assessment of prestin performance indicating that it can support cochlear amplification into a higher frequency range than previously thought.
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Affiliation(s)
- Joseph Santos-Sacchi
- Surgery (Otolaryngology), Yale University School of Medicine, New Haven, Connecticut 06510
- Neuroscience, Yale University School of Medicine, New Haven, Connecticut 06510
- Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
| | - Jun-Ping Bai
- Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
| | - Dhasakumar Navaratnam
- Surgery (Otolaryngology), Yale University School of Medicine, New Haven, Connecticut 06510
- Neurology, Yale University School of Medicine, New Haven, Connecticut 06510
- Neuroscience, Yale University School of Medicine, New Haven, Connecticut 06510
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Ashmore JF, Oghalai JS, Dewey JB, Olson ES, Strimbu CE, Wang Y, Shera CA, Altoè A, Abdala C, Elgoyhen AB, Eatock RA, Raphael RM. The Remarkable Outer Hair Cell: Proceedings of a Symposium in Honour of W. E. Brownell. J Assoc Res Otolaryngol 2023; 24:117-127. [PMID: 36648734 PMCID: PMC10121982 DOI: 10.1007/s10162-022-00852-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 05/02/2022] [Indexed: 01/18/2023] Open
Abstract
In 1985, Bill Brownell and colleagues published the remarkable observation that cochlear outer hair cells (OHCs) express voltage-driven mechanical motion: electromotility. They proposed OHC electromotility as the mechanism for the elusive "cochlear amplifier" required to explain the sensitivity of mammalian hearing. The finding and hypothesis stimulated an explosion of experiments that have transformed our understanding of cochlear mechanics and physiology, the evolution of hair cell structure and function, and audiology. Here, we bring together examples of current research that illustrate the continuing impact of the discovery of OHC electromotility.
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Affiliation(s)
| | - John S Oghalai
- Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, USA
| | - James B Dewey
- Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, USA
| | - Elizabeth S Olson
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, New York City, USA
| | - Clark E Strimbu
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, New York City, USA
| | - Yi Wang
- Department of Otolaryngology Head and Neck Surgery, Vagelos College of Physicians and Surgeons, Columbia University, New York City, USA
| | - Christopher A Shera
- Caruso Department of Otolaryngology and Department of Physics and Astronomy, University of Southern California, Los Angeles, USA
| | - Alessandro Altoè
- Caruso Department of Otolaryngology and Department of Physics and Astronomy, University of Southern California, Los Angeles, USA
| | - Carolina Abdala
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, USA
| | - Ana B Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
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9
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Altoè A, Shera CA. The Long Outer-Hair-Cell RC Time Constant: A Feature, Not a Bug, of the Mammalian Cochlea. J Assoc Res Otolaryngol 2023; 24:129-145. [PMID: 36725778 PMCID: PMC10121995 DOI: 10.1007/s10162-022-00884-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 12/23/2022] [Indexed: 02/03/2023] Open
Abstract
The cochlea of the mammalian inner ear includes an active, hydromechanical amplifier thought to arise via the piezoelectric action of the outer hair cells (OHCs). A classic problem of cochlear biophysics is that the RC (resistance-capacitance) time constant of the hair-cell membrane appears inconveniently long, producing an effective cut-off frequency much lower than that of most audible sounds. The long RC time constant implies that the OHC receptor potential-and hence its electromotile response-decreases by roughly two orders of magnitude over the frequency range of mammalian hearing, casting doubt on the hypothesized role of cycle-by-cycle OHC-based amplification in mammalian hearing. Here, we review published data and basic physics to show that the "RC problem" has been magnified by viewing it through the wrong lens. Our analysis finds no appreciable mismatch between the expected magnitude of high-frequency electromotility and the sound-evoked displacements of the organ of Corti. Rather than precluding significant OHC-based boosts to auditory sensitivity, the long RC time constant appears beneficial for hearing, reducing the effects of internal noise and distortion while increasing the fidelity of cochlear amplification.
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Affiliation(s)
- Alessandro Altoè
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA, USA.
| | - Christopher A Shera
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA, USA.
- Department of Physics & Astronomy, University of Southern California, Los Angeles, CA, USA.
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10
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Takahashi S, Zhou Y, Kojima T, Cheatham MA, Homma K. Prestin's fast motor kinetics is essential for mammalian cochlear amplification. Proc Natl Acad Sci U S A 2023; 120:e2217891120. [PMID: 36893263 PMCID: PMC10089206 DOI: 10.1073/pnas.2217891120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 02/06/2023] [Indexed: 03/11/2023] Open
Abstract
Prestin (SLC26A5)-mediated voltage-driven elongations and contractions of sensory outer hair cells within the organ of Corti are essential for mammalian cochlear amplification. However, whether this electromotile activity directly contributes on a cycle-by-cycle basis is currently controversial. By restoring motor kinetics in a mouse model expressing a slowed prestin missense variant, this study provides experimental evidence acknowledging the importance of fast motor action to mammalian cochlear amplification. Our results also demonstrate that the point mutation in prestin disrupting anion transport in other proteins of the SLC26 family does not alter cochlear function, suggesting that the potential weak anion transport of prestin is not essential in the mammalian cochlea.
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Affiliation(s)
- Satoe Takahashi
- Department of Otolaryngology–Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL60611
| | - Yingjie Zhou
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL60208
| | - Takashi Kojima
- Department of Otolaryngology–Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL60611
| | - Mary Ann Cheatham
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL60208
- The Hugh Knowles Center for Clinical and Basic Science in Hearing and Its Disorders, Northwestern University, Evanston, IL60208
| | - Kazuaki Homma
- Department of Otolaryngology–Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Chicago, IL60611
- The Hugh Knowles Center for Clinical and Basic Science in Hearing and Its Disorders, Northwestern University, Evanston, IL60208
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11
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Rabbitt RD, Bidone TC. A parametric blueprint for optimum cochlear outer hair cell design. J R Soc Interface 2023; 20:20220762. [PMID: 36789510 PMCID: PMC9929500 DOI: 10.1098/rsif.2022.0762] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023] Open
Abstract
The present work examines the hypothesis that cochlear outer hair cell (OHC) properties vary in precise proportions along the tonotopic map to optimize electromechanical power conversion. We tested this hypothesis using a very simple model of a single isolated OHC driving a mechanical load. Results identify three non-dimensional ratios that are predicted to optimize power conversion: the ratio of the resistive-capacitive (RC) corner to the characteristic frequency (CF), the ratio of nonlinear to linear capacitance and the ratio of OHC stiffness to cochlear load stiffness. Optimum efficiency requires all three ratios to be universal constants, independent of CF and species. The same ratios are cardinal control parameters that maximize power output by positioning the OHC operating point on the edge of a dynamic instability. Results support the hypothesis that OHC properties evolved to optimize electro-mechanical power conversion. Identification of the RC corner frequency as a control parameter reveals a powerful mechanism used by medial olivocochlear efferent system to control OHC power output. Results indicate the upper-frequency limit of OHC power output is not constrained by the speed of the motor itself but instead is probably limited by the size of the nucleus and membrane surface area available for ion-channel expression.
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Affiliation(s)
- Richard D. Rabbitt
- Biomedical Engineering, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Otolaryngology, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Neuroscience Program, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA
| | - Tamara C. Bidone
- Biomedical Engineering, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Molecular Pharmaceutics, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Department of Biochemistry, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA,Scientific Computing & Imaging Institute, University of Utah, 36 S Wasatch Drive, Salt Lake City, UT 84112, USA
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12
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He W, Burwood G, Fridberger A, Nuttall AL, Ren T. An outer hair cell-powered global hydromechanical mechanism for cochlear amplification. Hear Res 2022; 423:108407. [PMID: 34922772 PMCID: PMC9156726 DOI: 10.1016/j.heares.2021.108407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 11/23/2021] [Accepted: 11/30/2021] [Indexed: 11/04/2022]
Abstract
It is a common belief that the mammalian cochlea achieves its exquisite sensitivity, frequency selectivity, and dynamic range through an outer hair cell-based active process, or cochlear amplification. As a sound-induced traveling wave propagates from the cochlear base toward the apex, outer hair cells at a narrow region amplify the low level sound-induced vibration through a local feedback mechanism. This widely accepted theory has been tested by measuring sound-induced sub-nanometer vibrations within the organ of Corti in the sensitive living cochleae using heterodyne low-coherence interferometry and optical coherence tomography. The aim of this short review is to summarize experimental findings on the cochlear active process by the authors' group. Our data show that outer hair cells are able to generate substantial forces for driving the cochlear partition at all audible frequencies in vivo. The acoustically induced reticular lamina vibration is larger and more broadly tuned than the basilar membrane vibration. The reticular lamina and basilar membrane vibrate approximately in opposite directions at low frequencies and in the same direction at the best frequency. The group delay of the reticular lamina is larger than that of the basilar membrane. The magnitude and phase differences between the reticular lamina and basilar membrane vibration are physiologically vulnerable. These results contradict predictions based on the local feedback mechanism but suggest a global hydromechanical mechanism for cochlear amplification. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
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Affiliation(s)
- Wenxuan He
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States
| | - George Burwood
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States
| | - Anders Fridberger
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
| | - Alfred L Nuttall
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States
| | - Tianying Ren
- Department of Otolaryngology, Head and Neck Surgery, Oregon Health & Science University, Portland OR, United States.
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13
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Santos-Sacchi J, Tan WJT. Coupling between outer hair cell electromotility and prestin sensor charge depends on voltage operating point. Hear Res 2022; 423:108373. [PMID: 34776274 PMCID: PMC9054947 DOI: 10.1016/j.heares.2021.108373] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 08/16/2021] [Accepted: 10/13/2021] [Indexed: 11/16/2022]
Abstract
The OHC drives cochlear amplification, and prestin activity is the basis. The frequency response of nonlinear capacitance (NLC), which is a ratiometric measure of prestin's voltage-sensor charge movement (dQp/dVm), depends on the location of AC voltage excitation along prestin's operating voltage range, being slowest at the voltage (Vh) where NLC peaks. Here we directly investigate the coupling between prestin charge movement (Qp) and electromotility (eM) at frequencies up to 6.25 kHz, and find tight correspondence between the two at operating voltages displaced from Vh. Near Vh, however, eM shows a slower frequency response than Qp. We reason that coupling is more susceptible to molecular/cellular loads at Vh, where prestin compliance is expected to be maximal. Recent cryo-EM studies have begun to shed light on structural features of prestin that impact its performance against loads. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
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Affiliation(s)
- Joseph Santos-Sacchi
- Surgery (Otolaryngology), 333 Cedar Street, New Haven, CT 06510, USA; Neuroscience, 333 Cedar Street, New Haven, CT 06510, USA; Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA.
| | - Winston J T Tan
- Surgery (Otolaryngology), 333 Cedar Street, New Haven, CT 06510, USA
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14
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Quiñones PM, Meenderink SWF, Applegate BE, Oghalai JS. Unloading outer hair cell bundles in vivo does not yield evidence of spontaneous oscillations in the mouse cochlea. Hear Res 2022; 423:108473. [PMID: 35287989 PMCID: PMC9339463 DOI: 10.1016/j.heares.2022.108473] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 02/11/2022] [Accepted: 02/28/2022] [Indexed: 12/21/2022]
Abstract
Along with outer hair cell (OHC) somatic electromotility as the actuator of cochlear amplification, active hair bundle motility may be a complementary mechanism in the mammalian auditory system. Here, we searched the mouse cochlea for the presence of spontaneous bundle oscillations that have been observed in non-mammalian ears. In those systems, removal of the overlying membrane is necessary for spontaneous bundle oscillations to manifest. Thus, we used a genetic mouse model with a C1509G (cysteine-to-glycine) point mutation in the Tecta gene where the tectorial (TM) is lifted away from the OHC bundles, allowing us to explore whether unloaded bundles spontaneously oscillate. We used VOCTV in vivo to detect OHC length changes due to electromotility as a proxy for the spontaneous opening and closing of the mechanoelectrical transduction (MET) channels associated with bundle oscillation. In wild type mice with the TM attached to OHC bundles, we did find peaks in vibratory magnitude spectra. Such peaks were not observed in the mutants where the TM is detached from the OHC bundles. Statistical analysis of the time signals indicates that these peaks do not signify active oscillations. Rather, they are filtered responses of the sensitive wild type cochlea to weak background noise. We therefore conclude that, to the limits of our system (∼30 pm), there is no spontaneous mechanical activity that manifests as oscillations in OHC electromotility within the mouse cochlea, arguing that unloaded OHC bundles do not oscillate in vivo. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
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Affiliation(s)
- Patricia M Quiñones
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA
| | | | - Brian E Applegate
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA; Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA
| | - John S Oghalai
- Caruso Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Los Angeles, CA, USA.
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15
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Kost LA, Iunusova VA, Ivanova VO, Nikitin ES, Lukyanov KA, Bogdanov AM. The Electromotive Protein Prestin as a Sensitive Core of the Fluorescent Voltage Indicator. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2022. [DOI: 10.1134/s1068162022030098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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16
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Rabbitt RD. Analysis of outer hair cell electromechanics reveals power delivery at the upper-frequency limits of hearing. J R Soc Interface 2022; 19:20220139. [PMID: 35673856 PMCID: PMC9174718 DOI: 10.1098/rsif.2022.0139] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Outer hair cells are the cellular motors in the mammalian inner ear responsible for sensitive high-frequency hearing. Motor function over the frequency range of human hearing requires expression of the protein prestin in the OHC lateral membrane, which imparts piezoelectric properties to the cell membrane. In the present report, electrical power consumption and mechanical power output of the OHC membrane–motor complex are determined using previously published voltage-clamp data from isolated OHCs and membrane patches. Results reveal that power output peaks at a best frequency much higher than implied by the low-pass character of nonlinear capacitance, and much higher than the whole-cell resistive–capacitive corner frequency. High frequency power output is enabled by a −90° shift in the phase of electrical charge displacement in the membrane, manifested electrically as emergence of imaginary-valued nonlinear capacitance.
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Affiliation(s)
- Richard D. Rabbitt
- Biomedical Engineering, Otolaryngology, and Neuroscience Program, University of Utah, 36 S. Wasatch Drive, SMBB 3100, Salt Lake City, UT 84112, USA
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17
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Santos-Sacchi J, Tan W. On the frequency response of prestin charge movement in membrane patches. Biophys J 2022; 121:2371-2379. [PMID: 35598044 DOI: 10.1016/j.bpj.2022.05.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Revised: 04/14/2022] [Accepted: 05/17/2022] [Indexed: 11/18/2022] Open
Abstract
Outer hair cell (OHC) nonlinear membrane capacitance (NLC) derives from voltage-dependent sensor charge movements within the membrane protein prestin (SLC26a5) that drive OHC electromotility. The ability of the protein to influence hearing depends on its reaction to membrane receptor potentials across auditory frequency. Estimates of prestin's frequency response have been evaluated by several groups out to tens of kHz in voltage-clamped macro-patches of OHC membrane. The response is a power function of frequency which is down 40 dB at 77 kHz. Despite these observations, concerns remain that the macro-patch approach is flawed due to mechanical constraints of pipette solution column load or patch size itself. In the absence of these influences, prestin's frequency response is posited by some to be ultrasonic in nature. Here we evaluate the influence of these putative confounding factors on prestin's frequency response. We show that neither pipette column height, nor negative or positive pipette pressure substantially influence total sensor charge frequency response. Additionally, patch surface area has negligible influence. We conclude that the speed of voltage-driven conformational changes in prestin within the plasma membrane are accurately assessed with the macro-patch technique, permitting investigations of membrane characteristics that can substantially alter prestin's performance bandwidth. We illustrate significant alterations in bandwidth by perturbation of membrane fluidity and chloride anion concentration. Finally, we speculate that OHC membrane characteristics may differ along the tonotopic axis of the cochlea to tune NLC frequency cut-offs.
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Affiliation(s)
- Joseph Santos-Sacchi
- Surgery (Otolaryngology), Neuroscience, and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut.
| | - Winston Tan
- Surgery (Otolaryngology), Neuroscience, and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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18
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Physiology and Biophysics of Outer hair cells: The cells of Dallos. Hear Res 2022; 423:108525. [DOI: 10.1016/j.heares.2022.108525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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19
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Prestin-Mediated Frequency Selectivity Does not Cover Ultrahigh Frequencies in Mice. Neurosci Bull 2022; 38:769-784. [DOI: 10.1007/s12264-022-00839-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 12/24/2021] [Indexed: 02/08/2023] Open
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20
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Butan C, Song Q, Bai JP, Tan WJT, Navaratnam D, Santos-Sacchi J. Single particle cryo-EM structure of the outer hair cell motor protein prestin. Nat Commun 2022; 13:290. [PMID: 35022426 PMCID: PMC8755724 DOI: 10.1038/s41467-021-27915-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Accepted: 12/16/2021] [Indexed: 12/18/2022] Open
Abstract
The mammalian outer hair cell (OHC) protein prestin (Slc26a5) differs from other Slc26 family members due to its unique piezoelectric-like property that drives OHC electromotility, the putative mechanism for cochlear amplification. Here, we use cryo-electron microscopy to determine prestin’s structure at 3.6 Å resolution. Prestin is structurally similar to the anion transporter Slc26a9. It is captured in an inward-open state which may reflect prestin’s contracted state. Two well-separated transmembrane (TM) domains and two cytoplasmic sulfate transporter and anti-sigma factor antagonist (STAS) domains form a swapped dimer. The transmembrane domains consist of 14 transmembrane segments organized in two 7+7 inverted repeats, an architecture first observed in the bacterial symporter UraA. Mutation of prestin’s chloride binding site removes salicylate competition with anions while retaining the prestin characteristic displacement currents (Nonlinear Capacitance), undermining the extrinsic voltage sensor hypothesis for prestin function. Prestin, expressed in outer hair cell (OHC), belongs to the Slc26 transporter family and functions as a voltage-driven motor that drives OHC electromotility. Here, the authors report cryo-EM structure and characterization of gerbil prestin, with insights into its mechanism of action.
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Affiliation(s)
- Carmen Butan
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA
| | - Qiang Song
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA
| | - Jun-Ping Bai
- Department of Neurology, Yale University School of Medicine, New Haven, CT, USA
| | - Winston J T Tan
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA
| | - Dhasakumar Navaratnam
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA. .,Department of Neurology, Yale University School of Medicine, New Haven, CT, USA. .,Neuroscience, Yale University School of Medicine, New Haven, CT, USA.
| | - Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA. .,Neuroscience, Yale University School of Medicine, New Haven, CT, USA. .,Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA.
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21
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He J, Lu S, Mo W, Tang A, Tan S, Liu L, Fang Q, Xie L. Observation in inner ear of tree shrew using scanning electron microscope and the Atoh1 distribution in cochlea. Microsc Res Tech 2021; 85:1837-1844. [PMID: 34962020 DOI: 10.1002/jemt.24045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Revised: 11/29/2021] [Accepted: 12/16/2021] [Indexed: 11/07/2022]
Abstract
This study aimed to observe the ultrastructure on the surface of the inner ear of a normal tree shrew using scanning electron microscope (SEM). The specimens of cochlea, macula utriculi, macula sacculi, and crista ampullaris of the normal adult tree shrew were collected and observed by SEM. We used immunofluorescence for cochlear protein Atoh1 staining. We observed that cochlea of the tree shrew is centered on the cochlear axis, circling about 3.5 times from bottom to top of the cochlea. The organ of Corti is located between medial and lateral grooves, including inner and outer hair cells as well as supporting cells. Maculae staticae include macula of saccule and macula of utricle, and the surface of macula is covered with a large number of otoliths. We found a gelatinous layer below the otoliths, followed by the layer of the honeycomb structure. The hair cell cilia of macula and crista ampullaris include one kinocilium and more stereocilia. There is no obvious cross structure but numerous hair cell cilia on semicircular canal crista ampullaris. Immunofluorescence staining showed that protein Atoh1 is mainly distributed in the nucleus of the cochlea's inner and outer hair cells. The observation of the inner ear structure under SEM elucidate the fine surface morphological structure of the entire cochlea, the vestibular maculae staticae, and crista ampullaris, providing new insight into the structure and function of the inner ear of tree shrew. HIGHLIGHTS: This article is the first to describe the inner ear ultrastructure of a small primate tree shrew by scanning electron microscopy (SEM). Under an SEM, the phalangeal processes of Deiter cells in tree shrews were observed to be connected to the tip of a neighboring hair cell, which was different from that of Deiters' cells in guinea pigs, and this crossed one hair cell, and connected to the tip of the third hair cell. It was observed that the crista ampullaris of tree shrews were horseshoe-shaped, and similar to that of humans and monkeys, this had no obvious "cross-shaped hump" structure. Tree shrew's ABR threshold value curve conforms to the mammalian U-shaped curve, wave III is the main wave of ARB, its sensory frequency may be higher 8 kHz, and the characteristics of the stereocilia of tree shrew we have observed may be related to the perception of higher frequency hearing.
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Affiliation(s)
- Jinling He
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China.,Key Laboratory of Early Prevention and Treatment for High Frequency Tumor, Ministry of Education, Nanning, China.,Guangxi Key Laboratory of Early Prevention and Treatment for Regional High Frequency Tumor, Nanning, China.,Guangxi Medical University, Nanning, China
| | - Shunlan Lu
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China.,Key Laboratory of Early Prevention and Treatment for High Frequency Tumor, Ministry of Education, Nanning, China.,Guangxi Key Laboratory of Early Prevention and Treatment for Regional High Frequency Tumor, Nanning, China.,Guangxi Medical University, Nanning, China
| | - Weijian Mo
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China.,Guangxi Medical University, Nanning, China
| | - Anzhou Tang
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China.,Guangxi Medical University, Nanning, China
| | - Songhua Tan
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China
| | - Lei Liu
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China
| | - Qin Fang
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China
| | - Lihong Xie
- Department of Otorhinolaryngology Head and Neck Surgery, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi, China
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22
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Progress in understanding the structural mechanism underlying prestin's electromotile activity. Hear Res 2021; 423:108423. [PMID: 34987017 DOI: 10.1016/j.heares.2021.108423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 11/17/2021] [Accepted: 12/22/2021] [Indexed: 11/21/2022]
Abstract
Prestin (SLC26A5), a member of the SLC26 transporter family, is the molecular actuator that drives OHC electromotility (eM). A wealth of biophysical data indicates that eM is mediated by an area motor mechanism, in which prestin molecules act as elementary actuators by changing their area in the membrane in response to changes in membrane potential. The area changes of a large and densely packed population of prestin molecules sum up, resulting in macroscopic cellular movement. At the single protein level, this model implies major voltage-driven conformational rearrangements. However, the nature of these structural dynamics remained unknown. A main obstacle in elucidating the eM mechanism has been the lack of structural information about SLC26 transporters. The recent emergence of several high-resolution cryo-EM structures of prestin as well as other SLC26 transporter family members now provides a reliable picture of prestin's molecular architecture. Thus, SLC26 transporters including prestin generally are dimers, and each protomer is folded according to a 7+7 transmembrane domain inverted repeat (7TMIR) architecture. Here, we review these structural findings and discuss insights into a potential molecular mechanism. Most important, distinct conformations were observed when purifying and imaging prestin bound to either its physiological ligand, chloride, or to competitively inhibitory anions, sulfate or salicylate. Despite differences in detail, these structural snapshots indicate that the conformational landscape of prestin includes rearrangements between the two major domains of prestin's transmembrane region (TMD), core and scaffold ('gate') domains. Notably, distinct conformations differ in the area the TMD occupies in the membrane and in their impact on the immediate lipid environment. Both effects can contribute to generate membrane deformation and thus may underly electromotility. Further functional studies will be necessary to determine whether these or similar structural rearrangements are driven by membrane potential to mediate piezoelectric activity. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
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23
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Prestin derived OHC surface area reduction underlies age-related rescaling of frequency place coding. Hear Res 2021; 423:108406. [PMID: 34933788 DOI: 10.1016/j.heares.2021.108406] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 11/08/2021] [Accepted: 11/25/2021] [Indexed: 12/29/2022]
Abstract
Outer hair cells (OHC) are key to the mammalian cochlear amplifier, powered by the lateral membrane protein Prestin. In this study, we explored age-related OHC changes and how the changes affected hearing in mouse. OHC nonlinear membrane capacitance measurements revealed that, starting upon completion of postnatal auditory development, a continuous reduction of total Prestin in OHCs accompanied by a significant reduction in their cell surface area. Prestin's density is unaffected by Prestin level drop over the whole age range tested, suggesting that the OHC size reduction is Prestin-dependent. Stereocilia length in aged OHCs remained unchanged but the first row stereocilia on the aged inner hair cells (IHCs) were elongated. Distortion product otoacoustic emission (DPOAE) group delays became longer with aging, suggesting an apical shift in vibration on basilar membrane. Acoustic lesion experiments revealed an apical shift in damage place in old cochleae accompanied by a shallower progression in synaptic damage over a wider frequency range that was indicative of a broader frequency filter. Overall, these findings suggest that in aging cochlea, a shift in frequency place coding could occur due to the changes in cochlear active and passive mechanics. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
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24
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Cochlear outer hair cell electromotility enhances organ of Corti motion on a cycle-by-cycle basis at high frequencies in vivo. Proc Natl Acad Sci U S A 2021; 118:2025206118. [PMID: 34686590 DOI: 10.1073/pnas.2025206118] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/07/2021] [Indexed: 11/18/2022] Open
Abstract
Mammalian hearing depends on an amplification process involving prestin, a voltage-sensitive motor protein that enables cochlear outer hair cells (OHCs) to change length and generate force. However, it has been questioned whether this prestin-based somatic electromotility can operate fast enough in vivo to amplify cochlear vibrations at the high frequencies that mammals hear. In this study, we measured sound-evoked vibrations from within the living mouse cochlea and found that the top and bottom of the OHCs move in opposite directions at frequencies exceeding 20 kHz, consistent with fast somatic length changes. These motions are physiologically vulnerable, depend on prestin, and dominate the cochlea's vibratory response to high-frequency sound. This dominance was observed despite mechanisms that clearly low-pass filter the in vivo electromotile response. Low-pass filtering therefore does not critically limit the OHC's ability to move the organ of Corti on a cycle-by-cycle basis. Our data argue that electromotility serves as the primary high-frequency amplifying mechanism within the mammalian cochlea.
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25
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van der Heijden M, Vavakou A. Rectifying and sluggish: Outer hair cells as regulators rather than amplifiers. Hear Res 2021; 423:108367. [PMID: 34686384 DOI: 10.1016/j.heares.2021.108367] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 08/27/2021] [Accepted: 09/29/2021] [Indexed: 11/04/2022]
Abstract
In the cochlea, mechano-electrical transduction is preceded by dynamic range compression. Outer hair cells (OHCs) and their voltage dependent length changes, known as electromotility, play a central role in this compression process, but the exact mechanisms are poorly understood. Here we review old and new experimental findings and show that (1) just audible high-frequency tones evoke an ∼1-microvolt AC receptor potential in basal OHCs; (2) any mechanical amplification of soft high-frequency tones by OHC motility would have an adverse effect on their audibility; (3) having a higher basolateral K+ conductance, while increasing the OHC corner frequency, does not boost the magnitude of the high-frequency AC receptor potential; (4) OHC receptor currents display a substantial rectified (DC) component; (5) mechanical DC responses (baseline shifts) to acoustic stimuli, while insignificant on the basilar membrane, can be comparable in magnitude to AC responses when recorded in the organ of Corti, both in the apex and the base. In the basal turn, the DC component may even exceed the AC component, lending support to Dallos' suggestion that both apical and basal OHCs display a significant degree of rectification. We further show that (6) low-intensity cochlear traveling waves, by virtue of their abrupt transition from fast to slow propagation, are well suited to transport high-frequency energy with minimal losses (∼2-dB loss for 16-kHz tones in the gerbil); (7) a 90-dB, 16-kHz tone, if transmitted without loss to its tonotopic place, would evoke a destructive displacement amplitude of 564 nm. We interpret these findings in a framework in which local dissipation is regulated by OHC motility.
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Affiliation(s)
| | - Anna Vavakou
- Department of Neuroscience, Erasmus MC, Rotterdam, the Netherlands
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26
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Farrell B, Skidmore BL, Rajasekharan V, Brownell WE. A novel theoretical framework reveals more than one voltage-sensing pathway in the lateral membrane of outer hair cells. J Gen Physiol 2021; 152:151746. [PMID: 32384538 PMCID: PMC7335013 DOI: 10.1085/jgp.201912447] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 03/18/2020] [Indexed: 11/20/2022] Open
Abstract
Outer hair cell (OHC) electromotility amplifies acoustic vibrations throughout the frequency range of hearing. Electromotility requires that the lateral membrane protein prestin undergo a conformational change upon changes in the membrane potential to produce an associated displacement charge. The magnitude of the charge displaced and the mid-reaction potential (when one half of the charge is displaced) reflects whether the cells will produce sufficient gain at the resting membrane potential to boost sound in vivo. Voltage clamp measurements performed under near-identical conditions ex vivo show the charge density and mid-reaction potential are not always the same, confounding interpretation of the results. We compare the displacement charge measurements in OHCs from rodents with a theory shown to exhibit good agreement with in silico simulations of voltage-sensing reactions in membranes. This model equates the charge density to the potential difference between two pseudo-equilibrium states of the sensors when they are in a stable conformation and not contributing to the displacement current. The model predicts this potential difference to be one half of its value midway into the reaction, when one equilibrium conformation transforms to the other pseudo-state. In agreement with the model, we find the measured mid-reaction potential to increase as the charge density decreases to exhibit a negative slope of ∼1/2. This relationship suggests that the prestin sensors exhibit more than one stable hyperpolarized state and that voltage sensing occurs by more than one pathway. We determine the electric parameters for prestin sensors and use the analytical expressions of the theory to estimate the energy barriers for the two voltage-dependent pathways. This analysis explains the experimental results, supports the theoretical approach, and suggests that voltage sensing occurs by more than one pathway to enable amplification throughout the frequency range of hearing.
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Affiliation(s)
- Brenda Farrell
- Bobby R. Alford Department of Otolaryngology and Head & Neck Surgery, Baylor College of Medicine, Houston, TX
| | - Benjamin L Skidmore
- Bobby R. Alford Department of Otolaryngology and Head & Neck Surgery, Baylor College of Medicine, Houston, TX
| | - Vivek Rajasekharan
- Bobby R. Alford Department of Otolaryngology and Head & Neck Surgery, Baylor College of Medicine, Houston, TX
| | - William E Brownell
- Bobby R. Alford Department of Otolaryngology and Head & Neck Surgery, Baylor College of Medicine, Houston, TX
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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] [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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28
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State dependent effects on the frequency response of prestin's real and imaginary components of nonlinear capacitance. Sci Rep 2021; 11:16149. [PMID: 34373481 PMCID: PMC8352928 DOI: 10.1038/s41598-021-95121-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Accepted: 07/21/2021] [Indexed: 11/20/2022] Open
Abstract
The outer hair cell (OHC) membrane harbors a voltage-dependent protein, prestin (SLC26a5), in high density, whose charge movement is evidenced as a nonlinear capacitance (NLC). NLC is bell-shaped, with its peak occurring at a voltage, Vh, where sensor charge is equally distributed across the plasma membrane. Thus, Vh provides information on the conformational state of prestin. Vh is sensitive to membrane tension, shifting to positive voltage as tension increases and is the basis for considering prestin piezoelectric (PZE). NLC can be deconstructed into real and imaginary components that report on charge movements in phase or 90 degrees out of phase with AC voltage. Here we show in membrane macro-patches of the OHC that there is a partial trade-off in the magnitude of real and imaginary components as interrogation frequency increases, as predicted by a recent PZE model (Rabbitt in Proc Natl Acad Sci USA 17:21880–21888, 2020). However, we find similar behavior in a simple 2-state voltage-dependent kinetic model of prestin that lacks piezoelectric coupling. At a particular frequency, Fis, the complex component magnitudes intersect. Using this metric, Fis, which depends on the frequency response of each complex component, we find that initial Vh influences Fis; thus, by categorizing patches into groups of different Vh, (above and below − 30 mV) we find that Fis is lower for the negative Vh group. We also find that the effect of membrane tension on complex NLC is dependent, but differentially so, on initial Vh. Whereas the negative group exhibits shifts to higher frequencies for increasing tension, the opposite occurs for the positive group. Despite complex component trade-offs, the low-pass roll-off in absolute magnitude of NLC, which varies little with our perturbations and is indicative of diminishing total charge movement, poses a challenge for a role of voltage-driven prestin in cochlear amplification at very high frequencies.
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Comparative Molecular Dynamics Investigation of the Electromotile Hearing Protein Prestin. Int J Mol Sci 2021; 22:ijms22158318. [PMID: 34361083 PMCID: PMC8347359 DOI: 10.3390/ijms22158318] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 07/23/2021] [Accepted: 07/26/2021] [Indexed: 01/05/2023] Open
Abstract
The mammalian protein prestin is expressed in the lateral membrane wall of the cochlear hair outer cells and is responsible for the electromotile response of the basolateral membrane, following hyperpolarisation or depolarisation of the cells. Its impairment marks the onset of severe diseases, like non-syndromic deafness. Several studies have pointed out possible key roles of residues located in the Transmembrane Domain (TMD) that differentiate mammalian prestins as incomplete transporters from the other proteins belonging to the same solute-carrier (SLC) superfamily, which are classified as complete transporters. Here, we exploit the homology of a prototypical incomplete transporter (rat prestin, rPres) and a complete transporter (zebrafish prestin, zPres) with target structures in the outward open and inward open conformations. The resulting models are then embedded in a model membrane and investigated via a rigorous molecular dynamics simulation protocol. The resulting trajectories are analyzed to obtain quantitative descriptors of the equilibration phase and to assess a structural comparison between proteins in different states, and between different proteins in the same state. Our study clearly identifies a network of key residues at the interface between the gate and the core domains of prestin that might be responsible for the conformational change observed in complete transporters and hindered in incomplete transporters. In addition, we study the pathway of Cl− ions in the presence of an applied electric field towards their putative binding site in the gate domain. Based on our simulations, we propose a tilt and shift mechanism of the helices surrounding the ion binding cavity as the working principle of the reported conformational changes in complete transporters.
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Wang Z, Wang Q, Wu H, Huang Z. Identification and characterization of amphibian SLC26A5 using RNA-Seq. BMC Genomics 2021; 22:564. [PMID: 34294052 PMCID: PMC8296623 DOI: 10.1186/s12864-021-07798-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 06/10/2021] [Indexed: 11/17/2022] Open
Abstract
Background Prestin (SLC26A5) is responsible for acute sensitivity and frequency selectivity in the vertebrate auditory system. Limited knowledge of prestin is from experiments using site-directed mutagenesis or domain-swapping techniques after the amino acid residues were identified by comparing the sequence of prestin to those of its paralogs and orthologs. Frog prestin is the only representative in amphibian lineage and the studies of it were quite rare with only one species identified. Results Here we report a new coding sequence of SLC26A5 for a frog species, Rana catesbeiana (the American bullfrog). In our study, the SLC26A5 gene of Rana has been mapped, sequenced and cloned successively using RNA-Seq. We measured the nonlinear capacitance (NLC) of prestin both in the hair cells of Rana’s inner ear and HEK293T cells transfected with this new coding gene. HEK293T cells expressing Rana prestin showed electrophysiological features similar to that of hair cells from its inner ear. Comparative studies of zebrafish, chick, Rana and an ancient frog species showed that chick and zebrafish prestin lacked NLC. Ancient frog’s prestin was functionally different from Rana. Conclusions We mapped and sequenced the SLC26A5 of the Rana catesbeiana from its inner ear cDNA using RNA-Seq. The Rana SLC26A5 cDNA was 2292 bp long, encoding a polypeptide of 763 amino acid residues, with 40% identity to mammals. This new coding gene could encode a functionally active protein conferring NLC to both frog HCs and the mammalian cell line. While comparing to its orthologs, the amphibian prestin has been evolutionarily changing its function and becomes more advanced than avian and teleost prestin.
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Affiliation(s)
- Zhongying Wang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Qixuan Wang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Hao Wu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. .,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China. .,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China.
| | - Zhiwu Huang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. .,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China. .,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China.
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31
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Wang Z, Ma Q, Lu J, Cui X, Chen H, Wu H, Huang Z. Functional Parameters of Prestin Are Not Correlated With the Best Hearing Frequency. Front Cell Dev Biol 2021; 9:638530. [PMID: 34046403 PMCID: PMC8144510 DOI: 10.3389/fcell.2021.638530] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 03/23/2021] [Indexed: 11/29/2022] Open
Abstract
Among the vertebrate lineages with different hearing frequency ranges, humans lie between the low-frequency hearing (1 kHz) of fish and amphibians and the high-frequency hearing (100 kHz) of bats and dolphins. Little is known about the mechanism underlying such a striking difference in the limits of hearing frequency. Prestin, responsible for cochlear amplification and frequency selectivity in mammals, seems to be the only candidate to date. Mammalian prestin is densely expressed in the lateral plasma membrane of the outer hair cells (OHCs) and functions as a voltage-dependent motor protein. To explore the molecular basis for the contribution of prestin in hearing frequency detection, we collected audiogram data from humans, dogs, gerbils, bats, and dolphins because their average hearing frequency rises in steps. We generated stable cell lines transfected with human, dog, gerbil, bat, and dolphin prestins (hPres, dPres, gPres, bPres, and nPres, respectively). The non-linear capacitance (NLC) of different prestins was measured using a whole-cell patch clamp. We found that the Qmax/Clin of bPres and nPres was significantly higher than that of humans. The V1/2 of hPres was more hyperpolarized than that of nPres. The z values of hPres and bPres were higher than that of nPres. We further analyzed the relationship between the high-frequency hearing limit (Fmax) and the functional parameters (V1/2, z, and Qmax/Clin) of NLC among five prestins. Interestingly, no significant correlation was found between the functional parameters and Fmax. Additionally, a comparative study showed that the amino acid sequences and tertiary structures of five prestins were quite similar. There might be a common fundamental mechanism driving the function of prestins. These findings call for a reconsideration of the leading role of prestin in hearing frequency perception. Other intriguing kinetics underlying the hearing frequency response of auditory organs might exist.
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Affiliation(s)
- Zhongying Wang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Qingping Ma
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Jiawen Lu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Xiaochen Cui
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, Department of Bioinformatics and Biostatistics, National Experimental Teaching Center for Life Sciences and Biotechnology, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Haifeng Chen
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, Department of Bioinformatics and Biostatistics, National Experimental Teaching Center for Life Sciences and Biotechnology, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China.,Shanghai Center for Bioinformation Technology, Shanghai, China
| | - Hao Wu
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
| | - Zhiwu Huang
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China.,Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China
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32
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Effertz T, Moser T, Oliver D. Recent advances in cochlear hair cell nanophysiology: subcellular compartmentalization of electrical signaling in compact sensory cells. Fac Rev 2021; 9:24. [PMID: 33659956 PMCID: PMC7886071 DOI: 10.12703/r/9-24] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In recent years, genetics, physiology, and structural biology have advanced into the molecular details of the sensory physiology of auditory hair cells. Inner hair cells (IHCs) and outer hair cells (OHCs) mediate two key functions: active amplification and non-linear compression of cochlear vibrations by OHCs and sound encoding by IHCs at their afferent synapses with the spiral ganglion neurons. OHCs and IHCs share some molecular physiology, e.g. mechanotransduction at the apical hair bundles, ribbon-type presynaptic active zones, and ionic conductances in the basolateral membrane. Unique features enabling their specific function include prestin-based electromotility of OHCs and indefatigable transmitter release at the highest known rates by ribbon-type IHC active zones. Despite their compact morphology, the molecular machineries that either generate electrical signals or are driven by these signals are essentially all segregated into local subcellular structures. This review provides a brief account on recent insights into the molecular physiology of cochlear hair cells with a specific focus on organization into membrane domains.
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Affiliation(s)
- Thomas Effertz
- InnerEarLab, Department of Otorhinolaryngology, University Medical Center Göttingen, 37099 Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37099 Göttingen, Germany
- Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
- Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
- Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, 37075 Göttingen, Germany
| | - Dominik Oliver
- Institute for Physiology and Pathophysiology, Philipps University, Deutschhausstraße 2, 35037 Marburg, Germany
- Center for Mind, Brain and Behavior (CMBB), Universities of Marburg and Giessen, Germany
- DFG Research Training Group, Membrane Plasticity in Tissue Development and Remodelling, GRK 2213, Philipps University, Marburg, Germany
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33
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Iwasa KH. Kinetic Membrane Model of Outer Hair Cells. Biophys J 2020; 120:122-132. [PMID: 33248133 PMCID: PMC7820742 DOI: 10.1016/j.bpj.2020.11.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 10/12/2020] [Accepted: 11/17/2020] [Indexed: 12/02/2022] Open
Abstract
The effectiveness of outer hair cells (OHCs) in amplifying the motion of the organ of Corti, and thereby contributing to the sensitivity of mammalian hearing, depends on the mechanical power output of these cells. Electromechanical coupling in OHCs, which enables these cells to convert electrical energy into mechanical energy, has been analyzed in detail using isolated cells using primarily static membrane models. The mechanical output of OHCs was previously evaluated by developing a kinetic theory based on a simplified one-dimensional model for OHCs. Here, a kinetic description of OHCs is extended by using the membrane model, which was used for analyzing in vitro experiments. This theory predicts, for systems without inertial load, that elastic load enhances positive shift of voltage dependence of the membrane capacitance because of turgor pressure. The effect of turgor pressure increases with increasing elastic load. For systems with inertia, the magnitude of mechanical power output could be ∼5% higher than the value predicted by the one-dimensional model at the optimal turgor pressure.
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Affiliation(s)
- Kuni H Iwasa
- National Institutes of Health, NIDCD, Bethesda, Maryland.
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34
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Abstract
Cochlear outer hair cells (OHCs) are among the fastest known biological motors and are essential for high-frequency hearing in mammals. It is commonly hypothesized that OHCs amplify vibrations in the cochlea through cycle-by-cycle changes in length, but recent data suggest OHCs are low-pass filtered and unable to follow high-frequency signals. The fact that OHCs are required for high-frequency hearing but appear to be throttled by slow electromotility is the "OHC speed paradox." The present report resolves this paradox and reveals origins of ultrafast OHC function and power output in the context of the cochlear load. Results demonstrate that the speed of electromotility reflects how fast the cell can extend against the load, and does not reflect the intrinsic speed of the motor element itself or the nearly instantaneous speed at which the coulomb force is transmitted. OHC power output at auditory frequencies is revealed by emergence of an imaginary nonlinear capacitance reflecting the phase of electrical charge displacement required for the motor to overcome the viscous cochlear load.
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Affiliation(s)
- Richard D Rabbitt
- Biomedical Engineering, Otolaryngology, and Neuroscience Program, University of Utah, Salt Lake City, UT 84112
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35
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An In Vitro Study on Prestin Analog Gene in the Bullfrog Hearing Organs. Neural Plast 2020; 2020:3570732. [PMID: 32714383 PMCID: PMC7352134 DOI: 10.1155/2020/3570732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 04/22/2020] [Accepted: 05/20/2020] [Indexed: 11/18/2022] Open
Abstract
The prestin-based active process in the mammalian outer hair cells (OHCs) is believed to play a crucial role in auditory signal amplification in the cochlea. Prestin belongs to an anion transporter family (SLC26A). It is densely expressed in the OHC lateral plasma membrane and functions as a voltage-dependent motor protein. Analog genes can be found in the genome of nonmammalian species, but their functions in hearing are poorly understood. In the present study, we used the gerbil prestin sequence as a template and identified an analog gene in the bullfrog genome. We expressed the gene in a stable cell line (HEK293T) and performed patch-clamp recording. We found that these cells exhibited prominent nonlinear capacitance (NLC), a widely accepted assay for prestin functioning as a motor protein. Upon close examination, the key parameters of this NLC are comparable to that conferred by the gerbil prestin, and nontransfected cells failed to display NLC. Lastly, we performed patch-clamp recording in HCs of all three hearing organs in bullfrog. HCs in both the sacculus and the amphibian papilla exhibited a capacitance profile that is similar to NLC while HCs in the basilar papilla showed no sign of NLC. Whether or not this NLC-like capacitance change is involved in auditory signal amplification certainly requires further examination; our results represent the first and necessary step in revealing possible roles of prestin in the active hearing processes found in many nonmammalian species.
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36
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Jabeen T, Holt JC, Becker JR, Nam JH. Interactions between Passive and Active Vibrations in the Organ of Corti In Vitro. Biophys J 2020; 119:314-325. [PMID: 32579963 DOI: 10.1016/j.bpj.2020.06.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 04/23/2020] [Accepted: 06/11/2020] [Indexed: 01/19/2023] Open
Abstract
High sensitivity and selectivity of hearing require an active cochlea. The cochlear sensory epithelium, the organ of Corti, vibrates because of external and internal excitations. The external stimulation is acoustic pressures mediated by the scala fluids, whereas the internal excitation is generated by a type of sensory receptor cells (the outer hair cells) in response to the acoustic vibrations. The outer hair cells are cellular actuators that are responsible for cochlear amplification. The organ of Corti is highly structured for transmitting vibrations originating from acoustic pressure and active outer hair cell force to the inner hair cells that synapse on afferent nerves. Understanding how the organ of Corti vibrates because of acoustic pressure and outer hair cell force is critical for explaining cochlear function. In this study, cochleae were freshly isolated from young gerbils. The organ of Corti in the excised cochlea was subjected to mechanical and electrical stimulation that are analogous to acoustic and cellular stimulation in the natural cochlea. Organ of Corti vibrations, including those of individual outer hair cells, were measured using optical coherence tomography. Respective vibration patterns due to mechanical and electrical stimulation were characterized. Interactions between the two vibration patterns were investigated by applying the two forms of stimulation simultaneously. Our results show that the interactions could be either constructive or destructive, which implies that the outer hair cells can either amplify or reduce vibrations in the organ of Corti. We discuss a potential consequence of the two interaction modes for cochlear frequency tuning.
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Affiliation(s)
- Talat Jabeen
- Department of Biomedical Engineering, University of Rochester, Rochester, New York
| | - Joseph C Holt
- Department of Otolaryngology, University of Rochester, Rochester, New York; Department of Neuroscience, University of Rochester, Rochester, New York; Department of Pharmacology and Physiology, University of Rochester, Rochester, New York
| | - Jonathan R Becker
- Department of Mechanical Engineering, University of Rochester, Rochester, New York
| | - Jong-Hoon Nam
- Department of Biomedical Engineering, University of Rochester, Rochester, New York; Department of Mechanical Engineering, University of Rochester, Rochester, New York; Department of Neuroscience, University of Rochester, Rochester, New York.
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37
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Li H, Lv J, Zhou Q, Jin L, Kang Z, Huang Y. Establishment of sperm associated antigen 6 gene knockout mouse model and its mechanism of deafness. Saudi J Biol Sci 2020; 27:1289-1295. [PMID: 32346337 PMCID: PMC7182980 DOI: 10.1016/j.sjbs.2020.03.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 02/28/2020] [Accepted: 03/08/2020] [Indexed: 11/01/2022] Open
Abstract
To investigate the effects of knocking out the Sperm associated antigen6 (Spag6) gene on the auditory system of mice, the heterozygous type Spag6 knockout mouse model built in the previous period was used for mating and breeding, and homozygous type Spag6 gene knockout mouse (Spag-/-), heterozygous type Spag6 gene knockout mouse (Spag+/-) and wild type mouse (Spag+/+) were obtained. PCR technology was used to verify mouse models with different genotypes. After verification, the hearing threshold responses of Spag+/+ and Spag-/- genotype mice were detected. The localization of Spag6 gene in the basal membrane of the cochlea of the inner ear was detected by immunofluorescence staining. The changes of middle ear tissues were observed by H.E. staining sections. The relative expression of Prestin gene and Pgrn gene in different age mice was detected by fluorescence quantitative PCR. The relative expression of Prestin gene was detected by western blot. The results showed that Spag-/- mice had hearing impairment compared with Spag+/+ mice. And Spag6 protein is distributed in different genotypes of mouse hair cells; Spag-/- mice showed otitis media. The expression of Prestin mRNA and protein in Spag-/- mice was significantly higher than that in Spag+/+ mice (P < 0.01). The expression of Pgrn gene in Spag+/+ mice was significantly higher than that in Spag-/- mice (P < 0.05). It indicates that the loss of Spag6 gene would lead to the decline of hearing sense in mice. It is likely that the Spag6 gene could affect hearing by regulating the expression of Prestin gene. And the absence of the Spag6 gene causes otitis media in mice. The results of this study can lay a theoretical foundation for the follow-up studies of Spag6 gene in deafness diseases.
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Affiliation(s)
- He Li
- Department of Otolaryngology, First Affiliated Hospital of Wenzhou Medical University, Wenzhou city 325000, Zhejiang Province, China
| | - Jun Lv
- Department of Otolaryngology, First Affiliated Hospital of Wenzhou Medical University, Wenzhou city 325000, Zhejiang Province, China
| | - Qinshuang Zhou
- Department of Otolaryngology, First Affiliated Hospital of Wenzhou Medical University, Wenzhou city 325000, Zhejiang Province, China
| | - Lanlan Jin
- Department of Otolaryngology, First Affiliated Hospital of Wenzhou Medical University, Wenzhou city 325000, Zhejiang Province, China
| | - Zonghui Kang
- Department of Otolaryngology, Affiliated Wenzhou Hospital, Zhejiang University of Traditional Chinese Medicine, Wenzhou city 325000, Zhejiang Province, China
| | - Yideng Huang
- Department of Otolaryngology, First Affiliated Hospital of Wenzhou Medical University, Wenzhou city 325000, Zhejiang Province, China
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38
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Santos-Sacchi J, Tan W. Complex nonlinear capacitance in outer hair cell macro-patches: effects of membrane tension. Sci Rep 2020; 10:6222. [PMID: 32277153 PMCID: PMC7148382 DOI: 10.1038/s41598-020-63201-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Accepted: 03/26/2020] [Indexed: 11/18/2022] Open
Abstract
Outer hair cell (OHC) nonlinear capacitance (NLC) represents voltage sensor charge movements of prestin (SLC26a5), the protein responsible for OHC electromotility. Previous measures of NLC frequency response have employed methods which did not assess the influence of dielectric loss (sensor charge movements out of phase with voltage) that may occur, and such loss conceivably may influence prestin's frequency dependent activity. Here we evaluate prestin's complex capacitance out to 30 kHz and find that prestin's frequency response determined using this approach coincides with all previous estimates. We also show that membrane tension has no effect on prestin's frequency response, despite substantial shifts in its voltage operating range, indicating that prestin transition rate alterations do not account for the shifts. The magnitude roll-off of prestin activity across frequency surpasses the reductions of NLC caused by salicylate treatments that are known to abolish cochlear amplification. Such roll-off likely limits the effectiveness of prestin in contributing to cochlear amplification at the very high acoustic frequencies processed by some mammals.
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Affiliation(s)
- Joseph Santos-Sacchi
- Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA.
- Neuroscience, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA.
- Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA.
| | - Winston Tan
- Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA
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39
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Perez-Flores MC, Lee JH, Park S, Zhang XD, Sihn CR, Ledford HA, Wang W, Kim HJ, Timofeyev V, Yarov-Yarovoy V, Chiamvimonvat N, Rabbitt RD, Yamoah EN. Cooperativity of K v7.4 channels confers ultrafast electromechanical sensitivity and emergent properties in cochlear outer hair cells. SCIENCE ADVANCES 2020; 6:eaba1104. [PMID: 32285007 PMCID: PMC7141818 DOI: 10.1126/sciadv.aba1104] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 01/14/2020] [Indexed: 05/22/2023]
Abstract
The mammalian cochlea relies on active electromotility of outer hair cells (OHCs) to resolve sound frequencies. OHCs use ionic channels and somatic electromotility to achieve the process. It is unclear, though, how the kinetics of voltage-gated ionic channels operate to overcome extrinsic viscous drag on OHCs at high frequency. Here, we report ultrafast electromechanical gating of clustered Kv7.4 in OHCs. Increases in kinetics and sensitivity resulting from cooperativity among clustered-Kv7.4 were revealed, using optogenetics strategies. Upon clustering, the half-activation voltage shifted negative, and the speed of activation increased relative to solitary channels. Clustering also rendered Kv7.4 channels mechanically sensitive, confirmed in consolidated Kv7.4 channels at the base of OHCs. Kv7.4 clusters provide OHCs with ultrafast electromechanical channel gating, varying in magnitude and speed along the cochlea axis. Ultrafast Kv7.4 gating provides OHCs with a feedback mechanism that enables the cochlea to overcome viscous drag and resolve sounds at auditory frequencies.
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Affiliation(s)
- Maria C. Perez-Flores
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Jeong H. Lee
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Seojin Park
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Xiao-Dong Zhang
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655, USA
| | - Choong-Ryoul Sihn
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Hannah A. Ledford
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
| | - Wenying Wang
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Hyo Jeong Kim
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
| | - Valeriy Timofeyev
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655, USA
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA 95616, USA
| | - Nipavan Chiamvimonvat
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, CA 95616, USA
- Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655, USA
| | - Richard D. Rabbitt
- Departments of Biomedical Engineering, Otolaryngology, and Neuroscience Program, University of Utah, Salt Lake City, UT 84112, USA
- Corresponding author. (E.N.Y.); (R.D.R.)
| | - Ebenezer N. Yamoah
- Department of Physiology, School of Medicine, University of Nevada, Reno, Reno, NV 89557, USA
- Corresponding author. (E.N.Y.); (R.D.R.)
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40
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Zhai F, Song L, Bai JP, Dai C, Navaratnam D, Santos-Sacchi J. Maturation of Voltage-induced Shifts in SLC26a5 (Prestin) Operating Point during Trafficking and Membrane Insertion. Neuroscience 2020; 431:128-133. [PMID: 32061780 DOI: 10.1016/j.neuroscience.2020.02.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Revised: 01/31/2020] [Accepted: 02/04/2020] [Indexed: 12/24/2022]
Abstract
Prestin (SLC26a5) is an integral membrane motor protein in outer hair cells (OHC) that underlies cochlear amplification. As a voltage-dependent protein, it relies on intrinsic sensor charge to respond to transmembrane voltage (receptor potentials), thereby effecting conformational changes. The protein's electromechanical actively is experimentally monitored as a bell-shaped nonlinear capacitance (NLC), whose magnitude peaks at a characteristic voltage, Vh. This voltage denotes the midpoint of prestin's charge-voltage (Q-V) Boltzmann distribution and region of maximum gain of OHC electromotility. It is an important factor in hearing capabilities for mammals. A variety of biophysical forces can influence the distribution of charge, gauged by shifts in Vh, including prior holding voltage or membrane potential. Here we report that the effectiveness of prior voltage augments during the delivery of prestin to the membranes in an inducible HEK cell line. The augmentation coincides with an increase in prestin density, maturing at a characteristic membrane areal density of 870 functional prestin units per square micrometer, and is likely indicative of prestin-prestin cooperative interactions.
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Affiliation(s)
- Feng Zhai
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA; Department of Otolaryngology, Shanghai Children's Medical Center, Shanghai Jiao Tong University School of Medicine, Shanghai 200127, China
| | - Lei Song
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA; Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
| | - Jun-Ping Bai
- Department of Neurology, Yale University School of Medicine, New Haven, CT, USA
| | - Chunfu Dai
- Department of Otology and Skull Base Surgery, Eye Ear Nose and Throat Hospital, Fudan University, Shanghai, China
| | - Dhasakumar Navaratnam
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA; Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA; Department of Neurology, Yale University School of Medicine, New Haven, CT, USA
| | - Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT, USA; Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA; Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA.
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41
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Diverse Mechanisms of Sound Frequency Discrimination in the Vertebrate Cochlea. Trends Neurosci 2020; 43:88-102. [PMID: 31954526 DOI: 10.1016/j.tins.2019.12.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Revised: 12/05/2019] [Accepted: 12/10/2019] [Indexed: 01/17/2023]
Abstract
Discrimination of different sound frequencies is pivotal to recognizing and localizing friend and foe. Here, I review the various hair cell-tuning mechanisms used among vertebrates. Electrical resonance, filtering of the receptor potential by voltage-dependent ion channels, is ubiquitous in all non-mammals, but has an upper limit of ~1 kHz. The frequency range is extended by mechanical resonance of the hair bundles in frogs and lizards, but may need active hair-bundle motion to achieve sharp tuning up to 5 kHz. Tuning in mammals uses somatic motility of outer hair cells, underpinned by the membrane protein prestin, to expand the frequency range. The bird cochlea may also use prestin at high frequencies, but hair cells <1 kHz show electrical resonance.
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Santos-Sacchi J, Iwasa KH, Tan W. Outer hair cell electromotility is low-pass filtered relative to the molecular conformational changes that produce nonlinear capacitance. J Gen Physiol 2019; 151:1369-1385. [PMID: 31676485 PMCID: PMC6888751 DOI: 10.1085/jgp.201812280] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Revised: 08/24/2019] [Accepted: 09/30/2019] [Indexed: 11/20/2022] Open
Abstract
The outer hair cell (OHC) of the organ of Corti underlies a process that enhances hearing, termed cochlear amplification. The cell possesses a unique voltage-sensing protein, prestin, that changes conformation to cause cell length changes, a process termed electromotility (eM). The prestin voltage sensor generates a capacitance that is both voltage- and frequency-dependent, peaking at a characteristic membrane voltage (Vh), which can be greater than the linear capacitance of the OHC. Accordingly, the OHC membrane time constant depends upon resting potential and the frequency of AC stimulation. The confounding influence of this multifarious time constant on eM frequency response has never been addressed. After correcting for this influence on the whole-cell voltage clamp time constant, we find that both guinea pig and mouse OHC eM is low pass, substantially attenuating in magnitude within the frequency bandwidth of human speech. The frequency response is slowest at Vh, with a cut-off, approximated by single Lorentzian fits within that bandwidth, near 1.5 kHz for the guinea pig OHC and near 4.3 kHz for the mouse OHC, each increasing in a U-shaped manner as holding voltage deviates from Vh Nonlinear capacitance (NLC) measurements follow this pattern, with cut-offs about double that for eM. Macro-patch experiments on OHC lateral membranes, where voltage delivery has high fidelity, confirms low pass roll-off for NLC. The U-shaped voltage dependence of the eM roll-off frequency is consistent with prestin's voltage-dependent transition rates. Modeling indicates that the disparity in frequency cut-offs between eM and NLC may be attributed to viscoelastic coupling between prestin's molecular conformations and nanoscale movements of the cell, possibly via the cytoskeleton, indicating that eM is limited by the OHC's internal environment, as well as the external environment. Our data suggest that the influence of OHC eM on cochlear amplification at higher frequencies needs reassessment.
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Affiliation(s)
- Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT
| | - Kuni H Iwasa
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD
| | - Winston Tan
- Department of Surgery (Otolaryngology), Yale University School of Medicine, New Haven, CT
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43
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Santos-Sacchi J, Tan W. Voltage Does Not Drive Prestin (SLC26a5) Electro-Mechanical Activity at High Frequencies Where Cochlear Amplification Is Best. iScience 2019; 22:392-399. [PMID: 31812809 PMCID: PMC6911985 DOI: 10.1016/j.isci.2019.11.036] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 11/13/2019] [Accepted: 11/18/2019] [Indexed: 11/25/2022] Open
Abstract
Cochlear amplification denotes a boost to auditory sensitivity and selectivity that is dependent on outer hair cells from Corti's organ. Voltage-driven electromotility of the cell is believed to feed energy back into the cochlear partition via a cycle-by-cycle mechanism at very high acoustic frequencies. Here we show using wide-band macro-patch voltage-clamp to drive prestin, the molecular motor underlying electromotility, that its voltage-sensor charge movement is unusually low pass in nature, being incapable of following high-frequency voltage changes. Our data are incompatible with a cycle-by-cycle mechanism responsible for high-frequency tuning in mammals. Outer hair cells (OHC) boost auditory sensation for very high acoustic frequencies We studied the frequency response of OHC's electromechanical nonlinear capacitance The response is incommensurate with cycle-by-cycle feedback at very high frequencies OHCs likely use another mechanism to drive cochlear amplification at high frequencies
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Affiliation(s)
- Joseph Santos-Sacchi
- Surgery (Otolaryngology), Yale University School of Medicine, BML 224, 333 Cedar Street, New Haven, CT 06510, USA; Neuroscience, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA; Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA.
| | - Winston Tan
- Surgery (Otolaryngology), Yale University School of Medicine, BML 224, 333 Cedar Street, New Haven, CT 06510, USA
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Bai JP, Navaratnam D, Santos-Sacchi J. Prestin kinetics and corresponding frequency dependence augment during early development of the outer hair cell within the mouse organ of Corti. Sci Rep 2019; 9:16460. [PMID: 31712635 PMCID: PMC6848539 DOI: 10.1038/s41598-019-52965-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 10/25/2019] [Indexed: 12/23/2022] Open
Abstract
Several studies have documented the early development of OHC electromechanical behavior. The mechanical response (electromotility, eM) and its electrical correlate (nonlinear capacitance, NLC), resulting from prestin's voltage-sensor charge movement, increase over the course of several postnatal days in altricial animals. They increase until about p18, near the time of peripheral auditory maturity. The correspondence of auditory capabilities and prestin function indicates that mature activity of prestin occurs at this time. One of the major requirements of eM is its responsiveness across auditory frequencies. Here we evaluate the frequency response of prestin charge movement in mice over the course of development up to 8 months. We find that in apical turn OHCs prestin's frequency response increases during postnatal development and stabilizes when mature hearing is established. The low frequency component of NLC, within in situ explants, agrees with previously reported results on isolated cells. If prestin activity is independent of cochlear place, as might be expected, then these observations suggest that prestin activity somehow influences cochlear amplification at high frequencies in spite of its low pass behavior.
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Affiliation(s)
- Jun-Ping Bai
- Department of Neurology, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA
| | - Dhasakumar Navaratnam
- Department of Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar St, New Haven CT, USA.,Department of Neuroscience, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA.,Department of Neurology, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA
| | - Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology), Yale University School of Medicine, 333 Cedar St, New Haven CT, USA. .,Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA. .,Department of Neuroscience, Yale University School of Medicine, 333 Cedar St, New Haven CT, USA.
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45
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Vavakou A, Cooper NP, van der Heijden M. The frequency limit of outer hair cell motility measured in vivo. eLife 2019; 8:47667. [PMID: 31547906 PMCID: PMC6759357 DOI: 10.7554/elife.47667] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2019] [Accepted: 08/27/2019] [Indexed: 11/29/2022] Open
Abstract
Outer hair cells (OHCs) in the mammalian ear exhibit electromotility, electrically driven somatic length changes that are thought to mechanically amplify sound-evoked vibrations. For this amplification to work, OHCs must respond to sounds on a cycle-by-cycle basis even at frequencies that exceed the low-pass corner frequency of their cell membranes. Using in vivo optical vibrometry we tested this theory by measuring sound-evoked motility in the 13–25 kHz region of the gerbil cochlea. OHC vibrations were strongly rectified, and motility exhibited first-order low-pass characteristics with corner frequencies around 3 kHz– more than 2.5 octaves below the frequencies the OHCs are expected to amplify. These observations lead us to suggest that the OHCs operate more like the envelope detectors in a classical gain-control scheme than like high-frequency sound amplifiers. These findings call for a fundamental reconsideration of the role of the OHCs in cochlear function and the causes of cochlear hearing loss. Our ears give us our sense of hearing. Their job is to collect sounds and pass this information on to the brain. Hair cells, a special group of cells in the ear, are responsible for detecting sound vibrations and turning them into the electrical signals that our brains can understand. The ear contains two populations of hair cells: inner hair cells that send signals to the brain, and outer hair cells that act as a protective ‘buffer’ by modulating sound vibrations entering the innermost part of the ear. When outer hair cells are damaged, the vibrations picked up by inner hair cells are much smaller than in a healthy ear. This has led to the idea that outer hair cells actively amplify sounds before passing them on. That is, outer hair cells simultaneously act like microphones (by receiving sound from the environment) and loudspeakers (by re-emitting magnified vibrations). One problem with this amplifier theory is that it cannot explain how some animals are able to hear extremely high-pitched sounds. If the theory is true, outer hair cells should be able to re-emit ultrasonic vibrations. However, some observations suggest that they may not vibrate fast enough to do so. To test the amplifier theory, Vavakou et al. measured how outer hair cells in the ear of Mongolian gerbils responded to different sounds. This revealed that the motion of these cells could keep up with moderately high sounds (around the upper end of a piano’s range), but were too sluggish to amplify ultrasound despite gerbils having good ultrasonic hearing. Further experiments showed that instead of acting like amplifiers, outer hair cells seem to monitor the loudness of sound and adjust the level accordingly before passing the vibrations on to the inner hair cells. These results shed new light on how outer hair cells help our ears work. Since damage to these cells can cause hearing loss, understanding how they work could one day guide new methods of protecting or even restoring hearing in vulnerable patients.
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Affiliation(s)
- Anna Vavakou
- Department of Neuroscience, Erasmus MC, Rotterdam, Netherlands
| | - Nigel P Cooper
- Department of Neuroscience, Erasmus MC, Rotterdam, Netherlands
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46
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Abstract
The outer hair cell of Corti's organ provides mechanical feedback into the organ to boost auditory perception. The fidelity of voltage-dependent motility has been estimated to extend beyond 50 kHz, where its force generation is deemed a requirement for sensitive high-frequency mammalian hearing. Recent investigations have shown, however, that the frequency response is substantially more low pass at physiological membrane potentials where the kinetics of prestin impose their speed limit. Nevertheless, it is likely that the reduced magnitude of electromotility is sufficient to drive cochlear amplification at high frequencies.
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Affiliation(s)
- J Santos-Sacchi
- Surgery (Otolaryngology), Neuroscience, and Cellular and Molecular Physiology, Yale University School of Medicine, BML 224, 333 Cedar Street, CT 06510, New Haven, USA.
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47
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Diao H, Zhao L, Qin L, Bai W, Wang K, Zhang J, Chen X, Jiang H, Mao L. Lower expression of prestin and MYO7A correlates with menopause-associated hearing loss. Climacteric 2019; 22:361-369. [PMID: 30612476 DOI: 10.1080/13697137.2018.1547698] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- H. Diao
- Peking University Ninth School of Clinical Medicine, Beijing Shi, China
| | - L. Zhao
- Chinese PLA General Hospital, Beijing Shi, China
| | - L. Qin
- Peking University Health Science Centre, Beijing Shi, China
| | - W. Bai
- Peking University Ninth School of Clinical Medicine, Beijing Shi, China
| | - K. Wang
- Peking University Health Science Centre, Beijing Shi, China
| | - J. Zhang
- Peking University Ninth School of Clinical Medicine, Beijing Shi, China
| | - X. Chen
- Peking University First Hospital, Beijing Shi, China
| | - H. Jiang
- Peking University Health Science Centre, Beijing Shi, China
| | - L. Mao
- Peking University First Hospital, Beijing Shi, China
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48
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He W, Kemp D, Ren T. Timing of the reticular lamina and basilar membrane vibration in living gerbil cochleae. eLife 2018; 7:37625. [PMID: 30183615 PMCID: PMC6125122 DOI: 10.7554/elife.37625] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Accepted: 08/14/2018] [Indexed: 12/22/2022] Open
Abstract
Auditory sensory outer hair cells are thought to amplify sound-induced basilar membrane vibration through a feedback mechanism to enhance hearing sensitivity. For optimal amplification, the outer hair cell-generated force must act on the basilar membrane at an appropriate time at every cycle. However, the temporal relationship between the outer hair cell-driven reticular lamina vibration and the basilar membrane vibration remains unclear. By measuring sub-nanometer vibrations directly from outer hair cells using a custom-built heterodyne low-coherence interferometer, we demonstrate in living gerbil cochleae that the reticular lamina vibration occurs after, not before, the basilar membrane vibration. Both tone- and click-induced responses indicate that the reticular lamina and basilar membrane vibrate in opposite directions at the cochlear base and they oscillate in phase near the best-frequency location. Our results suggest that outer hair cells enhance hearing sensitivity through a global hydromechanical mechanism, rather than through a local mechanical feedback as commonly supposed. What is the quietest sound the ear can detect? All sounds begin as vibrating air molecules, which enter the ear and cause the eardrum to vibrate. We can detect vibrations that move the eardrum by a distance of less than one picometer. That’s one thousandth of a nanometer, or about 100 times smaller than a hydrogen atom. But how does the ear achieve this level of sensitivity? Vibrations of the eardrum cause three small bones within the middle ear to vibrate. The vibrations then spread to the cochlea, a fluid-filled spiral structure in the inner ear. Tiny hair cells lining the cochlea move as a result of the vibrations. There are two types of hair cells: inner and outer. Outer hair cells amplify the vibrations. It is this amplification that enables us to detect such small movements of the eardrum. Inner hair cells then convert the amplified vibrations into electrical signals, which travel via the auditory nerve to the brain. The bases of outer hair cells are connected to a structure called the basilar membrane, while their tops are anchored to a structure called the reticular lamina. It was generally assumed that outer hair cells amplify vibrations of the basilar membrane via a local positive feedback mechanism that requires the hair cells to vibrate first. But by comparing the timing of reticular lamina and basilar membrane vibrations in gerbils, He et al. show that this is not the case. Outer hair cells vibrate after the basilar membrane, not before. This indicates that outer hair cells use a mechanism other than commonly assumed local feedback to amplify sounds. The results presented by He et al. change our understanding of how the cochlea works, and may help bioengineers to design better hearing aids and cochlea implants. Millions of patients worldwide who suffer from hearing loss may ultimately stand to benefit.
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Affiliation(s)
- Wenxuan He
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, United States
| | - David Kemp
- University College London Ear Institute, University College London, London, United Kingdom
| | - Tianying Ren
- Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health & Science University, Portland, United States
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