1
|
Takahashi S, Zhou Y, Cheatham MA, Homma K. The frequency dependence of prestin-mediated fast electromotility for mammalian cochlear amplification. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.22.595389. [PMID: 38826260 PMCID: PMC11142200 DOI: 10.1101/2024.05.22.595389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Prestin's voltage-driven motor activity confers sound-elicited somatic electromotility in auditory outer hair cells (OHCs) and is essential for the exquisite sensitivity and frequency selectivity of mammalian hearing. Lack of prestin results in hearing threshold shifts across frequency, supporting the causal association of variants in the prestin-coding gene, SLC26A5 , with human hearing loss, DFNB61. However, cochlear function can tolerate reductions in prestin-mediated OHC electromotility. We found that two deafness-associated prestin variants, p.A100T and p.P119S, do not deprive prestin of its fast motor function but significantly reduce membrane expression, leading to large reductions in OHC electromotility that were only ∼30% of wildtype (WT). Mice harboring these missense variants suffered congenital hearing loss that was worse at high frequencies; however, they retained WT-like auditory brainstem response thresholds at 8 kHz, which is processed at the apex of the mouse cochlea. This observation suggests the increasing importance of prestin-driven cochlear amplification at higher frequencies relevant to mammalian hearing. The observation also suggests the promising clinical possibility that small enhancements of OHC electromotility could significantly ameliorate DFNB61 hearing loss in human patients. SIGNIFICANCE Prestin is abundantly expressed in the auditory outer hair cells and is essential for normal cochlear operation. Hence, reduction of prestin expression is often taken as indicative of reduced cochlear function in diseased or aged ears. However, this assumption overlooks the fact that cochlear function can tolerate large reductions in prestin motor activity. DFNB61 mouse models generated and characterized in this study provide an opportunity to gauge the amount of prestin motor activity needed to sustain normal hearing sensitivity. This knowledge is crucial not only for understanding the pathogenic roles of deafness-associated variants that impair OHC electromotility but also for unraveling how prestin contributes to cochlear amplification.
Collapse
|
2
|
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.
Collapse
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.
| |
Collapse
|
3
|
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: 9] [Impact Index Per Article: 9.0] [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.
Collapse
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
| |
Collapse
|
4
|
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.
Collapse
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
| |
Collapse
|
5
|
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]
|
6
|
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: 26] [Impact Index Per Article: 13.0] [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.
Collapse
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.
| |
Collapse
|
7
|
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.
Collapse
|
8
|
Molecular mechanism of prestin electromotive signal amplification. Cell 2021; 184:4669-4679.e13. [PMID: 34390643 PMCID: PMC8674105 DOI: 10.1016/j.cell.2021.07.034] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 05/26/2021] [Accepted: 07/23/2021] [Indexed: 11/21/2022]
Abstract
Hearing involves two fundamental processes: mechano-electrical transduction and signal amplification. Despite decades of studies, the molecular bases for both remain elusive. Here, we show how prestin, the electromotive molecule of outer hair cells (OHCs) that senses both voltage and membrane tension, mediates signal amplification by coupling conformational changes to alterations in membrane surface area. Cryoelectron microscopy (cryo-EM) structures of human prestin bound with chloride or salicylate at a common "anion site" adopt contracted or expanded states, respectively. Prestin is ensconced within a perimeter of well-ordered lipids, through which it induces dramatic deformation in the membrane and couples protein conformational changes to the bulk membrane. Together with computational studies, we illustrate how the anion site is allosterically coupled to changes in the transmembrane domain cross-sectional area and the surrounding membrane. These studies provide insight into OHC electromotility by providing a structure-based mechanism of the membrane motor prestin.
Collapse
|
9
|
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.
Collapse
|
10
|
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.
Collapse
|
11
|
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.
Collapse
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
| |
Collapse
|
12
|
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.
Collapse
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.
| |
Collapse
|
13
|
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.
Collapse
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
| |
Collapse
|
14
|
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.
Collapse
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.
| |
Collapse
|
15
|
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.
Collapse
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.
| |
Collapse
|
16
|
Wang Y, Fallah E, Olson ES. Adaptation of Cochlear Amplification to Low Endocochlear Potential. Biophys J 2019; 116:1769-1786. [PMID: 30992124 DOI: 10.1016/j.bpj.2019.03.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 02/14/2019] [Accepted: 03/21/2019] [Indexed: 01/15/2023] Open
Abstract
Endocochlear potential (EP) is essential for cochlear amplification by providing the voltage source needed to drive outer hair cell (OHC) transducer current, which leads to OHC electromechanical force. An early study using furosemide to reversibly reduce EP showed that distortion product otoacoustic emissions (DPOAEs) recovered before EP. This indicated that cochlear amplification may be able to adjust to a new, lower EP. To investigate the mechanism of this adjustment, the extracellular OHC voltage, which we term local cochlear microphonic (LCM), was measured simultaneously with DPOAE and EP while using intraperitoneal (IP) and intravenous injection of furosemide to reversibly reduce EP. With IP injection, the DPOAEs recovered fully, whereas the EP was reduced, but LCM showed a similar time course as EP. The DPOAEs failed to accurately report the variation of cochlear amplification. With intravenous injection, for which both reduction and recovery of EP are known to occur relatively quickly compared to IP, the cochlear amplification observed in LCM could attain nearly full or even full recovery with reduced EP. This showed the cochlea has an ability to adjust to diminished operating condition. Furthermore, the cochlear amplifier and EP recovered with different time courses: cochlear amplification just started to recover after the EP was nearly fully recovered and stabilized. Using a Boltzmann model and the second harmonic of the LCM to estimate the mechanoelectric transducer channel operating point, we found that the recovery of cochlear amplification occurred with recentering of the operating point.
Collapse
Affiliation(s)
- Yi Wang
- Biomedical Engineering, Columbia University, New York, New York
| | - Elika Fallah
- Biomedical Engineering, Columbia University, New York, New York
| | - Elizabeth S Olson
- Biomedical Engineering, Columbia University, New York, New York; Otalaryngology/Head & Neck Surgery, Columbia University, New York, New York.
| |
Collapse
|
17
|
Vachel L, Shcheynikov N, Yamazaki O, Fremder M, Ohana E, Son A, Shin DM, Yamazaki-Nakazawa A, Yang CR, Knepper MA, Muallem S. Modulation of Cl - signaling and ion transport by recruitment of kinases and phosphatases mediated by the regulatory protein IRBIT. Sci Signal 2018; 11:11/554/eaat5018. [PMID: 30377224 DOI: 10.1126/scisignal.aat5018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
IRBIT is a multifunctional protein that controls the activity of various epithelial ion transporters including NBCe1-B. Interaction with IRBIT increases NBCe1-B activity and exposes two cryptic Cl--sensing GXXXP sites that enable regulation of NBCe1-B by intracellular Cl- (Cl- in). Here, phosphoproteomic analysis revealed that IRBIT controlled five phosphorylation sites in NBCe1-B that determined both the active conformation of the transporter and its regulation by Cl- in Mutational analysis suggested that the phosphorylation status of Ser232, Ser233, and Ser235 was regulated by IRBIT and determined whether NBCe1 transporters are in active or inactive conformations. The absence of phosphorylation at Ser232, Ser233, or Ser235 produced NBCe1-B in the conformations pSer233/pSer235, pSer232/pSer235, or pSer232/pSer233, respectively. The activity of the pSer233/pSer235 form was similar to that of IRBIT-activated NBCe1-B, but it was insensitive to inhibition by Cl- in The properties of the pSer232/pSer235 form were similar to those of wild-type NBCe1-B, whereas the pSer232/pSer233 form was partially active, further activated by IRBIT, but retained inhibition by Cl- in Furthermore, IRBIT recruited the phosphatase PP1 and the kinase SPAK to control phosphorylation of Ser65, which affected Cl- in sensing by the 32GXXXP36 motif. IRBIT also recruited the phosphatase calcineurin and the kinase CaMKII to control phosphorylation of Ser12, which affected Cl- in sensing by the 194GXXXP198 motif. Ser232, Ser233, and Ser235 are conserved in all NBCe1 variants and affect their activity. These findings reveal how multiple kinase and phosphatase pathways use phosphorylation sites to fine-tune a transporter, which have important implications for epithelial fluid and HCO3 - secretion.
Collapse
Affiliation(s)
- Laura Vachel
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - Nikolay Shcheynikov
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - Osamu Yamazaki
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.,Apheresis and Dialysis Center/General Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-0016, Japan
| | - Moran Fremder
- Department of Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben Gurion University of the Negev, 84105 Beer Sheva, Israel
| | - Ehud Ohana
- Department of Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben Gurion University of the Negev, 84105 Beer Sheva, Israel
| | - Aran Son
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - Dong Min Shin
- Department of Oral Biology, BK 21 PLUS Project, Yonsei University College of Dentistry, Seoul 120-752, Korea
| | - Ai Yamazaki-Nakazawa
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - Chin-Rang Yang
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Mark A Knepper
- Epithelial Systems Biology Laboratory, Systems Biology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Shmuel Muallem
- Epithelial Signaling and Transport Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
| |
Collapse
|
18
|
Santos-Sacchi J, Tan W. The Frequency Response of Outer Hair Cell Voltage-Dependent Motility Is Limited by Kinetics of Prestin. J Neurosci 2018; 38:5495-5506. [PMID: 29899032 PMCID: PMC6001036 DOI: 10.1523/jneurosci.0425-18.2018] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 05/14/2018] [Accepted: 05/16/2018] [Indexed: 01/07/2023] Open
Abstract
The voltage-dependent protein SLC26a5 (prestin) underlies outer hair cell electromotility (eM), which is responsible for cochlear amplification in mammals. The electrical signature of eM is a bell-shaped nonlinear capacitance (NLC), deriving from prestin sensor-charge (Qp) movements, which peaks at the membrane voltage, Vh, where charge is distributed equally on either side of the membrane. Voltage dependencies of NLC and eM differ depending on interrogation frequency and intracellular chloride, revealing slow intermediate conformational transitions between anion binding and voltage-driven Qp movements. Consequently, NLC exhibits low-pass characteristics, substantially below prevailing estimates of eM frequency response. Here we study in guinea pig and mouse of either sex synchronous prestin electrical (NLC, Qp) and mechanical (eM) activity across frequencies under voltage clamp (whole cell and microchamber). We find that eM and Qp magnitude and phase correspond, indicating tight piezoelectric coupling. Electromechanical measures (both NLC and eM) show dual-Lorentzian, low-pass behavior, with a limiting (τ2) time constant at Vh of 32.6 and 24.8 μs, respectively. As expected for voltage-dependent kinetics, voltage excitation away from Vh has a faster, flatter frequency response, with our fastest measured τ2 for eM of 18.2 μs. Previous observations of ultrafast eM (τ ≈ 2 μs) were obtained at offsets far removed from Vh We hypothesize that trade-offs in eM gain-bandwith arising from voltage excitation at membrane potentials offset from Vh influence the effectiveness of cochlear amplification across frequencies.SIGNIFICANCE STATEMENT Of two types of hair cells within the organ of Corti, inner hair cells and outer hair cells, the latter evolved to boost sensitivity to sounds. Damage results in hearing loss of 40-60 dB, revealing amplification gains of 100-1000× that arise from voltage-dependent mechanical responses [electromotility (eM)]. eM, driven by the membrane protein prestin, may work beyond 70 kHz. However, this speed exceeds, by over an order of magnitude, kinetics of typical voltage-dependent membrane proteins. We find eM is actually low pass in nature, indicating that prestin bears kinetics typical of other membrane proteins. These observations highlight potential difficulties in providing sufficient amplification beyond a cutoff frequency near 20 kHz. Nevertheless, observed trade-offs in eM gain-bandwith may sustain cochlear amplification across frequency.
Collapse
Affiliation(s)
- Joseph Santos-Sacchi
- Department of Surgery (Otolaryngology),
- Department of Neuroscience, and
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
| | | |
Collapse
|
19
|
Bai JP, Moeini-Naghani I, Zhong S, Li FY, Bian S, Sigworth FJ, Santos-Sacchi J, Navaratnam D. Current carried by the Slc26 family member prestin does not flow through the transporter pathway. Sci Rep 2017; 7:46619. [PMID: 28422190 PMCID: PMC5395958 DOI: 10.1038/srep46619] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 03/21/2017] [Indexed: 01/01/2023] Open
Abstract
Prestin in the lateral membrane of outer hair cells, is responsible for electromotility (EM) and a corresponding nonlinear capacitance (NLC). Prestin’s voltage sensitivity is influenced by intracellular chloride. A regulator of intracellular chloride is a stretch-sensitive, non-selective conductance within the lateral membrane, GmetL. We determine that prestin itself possesses a stretch-sensitive, non-selective conductance that is largest in the presence of thiocyanate ions. This conductance is independent of the anion transporter mechanism. Prestin has been modeled, based on structural data from related anion transporters (SLC26Dg and UraA), to have a 7 + 7 inverted repeat structure with anion transport initiated by chloride binding at the intracellular cleft. Mutation of residues that bind intracellular chloride, and salicylate treatment which prevents chloride binding, have no effect on thiocyanate conductance. In contrast, other mutations reduce the conductance while preserving NLC. When superimposed on prestin’s structure, the location of these mutations indicates that the ion permeation pathway lies between the core and gate ring of helices, distinct from the transporter pathway. The uncoupled current is reminiscent of an omega current in voltage-gated ion channels. We suggest that prestin itself is the main regulator of intracellular chloride concentration via a route distinct from its transporter pathway.
Collapse
Affiliation(s)
- Jun-Ping Bai
- Dept. of Neurology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA
| | - Iman Moeini-Naghani
- Dept. of Neurology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA
| | - Sheng Zhong
- Dept. of Surgery, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA
| | - Fang-Yong Li
- Yale Center for Analytical Sciences, Yale School of Public Health, 300 George St., Ste Suite 555, New Haven, CT 06511, USA
| | - Shumin Bian
- Dept. of Neurology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA
| | - Fred J Sigworth
- Dept. of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA
| | - Joseph Santos-Sacchi
- Dept. of Surgery, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA.,Dept. of Cellular and Molecular Physiology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA.,Dept. of, Neuroscience, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA
| | - Dhasakumar Navaratnam
- Dept. of Neurology, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA.,Dept. of Surgery, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510 USA.,Dept. of, Neuroscience, Yale School of Medicine, 333 Cedar Street, New Haven, CT, 06510, USA
| |
Collapse
|