51
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Liu L, Chen Y, Qi J, Zhang Y, He Y, Ni W, Li W, Zhang S, Sun S, Taketo MM, Wang L, Chai R, Li H. Wnt activation protects against neomycin-induced hair cell damage in the mouse cochlea. Cell Death Dis 2016; 7:e2136. [PMID: 26962686 PMCID: PMC4823936 DOI: 10.1038/cddis.2016.35] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 01/11/2016] [Accepted: 01/25/2016] [Indexed: 12/17/2022]
Abstract
Recent studies have reported the role of Wnt/β-catenin signaling in hair cell (HC) development, regeneration, and differentiation in the mouse cochlea; however, the role of Wnt/β-catenin signaling in HC protection remains unknown. In this study, we took advantage of transgenic mice to specifically knockout or overactivate the canonical Wnt signaling mediator β-catenin in HCs, which allowed us to investigate the role of Wnt/β-catenin signaling in protecting HCs against neomycin-induced damage. We first showed that loss of β-catenin in HCs made them more vulnerable to neomycin-induced injury, while constitutive activation of β-catenin in HCs reduced HC loss both in vivo and in vitro. We then showed that loss of β-catenin in HCs increased caspase-mediated apoptosis induced by neomycin injury, while β-catenin overexpression inhibited caspase-mediated apoptosis. Finally, we demonstrated that loss of β-catenin in HCs led to increased expression of forkhead box O3 transcription factor (Foxo3) and Bim along with decreased expression of antioxidant enzymes; thus, there were increased levels of reactive oxygen species (ROS) after neomycin treatment that might be responsible for the increased aminoglycoside sensitivity of HCs. In contrast, β-catenin overexpression reduced Foxo3 and Bim expression and ROS levels, suggesting that β-catenin is protective against neomycin-induced HC loss. Our findings demonstrate that Wnt/β-catenin signaling has an important role in protecting HCs against neomycin-induced HC loss and thus might be a new therapeutic target for the prevention of HC death.
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Affiliation(s)
- L Liu
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Institutes of Biomedical Sciences, Fudan University, Shanghai, PR China
| | - Y Chen
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Laboratory Center, Affiliated Eye and ENT Hospital of Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
| | - J Qi
- Key Laboratory for Developmental Genes and Human Disease, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing, China.,Co-innovation Center of Neuroregeneration, Nantong University, Nantong, China
| | - Y Zhang
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Laboratory Center, Affiliated Eye and ENT Hospital of Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
| | - Y He
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Laboratory Center, Affiliated Eye and ENT Hospital of Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
| | - W Ni
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
| | - W Li
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Laboratory Center, Affiliated Eye and ENT Hospital of Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
| | - S Zhang
- Key Laboratory for Developmental Genes and Human Disease, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing, China.,Co-innovation Center of Neuroregeneration, Nantong University, Nantong, China
| | - S Sun
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Laboratory Center, Affiliated Eye and ENT Hospital of Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
| | - M M Taketo
- Department of Pharmacology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - L Wang
- Institutes of Biomedical Sciences, Fudan University, Shanghai, PR China
| | - R Chai
- Key Laboratory for Developmental Genes and Human Disease, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing, China.,Co-innovation Center of Neuroregeneration, Nantong University, Nantong, China
| | - H Li
- Otorhinolaryngology Department of Affiliated Eye and ENT Hospital, State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, PR China.,Institutes of Biomedical Sciences, Fudan University, Shanghai, PR China.,Key Laboratory of Hearing Medicine of National Health and Family Planning Commission, Shanghai, PR China
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52
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Baxendale S, Whitfield TT. Methods to study the development, anatomy, and function of the zebrafish inner ear across the life course. Methods Cell Biol 2016; 134:165-209. [PMID: 27312494 DOI: 10.1016/bs.mcb.2016.02.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The inner ear is a remarkably intricate structure able to detect sound, motion, and gravity. During development of the zebrafish embryo, the ear undergoes dynamic morphogenesis from a simple epithelial vesicle into a complex labyrinth, consisting of three semicircular canals and three otolithic sensory organs, each with an array of differentiated cell types. This microcosm of biology has led to advances in understanding molecular and cellular changes in epithelial patterning and morphogenesis, through to mechanisms of mechanosensory transduction and the origins of reflexive behavior. In this chapter, we describe different methods to study the zebrafish ear, including high-speed imaging of otic cilia, confocal microscopy, and light-sheet fluorescent microscopy. Many dyes, antibodies, and transgenic lines for labeling the ear are available, and we provide a comprehensive review of these resources. The developing ear is amenable to genetic, chemical, and physical manipulations, including injection and transplantation. Chemical modulation of developmental signaling pathways has paved the way for zebrafish to be widely used in drug discovery. We describe two chemical screens with relevance to the ear: a fluorescent-based screen for compounds that protect against ototoxicity, and an in situ-based screen for modulators of a signaling pathway involved in semicircular canal development. We also describe methods for dissection and imaging of the adult otic epithelia. We review both manual and automated methods to test the function of the inner ear and lateral line, defects in which can lead to altered locomotor behavior. Finally, we review a collection of zebrafish models that are generating new insights into human deafness and vestibular disorders.
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Affiliation(s)
- S Baxendale
- University of Sheffield, Sheffield, United Kingdom
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53
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Zhang QX, He XJ, Wong HC, Kindt KS. Functional calcium imaging in zebrafish lateral-line hair cells. Methods Cell Biol 2016; 133:229-52. [PMID: 27263415 DOI: 10.1016/bs.mcb.2015.12.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Sensory hair-cell development, function, and regeneration are fundamental processes that are challenging to study in mammalian systems. Zebrafish are an excellent alternative model to study hair cells because they have an external auxiliary organ called the lateral line. The hair cells of the lateral line are easily accessible, which makes them suitable for live, function-based fluorescence imaging. In this chapter, we describe methods to perform functional calcium imaging in zebrafish lateral-line hair cells. We compare genetically encoded calcium indicators that have been used previously to measure calcium in lateral-line hair cells. We also outline equipment required for calcium imaging and compare different imaging systems. Lastly, we discuss how to set up optimal imaging parameters and how to process and visualize calcium signals. Overall, using these methods, in vivo calcium imaging is a powerful tool to examine sensory hair-cell function in an intact organism.
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Affiliation(s)
- Q X Zhang
- National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD, United States
| | - X J He
- National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD, United States
| | - H C Wong
- National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD, United States
| | - K S Kindt
- National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD, United States
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54
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Live Imaging of Calcium Dynamics during Axon Degeneration Reveals Two Functionally Distinct Phases of Calcium Influx. J Neurosci 2016; 35:15026-38. [PMID: 26558774 DOI: 10.1523/jneurosci.2484-15.2015] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
UNLABELLED Calcium is a key regulator of axon degeneration caused by trauma and disease, but its specific spatial and temporal dynamics in injured axons remain unclear. To clarify the function of calcium in axon degeneration, we observed calcium dynamics in single injured neurons in live zebrafish larvae and tested the temporal requirement for calcium in zebrafish neurons and cultured mouse DRG neurons. Using laser axotomy to induce Wallerian degeneration (WD) in zebrafish peripheral sensory axons, we monitored calcium dynamics from injury to fragmentation, revealing two stereotyped phases of axonal calcium influx. First, axotomy triggered a transient local calcium wave originating at the injury site. This initial calcium wave only disrupted mitochondria near the injury site and was not altered by expression of the protective WD slow (WldS) protein. Inducing multiple waves with additional axotomies did not change the kinetics of degeneration. In contrast, a second phase of calcium influx occurring minutes before fragmentation spread as a wave throughout the axon, entered mitochondria, and was abolished by WldS expression. In live zebrafish, chelating calcium after the first wave, but before the second wave, delayed the progress of fragmentation. In cultured DRG neurons, chelating calcium early in the process of WD did not alter degeneration, but chelating calcium late in WD delayed fragmentation. We propose that a terminal calcium wave is a key instructive component of the axon degeneration program. SIGNIFICANCE STATEMENT Axon degeneration resulting from trauma or neurodegenerative disease can cause devastating deficits in neural function. Understanding the molecular and cellular events that execute axon degeneration is essential for developing treatments to address these conditions. Calcium is known to contribute to axon degeneration, but its temporal requirements in this process have been unclear. Live calcium imaging in severed zebrafish neurons and temporally controlled pharmacological treatments in both zebrafish and cultured mouse sensory neurons revealed that axonal calcium influx late in the degeneration process regulates axon fragmentation. These findings suggest that temporal considerations will be crucial for developing treatments for diseases associated with axon degeneration.
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55
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Chemical Ototoxicity of the Fish Inner Ear and Lateral Line. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 877:419-37. [PMID: 26515324 DOI: 10.1007/978-3-319-21059-9_18] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hair cell-driven mechanosensory systems are crucial for successful execution of a number of behaviors in fishes, and have emerged as good models for exploring questions relevant to human hearing. This review focuses on ototoxic effects in the inner ear and lateral line system of fishes. We specifically examine studies where chemical ototoxins such as aminoglycoside antibiotics have been employed as tools to disable the lateral line. Lateral line ablation results in alterations to feeding behavior and orientation to water current in a variety of species. However, neither behavior is abolished in the presence of additional sensory cues, supporting the hypothesis that many fish behaviors are driven by multisensory integration. Within biomedical research, the larval zebrafish lateral line has become an important model system for understanding signaling mechanisms that contribute to hair cell death and for developing novel pharmacological therapies that protect hair cells from ototoxic damage. Furthermore, given that fishes robustly regenerate damaged hair cells, ototoxin studies in fishes have broadened our understanding of the molecular and genetic events in an innately regenerative system, offering potential targets for mammalian hair cell regeneration. Collectively, studies of fish mechanosensory systems have yielded insight into fish behavior and in mechanisms of hair cell death, protection, and regeneration.
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56
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Bullen A, West T, Moores C, Ashmore J, Fleck RA, MacLellan-Gibson K, Forge A. Association of intracellular and synaptic organization in cochlear inner hair cells revealed by 3D electron microscopy. J Cell Sci 2015; 128:2529-40. [PMID: 26045447 PMCID: PMC4510854 DOI: 10.1242/jcs.170761] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 05/29/2015] [Indexed: 01/12/2023] Open
Abstract
The ways in which cell architecture is modelled to meet cell function is a poorly understood facet of cell biology. To address this question, we have studied the cytoarchitecture of a cell with highly specialised organisation, the cochlear inner hair cell (IHC), using multiple hierarchies of three-dimensional (3D) electron microscopy analyses. We show that synaptic terminal distribution on the IHC surface correlates with cell shape, and the distribution of a highly organised network of membranes and mitochondria encompassing the infranuclear region of the cell. This network is juxtaposed to a population of small vesicles, which represents a potential new source of neurotransmitter vesicles for replenishment of the synapses. Structural linkages between organelles that underlie this organisation were identified by high-resolution imaging. Taken together, these results describe a cell-encompassing network of membranes and mitochondria present in IHCs that support efficient coding and transmission of auditory signals. Such techniques also have the potential for clarifying functionally specialised cytoarchitecture of other cell types. Summary: 3D electron microscopy reconstructs the highly organised structure of the infranuclear region of the cochlear inner hair cell, which supports synaptic functions.
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Affiliation(s)
- Anwen Bullen
- Centre for Auditory Research, UCL Ear Institute, London WC1X 8EE, UK
| | - Timothy West
- Centre for Auditory Research, UCL Ear Institute, London WC1X 8EE, UK
| | - Carolyn Moores
- Institute of Structural and Molecular Biology, Birkbeck College, London WC1E 7HX, UK
| | - Jonathan Ashmore
- Centre for Auditory Research, UCL Ear Institute, London WC1X 8EE, UK Neuroscience, Physiology & Pharmacology, UCL, London WC1E 6BT, UK
| | - Roland A Fleck
- Centre for Ultrastructural Imaging, King's College London, London WC2R 2LS, UK
| | | | - Andrew Forge
- Centre for Auditory Research, UCL Ear Institute, London WC1X 8EE, UK
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57
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Majumder P, Duchen MR, Gale JE. Cellular glutathione content in the organ of Corti and its role during ototoxicity. Front Cell Neurosci 2015; 9:143. [PMID: 25972783 PMCID: PMC4412067 DOI: 10.3389/fncel.2015.00143] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 03/26/2015] [Indexed: 12/31/2022] Open
Abstract
Glutathione (GSH) is the major scavenger of reactive oxygen species (ROS) inside cells. We used live confocal imaging in order to clarify the role of GSH in the biology of the organ of Corti, the sensory epithelium of the cochlea, before, during and after the onset of hearing and in ~1 year old mice. GSH content was measured using monochlorobimane (MCB), a non-fluorescent cell permeant bimane that reacts with GSH, forming a fluorescent adduct through a reaction catalyzed by glutathione-S-transferase. GSH content increased significantly in inner hair cells during maturation in young adult animals, whereas there was no significant change in the outer hair cells. However, the GSH content in inner hair cells was significantly reduced in ~1 year old mice. The GSH content of supporting cells was comparatively stable over these ages. To test whether the GSH content played a significant protective role during ototoxicity, GSH synthesis was inhibited by buthionine sulfoximine (BSO) in organotypic cochlear explant cultures from immature mice. BSO treatment alone, which reduced GSH by 65 and 85% in inner hair cells and outer hair cells respectively, did not cause any significant cell death. Surprisingly, GSH depletion had no significant effect on hair cell survival even during exposure to the ototoxic aminoglycoside neomycin. These data suggest that the involvement of ROS during aminoglycoside-induced hair cell death is less clear than previously thought and requires further investigation.
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Affiliation(s)
| | - Michael R Duchen
- Department of Cell and Developmental Biology, University College London London, UK
| | - Jonathan E Gale
- UCL Ear Institute, University College London London, UK ; Department of Cell and Developmental Biology, University College London London, UK
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58
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Wong ACY, Ryan AF. Mechanisms of sensorineural cell damage, death and survival in the cochlea. Front Aging Neurosci 2015; 7:58. [PMID: 25954196 PMCID: PMC4404918 DOI: 10.3389/fnagi.2015.00058] [Citation(s) in RCA: 172] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 04/05/2015] [Indexed: 12/20/2022] Open
Abstract
The majority of acquired hearing loss, including presbycusis, is caused by irreversible damage to the sensorineural tissues of the cochlea. This article reviews the intracellular mechanisms that contribute to sensorineural damage in the cochlea, as well as the survival signaling pathways that can provide endogenous protection and tissue rescue. These data have primarily been generated in hearing loss not directly related to age. However, there is evidence that similar mechanisms operate in presbycusis. Moreover, accumulation of damage from other causes can contribute to age-related hearing loss (ARHL). Potential therapeutic interventions to balance opposing but interconnected cell damage and survival pathways, such as antioxidants, anti-apoptotics, and pro-inflammatory cytokine inhibitors, are also discussed.
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Affiliation(s)
- Ann C Y Wong
- Department of Surgery/Division of Otolaryngology, University of California, San Diego School of Medicine La Jolla, CA, USA ; Department of Physiology and Translational Neuroscience Facility, School of Medical Sciences, University of New South Wales Sydney, NSW, Australia
| | - Allen F Ryan
- Department of Surgery/Division of Otolaryngology, University of California, San Diego School of Medicine La Jolla, CA, USA ; Veterans Administration Medical Center La Jolla, CA, USA ; Department of Neurosciences, University of California, San Diego School of Medicine La Jolla, CA, USA
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59
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Stawicki TM, Esterberg R, Hailey DW, Raible DW, Rubel EW. Using the zebrafish lateral line to uncover novel mechanisms of action and prevention in drug-induced hair cell death. Front Cell Neurosci 2015; 9:46. [PMID: 25741241 PMCID: PMC4332341 DOI: 10.3389/fncel.2015.00046] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 01/30/2015] [Indexed: 01/01/2023] Open
Abstract
The majority of hearing loss and balance disorders are caused by the permanent loss of mechanosensory hair cells of the inner ear. Identification of genes and compounds that modulate susceptibility to hair cell death is frequently confounded by the difficulties of assaying for such complex phenomena in mammalian models. The zebrafish has emerged as a powerful animal model for genetic and chemical screening in many contexts. Several characteristics of the zebrafish, such as its small size and external location of mechanosensory hair cells within the lateral line sensory organ, uniquely position it as an ideal model organism for the study of hair cell toxicity. We have used this model to screen for genes and compounds that affect hair cell survival during ototoxin exposure and have identified agents that would not be expected to play a role in this process based on a priori knowledge of their function. The identification of such agents yields better understanding of hair cell death and holds promise to stem hearing loss and balance disorders in the human population.
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Affiliation(s)
- Tamara M Stawicki
- Virginia Merrill Bloedel Hearing Research Center, University of Washington Seattle, WA, USA ; Department of Biological Structure, University of Washington Seattle, WA, USA
| | - Robert Esterberg
- Virginia Merrill Bloedel Hearing Research Center, University of Washington Seattle, WA, USA ; Department of Otolaryngology, Head and Neck Surgery, University of Washington Seattle, WA, USA
| | - Dale W Hailey
- Virginia Merrill Bloedel Hearing Research Center, University of Washington Seattle, WA, USA ; Department of Biological Structure, University of Washington Seattle, WA, USA
| | - David W Raible
- Virginia Merrill Bloedel Hearing Research Center, University of Washington Seattle, WA, USA ; Department of Biological Structure, University of Washington Seattle, WA, USA
| | - Edwin W Rubel
- Virginia Merrill Bloedel Hearing Research Center, University of Washington Seattle, WA, USA ; Department of Otolaryngology, Head and Neck Surgery, University of Washington Seattle, WA, USA
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60
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Huth ME, Han KH, Sotoudeh K, Hsieh YJ, Effertz T, Vu AA, Verhoeven S, Hsieh MH, Greenhouse R, Cheng AG, Ricci AJ. Designer aminoglycosides prevent cochlear hair cell loss and hearing loss. J Clin Invest 2015; 125:583-92. [PMID: 25555219 DOI: 10.1172/jci77424] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 11/13/2014] [Indexed: 02/02/2023] Open
Abstract
Bacterial infections represent a rapidly growing challenge to human health. Aminoglycosides are widely used broad-spectrum antibiotics, but they inflict permanent hearing loss in up to ~50% of patients by causing selective sensory hair cell loss. Here, we hypothesized that reducing aminoglycoside entry into hair cells via mechanotransducer channels would reduce ototoxicity, and therefore we synthesized 9 aminoglycosides with modifications based on biophysical properties of the hair cell mechanotransducer channel and interactions between aminoglycosides and the bacterial ribosome. Compared with the parent aminoglycoside sisomicin, all 9 derivatives displayed no or reduced ototoxicity, with the lead compound N1MS 17 times less ototoxic and with reduced penetration of hair cell mechanotransducer channels in rat cochlear cultures. Both N1MS and sisomicin suppressed growth of E. coli and K. pneumoniae, with N1MS exhibiting superior activity against extended spectrum β lactamase producers, despite diminished activity against P. aeruginosa and S. aureus. Moreover, systemic sisomicin treatment of mice resulted in 75% to 85% hair cell loss and profound hearing loss, whereas N1MS treatment preserved both hair cells and hearing. Finally, in mice with E. coli-infected bladders, systemic N1MS treatment eliminated bacteria from urinary tract tissues and serially collected urine samples, without compromising auditory and kidney functions. Together, our findings establish N1MS as a nonototoxic aminoglycoside and support targeted modification as a promising approach to generating nonototoxic antibiotics.
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Abstract
Mechanosensory hair cells are vulnerable to environmental insult, resulting in hearing and balance disorders. We demonstrate that directional compartmental flow of intracellular Ca(2+) underlies death in zebrafish lateral line hair cells after exposure to aminoglycoside antibiotics, a well characterized hair cell toxin. Ca(2+) is mobilized from the ER and transferred to mitochondria via IP3 channels with little cytoplasmic leakage. Pharmacological agents that shunt ER-derived Ca(2+) directly to cytoplasm mitigate toxicity, indicating that high cytoplasmic Ca(2+) levels alone are not cytotoxic. Inhibition of the mitochondrial transition pore sensitizes hair cells to the toxic effects of aminoglycosides, contrasting with current models of excitotoxicity. Hair cells display efficient ER-mitochondrial Ca(2+) flow, suggesting that tight coupling of these organelles drives mitochondrial activity under physiological conditions at the cost of increased susceptibility to toxins.
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62
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Lush ME, Piotrowski T. Sensory hair cell regeneration in the zebrafish lateral line. Dev Dyn 2014; 243:1187-202. [PMID: 25045019 DOI: 10.1002/dvdy.24167] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 07/12/2014] [Accepted: 07/14/2014] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Damage or destruction of sensory hair cells in the inner ear leads to hearing or balance deficits that can be debilitating, especially in older adults. Unfortunately, the damage is permanent, as regeneration of the inner ear sensory epithelia does not occur in mammals. RESULTS Zebrafish and other non-mammalian vertebrates have the remarkable ability to regenerate sensory hair cells and understanding the molecular and cellular basis for this regenerative ability will hopefully aid us in designing therapies to induce regeneration in mammals. Zebrafish not only possess hair cells in the ear but also in the sensory lateral line system. Hair cells in both organs are functionally analogous to hair cells in the inner ear of mammals. The lateral line is a mechanosensory system found in most aquatic vertebrates that detects water motion and aids in predator avoidance, prey capture, schooling, and mating. Although hair cell regeneration occurs in both the ear and lateral line, most research to date has focused on the lateral line due to its relatively simple structure and accessibility. CONCLUSIONS Here we review the recent discoveries made during the characterization of hair cell regeneration in zebrafish.
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Affiliation(s)
- Mark E Lush
- Stowers Institute for Medical Research, Kansas City, Missouri
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63
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Guo D, Du Y, Wu Q, Jiang W, Bi H. Disrupted calcium homeostasis is involved in elevated zinc ion-induced photoreceptor cell death. Arch Biochem Biophys 2014; 560:44-51. [PMID: 25051343 DOI: 10.1016/j.abb.2014.07.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Revised: 07/01/2014] [Accepted: 07/11/2014] [Indexed: 01/02/2023]
Abstract
Zinc (Zn), the second abundant trace element in living organisms, plays an important role in regulating cell metabolism, signaling, proliferation, gene expression and apoptosis. Meanwhile, the overload of Zn will disrupt the intracellular calcium homeostasis via impairing mitochondrial function. However, the specific molecular mechanism underlying zinc-induced calcium regulation remains poorly understood. In the present study, using zinc chloride (ZnCl2) as a stressor, we investigated the effect of exogenous Zn(2+) in regulating murine photoreceptor cell viability, reactive oxygen species (ROS), cell cycle distribution and calcium homeostasis as well as plasma membrane calcium ATPase (PMCA) isoforms (PMCA1 and PMCA2, i.e., ATP2B1, ATP2B2) expression. We found that the exogenous Zn(2+) in the exposure range (31.25-125.0 μmol/L) results in the overgeneration of ROS, cell cycle arrest at G2/M phases, elevation of cytosolic [Ca(2+)], inactivation of Ca(2+)-ATPase and reduction of both PMCA1 and PMCA2 in 661 W cells, and thus induces cell death. In conclusion, ZnCl2 exposure can elevate the cytosolic [Ca(2+)], disrupt the intracellular calcium homeostasis, further initiate Ca(2+)-dependent signaling pathway in 661 W cells, and finally cause cell death. Our results will facilitate the understanding of cell death induced by the zinc ion-mediated calcium homeostasis disruption.
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Affiliation(s)
- Dadong Guo
- Shandong Provincial Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Therapy of Ocular Diseases, Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Therapy of Ocular Diseases in Universities of Shandong, Eye Institute of Shandong University of Traditional Chinese Medicine, Jinan 250002, China
| | - Yuxiang Du
- Shandong University of Traditional Chinese Medicine, Jinan 250002, China
| | - Qiuxin Wu
- Affiliated Eye Hospital of Shandong University of Traditional Chinese Medicine, Jinan 250002, China
| | - Wenjun Jiang
- Shandong Provincial Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Therapy of Ocular Diseases, Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Therapy of Ocular Diseases in Universities of Shandong, Eye Institute of Shandong University of Traditional Chinese Medicine, Jinan 250002, China
| | - Hongsheng Bi
- Shandong Provincial Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Therapy of Ocular Diseases, Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Therapy of Ocular Diseases in Universities of Shandong, Eye Institute of Shandong University of Traditional Chinese Medicine, Jinan 250002, China.
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64
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Loss of Pde6 reduces cell body Ca(2+) transients within photoreceptors. Cell Death Dis 2013; 4:e797. [PMID: 24030149 PMCID: PMC3789190 DOI: 10.1038/cddis.2013.332] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 07/21/2013] [Accepted: 07/29/2013] [Indexed: 11/30/2022]
Abstract
Modulation of Ca2+ within cells is tightly regulated through complex and dynamic interactions between the plasma membrane and internal compartments. In this study, we exploit in vivo imaging strategies based on genetically encoded Ca2+ indicators to define changes in perikaryal Ca2+ concentration of intact photoreceptors. We developed double-transgenic zebrafish larvae expressing GCaMP3 in all cones and tdTomato in long-wavelength cones to test the hypothesis that photoreceptor degeneration induced by mutations in the phosphodiesterase-6 (Pde6) gene is driven by excessive [Ca2+]i levels within the cell body. Arguing against Ca2+ overload in Pde6 mutant photoreceptors, simultaneous analysis of cone photoreceptor morphology and Ca2+ fluxes revealed that degeneration of pde6cw59 mutant cones, which lack the cone-specific cGMP phosphodiesterase, is not associated with sustained increases in perikaryal [Ca2+]i. Analysis of [Ca2+]i in dissociated Pde6βrd1mouse rods shows conservation of this finding across vertebrates. In vivo, transient and Pde6-independent Ca2+ elevations (‘flashes') were detected throughout the inner segment and the synapse. As the mutant cells proceeded to degenerate, these Ca2+ fluxes diminished. This study thus provides insight into Ca2+ dynamics in a common form of inherited blindness and uncovers a dramatic, light-independent modulation of [Ca2+]i that occurs in normal cones.
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Pan B, Géléoc GS, Asai Y, Horwitz GC, Kurima K, Ishikawa K, Kawashima Y, Griffith AJ, Holt JR. TMC1 and TMC2 are components of the mechanotransduction channel in hair cells of the mammalian inner ear. Neuron 2013; 79:504-15. [PMID: 23871232 DOI: 10.1016/j.neuron.2013.06.019] [Citation(s) in RCA: 297] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/11/2013] [Indexed: 02/02/2023]
Abstract
Sensory transduction in auditory and vestibular hair cells requires expression of transmembrane channel-like (Tmc) 1 and 2 genes, but the function of these genes is unknown. To investigate the hypothesis that TMC1 and TMC2 proteins are components of the mechanosensitive ion channels that convert mechanical information into electrical signals, we recorded whole-cell and single-channel currents from mouse hair cells that expressed Tmc1, Tmc2, or mutant Tmc1. Cells that expressed Tmc2 had high calcium permeability and large single-channel currents, while cells with mutant Tmc1 had reduced calcium permeability and reduced single-channel currents. Cells that expressed Tmc1 and Tmc2 had a broad range of single-channel currents, suggesting multiple heteromeric assemblies of TMC subunits. The data demonstrate TMC1 and TMC2 are components of hair cell transduction channels and contribute to permeation properties. Gradients in TMC channel composition may also contribute to variation in sensory transduction along the tonotopic axis of the mammalian cochlea.
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Affiliation(s)
- Bifeng Pan
- Department of Otolaryngology, F.M. Kirby Neurobiology Center, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Center for Life Sciences 12251, Boston, MA 02115, USA
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