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Some Ototoxic Drugs Destroy Cochlear Support Cells Before Damaging Sensory Hair Cells. Neurotox Res 2020; 37:743-752. [PMID: 31997155 DOI: 10.1007/s12640-020-00170-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 01/07/2020] [Accepted: 01/22/2020] [Indexed: 02/07/2023]
Abstract
A wide variety of ototoxic drugs are capable of damaging the sensory hair cells in the mammalian cochlea resulting in permanent hearing loss. However, the toxic properties of these drugs suggest that some could potentially damage cochlear support cells as well. To test the hypothesis, we treated postnatal day three rat cochlear cultures with toxic doses of gentamicin, cisplatin, mefloquine, and cadmium. Gentamicin primarily destroyed the hair cells and disrupted the intercellular connection with the surrounding support cells. Gentamicin-induced hair cell death was initiated through the caspase-9 intrinsic apoptotic pathway followed by activation of downstream executioner caspase-3. In contrast, cisplatin, mefloquine, and cadmium initially damaged the support cells and only later damaged the hair cells. Support cell death was initiated through the caspase-8 extrinsic apoptotic pathway followed later by downstream activation of caspase-3. Cisplatin, mefloquine, and cadmium significantly reduced the expression of actin and laminin, in the extracellular matrix, leading to significant disarray of the sensory epithelium.
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Francis SP, Cunningham LL. Non-autonomous Cellular Responses to Ototoxic Drug-Induced Stress and Death. Front Cell Neurosci 2017; 11:252. [PMID: 28878625 PMCID: PMC5572385 DOI: 10.3389/fncel.2017.00252] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 08/08/2017] [Indexed: 12/20/2022] Open
Abstract
The first major recognition of drug-induced hearing loss can be traced back more than seven decades to the development of streptomycin as an antimicrobial agent. Since then at least 130 therapeutic drugs have been recognized as having ototoxic side-effects. Two important classes of ototoxic drugs are the aminoglycoside antibiotics and the platinum-based antineoplastic agents. These drugs save the lives of millions of people worldwide, but they also cause irreparable hearing loss. In the inner ear, sensory hair cells (HCs) and spiral ganglion neurons (SGNs) are important cellular targets of these drugs, and most mechanistic studies have focused on the cell-autonomous responses of these cell types in response to ototoxic stress. Despite several decades of studies on ototoxicity, important unanswered questions remain, including the cellular and molecular mechanisms that determine whether HCs and SGNs will live or die when confronted with ototoxic challenge. Emerging evidence indicates that other cell types in the inner ear can act as mediators of survival or death of sensory cells and SGNs. For example, glia-like supporting cells (SCs) can promote survival of both HCs and SGNs. Alternatively, SCs can act to promote HC death and inhibit neural fiber expansion. Similarly, tissue resident macrophages activate either pro-survival or pro-death signaling that can influence HC survival after exposure to ototoxic agents. Together these data indicate that autonomous responses that occur within a stressed HC or SGN are not the only (and possibly not the primary) determinants of whether the stressed cell ultimately lives or dies. Instead non-cell-autonomous responses are emerging as significant determinants of HC and SGN survival vs. death in the face of ototoxic stress. The goal of this review is to summarize the current evidence on non-cell-autonomous responses to ototoxic stress and to discuss ways in which this knowledge may advance the development of therapies to reduce hearing loss caused by these drugs.
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Affiliation(s)
- Shimon P Francis
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesda, MD, United States
| | - Lisa L Cunningham
- National Institute on Deafness and Other Communication Disorders, National Institutes of HealthBethesda, MD, United States
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3
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Pollock LM, Gupta N, Chen X, Luna EJ, McDermott BM. Supervillin Is a Component of the Hair Cell's Cuticular Plate and the Head Plates of Organ of Corti Supporting Cells. PLoS One 2016; 11:e0158349. [PMID: 27415442 PMCID: PMC4944918 DOI: 10.1371/journal.pone.0158349] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 06/14/2016] [Indexed: 11/23/2022] Open
Abstract
The organ of Corti has evolved a panoply of cells with extraordinary morphological specializations to harness, direct, and transduce mechanical energy into electrical signals. Among the cells with prominent apical specializations are hair cells and nearby supporting cells. At the apical surface of each hair cell is a mechanosensitive hair bundle of filamentous actin (F-actin)-based stereocilia, which insert rootlets into the F-actin meshwork of the underlying cuticular plate, a rigid organelle considered to hold the stereocilia in place. Little is known about the protein composition and development of the cuticular plate or the apicolateral specializations of organ of Corti supporting cells. We show that supervillin, an F-actin cross-linking protein, localizes to cuticular plates in hair cells of the mouse cochlea and vestibule and zebrafish sensory epithelia. Moreover, supervillin localizes near the apicolateral margins within the head plates of Deiters’ cells and outer pillar cells, and proximal to the apicolateral margins of inner phalangeal cells, adjacent to the junctions with neighboring hair cells. Overall, supervillin localization suggests this protein may shape the surface structure of the organ of Corti.
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Affiliation(s)
- Lana M Pollock
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America.,Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America
| | - Nilay Gupta
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America.,Department of Biology, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America
| | - Xi Chen
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America.,Department of Biology, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America
| | - Elizabeth J Luna
- Department of Cell and Developmental Biology, University of Massachusetts Medical School, Worcester, Massachusetts, 01605, United States of America
| | - Brian M McDermott
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America.,Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America.,Department of Biology, Case Western Reserve University, Cleveland, Ohio, 44106, United States of America.,Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, 44016, United States of America
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Monzack EL, May LA, Roy S, Gale JE, Cunningham LL. Live imaging the phagocytic activity of inner ear supporting cells in response to hair cell death. Cell Death Differ 2015; 22:1995-2005. [PMID: 25929858 PMCID: PMC4816108 DOI: 10.1038/cdd.2015.48] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 02/20/2015] [Accepted: 03/04/2015] [Indexed: 01/12/2023] Open
Abstract
Hearing loss and balance disorders affect millions of people worldwide. Sensory transduction in the inner ear requires both mechanosensory hair cells (HCs) and surrounding glia-like supporting cells (SCs). HCs are susceptible to death from aging, noise overexposure, and treatment with therapeutic drugs that have ototoxic side effects; these ototoxic drugs include the aminoglycoside antibiotics and the antineoplastic drug cisplatin. Although both classes of drugs are known to kill HCs, their effects on SCs are less well understood. Recent data indicate that SCs sense and respond to HC stress, and that their responses can influence HC death, survival, and phagocytosis. These responses to HC stress and death are critical to the health of the inner ear. Here we have used live confocal imaging of the adult mouse utricle, to examine the SC responses to HC death caused by aminoglycosides or cisplatin. Our data indicate that when HCs are killed by aminoglycosides, SCs efficiently remove HC corpses from the sensory epithelium in a process that includes constricting the apical portion of the HC after loss of membrane integrity. SCs then form a phagosome, which can completely engulf the remaining HC body, a phenomenon not previously reported in mammals. In contrast, cisplatin treatment results in accumulation of dead HCs in the sensory epithelium, accompanied by an increase in SC death. The surviving SCs constrict fewer HCs and display impaired phagocytosis. These data are supported by in vivo experiments, in which cochlear SCs show reduced capacity for scar formation in cisplatin-treated mice compared with those treated with aminoglycosides. Together, these data point to a broader defect in the ability of the cisplatin-treated SCs, to preserve tissue health in the mature mammalian inner ear.
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Affiliation(s)
- E L Monzack
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | - L A May
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | - S Roy
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
| | - J E Gale
- UCL Ear Institute, University College, London WC1X 8EE, UK
| | - L L Cunningham
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, USA
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Kaur T, Hirose K, Rubel EW, Warchol ME. Macrophage recruitment and epithelial repair following hair cell injury in the mouse utricle. Front Cell Neurosci 2015; 9:150. [PMID: 25954156 PMCID: PMC4406144 DOI: 10.3389/fncel.2015.00150] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 04/01/2015] [Indexed: 11/13/2022] Open
Abstract
The sensory organs of the inner ear possess resident populations of macrophages, but the function of those cells is poorly understood. In many tissues, macrophages participate in the removal of cellular debris after injury and can also promote tissue repair. The present study examined injury-evoked macrophage activity in the mouse utricle. Experiments used transgenic mice in which the gene for the human diphtheria toxin receptor (huDTR) was inserted under regulation of the Pou4f3 promoter. Hair cells in such mice can be selectively lesioned by systemic treatment with diphtheria toxin (DT). In order to visualize macrophages, Pou4f3-huDTR mice were crossed with a second transgenic line, in which one or both copies of the gene for the fractalkine receptor CX3CR1 were replaced with a gene for GFP. Such mice expressed GFP in all macrophages, and mice that were CX3CR1(GFP/GFP) lacked the necessary receptor for fractalkine signaling. Treatment with DT resulted in the death of ∼70% of utricular hair cells within 7 days, which was accompanied by increased numbers of macrophages within the utricular sensory epithelium. Many of these macrophages appeared to be actively engulfing hair cell debris, indicating that macrophages participate in the process of 'corpse removal' in the mammalian vestibular organs. However, we observed no apparent differences in injury-evoked macrophage numbers in the utricles of CX3CR1(+/GFP) mice vs. CX3CR1(GFP/GFP) mice, suggesting that fractalkine signaling is not necessary for macrophage recruitment in these sensory organs. Finally, we found that repair of sensory epithelia at short times after DT-induced hair cell lesions was mediated by relatively thin cables of F-actin. After 56 days recovery, however, all cell-cell junctions were characterized by very thick actin cables.
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Affiliation(s)
- Tejbeer Kaur
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO USA
| | - Keiko Hirose
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO USA
| | - Edwin W Rubel
- The Virginia Merrill Bloedel Hearing Research Center and Department of Otolaryngology - Head and Neck Surgery, University of Washington School of Medicine Seattle, WA, USA
| | - Mark E Warchol
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, MO USA
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Anttonen T, Belevich I, Kirjavainen A, Laos M, Brakebusch C, Jokitalo E, Pirvola U. How to bury the dead: elimination of apoptotic hair cells from the hearing organ of the mouse. J Assoc Res Otolaryngol 2014; 15:975-92. [PMID: 25074370 DOI: 10.1007/s10162-014-0480-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Accepted: 07/01/2014] [Indexed: 12/20/2022] Open
Abstract
Hair cell death is a major cause of hearing impairment. Preservation of surface barrier upon hair cell loss is critical to prevent leakage of potassium-rich endolymph into the organ of Corti and to prevent expansion of cellular damage. Understanding of wound healing in this cytoarchitecturally complex organ requires ultrastructural 3D visualization. Powered by the serial block-face scanning electron microscopy, we penetrate into the cell biological mechanisms in the acute response of outer hair cells and glial-like Deiters' cells to ototoxic trauma in vivo. We show that Deiters' cells function as phagocytes. Upon trauma, their phalangeal processes swell and the resulting close cellular contacts allow engulfment of apoptotic cell debris. Apical domains of dying hair cells are eliminated from the inner ear sensory epithelia, an event thought to depend on supporting cells' actomyosin contractile activity. We show that in the case of apoptotic outer hair cells of the organ of Corti, elimination of their apices is preceded by strong cell body shrinkage, emphasizing the role of the dying cell itself in the cleavage. Our data reveal that the resealing of epithelial surface by junctional extensions of Deiters' cells is dynamically reinforced by newly polymerized F-actin belts. By analyzing Cdc42-inactivated Deiters' cells with defects in actin dynamics and surface closure, we show that compromised barrier integrity shifts hair cell death from apoptosis to necrosis and leads to expanded hair cell and nerve fiber damage. Our results have implications concerning therapeutic protective and regenerative interventions, because both interventions should maintain barrier integrity.
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Affiliation(s)
- Tommi Anttonen
- Department of Biosciences, University of Helsinki, P.O. Box 56 (Viikinkaari 1), 00014, Helsinki, Finland
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Responses to cell loss become restricted as the supporting cells in mammalian vestibular organs grow thick junctional actin bands that develop high stability. J Neurosci 2014; 34:1998-2011. [PMID: 24478379 DOI: 10.1523/jneurosci.4355-13.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Sensory hair cell (HC) loss is a major cause of permanent hearing and balance impairments for humans and other mammals. Yet, fish, amphibians, reptiles, and birds readily replace HCs and recover from such sensory deficits. It is unknown what prevents replacement in mammals, but cell replacement capacity declines contemporaneously with massive postnatal thickening of F-actin bands at the junctions between vestibular supporting cells (SCs). In non-mammals, SCs can give rise to regenerated HCs, and the bands remain thin even in adults. Here we investigated the stability of the F-actin bands between SCs in ears from chickens and mice and Madin-Darby canine kidney cells. Pharmacological experiments and fluorescence recovery after photobleaching (FRAP) of SC junctions in utricles from mice that express a γ-actin-GFP fusion protein showed that the thickening F-actin bands develop increased resistance to depolymerization and exceptional stability that parallels a sharp decline in the cell replacement capacity of the maturing mammalian ear. The FRAP recovery rate and the mobile fraction of γ-actin-GFP both decreased as the bands thickened with age and became highly stabilized. In utricles from neonatal mice, time-lapse recordings in the vicinity of dying HCs showed that numerous SCs change shape and organize multicellular actin purse strings that reseal the epithelium. In contrast, adult SCs appeared resistant to deformation, with resealing responses limited to just a few neighboring SCs that did not form purse strings. The exceptional stability of the uniquely thick F-actin bands at the junctions of mature SCs may play an important role in restricting dynamic repair responses in mammalian vestibular epithelia.
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8
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Simmons DD, Lohr R, Wotring H, Burton MD, Hooper RA, Baird RA. Recovery of otoacoustic emissions after high-level noise exposure in the American bullfrog. ACTA ACUST UNITED AC 2014; 217:1626-36. [PMID: 24501139 DOI: 10.1242/jeb.090092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The American bullfrog (Rana catesbeiana) has an amphibian papilla (AP) that senses airborne, low-frequency sound and generates distortion product otoacoustic emissions (DPOAEs) similar to other vertebrate species. Although ranid frogs are typically found in noisy environments, the effects of noise on the AP have not been studied. First, we determined the noise levels that diminished DPOAE at 2f1-f2 using an f2 stimulus level at 80 dB SPL and that also produced morphological damage of the sensory epithelium. Second, we compared DPOAE (2f1-f2) responses with histopathologic changes occurring in bullfrogs after noise exposure. Consistent morphological damage, such as fragmented hair cells and missing bundles, as well as elimination of DPOAE responses were seen only after very high-level (>150 dB SPL) sound exposures. The morphological response of hair cells to noise differed along the mediolateral AP axis: medial hair cells were sensitive to noise and lateral hair cells were relatively insensitive to noise. Renewed or repaired hair cells were not observed until 9 days post-exposure. Following noise exposure, DPOAE responses disappeared within 24 h and then recovered to normal pre-exposure levels within 3-4 days. Our results suggest that DPOAEs in the bullfrog are sensitive to the initial period of hair cell damage. After noise-induced damage, the bullfrog AP has functional recovery mechanisms that do not depend on substantial hair cell regeneration or repair. Thus, the bullfrog auditory system might serve as an interesting model for investigation of ways to prevent noise damage.
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Affiliation(s)
- Dwayne D Simmons
- Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Drive East, Los Angeles, CA 90095, USA
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9
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Vestibular damage in chronic ototoxicity: a mini-review. Neurotoxicology 2013; 43:21-27. [PMID: 24333467 DOI: 10.1016/j.neuro.2013.11.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 11/28/2013] [Accepted: 11/28/2013] [Indexed: 01/26/2023]
Abstract
Ototoxicity is a major cause of the loss of hearing and balance in humans. Ototoxic compounds include pharmaceuticals such as aminoglycoside antibiotics, anti-malarial drugs, loop diuretics and chemotherapeutic platinum agents, and industrial chemicals including several solvents and nitriles. Human and rodent data indicate that the main target of toxicity is hair cells (HCs), which are the mechanosensory cells responsible for sensory transduction in both the auditory and the vestibular system. Nevertheless, the compounds may also affect the auditory and vestibular ganglion neurons. Exposure to ototoxic compounds has been found to cause HC apoptosis, HC necrosis, and damage to the afferent terminals, of differing severity depending on the ototoxicity model. One major pathway frequently involved in HC apoptosis is the c-jun N-terminal kinase (JNK) signaling pathway activated by reactive oxygen species, but other apoptotic pathways can also play a role in ototoxicity. Moreover, little is known about the effects of chronic low-dose exposure. In rodent vestibular epithelia, extrusion of live HCs from the sensory epithelium may be the predominant form of cell demise during chronic ototoxicity. In addition, greater involvement of the afferent terminals may occur, particularly the calyx units contacting type I vestibular HCs. As glutamate is the neurotransmitter in this synapse, excitotoxic phenomena may participate in afferent and ganglion neuron damage. Better knowledge of the events that take place in chronic ototoxicity is of great interest, as it will increase understanding of the sensory loss associated with chronic exposure and aging.
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Rúa F, Buffard M, Sedó-Cabezón L, Hernández-Mir G, de la Torre A, Saldaña-Ruíz S, Chabbert C, Bayona JM, Messeguer A, Llorens J. Vestibulotoxic properties of potential metabolites of allylnitrile. Toxicol Sci 2013; 135:182-92. [PMID: 23761299 DOI: 10.1093/toxsci/kft127] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This study addressed the hypothesis that epoxidation of the double bond in allylnitrile mediates its vestibular toxicity, directly or after subsequent metabolism by epoxide hydrolases. The potential metabolites 3,4-epoxybutyronitrile and 3,4-dihydroxybutyronitrile were synthesized and characterized. In aqueous solutions containing sodium or potassium ions, 3,4-epoxybutyronitrile rearranged to 4-hydroxybut-2-enenitrile, and this compound was also isolated for study. Male adult Long-Evans rats were exposed to allylnitrile or 3,4-epoxybutyronitrile by bilateral transtympanic injection, and vestibular toxicity was assessed using a behavioral test battery and scanning electron microscopy (SEM) observation of the sensory epithelia. Overt vestibular toxicity was caused by 3,4-epoxybutyronitrile at 0.125 mmol/ear and by allylnitrile in some animals at 0.25 mmol/ear. Additional rats were exposed by unilateral transtympanic injection. In these studies, behavioral evidences and SEM observations demonstrated unilateral vestibular toxicity after 0.125 mmol of 3,4-epoxybutyronitrile and bilateral vestibular toxicity after 0.50 mmol of allylnitrile. However, 0.25 mmol of allylnitrile did not cause vestibular toxicity. Unilateral administration of 0.50 mmol of 3,4-dihydroxybutyronitrile or 4-hydroxybut-2-enenitrile caused no vestibular toxicity. The four compounds were also evaluated in the mouse utricle explant culture model. In 8-h exposure experiments, hair cells completely disappeared after 3,4-epoxybutyronitrile at concentrations of 325 or 450μM but not at concentrations of 150μM or lower. In contrast, no difference from controls was recorded in utricles exposed to 450μM or 1.5mM of allylnitrile, 3,4-dihydroxybutyronitrile, or 4-hydroxybut-2-enenitrile. Taken together, the present data support the hypothesis that 3,4-epoxybutyronitrile is the active metabolite of allylnitrile for vestibular toxicity.
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Affiliation(s)
- Federico Rúa
- Departament de Nanotecnologia Química i Biomolecular, Institut de Química Avançada de Catalunya-CSIC, 08034 Barcelona, Catalunya, Spain
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11
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Oesterle EC. Changes in the adult vertebrate auditory sensory epithelium after trauma. Hear Res 2013; 297:91-8. [PMID: 23178236 PMCID: PMC3637947 DOI: 10.1016/j.heares.2012.11.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Revised: 10/30/2012] [Accepted: 11/06/2012] [Indexed: 01/12/2023]
Abstract
Auditory hair cells transduce sound vibrations into membrane potential changes, ultimately leading to changes in neuronal firing and sound perception. This review provides an overview of the characteristics and repair capabilities of traumatized auditory sensory epithelium in the adult vertebrate ear. Injured mammalian auditory epithelium repairs itself by forming permanent scars but is unable to regenerate replacement hair cells. In contrast, injured non-mammalian vertebrate ear generates replacement hair cells to restore hearing functions. Non-sensory support cells within the auditory epithelium play key roles in the repair processes.
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Affiliation(s)
- Elizabeth C Oesterle
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery, CHDD CD176, Box 357923, Univ. of Washington, Seattle, WA 98195-7923, USA.
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12
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Zhu HY, Yeo SW, Ng J, Htoon HM, Beuerman RW. Moesin as a key cytoskeleton regulator in corneal fibrosis. Ocul Surf 2013; 11:119-32. [PMID: 23583046 DOI: 10.1016/j.jtos.2013.01.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Revised: 07/18/2012] [Accepted: 12/01/2012] [Indexed: 11/30/2022]
Abstract
PURPOSE : Corneal fibrosis is the third leading cause of blindness worldwide. α-Smooth muscle actin (SMA), a marker of fibrosis, is closely regulated through an intermediate group of submembrane molecules - cytoskeleton regulators. The purpose of this study was to elucidate the role of specific cytoskeleton regulators in a mouse model of corneal fibrosis. METHODS : A mouse model of corneal fibrosis was developed using anterior keratectomy (AK) and the topical application of transforming growth factor (TGF)-β1 (1 μg/ml). The RT² Profiler™ PCR Array for cytoskeleton regulators was used to assay changes in levels of specific members of this class of proteins. Moesin siRNA was delivered into the corneal stroma by iontophoresis in vivo. Transformation of the corneal keratocyte-to-myofibroblast in corneal fibrosis, as defined by the expression of α-SMA, was determined by Western blot. RESULTS : After AK and topical application of TGF-β1, moesin was the most highly upregulated gene among 84 cytoskeleton regulator genes; iontophoresing moesin siRNA into the corneal stroma reduced the expression of α-SMA to 0.22-, 0.52-, and 0.31-fold of control at postoperative (PO) day 1, 3, and 5, respectively; also, upregulation of phospho-Smad 2 induced by TGF-β1 was reduced by moesin siRNA to 0.59-, 0.56-, and 0.31-fold of control and expression of phospho-Smad 3 was reduced to 0.58-, 0.53-, and 0.47-fold of control at the same PO days. CONCLUSIONS : Moesin may be a potential drug target for inhibiting corneal fibrosis, and the details of moesin-related signaling pathways would be critical for understanding corneal fibrosis.
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Monzack EL, Cunningham LL. Lead roles for supporting actors: critical functions of inner ear supporting cells. Hear Res 2013; 303:20-9. [PMID: 23347917 DOI: 10.1016/j.heares.2013.01.008] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Revised: 12/20/2012] [Accepted: 01/10/2013] [Indexed: 12/27/2022]
Abstract
Many studies that aim to investigate the underlying mechanisms of hearing loss or balance disorders focus on the hair cells and spiral ganglion neurons of the inner ear. Fewer studies have examined the supporting cells that contact both of these cell types in the cochlea and vestibular end organs. While the roles of supporting cells are still being elucidated, emerging evidence indicates that they serve many functions vital to maintaining healthy populations of hair cells and spiral ganglion neurons. Here we review recent studies that highlight the critical roles supporting cells play in the development, function, survival, death, phagocytosis, and regeneration of other cell types within the inner ear. Many of these roles have also been described for glial cells in other parts of the nervous system, and lessons from these other systems continue to inform our understanding of supporting cell functions. This article is part of a Special Issue entitled "Annual Reviews 2013".
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Affiliation(s)
- Elyssa L Monzack
- National Institute on Deafness and Other Communication Disorders, 5 Research Court, Rockville, MD 20850, USA.
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Anttonen T, Kirjavainen A, Belevich I, Laos M, Richardson WD, Jokitalo E, Brakebusch C, Pirvola U. Cdc42-dependent structural development of auditory supporting cells is required for wound healing at adulthood. Sci Rep 2012; 2:978. [PMID: 23248743 PMCID: PMC3523287 DOI: 10.1038/srep00978] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Accepted: 11/14/2012] [Indexed: 11/20/2022] Open
Abstract
Cdc42 regulates the initial establishment of cytoskeletal and junctional structures, but only little is known about its role at later stages of cellular differentiation. We studied Cdc42′s role in vivo in auditory supporting cells, epithelial cells with high structural complexity. Cdc42 inactivation was induced early postnatally using the Cdc42loxP/loxP;Fgfr3-iCre-ERT2 mice. Cdc42 depletion impaired elongation of adherens junctions and F-actin belts, leading to constriction of the sensory epithelial surface. Fragmented F-actin belts, junctions containing ectopic lumens and misexpression of a basolateral membrane protein in the apical domain were observed. These defects and changes in aPKCλ/ι expression suggested that apical polarization is impaired. Following a lesion at adulthood, supporting cells with Cdc42 loss-induced maturational defects collapsed and failed to remodel F-actin belts, a process that is critical to scar formation. Thus, Cdc42 is required for structural differentiation of auditory supporting cells and this proper maturation is necessary for wound healing in adults.
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Affiliation(s)
- Tommi Anttonen
- Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
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15
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Karasawa T, Steyger PS. Intracellular mechanisms of aminoglycoside-induced cytotoxicity. Integr Biol (Camb) 2011; 3:879-86. [PMID: 21799993 DOI: 10.1039/c1ib00034a] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Since introduction into clinical practice over 60 years ago, aminoglycoside antibiotics remain important drugs in the treatment of bacterial infections, cystic fibrosis and tuberculosis. However, the ototoxic and nephrotoxic properties of these drugs are still a major clinical problem. Recent advances in molecular biology and biochemistry have begun to uncover the intracellular actions of aminoglycosides that lead to cytotoxicity. In this review, we discuss intracellular binding targets of aminoglycosides, highlighting specific aminoglycoside-binding proteins (HSP73, calreticulin and CLIMP-63) and their potential for triggering caspases and Bcl-2 signalling cascades that are involved in aminoglycoside-induced cytotoxicity. We also discuss potential strategies to reduce aminoglycoside cytotoxicity, which are necessary for greater bactericidal efficacy during aminoglycoside pharmacotherapy.
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Affiliation(s)
- Takatoshi Karasawa
- Oregon Hearing Research Center, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
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Supporting cells eliminate dying sensory hair cells to maintain epithelial integrity in the avian inner ear. J Neurosci 2010; 30:12545-56. [PMID: 20844149 DOI: 10.1523/jneurosci.3042-10.2010] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Epithelial homeostasis is essential for sensory transduction in the auditory and vestibular organs of the inner ear, but how it is maintained during trauma is poorly understood. To examine potential repair mechanisms, we expressed β-actin-enhanced green fluorescent protein (EGFP) in the chick inner ear and used live-cell imaging to study how sensory epithelia responded during aminoglycoside-induced hair cell trauma. We found that glial-like supporting cells used two independent mechanisms to rapidly eliminate dying hair cells. Supporting cells assembled an actin cable at the luminal surface that extended around the pericuticular junction and constricted to excise the stereocilia bundle and cuticular plate from the hair cell soma. Hair bundle excision could occur within 3 min of actin-cable formation. After bundle excision, typically with a delay of up to 2-3 h, supporting cells engulfed and phagocytosed the remaining bundle-less hair cell. Dual-channel recordings with β-actin-EGFP and vital dyes revealed phagocytosis was concurrent with loss of hair cell integrity. We conclude that supporting cells repaired the epithelial barrier before hair cell plasmalemmal integrity was lost and that supporting cell activity was closely linked to hair cell death. Treatment with the Rho-kinase inhibitor Y-27632 did not prevent bundle excision but prolonged phagocytic engulfment and resulted in hair cell corpses accumulating within the epithelium. Our data show that supporting cells not only maintain epithelial integrity during trauma but suggest they may also be an integral part of the hair cell death process itself.
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Khorshid F, Ali SS, Alsofyani T, Albar H. Plectranthus tenuiflorus (Shara) Promotes Wound Healing: In vitro and in vivo Studies. ACTA ACUST UNITED AC 2010. [DOI: 10.3923/ijb.2010.69.80] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Schultz JM, Khan SN, Ahmed ZM, Riazuddin S, Waryah AM, Chhatre D, Starost MF, Ploplis B, Buckley S, Velásquez D, Kabra M, Lee K, Hassan MJ, Ali G, Ansar M, Ghosh M, Wilcox ER, Ahmad W, Merlino G, Leal SM, Riazuddin S, Friedman TB, Morell RJ. Noncoding mutations of HGF are associated with nonsyndromic hearing loss, DFNB39. Am J Hum Genet 2009; 85:25-39. [PMID: 19576567 DOI: 10.1016/j.ajhg.2009.06.003] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 05/22/2009] [Accepted: 06/01/2009] [Indexed: 11/16/2022] Open
Abstract
A gene causing autosomal-recessive, nonsyndromic hearing loss, DFNB39, was previously mapped to an 18 Mb interval on chromosome 7q11.22-q21.12. We mapped an additional 40 consanguineous families segregating nonsyndromic hearing loss to the DFNB39 locus and refined the obligate interval to 1.2 Mb. The coding regions of all genes in this interval were sequenced, and no missense, nonsense, or frameshift mutations were found. We sequenced the noncoding sequences of genes, as well as noncoding genes, and found three mutations clustered in intron 4 and exon 5 in the hepatocyte growth factor gene (HGF). Two intron 4 deletions occur in a highly conserved sequence that is part of the 3' untranslated region of a previously undescribed short isoform of HGF. The third mutation is a silent substitution, and we demonstrate that it affects splicing in vitro. HGF is involved in a wide variety of signaling pathways in many different tissues, yet these putative regulatory mutations cause a surprisingly specific phenotype, which is nonsydromic hearing loss. Two mouse models of Hgf dysregulation, one in which an Hgf transgene is ubiquitously overexpressed and the other a conditional knockout that deletes Hgf from a limited number of tissues, including the cochlea, result in deafness. Overexpression of HGF is associated with progressive degeneration of outer hair cells in the cochlea, whereas cochlear deletion of Hgf is associated with more general dysplasia.
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Collado MS, Burns JC, Hu Z, Corwin JT. Recent advances in hair cell regeneration research. Curr Opin Otolaryngol Head Neck Surg 2009; 16:465-71. [PMID: 18797290 DOI: 10.1097/moo.0b013e32830f4ab5] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
PURPOSE OF REVIEW This review discusses recent progress in research that seeks to understand the regeneration of hair cells and highlights findings that may hold importance for the eventual development of regenerative therapies for hearing and balance impairments. RECENT FINDINGS Signaling via the Notch receptor and the basic helix-loop-helix transcription factors has important roles in the development and regeneration of hair cells. The cytoskeletal properties and cell-matrix interactions of supporting cells in mice of different ages may hold part of the explanation for the age-related differences in their proliferative responses to damage and the differences between mammals and nonmammals in hair cell regeneration. Progress also has been made in deriving stem cells from inner ear tissues and other sources and in the evaluation of their potential uses as sources of new hair cells and as tools for biomedical research. SUMMARY Much has been accomplished since the discovery of postembryonic hair cell production and hair cell regeneration in nonmammals decades ago. No therapies for hair cell regeneration are under clinical trials, but research is yielding potentially important discoveries that are likely to lead to the development of therapeutic methods for inducing hair cell regeneration in the mammalian inner ear.
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Affiliation(s)
- Maria Sol Collado
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
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Current World Literature. Curr Opin Otolaryngol Head Neck Surg 2008; 16:490-5. [DOI: 10.1097/moo.0b013e3283130f63] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Cotanche DA. Genetic and pharmacological intervention for treatment/prevention of hearing loss. JOURNAL OF COMMUNICATION DISORDERS 2008; 41:421-443. [PMID: 18455177 PMCID: PMC2574670 DOI: 10.1016/j.jcomdis.2008.03.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2008] [Accepted: 03/12/2008] [Indexed: 05/26/2023]
Abstract
UNLABELLED Twenty years ago it was first demonstrated that birds could regenerate their cochlear hair cells following noise damage or aminoglycoside treatment. An understanding of how this structural and functional regeneration occurred might lead to the development of therapies for treatment of sensorineural hearing loss in humans. Recent experiments have demonstrated that noise exposure and aminoglycoside treatment lead to apoptosis of the hair cells. In birds, this programmed cell death induces the adjacent supporting cells to undergo regeneration to replace the lost hair cells. Although hair cells in the mammalian cochlea undergo apoptosis in response to noise damage and ototoxic drug treatment, the supporting cells do not possess the ability to undergo regeneration. However, current experiments on genetic manipulation, gene therapy, and stem cell transplantation suggest that regeneration in the mammalian cochlea may eventually be possible and may 1 day provide a therapeutic tool for hearing loss in humans. LEARNING OUTCOMES The reader should be able to: (1) Describe the anatomy of the avian and mammalian cochlea, identify the individual cell types in the organ of Corti, and distinguish major features that participate in hearing function, (2) Demonstrate a knowledge of how sound damage and aminoglycoside poisoning induce apoptosis of hair cells in the cochlea, (3) Define how hair cell loss in the avian cochlea leads to regeneration of new hair cells and distinguish this from the mammalian cochlea where there is no regeneration following damage, and (4) Interpret the potential for new approaches, such as genetic manipulation, gene therapy and stem cell transplantation, could provide a therapeutic approach to hair cell loss in the mammalian cochlea.
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MESH Headings
- Aminoglycosides/toxicity
- Animals
- Apoptosis/drug effects
- Apoptosis/genetics
- Apoptosis/physiology
- Birds
- Cell Proliferation/drug effects
- Genetic Therapy
- Guinea Pigs
- Hair Cells, Auditory/drug effects
- Hair Cells, Auditory/pathology
- Hair Cells, Auditory/physiology
- Hearing Loss, Noise-Induced/pathology
- Hearing Loss, Noise-Induced/physiopathology
- Hearing Loss, Noise-Induced/therapy
- Hearing Loss, Sensorineural/pathology
- Hearing Loss, Sensorineural/physiopathology
- Hearing Loss, Sensorineural/therapy
- Humans
- Mice
- Mice, Knockout
- Microscopy, Confocal
- Nerve Regeneration/drug effects
- Nerve Regeneration/genetics
- Nerve Regeneration/physiology
- Organ of Corti/drug effects
- Organ of Corti/pathology
- Organ of Corti/physiopathology
- Stem Cell Transplantation
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Affiliation(s)
- Douglas A Cotanche
- Laboratory of Cellular and Molecular Hearing Research, Department of Otolaryngology, Children's Hospital Boston, Boston, MA, USA.
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Damage-induced activation of ERK1/2 in cochlear supporting cells is a hair cell death-promoting signal that depends on extracellular ATP and calcium. J Neurosci 2008; 28:4918-28. [PMID: 18463245 DOI: 10.1523/jneurosci.4914-07.2008] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Acoustic overstimulation and ototoxic drugs can cause permanent hearing loss as a result of the damage and death of cochlear hair cells. Relatively little is known about the signaling pathways triggered by such trauma, although a significant role has been described for the c-Jun N-terminal kinase [one of the mitogen-activated protein kinases (MAPKs)] pathway. We investigated the role of another MAPK family, the extracellularly regulated kinases 1 and 2 (ERK1/2) during hair cell damage in neonatal cochlear explants. Within minutes of subjecting explants to mechanical damage, ERK1/2 were transiently activated in Deiters' and phalangeal cells but not in hair cells. The activation of ERK1/2 spread along the length of the cochlea, reaching its peak 5-10 min after damage onset. Release of extracellular ATP and the presence of functional connexin proteins were critical for the activation and spread of ERK1/2. Damage elicited an intercellular Ca(2+) wave in the hair cell region in the first seconds after damage. In the absence of Ca(2+) influx, the intercellular Ca(2+) wave and the magnitude and spread of ERK1/2 activation were reduced. Treatment with the aminoglycoside neomycin produced a similar pattern of ERK1/2 activation in supporting cells surrounding pyknotic hair cells. When ERK1/2 activation was prevented, there was a reduction in the number of pyknotic hair cells. Thus, activation of ERK1/2 in cochlear supporting cells in vitro is a common damage signaling mechanism that acts to promote hair cell death, indicating a direct role for supporting cells in regulating hair cell death.
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