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Loss of Slc4a1b chloride/bicarbonate exchanger function protects mechanosensory hair cells from aminoglycoside damage in the zebrafish mutant persephone.

ABSTRACT: Mechanosensory hair cell death is a leading cause of hearing and balance disorders in the human population. Hair cells are remarkably sensitive to environmental insults such as excessive noise and exposure to some otherwise therapeutic drugs. However, individual responses to damaging agents can vary, in part due to genetic differences. We previously carried out a forward genetic screen using the zebrafish lateral line system to identify mutations that alter the response of larval hair cells to the antibiotic neomycin, one of a class of aminoglycoside compounds that cause hair cell death in humans. The persephone mutation confers resistance to aminoglycosides. 5 dpf homozygous persephone mutants are indistinguishable from wild-type siblings, but differ in their retention of lateral line hair cells upon exposure to neomycin. The mutation in persephone maps to the chloride/bicarbonate exchanger slc4a1b and introduces a single Ser-to-Phe substitution in zSlc4a1b. This mutation prevents delivery of the exchanger to the cell surface and abolishes the ability of the protein to import chloride across the plasma membrane. Loss of function of zSlc4a1b reduces hair cell death caused by exposure to the aminoglycosides neomycin, kanamycin, and gentamicin, and the chemotherapeutic drug cisplatin. Pharmacological block of anion transport with the disulfonic stilbene derivatives DIDS and SITS, or exposure to exogenous bicarbonate, also protects hair cells against damage. Both persephone mutant and DIDS-treated wild-type larvae show reduced uptake of labeled aminoglycosides. persephone mutants also show reduced FM1-43 uptake, indicating a potential impact on mechanotransduction-coupled activity in the mutant. We propose that tight regulation of the ionic environment of sensory hair cells, mediated by zSlc4a1b activity, is critical for their sensitivity to aminoglycoside antibiotics.

SUBMITTER: Hailey DW

PROVIDER: S-EPMC3469417 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Aminoglycosides exhibit ototoxicity by damaging mitochondria, which in turn generate reactive oxygen species that induce hair cell death and subsequent hearing loss. It is well known that damaged mitochondria are degraded by mitophagy, an important mitochondrial quality control system that maintains mitochondrial homeostasis and ensures cell survival. However, it is unclear whether dysregulation of mitophagy contributes to aminoglycoside-induced hair cell injury. In the current study, we found that PINK1-PRKN-mediated mitophagy was impaired in neomycin-treated hair cells. Our data suggested that mitochondrial recruitment of PRKN and phagophore recognition of damaged mitochondria during mitophagy were blocked following neomycin treatment. In addition, the degradation of damaged mitochondria by lysosomes was significantly decreased as indicated by the mitophagic flux reporter mt-mKeima. Moreover, we demonstrated that neomycin disrupted mitophagy through transcriptional inhibition of Pink1 expression, the key initiator of mitophagy. Moreover, we found that neomycin impaired mitophagy by inducing ATF3 expression. Importantly, treatment with a mitophagy activator could rescue neomycin-treated hair cells by increasing mitophagy, indicating that genetic modulation or drug intervention in mitophagy may have therapeutic potential for aminoglycoside-induced hearing loss.Abbreviations: AAV: adeno-associated virus; ABR: auditory brainstem response; ATF3: activating transcription factor 3; ATOH1/MATH1: atonal bHLH transcription factor 1; BafA1: bafilomycin A1; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; COX4I1/COXIV: cytochrome c oxidase subunit 4I1; CTBP2/RIBEYE: C-terminal binding protein 2; DFP: deferiprone; EGFP: enhanced green fluorescent protein; FOXO3: forkhead box O3; GRIA2/GLUR2: glutamate receptor, ionotropic, AMPA2 (alpha 2); HC: hair cell; HSPD1/HSP60: heat shock protein 1 (chaperonin); IHC: inner hair cell; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MYO7A: myosin VIIA; OPTN: optineurin; OMM: outer mitochondrial membrane; PRKN: parkin RBR E3 ubiquitin protein ligase; PINK1: PTEN induced putative kinase 1; RT-qPCR: real-time quantitative polymerase chain reaction; TOMM20/TOM20: translocase of outer mitochondrial membrane 20; TUNEL: Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling; USP30: ubiquitin specific peptidase 30; XBP1: X-box binding protein 1.

Project description:In humans, the absence or irreversible loss of hair cells, the sensory mechanoreceptors in the cochlea, accounts for a large majority of acquired and congenital hearing disorders. In the auditory and vestibular neuroepithelia of the inner ear, hair cells are accompanied by another cell type called supporting cells. This second cell population has been described as having stem cell-like properties, allowing efficient hair cell replacement during embryonic and larval/fetal development of all vertebrates. However, mammals lose their regenerative capacity in most inner ear neuroepithelia in postnatal life. Remarkably, reptiles, birds, amphibians, and fish are different in that they can regenerate hair cells throughout their lifespan. The lateral line in amphibians and in fish is an additional sensory organ, which is used to detect water movements and is comprised of neuroepithelial patches, called neuromasts. These are similar in ultra-structure to the inner ear's neuroepithelia and they share the expression of various molecular markers. We examined the regeneration process in hair cells of the lateral line of zebrafish larvae carrying a retroviral integration in a previously uncharacterized gene, phoenix (pho). Phoenix mutant larvae develop normally and display a morphologically intact lateral line. However, after ablation of hair cells with copper or neomycin, their regeneration in pho mutants is severely impaired. We show that proliferation in the supporting cells is strongly decreased after damage to hair cells and correlates with the reduction of newly formed hair cells in the regenerating phoenix mutant neuromasts. The retroviral integration linked to the phenotype is in a novel gene with no known homologs showing high expression in neuromast supporting cells. Whereas its role during early development of the lateral line remains to be addressed, in later larval stages phoenix defines a new class of proteins implicated in hair cell regeneration.

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Loss of Slc4a1b chloride/bicarbonate exchanger function protects mechanosensory hair cells from aminoglycoside damage in the zebrafish mutant persephone.

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