Disruption of Atg7-dependent autophagy causes electromotility disturbances, outer hair cell loss, and deafness in mice

Abstract Atg7 is an indispensable factor that plays a role in canonical nonselective autophagy. Here we show that genetic ablation of Atg7 in outer hair cells (OHCs) in mice caused stereocilium damage, somatic electromotility disturbances, and presynaptic ribbon degeneration over time, which led to the gradual wholesale loss of OHCs and subsequent early-onset profound hearing loss. Impaired autophagy disrupted OHC mitochondrial function and triggered the accumulation of dysfunctional mitochondria that would otherwise be eliminated in a timely manner. Atg7-independent autophagy/mitophagy processes could not compensate for Atg7 deficiency and failed to rescue the terminally differentiated, non-proliferating OHCs. Our results show that OHCs orchestrate intricate nonselective and selective autophagic/mitophagy pathways working in concert to maintain cellular homeostasis. Overall, our results demonstrate that Atg7-dependent autophagy plays a pivotal cytoprotective role in preserving OHCs and maintaining hearing function.

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Oral Ethanol Potentiates the Loss of Outer Hair Cells in Cisplatin-Exposed Rats

Otolaryngology ◽

10.1016/j.otohns.2007.03.006 ◽

2007 ◽

Vol 137 (2) ◽

pp. 327-331 ◽

Cited By ~ 1

Author(s):

Dilip Madnani ◽

Geming Li ◽

Christopher M. Frenz ◽

Dorothy A. Frenz

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Outer Hair Cell ◽

Fold Increase ◽

Cell Loss ◽

Saline Group ◽

Outer Hair Cells ◽

Hair Cell Loss ◽

Auditory Hair Cells ◽

Ethanol Group

OBJECTIVE: The aim of this study was to examine the effect of oral ethanol on cisplatin ototoxicity. STUDY DESIGN AND SETTING: Twenty-seven-week-old, female Fisher 344 rats were divided into 4 experimental groups. The animals were administered per os (PO) saline (group 1), PO ethanol (group 2), PO saline with intraperitoneal (IP) cisplatin (group 3), or PO ethanol with IP cisplatin (group 4). After 3 days, scanning electron microscopy and counts of outer auditory hair cells were performed. RESULTS: A 2-fold increase in outer hair cell loss was obtained in the basal cochlear turn of rats receiving concomitant cisplatin and ethanol compared with animals receiving cisplatin and saline. No hair cell loss was observed in the middle cochlear turn of any experimental group. CONCLUSION: Our findings support potentiation of ototoxicity when cisplatin is combined with oral ethanol. SIGNIFICANCE: Contraindications for alcohol use in cancer patients receiving cisplatin are implicated.

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Disruption of Hars2 in Cochlear Hair Cells Causes Progressive Mitochondrial Dysfunction and Hearing Loss in Mice

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2021.804345 ◽

2021 ◽

Vol 15 ◽

Author(s):

Pengcheng Xu ◽

Longhao Wang ◽

Hu Peng ◽

Huihui Liu ◽

Hongchao Liu ◽

...

Keyword(s):

Hearing Loss ◽

Hair Cell ◽

Mitochondrial Dysfunction ◽

Hair Cells ◽

Cell Loss ◽

Outer Hair Cells ◽

Hair Cell Loss ◽

Progressive Hearing Loss ◽

Cochlear Hair Cells ◽

Inner Hair Cells

Mutations in a number of genes encoding mitochondrial aminoacyl-tRNA synthetases lead to non-syndromic and/or syndromic sensorineural hearing loss in humans, while their cellular and physiological pathology in cochlea has rarely been investigated in vivo. In this study, we showed that histidyl-tRNA synthetase HARS2, whose deficiency is associated with Perrault syndrome 2 (PRLTS2), is robustly expressed in postnatal mouse cochlea including the outer and inner hair cells. Targeted knockout of Hars2 in mouse hair cells resulted in delayed onset (P30), rapidly progressive hearing loss similar to the PRLTS2 hearing phenotype. Significant hair cell loss was observed starting from P45 following elevated reactive oxygen species (ROS) level and activated mitochondrial apoptotic pathway. Despite of normal ribbon synapse formation, whole-cell patch clamp of the inner hair cells revealed reduced calcium influx and compromised sustained synaptic exocytosis prior to the hair cell loss at P30, consistent with the decreased supra-threshold wave I amplitudes of the auditory brainstem response. Starting from P14, increasing proportion of morphologically abnormal mitochondria was observed by transmission electron microscope, exhibiting swelling, deformation, loss of cristae and emergence of large intrinsic vacuoles that are associated with mitochondrial dysfunction. Though the mitochondrial abnormalities are more prominent in inner hair cells, it is the outer hair cells suffering more severe cell loss. Taken together, our results suggest that conditional knockout of Hars2 in mouse cochlear hair cells leads to accumulating mitochondrial dysfunction and ROS stress, triggers progressive hearing loss highlighted by hair cell synaptopathy and apoptosis, and is differentially perceived by inner and outer hair cells.

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Structural Abnormalities in Inner Hair Cells Following Kanamycin-Induced Outer Hair Cell Loss

Lecture Notes in Biomathematics - The Mechanics and Biophysics of Hearing ◽

10.1007/978-1-4757-4341-8_2 ◽

1990 ◽

pp. 10-17 ◽

Cited By ~ 3

Author(s):

Carole M. Hackney ◽

David N. Furness ◽

Peter S. Steyger

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Outer Hair Cell ◽

Cell Loss ◽

Hair Cell Loss ◽

Inner Hair Cells ◽

Structural Abnormalities

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Permanent Threshold Shift and Cochlear Hair Cell Loss in the Kanamycin-Treated Guinea Pig

Otolaryngology ◽

10.1177/019459987808600609 ◽

1978 ◽

Vol 86 (6) ◽

pp. ORL-886-ORL-887 ◽

Cited By ~ 3

Author(s):

Cynthia A. Prosen ◽

Michael R. Petersen ◽

David. B. Moody ◽

William C. Stebbins ◽

Joseph E. Hawkins

Keyword(s):

Guinea Pig ◽

Hair Cell ◽

Hair Cells ◽

Guinea Pigs ◽

Cell Loss ◽

Outer Hair Cells ◽

Hair Cell Loss ◽

Hearing Sensitivity ◽

Cochlear Hair Cell ◽

Differential Contribution

The differential contribution of the inner hair cells (IHC) and the outer hair cells (OHC) in the mammalian cochlea to hearing sensitivity was assessed in six behaviorally-trained guinea pigs by comparing audiograms preadministration and postadministration of kanamycin, an antibiotic that predominantly destroys guinea pig OHC while leaving the IHC structurally unchanged. The results support the hypothesis that only the IHC of the cochlea responds to tones approximately 50 to 60 dB above the threshold of the intact cochlea.

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Cochlear Hair Cell Loss in Ears with Cholesteatomas Scanning Electron Microscopy Study

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348948809700113 ◽

1988 ◽

Vol 97 (1) ◽

pp. 78-82 ◽

Cited By ~ 4

Author(s):

Richard A. Chole ◽

Maggie Chiu

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Hair Cell ◽

Hair Cells ◽

Cell Loss ◽

Outer Hair Cells ◽

Mongolian Gerbils ◽

Hair Cell Loss ◽

Cochlear Hair Cell ◽

Scanning Electron

Cochleas from 16 Mongolian gerbils with spontaneous aural cholesteatomas, and four of similar age without cholesteatomas, were examined by scanning electron microscopy to quantify cochlear hair cell loss. Loss of hair cell stereocilia was found in all ears with cholesteatomas and was increased when compared with uninvolved ears from animals of similar age. The hair cell loss assorted with gerbilline cholesteatomas appeared to be most marked in the middle turn of the cochlea and increased in severity with increasing size of the cholesteatomas. Outer hair cells were affected more than inner hair cells. Inner and outer hair cell loss was not significantly different infected cholesteatomas versus sterile cholesteatomas. The greater damage to hair cels at the middle turn compared to the basal turn suggests that these losses may be the result of some agent acting through the cochlear wall rather than through the round window.

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Selective Inner Hair Cell Loss in a Neonate Harbor Seal (Phoca vitulina)

Animals ◽

10.3390/ani12020180 ◽

2022 ◽

Vol 12 (2) ◽

pp. 180

Author(s):

Maria Morell ◽

Laura Rojas ◽

Martin Haulena ◽

Björn Busse ◽

Ursula Siebert ◽

...

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Marine Mammal ◽

Cell Loss ◽

Harbor Seal ◽

Phoca Vitulina ◽

Outer Hair Cells ◽

Hair Cell Loss ◽

Inner Hair Cell ◽

Inner Hair Cells

Congenital hearing loss is recognized in humans and other terrestrial species. However, there is a lack of information on its prevalence or pathophysiology in pinnipeds. It is important to have baseline knowledge on marine mammal malformations in the inner ear, to differentiate between congenital and acquired abnormalities, which may be caused by infectious pathogens, age, or anthropogenic interactions, such as noise exposure. Ultrastructural evaluation of the cochlea of a neonate harbor seal (Phoca vitulina) by scanning electron microscopy revealed bilateral loss of inner hair cells with intact outer hair cells. The selective inner hair cell loss was more severe in the basal turn, where high-frequency sounds are encoded. The loss of inner hair cells started around 40% away from the apex or tip of the spiral, reaching a maximum loss of 84.6% of hair cells at 80–85% of the length from the apex. Potential etiologies and consequences are discussed. This is believed to be the first case report of selective inner hair cell loss in a marine mammal neonate, likely congenital.

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Near-infrared-light pre-treatment attenuates noise-induced hearing loss in mice

PeerJ ◽

10.7717/peerj.9384 ◽

2020 ◽

Vol 8 ◽

pp. e9384

Author(s):

Dietmar Basta ◽

Moritz Gröschel ◽

Ira Strübing ◽

Patrick Boyle ◽

Felix Fröhlich ◽

...

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Near Infrared ◽

Noise Exposure ◽

Cell Loss ◽

Outer Hair Cells ◽

Infrared Light ◽

Hair Cell Loss ◽

Nir Light ◽

Pre Treatment

Noise induced hearing loss (NIHL) is accompanied by a reduction of cochlear hair cells and spiral ganglion neurons. Different approaches have been applied to prevent noise induced apoptosis / necrosis. Physical intervention is one technique currently under investigation. Specific wavelengths within the near-infrared light (NIR)-spectrum are known to influence cytochrome-c-oxidase activity, which leads in turn to a decrease in apoptotic mechanisms. It has been shown recently that NIR can significantly decrease the cochlear hair cell loss if applied daily for 12 days after a noise exposure. However, it is still unclear if a single NIR-treatment, just before a noise exposure, could induce similar protective effects. Therefore, the present study was conducted to investigate the effect of a single NIR-pre-treatment aimed at preventing or limiting NIHL. The cochleae of adult NMRI-mice were pre-treated with NIR-light (808 nm, 120 mW) for 5, 10, 20, 30 or 40 minutes via the external ear canal. All animals were noised exposed immediately after the pre-treatment by broad band noise (5–20 kHz) for 30 minutes at 115 dB SPL. Frequency specific ABR-recordings to determine auditory threshold shift were carried out before the pre-treatment and two weeks after the noise exposure. The amplitude increase for wave IV and cochlear hair cell loss were determined. A further group of similar mice was noise exposed only and served as a control for the NIR pre-exposed groups. Two weeks after noise exposure, the ABR threshold shifts of NIR-treated animals were significantly lower (p < 0.05) than those of the control animals. The significance was at three frequencies for the 5-minute pre-treatment group and across the entire frequency range for all other treatment groups. Due to NIR light, the amplitude of wave four deteriorates significantly less after noise exposure than in controls. The NIR pre-treatment had no effect on the loss of outer hair cells, which was just as high with or without NIR-light pre-exposure. Relative to the entire number of outer hair cells across the whole cochlea, outer hair cell loss was rather negligible. No inner hair cell loss whatever was detected. Our results suggest that a single NIR pre-treatment induces a very effective protection of cochlear structures from noise exposure. Pre-exposure of 10 min seems to emerge as the optimal dosage for our experimental setup. A saturated effect occurred with higher dosage-treatments. These results are relevant for protection of residual hearing in otoneurosurgery such as cochlear implantation.

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Assessment of cochlear toxicity in response to chronic 3,3′-iminodipropionitrile in mice reveals early and reversible functional loss that precedes overt histopathology

Archives of Toxicology ◽

10.1007/s00204-020-02962-5 ◽

2021 ◽

Vol 95 (3) ◽

pp. 1003-1021

Author(s):

Erin A. Greguske ◽

Jordi Llorens ◽

Sonja J. Pyott

Keyword(s):

Hearing Loss ◽

Hair Cell ◽

Auditory System ◽

Hair Cells ◽

Time Course ◽

Cell Loss ◽

Outer Hair Cells ◽

Hair Cell Loss ◽

Brainstem Response ◽

Peripheral Auditory System

AbstractThe peripheral auditory and vestibular systems rely on sensorineural structures that are vulnerable to ototoxic agents that cause hearing loss and/or equilibrium deficits. Although attention has focused on hair cell loss as the primary pathology underlying ototoxicity, evidence from the peripheral vestibular system indicates that hair cell loss during chronic exposure is preceded by synaptic uncoupling from the neurons and is potentially reversible. To determine if synaptic pathology also occurs in the peripheral auditory system, we examined the extent, time course, and reversibility of functional and morphological alterations in cochleae from mice exposed to 3,3′-iminodipropionitrile (IDPN) in drinking water for 2, 4 or 6 weeks. Functionally, IDPN exposure caused progressive high- to low-frequency hearing loss assessed by measurement of auditory brainstem response wave I absolute thresholds and amplitudes. The extent of hearing loss scaled with the magnitude of vestibular dysfunction assessed behaviorally. Morphologically, IDPN exposure caused progressive loss of outer hair cells (OHCs) and synapses between the inner hair cells (IHCs) and primary auditory neurons. In contrast, IHCs were spared from ototoxic damage. Importantly, hearing loss consistent with cochlear synaptopathy preceded loss of OHCs and synapses and, moreover, recovered if IDPN exposure was stopped before morphological pathology occurred. Our observations suggest that synaptic uncoupling, perhaps as an early phase of cochlear synaptopathy, also occurs in the peripheral auditory system in response to IDPN exposure. These findings identify novel mechanisms that contribute to the earliest stages of hearing loss in response to ototoxic agents and possibly other forms of acquired hearing loss.

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The location and mechanism of electromotility in guinea pig outer hair cells

Journal of Neurophysiology ◽

10.1152/jn.1993.70.2.549 ◽

1993 ◽

Vol 70 (2) ◽

pp. 549-558 ◽

Cited By ~ 38

Author(s):

R. Hallworth ◽

B. N. Evans ◽

P. Dallos

Keyword(s):

Guinea Pig ◽

Hair Cells ◽

Outer Hair Cell ◽

Length Change ◽

Opposite Polarity ◽

Outer Hair Cells ◽

Response Amplitude ◽

Change Function ◽

Length Changes ◽

Diameter Change

1. The microchamber method was used to examine the motile responses of isolated guinea pig outer hair cells to electrical stimulation. In the microchamber method, an isolated cell is drawn partway into a suction pipette and stimulated transcellularly. The relative position of the cell in the microchamber is referred to as the exclusion fraction. 2. The length changes of the included and excluded segments were compared for constant sinusoidal stimulus amplitude as functions of the exclusion fraction. Both included and excluded segments showed maximal responses when the cell was excluded approximately halfway. Both segments showed smaller or absent responses when the cell was almost fully excluded or almost fully included. 3. When the cell was near to, but not at, the maximum exclusion, the included segment response amplitude was zero, whereas the excluded segment response amplitude was nonzero. In contrast, when the cell was nearly fully included, the excluded segment response amplitude was zero, but the included segment response amplitude was still detectable. A simple model of outer hair cell motility based on these results suggests that the cell has finite-resistance terminations and that the motors are restricted to a region above the nucleus and below its ciliated apex (cuticular plate). 4. The function describing length change as a function of command voltage was measured for each segment as the exclusion fraction was varied. The functions were similar at midrange exclusions (i.e., when the segments were about equal length), showing nonlinearity and saturability. The functions were strikingly different when the segment lengths were different. The effects of exclusion on the voltage to length-change functions suggested that the nonlinearity and saturability are local properties of the motility mechanism. 5. The diameter changes of both segments were examined. The segment diameter changes were always antiphasic to the length changes. This finding implies that the motility mechanism has an active antiphasic diameter component. The diameter change amplitude was a monotonically increasing function of exclusion for the included segment, and a decreasing function for the excluded segment. 6. The voltage to length-change and voltage to diameter-change functions were measured for the same cell and exclusion fraction. The voltage to diameter-change function was smaller in amplitude than the voltage to length-change function. The functions were of opposite polarity to each other, but were otherwise similar in character. Thus it is likely that the same motor mechanism is responsible for both axial and diameter deformations.

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