In vivo notch reactivation in differentiating cochlear hair cells induces sox2 and prox1 expression but does not disrupt hair cell maturation

AbstractCurrent clinical interest lies in the relationship between hearing loss and cognitive impairment. Previous work demonstrated that noise exposure, a common cause of sensorineural hearing loss (SNHL), leads to cognitive impairments in mice. However, in noise-induced models, it is difficult to distinguish the effects of noise trauma from subsequent SNHL on central processes. Here, we use cochlear hair cell ablation to isolate the effects of SNHL. Cochlear hair cells were conditionally and selectively ablated in mature, transgenic mice where the human diphtheria toxin (DT) receptor was expressed behind the hair-cell specific Pou4f3 promoter. Due to higher Pou4f3 expression in cochlear hair cells than vestibular hair cells, administration of a low dose of DT caused profound SNHL without vestibular dysfunction and had no effect on wild-type (WT) littermates. Spatial learning/memory was assayed using an automated radial 8-arm maze (RAM), where mice were trained to find food rewards over a 14-day period. The number of working memory errors (WME) and reference memory errors (RME) per training day were recorded. All animals were injected with DT during P30–60 and underwent the RAM assay during P90–120. SNHL animals committed more WME and RME than WT animals, demonstrating that isolated SNHL affected cognitive function. Duration of SNHL (60 versus 90 days post DT injection) had no effect on RAM performance. However, younger age of acquired SNHL (DT on P30 versus P60) was associated with fewer WME. This describes the previously undocumented effect of isolated SNHL on cognitive processes that do not directly rely on auditory sensory input.

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Shaker-1 mutations reveal roles for myosin VIIA in both development and function of cochlear hair cells

Development ◽

10.1242/dev.125.4.557 ◽

1998 ◽

Vol 125 (4) ◽

pp. 557-566 ◽

Cited By ~ 3

Author(s):

T. Self ◽

M. Mahony ◽

J. Fleming ◽

J. Walsh ◽

S.D. Brown ◽

...

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Usher Syndrome ◽

Orthologous Gene ◽

Cell Development ◽

Cochlear Hair Cells ◽

Cochlear Hair Cell ◽

Show Evidence ◽

Myosin Viia ◽

And Function

The mouse shaker-1 locus, Myo7a, encodes myosin VIIA and mutations in the orthologous gene in humans cause Usher syndrome type 1B or non-syndromic deafness. Myo7a is expressed very early in sensory hair cell development in the inner ear. We describe the effects of three mutations on cochlear hair cell development and function. In the Myo7a816SB and Myo7a6J mutants, stereocilia grow and form rows of graded heights as normal, but the bundles become progressively more disorganised. Most of these mutants show no gross electrophysiological responses, but some did show evidence of hair cell depolarisation despite the disorganisation of their bundles. In contrast, the original shaker-1 mutants, Myo7ash1, had normal early development of stereocilia bundles, but still showed abnormal cochlear responses. These findings suggest that myosin VIIA is required for normal stereocilia bundle organisation and has a role in the function of cochlear hair cells.

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LIN28B/let-7control the ability of neonatal murine auditory supporting cells to generate hair cells through mTOR signaling

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2000417117 ◽

2020 ◽

Vol 117 (36) ◽

pp. 22225-22236

Author(s):

Xiao-Jun Li ◽

Angelika Doetzlhofer

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Rna Binding ◽

Mammalian Target Of Rapamycin ◽

Cell Loss ◽

Supporting Cell ◽

Dependent Manner ◽

Cell Plasticity ◽

Supporting Cells ◽

Cochlear Hair Cells

Mechano-sensory hair cells within the inner ear cochlea are essential for the detection of sound. In mammals, cochlear hair cells are only produced during development and their loss, due to disease or trauma, is a leading cause of deafness. In the immature cochlea, prior to the onset of hearing, hair cell loss stimulates neighboring supporting cells to act as hair cell progenitors and produce new hair cells. However, for reasons unknown, such regenerative capacity (plasticity) is lost once supporting cells undergo maturation. Here, we demonstrate that the RNA binding protein LIN28B plays an important role in the production of hair cells by supporting cells and provide evidence that the developmental drop in supporting cell plasticity in the mammalian cochlea is, at least in part, a product of declining LIN28B-mammalian target of rapamycin (mTOR) activity. Employing murine cochlear organoid and explant cultures to model mitotic and nonmitotic mechanisms of hair cell generation, we show that loss of LIN28B function, due to its conditional deletion, or due to overexpression of the antagonistic miRNAlet-7g, suppressed Akt-mTOR complex 1 (mTORC1) activity and renders young, immature supporting cells incapable of generating hair cells. Conversely, we found that LIN28B overexpression increased Akt-mTORC1 activity and allowed supporting cells that were undergoing maturation to de-differentiate into progenitor-like cells and to produce hair cells via mitotic and nonmitotic mechanisms. Finally, using the mTORC1 inhibitor rapamycin, we demonstrate that LIN28B promotes supporting cell plasticity in an mTORC1-dependent manner.

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A modified adenovirus can transfect cochlear hair cells in vivo without compromising cochlear function

Gene Therapy ◽

10.1038/sj.gt.3301445 ◽

2001 ◽

Vol 8 (10) ◽

pp. 789-794 ◽

Cited By ~ 56

Author(s):

A E Luebke ◽

J D Steiger ◽

B L Hodges ◽

A Amalfitano

Keyword(s):

Hair Cells ◽

Cochlear Function ◽

Cochlear Hair Cells

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Overexpression of SK2 Channels Enhances Efferent Suppression of Cochlear Responses Without Enhancing Noise Resistance

Journal of Neurophysiology ◽

10.1152/jn.01183.2006 ◽

2007 ◽

Vol 97 (4) ◽

pp. 2930-2936 ◽

Cited By ~ 15

Author(s):

Stéphane F. Maison ◽

Lisan L. Parker ◽

Lucy Young ◽

John P. Adelman ◽

Jian Zuo ◽

...

Keyword(s):

Nicotinic Acetylcholine Receptors ◽

Hair Cells ◽

Otoacoustic Emissions ◽

Outer Hair Cell ◽

Outer Hair Cells ◽

Sk Channels ◽

Cochlear Function ◽

Cochlear Hair Cells ◽

Efferent Suppression

Cochlear hair cells express SK2, a small-conductance Ca2+-activated K+ channel thought to act in concert with Ca2+-permeable nicotinic acetylcholine receptors (nAChRs) α9 and α10 in mediating suppressive effects of the olivocochlear efferent innervation. To probe the in vivo role of SK2 channels in hearing, we examined gene expression, cochlear function, efferent suppression, and noise vulnerability in mice overexpressing SK2 channels. Cochlear thresholds, as measured by auditory brain stem responses and otoacoustic emissions, were normal in overexpressers as was overall cochlear morphology and the size, number, and distribution of efferent terminals on outer hair cells. Cochlear expression levels of SK2 channels were elevated eightfold without striking changes in other SK channels or in the α9/α10 nAChRs. Shock-evoked efferent suppression of cochlear responses was significantly enhanced in overexpresser mice as seen previously in α9 overexpresser mice; however, in contrast to α9 overexpressers, SK2 overexpressers were not protected from acoustic injury. Results suggest that efferent-mediated cochlear protection is mediated by other downstream effects of ACh-mediated Ca2+ entry different from those involving SK2-mediated hyperpolarization and the associated reduction in outer hair cell electromotility.

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Calcium Modulates the Frequency and Amplitude of Spontaneous Otoacoustic Emissions in the Bobtail Skink

Journal of Neurophysiology ◽

10.1152/jn.00267.2004 ◽

2004 ◽

Vol 92 (5) ◽

pp. 2685-2693 ◽

Cited By ~ 20

Author(s):

Geoffrey A. Manley ◽

Ulrike Sienknecht ◽

Christine Köppl

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Otoacoustic Emissions ◽

Calcium Concentration ◽

Chelating Agent ◽

Lizard Species ◽

Spontaneous Otoacoustic Emissions ◽

Active Processes

Active processes in the inner ear of lizards can be monitored using spontaneous otoacoustic emissions (SOAE) measured outside the eardrum. In the Australian bobtail lizard, SOAE are generated by an active motility process in the hair-cell bundle. This mechanism has been shown to be sensitive to the calcium-chelating agent 1,2-bis(o-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid and is presumed to be related to the calcium-sensitive transduction-channel motor implicated in other nonmammalian hair cell systems. In studies of frog saccular and turtle auditory papillar hair cells in vitro, the frequency and amplitude of bundle oscillations depend on the concentration of calcium in the bathing solutions. In the present study, the calcium concentration in the endolymph was changed in vivo in the Australian bobtail lizard Tiliqua rugosa, and SOAE were monitored. Glass pipettes with large tips and containing different calcium concentrations in their fluids were introduced into scala media, and their contents were allowed to passively flow into the endolymph. Low calcium concentrations resulted in a downward shift in the frequency of SOAE spectral peaks and generally an increase in their amplitudes. Calcium concentrations >2 mM resulted in increases in frequency of SOAE peaks and generally a loss in amplitude. These frequency shifts were consistent with in vitro data on the frequencies and amplitudes of spontaneous oscillation of hair cell bundles and thus also implicate calcium ions in the generation of active motility in nonmammalian hair cells. The data also suggest that in this lizard species, the ionic calcium concentration in the cochlear endolymph is ≥1 mM.

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The coding of sound pressure and frequency in cochlear hair cells of the terrapin

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1978.0101 ◽

1978 ◽

Vol 203 (1151) ◽

pp. 209-218 ◽

Cited By ~ 33

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Characteristic Frequency ◽

Voltage Response ◽

Recording Electrode ◽

Small Current ◽

Cochlear Hair Cells ◽

Damped Oscillations ◽

Current Steps ◽

Two Stages

Intracellular recordings have been made from single hair cells in the cochlea of the terrapin, and the site of recording has been verified by injection of a fluorescent dye through the recording electrode. A hair cell gives periodic voltage responses graded with the intensity and frequency of the sound stimulus, and produces the largest response at its characteristic frequency. When small current steps are injected through the recording electrode, the voltage response of the cell exhibits damped oscillations at its characteristic frequency. The results are consistent with the idea that the cochlear frequency selectivity arises in two stages and it is suggested that the second stage resides within the hair cell itself.

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Olivocochlear suppression of outer hair cells in vivo: evidence for combined action of BK and SK2 channels throughout the cochlea

Journal of Neurophysiology ◽

10.1152/jn.00924.2012 ◽

2013 ◽

Vol 109 (6) ◽

pp. 1525-1534 ◽

Cited By ~ 27

Author(s):

Stéphane F. Maison ◽

Sonja J. Pyott ◽

Andrea L. Meredith ◽

M. Charles Liberman

Keyword(s):

Hair Cells ◽

In Vitro Study ◽

Bk Channels ◽

Outer Hair Cells ◽

Cochlear Hair Cells ◽

Α Subunit ◽

Combined Action ◽

Cholinergic Effects

Cholinergic inhibition of cochlear hair cells via olivocochlear (OC)-efferent feedback is mediated by Ca2+ entry through α9-/α10-nicotinic receptors, but the nature of the K+ channels activated by this Ca2+ entry has been debated (Yoshida N, Hequembourg SJ, Atencio CA, Rosowski JJ, Liberman MC. J Neurophysiol 85: 84–88, 2001). A recent in vitro study (Wersinger E, McLean WJ, Fuchs PA, Pyott SJ. PLoS One 5: e13836, 2010) suggests that small-conductance (SK2) channels mediate cholinergic effects in the apical turn, whereas large-conductance (BK) channels mediate basal turn effects. Here, we measure, as a function of cochlear frequency, the magnitude of BK and SK2 expression in outer hair cells and the strength of in vivo OC suppression in BK+/+ mice vs. BK−/− lacking the obligatory α-subunit (Meredith AL, Thorneloe KS, Werner ME, Nelson MT, Aldrich RW. J Biol Chem 279: 36746–36752, 2004). Except at the extreme apical tip, we see immunostaining for both BK and SK2 in BK+/+. Correspondingly, at all testable frequencies (8–45 kHz), we see evidence for both SK2 and BK contributions to OC effects evoked by electrically stimulating the OC bundle: OC-mediated suppression was reduced, but not eliminated, at all frequencies in the BK−/− ears. The suppression remaining in BK nulls was blocked by strychnine, suggesting involvement of α9-/α10-cholinergic receptors, coupled to activation of the remaining SK2 channels.

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