Anion Transport Proteins ; physiology ; Hair Cells, Auditory, Outer ; physiology ; Humans

Hearing loss has become increasingly prevalent and causes considerable disability, thus gravely burdening the global economy. Irreversible loss of hair cells is a main cause of sensorineural hearing loss, and currently, the only relatively effective clinical treatments are limited to digital hearing equipment like cochlear implants and hearing aids, but these are of limited benefit in patients. It is therefore urgent to understand the mechanisms of damage repair in order to develop new neuroprotective strategies. At present, how to promote the regeneration of functional hair cells is a key scientific question in the field of hearing research. Multiple signaling pathways and transcriptional factors trigger the activation of hair cell progenitors and ensure the maturation of newborn hair cells, and in this article, we first review the principal mechanisms underlying hair cell reproduction. We then further discuss therapeutic strategies involving the co-regulation of multiple signaling pathways in order to induce effective functional hair cell regeneration after degeneration, and we summarize current achievements in hair cell regeneration. Lastly, we discuss potential future approaches, such as small molecule drugs and gene therapy, which might be applied for regenerating functional hair cells in the clinic.
Infant, Newborn ; Humans ; Hair Cells, Auditory, Inner/physiology* ; Ear, Inner/physiology* ; Hair Cells, Auditory/physiology* ; Regeneration/genetics* ; Stem Cells

BACKGROUNDPrevious studies have suggested that primary degeneration of hair cells causes secondary degeneration of spiral ganglion neurons (SGNs), but the effect of SGN degeneration on hair cells has not been studied. In the adult mouse inner ear ouabain can selectively and permanently induce the degeneration of type 1 SGNs while leaving type 2 SGNs, efferent fibers, and sensory hair cells relatively intact. This study aimed to investigate the dynamic changes in hair cell ribbon synapse induced by loss of SGNs using ouabain application to the round window niche of adult mice.

METHODSIn the analysis, 24 CBA/CAJ mice aged 8-10 weeks, were used, of which 6 normal mice were used as the control group. After ouabain application in the round window niche 6 times in an hour, ABR threshold shifts at least 30 dB in the three experimental groups which had six mice for 1-week group, six for 1-month group, and six for 3-month group. All 24 animals underwent function test at 1 week and then immunostaining at 1 week, 1 month, and 3 months.

RESULTSThe loss of neurons was followed by degeneration of postsynaptic specializations at the afferent synapse with hair cells. One week after ouabain treatment, the nerve endings of type 1 SGNs and postsynaptic densities, as measured by Na/K ATPase and PSD-95, were affected but not entirely missing, but their partial loss had consequences for synaptic ribbons that form the presynaptic specialization at the synapse between hair cells and primary afferent neurons. Ribbon numbers in inner hair cells decreased (some of them broken and the ribbon number much decreased), and the arrangement of the synaptic ribbons had undergone a dynamic reorganization: ribbons with or without associated postsynaptic densities moved from their normal location in the basal membrane of the cell to a more apical location and the neural endings alone were also found at more apical locations without associated ribbons. After 1 month, when the neural postsynaptic densities had completed their degeneration, most ribbons were lost and the remaining ribbons had no contact with postsynaptic densities; after 3 months, the ribbon synapses were gone except for an occasional remnant of a CtBP2-positive vesicle. Hair cells were intact other than the loss of ribbons (based on immunohistochemistry and DPOAE).

CONCLUSIONThese findings define the effect of SGN loss on the precise spatiotemporal size and location of ribbons and the time course of synaptic degeneration and provide a model for studying plasticity and regeneration.

Animals ; Female ; Hair Cells, Auditory ; cytology ; physiology ; Hair Cells, Auditory, Inner ; cytology ; physiology ; Mice ; Mice, Inbred CBA ; Synapses ; physiology

Hair Cells, Auditory, Inner ; cytology ; Synapses ; physiology ; ultrastructure

Auditory function in vertebrates depends on the transduction of sound vibrations into electrical signals by inner ear hair cells. In general, hearing loss resulting from hair cell damage is irreversible because the human ear has been considered to be incapable of regenerating or repairing these sensory elements following severe injury. Therefore, regeneration and protection of inner ear hair cells have become an exciting, rapidly evolving field of research during the last decade. However, mammalian auditory hair cells are few in number, experimentally inaccessible, and barely proliferate postnatally in vitro. Various in vitro primary culture systems of inner ear hair cells have been established by different groups, although many challenges remain unresolved. Here, we briefly explain the structure of the inner ear, summarize the published methods of in vitro hair cell cultures, and propose a feasible protocol for culturing these cells, which gave satisfactory results in our study. A better understanding of in vitro hair cell cultures will substantially facilitate research involving auditory functions, drug development, and the isolation of critical molecules involved in hair cell biology.
Animals ; Cells, Cultured ; Hair Cells, Auditory/physiology* ; Mice ; Mice, Inbred C57BL

OBJECTIVE: We used electrophysiological methods to study that whether GABA could elicit OHCs outward currents provide evidence for exsitence of GABA-A receptor and investige the relationship between the effect of GABA and the development of OHCs. METHOD: We used whole-cell recording OHCs at current-clamp or voltage-clamp to verify the function of GABA receptor on OHCs. Then we counteds the responsive cells vs. total number cells, and according to results to study the relationships between the GABA receptor and development of OHCs. RESULT: OHC was elicited outward current or hyperpolarized by GABA and the responsive cells were decreased with development. CONCLUSION The result of GABA receptor decreasing with development suggested that the receptor may draw efferents to OHCs or facilitate the MOC-OHC synapse formation.
Animals ; Electrophysiological Phenomena ; Hair Cells, Auditory, Outer ; physiology ; Patch-Clamp Techniques ; Rats ; Receptors, GABA-A ; physiology ; gamma-Aminobutyric Acid ; physiology

High level noise can damage cochlear hair cells, auditory nerve and synaptic connections between cochlear hair cells and auditory nerve, resulting in noise-induced hearing loss (NIHL). Recent studies have shown that animal cochleae have circadian rhythm, which makes them different in sensitivity to noise throughout the day. Cochlear circadian rhythm has a certain relationship with brain-derived neurotrophic factor and glucocorticoids, which affects the degree of hearing loss after exposure to noise. In this review, we summarize the research progress of the regulation of cochlear sensitivity to noise by circadian rhythm and prospect the future research direction.
Animals ; Auditory Threshold ; Circadian Rhythm ; Cochlea ; Evoked Potentials, Auditory, Brain Stem/physiology* ; Hair Cells, Auditory ; Hearing Loss, Noise-Induced ; Noise/adverse effects*

OBJECTIVEIn this study, we investigated the potential of mouse induced pluripotent stem cells (iPSC) for use as a source of transplants for the restoration of auditory hair cells and spiral ganglion neurons.

METHODSWe co-cultured the mouse iPSC with the cells of the cochlear organ of Corti or the modiolus in vitro. The cochlear organ of Corti (which contains cochlear hair cells) and the modiolus (which contains auditory spiral ganglion neurons) were obtained from postnatal day 3 (P3) CD-1 ICR mice. After 18 days of coculture with the cells of newborn mouse cochleae. The expressions of hair cell markers (Myosin VIIa, Math1, Calretinin, Espin) and Spiral ganglion neuron markers [Nestin, Neurofilament-M, β-III Tubulin, Vesicular glutamate transporter 1(VGluT1)] were detected by immunocytochemical analysis.

RESULTSImmunocytochemical analysis results indicated that the differentiated iPSC expressed auditory hair cell markers (MyosinVIIa,Math1, Calretinin, Espin ) and spiral ganglion markers (Nestin, Neurofilament-M,β-III Tubulin,VGluT1).

CONCLUSIONMouse iPSC in virto cultured could successfully be induced to differentiate into hair cell-like cells and spiral ganglion-like cells with hair cell and spiral ganglion molecular markers.

Animals ; Cell Differentiation ; Cochlea ; physiology ; Coculture Techniques ; Hair ; Hair Cells, Auditory ; In Vitro Techniques ; Induced Pluripotent Stem Cells ; Mice ; Mice, Inbred ICR ; Neurons ; Spiral Ganglion ; physiology

AIMThe comparison of several methods which were used to isolate cochlear outer hair cells and the observations of morphology were researched.

METHODSThree different separating methods of outer hair cells in cochlea were adopted; the morphology of outer hair cells in cochlea and the morphology of cochlear stretched preparation in Silver Nitrate staining were also investigated.

RESULTSSingle alive OHC in cochlea was disassociated by all methods, with microscope and cochlear stretched preparation's staining. We could also observe appearances and distributions of OHC in cochlea.

CONCLUSIONIt is successful to isolate single alive cochlear OHC, and it will be very important to investigate deeply normal physiological functions and changes of functions and morphology in some pathologic status in cochlear OHCs.

Animals ; Cell Separation ; methods ; Cochlea ; cytology ; physiology ; Female ; Guinea Pigs ; Hair Cells, Auditory, Outer ; cytology ; physiology ; Male ; Silver Staining

OBJECTIVETo compare the influences of stapedectomy and small fenestra stapedotomy on the hearing of guinea pigs.

METHODSTwenty-four (48 ears) guinea pigs were randomized equally into two groups, and the left ears were subjected to stapedectomy and total stapes replacement with a prosthesis, or sham operation (12 ears) to expose the footplate of the stapes and the round window. Each guinea pig was tested by ABR perioperatively. Four guinea pigs were chosen randomly from each group and decapitated for morphological examination by light microscopy and scanning electron microscopy after ABR test.

RESULTSIn the sham operation group, the post-operative latencies of each wave, the intervals and the hearing threshold exhibited no significant changes other than prolonged latency of wave I. In stapedectomy group, the hearing threshold increased to 23.75-/+3.77 dBSPL 1 h after operation with significantly prolonged post-operative latencies of all the waves and intervals but for III-IV interval, which was shortened. The latencies of each wave (especially waves I and III) in the stapedectomy group were increased by a greater magnitude than those in the sham operation group, but the intervals were comparable between the two groups. No significant difference was noted in the parameters of ABR either 1 h or 1 day after the operation between the two groups, in which the architecture of cochleas remained intact with similar number of spiral ganglion cells. The stereocilia of the outer hearing cells (OHC) were normal in the sham operation group while in stapedectomy group, slight stereocilia disorder occurred but became normal 1 day after operation. No obvious changes were found in the stereocilia of the inner hearing cell (IHC) in either groups.

CONCLUSIONStapedectomy can induce mild hearing loss without seriously damaging the function of the cochlea in guinea pigs.

Animals ; Auditory Threshold ; physiology ; Evoked Potentials, Auditory, Brain Stem ; physiology ; Female ; Guinea Pigs ; Hair Cells, Auditory ; cytology ; Hearing ; physiology ; Male ; Round Window, Ear ; cytology ; physiology ; surgery ; Stapes Surgery ; adverse effects ; Time Factors