Cochlea ; metabolism ; Deafness ; genetics ; Humans ; Mutation

Progressive functional deterioration in the cochlea is associated with age-related hearing loss (ARHL). However, the cellular and molecular basis underlying cochlear aging remains largely unknown. Here, we established a dynamic single-cell transcriptomic landscape of mouse cochlear aging, in which we characterized aging-associated transcriptomic changes in 27 different cochlear cell types across five different time points. Overall, our analysis pinpoints loss of proteostasis and elevated apoptosis as the hallmark features of cochlear aging, highlights unexpected age-related transcriptional fluctuations in intermediate cells localized in the stria vascularis (SV) and demonstrates that upregulation of endoplasmic reticulum (ER) chaperon protein HSP90AA1 mitigates ER stress-induced damages associated with aging. Our work suggests that targeting unfolded protein response pathways may help alleviate aging-related SV atrophy and hence delay the progression of ARHL.
Mice ; Animals ; Transcriptome ; Aging/metabolism* ; Cochlea ; Stria Vascularis ; Presbycusis

OBJECTIVETo investigate the distribution and role of alpha, beta and gamma subunits of epithelial sodium channel (ENaC) in the cochlea and endolymphatic sac of guinea pig.

METHODSThe expression of alpha-, beta- and gamma-ENaC subunits proteins was studied by immunohistochemistry with the specific polyclonal rabbit antibodies against the alpha, beta and gamma subunits of rat ENaC. Alpha-ENaC mRNA was detected by in situ hybridization with digoxin labeled cDNA probe.

RESULTSAll three subunits of ENaC, alpha-, beta- and gamma-, were widely distributed in the labyrinth. In the cochlea, strong labeling of alpha-ENaC protein was found in the spiral limbus, and to a less extent, in the spiral ligament, organ of Corti and Reissner's membrane. The immunoreactivity of beta-ENaC was observed in the spiral ligament, spiral limbus, spiral ganglion, organ of Corti and Reissner's membrane with a less intensity than that of alpha-ENaC. Gamma-ENaC was presented primarily in the superior part of the spiral ligament, spiral limbus, spiral ganglion, and weakly in the organ of Corti and Reissner's membrane. In the endolymphatic sac, intensive immunoreactivities of all three subunits were seen in the epithelial cells and the subepithelial cells at similar intensity. Alpha-ENaC mRNA was localized in the spiral limbus, the inferior part of spiral ligament, stria vascularis, and epithelial cells and subepithelial cells of endolymphatic sac.

CONCLUSIONDifferent subunits of the ENaC expressed in various cell regions of the cochlea and endolymphatic sac in distinct patterns may form the functional sodium channel to regulate the endolymph, thus serve to maintain homeostasis in inner ear.

Animals ; Cochlea ; metabolism ; Endolymphatic Sac ; metabolism ; Epithelial Sodium Channels ; metabolism ; Guinea Pigs

OBJECTIVE: To study the expression of nuclear factor kappa B p65 in hyperlipemia model of mice, and the relationship between hyperlipemia and deaf. METHOD: Twenty mice were divided into two group. The hyperlipemia diet group was established in ten mice,and the normal diet group was served as normal control. Six weeks later, immunohistostaining was used to detected the express of NF-kappa B p65 in all mouse cochlear. ABR threshold was obtained from both normal group and hyperlipemia group. RESULT: Immunoreactivity NF-kappa B p65 in mouse cochlea of hyperlipemia was localized in the organ of Corti, tectorial membrane, stria vascularis, spiral ligament, spiral ganglion and nerve fibers. The NF-kappa B p65 expression was markedly increased in mouse cochlea of hyperlipemia ABR threshold was significant difference between hyperlipemia group mice and control group mice (P < 0.01). CONCLUSION The expression of NF-kappa B p65 in mouse cochlea can be induced by hyperlipemia. And ABR threshold increased in hyperlipemia group mice. This shows that hyperlipidemia can damage acouesthesia of mice.
Animals ; Cochlea ; metabolism ; Disease Models, Animal ; Hyperlipidemias ; metabolism ; Mice ; Mice, Inbred Strains ; Transcription Factor RelA ; metabolism

OBJECTIVETo investigate the distribution and pharmacokinetics of dexamethasone of different concentrations in the inner ears of SD rats after intratympanic injection.

METHODSTotally 144 adult SD rats were anaesthetized and dexamethasone sodium phosphate of different concentrations (5 mg/ml, 10 mg/ml, 20 mg/ml) was injected into the tympanums. The rats were sacrificed at various postinjection survival times (5 min, 10 min, 15 min, 30 min, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 48 h, 72 h), and every 4 rats were included into each group. Then after a series of processes the inner ear tissue was cryostat sectioned. The distribution of dexamethasone was evaluated using immunofluorescence with semiquantitative analysis. Immunofluorescence was also used in another 4 normal SD rats to detect the distribution of Glucocorticoid receptor (GR) in the inner ear.

RESULTSDexamethasone was observed initially 15 min after local drug administration and 30 min to its peak level. The highest concentration of dexamethasone labeling was seen in the spiral ligament, organ of Corti and spiral ganglion, which paralleled the distribution of GR. The tissue concentration of 10 mg/ml and 20 mg/ml groups was higher than 5 mg/ml every corresponding time point, and the lasting time was also prolonged from 48 hours to 72 hours.

CONCLUSIONSDexamethasone can enter into the cochlear tissue quickly after transtympanic injection, and its distribution accords nearly exactly with that of GR. Increase of the concentration of dexamethasone results in higher tissue distribution and longer lasting time.

Animals ; Cochlea ; metabolism ; Dexamethasone ; pharmacokinetics ; Rats ; Rats, Sprague-Dawley ; Receptors, Glucocorticoid ; metabolism

Animals ; Cochlea ; growth & development ; metabolism ; Female ; Guinea Pigs ; Male ; Nerve Growth Factor ; metabolism

Recent studies have revealed great functional and structural heterogeneity in the ribbon-type synapses at the basolateral pole of the isopotential inner hair cell (IHC). This feature is believed to be critical for audition over a wide dynamic range, but whether the spatial gradient of ribbon morphology is fine-tuned in each IHC and how the mitochondrial network is organized to meet local energy demands of synaptic transmission remain unclear. By means of three-dimensional electron microscopy and artificial intelligence-based algorithms, we demonstrated the cell-wide structural quantification of ribbons and mitochondria in mature mid-cochlear IHCs of mice. We found that adjacent IHCs in staggered pairs differ substantially in cell body shape and ribbon morphology gradient as well as mitochondrial organization. Moreover, our analysis argues for a location-specific arrangement of correlated ribbon and mitochondrial function at the basolateral IHC pole.
Animals ; Artificial Intelligence ; Cochlea/metabolism* ; Hair Cells, Auditory, Inner ; Mice ; Mitochondria ; Synapses/metabolism*

OBJECTIVETo study the interaction among aquaporin1 (AQP), aquaporin2 (AQP2) and antisecretory factor( AF) , and their expression in the rat inner ear for furthur understanding of Meniere' s disease.

METHODSInner ear tissue section of six healthy male Sprague-Dawley rats was performed and Envision immunochemical staining was applied to detect the expression of AF, AQP1 and AQP2 in the rat inner ear. Vestibular and cochlear tissues of twenty healthy male Sprague-Dawley rats were dissected. Coimmunoprecipitation and Western Blot were used to specifically immunoprecipitate AF protein in the vestibular and cochlear tissues with monoclonal antibodies against AQP1 and polyclonal antibodies antibodies against AQP2 to detect the above precipitate with specific antibodies against AF.

RESULTS(1) AF was widely distributed in the inner ear, such as marginal cells of stria vascularis , five classes of spiral ligament fibrocyte , Reissner's membrane, basilar membrane, ampullar crest and so on with mild or moderate staining. In addition, round membrane was moderately or markedly stained. Positive immunostaining was found in the cochlear spiral ganglion, vestibular nerve and cochlear nerve. AQP1 was distributed in the intermediate cells in stria vascularis, type III fibrocyte of spiral ligament, basilar membrane and round membrane with moderate to marked degree of immunostaining intensity. AQP2 was mainly localized to the type II, IV, and V fibrocyte of spiral ligament, with moderate to marked degree of immunostaining intensity, round membrane was weakly stained. (2) No band was observed in the control and a single immunoreactive band of 60 000 was observed, which was equal to the molecular mass of AF.

CONCLUSIONS(1) AF, AQP1 and AQP2 have its individual specific localization in the rat inner ear, which was close to the parts of endolymph, so regulating water of the endolymph may be possible. (2) The range of localization of AF overlapped the distribution of AQP1 and AQP2. The results showed the existence of AF protein in the immunoprecipitate using co-immunoprecipitation combined with Western Blot. It suggested that the interaction between AQP1, AQP2 and AF might be possible.

Animals ; Aquaporin 1 ; metabolism ; Aquaporin 2 ; metabolism ; Cochlea ; metabolism ; Ear, Inner ; metabolism ; Male ; Neuropeptides ; metabolism ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo study the expression of aquaporin 1 (AQP1) in cochlea and endolymphatic sac of guinea pig of two types of animal model of endolymphatic hydrops.

METHODSThirty guinea pigs were divided into three groups at random: surgery group; aldosterone group and control group. Each group included 10 animals. Surgical endolymphatic sac obstruction or aldosterone intraperitoneal injection was used to build the animal models of endolymphatic hydrops. Immunohistochemistry and western blot were used to examine the expression of AQP1 in cochlea and endolymphatic sac of animal models. Image processing soft (Image Tool) was used to do the semiquantitative analysis.

RESULTSMiddle to high grade endolymphatic hydrops were found in surgery group. It was most significant in the apical coil, and lessened from the apical coil to the basal coil. Low to middle expression grade in endolymphatic hydrops was found in aldosterone group. Most of them were found in the basal coil. The positions of AQP1 expression in two animal models of endolymphatic hydrops were identical with the control group. In cochlea, no difference of AQP1 expression was found in the surgery and control group (t = 0.718 , P > 0.05) , but the expression of AQP1 was down regulated in the cochlea of aldosterone group (t = 6.609, P < 0.01) while the expressions of AQP1 in endolymphatic sac of aldosterone and control group were no difference between them (t = 0.998, P > 0.05). The quantization of AQP1 protein in the lateral wall of cochlea of aldosterone group was lower than that of control group (t = 13.626 , P < 0.01).

CONCLUSIONSThe expression of AQP1 is no change in surgery and control group, but decreased in aldosterone group. The expression of AQP1 may be regulated by the ionic concentration in inner ear of guinea pig.

Animals ; Aquaporin 1 ; metabolism ; Cochlea ; metabolism ; Disease Models, Animal ; Endolymphatic Hydrops ; metabolism ; Endolymphatic Sac ; metabolism ; Guinea Pigs

OBJECTIVETo investigate the expression of Dynamin subtypes in inner hair cell (IHC) of mice, and to discuss their possible roles in age-related hearing loss.

METHODSAuditory brainstem response (ABR) was recorded from the Kunming mice on postnatal 3 weeks (young), 10 weeks (adult), and 16 months (aged), 10 mice in each group. The expression of each Dynamin isoforms in the hair cells of the cochlea was observed by immunofluorescence staining and confocal microscope, and the transcription level of Dynamin subtypes mRNA was detected in qRT-PCR. Data analysis using SPSS 18 software.

RESULTSABR threshold showed no significant difference between the group of young and adult (t = -5.273, P = 0.076), but the threshold of the aged group increased comparing with young group (t = -8.365, P = 0.000), and adult group (t = -6.191, P = 0.000). All subtypes expressed in the inner hair cell of mice, of which Dynamin-1 and 2 expressed in the whole inner hair cell in the group of young and adult. In the aged group, Dynamin-1 was lost beneath the nucleus, and Dynamin-2 only be found near the nucleus. In addition, Dynamin-3 was scattered in the region of the basal part of the cells beneath the nucleus and near the spiral ganglion. The qRT-PCR revealed that mRNA of Dynamin-1 reduced with age (F = 10.410, P = 0.011), mRNA of Dynamin-2 increased to a peak in the adult group and then reduced with age (F = 24.575, P = 0.000). Meanwhile, mRNA of Dynamin-3 was not be detected.

CONCLUSIONSAll subtypes of Dynamin express in IHC. The expression of Dynamin-1 and 2 is up-regulated during maturity, which might alter the endocytosis of IHC; and the disorder of endocytosis might modulate the synaptic transmission of IHC. Whether Dynamin-3 plays a role in inner hair cells remains unclear because of the low expression.

Aging ; metabolism ; Animals ; Cochlea ; metabolism ; Dynamins ; metabolism ; Evoked Potentials, Auditory, Brain Stem ; Hair Cells, Auditory, Inner ; metabolism ; Mice