Human Inner Ear Research Articles

CHD7 regulates otic lineage specification and hair cell differentiation in human inner ear organoids

Mutations in CHD7 cause CHARGE syndrome, affecting multiple organs including the inner ear in humans. We investigate how CHD7 mutations affect inner ear development using human pluripotent stem cell-derived organoids as a model system. We find that loss of CHD7 or its chromatin remodeling activity leads to complete absence of hair cells and supporting cells, which can be explained by dysregulation of key otic development-associated genes in mutant otic progenitors. Further analysis of the mutant otic progenitors suggests that CHD7 can regulate otic genes through a chromatin remodeling-independent mechanism. Results from transcriptome profiling of hair cells reveal disruption of deafness gene expression as a potential underlying mechanism of CHARGE-associated sensorineural hearing loss. Notably, co-differentiating CHD7 knockout and wild-type cells in chimeric organoids partially rescues mutant phenotypes by restoring otherwise severely dysregulated otic genes. Taken together, our results suggest that CHD7 plays a critical role in regulating human otic lineage specification and hair cell differentiation.

The Interplay of Cx26, Cx32, Cx37, Cx40, Cx43, Cx45, and Panx1 in Inner-Ear Development of Yotari (dab1-/-) Mice and Humans.

We investigated DAB1-protein deficiency in the inner-ear development of yotari in comparison to humans and wild-type (wt) mice by immunofluorescence for the expression of connexins (Cxs) and the pannexin Panx1. The spatial and temporal dynamics of Cx26, Cx32, Cx37, Cx40, Cx43, Cx45, and Panx1 were determined in the sixth and eighth weeks of human development and at the corresponding mouse embryonic E13.5 and E15.5, in order to examine gap junction intercellular communication (GJIC) and hemichannel formation. The quantification of the area percentage covered by positive signal was performed for the epithelium and mesenchyme of the cochlear and semicircular ducts and is expressed as the mean ± SD. The data were analysed by one-way ANOVA. Almost all of the examined Cxs were significantly decreased in the cochlear and semicircular ducts of yotari compared to wt and humans, except for Cx32, which was significantly higher in yotari. Cx40 dominated in human inner-ear development, while yotari and wt had decreased expression. The Panx1 expression in yotari was significantly lower than that in the wt and human inner ear, except at E13.5 in the mesenchyme of the wt and epithelium and mesenchyme of humans. Our results emphasize the relevance of GJIC during the development of vestibular and cochlear functions, where they can serve as potential therapeutic targets in inner-ear impairments.

Genetic Causes of Inner Ear Anomalies: a Review from the Turkish Study Group for Inner Ear Anomalies

Inner ear anomalies diagnosed using a radiological study are detected in almost 30% of cases with congenital or prelingual-onset sensorineural hearing loss. Inner ear anomalies can be isolated or occur along with a part of a syndrome involving other systems. Although astonishing progress has been made in research aimed at revealing the genetic causes of hearing loss in the past few decades, only a few genes have been linked to inner ear anomalies. The aim of this review is to discuss the known genetic causes of inner ear anomalies. Identifying the genetic causes of inner ear anomalies is important for guiding clinical care that includes empowered reproductive decisions provided to the affected individuals. Furthermore, understanding the molecular underpinnings of the development of the inner ear in humans is important to develop novel treatment strategies for people with hearing loss.

CT Scan Imaging of the Human Fetal Labyrinth: Case Series Data Throughout Gestation.

The inner ear in humans reaches its final configuration and its adult size during fetal life. According to the literature, this occurs between 18 and 25 weeks of amenorrhea (WA). Our goal is to clarify the course of inner ear size development. Using computed tomography (CT) scanner, we studied 13 measurements in the inner ear of a collection of 153 fetuses from 21 to 40 WA. We found no side-related differences or sexual dimorphism in the measurements. Cochlear and vestibular bone measurements did not show growth from 21 to 40 WA, with the exception of the lateral semicircular canal (LSCC) bony island, which grows until 25 WA. Internal auditory canal (IAC) and cochlear aqueduct (CA) growth are correlated with gestational age. As our cochlear measurements are similar to those of infants and adults, in accordance with the literature we conclude that the cochlea has reached its adult size before 21 WA. The continuous growth of the IAC and CA is linked to petrous ossification that continues during fetal gestation and after birth. We confirm that the cochlea reaches its adult size during the second trimester of fetal life.

Tonic eye movements induced by bilateral and unilateral galvanic vestibular stimulation (GVS) in guinea pigs

Galvanic vestibular stimulation (GVS) stimulates primary vestibular afferents innervating the semicircular canals (SCCs) and otoliths found in the inner ear of humans and other mammals, including guinea pigs. To determine which pathways contribute to eye movements generated by this artificial vestibular stimulation in guinea pigs, low current intensities of GVS were passed either bilaterally between the tensor-tympani muscles of the two ears (up to 30 μA) or unilaterally between one tensor-tympani electrode and an indifferent on the back of the neck (up to 60 μA). Both forms of GVS were found to selectively generate tonic eye movements without nystagmus, characteristic of the otolith-ocular reflex; the axis of eye rotation did not align with any semicircular canal plane, but was oriented close to the expected axis of eye rotation that would occur in response to the net stimulation of otolith afferents. The induced eye rotation was predominantly vertical with a smaller horizontal deviation and very little torsion. Consistent with the results of previous human studies, the tonic eye movements were found to exhibit bilateral gain enhancement, whereby bilateral GVS generated twice the amplitude of eye rotation as unilateral anodal or cathodal stimulation alone. Eye movement responses to unilateral GVS were symmetrical in amplitude during equivalent intensities of anodal and cathodal stimulation, consistent with the known responses of more regularly and intermediately discharging primary vestibular afferents to GVS. These results together suggest that more regularly discharging otolith-ocular projections may mediate the tonic changes in eye position induced during maintained, low-intensity GVS in guinea pigs.

Effect of long-standing hypoxic and/or hypercapnic conditions on the sensory epithelia and the neurons in the inner ear of humans

Effect of long-standing hypoxic and/or hypercapnic conditions on the sensory epithelia and the neurons in the inner ear of humans

「内耳形態と細胞機能の研究手法」３．ＭＲＩによる内耳形態の観察

We introduce a method to diagnose sensorineural hearing loss and vestibular disorder using magnetic resonance imaging (MRI). The main pathological finding in patients with Meniere's disease is distention of the entire endolymphatic system, i.e., endolymphatic hydrops, and its diagnosis depends primarily upon a history of fluctuating hearing loss and tinnitus, as well as episodic vertigo associated with vegetative symptoms. Therefore, the development of a practical tool to obtain objective evidence of the existence of endolymphatic hydrops is important. We applied a high-resolution magnetic resonance imaging device running at 2.11 T, 4.7 T, and 7.05 T for the non-invasive depiction of the fine structure of the inner ear in humans and guinea pigs. We have succeeded in depicting both the basilar and Reissner's membranes of the basal turn of the cochlea. In this paper, we present our results using high-resolution MRI and discuss the current status in this field. We suggest the possibility of using MRI for the morphological and functional diagnosis of inner ear pathology in the near future.

NF‐κB mediated glucocorticoid response in the inner ear after acoustic trauma

The inner ear of humans and experimental animals demonstrate an abundance of glucocorticoid receptors (GR). Glucocorticoids (GC) are widely used to treat different hearing disorders; yet the mechanisms of GC action on the inner ear are unknown. We demonstrate how GR can directly modulate hearing sensitivity in response to a moderate acoustic trauma that results in a hearing loss (10-30 dB). The GC agonist (dexamethasone) and the drugs (metyrapone + RU 486) showed opposing effects on hearing threshold shifts. GC agonist (dexamethasone) decreased the hearing threshold whereas pre-treatment with a GC synthesis inhibitor (metyrapone) in combination with a GR antagonist (RU 486) exacerbated auditory threshold shifts (25-60 dB) after acoustic trauma with statistically significant increase in GR mRNA and GR protein compared with the vehicle and acoustic trauma group. Acoustic trauma caused a significant increase in the nuclear transport of NF-kappaB, whereas pre-treatment with the drugs (metyrapone and RU 486) blocked NF-kappaB nuclear transport into spiral ganglion nuclei. An NF-kappaB inhibitor, pyrrolidine dithiocarbamate ammonium blocked the trauma-induced translocation of NF-kappaB and resulted in a hearing loss (45-60) dB. These results indicate that several factors define the responsiveness of the inner ear to GC, including the availability of ligand or receptor, and the nuclear translocation of GR and NF-kappaB. These findings will further our understanding of individual GC responsiveness to steroid treatment, and will help improve the development of pharmaceuticals to selectively target GR in the inner ear for individuals with increased sensitivity to acoustic trauma.

Effect of Cochlear Implantation on Residual Spiral Ganglion Cell Count as Determined by Comparison with the Contralateral Nonimplanted Inner Ear in Humans

It is generally assumed that at least a minimal number of spiral ganglion cells is essential for successful speech perception with a cochlear implant. Although the insertion of a multichannel cochlear implant frequently results in loss of residual hearing in the implanted ear, this outcome does not imply that significant damage to residual populations of spiral ganglion cells has occurred. The purpose of the current study was to compare spiral ganglion cell counts in implanted and nonimplanted cochleas in 11 patients for whom both temporal bones were available and in whom a multichannel cochlear implant had been placed unilaterally. The temporal bones were processed for light microscopy by standard techniques. The cochleas were reconstructed by 2-dimensional methods. Spiral ganglion cell counts of the implanted and nonimplanted sides were compared by a paired t-test (2-tailed). The mean spiral ganglion cell counts for implanted and nonimplanted ears were not statistically different in the most basal three segments of the cochlea. However, the mean spiral ganglion cell count in segment 4 (apical segment) and the mean total spiral ganglion cell count were lower in the implanted cochleas than in the nonimplanted cochleas (p < .01). The results of this study suggest a modest decrease in the total spiral ganglion cell count in the implanted ears as compared to the nonimplanted ears, principally in the apical segment. Possible interpretations of this finding are discussed.

Characterization of a New Mouse Mutant, Flouncer, with a Balance Defect and Inner Ear Malformation

Balance anomalies are often associated with abnormalities of the vestibular part of the inner ear. We studied a newly generated mouse mutant with balance defects and asked whether its behavioral anomalies were associated with inner ear defects. Furthermore, we asked whether the mutation responsible for the defects was located in the same region of mouse chromosome 4 as several other mouse mutations that we have previously described. Phenotypic and genotypic analysis of mouse mutants with hearing or balance problems has helped greatly with the identification of the genes involved in deafness and has contributed to the understanding of mechanisms of normal hearing and balance. This article describes a new mouse mutant, flouncer, that shows a balance defect. The flouncer mutation shows semidominant inheritance, and was generated by mutagenesis using N- ethyl-N- nitrosourea. Hearing was assessed by the Preyer reflex (ear-flick) test. Behavioral tests including open field and swimming tests were performed. The morphology of the middle and inner ears was investigated by microdissection, clearing using glycerol, paint-filling of the labyrinth, and scanning electron microscopy. Flouncer mutants showed vestibular dysfunction but do respond to sounds. Phenotypically, mutants had various degrees of truncation of the lateral semicircular canals, small or obliterated round window of the cochlea, and mild morphologic anomalies of the stapes. Flouncer mutants showed circling behavior and hyperactivity. Linkage mapping using a backcross has indicated that the mutation lies in proximal chromosome 4 proximal to D4Mit171. The lateral semicircular canal has been described to be the most commonly affected part of the inner ear in humans, and flouncer provides a mouse model for genetic and developmental analysis of such defects.

Ear and Hearing Problems in Turner's Syndrome

Objectives—To report hearing results in Swedish women with Turner's syndrome (TS), describe the recommendations of the Otologic Section of the Swedish Turner Academy for handling these patients and discuss the effect of estrogen on hearing in animals.Material and Methods—Audiometric and karyotype tests were performed in 325 Swedish women with TS. A questionnaire was completed by 143 females with TS. Immunohistochemical staining of inner ear specimens was undertaken using antibodies against estrogen receptors in both human fetuses with TS and middle-aged women. Temporal bones obtained from various animal species were also studied immunohistochemically.Results—A total of 61% of the women had suffered from otitis media. A senorineural dip in hearing could be observed as early as the age of 6 years, progressed over time and was related to karyotype. The results of the questionnaire revealed that hearing impairment was rated as the fourth most serious problem associated with TS. The immunohistochemical study confirmed that estrogen receptors are present in the inner ear of humans. The animal experiments showed that estrogen receptors were present at almost equal amounts in rats, mice, TS mice, β knockout mice and ovariectomized rats and at the same localization as in the human inner ear.Conclusions—Both the senorineural dip in hearing and the karyotype can be used to predict the future course of hearing problems in TS patients. Estrogen may have an effect on hearing loss in TS patients but this phenomenon requires further investigation.

Human autoantibodies and monoclonal antibody KHRI-3 bind to a phylogenetically conserved inner-ear-supporting cell antigen.

Autoimmunity is thought to be one cause of sensorineural hearing loss (SNHL). Sera from patients with rapidly progressive hearing loss have been shown to contain antibodies to a 68-kD protein in heterologous inner-ear tissue. Using guinea pig inner-ear tissue as the antigenic substrate and either Western blot or immunofluorescence (IF) or both, we tested sera from 74 patients suspected to have autoimmune hearing loss for inner-ear antibodies. Sera from 73 patients were tested by Western blot, and sera from 36 were tested by IF. Thirty-seven of 73 (51%) had antibody to a 68-70-kD protein by Western blot. Sera positive by IF stained supporting cells with a staining pattern like that previously observed with the KHRI-3 monoclonal antibody. There was concordance between Western blot and IF assays. Of 36 patients tested by both assays, 29/31 (94%) that were positive in Western blot were also positive by IF, three were negative by both tests, and two each were positive by one assay but negative by the other. Absorption of patient sera with human inner-ear tissue removed antibody reactivity to the guinea pig supporting cells, indicating that the antigen detected by the autoantibody is also present in the human inner ear. Absorption with an equal volume of white or red blood cells from the tissue donor did not remove the antibody reactivity to inner ear, showing that the absorption by inner-ear tissue is specific. Sera from three patients positive in both assays also stained a 68-70-kD inner-ear protein immunoprecipitated by the KHRI-3 monoclonal antibody, indicating that the monoclonal and human antibodies recognize the same antigen. The results support the hypothesis that patients with autoimmune sensorineural hearing loss produce autoantibodies to an inner-ear supporting cell antigen that is phylogenetically conserved and defined by the murine monoclonal antibody KHRI-3. Since KHRI-3 can induce hearing loss after infusion into the inner ear, it is likely that autoantibodies with the same antigenic target are also pathogenic in humans.

System and method for measuring acoustic reflectance

A system and method of measuring the linear and nonlinear response of an unknown acoustic termination uses a small probe assembly containing a sound source and microphone to determine the reflection function of the unknown acoustic termination. The probe assembly is used with a calibration tube to calculate an electrical signal that will provide a desired acoustic stimulus signal to the acoustic termination. The calibration tube is also used to characterize the signal processing properties of the sound source and microphone, as well as other associated signal processing circuits such as amplifiers, filters, and the like. The calibrated system is subsequently coupled to the unknown acoustic termination to deliver the acoustic stimulus signal. The reflection function is indicative of the power transferred to the unknown acoustic termination. The measurement of the linear transfer characteristic is applicable to any unknown acoustic termination such as a musical instrument or the auditory system. The probe assembly is sized to be positioned directly within the outer portion of the ear and measure the linear characteristics of the ear. The system is further able to measure the nonlinear transfer characteristics of the ear by measuring the linear response at multiple levels of the acoustic stimulus. The system is particularly useful in testing the response of the middle ear and inner ear of humans or other animals.

A study on the vasculature of the internal auditory artery in humans by casts.

Vascular casting has so far been used mainly for observation of the vascular system of the inner ear in experimental animals. In the present study, this method was applied to analysis of the three-dimensional vascular structure in the inner ear in humans. To date there has been no comparative study of overall pictures of blood vessels in the human inner ear. Seven cases were observed mainly by means of scanning electron microscopy. Even with this new method, the results in many respects obtained confirmed those of previous reports. However, the following findings which have not been previously reported or are currently in dispute, were observed: i) In two cases, spring coil-like structures of blood vessels were found in the internal auditory canal; ii) We corroborated the pattern of arrangement of cochlear arteries previously described in words and schemata, i.e., the following two types were confirmed: the first type showing the cochlear branch of vestibulocochlear artery and the spiral modiolar artery running into the cochlea, and the second type showing the cochlea supported by arteries derived from the artery corresponding to the vestibulocochlear artery, alone; and iii) A right-angled arteriolar branch of the spiral modiolar artery was found to further bifurcate to form radiating arterioles extending in two directions: both over the scala vestibuli and along the spiral lamina.

Partitioning the labyrinth for the treatment of benign paroxysmal positional vertigo

Partitioning the labyrinth is a new laser technique for the creation of controlled fibrous bands in the inner ear without permanent hearing loss .' The application of partitioning in benign paroxysmal positional vertigo (BPPV) is the first application of this ability to divide the inner ear in humans. Partitioning the posterior semicircular canal creates a fibrous band across both the perilymphatic and endolymphatic fluid spaces of the posterior semicircular canal. This fibrous band stops movement of the posterior semicircular canal endolymph. I hypothesize that when the movement of the endolymphatic fluid was halted, and because the interface between the cupula and the membranous labyrinth within ampulla was watertight, the motion of the cupula was halted both from angular motion (physiologic action) and from linear motion (as in cupulolithiasis). Indications for surgery include severe symptoms that are incapacitating to the point that they significantly affect the patient's occupation or life-style. Fourteen patients have undergone unilateral partitioning of a posterior semicircular canal. Mean age at the time of surgery was 51 years, with a range from 33 to 64 years. Ten were women and four were men. The positional vertigo was traumatic in five (three men and two women), and spontaneous in nine patients (one man and eight women). Mean symptom duration was 5.8 years, with range from 3 months to 20 years. Nine patients had continuous symptoms (mean 26 months, range 3 to 96 months). Five patients had intermittent symptoms (mean 11.2 years, range 16 to 240 months) . Eight patients had normal preoperative hearing (0 to 12 dB 3 frequency average), two patients had 17-dB hearing levels, and four patients had 30to 65-dB hearing levels. No pathological origin of the hearing losses was found during evaluation. , BPPV resolution occurred from 1 to 14 days postoperatively. As the applied laser energy was decreased (from 12 J to 1.2 1)1 the BPPV resolved more slowly. All 14 patients have remained free of positional symptoms during their 3 to 21 months postoperative period. Postoperative motion sensitivity was seen in all patients . The motion sensitivity was mild and of 1 to 6 weeks' duration when postoperative steroids are used (10 mg prednisone four times a day for 7 days). When postoperative steroids were not used, the motion sensitivity can be severe and of 8 to 10 weeks' duration. All patients followed up on a daily basis postopera-