Cochlin expression in vestibular endorgans obtained from patients with Meniere's disease

MiR-29a-deficiency causes thickening of the basilar membrane and age-related hearing loss by upregulating collagen IV and laminin

Age-related hearing loss (ARHL) is the most common sensory degenerative disease and can significantly impact the quality of life in elderly people. A previous study using GeneChip miRNA microarray assays showed that the expression of miR-29a changes with age, however, its role in hearing loss is still unclear. In this study, we characterized the cochlear phenotype of miR-29a knockout (miR-29a^-/-) mice and found that miR-29a-deficient mice had a rapid progressive elevation of the hearing threshold from 2 to 5 months of age compared with littermate controls as measured by the auditory brainstem response. Stereocilia degeneration, hair cell loss and abnormal stria vascularis (SV) were observed in miR-29a^-/- mice at 4 months of age. Transcriptome sequencing results showed elevated extracellular matrix (ECM) gene expression in miR-29a^-/- mice. Both Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that the key differences were closely related to ECM. Further examination with a transmission electron microscope showed thickening of the basilar membrane in the cochlea of miR-29a^-/- mice. Five Col4a genes (Col4a1-a5) and two laminin genes (Lamb2 and Lamc1) were validated as miR-29a direct targets by dual luciferase assays and miR-29a inhibition assays with a miR-29a inhibitor. Consistent with the target gene validation results, the expression of these genes was significantly increased in the cochlea of miR-29a^-/- mice, as shown by RT-PCR and Western blot. These findings suggest that miR-29a plays an important role in maintaining cochlear structure and function by regulating the expression of collagen and laminin and that the disturbance of its expression could be a cause of progressive hearing loss.

Involvement of cochlin binding to sulfated heparan sulfate/heparin in the pathophysiology of autosomal dominant late-onset hearing loss (DFNA9)

Late-onset non-syndromic autosomal dominant hearing loss 9 (DFNA9) is a hearing impairment caused by mutations in the coagulation factor C homology gene (COCH). COCH encodes for cochlin, a major component of the cochlear extracellular matrix. Though biochemical and genetic studies have characterized the properties of wild-type and mutated cochlins derived from DFNA9, little is known about the underlying pathogenic mechanism. In this study, we established a cochlin reporter cell, which allowed us to monitor the interaction of cochlin with its ligand(s) by means of a β-galactosidase assay. We found a class of highly sulfated glycosaminoglycans (GAGs), heparin, that were selectively bound to cochlin. The interaction was distinctly abrogated by N-desulfation, but not by 2-O- or 6-O-desulfation. The binding of cochlin to GAG was diminished by all of the point mutations found in DFNA9 patients. Through GAG composition analysis and immunostaining using mouse cochlin/immunoglobulin-Fc fusion protein, we identified moderately sulfated GAGs in mouse cochlea tissue; this implies that cochlin binds to such sulfated GAGs in the cochlea. Since GAGs play an important role in cell growth and survival as co-receptors of signal transduction mechanisms, the interaction of cochlin with GAGs in the extracellular matrix could aid the pathological research of autosomal dominant late-onset hearing loss in DFNA9.

Advances in otolith-related protein research

Otoliths are biological crystals formed by a layer of calcium carbonate crystal that adhere to the ciliary surface of the utricular and saccular receptors in the vestibule of all vertebrates inner ear, enabling the utricle and saccule to better perceive the changes in linear and gravitational acceleration. However, the molecular etiology of otolith related diseases is still unclear. In this review, we have summarized the recent findings and provided an overview of the proteins that play important roles in otolith formation and maintenance (Otoconin-90, Otolin-1, Otolith Matrix Protein-1, Cochlin, Otogelin, α-Tectorin, β-Tectorin, Otopetrin-1, and Otopetrin-2, PMCA2, etc.), providing new insight for the prevention and management of benign paroxysmal positional vertigo (BPPV) with basis for otolith-related proteins as potential biomarkers of vestibular disease.

Personalized Proteomics for Precision Diagnostics in Hearing Loss: Disease-Specific Analysis of Human Perilymph by Mass Spectrometry

Despite a vast amount of data generated by proteomic analysis on cochlear fluid, novel clinically applicable biomarkers of inner ear diseases have not been identified hitherto. The aim of the present study was to analyze the proteome of human perilymph from cochlear implant patients, thereby identifying putative changes of the composition of the cochlear fluid perilymph due to specific diseases. Sampling of human perilymph was performed during cochlear implantation from patients with clinically or radiologically defined inner ear diseases like enlarged vestibular aqueduct (EVA; n = 14), otosclerosis (n = 10), and Ménière's disease (n = 12). Individual proteins were identified by a shotgun proteomics approach and data-dependent acquisition, thereby revealing 895 different proteins in all samples. Based on quantification values, a disease-specific protein distribution in the perilymph was demonstrated. The proteins short-chain dehydrogenase/reductase family 9C member 7 and esterase D were detected in nearly all samples of Ménière's disease patients, but not in samples of patients suffering from EVA and otosclerosis. The presence of both proteins in the inner ear tissue of adult mice and neonatal rats was validated by immunohistochemistry. Whether these proteins have the potential for a biomarker in the perilymph of Ménière's disease patients remains to be elucidated.

Ciliopathy genes are required for apical secretion of Cochlin, an otolith crystallization factor

Here, we report that important regulators of cilia formation and ciliary compartment-directed protein transport function in secretion polarity. Mutations in cilia genes cep290 and bbs2, involved in human ciliopathies, affect apical secretion of Cochlin, a major otolith component and a determinant of calcium carbonate crystallization form. We show that Cochlin, defective in human auditory and vestibular disorder, DFNA9, is secreted from small specialized regions of vestibular system epithelia. Cells of these regions secrete Cochlin both apically into the ear lumen and basally into the basal lamina. Basally secreted Cochlin diffuses along the basal surface of vestibular epithelia, while apically secreted Cochlin is incorporated into the otolith. Mutations in a subset of ciliopathy genes lead to defects in Cochlin apical secretion, causing abnormal otolith crystallization and behavioral defects. This study reveals a class of ciliary proteins that are important for the polarity of secretion and delineate a secretory pathway that regulates biomineralization.

Reliability of Serological Prestin Levels in Humans and its Relation to Otoacoustic Emissions, a Functional Measure of Outer Hair Cells

OBJECTIVES

Serological biomarkers, common to many areas of medicine, have the potential to inform on the health of the human body and to give early warning of risk of compromised function or illness before symptoms are experienced. Serological measurement of prestin, a motor protein uniquely produced and expressed in outer hair cells, has recently been identified as a potential biomarker to inform on the health of the cochlea. Before any test can be introduced into the clinical toolkit, the reproducibility of the measurement when repeated in the same subject must be considered. The primary objective of this study is to outline the test-retest reliability estimates and normative ranges for serological prestin in healthy young adults with normal hearing. In addition, we examine the relation between serum prestin levels and otoacoustic emissions (OAEs) to compare this OHC-specific protein to the most common measure of OHC function currently used in hearing assessments.

DESIGN

We measured prestin levels serologically from circulating blood in 34 young adults (18 to 24 years old) with clinically normal pure-tone audiometric averages at five different timepoints up to six months apart (average intervals between measurements ranged from <1 week to 7 weeks apart). To guide future studies of clinical populations, we present the standard error of the measurement, reference normative values, and multiple measures of reliability. Additionally, we measured transient evoked OAEs at the same five timepoints and used correlation coefficients to examine the relation between OAEs and prestin levels (pg/mL).

RESULTS

Serum prestin levels demonstrated good to excellent reliability between and across the five different time points, with correlation coefficients and intraclass correlations >0.8. Across sessions, the average serum prestin level was 250.20 pg/mL, with a standard error of measurement of 7.28 pg/mL. Moreover, positive correlations (generally weak to moderate) were found between prestin levels and OAE magnitudes and signal-to-noise ratios.

CONCLUSIONS

Findings characterize serum prestin in healthy young adults with normal hearing and provide initial normative data that may be critical to interpreting results from individuals with sensorineural hearing loss. Our results demonstrate reliability of serum prestin levels in a sample of normal-hearing young adults across five test sessions up to 6 months apart, paving the way for testing larger samples to more accurately estimate test-retest standards for clinical protocols, including those involving serial monitoring. The positive correlations between serum prestin and OAE levels, although weak to moderate, reinforce that the source of serum prestin is likely the outer hair cells in the inner ear, but also that serum prestin and OAEs each may also index aspects of biologic function not common to the other.

Attitudes of Potential Participants Towards Potential Gene Therapy Trials in Autosomal Dominant Progressive Sensorineural Hearing Loss

BACKGROUND

Advances in gene therapeutic approaches to treat sensorineural hearing loss (SNHL) confront us with future challenges of translating these animal studies into clinical trials. Little is known on patient attitudes towards future innovative therapies.

OBJECTIVE

We aimed to better understand the willingness of patients with progressive SNHL and vestibular function loss of autosomal dominant (AD) inheritance to participate in potential gene therapy trials to prevent, stabilize, or slow down hearing loss.

METHODS

A survey was performed in carriers of the P51S and G88E pathogenic variant in the COCH gene (DFNA9). Various hypothetical scenarios were presented while using a Likert scale.

RESULTS

Fifty three participants were included, incl. 49 symptomatic patients, one presymptomatic patient, and three participants at risk. Their attitude towards potential trials studying innovative therapies was overall affirmative, even if the treatment would only slow down the decline of hearing and vestibular function, rather than cure the disease. Among the different potential scenarios, the less invasive and less frequent treatments increased the likelihood to enroll. Daily oral medication and annual intravenous infusion were awarded the highest scores. The more invasive, more frequent, and more at-risk treatments were still likely to be accepted but decreased the willingness to participate. The presence of a placebo arm was met with the lowest scores of willingness to participate.

CONCLUSIONS

Overall, most symptomatic DFNA9 patients would likely consider participation in future innovative inner ear therapy trials, even if it would only slow down the decline of hearing and vestibular function.

On the pathophysiology of DFNA9: Effect of pathogenic variants in the COCH gene on inner ear functioning in human and transgenic mice

DeaFNess Autosomal Dominant 9 (DFNA9) is a dominant hereditary non-syndromic form of progressive sensorineural hearing loss often associated with vestibular dysfunction. DFNA9 is caused by pathogenic variants in the COCH gene. This gene encodes for cochlin, a protein that is abundantly expressed in the spiral ligament and spiral limbus of the inner ear but the function of cochlin is still not fully understood. There are 22 known pathogenic variants located in different domains of the COCH gene that can cause DFNA9, all expressing slightly different phenotypes. It is believed that COCH mutations affect the intracellular trafficking of cochlin which could explain the characteristic pathology seen in temporal bones of DFNA9 patients. This pathology involves a widespread accumulation of acellular eosinophilic deposits throughout the labyrinth. To gain a better understanding of the pathology underlying DFNA9, different mouse models were developed. The objective of this review is to describe the different pathogenic variants in the COCH gene and their effect on intracellular trafficking, associated phenotypes and histopathological findings in both patients and mouse models.

Biomarkers for Inner Ear Disorders: Scoping Review on the Role of Biomarkers in Hearing and Balance Disorders

The diagnostics of inner ear diseases are primarily functional, but there is a growing interest in inner ear biomarkers. The present scoping review aimed to elucidate gaps in the literature regarding the definition, classification system, and an overview of the potential uses of inner ear biomarkers. Relevant biomarkers were categorized, and their possible benefits were evaluated. The databases OVID Medline, EMBASE, EBSCO COINAHL, CA PLUS, WOS BIOSIS, WOS Core Collection, Proquest Dissertations, Theses Global, PROSPERO, Cochrane Library, and BASE were searched using the keywords “biomarker” and “inner ear”. Of the initially identified 1502 studies, 34 met the inclusion criteria. The identified biomarkers were classified into diagnostic, prognostic, therapeutic, and pathognomonic; many were detected only in the inner ear or temporal bone. The inner-ear-specific biomarkers detected in peripheral blood included otolin-1, prestin, and matrilin-1. Various serum antibodies correlated with inner ear diseases (e.g., anti-type II collagen, antinuclear antibodies, antibodies against cytomegalovirus). Further studies are advised to elucidate the clinical significance and diagnostic or prognostic usage of peripheral biomarkers for inner ear disorders, filling in the literature gaps with biomarkers pertinent to the otology clinical practice and integrating functional and molecular biomarkers. These may be the building blocks toward a well-structured guideline for diagnosing and managing some audio-vestibular disorders.

Vestibular and audiological findings in the Alport syndrome

Alport syndrome (AS) is caused by mutations in collagen IV, which is widespread in the basement membranes of many organs, including the kidneys, eyes, and ears. Whereas the effects of collagen IV changes in the cochlea are well known, no changes have been described in the posterior labyrinth. The aim of this study was to investigate both the auditory and the vestibular function of a group of individuals with AS. Seventeen patients, aged 9-52, underwent audiological tests including pure-tone and speech audiometry, immittance test and otoacoustic emissions and vestibular tests including video head impulse test, rotatory test, and vestibular evoked myogenic potentials. Hearing loss affected 25% of the males and 27.3% of the females with X-linked AS. It was sensorineural with a cochlear localization and a variable severity. 50% of the males and 45.4% of the females had a hearing impairment in the high-frequency range. Otoacoustic emissions were absent in about one-third of the individuals. A peripheral vestibular dysfunction was present in 75% of the males and 45.4% of the females, with no complaints of vertigo or dizziness. The vestibular impairment was compensated and the vestibulo-ocular reflex asymmetry was more evident in rotatory tests carried out at lower than higher speeds; a vestibular hypofunction was present in all hearing impaired ears although it was also found in subjects with normal hearing. A posterior labyrinth injury should be hypothesized in AS even when the patient does not manifest hearing disorders or evident signs of renal failure.

The Price of Immune Responses and the Role of Vitamin D in the Inner Ear

OBJECTIVE

In this review the authors discuss evidence from the literature concerning vitamin D and temporal bone diseases (benign paroxysmal positional vertigo [BPPV], Menière's disease [MD], vestibular neuritis, idiopathic facial paralysis, idiopathic acute hearing loss). Common features shared by Menière's disease, glaucoma, and the possible influence by vitamin D are briefly discussed.

DATA SOURCES, STUDY SELECTION

Publications from 1970 until recent times have been reviewed according to a keyword search (see above) in PubMed.

CONCLUSIONS

MD, BPPV, vestibular neuritis, idiopathic facial paralysis, idiopathic acute hearing loss may all have several etiological factors, but a common feature of the current theories is that an initial viral infection and a subsequent autoimmune/autoinflammatory reaction might be involved. Additionally, in some of these entities varying degrees of demyelination have been documented. Given the immunomodulatory effect of vitamin D, we postulate that it may play a role in suppressing an eventual postviral autoimmune reaction. This beneficial effect may be enhanced by the antioxidative activity of vitamin D and its potential in stabilizing endothelial cells. The association of vitamin D deficiency with demyelination has already been established in other entities such as multiple sclerosis and experimental autoimmune encephalitis. Mice without vitamin D receptor show degenerative features in inner ear ganglia, hair cells, as well as otoconia. The authors suggest further studies concerning the role of vitamin D deficiency in diseases of the temporal bone. Additionally, the possible presence and degree of demyelination in these entities will have to be elucidated more systematically in the future.

Making the Case for Research on Disease-Modifying Treatments to Tackle Post-lingual Progressive Sensorineural Hearing Loss

Hearing loss not only has a significant impact on the quality of life of patients and society, but its correlation with cognitive decline in an aging population will also increase the risk of incident dementia. While current management of hearing loss is focused on hearing rehabilitation (and essentially symptomatic), patients are suffering from the burden of progressive hearing loss before hearing aids or cochlear implants are fitted. Although these devices have a significant effect on speech understanding, they do not always lead to normal speech understanding, especially in noisy environments. A significant number of patients suffer from autosomal dominantly inherited disorders that can produce progressive sensorineural hearing loss. This includes DFNA9, a disorder caused by pathologic variants in the COCH gene that leads to post-lingual profound sensorineural hearing loss and bilateral vestibulopathy. Carriers of a pathogenic variant leading to DFNA9 can be diagnosed at the pre-symptomatic or early symptomatic stage which creates a window of opportunity for treatment. Preventing hearing loss from occurring or stabilizing progression would provide the opportunity to avoid hearing aids or cochlear implants and would be able to reduce the increased incidence of dementia. While innovative therapies for restoration of hearing have been studied for restoration of hearing in case of severe-to-profound sensorineural hearing loss and congenital hearing loss, further research is needed to study how we can modify disease progression in late-onset autosomal dominant hereditary sensorineural hearing loss. Recently, gene editing strategies have been explored in autosomal dominant disorders to disrupt dominant mutations selectively without affecting wild-type alleles.

Investigations of the Microvasculature of the Human Macula Utricle in Meniere's Disease

The integrity and permeability of the blood labyrinthine barrier (BLB) in the inner ear is important to maintain adequate blood supply, and to control the passage of fluids, molecules and ions. Identifying the cellular and structural components of the BLB, the vascular endothelial cells (VECs), pericytes, and the perivascular basement membrane, is critical to understand the pathophysiology of the inner ear microvasculature and to design efficient delivery of therapeutics across the BLB. A recent study of the normal and pathological ultrastructural changes in the human macula utricle microvasculature demonstrated that the VECs are damaged in Meniere’s disease (MD), and further studies identified oxidative stress markers (iNOS and nitrotyrosine) in the VECs. Using fluorescence microscopy, the microvasculature was studied in the macula utricle of patients diagnosed with MD that required transmastoid labyrinthectomy for intractable vertigo (n = 5), and patients who required a translabyrinthine approach for vestibular schwannoma (VS) resection (n = 3). Normal utricles (controls) were also included (n = 3). VECs were identified using rabbit polyclonal antibodies against the glucose transporter-1 (GLUT-1) and pericytes were identified using mouse monoclonal antibodies against alpha-smooth muscle actin (α-SMA). Immunofluorescence (IF) staining was made in half of the utricle and flat mounted. The other half was used to study the integrity of the BLB using transmission electron microscopy (TEM). GLUT-1-IF, allowed delineation of the macula utricle microvasculature (located in the stroma underneath the sensory epithelia) in both MD and VS specimens. Three sizes of vessels were present in the utricle vasculature: Small size (<15 μm), medium size (15–25 μm) and large size >25 μm. α-SMA-IF was present in pericytes that surround the VECS in medium and thick size vessels. Thin size vessels showed almost no α-SMA-IF. AngioTool software was used for quantitative analysis. A significant decreased number of junctions, total vessel length, and average vessel length was detected in the microvasculature in MD specimens compared with VS and control specimens. The deeper understanding of the anatomy of the BLB in the human vestibular periphery and its pathological changes in disease will enable the development of non-invasive delivery strategy for the treatment of hearing and balance disorders.

Oxidative Stress in the Blood Labyrinthine Barrier in the Macula Utricle of Meniere's Disease Patients

The blood labyrinthine barrier (BLB) is critical in the maintenance of inner ear ionic and fluid homeostasis. Recent studies using imaging and histopathology demonstrate loss of integrity of the BLB in the affected inner ear of Meniere's disease (MD) patients. We hypothesized that oxidative stress is involved in the pathogenesis of BLB degeneration, and to date there are no studies of oxidative stress proteins in the human BLB. We investigated the ultrastructural and immunohistochemical changes of the BLB in the vestibular endorgan, the macula utricle, from patients with MD (n = 10), acoustic neuroma (AN) (n = 6) and normative autopsy specimens (n = 3) with no inner ear disease. Each subject had a well-documented clinical history and audiovestibular testing. Utricular maculae were studied using light and transmission electron microscopy and double labeling immunofluorescence. Vascular endothelial cells (VECs) were identified using isolectin B4 (IB4) and glucose-transporter-1 (GLUT-1). Pericytes were identified using alpha smooth muscle actin (αSMA) and phalloidin. IB4 staining of VECS was consistently seen in both AN and normative. In contrast, IB4 was nearly undetectable in all MD specimens, consistent with the significant VEC damage confirmed on transmission electron microscopy. GLUT-1 was present in MD, AN, and normative. αSMA and phalloidin were expressed consistently in the BLB pericytes in normative, AN specimen, and Meniere's specimens. Endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and nitrotyrosine were used as markers of oxidative stress. The VECs of the BLB in Meniere's had significantly higher levels of expression of iNOS and nitrotyrosine compared with normative and AN specimen. eNOS-IF staining showed similar patterns in normative and Meniere's specimens. Microarray-based gene expression profiling confirmed upregulation of iNOS mRNA from the macula utricle of Meniere's patients compared with AN. Nitrotyrosine, a marker recognized as a hallmark of inflammation, especially when seen in association with an upregulation of iNOS, was detected in the epithelial and stromal cells in addition to VECs in MD. Immunohistochemical and ultrastructural degenerative changes of the VEC suggest that these cells are the primary targets of oxidative stress, and pericyte pathology including degeneration and migration, likely also plays a role in the loss of integrity of the BLB and triggering of inflammatory pathways in MD. These studies advance our scientific understanding of oxidative stress in the human inner ear BLB and otopathology.

Immunohistochemical localization of Nrf2 in the human cochlea

Oxidative stress plays an important role in several inner ear diseases and normal aging. Nuclear (erythroid-derived 2)-like 2, also known as Nrf2, is a transcription factor encoded by the NFE2L2 gene that controls the expression of genes necessary to reduce oxidative stress. There are no studies to the date on the localization of Nrf2 in the human inner ear in normal or pathological conditions. Therefore, we investigated the immunohistochemical localization of Nrf2 in the human cochlea and vestibule using formalin-fixed celloidin-embedded human temporal bone sections. Nrf2 immunoreactivity (IR) was found in the inner and outer hair cells and supporting cells of the organ of Corti throughout the cochlea. Nfr2-IR was also found in hair cells and supporting cells of the maculae and cristae vestibular sensory epithelia. Nrf2-IR was decreased in the organ of Corti of older age individuals. The immunolocalization of Nrf2 in both auditory and vestibular sensory epithelia suggest that this transcription factor may play a relevant role in protecting sensory hair cells from oxidative stress.

A network-based method using a random walk with restart algorithm and screening tests to identify novel genes associated with Menière's disease

As a chronic illness derived from hair cells of the inner ear, Menière’s disease (MD) negatively influences the quality of life of individuals and leads to a number of symptoms, such as dizziness, temporary hearing loss, and tinnitus. The complete identification of novel genes related to MD would help elucidate its underlying pathological mechanisms and improve its diagnosis and treatment. In this study, a network-based method was developed to identify novel MD-related genes based on known MD-related genes. A human protein-protein interaction (PPI) network was constructed using the PPI information reported in the STRING database. A classic ranking algorithm, the random walk with restart (RWR) algorithm, was employed to search for novel genes using known genes as seed nodes. To make the identified genes more reliable, a series of screening tests, including a permutation test, an interaction test and an enrichment test, were designed to select essential genes from those obtained by the RWR algorithm. As a result, several inferred genes, such as CD4, NOTCH2 and IL6, were discovered. Finally, a detailed biological analysis was performed on fifteen of the important inferred genes, which indicated their strong associations with MD.

The blood labyrinthine barrier in the human normal and Meniere's disease macula utricle

The ultrastructural organization of the blood labyrinthine barrier (BLB) was investigated in the human vestibular endorgan, the utricular macula, using postmortem specimens from individuals with documented normal auditory and vestibular function and surgical specimens from patients with intractable Meniere’s disease. Transmission electron microscopic analysis of capillaries located in the normal human utricular stroma showed vascular endothelial cells with few pinocytotic vesicles, covered by a smooth and uniform basement membrane surrounded by pericyte processes. Meniere’s disease specimens revealed differential ultrastructural pathological changes in the cellular elements of the microvasculature. With moderate degeneration of the BLB, there were numerous vesicles within the vascular endothelial cells (VECs), with increased numbers at the abluminal face, pericyte process detachment and disruption of the perivascular basement membrane surrounding the VECs. With severe degeneration of the BLB, there was severe vacuolization or frank apparent necrosis of VECs and loss of subcellular organelles. A higher severity of BLB degenerative changes was associated with a higher degree of basement membrane thickening and edematous changes within the vestibular stroma. This study presents the first ultrastructural analysis of the capillaries constituting the BLB in the human vestibular macula utricle from normal and Meniere’s disease.

Immunohistochemical techniques for the human inner ear

In this review, we provide a description of the recent methods used for immunohistochemical staining of the human inner ear using formalin-fixed frozen, paraffin and celloidin-embedded sections. We also show the application of these immunohistochemical methods in auditory and vestibular endorgans microdissected from the human temporal bone. We compare the advantages and disadvantages of immunohistochemistry (IHC) in the different types of embedding media. IHC in frozen and paraffin-embedded sections yields a robust immunoreactive signal. Both frozen and paraffin sections would be the best alternative in the case where celloidin-embedding technique is not available. IHC in whole endorgans yields excellent results and can be used when desiring to detect regional variations of protein expression in the sensory epithelia. One advantage of microdissection is that the tissue is processed immediately and IHC can be made within 1 week of temporal bone collection. A second advantage of microdissection is the excellent preservation of both morphology and antigenicity. Using celloidin-embedded inner ear sections, we were able to detect several antigens by IHC and immunofluorescence using antigen retrieval methods. These techniques, previously applied only in animal models, allow for the study of numerous important proteins expressed in the human temporal bone potentially opening up a new field for future human inner ear research.

The expression of glutamate aspartate transporter (GLAST) within the human cochlea and its distribution in various patient populations

Glutamate plays an important role in the central nervous system as an excitatory neurotransmitter. However, its abundance can lead to excitotoxicity which necessitates the proper function of active glutamate transporters. The glutamate-aspartate transporter (GLAST) has been shown to exist and function within non-human cochlear specimens regulating the inner ear glutamate concentration. In this study, we examined human cochleas from formalin-fixed celloidin-embedded temporal bone specimens of three different types of patients (Meniere's disease, normal controls, and other otopathologic conditions) and examined the differential expression of GLAST in the spiral ligament of the basal, middle, and apical turns of the cochlea. Immunohistochemical staining was performed with polyclonal antibodies against GLAST and image analysis was carried out with the Image J analysis software. In contrast to other studies with non-human specimens, GLAST was expressed in the spiral ligament fibrocytes but was not detected in the satellite cells of the spiral ganglia or supporting cells of the Organ of Corti in the human cochlea. Our data also showed that GLAST expression significantly differs in the basal and apical turns of the cochlea. Lastly, post-hoc analysis showed a difference in the GLAST immunoreactive area of patients with Meniere's disease when compared to that of patients with other otopathologic conditions-such as presbycusis or ototoxicity. These results may potentially lead to further understanding of different disease states that affect hearing.