Cochlin immunostaining of inner ear pathologic deposits and proteomic analysis in DFNA9 deafness and vestibular dysfunction

Detailed hearing and vestibular profiles in the patients with COCH mutations

OBJECTIVES

To evaluate the clinical features of Japanese DFNA9 families with mutations of the COCH gene.

METHODS

Mutation screening was performed using targeted next-generation sequencing (NGS) for 63 previously reported deafness genes. The progression of hearing loss and vestibular dysfunction were evaluated by pure-tone audiometry, caloric testing, cVEMP, and computed dynamic posturography.

RESULTS

We detected 1 reported mutation of p.G88E and 2 novel mutations of p.I372T and p.C542R. The patients with the novel mutations of p.I372T and p.C542R within the vWFA2 domain showed early onset progressive hearing loss, and the patients with the p.G88E mutation showed late onset hearing loss and acute hearing deterioration over a short period. Vestibular symptoms were reported in the patients with p.G88E and p.C542R. Vestibular testing was performed for the family with the p.G88E mutation. Severe vestibular dysfunction was observed in the proband, and the proband's son showed unilateral semicircular canal dysfunction with mild hearing loss.

CONCLUSIONS

Targeted exon resequencing of selected genes using NGS successfully identified mutations in the relatively rare deafness gene, COCH, in the Japanese population. The phenotype is compatible with that described in previous reports. Additional supporting evidence concerning progressive hearing loss and deterioration of vestibular function was obtained from our study.

Cochlin in normal middle ear and abnormal middle ear deposits in DFNA9 and Coch (G88E/G88E) mice

DFNA9 sensorineural hearing loss and vestibular disorder, caused by mutations in COCH, has a unique identifying histopathology including prominent acellular deposits in cochlear and vestibular labyrinths. A recent study has shown presence of deposits also in middle ear structures of DFNA9-affected individuals (McCall et al., J Assoc Res Otolaryngol 12:141-149, 2004). To investigate the possible role of cochlin in the middle ear and in relation to aggregate formation, we evaluated middle ear histopathology in our Coch knock-in (Coch (G88E/G88E) ) mouse model, which harbors one of the DFNA9-causative mutations. Our findings reveal accumulation of acellular deposits in the incudomalleal and incudostapedial joints in Coch (G88E/G88E) mice, similar to those found in human DFNA9-affected temporal bones. Aggregates are absent in negative control Coch (+/+) and Coch (-/-) mice. Thickening of the tympanic membrane (TM) found in humans with DFNA9 was not appreciably detected in Coch (G88E/G88E) mice at the evaluated age. We investigated cochlin localization first in the Coch (+/+)mouse and in normal human middle ears, and found prominent and specific cochlin staining in the incudomalleal joint, incudostapedial joint, and the pars tensa of the TM, which are the three sites where abnormal deposits are detected in DFNA9-affected middle ears. Cochlin immunostaining of Coch (G88E/G88E) and DFNA9-affected middle ears showed mutant cochlin localization within areas of aggregates. Cochlin staining was heterogeneous throughout DFNA9 middle ear deposits, which appear as unorganized and overlapping mixtures of both eosinophilic and basophilic substances. Immunostaining for type II collagen colocalized with cochlin in pars tensa of the tympanic membrane. In contrast, immunostaining for type II collagen did not overlap with cochlin in interossicular joints, where type II collagen was localized in the region of the chondrocytes, but not in the thin layer of the articular surface of the ossicles nor in the eosinophilic deposits with specific cochlin staining.

Progress and prospects in human genetic research into age-related hearing impairment

Age-related hearing impairment (ARHI) is a complex, multifactorial disorder that is attributable to confounding intrinsic and extrinsic factors. The degree of impairment shows substantial variation between individuals, as is also observed in the senescence of other functions. This individual variation would seem to refute the stereotypical view that hearing deterioration with age is inevitable and may indicate that there is ample scope for preventive intervention. Genetic predisposition could account for a sizable proportion of interindividual variation. Over the past decade or so, tremendous progress has been made through research into the genetics of various forms of hearing impairment, including ARHI and our knowledge of the complex mechanisms of auditory function has increased substantially. Here, we give an overview of recent investigations aimed at identifying the genetic risk factors involved in ARHI and of what we currently know about its pathophysiology. This review is divided into the following sections: (i) genes causing monogenic hearing impairment with phenotypic similarities to ARHI; (ii) genes involved in oxidative stress, biologic stress responses, and mitochondrial dysfunction; and (iii) candidate genes for senescence, other geriatric diseases, and neurodegeneration. Progress and prospects in genetic research are discussed.

Clinical characterization of a novel COCH mutation G87V in a Chinese DFNA9 family

OBJECTIVES

To characterize the clinical features of a Chinese DFNA9 family associated with a novel COCH mutation and to confirm the proposed genotype-phenotype correlation of COCH.

METHODS

Mutation screening of 79 deafness genes was performed in the proband by targeted next-generation sequencing. Co-segregation of the disease phenotype and the detected variants was confirmed in all family members by PCR amplification and Sanger sequencing. The progression of hearing impairment in affected family members was followed and the concomitant vestibular dysfunction was verified by the caloric vestibulo-ocular reflex test.

RESULTS

A novel COCH mutation p.G87V was identified in the family segregating with late-onset, progressive sensorineural hearing impairment and consistent vestibular dysfunction.

CONCLUSION

The p.G87V mutation leads to a very similar phenotype as a previously reported p.G87W mutation of COCH. Our study suggested that the G87 residue is critical for function of COCH and further confirms a previously proposed genotype-phenotype correlation for DFNA9.

Cochlin produced by follicular dendritic cells promotes antibacterial innate immunity

Cochlin, an extracellular matrix protein, shares homologies with the Factor C, a serine protease found in horseshoe crabs, which is critical for antibacterial responses. Mutations in the COCH gene are responsible for human DFNA9 syndrome, a disorder characterized by neurodegeneration of the inner ear that leads to hearing loss and vestibular impairments. The physiological function of cochlin, however, is unknown. Here, we report that cochlin is specifically expressed by follicular dendritic cells and selectively localized in the fine extracellular network of conduits in the spleen and lymph nodes. During inflammation, cochlin was cleaved by aggrecanases and secreted into blood circulation. In models of lung infection with Pseudomonas aeruginosa and Staphylococcus aureus, Coch(-/-) mice show reduced survival linked to defects in local cytokine production, recruitment of immune effector cells, and bacterial clearance. By producing cochlin, FDCs thus contribute to the innate immune response in defense against bacteria.

Inherited hearing loss: molecular genetics and diagnostic testing

BACKGROUND

Hearing loss is a clinically and genetically heterogeneous condition with major medical and social consequences. It affects up to 8% of the general population.

OBJECTIVE

This review recapitulates the principles of auditory physiology and the molecular basis of hearing loss, outlines the main types of non-syndromic and syndromic deafness by mode of inheritance, and provides an overview of current clinically available genetic testing.

METHODS

This paper reviews the literature on auditory physiology and on genes, associated with hearing loss, for which genetic testing is presently offered.

RESULTS/CONCLUSION

The advent of molecular diagnostic assays for hereditary hearing loss permits earlier detection of the underlying causes, facilitates appropriate interventions, and is expected to generate the data necessary for more specific genotype-phenotype correlations.

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

The distribution of cochlin and its associated basement membrane proteins (collagen IV, collagen II, laminin-β2, and nidogen-1) were evaluated in the vestibular endorgans of subjects with Meniere's disease and compared with normal specimens. Cochlin mRNA expression in vestibular endorgans from Meniere's disease specimens was also investigated. Specimens were obtained from patients who had Meniere's disease and who were undergoing ablative labyrinthectomy. Control specimens were obtained both from autopsy specimens with documented normal audiovestibular function and from patients undergoing labyrinthectomy for acoustic neuroma excision. In the normal control specimens, cochlin immunoreactivity was found evenly distributed in the stroma of the cristae ampullaris and maculae of the utricle. In Meniere's specimens, cochlin immunoreactivity was markedly increased; this was associated with an increase in cochlin mRNA expression as shown by real-time reverse transcription with the polymerase chain reaction. Collagen IV and laminin-β2 immunoreactivity was significantly decreased in Meniere's specimens. Nidogen-1 and collagen II immunoreactivity was unchanged in Meniere's specimens when compared with normal samples. Cochlin upregulation has been implicated in the hereditary audiovestibulopathy, DFNA9. The increased expression of cochlin and decreased expression of collagen IV and laminin in Meniere's disease are suggestive that the overexpression of cochlin contributes to the dysfunctional inner ear homeostasis seen in this disease.

Cochlin expression in the rat perilymph during postnatal development

CONCLUSIONS

The changes in the cochlin isoforms in the perilymph may provide important insights to the understanding of cochlin function and the pathogenesis of related inner ear diseases.

OBJECTIVES

Cochlin is involved in various pathologies of the inner ear. Altered levels of cochlin isoforms in developing inner ear tissue were reported previously. The purpose of this study was to elucidate the cochlin isoform expression in the perilymph of rats during postnatal development in relation to Coch gene mRNA expression.

METHODS

We studied the cochlin isoforms in the rat perilymph during postnatal development by Western blot analysis. Real-time PCR was also performed to elucidate the expression level of Coch mRNA in the developing inner ear of rats.

RESULTS

Western blot analysis showed that the expression of p63s in the perilymph was highest on the 12th day after birth (DAB12), the earliest age at which we could identify the perilymphatic space microscopically, and it decreased gradually as the cochlea developed. On the other hand, the expression of Cochlin-tomoprotein (CTP)was lowest on DAB12 and increased gradually up to DAB24. COCH mRNA was detected from DAB3 and gradually increased to DAB15, and then gradually decreased to DAB70.

Proteomic analysis of the organ of corti using nanoscale liquid chromatography coupled with tandem mass spectrometry

The organ of Corti (OC) in the cochlea plays an essential role in auditory signal transduction in the inner ear. For its minute size and trace amount of proteins, the identification of the molecules in pathophysiologic processes in the bone-encapsulated OC requires both delicate separation and a highly sensitive analytical tool. Previously, we reported the development of a high resolution metal-free nanoscale liquid chromatography system for highly sensitive phosphoproteomic analysis. Here this system was coupled with a LTQ-Orbitrap XL mass spectrometer to investigate the OC proteome from normal hearing FVB/N male mice. A total of 628 proteins were identified from six replicates of single LC-MS/MS analysis, with a false discovery rate of 1% using the decoy database approach by the OMSSA search engine. This is currently the largest proteome dataset for the OC. A total of 11 proteins, including cochlin, myosin VI, and myosin IX, were identified that when defective are associated with hearing impairment or loss. This study demonstrated the effectiveness of our nanoLC-MS/MS platform for sensitive identification of hearing loss-associated proteins from minute amount of tissue samples.

Age-related changes of myelin basic protein in mouse and human auditory nerve

Age-related hearing loss (presbyacusis) is the most common type of hearing impairment. One of the most consistent pathological changes seen in presbyacusis is the loss of spiral ganglion neurons (SGNs). Defining the cellular and molecular basis of SGN degeneration in the human inner ear is critical to gaining a better understanding of the pathophysiology of presbyacusis. However, information on age-related cellular and molecular alterations in the human spiral ganglion remains scant, owing to the very limited availably of human specimens suitable for high resolution morphological and molecular analysis. This study aimed at defining age-related alterations in the auditory nerve in human temporal bones and determining if immunostaining for myelin basic protein (MBP) can be used as an alternative approach to electron microscopy for evaluating myelin degeneration. For comparative purposes, we evaluated ultrastructural alternations and changes in MBP immunostaining in aging CBA/CaJ mice. We then examined 13 temporal bones from 10 human donors, including 4 adults aged 38-46 years (middle-aged group) and 6 adults aged 63-91 years (older group). Similar to the mouse, intense immunostaining of MBP was present throughout the auditory nerve of the middle-aged human donors. Significant declines in MBP immunoreactivity and losses of MBP(+) auditory nerve fibers were observed in the spiral ganglia of both the older human and aged mouse ears. This study demonstrates that immunostaining for MBP in combination with confocal microscopy provides a sensitive, reliable, and efficient method for assessing alterations of myelin sheaths in the auditory nerve. The results also suggest that myelin degeneration may play a critical role in the SGN loss and the subsequent decline of the auditory nerve function in presbyacusis.

Phenotype analysis of an Australian DFNA9 family with the 1109N COCH mutation

OBJECTIVES

We studied the clinical characteristics of an Australian family with an autosomal dominant sensorineural hearing impairment (DFNA9) caused by an I109N mutation in COCH.

METHODS

Retrospective analyses of audiometric data from 8 mutation carriers of an Australian DFNA9 family with the I109N COCH mutation were performed. Cross-sectional hearing levels related to age, age-related typical audiograms, and speech recognition scores related to age and to the level of hearing impairment were investigated. Data were compared to those obtained in previously identified DFNA9 families with P51S, V66G, G87W, G88E, I109T, and C542F COCH mutations.

RESULTS

Deterioration of hearing in the I109N mutation carriers started before the age of 40 years. The audiometric characteristics of the I109N mutation carriers are essentially similar to those previously established in I109T mutation carriers and, to a lesser extent, in P51S, G87W, and G88E mutation carriers.

CONCLUSIONS

The phenotype associated with the I109N COCH mutation is largely similar to that associated with the I109T, P51S, G87W, and G88E mutation carriers. However, subtle differences seem to exist in terms of age of onset and rate of progression.

A novel mutation in COCH-implications for genotype-phenotype correlations in DFNA9 hearing loss

OBJECTIVES/HYPOTHESIS

To determine the cause of autosomal dominant hearing loss segregating in an American family.

STUDY DESIGN

Family study.

METHODS

Otologic and audiometric examination was performed on affected family members. Genome wide parametric multipoint linkage mapping using a dominant model was performed with Affymetrix 50K GeneChip data. Direct sequencing was used to confirm the causative mutation.

RESULTS

In American family 467, segregating autosomal dominant nonsyndromic hearing loss, a novel heterozygous missense mutation (c.362T>C; p.F121S) was identified in the COCH gene. This mutation was also associated with vestibular dysfunction typical of other DFNA9 families. However, affected family members also exhibited memory loss and night blindness.

CONCLUSIONS

The novel COCH mutation affects the functionally important limulus factor C, Coch-5b2 and Lgl1 domain where most DFNA9 mutations have been localized. The onset of the hearing loss, in the 2nd or 3rd decade of life, is earlier than in most DFNA9 families. The progression of hearing loss and vestibular dysfunction in the American family is typical of other DFNA9 families with mutations in this domain. Memory loss and night blindness have not been previously reported in DFNA9 families.

Immunocytochemical distribution of WARP (von Willebrand A domain-related protein) in the inner ear

The basic components of the epithelial, perineural, and perivascular basement membranes in the inner ear have been well-documented in several animal models and in the human inner ear. The von Willebrand A domain-related protein (WARP) is an extracellular matrix molecule with restricted expression in cartilage, and a subset of basement membranes in peripheral nerves, muscle, and central nervous system vasculature. It has been suggested that WARP has an important role in maintaining the blood-brain barrier. To date no studies on WARP distribution have been performed in the inner ear, which is equipped with an intricate vasculature network. In the present study, we determined the distribution of WARP by immunocytochemistry in the human inner ear using auditory and vestibular endorgans microdissected from human temporal bones obtained at autopsy. All subjects (n=5, aged 55-87years old) had documented normal auditory and vestibular function. We also determined the WARP immunolocalization in the mouse inner ear. WARP immunoreactivity localized to the vasculature throughout the stroma of the cristae ampullaris, the maculae utricle, and saccule in the human and mouse. In the human and mouse inner ear, WARP immunoreactivity delineated blood vessels located in the stria vascularis, spiral ligament, sub-basilar region, stromal tissue, and the spiral and vestibular ganglia. The distinct localization of WARP in the inner ear vasculature suggests an important role in maintaining its integrity. In addition, WARP allows delineation of microvessels in the inner ear allowing the study of vascular pathology in the development of otological diseases.

Extralabyrinthine manifestations of DFNA9

DFNA9 is an autosomal dominant cause of non-syndromic adult-onset sensorineural hearing loss with associated variable vestibular dysfunction caused by mutations in the COCH gene. DFNA9 has previously been characterized by the presence of unique histopathologic features limited to the cochlear and vestibular labyrinth. This report describes newly discovered extralabyrinthine findings within the middle ear in DFNA9 and discusses their implications. The histopathologic anatomy of extralabyrinthine structures was reviewed in 12 temporal bones from seven individuals with DFNA9 and compared with age-matched controls. All temporal bones with DFNA9 had abnormal deposits within the tympanic membrane, incudomalleal joint, and incudostapedial joint. Hematoxylin and eosin stain and Movat's pentachrome stain both revealed different staining patterns of the extralabyrinthine deposits compared with the intralabyrinthine deposits suggesting that the composition of the deposits varies with location. The deposits within the tympanic membrane resembled cartilage morphologically and stained positively for aggrecan, an extracellular matrix protein found in cartilage. However, the cellular component of the tympanic membrane deposits did not stain with immunomarkers for chondrocytes (s100 and connective tissue growth factor). These novel findings in DFNA9 have implications for the phenotypic expression of the disorder and the clinical workup of adult-onset sensorineural hearing loss.

Proteomic analysis of formalin-fixed celloidin-embedded whole cochlear and laser microdissected spiral ganglion tissues

CONCLUSION

The results of this study demonstrate that proteomic analysis can be successfully performed on formalin-fixed celloidin-embedded (FFCE) archival human cochlear tissues.

OBJECTIVE

To investigate the feasibility of analyzing protein expression in archival cochlear tissues.

MATERIAL AND METHODS

A new methodology, referred to as Liquid Tissue(TM), was used to extract proteins from human cochlear tissue sections and spiral ganglion tissue isolated by laser microdissection (LMD). Protein identification was performed by bioinformatic analysis of high resolution tandem mass spectrometric data from fractionated tryptic peptide samples.

RESULTS

Twenty-six proteins were identified with a minimum of 2 unique peptides and 450 proteins were identified with 1 unique peptide at a confidence level of 95% in cochlear tissue. Ten proteins were identified with a minimum of 2 unique peptides and 485 proteins were identified with 1 unique peptide at a confidence level of 95% in spiral ganglion tissue.

Modified paraffin-embedding method for the human cochlea that reveals a fine morphology and excellent immunostaining results

CONCLUSION

A modified paraffin-embedding method could be applied to histopathological and immunohistochemical studies of the human cochlea. The complementary use of molecular and immunohistochemical techniques by means of this method is thus considered to be a valuable tool for the future study of the human inner ear.

OBJECTIVE

To propose a new paraffin-embedding method for the morphological and immunohistochemical study of the human cochlea.

METHODS

Five human temporal bones were harvested at autopsy. The temporal bone specimens were fixed in 20% buffered formalin, decalcified with EDTA, cropped to a cube of approximately 15 mm, embedded in paraffin, and then cut into 6 microm thick sections. The sections were stained with hematoxylin and eosin, and immunostained with anti-prestin and anti-neurofilament antibodies.

RESULTS

Although paraffin-embedded sections cannot show the excellent morphology of the delicate membranous labyrinth obtained with celloidin, this technique successfully preserved the morphology of the cochlea, especially the organ of Corti, thereby enabling us to obtain excellent immunostaining results.

Proteome bioprofiles distinguish between M1 priming and activation states in human macrophages

Macrophage activation is a dynamic process that results in diverse functional outcomes ranging from immunoregulation to inflammation. The proinflammatory, or M1, response is a complex, bimodal progression composed of a "prime," classically through IFN-gamma, and "trigger," such as LPS. To characterize the physiological response of M1 activation, a systems biology approach was applied to determine the intracellular proteome bioprofiles of IFN-gamma-and LPS-treated primary human macrophages. Our goal was to develop intracellular proteomic fingerprints to serve as novel correlates of macrophage priming and/or activation to augment the existing approaches of analyzing secreted cytokines and cell-surface protein expression. The majority of the proteome, approximately 78%, remained stable during activation, representing the core proteome. In contrast, three distinct patterns defined response proteomes: IFN-gamma-specific, LPS-specific, or IFN-gamma- and LPS-shared or M1-specific. Although steady-state expression levels of proteins involved in energy metabolism and immune response were increased during priming and triggering, changes in protein and fatty acid metabolism, signaling, and transport pathways were most apparent. Unique proteomic fingerprints distinguish among IFN-gamma-specific, LPS-specific, or M1-specific activation states and provide a clear molecular, archeological profile to infer recent history of cells, as well as correlates for chronic macrophage activation in health and disease.

Proteomics, bioinformatics and targeted gene expression analysis reveals up-regulation of cochlin and identifies other potential biomarkers in the mouse model for deafness in Usher syndrome type 1F

Proteins and protein networks associated with cochlear pathogenesis in the Ames waltzer (av) mouse, a model for deafness in Usher syndrome 1F (USH1F), were identified. Cochlear protein from wild-type and av mice at postnatal day 30, a time point in which cochlear pathology is well established, was analyzed by quantitative 2D gel electrophoresis followed by mass spectrometry (MS). The analytic gel resolved 2270 spots; 69 spots showed significant changes in intensity in the av cochlea compared with the control. The cochlin protein was identified in 20 peptide spots, most of which were up-regulated, while a few were down-regulated. Analysis of MS sequence data showed that, in the av cochlea, a set of full-length isoforms of cochlin was up-regulated, while isoforms missing the N-terminal FCH/LCCL domain were down-regulated. Protein interaction network analysis of all differentially expressed proteins was performed with Metacore software. That analysis revealed a number of statistically significant candidate protein networks predicted to be altered in the affected cochlea. Quantitative PCR (qPCR) analysis of select candidates from the proteomic and bioinformatic investigations showed up-regulation of Coch mRNA and those of p53, Brn3a and Nrf2, transcription factors linked to stress response and survival. Increased mRNA of Brn3a and Nrf2 has previously been associated with increased expression of cochlin in human glaucomatous trabecular meshwork. Our report strongly suggests that increased level of cochlin is an important etiologic factor leading to the degeneration of cochlear neuroepithelia in the USH1F model.

COCH transgene expression in cultured human trabecular meshwork cells and its effect on outflow facility in monkey organ cultured anterior segments

Purpose. To determine the effects of COCH transgene expression on cultured human trabecular meshwork (HTM) cell morphology and on outflow facility (OF) in monkey organ cultured anterior segments (MOCAS). Methods. An adenoviral (Ad) vector expressing both cochlin (COCH) and green fluorescent protein (GFP) (AdCOCHGFP) or GFP alone (AdGFP) was used to transduce cultured HTM cells (multiplicity of transduction, 2.8 and 28). COCH transgene expression in transduced HTM cells and the culture medium was verified by Western blot analysis and immunofluorescence detection 5 days after transduction. MOCAS were used to test the effect of Ad vectors (2.8 x 10(10) viral particles per segment) on OF. The morphology of transduced MOCAS was evaluated by light microscopy. Results. Western blot analysis showed a viral vector dose-dependent expression of cochlin in transduced cells and the culture medium. There was no notable morphologic change in transduced cells. In MOCAS, cochlin expression was detectable in the medium by 3 days after transduction. A 35% decrease in OF in AdCOCHGFP-transduced MOCAS was detected after 3 days, decreasing by 76% after 12 days when compared to control segments injected with AdGFP. Anterior segment pressure (ASP) more than doubled (P < 0.05) in segments injected with AdCOCHGFP at 12 days after transduction. Light microscopy revealed normal angle structures in transduced segments. Conclusions. Ad vector delivery of the COCH transgene resulted in cochlin expression in HTM cells and MOCAS. Cochlin expression was effective in decreasing OF and increasing ASP in MOCAS, suggesting possible involvement of cochlin in IOP elevation in vivo. COCH gene delivery has potential for use in developing a glaucoma model.

The second von Willebrand type A domain of cochlin has high affinity for type I, type II and type IV collagens

Cochlin is colocalized with type II collagen in the extracellular matrix of cochlea and has been suggested to interact with this collagen. Here we show that the second von Willebrand type A domain of cochlin has affinity for type II collagen, as well as type I and type IV collagens whereas the LCCL-domain of cochlin has no affinity for these proteins. The implications of these findings for the mechanism whereby cochlin mutations cause the dominant negative DFNA9-type hearing loss are discussed.

Cochlin expression in anterior segment organ culture models after TGFbeta2 treatment

PURPOSE

To determine the effect of transforming growth factor (TGF)-beta2 treatment on intraocular pressure (IOP), outflow facility, and cochlin expression in vitro in monkey and pig organ-cultured anterior segments (MOCAS and POCAS).

METHODS

MOCAS (rhesus and cynomolgus) or POCAS were infused with media containing 10 ng/mL TGFbeta2 to one segment of each pair and 0.1% BSA (vehicle) to the contralateral segment for up to 14 days at a constant rate. Cochlin expression was determined by immunohistochemical study, ELISA, and Western blot analysis using chicken polyclonal antibodies against different regions of cochlin.

RESULTS

TGFbeta2 infusion produced elevated IOP in MOCAS (usually after 5 days), that was approximately 45% greater than baseline and compared to control segments. Outflow facility (OF) was decreased by approximately 40% compared with pretreatment baseline (n=5). In POCAS (n=7), IOP was increased (approximately 3 days) by approximately 75% compared with baseline and contralateral changes. The IOP elevation subsided thereafter. Cochlin levels increased with duration of TGFbeta2 treatment in the media and in the region of the trabecular meshwork in both species.

CONCLUSIONS

TGFbeta2-induced IOP elevation was associated with an increase in cochlin secretion into the media and expression in the tissue of MOCAS and POCAS. Whether cochlin overexpression contributes to elevated IOP or is a consequence of other changes relevant to IOP elevation remains to be determined.

A targeted Coch missense mutation: a knock-in mouse model for DFNA9 late-onset hearing loss and vestibular dysfunction

Mutations in COCH (coagulation factor C homology) are etiologic for the late-onset, progressive, sensorineural hearing loss and vestibular dysfunction known as DFNA9. We introduced the G88E mutation by gene targeting into the mouse and have created a Coch(G88E/G88E) mouse model for the study of DFNA9 pathogenesis and cochlin function. Vestibular-evoked potential (VsEP) thresholds of Coch(G88E/G88E) mice were elevated at all ages tested compared with wild-type littermates. At the oldest ages, two out of eight Coch(G88E/G88E) mice had no measurable VsEP. Auditory brainstem response (ABR) thresholds of Coch(G88E/G88E) mice were substantially elevated at 21 months but not at younger ages tested. At 21 months, four of eight Coch(G88E/G88E) mice had absent ABRs at all frequencies tested and two of three Coch(G88E)(/+) mice had absent ABRs at three of four frequencies tested. Distortion product otoacoustic emission amplitudes of Coch(G88E/G88E) mice were substantially lower than Coch(+/+) mice and absent in the same Coch(G88E/G88E) mice with absent ABRs. These results suggest that vestibular function is affected beginning as early as 11 months when cochlear function appears to be normal, and dysfunction increases with age. Hearing loss declines substantially at 21 months of age and progresses to profound hearing loss at some to all frequencies tested. This is the only mouse model developed to date where hearing loss begins at such an advanced age, providing an opportunity to study both progressive age-related hearing loss and possible interventional therapies.

Spatiotemporal expression of cochlin in the inner ear of rats during postnatal development

Cochlin (encoded by COCH) constitutes 70% of non-collagenous protein in the inner ear, and the expression of cochlin is highly specific to the inner ear. Eleven missense mutation and one in-frame deletion have been reported in the COCH gene, causing hereditary progressive sensorineural hearing loss and vestibular dysfunction, DFNA9. These data imply that cochlin should bear an essential and crucial role in the inner ear function. However, the role of cochlin has not been fully clarified. We have investigated the spatiotemporal expression of cochlin in the inner ear of rats during postnatal development to better understand the functional role of cochlin. By immunohistochemistry, cochlin expression was faint in the cochlea and vestibule on the 6th day after birth (DAB6). At DAB70, strong expression of cochlin was detected in the spiral limbus and spiral ligament within the cochlea, and in the stromata of the maculae of otolithic organs and crista ampullaris within the vestibule. Immunoreactivity for cochlin increased during the postnatal development. Western blot analysis also showed an increase in the expression of cochlin isoforms. Furthermore, the dominant isoform of cochlin expressed changed from p63s to p40s between DAB24 and DAB70. These results suggest that the expression of cochlin may be related to the maturation of inner ear function, and the change in isoforms of cochlin expressed will provide important insight into the understanding of both cochlin function and formation of cochlin isoforms. This is the first to report about the spatiotemporal expression of cochlin in the developing rat inner ear.

Ultrastructural co-localization of cochlin and type II collagen in the rat semicircular canal

Cochlin and type II collagen are major constituents of the inner ear extracellular matrix. To investigate the morphological relation of cochlin and type II collagen in the rat semicircular canal, immuno-electronmicroscopic analysis was performed using the post-embedding immunogold method. Immunolabeling for cochlin was detected in the fibrillar substance underlying the supporting epithelium of the sensory cells and beneath the epithelial cells facing the endolymph in the semicircular canals. Immunolabeling for type II collagen was observed in the same fibrillar substance in the subepithelial area. The co-localization of cochlin and type II collagen in the fibrillar substance in the subepithelial area indicate that cochlin may play a role in the structural homeostasis of the vestibule acting in concert with the fibrillar type II collagen bundles.

Deafness mutation mining using regular expression based pattern matching

Background

While keyword based queries of databases such as Pubmed are frequently of great utility, the ability to use regular expressions in place of a keyword can often improve the results output by such databases. Regular expressions can allow for the identification of element types that cannot be readily specified by a single keyword and can allow for different words with similar character sequences to be distinguished.

Results

A Perl based utility was developed to allow the use of regular expressions in Pubmed searches, thereby improving the accuracy of the searches.

Conclusion

This utility was then utilized to create a comprehensive listing of all DFN deafness mutations discussed in Pubmed records containing the keywords "human ear".

Cochlin isoforms and their interaction with CTL2 (SLC44A2) in the inner ear

Choline transporter-like protein 2 (CTL2) is a multi-transmembrane protein expressed on inner ear supporting cells that was discovered as a target of antibody-induced hearing loss. Its function is unknown. A 64 kDa band that consistently co-precipitates with CTL2 from inner ear extracts was identified by mass spectroscopy as cochlin. Cochlin is an abundant inner ear protein expressed as multiple isoforms. Its function is also unknown, but it is suspected to be an extracellular matrix component. Cochlin is mutated in individuals with DFNA9 hearing loss. To investigate the CTL2-cochlin interaction, antibodies were raised to a cochlin-specific peptide. The antibodies identify several cochlin polypeptides on western blots and are specific for cochlin. We show that the heterogeneity of the cochlin isoforms is caused, in part, by in vivo post-translational modification by N-glycosylation and, in part, caused by alternative splicing. We verified that antibody to CTL2 co-immunoprecipitates cochlin from the inner ear and antibody to cochlin co-immunoprecipitates CTL2. Using cochlear cross-sections, we show that CTL2 is more widely distributed than previously described, and its prominent expression on cells facing the scala media suggests a possible role in homeostasis. A prominent but previously unreported ribbon-like pattern of cochlin in the basilar membrane was demonstrated, suggesting an important role for cochlin in the structure of the basilar membrane. CTL2 and cochlin are expressed in close proximity in the inner sulcus, the spiral prominence, vessels, limbus, and spiral ligament. The possible functional significance of CTL2-cochlin interactions remains unknown.

Quantitative analysis of mRNA in human temporal bones

CONCLUSION

Well-preserved mRNA could be extracted from frozen human inner ears. Therefore, this study demonstrates that analysis of mRNA could be performed to study the molecular mechanisms of inner ear disorders using human specimens.

OBJECTIVES

Analysis of RNA as well DNA is requisite to study the molecular mechanisms of inner ear disorders. Methods of isolating RNA from experimental animals have been established, while isolation of RNA from human inner ears is much more challenging. In the present study, we demonstrate a method by which messenger RNA (mRNA) was extracted from human inner ears and quantitatively analyzed.

MATERIALS AND METHODS

COCH mRNA as well as GAPDH mRNA was extracted from membranous labyrinths dissected from three formalin-fixed and three frozen human temporal bones, removed at autopsy. The length of COCH mRNA and quantity of GAPDH mRNA was compared between the two groups by quantitative RT-PCR.

RESULTS

COCH mRNA could be amplified as much as 976 bp in all three frozen specimens. By contrast, it was amplified to 249 bp in two of the three formalin-fixed specimens, with no amplification observed in the remaining. The quantity of amplifiable GAPDH mRNA in the formalin specimens was only 1% of that of the frozen specimens.

Cochlin in the eye: functional implications

Aqueous humor is actively produced in the ciliary epithelium of the anterior chamber and has important functions for the eye. Under normal physiological conditions, the inflow and outflow of the aqueous humor are tightly regulated, but in the pathologic state this balance is lost. Aqueous outflow involves structures of the anterior chamber and experiences most resistance at the level of the trabecular meshwork (TM) that acts as a filter. The modulation of the TM structure regulates the filter and its mechanism remains poorly understood. Proteomic analyses have identified cochlin, a protein of poorly understood function, in the glaucomatous TM but not in healthy control TM from human cadaver eyes. The presence of cochlin has subsequently been confirmed by Western and immunohistochemical analyses. Functionally, cochlin undergoes multimerization induced by shear stress and other changes in the microenvironment. Cochlin along with mucopolysaccharide deposits has been found in the TM of glaucoma patients and in the inner ear of subjects affected by the hearing disorder DNFA9, a late-onset, progressive disease that also involves alterations in fluid shear regimes. In vitro, cochlin induces aggregation of primary TM cells suggesting a role in cell adhesion, possibly in mechanosensation, and in modulation of the TM filter.

Vertical corneal striae in families with autosomal dominant hearing loss: DFNA9/COCH

PURPOSE

Investigation of a possible association between vertical corneal striae and mutations in the COCH gene, observed in four DFNA9 families with autosomal dominant hearing loss and vestibular dysfunction.

DESIGN

Prospective case series.

METHODS

Ophthalmologic examinations with photography of the cornea after instillation of fluorescein were performed in 98 family members with 61 mutation carriers of four DFNA9 families at the Radboud University Nijmegen Medical Centre. Families 1 and 2 harbor the Pro51Ser mutation, and families 3 and 4 harbor the Gly88Glu and the Gly87Trp mutation, respectively. Statistical analysis was performed to find an association between the vertical corneal striae and the COCH mutation for each family and to test whether the four families were different in this respect.

RESULTS

The vertical corneal striae were exclusively visible after instillation of fluorescein. They caused minor problems, as dry eye symptoms, and were not present in the general Dutch ophthalmologic population. The striae were present from an age of 47 years in 32 individuals, of whom 27 individuals had a COCH mutation. Statistical analysis on the striae and the COCH mutations showed a significant association in families 1, 2, and 3 (P = .0006), but not in family 4 (P = .63).

CONCLUSIONS

Data analysis demonstrated a significant association between vertical corneal striae and the Pro51Ser and Gly88Glu mutations in the COCH gene in DFNA9 families 1, 2, and 3 with cochleovestibular dysfunction. Our findings suggest that the vertical corneal striae and cochleovestibular dysfunction may be caused by the same COCH mutations.

Clinical Characteristics of a Dutch DFNA9 Family with a Novel COCH Mutation, G87W

The present study aims to report audiological and vestibular characteristics of a Dutch DFNA9 family with a novel mutation, G87W, in the LCCL domain of COCH. From the family with the novel G87W COCH mutation audiometric data were collected and analyzed longitudinally. Results were compared with those obtained in previously identified P51S COCH mutation carriers (n = 74) and with those obtained in G88E mutation carriers. Special attention was also given to a comparison of age-related features, such as progressive hearing loss and vestibular impairment. A novel mutation (G87W) in COCH is indicative of hearing impairment and vestibular dysfunction in the present family. Pure-tone thresholds, phoneme recognition scores, and vestibular responses of the G87W mutation carriers were essentially similar to those previously established in the P51S and G88E mutation carriers. Deterioration of hearing and vestibular function in the G87W mutation carriers started at the age of 43 years. Remarkably, similar to G88E mutation carriers, the proportion of patients over 40 years of age who developed complete vestibular areflexia was significantly lower for the G87W mutation carriers than for the P51S mutation carriers. In conclusion, the phenotype associated with the novel COCH (G87W) mutation is largely similar to that associated with the P51S and G88E mutation carriers. However, subtle differences in terms of onset age and rate of progression seem to exist.