Prox1 interacts with Atoh1 and Gfi1, and regulates cellular differentiation in the inner ear sensory epithelia.

Inner ear hair cells and supporting cells arise from common precursors and, in mammals, do not show phenotypic conversion. Here, we studied the role of the homeodomain transcription factor Prox1 in the inner ear sensory epithelia. Adenoviral-mediated Prox1 transduction into hair cells in explant cultures led to strong repression of Atoh1 and Gfi1, two transcription factors critical for hair cell differentiation and survival. Luciferase assays showed that Prox1 can repress transcriptional activity of Gfi1 independently of Atoh1. Prox1 transduction into cochlear outer hair cells resulted in degeneration of these cells, consistent with the known phenotype of Gfi1-deficient mice. These results together with the widespread expression of endogenous Prox1 within the population of inner ear supporting cells point to the role for Prox1 in antagonizing the hair cell phenotype in these non-sensory cells. Further, in vivo analyses of hair cells from Gfi1-deficient mice suggest that the cyclin-dependent kinase inhibitor p57(Kip2) mediates the differentiation- and survival-promoting functions of Gfi1. These data reveal novel gene interactions and show that these interactions regulate cellular differentiation within the inner ear sensory epithelia. The data point to the tight regulation of phenotypic characteristics of hair cells and supporting cells.

Should Koos grade I vestibular schwannomas be treated early with gamma knife surgery? A subgroup analysis in a series of 190 consecutive patients.

INTRODUCTION: Gamma knife surgery (GKS) for vestibular schwannomas (VS) has a long-term clinical and scientific track record. After a period of de-escalation of dose prescription, results show a high rate of tumor control with improvement of clinical outcome (less than 1% facial palsy, 50-70% hearing preservation). Régis et al. (J Neurosurg 2013;119 Suppl.:105-11) suggested recently that proactive GKS management in intracanalicular tumors is better than a « wait and see » strategy when hearing is still useful at the time of diagnosis. MATERIALS AND METHODS: Based on these previous findings, we prospectively analyzed 190 vestibular schwannomas (VS), treated with GKS as first intention over a period of 4 years (2010-2014). We concentrated on patient, tumor and dosimetric characteristics. Special attention was given on the dose to the cochlea and its impact in maintaining serviceable hearing. RESULTS: The mean follow-up period was 1.3years (range 0.6-3.6). Preoperative serviceable hearing was present in 63.11% patients. The mean maximal diameter was 15.1mm (range 5-29.5). The size and volume of the tumor corresponded to Koos grade I, II, III and IV in 15.9%, 34.8%, 45.4% and 3.8% of the cases, respectively. The mean target volume was 1.24cm(3) (0.017-7.8). The mean prescription isodose volume was 1.6 cc (0.032-8.5). The mean marginal dose was 12Gy (11-12). The mean maximal dose received by the cochlea in patients with GR class 1 and 2 was 4.1Gy (1.5-7.6). Our preliminary neuroradiological follow-up shows 97% tumor control, with 45% shrinkage. Patients presenting with GR class 1 and class 2 at baseline retained serviceable hearing in 85% of cases. Among the patients with a follow-up of at least one year, those with Koos I tumors had the highest probability to maintain identical level of hearing after GKS. CONCLUSION: Our preliminary data suggest that Koos I patients should be treated early with GKS, before tumor growth and/or hearing deterioration, as they have the highest probability of hearing preservation.

N-myc controls proliferation, morphogenesis, and patterning of the inner ear

Myc family members play crucial roles in regulating cell proliferation, size, and differentiation during organogenesis. Both N-myc and c-myc are expressed throughout inner ear development. To address their function in the mouse inner ear, we generated mice with conditional deletions in either N-myc or c-myc. Loss of c-myc in the inner ear causes no apparent defects, whereas inactivation of N-myc results in reduced growth caused by a lack of proliferation. Reciprocally, the misexpression of N-myc in the inner ear increases proliferation. Morphogenesis of the inner ear in N-myc mouse mutants is severely disturbed, including loss of the lateral canal, fusion of the cochlea with the sacculus and utriculus, and stunted outgrowth of the cochlea. Mutant cochleas are characterized by an increased number of cells exiting the cell cycle that express the cyclin-dependent kinase inhibitor p27Kip1 and lack cyclin D1, both of which control the postmitotic state of hair cells. Analysis of different molecular markers in N-myc mutant ears reveals the development of a rudimentary organ of Corti containing hair cells and the underlying supporting cells. Differentiated cells, however, fail to form the highly ordered structure characteristic for the organ of Corti but appear as rows or clusters with an excess number of hair cells. The Kölliker's organ, a transient structure neighboring the organ of Corti and a potential source of ectopic hair cells, is absent in the mutant ears. Collectively, our data suggest that N-myc regulates growth, morphogenesis, and pattern formation during the development of the inner ear.

A peptide inhibitor of c-Jun N-terminal kinase protects against both aminoglycoside and acoustic trauma-induced auditory hair cell death and hearing loss.

Hearing loss can be caused by a variety of insults, including acoustic trauma and exposure to ototoxins, that principally effect the viability of sensory hair cells via the MAP kinase (MAPK) cell death signaling pathway that incorporates c-Jun N-terminal kinase (JNK). We evaluated the otoprotective efficacy of D-JNKI-1, a cell permeable peptide that blocks the MAPK-JNK signal pathway. The experimental studies included organ cultures of neonatal mouse cochlea exposed to an ototoxic drug and cochleae of adult guinea pigs that were exposed to either an ototoxic drug or acoustic trauma. Results obtained from the organ of Corti explants demonstrated that the MAPK-JNK signal pathway is associated with injury and that blocking of this signal pathway prevented apoptosis in areas of aminoglycoside damage. Treatment of the neomycin-exposed organ of Corti explants with D-JNKI-1 completely prevented hair cell death initiated by this ototoxin. Results from in vivo studies showed that direct application of D-JNKI-1 into the scala tympani of the guinea pig cochlea prevented nearly all hair cell death and permanent hearing loss induced by neomycin ototoxicity. Local delivery of D-JNKI-1 also prevented acoustic trauma-induced permanent hearing loss in a dose-dependent manner. These results indicate that the MAPK-JNK signal pathway is involved in both ototoxicity and acoustic trauma-induced hair cell loss and permanent hearing loss. Blocking this signal pathway with D-JNKI-1 is of potential therapeutic value for long-term protection of both the morphological integrity and physiological function of the organ of Corti during times of oxidative stress.

Should Koos I Vestibular Schwannomas Be Treated Early with Gamma Knife Surgery? A Prospective Series of 42 Consecutive Cases

Background: Gamma Knife surgery (GKS) for vestibular schwannomas (VS) has a long-term clinical and scientific track record. After a period of de-escalation of dose prescription, results show a high rate of tumor control with improvement of clinical outcome (less than 1% facial palsy, 50-70% hearing preservation). Currently, there is controversial data about the active early treatment of intracanalicular (Koos I) VS. Methods: We prospectively analyzed 208 VS, focusing on 42 Koos I patients treated with GKS as first intention in Lausanne University Hospital, between July 2010 and February 2015. We concentrated on patient, tumor, and dosimetric characteristics. Special attention was given on the dose to the cochlea and its impact in maintaining serviceable hearing. Results: The mean follow-up period was 1.7 years (range 0.6-4.2). Twenty-six (61.9%) were females and 16 (38.1%) males. Preoperative serviceable hearing was present in 33 (78.57%) patients. The mean maximal diameter was 7.7 (5-10). The median target volume at the moment of GKS was 90 mm3 (range 17-317). The median prescription isodose volume was 118 mm3 (range 37-603). The median marginal dose administrated was 12 Gy (range 11-12). The median number of shots was 2 (range 1-9). The median isodose prescription was 50% (range 45-80%). The median maximal dose received by the cochlea in patients in GR class 1 and 2 was 4.2 Gy (mean 4.4 Gy, range 1.8-7.6). Our preliminary results showed 98% tumor control, with 30% shrinkage on MRI. The actuarial probability of keeping the same audition class for those with functional hearing at GKS was 80% at 3 years; the probability of keeping a functional hearing was more than 90%. A paraclinical evolution (on MRI and/or audiometry) at the time diagnosis, before GKS, was associated with a less good prognosis (p < 0.05). Conclusions: Our preliminary data suggest that Koos I patients should be treated early with GKS, before tumor growth, and/or hearing deterioration, as they have the highest probability of hearing preservation. The results in terms of functional outcome seemed comparable to, or even better than, the other Koos classes (i.e., larger lesions).

Transplantation and survival of mouse inner ear progenitor/stem cells in the organ of Corti after cochleostomy of hearing-impaired guinea pigs: preliminary results

In mammals, damage to sensory receptor cells (hair cells) of the inner ear results in permanent sensorineural hearing loss. Here, we investigated whether postnatal mouse inner ear progenitor/stem cells (mIESCs) are viable after transplantation into the basal turns of neomycin-injured guinea pig cochleas. We also examined the effects of mIESC transplantation on auditory functions. Eight adult female Cavia porcellus guinea pigs (250-350g) were deafened by intratympanic neomycin delivery. After 7 days, the animals were randomly divided in two groups. The study group (n=4) received transplantation of LacZ-positive mIESCs in culture medium into the scala tympani. The control group (n=4) received culture medium only. At 2 weeks after transplantation, functional analyses were performed by auditory brainstem response measurement, and the animals were sacrificed. The presence of mIESCs was evaluated by immunohistochemistry of sections of the cochlea from the study group. Non-parametric tests were used for statistical analysis of the data. Intratympanic neomycin delivery damaged hair cells and increased auditory thresholds prior to cell transplantation. There were no significant differences between auditory brainstem thresholds before and after transplantation in individual guinea pigs. Some mIESCs were observed in all scalae of the basal turns of the injured cochleas, and a proportion of these cells expressed the hair cell marker myosin VIIa. Some transplanted mIESCs engrafted in the cochlear basilar membrane. Our study demonstrates that transplanted cells survived and engrafted in the organ of Corti after cochleostomy.

Immunohistochemistry of synergistic effects of kanamycin and furosemide in the murine model

Adult CBA/CaJ mice were injected with large single dose of both kanamycin and furosemide in order to study hair cell lesion and macrophage recruitment within the cochlea.

A study of cochlear potentials

This paper is a review of the electrophysiology of the cochlea and the auditory nerve--the behavior of the acting potential, the cochlear microphonics and the summating potential under identical conditions.

The effects of noise exposure on nitric oxide synthase knockout mice

This paper studies the role of nitric oxide (NOS 1, NOS 2, and NOS 3 genes) in the mouse cochlea and in noise-induced hearing loss (NIHL). Mice genetically deficient of the NOS 2 and NOS 3 genes were protected from NIHL, indicating that one or both of these genes may be responsible for producing nitric oxide that damages the inner ear when exposed to harmful levels of noise.

Histological and functional aspects of Alpha-synuclein in neurodegeneration

Alpha-synuclein has been implicated in the cellular mechanisms that control auditory sensitivity. In other systems it can also confer protection against cellular injury. Auditory brainstem response thresholds and immunohistochemistry were used to assess the ability of alpha-synuclein to protect against oxidative damage to the cochlea.

Acoustic and psychoacoustic analysis of the noise produced by the police force firearms

Police officers are exposed to impact noise coming from firearms, which may cause irreversible injuries to the hearing system.Aim: To evaluate the noise exposure in shooting stands during gunfire exercises, to analyze the acoustic impact of the noise produced by the firearms and to associate it with tonal audiometry results.Study design: Cross-sectional.Materials and methods: To measure noise intensity we used a digital sound level meter, and the acoustic analysis was carried out by means of the oscillations and cochlear response curves provided by the Praat software. 30 police officers were selected (27 males and 3 females).Results: The peak level measured was 113.1 dB(C) from a .40 pistol and 116.8 dB(C) for a .38 revolver. The values obtained for oscillation and Praat was 17.9 +/- 0.3 Barks, corresponding to the rate of 4,120 and 4,580 Hz. Audiometry indicated greater hearing loss at 4,000Hz in 86.7% of the cases.Conclusion: With the acoustic analysis it was possible to show cause and effect between the main areas of energy excitation of the cochlea (Praat cochlear response curve) and the frequencies of low hearing acuity.

Age impact on the eferent system actitivies in cochlear mechanical properties in normal hearing individuals

O trato olivococlear medial realiza o controle eferente das células ciliadas externas, regulando as contrações lentas e atenuando as rápidas. Com a pesquisa da amplitude das emissões otoacústicas sem e com estimulação acústica contra, ipsi ou bilateralmente, é possível estimar as condições desse trato, uma vez que o efeito resultante de redução/supressão das emissões indica seu funcionamento. O envelhecimento implica em diminuição da atividade do sistema auditivo central, em função da degeneração das estruturas envolvidas nas habilidades auditivas. OBJETIVO: O objetivo foi investigar o efeito da idade na atividade do trato sobre a cóclea, com a análise da amplitude das emissões com estimulação acústica contralateral. MATERIAL E MÉTODO: A casuística foi composta por 75 indivíduos agrupados conforme a idade. A metodologia foi o modo convencional, com clique linear e o ruído branco. ESTUDO DE CASO: A análise considerou a resposta das orelhas e a comparação entre os grupos. RESULTADOS: Os resultados revelam diferenças estatisticamente significantes entre o response das emissões sem e com estimulação acústica contralateral, nos indivíduos (20 a 39 anos). O efeito redução/supressão das emissões diminui com a idade (quarta década). CONCLUSÃO: O envelhecimento prejudica a efetividade da atividade do trato.

Identificação de zonas mortas da cóclea por meio do teste TEN

O audiograma ou o relato do paciente não é suficiente para determinar a presença ou não de zonas mortas na cóclea (ZMC), nem identificar sua extensão. OBJETIVO: Investigar, utilizando o teste TEN, ZMC de indivíduos com perda auditiva neurossensorial (PANS). CEDALVI/ HRAC-USP-Bauru, de agosto de 2003 a fevereiro de 2004. TIPO DE ESTUDO: Estudo de coorte contemporânea com corte transversal. Casuística e Métodos: O TEN foi aplicado nos grupos G1 (5 mulheres com limiares tonais aéreos dentro do padrão de normalidade); G2 (4 mulheres e 5 homens com PANS moderada plana); G3 (19 mulheres e 24 homens com PANS com o grau variando entre leve a profundo). RESULTADOS: Para G1, o valor de TEN para eliminar o tom de teste foi, em média, próximo ao limiar absoluto para todas as freqüências. Não foi observada ZMC em nenhuma das orelhas testadas do G2. Para as 76 orelhas do G3, 6 não apresentaram indício de ZM. CONCLUSÕES: O TEN é efetivo para indicar ZMC em indivíduos com PANS descendente. Há evidência de diferença na detecção do tom puro na presença de ruído entre indivíduos com PANS em altas freqüências e com PANS plana, pois se observou diferença significativa entre o limiar mascarado e absoluto apenas para PANS descendentes e não para as planas.

Operant measurement of auditory threshold in prelingually deaf users of cochlear implants: II

Two experiments evaluated an operant procedure for establishing stimulus control using auditory and electrical stimuli as a baseline for measuring the electrical current threshold of electrodes implanted in the cochlea. Twenty-one prelingually deaf children, users of cochlear implants, learned a Go/No Go auditory discrimination task (i.e., pressing a button in the presence of the stimulus but not in its absence). When the simple discrimination baseline became stable, the electrical current was manipulated in descending and ascending series according to an adapted staircase method. Thresholds were determined for three electrodes, one in each location in the cochlea (basal, medial, and apical). Stimulus control was maintained within a certain range of decreasing electrical current but was eventually disrupted. Increasing the current recovered stimulus control, thus allowing the determination of a range of electrical currents that could be defined as the threshold. The present study demonstrated the feasibility of the operant procedure combined with a psychophysical method for threshold assessment, thus contributing to the routine fitting and maintenance of cochlear implants within the limitations of a hospital setting.

Potenciais evocados auditivos de tronco encefálico e emissões otoacústicas evocadas transientes: achados em pacientes com doença renal crônica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)