From Bench to Booth: Examining Hair-Cell Regeneration Through an Audiologist's Scope.

Damage to auditory hair cells is a key feature of sensorineural hearing loss due to aging, noise exposure, or ototoxic drugs. Though hair-cell loss is permanent in humans, research in bird species led to the discovery that analogous hair cells of the avian basilar papilla are able to regenerate after being damaged by ototoxic agents. Regeneration appears to occur through a combination of the mitotic expansion of a precursor population of supporting cells and direct transdifferentiation of supporting cells into functioning hair cells. This review will synthesize the relevant anatomy and pathophysiology of sensorineural hearing loss, the historical observations that led to the genesis of the hair-cell regeneration field, and perspectives on initial human hair-cell regeneration trials.

Hearing Vital Signs: Mobile Audiometry in the Emergency Department for Evaluation of Sudden Hearing Loss.

Emergency departments (EDs) are a common location for patients to present with sudden hearing loss (SHL). Unfortunately, high-quality, rapid quantitative measurement of hearing loss is challenging. Herein, we aim to evaluate the accuracy of tablet-based audiometry in patients complaining of SHL. Prospective tablet-based testing was completed in the ED in patients complaining of SHL. Air conduction thresholds (ACTs) obtained via tablet-based audiometry were compared to same-day measurements with a clinical-grade audiometer. Hearing loss (HL) was defined as >20 dB ACT for any frequency. In participant-level analysis, 30+ dB HL in 3 consecutive frequencies was used to define SHL. In the ED, mobile audiogram ACTs were within 5 dB (77%) and 10 dB (89.6%) of those determined by conventional audiometry. The sensitivity and specificity for mobile audiometry to detect 3 or more consecutive thresholds with 30+ dB HL were 100% and 62.5%, respectively. Findings have implications for increasing access to high-quality audiometry.

Data-driven segmentation of audiometric phenotypes across a large clinical cohort.

Pure tone audiograms are used to assess the degree and underlying source of hearing loss. Audiograms are typically categorized into a few canonical types, each thought to reflect distinct pathologies of the ear. Here, we analyzed 116,400 patient records from our clinic collected over a 24-year period and found that standard categorization left 46% of patient records unclassified. To better account for the full spectrum of hearing loss profiles, we used a Gaussian Mixture Model (GMM) to segment audiograms without any assumptions about frequency relationships, interaural symmetry or etiology. The GMM converged on ten types, featuring varying degrees of high-frequency hearing loss, flat loss, mixed loss, and notched profiles, with predictable relationships to patient age and sex. A separate GMM clustering of 15,380 audiograms from the National Health and Nutrition Examination Survey (NHANES) identified six similar types, that only lacked the more extreme hearing loss configurations observed in our patient cohort. Whereas traditional approaches distill hearing loss configurations down to a few canonical types by disregarding much of the underlying variability, an objective probabilistic model that accounted for all of the data identified an organized, but more heterogenous set of audiogram types that was consistent across two large clinical databases.

Audiometric Predictors of Bothersome Tinnitus in a Large Clinical Cohort of Adults With Sensorineural Hearing Loss.

OBJECTIVE: To identify demographic and audiometric predictors of bothersome tinnitus within a large clinical cohort. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary care hospital. PATIENTS: 51,989 English-speaking patients between 18 and 80 years of age that received initial audiometric evaluations at the Massachusetts Eye and Ear Infirmary between the years 2000 and 2016. MAIN OUTCOME MEASURES: Patients were categorized according to whether or not tinnitus was the primary reason for their visit. The likelihood of tinnitus as a primary complaint (TPC) was evaluated as a function of age, sex, and audiometric configuration. Patient-reported tinnitus percepts were qualitatively assessed in relation to audiometric configuration. RESULTS: Approximately 20% of adults who presented for an initial hearing evaluation reported TPC. The prevalence of TPC increased with advancing age until approximately 50 to 54 years, and then declined thereafter. In general, men were significantly more likely to report TPC than women. TPC was statistically associated with specific audiogram configurations. In particular, TPC was most prevalent for notched and steeply sloping hearing losses, but was relatively uncommon in adults with flat losses. Patients with frequency-restricted threshold shifts often reported tonal tinnitus percepts, while patients with asymmetric configurations tended to report broadband percepts. CONCLUSIONS: The probability of seeking audiological evaluation for bothersome tinnitus is highest for males, middle-aged patients, and those with notched or high-frequency hearing losses. These findings support the theory that tinnitus arises from sharp discontinuities in peripheral afferent innervation and cochlear amplification, which may induce topographically restricted changes in the central auditory pathway.

Gene therapy with apoptosis-associated speck-like protein, a newly described schwannoma tumor suppressor, inhibits schwannoma growth in vivo.

BACKGROUND: We evaluated apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) as a schwannoma tumor suppressor and explored its utilization in a schwannoma gene therapy strategy that may be translated to clinical use. METHODS: ASC protein expression and mRNA level were assessed in human schwannoma by immunohistochemistry and quantitative PCR, respectively. Methylation- specific PCR was used to assess ASC promoter methylation. The effect of ASC overexpression in schwannoma cells was evaluated through ATP-based viability, lactate dehydrogenase release, and apoptosis staining. Western blotting and colorimetric assay were used to test the effect of ASC overexpression on endogenous pro-apoptotic pathways. Bioluminescence imaging, behavioral testing, and immunohistochemistry in human xenograft and murine allograft schwannoma models were used to examine the efficacy and toxicity of intratumoral injection of adeno-associated virus (AAV) vector encoding ASC. RESULTS: ASC expression was suppressed via promoter methylation in over 80% of the human schwannomas tested. ASC overexpression in schwannoma cells results in cell death and is associated with activation of endogenous caspase-9, caspase-3, and upregulation of BH3 interacting-domain death agonist. In a human xenograft schwannoma model, AAV1-mediated ASC delivery reduced tumor growth and resolved tumor-associated pain without detectable toxicity, and tumor control was associated with reduced Ki67 mitotic index and increased tumor-cell apoptosis. Efficacy of this schwannoma gene therapy strategy was confirmed in a murine schwannoma model. CONCLUSION: We have identified ASC as a putative schwannoma tumor suppressor with high potential clinical utility for schwannoma gene therapy and generated a vector that treats schwannomas via a novel mechanism that does not overlap with current treatments.

Intracochlear Perfusion of Tumor Necrosis Factor-Alpha Induces Sensorineural Hearing Loss and Synaptic Degeneration in Guinea Pigs.

Tumor necrosis factor-alpha (TNF-α) is a proinflammatory cytokine that plays a prominent role in the nervous system, mediating a range of physiologic and pathologic functions. In the auditory system, elevated levels of TNF-α have been implicated in several types of sensorineural hearing loss, including sensorineural hearing loss induced by vestibular schwannoma, a potentially fatal intracranial tumor that originates from the eighth cranial nerve; however, the mechanisms underlying the tumor's deleterious effects on hearing are not well-understood. Here, we investigated the effect of acute elevations of TNF-α in the inner ear on cochlear function and morphology by perfusing the cochlea with TNF-α in vivo in guinea pigs. TNF-α perfusion did not significantly change thresholds for compound action potential (CAP) responses, which reflect cochlear nerve activity, or distortion product otoacoustic emissions, which reflect outer hair cell integrity. However, intracochlear TNF-α perfusion reduced CAP amplitudes and increased the number of inner hair cell synapses without paired post-synaptic terminals, suggesting a pattern of synaptic degeneration that resembles that observed in primary cochlear neuropathy. Additionally, etanercept, a TNF-α blocker, protected against TNF-α-induced synaptopathy when administered systemically prior to intracochlear TNF-α perfusion. Findings motivate further investigation into the harmful effects of chronically elevated intracochlear levels of TNF-α, and the potential for etanercept to counter these effects.

Publisher Correction: Computational repositioning and preclinical validation of mifepristone for human vestibular schwannoma.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Bone morphogenetic protein 4 antagonizes hair cell regeneration in the avian auditory epithelium.

Permanent hearing loss is often a result of damage to cochlear hair cells, which mammals are unable to regenerate. Non-mammalian vertebrates such as birds replace damaged hair cells and restore hearing function, but mechanisms controlling regeneration are not understood. The secreted protein bone morphogenetic protein 4 (BMP4) regulates inner ear morphogenesis and hair cell development. To investigate mechanisms controlling hair cell regeneration in birds, we examined expression and function of BMP4 in the auditory epithelia (basilar papillae) of chickens of either sex after hair cell destruction by ototoxic antibiotics. In mature basilar papillae, BMP4 mRNA is highly expressed in hair cells, but not in hair cell progenitors (supporting cells). Supporting cells transcribe genes encoding receptors for BMP4 (BMPR1A, BMPR1B, and BMPR2) and effectors of BMP4 signaling (ID transcription factors). Following hair cell destruction, BMP4 transcripts are lost from the sensory epithelium. Using organotypic cultures, we demonstrate that treatments with BMP4 during hair cell destruction prevent supporting cells from upregulating expression of the pro-hair cell transcription factor ATOH1, entering the cell cycle, and fully transdifferentiating into hair cells, but they do not induce cell death. By contrast, noggin, a BMP4 inhibitor, increases numbers of regenerated hair cells. These findings demonstrate that BMP4 antagonizes hair cell regeneration in the chicken basilar papilla, at least in part by preventing accumulation of ATOH1 in hair cell precursors.

Computational repositioning and preclinical validation of mifepristone for human vestibular schwannoma.

The computational repositioning of existing drugs represents an appealing avenue for identifying effective compounds to treat diseases with no FDA-approved pharmacotherapies. Here we present the largest meta-analysis to date of differential gene expression in human vestibular schwannoma (VS), a debilitating intracranial tumor, and use these data to inform the first application of algorithm-based drug repositioning for this tumor class. We apply an open-source computational drug repositioning platform to gene expression data from 80 patient tumors and identify eight promising FDA-approved drugs with potential for repurposing in VS. Of these eight, mifepristone, a progesterone and glucocorticoid receptor antagonist, consistently and adversely affects the morphology, metabolic activity, and proliferation of primary human VS cells and HEI-193 human schwannoma cells. Mifepristone treatment reduces VS cell viability more significantly than cells derived from patient meningiomas, while healthy human Schwann cells remain unaffected. Our data recommend a Phase II clinical trial of mifepristone in VS.

Enlarged Vestibular Aqueduct and Cochlear Implants: The Effect of Early Counseling on the Length of Time Between Candidacy and Implantation.

OBJECTIVE: To determine if discussing cochlear implantation (CI) with patients with enlarged vestibular aqueducts (EVA) and their families before reaching audiological criteria for CI candidacy effects the length of time between reaching audiological candidacy and CI surgery, and to describe the universal newborn hearing screening (UNHS) results and communication modality in this sample. PATIENTS: Forty-two patients (25 females) with confirmed EVA and cochlear implants. INTERVENTION(S): Diagnostic CI visit. MAIN OUTCOME MEASURES: The primary outcome measure is the difference in length of time between reaching audiological candidacy for CI and surgical implantation between those who had preliminary discussions regarding CI with their medical and healthcare providers before reaching audiological candidacy versus who had discussions after reaching candidacy. The secondary outcome measure is the result of the UNHS and primary mode of communication used by each patient. RESULTS: Discussing CI before reaching audiological candidacy was associated with a significantly shorter duration between reaching audiological candidacy and receiving CI (median = 3.1 mo; interquartile range [IQR] = 1.7-5.4) as compared with discussing CI after reaching candidacy (median = 5.8 mo; IQR = 3.2-11.2; p = 0.012). Participants born after the implementation of the UNHS, 16 of 24 patients referred on one or both ears. Communication modalities were evenly divided between utilizing sign-support English and oral/aural communicators only. CONCLUSIONS: Discussion of CI in patients with EVA before reaching audiological candidacy reduces the amount of time the child is without adequate auditory access and contributes to a constructive and interactive preparatory experience.

Atoh1 expression and function during auditory hair cell regeneration in post-hatch chickens.

Loss of hair cells in humans leads to irreversible hearing deficits, since auditory hair cells are not replaced. In contrast, hair cells are regenerated in the auditory epithelium of mature birds after damage by non-sensory supporting cells that transdifferentiate into hair cells by mitotic and/or non-mitotic mechanisms. Factors controlling these processes are poorly understood. The basic helix-loop-helix transcription factor ATOH1 is both necessary and sufficient for developmental hair cell differentiation, but it is unclear if it plays the same role in the mitotic and non-mitotic pathways in hair cell regeneration. We examined Atoh1 expression and function during hair cell regeneration in chickens. Atoh1 transcripts were increased in many supporting cells in the damaged auditory epithelium shortly after ototoxin administration and later became restricted to differentiating hair cells. Fate-mapping in vitro using an Atoh1 enhancer reporter demonstrated that only 56% of the supporting cells that spontaneously upregulate Atoh1 enhancer activity after damage acquired the hair cell fate. Inhibition of notch signaling using a gamma secretase antagonist stimulated an increase in Atoh1 reporter activity and induced a higher proportion of supporting cells with Atoh1 activity (73%) to differentiate as hair cells. Forced overexpression of Atoh1 in supporting cells triggered 66% of them to acquire the hair cell fate and nearly tripled their likelihood of cell cycle entry. These findings demonstrate that Atoh1 is broadly upregulated in supporting cells after damage, but a substantial proportion of supporting cells with Atoh1 activation fails to acquire hair cell features, in part due to gamma secretase-dependent activities.

Delayed plumage maturation increases overwinter survival in North Island robins.

Many bird species show delayed plumage maturation (DPM), retaining sub-adult plumage until after their first breeding season. Most explanations assume that DPM increases fitness over the breeding season. However, unless birds undergo a full moult before breeding, DPM could also be an adaptation to increase survival over the previous winter. The winter adaptation hypothesis has never been tested owing to the difficulty of measuring overwinter survival. We experimentally tested this hypothesis in North Island robins (Petroica longipes) using a closed island population where we could accurately estimate survival. The experiment involved dyeing 41 juveniles to mimic adult males, and comparing their survival with 41 control juveniles treated with the same peroxide base minus the pigment. The population was monitored with a series of resighting surveys, and mark-recapture analysis used to estimate overwinter survival. Survival probability was estimated to be 10% for dyed birds versus 61% for control birds in 2001, and 29% for dyed birds versus 40% for control birds in the winter of 2002, supporting the winter adaptation hypothesis for DPM. Access to suitable habitat is the key factor limiting juvenile survival in this population, and the locations where dyed juveniles were sighted suggest that they were often excluded from suitable areas.