Cataloging Existing Hearing Loss Cohort Data to Guide the Development of Precision Medicine for Sensorineural Hearing Loss: A Systematic Review of Hearing Repositories.

Recent breakthroughs in our understanding of sensorineural hearing loss etiology have encouraged the identification of novel hearing therapeutics, paving the way for precision hearing medicine. Critical to this field is the curation of health resources on hearing data. A systematic review of the literature was conducted to map existing (inter)national and regional datasets that include hearing data to inform the development of future hearing repositories. Systematic literature review was performed adhering to Preferred Reporting Items for Systematic Review and MetaAnalysis recommendations. Databases, including those from gray literature, were searched to identify publications reporting on phenotypic and/ or genotypic hearing data in May 2019. The databases reviewed were Medline, PubMed, Embase databases, and Google Scholar. Publications on local datasets were excluded. All hearing datasets identified in the screening process were noted. For each dataset, geography, context, objective, period of time run, numbers and demographics of participants, genomic data, hearing measures and instruments used were extracted and cataloged. One hundred and eighty-eight datasets were identified, containing hearing data on populations ranging from 100 to 1.39 million individuals, and all extracted data have been cataloged. This searchable resource has been made accessible online. This unique catalog provides an overview of existing datasets that contain valuable information on hearing. This can be used to inform the development of national and international patient data repositories for hearing loss and guide strategic collaboration between key stakeholder groups, pivotal to the delivery and development of sensorineural hearing loss precision diagnostics and treatments.

French Version of the Antiphasic Digits-in-Noise Test for Smartphone Hearing Screening.

In France 58% of persons with hearing loss still do not wear hearing aids. Pure-tone audiometry is the traditional gold standard in assessment and screening of hearing impairment, but it requires the use of calibrated devices and soundproof booth. The antiphasic digits-in-noise (DIN) test does not require calibrated material and can run on a standard headset or earbuds connected to a smartphone or a computer. The DIN test is highly correlated with pure tone audiometry and has already shown to be effective in hearing loss screening in its English version promoted by the WHO. The aim of the present study was to develop and validate a French version of the antiphasic DIN test for implementation on a national screening test offered as a smartphone app. The audio files recorded from a French native female speaker were selected and normalized in intensity according to their recognition probability. The French DIN test application was then tested on normal hearing- and hearing-impaired subjects. Based on the strong correlation between pure tone audiometry (PTA) and DIN SRT, we calculated ROC curves and Z-score. For PTA > 20 dB HL, a SNR cutoff of 12.9 dB corresponds to a sensitivity and specificity of 0.96 and 0.93, respectively. To detect moderate and more severe hearing loss (PTA > 40 dB HL), the SNR cutoff was -10.9 dB, corresponding to a sensitivity and specificity of 0.99 and 0.83, respectively. The Z-score was calculated to define statistical criteria of normality for speech-in-noise evaluation. While a score of 0 roughly corresponds to the normality (DIN SRT = -15.4 dB SNR), a subject with DIN SRT > -12.2 (Z-score > 2) is ranked in the hearing loss population. Next, the French antiphasic DIN test was implemented in the Höra iOS and Android apps. In total, 19,545 Höra tests were completed and analyzed. Three quarters of them were classified as normal (74 %) and one quarter presented mild (9%) or more severe loss (17%). Together, results argue for the use of the French version of antiphasic DIN test in the general population to improve the screening of hearing-impaired individuals.

Delivering Therapeutics to the Cochlea: The Importance of the Patient's Perspective.

Hearing loss represents a major sensory impairment in humans with a strong impact on quality of life. The current standard of care for chronic sensorineural hearing loss is limited to hearing aids and implantable devices like cochlear implants. Treatments for acute hearing loss consist of systemic or intratympanic corticosteroids. Emerging therapies are being developed to prevent hearing loss or to restore it at the cellular level. Many challenges and questions remain as to the delivery of these therapeutics into the inner ear. Scientists, clinicians, and industry stakeholders should always consider the treatment burden from the patient's perspective when designing new drug delivery approaches. This article highlights key issues to consider.

Critical role of the isoform-specific region in alpha1-Na,K-ATPase trafficking and protein Kinase C-dependent regulation.

The isoform-specific region (ISR) is a region of structural heterogeneity among the four isoforms of the catalytic alpha-subunit of the Na,K-ATPase and an important structural determinant for isoform-specific functions. In the present study, we examined the role of a potential dileucine clathrin adaptor recognition motif [DE]XXXL[LI] embedded within the alpha1-ISR. To this end, a rat alpha1 construct where leucine 499 was replaced by a valine (as found in the alpha2 isoform sequence) was compared to wild-type rat alpha1 after stable expression in opossum kidney cells. Total Na,K-ATPase expression, activity, or in situ (86)Rb(+) transport was not affected by the L499V mutation. However, surface Na,K-ATPase expression was nearly doubled. This increase was associated with a reduced rate of internalization from the cell surface of about 50% after a 4 h chase and became undetectable if clathrin-coated pit-mediated trafficking was blocked with chlorpromazine. Further, PKC-induced stimulation of Na,K-ATPase-mediated (86)Rb(+) uptake was doubled in mutant-expressing cells, comparable to the chimera containing the intact alpha2-ISR. Similar results were observed when the potential motif was disrupted by means of an E495S mutation. These findings suggest that a dileucine motif embedded within the Na,K-ATPase alpha1-ISR plays a critical role in the surface expression of Na,K-ATPase alpha1 polypeptides at steady state and in the response to PKC activation.

Regions conferring isoform-specific function in the catalytic subunit of the Na,K-pump.

The Na,K-pump (i.e., Na,K-ATPase) is critical for maintaining the ionic gradients across the plasma membranes of animal cells. Its component subunits are expressed in multiple forms, but the physiological relevance of this subunit diversity remains unknown. The primary contributor to overall catalysis, the alpha subunit, exists in four isoforms. There are observed kinetic differences among these isoforms, but their subtlety makes them an unlikely basis for physiological significance. Instead, recent work suggests that the major functional distinction among the isoforms is their interaction with regulatory proteins. Moreover, the isoform-specific effects of modulatory agents such as protein kinase C seem to originate within two regions of structural divergence: the amino terminus and eleven residues near the center of the alpha subunit, the isoform-specific region.

Increased endothelin activity mediates augmented distal nephron acidification induced by dietary protein.

We tested the hypothesis that increased dietary protein augments distal nephron acidification through an endothelin-dependent mechanism. Munich-Wistar rats ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard chow. HiPro vs. CON had higher distal nephron H+ secretion (41.3 +/- 4.0 vs. 23.0 +/- 2.1 pmol/mm.min, p < 0.002) mediated by augmented Na+/H+ exchange and H(+)-ATPase activity. Renal cortex of HiPro vs. CON had higher ET-1 addition to microdialysate and higher ET-1 mRNA, consistent with increased renal ET-1 production. Bosentan, an endothelin A/B receptor antagonist, decreased HiPro distal nephron H+ secretion (28.4 +/- 2.4 vs. 41.3 +/- 4.0 pmol/mm.min, p < 0.016) through decreased Na+/H+ exchange and decreased H(+)-ATPase activity. Increased dietary protein augments distal nephron acidification through an endothelin-sensitive increase in Na+/H+ exchange and H(+)-ATPase activity, supporting an endothelin role in the distal nephron response to this common challenge to acid-base status.

The isoform-specific region of the Na,K-ATPase catalytic subunit: role in enzyme kinetics and regulation by protein kinase C.

Comparisons of the primary structures of the Na,K-ATPase alpha-isoforms reveal the existence of regions of structural divergence, suggesting that they are involved in unique functions. One of these regions is the isoform-specific region (ISR), located near the ATP binding site in the major cytoplasmic loop. To evaluate its importance, we constructed mutants of the rodent wild-type alpha1 and alpha3 isoforms in which the ISR was replaced with irrelevant sequences, i.e., the analogous region from the rat gastric H,K-ATPase catalytic subunit or a region from the human c-myc oncogene. Opossum kidney (OK) cells were transfected with wild-type rat alpha1, alpha3, or their corresponding chimeras and selected in ouabain. Introduction of either mutant produced ouabain-resistant colonies, consistent with functional expression of the chimeric protein and indicating that the ISR is not essential for overall Na,K-ATPase function. The introduced chimeras were then characterized enzymatically by measuring the relative rate of K(+) and Li(+) deocclusions. Results showed that exchanges of both alpha1 and alpha3 ISRs significantly modified the sensitivity for the enzyme to either K(+) or Li(+). Subsequent treatment of the cells with phorbol esters revealed an altered Na,K-ATPase transport in response to protein kinase C activation for the alpha1 chimeras. No changes were observed for the alpha3 isoform, suggesting that it is not sensitive to PKC regulation. These results demonstrated that the ISR plays an important role in ion deocclusion and in the response to PKC (only for the alpha1 isoform).

Increased endothelin activity mediates augmented distal nephron acidification induced by dietary protein.

The hypothesis that increased dietary protein augments distal nephron acidification and does so through an endothelin (ET-1)-dependent mechanism was tested. Munich-Wistar rats that ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard diet, were compared. HiPro versus CON had higher distal nephron net HCO(3) reabsorption by in vivo microperfusion (37.8 +/- 3.2 versus 16.6 +/- 1.5 pmol/mm per min; P < 0.001) as a result of higher H(+) secretion (41.3 +/- 4.0 versus 23.0 +/- 2.1 pmol/mm per min; P < 0.002) and lower HCO(3) secretion (-3.5 +/- 0.4 versus -6.4 +/- 0.8 pmol/mm per min; P < 0.001). Perfusion with H(+) inhibitors support that increased H(+) secretion was mediated by augmented Na(+)/H(+) exchange and H(+)-ATPase activity without augmented H(+),K(+)-ATPase activity. HiPro versus CON had higher levels of urine ET-1 excretion, renal cortical ET-1 addition to microdialysate in vivo, and renal cortical ET-1 mRNA, consistent with increased renal ET-1 production. Oral bosentan, an ET A/B receptor antagonist, decreased distal nephron net HCO(3) reabsorption (22.4 +/- 1.9 versus 37.8 +/- 3.2 pmol/mm per min; P < 0.001) as a result of lower H(+) secretion (28.4 +/- 2.4 versus 41.3 +/- 4.0 pmol/mm per min; P < 0.016) and higher HCO(3) secretion (-6.0 +/- 0.7 versus -3.5 +/- 0.4 pmol/mm per min; P < 0.006). The H(+) inhibitors had no additional effect in HiPro ingesting bosentan, supporting that ET mediated the increased distal nephron Na(+)/H(+) exchange and H(+)-ATPase activity in HiPro. Increased dietary protein augments distal nephron acidification that is mediated through an ET-sensitive increase in Na(+)/H(+) exchange and H(+)-ATPase activity.

Remodeling of Na,K-ATPase, and membrane fluidity after atrial fibrillation in sheep.

UNLABELLED: Atrial fibrillation (AF) is accompanied by various changes in ion channels that cause atrial electrophysiological remodeling. The enzyme Na,K-ATPase is also a major cellular mechanism for the regulation of ion homeostasis. During AF, Na,K-ATPase may be regulated by synthesis of its alpha- and beta-subunits as well as changes in membrane fluidity. To test this hypothesis, we studied the effect of pacing-induced AF in sheep on atrial Na,K-ATPase alpha- and beta-subunits and on membrane fluidity as well. METHODS: A group of six sheep (AF group) was subjected to overdrive electrical stimulation of the right atrium in order to induce AF. A group of six sham operated sheep served as control. All paced sheep developed multiple episodes of sustained AF with a mean total duration of 110 min over a 2-hours period. Protein expression of Na,K-ATPase alpha- and beta-subunits in atrial microsomal membranes was assayed by Western blotting analysis. When significant changes in membrane expression were observed, transcriptional regulation was analysed by Northern blotting. Membrane fluidity was assessed on atrial microsomal fractions by anisotropy measurements using the fluorescent probe diphenylhexatriene. RESULTS: Atrial fibrillation enhanced the expression of the Na,K-ATPase beta1-subunit at both membrane and mRNA levels. Anisotropy values were higher in AF group than in control group, indicating a decreased fluidity of the membranes isolated from paced sheep atria. CONCLUSION: These data are the first evidence for an enhanced Na,K-ATPase beta1-subunit expression in membrane during AF. Membrane rigification represents a new factor of tachycardia-induced atrial remodeling.

Structure/function analysis of Na(+)-K(+)-ATPase central isoform-specific region: involvement in PKC regulation.

Specific functions served by the various Na(+)-K(+)-ATPase alpha-isoforms are likely to originate in regions of structural divergence within their primary structures. The isoforms are nearly identical, with the exception of the NH(2) terminus and a 10-residue region near the center of each molecule (isoform-specific region; ISR). Although the NH(2) terminus has been clearly identified as a source of isoform functional diversity, other regions seem to be involved. We investigated whether the central ISR could also contribute to isoform variability. We constructed chimeric molecules in which the central ISRs of rat alpha(1)- and alpha(2)-isoforms were exchanged. After stable transfection into opossum kidney cells, the chimeras were characterized for two properties known to differ dramatically among the isoforms: their K(+) deocclusion pattern and their response to PKC activation. Comparisons with rat full-length alpha(1)- and alpha(2)-isoforms expressed under the same conditions suggest an involvement of the central ISR in the response to PKC but not in K(+) deocclusion.

Ginkgo biloba extract (EGb 761) protects Na,K-ATPase isoenzymes during cerebral ischemia.

Disturbances of Na,K-ATPase activity are implicated in the pathophysiology of cerebral ischemia. Previous experiments have shown that EGb 761 protects NaK-ATPase activity against one hour of cerebral ischemia. In the brain however, the 3 isoenzymes responsible for Na,K-ATPase activity may be differentially affected by various times of ischemia. In the present study, we investigated the effect of a longer period of ischemia, and the protection provided by a pre-treatment with EGb 761 on each of the 3 cerebral NaK-ATPase isoenzymes. In control and EGb 761 pre-treated mice exposed to a 6 hr unilateral occlusion of the middle cerebral artery, Na,K-ATPase activity was decreased by 60% and lipid peroxidation was increased by 40% in the ipsilateral (ischemic) cortex compared to the contralateral one. In parallel, membrane integrity was altered. The alteration of NaK-ATPase activity, as a whole, resulted from a decrease in the activity of the 3 isoenzymes. The two isoenzymes of high ouabain affinity however, had their affinities decreased while the sensitivity of the lowest affinity isoenzyme was increased. Pre-treatment with EGb 761 abolished the differences observed between ipsi- and contralateral cortex, with the exception of the change in ouabain affinity of the low affinity isoenzyme. Ischemia also induced changes in Na,K-ATPase isoenzyme ouabain affinities in the contralateral cortex that where not prevented by EGb 761.