Indispensable Role of Ion Channels and Transporters in the Auditory System

Molecular specializations underlying phenotypic differences in inner ear hair cells of zebrafish and mice

Introduction

Hair cells (HCs) are the sensory receptors of the auditory and vestibular systems in the inner ears of vertebrates that selectively transduce mechanical stimuli into electrical activity. Although all HCs have the hallmark stereocilia bundle for mechanotransduction, HCs in non-mammals and mammals differ in their molecular specialization in the apical, basolateral, and synaptic membranes. HCs of non-mammals, such as zebrafish (zHCs), are electrically tuned to specific frequencies and possess an active process in the stereocilia bundle to amplify sound signals. Mammalian HCs, in contrast, are not electrically tuned and achieve amplification by somatic motility of outer HCs (OHCs).

Methods

To understand the genetic mechanisms underlying differences between adult zebrafish and mammalian HCs, we compared their RNA-seq-characterized transcriptomes, focusing on protein-coding orthologous genes related to HC specialization.

Results

There was considerable shared expression of gene orthologs among the HCs, including those genes associated with mechanotransduction, ion transport/channels, and synaptic signaling. However, there were some notable differences in expression among zHCs, OHCs, and inner HCs (IHCs), which likely underlie the distinctive physiological properties of each cell type. For example, OHCs highly express Slc26a5 which encodes the motor protein prestin that contributes to OHC electromotility. However, zHCs have only weak expression of slc26a5, and subsequently showed no voltage-dependent electromotility when measured. Notably, the zHCs expressed more paralogous genes including those associated with HC-specific functions and transcriptional activity, though it is unknown whether they have functions similar to their mammalian counterparts. There was overlap in the expressed genes associated with a known hearing phenotype.

Discussion

Our analyses unveil substantial differences in gene expression patterns that may explain phenotypic specialization of zebrafish and mouse HCs. This dataset also includes several protein-coding genes to further the functional characterization of HCs and study of HC evolution from non-mammals to mammals.

Bioinspired multi-scale interface design for wet gas sensing based on rational water management

Natural organisms have evolved multi-scale wet gas sensing interfaces with optimized mass transport pathways in biological fluid environments, which sheds light on developing artificial counterparts with improved wet gas sensing abilities and practical applications. Herein, we highlighted current advances in wet gas sensing taking advantage of optimized mass transport pathways endowed by multi-scale interface design. Common moisture resistance (e.g., employing moisture resistant sensing materials, post-modifying moisture resistant coatings, physical heating for moisture resistance, and self-removing hydroxyl groups) and moisture absorption (e.g., employing moisture absorption sensing materials and post-modifying moisture absorption coatings) strategies for wet gas sensing were discussed. Then, the design principles of bioinspired multi-scale wet gas sensing interfaces were provided, including macro-level condensation mediation, micro/nano-level transport pathway adjustment and molecular level moisture-proof design. Finally, perspectives on constructing bioinspired multi-scale wet gas sensing interfaces were presented, which will not only deepen our understanding of the underlying principles, but also promote practical applications.

Molecular Specializations Underlying Phenotypic Differences in Inner Ear Hair Cells of Zebrafish and Mice

Hair cells (HCs) are the sensory receptors of the auditory and vestibular systems in the inner ears of vertebrates that selectively transduce mechanical stimuli into electrical activity. Although all HCs have the hallmark stereocilia bundle for mechanotransduction, HCs in non-mammals and mammals differ in their molecular specialization in the apical, basolateral and synaptic membranes. HCs of non-mammals, such as zebrafish (zHCs), are electrically tuned to specific frequencies and possess an active process in the stereocilia bundle to amplify sound signals. Mammalian cochlear HCs, in contrast, are not electrically tuned and achieve amplification by somatic motility of outer HCs (OHCs). To understand the genetic mechanisms underlying differences among adult zebrafish and mammalian cochlear HCs, we compared their RNA-seq-characterized transcriptomes, focusing on protein-coding orthologous genes related to HC specialization. There was considerable shared expression of gene orthologs among the HCs, including those genes associated with mechanotransduction, ion transport/channels, and synaptic signaling. For example, both zebrafish and mouse HCs express Tmc1, Lhfpl5, Tmie, Cib2, Cacna1d, Cacnb2, Otof, Pclo and Slc17a8. However, there were some notable differences in expression among zHCs, OHCs, and inner HCs (IHCs), which likely underlie the distinctive physiological properties of each cell type. Tmc2 and Cib3 were not detected in adult mouse HCs but tmc2a and b and cib3 were highly expressed in zHCs. Mouse HCs express Kcna10, Kcnj13, Kcnj16, and Kcnq4, which were not detected in zHCs. Chrna9 and Chrna10 were expressed in mouse HCs. In contrast, chrna10 was not detected in zHCs. OHCs highly express Slc26a5 which encodes the motor protein prestin that contributes to OHC electromotility. However, zHCs have only weak expression of slc26a5, and subsequently showed no voltage dependent electromotility when measured. Notably, the zHCs expressed more paralogous genes including those associated with HC-specific functions and transcriptional activity, though it is unknown whether they have functions similar to their mammalian counterparts. There was overlap in the expressed genes associated with a known hearing phenotype. Our analyses unveil substantial differences in gene expression patterns that may explain phenotypic specialization of zebrafish and mouse HCs. This dataset also includes several protein-coding genes to further the functional characterization of HCs and study of HC evolution from non-mammals to mammals.

NcRNA: key and potential in hearing loss

Hearing loss has an extremely high prevalence worldwide and brings incredible economic and social burdens. Mechanisms such as epigenetics are profoundly involved in the initiation and progression of hearing loss and potentially yield definite strategies for hearing loss treatment. Non-coding genes occupy 97% of the human genome, and their transcripts, non-coding RNAs (ncRNAs), are widely participated in regulating various physiological and pathological situations. NcRNAs, mainly including micro-RNAs (miRNAs), long-stranded non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), are involved in the regulation of cell metabolism and cell death by modulating gene expression and protein-protein interactions, thus impacting the occurrence and prognosis of hearing loss. This review provides a detailed overview of ncRNAs, especially miRNAs and lncRNAs, in the pathogenesis of hearing loss. We also discuss the shortcomings and issues that need to be addressed in the study of hearing loss ncRNAs in the hope of providing viable therapeutic strategies for the precise treatment of hearing loss.

LINE-1 global DNA methylation, iron homeostasis genes, sex and age in sudden sensorineural hearing loss (SSNHL)

BACKGROUND

Sudden sensorineural hearing loss (SSNHL) is an abrupt loss of hearing, still idiopathic in most of cases. Several mechanisms have been proposed including genetic and epigenetic interrelationships also considering iron homeostasis genes, ferroptosis and cellular stressors such as iron excess and dysfunctional mitochondrial superoxide dismutase activity.

RESULTS

We investigated 206 SSNHL patients and 420 healthy controls for the following genetic variants in the iron pathway: SLC40A1 - 8CG (ferroportin; FPN1), HAMP - 582AG (hepcidin; HEPC), HFE C282Y and H63D (homeostatic iron regulator), TF P570S (transferrin) and SOD2 A16V in the mitochondrial superoxide dismutase-2 gene. Among patients, SLC40A1 - 8GG homozygotes were overrepresented (8.25% vs 2.62%; P = 0.0015) as well SOD2 16VV genotype (32.0% vs 24.3%; P = 0.037) accounting for increased SSNHL risk (OR = 3.34; 1.54-7.29 and OR = 1.47; 1.02-2.12, respectively). Moreover, LINE-1 methylation was inversely related (r2 = 0.042; P = 0.001) with hearing loss score assessed as pure tone average (PTA, dB HL), and the trend was maintained after SLC40A1 - 8CG and HAMP - 582AG genotype stratification (ΔSLC40A1 = + 8.99 dB HL and ΔHAMP = - 6.07 dB HL). In multivariate investigations, principal component analysis (PCA) yielded PC1 (PTA, age, LINE-1, HAMP, SLC40A1) and PC2 (sex, HFEC282Y, SOD2, HAMP) among the five generated PCs, and logistic regression analysis ascribed to PC1 an inverse association with moderate/severe/profound HL (OR = 0.60; 0.42-0.86; P = 0.0006) and with severe/profound HL (OR = 0.52; 0.35-0.76; P = 0.001).

CONCLUSION

Recognizing genetic and epigenetic biomarkers and their mutual interactions in SSNHL is of great value and can help pharmacy science to design by pharmacogenomic data classical or advanced molecules, such as epidrugs, to target new pathways for a better prognosis and treatment of SSNHL.

CMV-induced Hearing Loss

Congenital cytomegalovirus (cCMV) infection is the most common fetal viral infection and contributes to about 25% of childhood hearing loss by the age of 4 years. It is the leading nongenetic cause of sensorineural hearing loss (SNHL). Infants born to seroimmune mothers are not completely protected from SNHL, although the severity of their hearing loss may be milder than that seen in those whose mothers had a primary infection. Both direct cytopathic effects and localized inflammatory responses contribute to the pathogenesis of cytomegalovirus (CMV)-induced hearing loss. Hearing loss may be delayed onset, progressive or fluctuating in nature, and therefore, a significant proportion will be missed by universal newborn hearing screening (NHS) and warrants close monitoring of hearing function at least until 5-6 years of age. A multidisciplinary approach is required for the management of hearing loss. These children may need assistive hearing devices or cochlear implantation depending on the severity of their hearing loss. In addition, early intervention services such as speech or occupational therapy could help better communication, language, and social skill outcomes. Preventive measures to decrease intrauterine CMV transmission that have been evaluated include personal protective measures, passive immunoprophylaxis and valacyclovir treatment during pregnancy in mothers with primary CMV infection. Several vaccine candidates are currently in testing and one candidate vaccine in phase 3 trials. Until a CMV vaccine becomes available, behavioral and educational interventions may be the most effective strategy to prevent maternal CMV infection.

ZBTB20 is essential for cochlear maturation and hearing in mice

The mammalian cochlear epithelium undergoes substantial remodeling and maturation before the onset of hearing. However, very little is known about the transcriptional network governing cochlear late-stage maturation and particularly the differentiation of its lateral nonsensory region. Here, we establish ZBTB20 as an essential transcription factor required for cochlear terminal differentiation and maturation and hearing. ZBTB20 is abundantly expressed in the developing and mature cochlear nonsensory epithelial cells, with transient expression in immature hair cells and spiral ganglion neurons. Otocyst-specific deletion of Zbtb20 causes profound deafness with reduced endolymph potential in mice. The subtypes of cochlear epithelial cells are normally generated, but their postnatal development is arrested in the absence of ZBTB20, as manifested by an immature appearance of the organ of Corti, malformation of tectorial membrane (TM), a flattened spiral prominence (SP), and a lack of identifiable Boettcher cells. Furthermore, these defects are related with a failure in the terminal differentiation of the nonsensory epithelium covering the outer border Claudius cells, outer sulcus root cells, and SP epithelial cells. Transcriptome analysis shows that ZBTB20 regulates genes encoding for TM proteins in the greater epithelial ridge, and those preferentially expressed in root cells and SP epithelium. Our results point to ZBTB20 as an essential regulator for postnatal cochlear maturation and particularly for the terminal differentiation of cochlear lateral nonsensory domain.

Novel POU3F4 variants identified in patients with inner ear malformations exhibit aberrant cellular distribution and lack of SLC6A20 transcriptional upregulation

Hearing loss (HL) is the most common sensory defect and affects 450 million people worldwide in a disabling form. Pathogenic sequence alterations in the POU3F4 gene, which encodes a transcription factor, are causative of the most common type of X-linked deafness (X-linked deafness type 3, DFN3, DFNX2). POU3F4-related deafness is characterized by a typical inner ear malformation, namely an incomplete partition of the cochlea type 3 (IP3), with or without an enlargement of the vestibular aqueduct (EVA). The pathomechanism underlying POU3F4-related deafness and the corresponding transcriptional targets are largely uncharacterized. Two male patients belonging to a Caucasian cohort with HL and EVA who presented with an IP3 were submitted to genetic analysis. Two novel sequence variants in POU3F4 were identified by Sanger sequencing. In cell-based assays, the corresponding protein variants (p.S74Afs*8 and p.C327*) showed an aberrant expression and subcellular distribution and lack of transcriptional activity. These two protein variants failed to upregulate the transcript levels of the amino acid transporter gene SLC6A20, which was identified as a novel transcriptional target of POU3F4 by RNA sequencing and RT-qPCR. Accordingly, POU3F4 silencing by siRNA resulted in downregulation of SLC6A20 in mouse embryonic fibroblasts. Moreover, we showed for the first time that SLC6A20 is expressed in the mouse cochlea, and co-localized with POU3F4 in the spiral ligament. The findings presented here point to a novel role of amino acid transporters in the inner ear and pave the way for mechanistic studies of POU3F4-related HL.

Role of the Stria Vascularis in the Pathogenesis of Sensorineural Hearing Loss: A Narrative Review

Sensorineural hearing loss is a common sensory impairment in humans caused by abnormalities in the inner ear. The stria vascularis is regarded as a major cochlear structure that can independently degenerate and influence the degree of hearing loss. This review summarizes the current literature on the role of the stria vascularis in the pathogenesis of sensorineural hearing loss resulting from different etiologies, focusing on both molecular events and signaling pathways, and further attempts to explore the underlying mechanisms at the cellular and molecular biological levels. In addition, the deficiencies and limitations of this field are discussed. With the rapid progress in scientific technology, new opportunities are arising to fully understand the role of the stria vascularis in the pathogenesis of sensorineural hearing loss, which, in the future, will hopefully lead to the prevention, early diagnosis, and improved treatment of sensorineural hearing loss.

Congenital Human Cytomegalovirus Infection Inducing Sensorineural Hearing Loss

Human cytomegalovirus (HCMV) is the primary cause of congenital infections. Despite its clinical significance, congenital HCMV infection is frequently overlooked clinically since most affected infants are asymptomatic. Sensorineural hearing loss (SNHL) is one of the most widely known disorders caused by congenital HCMV infection. The potential mechanism, however, remains unknown to date. The mechanism by which congenital HCMV infection induces sensorineural deafness has been partly characterized, leading to advancements in diagnosis, therapy, and prevention strategies. HCMV-induced hearing loss primarily involves immune responses, the release of inflammatory factors by natural killer (NK) cells, apoptosis of cochlear spiral ganglion, and potential changes due to vascular dysfunction. The diagnosis of HCMV induced SNHL includes serological examination to mothers, imaging, and amniotic fluid examination. Ganciclovir, mainly used for antiviral therapy and behavioral prevention, can, to some degree, prevent congenital HCMV infection. The role of HCMV infection in hearing loss needs further investigation since the mechanism of hearing loss caused by cytomegalovirus infection is not well understood. Although some advancement has been made in diagnosing and treating SNHL, more improvement is needed. A comprehensive understanding of cytomegalovirus’s pathogenesis is of key importance for preventing, diagnosing, and treating SNHL.

Molecular simulation of the Kv7.4[ΔS269] mutant channel reveals that ion conduction in the cavity is perturbed due to hydrophobic gating

Mutations in the voltage-gated potassium channel Kv7.4 (encoded as KCNQ4) lead to the early onset of non-syndromic hearing loss, which is significant during language acquisition. The deletion of the S269 pore residue (genetic Δ mutation) in Kv7.4 has been reported to be associated with hearing loss. So far, there is no mechanistic understanding of how this mutation modulates channel function. To understand the role of S269 in ion conduction, we performed molecular dynamics simulations for both wild type and ΔS269 mutant channels. Simulations indicate that the ΔS269 mutation suppresses the fluctuations in the neighboring Y269 residue and thereby consolidates the ring formed by I307 and F310 residues in the adjacent S6 helixes in the cavity region. We show that the long side chains of I307 near the entrance to the cavity form a hydrophobic gate. Comparison of the free energy profiles of a cavity ion in Kv7.4 and Kv7.4[ΔS269] channels reveals a sizable energy barrier in the latter case, which suppresses ion conduction. Thus the simulation studies reveal that the hydrophobic gate resulting from the ΔS269 mutation appears to be responsible for sensorineural hearing loss.

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DeltaS269 mutation in the Kv7.4 channel is associated with hearing loss (SNHL).

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The mutation effects on channel function are studied via MD simulations.

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DeltaS269 mutation imposes a constriction at the cavity to suppress K⁺ conductance.

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Understanding the mutation effects on channel function will help to treat SNHL.

Recent advancements in understanding the role of epigenetics in the auditory system

Sensorineural deafness in mammals is most commonly caused by damage to inner ear sensory epithelia, or hair cells, and can be attributed to genetic and environmental causes. After undergoing trauma, many non-mammalian organisms, including reptiles, birds, and zebrafish, are capable of regenerating damaged hair cells. Mammals, however, are not capable of regenerating damaged inner ear sensory epithelia, so that hair cell damage is permanent and can lead to hearing loss. The field of epigenetics, which is the study of various phenotypic changes caused by modification of genetic expression rather than alteration of DNA sequence, has seen numerous developments in uncovering biological mechanisms of gene expression and creating various medical treatments. However, there is a lack of information on the precise contribution of epigenetic modifications in the auditory system, specifically regarding their correlation with development of inner ear (cochlea) and consequent hearing impairment. Current studies have suggested that epigenetic modifications influence differentiation, development, and protection of auditory hair cells in cochlea, and can lead to hair cell degeneration. The objective of this article is to review the existing literature and discuss the advancements made in understanding epigenetic modifications of inner ear sensory epithelial cells. The analysis of the emerging epigenetic mechanisms related to inner ear sensory epithelial cells development, differentiation, protection, and regeneration will pave the way to develop novel therapeutic strategies for hearing loss.

Transcript Profiles of Stria Vascularis in Models of Waardenburg Syndrome

Background

Waardenburg syndrome is an uncommon genetic condition characterized by at least some degree of congenital hearing loss and pigmentation deficiencies. However, the genetic pathway affecting the development of stria vascularis is not fully illustrated.

Methods

The transcript profile of stria vascularis of Waardenburg syndrome was studied using Mitf-M mutant pig and mice models. Therefore, GO analysis was performed to identify the differential gene expression caused by Mitf-M mutation.

Results

There were 113 genes in tyrosine metabolism, melanin formation, and ion transportations showed significant changes in pig models and 191 genes in mice models. In addition, there were some spice's specific gene changes in the stria vascularis in the mouse and porcine models. The expression of tight junction-associated genes, including Cadm1, Cldn11, Pcdh1, Pcdh19, and Cdh24 genes, were significantly higher in porcine models compared to mouse models. Vascular-related and ion channel-related genes in the stria vascularis were also shown significantly difference between the two species. The expression of Col2a1, Col3a1, Col11a1, and Col11a2 genes were higher, and the expression of Col8a2, Cd34, and Ncam genes were lower in the porcine models compared to mouse models.

Conclusions

Our data suggests that there is a significant difference on the gene expression and function between these two models.

In vitro and in silico characterization of the inhibition of Kir4.1 channels by aminoglycoside antibiotics

BACKGROUND AND PURPOSE

Aminoglycoside antibiotics are positively charged molecules that are known to inhibit several ion channels. In this study, we have shown that aminoglycosides also inhibit the activity of Kir4.1 channels. Aminoglycosides inhibit Kir4.1 channels by a pore-blocking mechanism, plugging the central vestibule of the channel.

EXPERIMENTAL APPROACH

Patch-clamp recordings were made in HEK-293 cells transiently expressing Kir4.1 channels to analyse the effects of gentamicin, neomycin and kanamycin. In silico modelling followed by mutagenesis were realized to identify the residues critical for aminoglycosides binding to Kir4.1.

KEY RESULTS

Aminoglycoside antibiotics block Kir4.1 channels in a concentration- and voltage-dependent manner, getting access to the protein from the intracellular side of the plasma membrane. Aminoglycosides block Ki4.1 with a rank order of potency as follows: gentamicin ˃ neomycin ˃ kanamycin. The residues T128 and principally E158, facing the central cavity of Kir4.1, are important structural determinants for aminoglycosides binding to the channel, as determined by our in silico modelling and confirmed by mutagenesis experiments.

CONCLUSION AND IMPLICATIONS

Kir4.1 channels are also target of aminoglycoside antibiotics, which could affect potassium transport in several tissues.

Membrane-anchored serine proteases as regulators of epithelial function

Cleavage of proteins in the extracellular milieu, including hormones, growth factors and their receptors, ion channels, and various cell adhesion and extracellular matrix molecules, plays a key role in the regulation of cell behavior. Among more than 500 proteolytic enzymes encoded by mammalian genomes, membrane-anchored serine proteases (MASPs), which are expressed on the surface of epithelial cells of all major organs, are excellently suited to mediate signal transduction across the epithelia and are increasingly being recognized as important regulators of epithelial development, function, and disease [ 1-3]. In this minireview, we summarize current knowledge of the in vivo roles of MASPs in acquisition and maintenance of some of the defining functions of epithelial tissues, such as barrier formation, ion transport, and sensory perception.

Single Cell and Single Nucleus RNA-Seq Reveal Cellular Heterogeneity and Homeostatic Regulatory Networks in Adult Mouse Stria Vascularis

The stria vascularis (SV) generates the endocochlear potential (EP) in the inner ear and is necessary for proper hair cell mechanotransduction and hearing. While channels belonging to SV cell types are known to play crucial roles in EP generation, relatively little is known about gene regulatory networks that underlie the ability of the SV to generate and maintain the EP. Using single cell and single nucleus RNA-sequencing, we identify and validate known and rare cell populations in the SV. Furthermore, we establish a basis for understanding molecular mechanisms underlying SV function by identifying potential gene regulatory networks as well as druggable gene targets. Finally, we associate known deafness genes with adult SV cell types. This work establishes a basis for dissecting the genetic mechanisms underlying the role of the SV in hearing and will serve as a basis for designing therapeutic approaches to hearing loss related to SV dysfunction.

Whole exome sequencing identified a second pathogenic variant in HOMER2 for autosomal dominant non-syndromic deafness

Hearing loss is one of the most common sensory disorders worldwide, and about half of all occurrences are attributable to genetic factors. Here, we have identified a novel pathogenic variant in HOMER2 in a Chinese family with autosomal dominant, non-syndromic hearing loss. This is the second family reported globally with hearing loss caused by a variant in HOMER2. The pathogenic variant c.840_841insC in HOMER2 (NM_199330), segregating with the hearing-loss phenotype in the family, leads to a premature stop codon producing a truncated protein. The coiled-coil domain in the C-terminal of HOMER2 protein is essential for protein multimerization and HOMER2-CDC42 interaction. We compared the phenotypes in the two families and found that hearing impairment in this Chinese family was more severe. Furthermore, we found that the ability of this insertion mutant type HOMER2 (HOMER2_MU ) to multimerize decreased more significantly than wild-type HOMER2 (HOMER2_WT ) and the reported c.554G>C (NM_004839) mutant HOMER2. HOMER2_MU protein tended to be distributed in a diffuse manner, whereas HOMER2_WT and the reported mutant HOMER2 tended to cluster together. Our research provides a validating second family for variants in HOMER2 causing non-syndromic sensorineural hearing loss. HOMER2 homo-/hetero-multimerization might be the first step in exerting its normal function.

Endolymphatic hydrops induced by different mechanisms responds differentially to spironolactone: a rationale for understanding the diversity of treatment responses in hydropic inner ear disease

Background: The exact pathophysiological mechanism(s) underlying endolymphatic hydrops (EH) remain elusive. We have previously shown that chronic administration of vasopressin and inhibitors of the cAMP/cGMP degrading enzymes (PDE3, PDE4, PDE5) results in the development of EH to mice. Aims/objectives: Evaluate the ability of spironolactone, an aldosterone antagonist, to prevent EH, when induced by different pathways. Material and methods: Mice were treated for 4 weeks with vasopressin, the PDE3 inhibitor cilostamide and the PDE4 inhibitor rolipram in the presence or absence of spironolactone. EH was assessed using high resolution 9.4T MRI. The expression of proteins in human saccule sensory epithelium was studied with immunohistochemistry. Results: Spironolactone prevents EH induced by vasopressin and rolipram, but not hydrops induced by cilostamide. The aldosterone target ENaC and the mineralocorticoid receptor were expressed in the human saccule sensory epithelium. Conclusions: The effect of spironolactone on EH appears to be pathway-dependent and may provide explanations why certain drugs may be effective in some patients with hydropic ear disease while not in others. Significance: Extrapolating this finding to the clinic supports that a personalized medicine approach is probably necessary in the treatment of diseases involving EH, as different pathways may be needed to be targeted for treatment.

Semicircular canal biomechanics in health and disease

The semicircular canals are responsible for sensing angular head motion in three-dimensional space and for providing neural inputs to the central nervous system (CNS) essential for agile mobility, stable vision, and autonomic control of the cardiovascular and other gravity-sensitive systems. Sensation relies on fluid mechanics within the labyrinth to selectively convert angular head acceleration into sensory hair bundle displacements in each of three inner ear sensory organs. Canal afferent neurons encode the direction and time course of head movements over a broad range of movement frequencies and amplitudes. Disorders altering canal mechanics result in pathological inputs to the CNS, often leading to debilitating symptoms. Vestibular disorders and conditions with mechanical substrates include benign paroxysmal positional nystagmus, direction-changing positional nystagmus, alcohol positional nystagmus, caloric nystagmus, Tullio phenomena, and others. Here, the mechanics of angular motion transduction and how it contributes to neural encoding by the semicircular canals is reviewed in both health and disease.

Pathophysiology of Subjective Tinnitus: Triggers and Maintenance

Tinnitus is the conscious perception of a sound without a corresponding external acoustic stimulus, usually described as a phantom perception. One of the major challenges for tinnitus research is to understand the pathophysiological mechanisms triggering and maintaining the symptoms, especially for subjective chronic tinnitus. Our objective was to synthesize the published literature in order to provide a comprehensive update on theoretical and experimental advances and to identify further research and clinical directions. We performed literature searches in three electronic databases, complemented by scanning reference lists from relevant reviews in our included records, citation searching of the included articles using Web of Science, and manual searching of the last 6 months of principal otology journals. One-hundred and thirty-two records were included in the review and the information related to peripheral and central mechanisms of tinnitus pathophysiology was collected in order to update on theories and models. A narrative synthesis examined the main themes arising from this information. Tinnitus pathophysiology is complex and multifactorial, involving the auditory and non-auditory systems. Recent theories assume the necessary involvement of extra-auditory brain regions for tinnitus to reach consciousness. Tinnitus engages multiple active dynamic and overlapping networks. We conclude that advancing knowledge concerning the origin and maintenance of specific tinnitus subtypes origin and maintenance mechanisms is of paramount importance for identifying adequate treatment.

Role of microRNAs in inner ear development and hearing loss

The etiology of hearing loss tends to be multi-factorial and affects a significant proportion of the global population. Despite the differences in etiology, a common physical pathological change that leads to hearing loss is damage to the mechanosensory hair cells of the inner ear. MicroRNAs (miRNAs) have been shown to play a role in inner ear development and thus, may play a role in the development or prevention of hearing loss. In this paper, we review the mechanism of action of miRNAs in the auditory system. We present an overview about the role of miRNAs in inner ear development, summarize the current research on the role of miRNAs in gene regulation, and discuss the effects of both miRNA mutations as well as overexpression. We discuss the crucial role of miRNAs in ensuring normal physiological development of the inner ear. Any deviation from the proper function of miRNA in the cochlea seems to contribute to deleterious damage to the structure of the auditory system and subsequently results in hearing loss. As interest for miRNA research increases, this paper serves as a platform to review current understandings and postulate future avenues for research. A better knowledge about the role of miRNA in the auditory system will help in developing novel treatment modalities for restoring hearing function based on regeneration of damaged inner ear hair cells.

Genetics of guanylyl cyclase pathways in the cochlea and their influence on hearing

Although hearing loss is the most common sensory deficit in Western societies, there are no successful pharmacological treatments for this disorder. Recent experiments have demonstrated that manipulation of intracellular cyclic guanosine monophosphate (cGMP) concentrations can have both beneficial and harmful effects on hearing. In this review, we will examine the role of cGMP as a key second messenger involved in many aspects of cochlear function and discuss the known functions of downstream effectors of cGMP in sound processing. The nitric oxide-stimulated soluble guanylyl cyclase system (sGC) and the two natriuretic peptide-stimulated particulate GCs (pGCs) will be more extensively covered because they have been studied most thoroughly. The cochlear GC systems are attractive targets for medical interventions that improve hearing while simultaneously representing an under investigated source of sensorineural hearing loss.

Genetic basis of hearing loss in Spanish, Hispanic and Latino populations

Hearing loss (HL) is the most common neurosensory disorder affecting humans. The screening, prevention and treatment of HL require a better understanding of the underlying molecular mechanisms. Genetic predisposition is one of the most common factors that leads to HL. Most HL studies include few Spanish, Hispanic and Latino participants, leaving a critical gap in our understanding about the prevalence, impact, unmet health care needs, and genetic factors associated with hearing impairment among Spanish, Hispanic and Latino populations. The few studies which have been performed show that the gene variants commonly associated with HL in non-Spanish and non-Hispanic populations are infrequently responsible for hearing impairment in Spanish as well as Hispanic and Latino populations (hereafter referred to as Hispanic). To design effective screening tools to detect HL in Spanish and Hispanic populations, studies must be conducted to determine the gene variants that are most commonly associated with hearing impairment in this racial/ethnic group. In this review article, we summarize gene variants and loci associated with HL in Spanish and Hispanic populations. Identifying new genetic variants associated with HL in Spanish and Hispanic populations will pave the way to develop effective screening tools and therapeutic strategies for HL.

Single-channel recordings of RyR1 at microsecond resolution in CMOS-suspended membranes

Single-channel recordings are widely used to explore functional properties of ion channels. Typically, such recordings are performed at bandwidths of less than 10 kHz because of signal-to-noise considerations, limiting the temporal resolution available for studying fast gating dynamics to greater than 100 µs. Here we present experimental methods that directly integrate suspended lipid bilayers with high-bandwidth, low-noise transimpedance amplifiers based on complementary metal-oxide-semiconductor (CMOS) integrated circuits (IC) technology to achieve bandwidths in excess of 500 kHz and microsecond temporal resolution. We use this CMOS-integrated bilayer system to study the type 1 ryanodine receptor (RyR1), a Ca²⁺-activated intracellular Ca²⁺-release channel located on the sarcoplasmic reticulum. We are able to distinguish multiple closed states not evident with lower bandwidth recordings, suggesting the presence of an additional Ca²⁺ binding site, distinct from the site responsible for activation. An extended beta distribution analysis of our high-bandwidth data can be used to infer closed state flicker events as fast as 35 ns. These events are in the range of single-file ion translocations.

Sound shock response in larval zebrafish: A convenient and high-throughput assessment of auditory function

Given that hearing ability can be challenged in diverse ways, it is necessary to develop an easily conducted, high-throughput method for assessing potential auditory risks. Measuring the acoustic startle response (ASR) has become a critical behavioral method in hearing research using zebrafish (Danio rerio). In this study, changes in the activity of zebrafish larvae (10 days post fertilization (dpf)) due to exposure to a sudden easily-generated broad-band noise were automatically and objectively recorded and analyzed without building sophisticated equipments. A significant increase in activity was induced by the noise stimulation and the alterations were impaired by gentamicin. In addition, a clear dose-response trend was observed between gentamicin exposure and the impaired activity, and a similar phenomenon was observed between gentamicin exposure and damage to hair cells. Our results suggested that alterations in the activity induced by a broad-band noise can potentially be used as an efficient assay for assessing hearing ability.

Recent advances in understanding the pathogenesis and management of reticular dysgenesis

Reticular Dysgenesis is a rare immunodeficiency which is clinically characterized by the combination of Severe Combined Immunodeficiency (SCID) with agranulocytosis and sensorineural deafness. Mutations in the gene encoding adenylate kinase 2 (AK2) were identified to cause this phenotype. In this review, we will demonstrate important clinical differences between reticular dysgenesis and other SCID entities and summarize recent concepts in the understanding of the pathophysiology of the disease and the management strategies for this difficult condition.

A perspective on stem cell therapy for ear disorders

The use of stem cells in cell-based therapy is an emerging concept for the treatment of ear disorders. Tympanic membrane perforation (TMP) and inner ear disorders are some of the most commonly presented otologic disorders that can benefit from advances in cell-based therapy. Studies have already demonstrated that stem cell-based therapy can potentially be an effective treatment modality for acute and chronic TMP. Recent studies have also shown promise in application of cell-based approach to treat inner ear dysfunction. In this perspective, we will discuss the recent advancements regarding the use of cell-based therapy for ear disorders.

Recent Advancements in the Regeneration of Auditory Hair Cells and Hearing Restoration

Neurosensory responses of hearing and balance are mediated by receptors in specialized neuroepithelial sensory cells. Any disruption of the biochemical and molecular pathways that facilitate these responses can result in severe deficits, including hearing loss and vestibular dysfunction. Hearing is affected by both environmental and genetic factors, with impairment of auditory function being the most common neurosensory disorder affecting 1 in 500 newborns, as well as having an impact on the majority of elderly population. Damage to auditory sensory cells is not reversible, and if sufficient damage and cell death have taken place, the resultant deficit may lead to permanent deafness. Cochlear implants are considered to be one of the most successful and consistent treatments for deaf patients, but only offer limited recovery at the expense of loss of residual hearing. Recently there has been an increased interest in the auditory research community to explore the regeneration of mammalian auditory hair cells and restoration of their function. In this review article, we examine a variety of recent therapies, including genetic, stem cell and molecular therapies as well as discussing progress being made in genome editing strategies as applied to the restoration of hearing function.

Progression of changes in the sensorial elements of the cochlear and peripheral vestibular systems: The otitis media continuum

Our study aimed to evaluate pathologic changes in the cochlear (inner and outer hair cells and stria vascularis) and vestibular (vestibular hair cells, dark, and transitional cells) sensorial elements in temporal bones from donors who had otitis media. We studied 40 temporal bones from such donors, which were categorized in serous otitis media (SOM), serous-purulent otitis media (SPOM), mucoid/mucoid-purulent otitis media (MOM/MPOM), and chronic otitis media (COM); control group comprised 10 nondiseased temporal bones. We found significant loss of inner and outer cochlear hair cells in the basal turn of the SPOM, MOM/MPOM and COM groups; significant loss of vestibular hair cells was observed in the MOM/MPOM and COM groups. All otitis media groups had smaller mean area of the stria vascularis in the basal turn of the cochlea when compared to controls. In conclusion, our study demonstrated more severe pathologic changes in the later stages of the continuum of otitis media (MOM/MPOM and COM). Those changes seem to progress from the basal turn of the cochlea (stria vascularis, then inner and outer hair cells) to the middle turn of the cochlea and to the saccule and utricle in the MOM/MPOM and COM stages.