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1.
J Physiol ; 602(6): 1199-1210, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38431907

RESUMO

DFNB61 is a recessively inherited nonsyndromic hearing loss caused by mutations in SLC26A5, the gene that encodes the voltage-driven motor protein, prestin. Prestin is abundantly expressed in the auditory outer hair cells that mediate cochlear amplification. Two DFNB61-associated SLC26A5 variants, p.W70X and p.R130S, were identified in patients who are compound heterozygous for these nonsense and missense changes (SLC26A5W70X/R130S ). Our recent study showed that mice homozygous for p.R130S (Slc26a5R130S/R130S ) suffer from hearing loss that is ascribed to significantly reduced motor kinetics of prestin. Given that W70X-prestin is nonfunctional, compound heterozygous Slc26a5R130S/- mice were used as a model for human SLC26A5W70X/R130S . By examining the pathophysiological consequences of p.R130S prestin when it is the sole allele for prestin protein production, we determined that this missense change results in progressive outer hair cell loss in addition to its effects on prestin's motor action. Thus, this study defines the pathogenic roles of p.R130S prestin and identifies a limited time window for potential clinical intervention. KEY POINTS: The voltage-driven motor protein, prestin, is encoded by SLC26A5 and expressed abundantly in cochlear outer hair cells (OHCs). The importance of prestin for normal hearing was demonstrated in mice lacking prestin; however, none of the specific SLC26A5 variants identified to date in human patients has been experimentally demonstrated to be pathogenic. In this study we used both cell lines and a mouse model to define the pathogenic role of compound heterozygous p.W70X (c.209G>A) and p.R130S (c.390A>C) SLC26A5 variants identified in patients with moderate to profound hearing loss. As in patients, mice carrying one copy of p.R130S Slc26a5 showed OHC dysfunction and progressive degeneration, which results in congenital progressive hearing loss. This is the first functional study reporting pathogenic SLC26A5 variants and pointing to the presence of a therapeutic time window for potential clinical interventions targeting the affected OHCs before they are lost.


Assuntos
Surdez , Perda Auditiva , Animais , Humanos , Camundongos , Células Ciliadas Auditivas Externas/fisiologia , Perda Auditiva/genética , Perda Auditiva/metabolismo , Proteínas Motores Moleculares/genética , Proteínas Motores Moleculares/metabolismo , Mutação , Proteínas/genética
2.
Proc Natl Acad Sci U S A ; 121(3): e2318270121, 2024 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-38194445

RESUMO

During auditory transduction, sound-evoked vibrations of the hair cell stereociliary bundles open mechanotransducer (MET) ion channels via tip links extending from one stereocilium to its neighbor. How tension in the tip link is delivered to the channel is not fully understood. The MET channel comprises a pore-forming subunit, transmembrane channel-like protein (TMC1 or TMC2), aided by several accessory proteins, including LHFPL5 (lipoma HMGIC fusion partner-like 5). We investigated the role of LHFPL5 in transduction by comparing MET channel activation in outer hair cells of Lhfpl5-/- knockout mice with those in Lhfpl5+/- heterozygotes. The 10 to 90 percent working range of transduction in Tmc1+/+; Lhfpl5+/- was 52 nm, from which the single-channel gating force, Z, was evaluated as 0.34 pN. However, in Tmc1+/+; Lhfpl5-/- mice, the working range increased to 123 nm and Z more than halved to 0.13 pN, indicating reduced sensitivity. Tip link tension is thought to activate the channel via a gating spring, whose stiffness is inferred from the stiffness change on tip link destruction. The gating stiffness was ~40 percent of the total bundle stiffness in wild type but was virtually abolished in Lhfpl5-/-, implicating LHFPL5 as a principal component of the gating spring. The mutation Tmc1 p.D569N reduced the LHFPL5 immunolabeling in the stereocilia and like Lhfpl5-/- doubled the MET working range, but other deafness mutations had no effect on the dynamic range. We conclude that tip-link tension is transmitted to the channel primarily via LHFPL5; residual activation without LHFPL5 may occur by direct interaction between PCDH15 and TMC1.


Assuntos
Células Ciliadas Auditivas Externas , Células Ciliadas Vestibulares , Animais , Camundongos , Heterozigoto , Proteínas de Membrana/genética , Camundongos Knockout , Estereocílios , Vibração
3.
BMC Neurosci ; 25(1): 5, 2024 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-38291397

RESUMO

BACKGROUND: The cochlear sympathetic system plays a key role in auditory function and susceptibility to noise-induced hearing loss (NIHL). The formation of reactive oxygen species (ROS) is a well-documented process in NIHL. In this study, we aimed at investigating the effects of a superior cervical ganglionectomy (SCGx) on NIHL in Sprague-Dawley rats. METHODS: We explored the effects of unilateral and bilateral Superior Cervical Ganglion (SCG) ablation in the eight-ten weeks old Sprague-Dawley rats of both sexes on NIHL. Auditory function was evaluated by auditory brainstem response (ABR) testing and Distortion product otoacoustic emissions (DPOAEs). Outer hair cells (OHCs) counts and the expression of α2A-adrenergic receptor (AR) in the rat cochlea using immunofluorescence analysis. Cells culture and treatment, CCK-8 assay, Flow cytometry staining and analysis, and western blotting were to explore the mechanisms of SCG fibers may have a protective role in NIHL. RESULTS: We found that neither bilateral nor unilateral SCGx protected the cochlea against noise exposure. In HEI-OC1 cells, H2O2-induced oxidative damage and cell death were inhibited by the application of norepinephrine (NE). NE may prevent ROS-induced oxidative stress in OHCs and NIHL through the α2A-AR. CONCLUSION: These results demonstrated that sympathetic innervation mildly affected cochlear susceptibility to acoustic trauma by reducing oxidative damage in OHCs through the α2A-AR. NE may be a potential therapeutic strategy for NIHL prevention.


Assuntos
Perda Auditiva Provocada por Ruído , Ratos , Masculino , Feminino , Animais , Perda Auditiva Provocada por Ruído/tratamento farmacológico , Células Ciliadas Auditivas Externas , Espécies Reativas de Oxigênio , Ratos Sprague-Dawley , Norepinefrina , Peróxido de Hidrogênio/farmacologia , Peróxido de Hidrogênio/uso terapêutico , Cóclea , Potenciais Evocados Auditivos do Tronco Encefálico , Receptores Adrenérgicos/uso terapêutico
4.
Hear Res ; 443: 108951, 2024 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-38277880

RESUMO

Auditory sensation is based in nanoscale vibration of the sensory tissue of the cochlea, the organ of Corti complex (OCC). Motion within the OCC is now observable due to optical coherence tomography. In a previous study (Cooper et al., 2018), the region that includes the electro-motile outer hair cells (OHC) and Deiters cells (DC) was observed to move with larger amplitude than the basilar membrane (BM) and surrounding regions and was termed the "hotspot." In addition to this quantitative distinction, the hotspot moved qualitatively differently than the BM, in that its motion scaled nonlinearly with stimulus level at all frequencies, evincing sub-BF activity. Sub-BF activity enhances non-BF motion; thus the frequency tuning of the OHC/DC region was reduced relative to the BM. In this work we further explore the motion of the gerbil basal OCC and find that regions that lack significant sub-BF activity include the BM, the medial and lateral OCC, and the reticular lamina (RL) region. The observation that the RL region does not move actively sub-BF (already observed in Cho and Puria 2022), suggests that hair cell stereocilia are not exposed to sub-BF activity in the cochlear base. The observation that the lateral and RL regions move approximately linearly sub-BF indicates that linear forces dominate non-linear OHC-based forces on these components at sub-BF frequencies. A complex difference analysis was performed to reveal the internal motion of the OHC/DC region and showed that amplitude structure and phase shifts in the directly measured OHC/DC motion emerge due to the internal OHC/DC motion destructively interfering with BM motion.


Assuntos
Cóclea , Órgão Espiral , Animais , Gerbillinae , Estimulação Acústica , Células Ciliadas Auditivas Externas , Membrana Basilar , Vibração
5.
J Neurosci ; 44(4)2024 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-38050104

RESUMO

Outer hair cells (OHCs) of the organ of Corti (OoC), acting as bidirectional cellular mechanoelectrical transducers, generate, receive, and exchange forces with other major elements of the cochlear partition, including the sensory inner hair cells (IHCs). Force exchange is mediated via a supporting cell scaffold, including Deiters' (DC) and outer pillar cells (OPC), to enable the sensitivity and exquisite frequency selectivity of the mammalian cochlea and to transmit its responses to the auditory nerve. To selectively activate DCs and OPCs in male and female mice, we conditionally expressed in them a hyperpolarizing halorhodopsin (HOP), a light-gated inward chloride ion pump, and measured extracellular receptor potentials (ERPs) and their DC component (ERPDCs) from the cortilymph, which fills the OoC fluid spaces, and compared the responses with similar potentials from HOP-/- littermates. The compound action potentials (CAP) of the auditory nerve were measured as an indication of IHC activity and transmission of cochlear responses to the CNS. HOP light-activated hyperpolarization of DCs and OPCs suppressed cochlear amplification through changing the timing of its feedback, altered basilar membrane (BM) responses to tones at all measured levels and frequencies, and reduced IHC excitation. HOP activation findings reported here complement recent studies that revealed channelrhodopsin activation depolarized DCs and OPCs and effectively bypassed, rather than blocked, the control of OHC mechanical and electrical responses to sound and their contribution to timed and directed electromechanical feedback to the mammalian cochlea. Moreover, our findings identify DCs and OPCs as potential targets for the treatment of noise-induced hearing loss.


Assuntos
Células Ciliadas Auditivas Externas , Células Ciliadas Vestibulares , Feminino , Masculino , Camundongos , Animais , Células Ciliadas Auditivas Externas/fisiologia , Optogenética , Cóclea/fisiologia , Células Ciliadas Auditivas Internas/fisiologia , Órgão Espiral/fisiologia , Mamíferos
6.
Elife ; 122023 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-38054956

RESUMO

Prestin responds to transmembrane voltage fluctuations by changing its cross-sectional area, a process underlying the electromotility of outer hair cells and cochlear amplification. Prestin belongs to the SLC26 family of anion transporters yet is the only member capable of displaying electromotility. Prestin's voltage-dependent conformational changes are driven by the putative displacement of residue R399 and a set of sparse charged residues within the transmembrane domain, following the binding of a Cl- anion at a conserved binding site formed by the amino termini of the TM3 and TM10 helices. However, a major conundrum arises as to how an anion that binds in proximity to a positive charge (R399), can promote the voltage sensitivity of prestin. Using hydrogen-deuterium exchange mass spectrometry, we find that prestin displays an unstable anion-binding site, where folding of the amino termini of TM3 and TM10 is coupled to Cl- binding. This event shortens the TM3-TM10 electrostatic gap, thereby connecting the two helices, resulting in reduced cross-sectional area. These folding events upon anion binding are absent in SLC26A9, a non-electromotile transporter closely related to prestin. Dynamics of prestin embedded in a lipid bilayer closely match that in detergent micelle, except for a destabilized lipid-facing helix TM6 that is critical to prestin's mechanical expansion. We observe helix fraying at prestin's anion-binding site but cooperative unfolding of multiple lipid-facing helices, features that may promote prestin's fast electromechanical rearrangements. These results highlight a novel role of the folding equilibrium of the anion-binding site, and help define prestin's unique voltage-sensing mechanism and electromotility.


Assuntos
Cóclea , Células Ciliadas Auditivas Externas , Ânions , Sítios de Ligação , Bicamadas Lipídicas , Proteínas de Membrana Transportadoras
7.
Int J Mol Sci ; 24(23)2023 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-38068993

RESUMO

Tinnitus is the perception of noise in the absence of acoustic stimulation (phantom noise). In most patients suffering from chronic peripheral tinnitus, an alteration of outer hair cells (OHC) starting from the stereocilia (SC) occurs. This is common following ototoxic drugs, sound-induced ototoxicity, and acoustic degeneration. In all these conditions, altered coupling between the tectorial membrane (TM) and OHC SC is described. The present review analyzes the complex interactions involving OHC and TM. These need to be clarified to understand which mechanisms may underlie the onset of tinnitus and why the neuropathology of chronic degenerative tinnitus is similar, independent of early triggers. In fact, the fine neuropathology of tinnitus features altered mechanisms of mechanic-electrical transduction (MET) at the level of OHC SC. The appropriate coupling between OHC SC and TM strongly depends on autophagy. The involvement of autophagy may encompass degenerative and genetic tinnitus, as well as ototoxic drugs and acoustic trauma. Defective autophagy explains mitochondrial alterations and altered protein handling within OHC and TM. This is relevant for developing novel treatments that stimulate autophagy without carrying the burden of severe side effects. Specific phytochemicals, such as curcumin and berberin, acting as autophagy activators, may mitigate the neuropathology of tinnitus.


Assuntos
Zumbido , Humanos , Células Ciliadas Auditivas Externas , Estereocílios , Som , Estimulação Acústica
8.
Int J Mol Sci ; 24(23)2023 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-38069416

RESUMO

Mammalian auditory hair cells transduce sound-evoked traveling waves in the cochlea into nerve stimuli, which are essential for hearing function. Pillar cells located between the inner and outer hair cells are involved in the formation of the tunnel of Corti, which incorporates outer-hair-cell-driven fluid oscillation and basilar membrane movement, leading to the fine-tuned frequency-specific perception of sounds by the inner hair cells. However, the detailed molecular mechanism underlying the development and maintenance of pillar cells remains to be elucidated. In this study, we examined the expression and function of brain-specific angiogenesis inhibitor 3 (Bai3), an adhesion G-protein-coupled receptor, in the cochlea. We found that Bai3 was expressed in hair cells in neonatal mice and pillar cells in adult mice, and, interestingly, Bai3 knockout mice revealed the abnormal formation of pillar cells, with the elevation of the hearing threshold in a frequency-dependent manner. Furthermore, old Bai3 knockout mice showed the degeneration of hair cells and spiral ganglion neurons in the basal turn. The results suggest that Bai3 plays a crucial role in the development and/or maintenance of pillar cells, which, in turn, are necessary for normal hearing function. Our results may contribute to understanding the mechanisms of hearing loss in human patients.


Assuntos
Cóclea , Audição , Proteínas de Membrana , Proteínas do Tecido Nervoso , Animais , Camundongos , Encéfalo , Cóclea/metabolismo , Células Ciliadas Auditivas Externas , Camundongos Knockout , Proteínas do Tecido Nervoso/genética , Proteínas de Membrana/genética
9.
Nat Commun ; 14(1): 7145, 2023 11 06.
Artigo em Inglês | MEDLINE | ID: mdl-37932294

RESUMO

The outstanding acuity of the mammalian ear relies on cochlear amplification, an active mechanism based on the electromotility (eM) of outer hair cells. eM is a piezoelectric mechanism generated by little-understood, voltage-induced conformational changes of the anion transporter homolog prestin (SLC26A5). We used a combination of molecular dynamics (MD) simulations and biophysical approaches to identify the structural dynamics of prestin that mediate eM. MD simulations showed that prestin samples a vast conformational landscape with expanded (ES) and compact (CS) states beyond previously reported prestin structures. Transition from CS to ES is dominated by the translational-rotational movement of prestin's transport domain, akin to elevator-type substrate translocation by related solute carriers. Reversible transition between CS and ES states was supported experimentally by cysteine accessibility scanning, cysteine cross-linking between transport and scaffold domains, and voltage-clamp fluorometry (VCF). Our data demonstrate that prestin's piezoelectric dynamics recapitulate essential steps of a structurally conserved ion transport cycle.


Assuntos
Cisteína , Células Ciliadas Auditivas Externas , Animais , Células Ciliadas Auditivas Externas/metabolismo , Cisteína/metabolismo , Ânions/metabolismo , Transporte de Íons , Proteínas de Membrana Transportadoras/metabolismo , Proteínas de Transporte de Ânions/metabolismo , Mamíferos/metabolismo
10.
J Neurosci ; 43(50): 8801-8811, 2023 12 13.
Artigo em Inglês | MEDLINE | ID: mdl-37863653

RESUMO

Several lines of evidence have suggested that steeply sloping audiometric losses are caused by hair cell degeneration, while flat audiometric losses are caused by strial atrophy, but this concept has never been rigorously tested in human specimens. Here, we systematically compare audiograms and cochlear histopathology in 160 human cases from the archival collection of celloidin-embedded temporal bones at the Massachusetts Eye and Ear. The dataset included 106 cases from a prior study of normal-aging ears, and an additional 54 cases selected by combing the database for flat audiograms. Audiogram shapes were classified algorithmically into five groups according to the relation between flatness (i.e., SD of hearing levels across all frequencies) and low-frequency pure-tone average (i.e., mean at 0.25, 0.5, and 1.0 kHz). Outer and inner hair cell losses, neural degeneration, and strial atrophy were all quantified as a function of cochlear location in each case. Results showed that strial atrophy was worse in the apical than the basal half of the cochlea and was worse in females than in males. The degree of strial atrophy was uncorrelated with audiogram flatness. Apical atrophy was correlated with low-frequency thresholds and basal atrophy with high-frequency thresholds, and the former correlation was higher. However, a multivariable regression with all histopathological measures as predictors and audiometric thresholds as the outcome showed that strial atrophy was a significant predictor of threshold shift only in the low-frequency region, and, even there, the contribution of outer hair cell damage was larger.SIGNIFICANCE STATEMENT Cochlear pathology can only be assessed postmortem; thus, human cochlear histopathology is critical to our understanding of the mechanisms of hearing loss. Dogma holds that relative damage to sensory cells, which transduce mechanical vibration into electrical signals, versus the stria vascularis, the cellular battery that powers transduction, can be inferred by the shape of the audiogram, that is, down-sloping (hair cell damage) versus flat (strial atrophy). Here we quantified hair cell and strial atrophy in 160 human specimens to show that it is the degree of low-frequency hearing loss, rather than the audiogram slope, that predicts strial atrophy. Results are critical to the design of clinical trials for hearing-loss therapeutics, as current drugs target only hair cell, not strial, regeneration.


Assuntos
Surdez , Estria Vascular , Masculino , Feminino , Humanos , Estria Vascular/patologia , Cóclea/patologia , Surdez/patologia , Atrofia/patologia , Células Ciliadas Auditivas Externas/patologia
11.
Proc Natl Acad Sci U S A ; 120(41): e2305921120, 2023 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-37796989

RESUMO

The intricate, crystalline cytoarchitecture of the mammalian organ of Corti presumably plays an important role in cochlear amplification. As currently understood, the oblique, Y-shaped arrangement of the outer hair cells (OHCs) and phalangeal processes of the Deiters cells serves to create differential "push-pull" forces that drive the motion of the basilar membrane via the spatial feedforward and/or feedbackward of OHC forces. In concert with the cochlear traveling wave, the longitudinal separation between OHC sensing and forcing creates phase shifts that yield a form of negative damping, amplifying waves as they propagate. Unlike active forces that arise and act locally, push-pull forces are inherently directional-whereas forward-traveling waves are boosted, reverse-traveling waves are squelched. Despite their attractions, models based on push-pull amplification must contend with otoacoustic emissions (OAEs), whose existence implies that amplified energy escapes from the inner ear via mechanisms involving reverse traveling waves. We analyze hybrid local/push-pull models to determine the constraints that reflection-source OAEs place on the directionality of cochlear wave propagation. By implementing a special force-mixing control knob, we vary the mix of local and push-pull forces while leaving the forward-traveling wave unchanged. Consistency with stimulus-frequency OAEs requires that the active forces underlying cochlear wave amplification be primarily local in character, contradicting the prevailing view. By requiring that the oblique cytoarchitecture produce predominantly local forces, we reinterpret the functional role of the Y-shaped geometry, proposing that it serves not as a push-pull amplifier, but as a mechanical funnel that spatially integrates local OHC forces.


Assuntos
Cóclea , Emissões Otoacústicas Espontâneas , Animais , Membrana Basilar , Células Ciliadas Auditivas Externas , Osso e Ossos , Mamíferos
12.
J Chin Med Assoc ; 86(12): 1101-1108, 2023 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-37820291

RESUMO

BACKGROUND: Hearing loss is a global health issue and its etiopathologies involve complex molecular pathways. The ubiquitin-proteasome system has been reported to be associated with cochlear development and hearing loss. The gene related to anergy in lymphocytes ( GRAIL ), as an E3 ubiquitin ligase, has not, as yet, been examined in aging-related and noise-induced hearing loss mice models. METHODS: This study used wild-type (WT) and GRAIL knockout (KO) mice to examine cochlear hair cells and synaptic ribbons using immunofluorescence staining. The hearing in WT and KO mice was detected using auditory brainstem response. Gene expression patterns were compared using RNA-sequencing to identify potential targets during the pathogenesis of noise-induced hearing loss in WT and KO mice. RESULTS: At the 12-month follow-up, GRAIL KO mice had significantly less elevation in threshold level and immunofluorescence staining showed less loss of outer hair cells and synaptic ribbons in the hook region compared with GRAIL WT mice. At days 1, 14, and 28 after noise exposure, GRAIL KO mice had significantly less elevation in threshold level than WT mice. After noise exposure, GRAIL KO mice showed less loss of outer hair cells in the cochlear hook and basal regions compared with WT mice. Moreover, immunofluorescence staining showed less loss of synaptic ribbons in the hook regions of GRAIL KO mice than of WT mice. RNA-seq analysis results showed significant differences in C-C motif chemokine ligand 19 ( CCL19 ), C-C motif chemokine ligand 21 ( CCL21 ), interleukin 25 ( IL25 ), glutathione peroxidase 6 ( GPX6 ), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 1 ( NOX1 ) genes after noise exposure. CONCLUSION: The present data demonstrated that GRAIL deficiency protects against aging-related and noise-induced hearing loss. The mechanism involved needs to be further clarified from the potential association with synaptic modulation, inflammation, and oxidative stress.


Assuntos
Perda Auditiva Provocada por Ruído , Animais , Camundongos , Envelhecimento/fisiologia , Limiar Auditivo/fisiologia , Quimiocinas/metabolismo , Potenciais Evocados Auditivos do Tronco Encefálico/fisiologia , Técnicas de Inativação de Genes , Células Ciliadas Auditivas Externas/metabolismo , Células Ciliadas Auditivas Externas/patologia , Perda Auditiva Provocada por Ruído/genética , Perda Auditiva Provocada por Ruído/prevenção & controle , Ligantes , Ruído/efeitos adversos
13.
PLoS One ; 18(9): e0291780, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37733709

RESUMO

The most common cause of sensorineural hearing loss is damage of auditory hair cells. Tumor necrosis factor-alpha (TNF-α) is closely associated with sensorineural hearing loss. The present study examined the preconditioning effect of dexamethasone (DEX) on TNF-α-induced ototoxicity in mouse auditory hair cells (HEI-OC1) and cochlear explants. Treatment of HEI-OC1 with 10 ng/ml TNF-α for 24 h decreased cell viability, increased the accumulation of reactive oxygen species (ROS), and induced caspase-mediated apoptotic signaling pathways. Pretreatment with 10 nM DEX for 6 h before TNF-α exposure restored cell viability, decreased ROS accumulation, and attenuated apoptotic signaling activation induced by TNF-α. Incubation of cochlear explants with 20 ng/ml TNF-α for 24 h resulted in significant loss of both inner hair cells (IHCs) and outer hair cells (OHCs) and an increase in apoptotic activation accessed by annexin V staining. The cochlear explants pre-incubated with 10 nM DEX attenuated TNF-α ototoxicity in both IHCs and OHCs and apoptotic cell death. These results indicated that DEX plays a protective role in ototoxicity induced by TNF-α through attenuation of caspase-dependent apoptosis signaling pathway and ROS accumulation.


Assuntos
Perda Auditiva Neurossensorial , Ototoxicidade , Animais , Camundongos , Fator de Necrose Tumoral alfa , Espécies Reativas de Oxigênio , Células Ciliadas Auditivas Externas , Dexametasona/farmacologia
14.
PLoS Genet ; 19(9): e1010933, 2023 09.
Artigo em Inglês | MEDLINE | ID: mdl-37738262

RESUMO

Autosomal recessive mutation of HOXB1 and Hoxb1 causes sensorineural hearing loss in patients and mice, respectively, characterized by the presence of higher auditory thresholds; however, the origin of the defects along the auditory pathway is still unknown. In this study, we assessed whether the abnormal auditory threshold and malformation of the sensory auditory cells, the outer hair cells, described in Hoxb1null mutants depend on the absence of efferent motor innervation, or alternatively, is due to altered sensory auditory components. By using a whole series of conditional mutant mice, which inactivate Hoxb1 in either rhombomere 4-derived sensory cochlear neurons or efferent motor neurons, we found that the hearing phenotype is mainly reproduced when efferent motor neurons are specifically affected. Our data strongly suggest that the interactions between olivocochlear motor neurons and outer hair cells during a critical postnatal period are crucial for both hair cell survival and the establishment of the cochlear amplification of sound.


Assuntos
Células Ciliadas Auditivas Externas , Perda Auditiva Neurossensorial , Humanos , Animais , Camundongos , Perda Auditiva Neurossensorial/genética , Audição , Neurônios Motores , Sobrevivência Celular
15.
J Physiol ; 601(19): 4291-4308, 2023 10.
Artigo em Inglês | MEDLINE | ID: mdl-37642186

RESUMO

Cochlear outer hair cells (OHCs) are responsible for the exquisite frequency selectivity and sensitivity of mammalian hearing. During development, the maturation of OHC afferent connectivity is refined by coordinated spontaneous Ca2+ activity in both sensory and non-sensory cells. Calcium signalling in neonatal OHCs can be modulated by oncomodulin (OCM, ß-parvalbumin), an EF-hand calcium-binding protein. Here, we investigated whether OCM regulates OHC spontaneous Ca2+ activity and afferent connectivity during development. Using a genetically encoded Ca2+ sensor (GCaMP6s) expressed in OHCs in wild-type (Ocm+/+ ) and Ocm knockout (Ocm-/- ) littermates, we found increased spontaneous Ca2+ activity and upregulation of purinergic receptors in OHCs from Ocm-/- cochlea immediately following birth. The afferent synaptic maturation of OHCs was delayed in the absence of OCM, leading to an increased number of ribbon synapses and afferent fibres on Ocm-/- OHCs before hearing onset. We propose that OCM regulates the spontaneous Ca2+ signalling in the developing cochlea and the maturation of OHC afferent innervation. KEY POINTS: Cochlear outer hair cells (OHCs) exhibit spontaneous Ca2+ activity during a narrow period of neonatal development. OHC afferent maturation and connectivity requires spontaneous Ca2+ activity. Oncomodulin (OCM, ß-parvalbumin), an EF-hand calcium-binding protein, modulates Ca2+ signals in immature OHCs. Using transgenic mice that endogenously expressed a Ca2+ sensor, GCaMP6s, we found increased spontaneous Ca2+ activity and upregulated purinergic receptors in Ocm-/- OHCs. The maturation of afferent synapses in Ocm-/- OHCs was also delayed, leading to an upregulation of ribbon synapses and afferent fibres in Ocm-/- OHCs before hearing onset. We propose that OCM plays an important role in modulating Ca2+ activity, expression of Ca2+ channels and afferent innervation in developing OHCs.


Assuntos
Cálcio , Células Ciliadas Auditivas Externas , Camundongos , Animais , Células Ciliadas Auditivas Externas/fisiologia , Cálcio/metabolismo , Parvalbuminas/metabolismo , Cóclea/fisiologia , Proteínas de Ligação ao Cálcio/metabolismo , Camundongos Transgênicos , Receptores Purinérgicos/metabolismo , Mamíferos/metabolismo
16.
J Assoc Res Otolaryngol ; 24(4): 413-428, 2023 08.
Artigo em Inglês | MEDLINE | ID: mdl-37464091

RESUMO

Normal hearing is associated with cochlear nonlinearity. When two tones (f1 and f2) are presented, the intracochlear response contains additional components that can be recorded from the ear canal as distortion product otoacoustic emissions (DPOAEs). Although the most prominent intermodulation distortion component is at 2f1-f2, other cubic distortion products are also generated. Because these measurements are noninvasive, they are used in humans and in animal models to detect hearing loss. This study evaluated how loss of sensitivity affects DPOAEs with frequencies above and below the stimulating primaries, i.e., for upper sideband (USB) components like 2f2-f1 and for lower sideband (LSB) components like 2f1-f2. DPOAEs were recorded in several mouse mutants with varying degrees of hearing loss associated with structural changes to the tectorial membrane (TM), or with loss of outer hair cell (OHC) somatic electromotility due to lack of prestin or to the expression of a non-functional prestin. In mice with changes in sensitivity, magnitude reductions were observed for 2f1-f2 relative to controls with mice lacking prestin showing the greatest changes. In contrast, 2f2-f1 was minimally affected by reductions in cochlear gain due to changes in the TM or by the loss of OHC somatic electromotility. In addition, TM mutants with spontaneous otoacoustic emissions (SOAEs) generated larger responses than controls at 2f2-f1 when its frequency was similar to that for the SOAEs. Although cochlear pathologies appear to affect USB and LSB DPOAEs in different ways, both 2f1-f2 and 2f2-f1 reflect nonlinearities associated with the transducer channels. However, in mice, the component at 2f2-f1 does not appear to receive enhancement due to prestin's motor action.


Assuntos
Surdez , Perda Auditiva , Humanos , Animais , Camundongos , Emissões Otoacústicas Espontâneas/fisiologia , Cóclea/fisiologia , Células Ciliadas Auditivas Externas , Estimulação Acústica
17.
Otol Neurotol ; 44(6): 605-610, 2023 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-37315234

RESUMO

OBJECTIVE: Our objective was to determine whether the receptor CX3CR1 is necessary for the recruitment of macrophages to the cochlea in chronic suppurative otitis media (CSOM) and if its deletion can prevent hair cell loss in CSOM. BACKGROUND: CSOM is a neglected disease that afflicts 330 million people worldwide and is the most common cause of permanent hearing loss among children in the developing world. It is characterized by a chronically discharging infected middle ear. We have previously demonstrated that CSOM causes macrophage associated sensory hearing loss. The receptor CX3CR1 is expressed on macrophages, which have been shown to be increased at the time point of outer hair cell (OHC) loss in CSOM. METHODS: In this report, we examine the influence of CX3CR1 deletion (CX3CR1-/-) in a validated model of Pseudomonas aeruginosa (PA) CSOM. RESULTS: The data show no difference in OHC loss between the CX3CR1-/- CSOM group and CX3CR1+/+ CSOM group (p = 0.28). We observed partial OHC loss in the cochlear basal turn, no OHC loss in the middle and apical turns in both CX3CR1-/- and CX3CR1+/+ CSOM mice at 14 days after bacterial inoculation. No inner hair cell (IHC) loss was found in all cochlear turns in all groups. We also counted F4/80 labeled macrophages in the spiral ganglion, spiral ligament, stria vascularis and spiral limbus of the basal, middle, and apical turn in cryosections. We did not find a significant difference in the total number of cochlear macrophages between CX3CR1-/- mice and CX3CR1+/+ mice (p = 0.97). CONCLUSION: The data did not support a role for CX3CR1 macrophage associated HC loss in CSOM.


Assuntos
Receptor 1 de Quimiocina CX3C , Surdez , Otite Média Supurativa , Animais , Camundongos , Cóclea , Células Ciliadas Auditivas Externas , Macrófagos , Otite Média Supurativa/genética , Receptor 1 de Quimiocina CX3C/genética
18.
Curr Opin Neurobiol ; 81: 102745, 2023 08.
Artigo em Inglês | MEDLINE | ID: mdl-37356371

RESUMO

The auditory organ cochlea harbors two types of sound receptors, inner hair cells (IHCs) and outer hair cells (OHCs), which are innervated by spiral (auditory) ganglion neurons (SGNs). Recent transcriptomic, epigenetic, and genetic studies have started to reveal various aspects of cochlear development, including how prosensory progenitors are specified and diversified into IHCs or OHCs, as well as the heterogeneity among SGNs and how SGN subtypes are formed. Here, we primarily review advances in this line of research over the past five years and discuss a few key studies (from the past two years) to elucidate (1) how prosensory progenitors are specified; (2) the cis-regulatory control of Atoh1 expression and the synergistic interaction between Atoh1 and Pou4f3; and (3) the essential roles of Insm1 and Ikzf2 in OHC development and Tbx2 in IHC development. Moreover, we highlight the contribution of recent molecular studies on cochlear development toward the goal of regenerating IHCs and OHCs, which holds considerable potential for application in treating human deafness. Lastly, we briefly summarize the most recent progress on uncovering when and how SGN diversity is generated.


Assuntos
Cóclea , Células Ciliadas Auditivas Internas , Humanos , Células Ciliadas Auditivas Internas/fisiologia , Células Ciliadas Auditivas Externas/metabolismo , Neurônios/metabolismo , Transcriptoma
19.
Cell Rep ; 42(5): 112504, 2023 05 30.
Artigo em Inglês | MEDLINE | ID: mdl-37171961

RESUMO

The cochlea harbors two types of sound receptors, outer hair cells (OHCs) and inner hair cells (IHCs). OHCs transdifferentiate into IHCs in Insm1 mutants, and OHCs in Ikzf2-deficient mice are dysfunctional and maintain partial IHC gene expression. Insm1 potentially acts as a positive but indirect regulator of Ikzf2, considering that Insm1 is expressed earlier than Ikzf2 and primarily functions as a transcriptional repressor. However, direct evidence of this possibility is lacking. Here, we report the following results: first, Insm1 overexpression in IHCs leads to ectopic Ikzf2 expression. Second, Ikzf2 expression is repressed in Insm1-deficient OHCs, and forced expression of Ikzf2 mitigates the OHC abnormality in Insm1 mutants. Last, dual ablation of Insm1 and Ikzf2 generates a similar OHC phenotype as does Insm1 ablation alone. Collectively, our findings reveal the transcriptional cascade from Insm1 to Ikzf2, which should facilitate future investigation of the molecular mechanisms underlying OHC development and regeneration.


Assuntos
Células Ciliadas Auditivas Internas , Células Ciliadas Auditivas Externas , Animais , Camundongos , Cóclea/metabolismo , Células Ciliadas Auditivas Internas/metabolismo , Células Ciliadas Auditivas Externas/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Fatores de Transcrição/metabolismo
20.
Comput Biol Med ; 161: 106986, 2023 07.
Artigo em Inglês | MEDLINE | ID: mdl-37230014

RESUMO

Damage to the sensory hair cells in the cochlea is a major cause of hearing loss since human sensory hair cells do not regenerate naturally after damage. As these sensory hair cells are exposed to a vibrating lymphatic environment, they may be affected by physical flow. It is known that the outer hair cells (OHCs) are physically more damaged by sound than the inner hair cells (IHCs). In this study, the lymphatic flow is compared using computational fluid dynamics (CFD) based on the arrangement of the OHCs, and the effects of such flow on the OHCs is analyzed. In addition, flow visualization is used to validate the Stokes flow. The Stokes flow behavior is attributed to the low Reynolds number, and the same behavior is observed even when the flow direction is reversed. When the distance between the rows of the OHCs is large, each row is independent, but when this distance is short, the flow change in each row influences the other rows. The stimulation caused by flow changes on the OHCs is confirmed through surface pressure and shear stress. The OHCs located at the base with a short distance between the rows receive excess hydrodynamic stimulation, and the tip of the V-shaped pattern receives an excess mechanical force. This study attempts to understand the contributions of lymphatic flow to OHC damage by quantitatively suggesting stimulation of the OHCs and is expected to contribute to the development of OHC regeneration technologies in the future.


Assuntos
Células Ciliadas Auditivas Externas , Hidrodinâmica , Humanos , Células Ciliadas Auditivas Externas/fisiologia , Cóclea/fisiologia , Células Ciliadas Auditivas Internas/fisiologia
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