RESUMO
Sgms1 encodes sphingomyelin synthase 1, an enzyme in the sphingosine-1-phosphate signalling pathway, and was previously reported to underlie hearing impairment in the mouse. A new mouse allele, Sgms1tm1a, unexpectedly showed normal Auditory Brainstem Response thresholds. We found that the Sgms1tm1a mutation led to incomplete knockdown of transcript to 20 % of normal values, which was enough to support normal hearing. The Sgms1tm1b allele was generated by knocking out exon 7, leading to a complete lack of detectable transcript in the inner ear. Sgms1tm1b homozygotes showed largely normal auditory brainstem response thresholds at first, followed by progressive loss of sensitivity until they showed severe impairment at 6 months old. The endocochlear potential was consistently reduced in Sgms1tm1b mutants at 3, 4 and 8 weeks old, to around 80 mV compared with around 120 mV in control littermates. The stria vascularis showed a characteristic irregularity of marginal cell surfaces and patchy loss of Kcnq1 expression at their apical membrane, and expression analysis of the lateral wall suggested that marginal cells were the most likely initial site of dysfunction in the mutants. Finally, significant association of auditory thresholds with DNA markers within and close to the human SGMS1 gene were found in the 1958 Birth Cohort, suggesting that SGMS1 variants may play a role in the range of hearing abilities in the human population.
Assuntos
Potenciais Evocados Auditivos do Tronco Encefálico , Perda Auditiva , Estria Vascular , Transferases (Outros Grupos de Fosfato Substituídos) , Animais , Feminino , Masculino , Camundongos , Limiar Auditivo , Cóclea/fisiopatologia , Cóclea/metabolismo , Modelos Animais de Doenças , Predisposição Genética para Doença , Audição/genética , Perda Auditiva/genética , Perda Auditiva/fisiopatologia , Homozigoto , Camundongos Endogâmicos C57BL , Camundongos Knockout , Mutação , Fenótipo , Estria Vascular/metabolismo , Transferases (Outros Grupos de Fosfato Substituídos)/genéticaRESUMO
Hearing loss is highly heterogeneous, but one common form involves a failure to maintain the local ionic environment of the sensory hair cells reflected in a reduced endocochlear potential. We used a genetic approach to ask whether this type of pathology can be reversed, using the Spns2tm1a mouse mutant known to show this defect. By activating Spns2 gene transcription at different ages after the onset of hearing loss, we found that an existing auditory impairment can be reversed to give close to normal thresholds for an auditory brainstem response (ABR), at least at low to mid stimulus frequencies. Delaying the activation of Spns2 led to less effective recovery of ABR thresholds, suggesting that there is a critical period for intervention. Early activation of Spns2 not only led to improvement in auditory function but also to protection of sensory hair cells from secondary degeneration. The genetic approach we have used to establish that this type of hearing loss is in principle reversible could be extended to many other diseases using available mouse resources.
Assuntos
Proteínas de Transporte de Ânions , Terapia Genética , Perda Auditiva , Animais , Camundongos , Perda Auditiva/genética , Perda Auditiva/patologia , Perda Auditiva/terapia , Proteínas de Transporte de Ânions/genética , Ativação Transcricional , Potenciais Microfônicos da Cóclea , Células Ciliadas Auditivas/patologiaRESUMO
Deafness affects 5% of the world's population, yet there is a lack of treatments to prevent hearing loss due to genetic causes. Norrie disease is a recessive X-linked disorder, caused by NDP gene mutation. It manifests as blindness at birth and progressive sensorineural hearing loss, leading to debilitating dual sensory deprivation. To develop a gene therapy, we used a Norrie disease mouse model (Ndptm1Wbrg ), which recapitulates abnormal retinal vascularisation and progressive hearing loss. We delivered human NDP cDNA by intravenous injection of adeno-associated viral vector (AAV)9 at neonatal, juvenile and young adult pathological stages and investigated its therapeutic effects on the retina and cochlea. Neonatal treatment prevented the death of the sensory cochlear hair cells and rescued cochlear disease biomarkers as demonstrated by RNAseq and physiological measurements of auditory function. Retinal vascularisation and electroretinograms were restored to normal by neonatal treatment. Delivery of NDP gene therapy after the onset of the degenerative inner ear disease also ameliorated the cochlear pathology, supporting the feasibility of a clinical treatment for progressive hearing loss in people with Norrie disease.
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Non-syndromic sensorineural hearing loss (SNHL) is the most common sensory disorder, and it presents a high genetic heterogeneity. As part of our clinical genetic studies, we ascertained a previously unreported mutation in CCDC50 [c.828_858del, p.(Asp276Glufs*40)] segregating with hearing impairment in a Spanish family with SNHL associated with the autosomal dominant deafness locus DFNA44, which is predicted to disrupt protein function. To gain insight into the mechanism behind DFNA44 mutations, we analysed two Ccdc50 presumed loss-of-function mouse mutants, which showed normal hearing thresholds up to 6â months of age, indicating that haploinsufficiency is unlikely to be the pathogenic mechanism. We then carried out in vitro studies on a set of artificial mutants and on the p.(Asp276Glufs*40) and p.(Phe292Hisfs*37) human mutations, and determined that only the mutants containing the six-amino-acid sequence CLENGL as part of their aberrant protein tail showed an abnormal distribution consisting of perinuclear aggregates of the CCDC50 protein (also known as Ymer). Therefore, we conclude that the CLENGL sequence is necessary to form these aggregates. Taken together, the in vivo and in vitro results obtained in this study suggest that the two identified mutations in CCDC50 exert their effect through a dominant-negative or gain-of-function mechanism rather than by haploinsufficiency.
Assuntos
Perda Auditiva Neurossensorial , Perda Auditiva , Humanos , Animais , Camundongos , Perda Auditiva Neurossensorial/genética , Perda Auditiva/genética , Mutação da Fase de Leitura , Mutação/genética , Linhagem , Peptídeos e Proteínas de Sinalização Intracelular/genéticaRESUMO
Peroxisome biogenesis disorders (due to PEX gene mutations) are associated with symptoms that range in severity and can lead to early childhood death, but a common feature is hearing impairment. In this study, mice carrying Pex3 mutations were found to show normal auditory development followed by an early-onset progressive increase in auditory response thresholds. The only structural defect detected in the cochlea at four weeks old was the disruption of synapses below inner hair cells. A conditional approach was used to establish that Pex3 expression is required locally within the cochlea for normal hearing, rather than hearing loss being due to systemic effects. A lipidomics analysis of the inner ear revealed a local reduction in plasmalogens in the Pex3 mouse mutants, comparable to the systemic plasmalogen reduction reported in human peroxisome biogenesis disorders. Thus, mice with Pex3 mutations may be a useful tool to understand the physiological basis of peroxisome biogenesis disorders.
Assuntos
Orelha Interna , Perda Auditiva , Animais , Pré-Escolar , Humanos , Camundongos , Orelha Interna/metabolismo , Audição/fisiologia , Perda Auditiva/genética , Perda Auditiva/metabolismo , Lipoproteínas/metabolismo , Proteínas de Membrana/metabolismo , Mutação/genética , Peroxinas/genética , PlasmalogêniosRESUMO
Discovery of deafness genes and elucidating their functions have substantially contributed to our understanding of hearing physiology and its pathologies. Here we report on DNA variants in MINAR2, encoding membrane integral NOTCH2-associated receptor 2, in four families underlying autosomal recessive nonsyndromic deafness. Neurologic evaluation of affected individuals at ages ranging from 4 to 80 y old does not show additional abnormalities. MINAR2 is a recently annotated gene with limited functional understanding. We detected three MINAR2 variants, c.144G > A (p.Trp48*), c.412_419delCGGTTTTG (p.Arg138Valfs*10), and c.393G > T, in 13 individuals with congenital- or prelingual-onset severe-to-profound sensorineural hearing loss (HL). The c.393G > T variant is shown to disrupt a splice donor site. We show that Minar2 is expressed in the mouse inner ear, with the protein localizing mainly in the hair cells, spiral ganglia, the spiral limbus, and the stria vascularis. Mice with loss of function of the Minar2 protein (Minar2tm1b/tm1b) present with rapidly progressive sensorineural HL associated with a reduction in outer hair cell stereocilia in the shortest row and degeneration of hair cells at a later age. We conclude that MINAR2 is essential for hearing in humans and mice and its disruption leads to sensorineural HL. Progressive HL observed in mice and in some affected individuals and as well as relative preservation of hair cells provides an opportunity to interfere with HL using genetic therapies.
Assuntos
Perda Auditiva Neurossensorial , Receptor Notch2 , Receptores de Superfície Celular , Animais , Perda Auditiva Neurossensorial/genética , Humanos , Mutação com Perda de Função , Camundongos , Receptor Notch2/genética , Receptor Notch2/metabolismo , Receptores de Superfície Celular/genética , Estereocílios/metabolismoRESUMO
BACKGROUND: Mice carrying targeted mutations are important for investigating gene function and the role of genes in disease, but off-target mutagenic effects associated with the processes of generating targeted alleles, for instance using Crispr, and culturing embryonic stem cells, offer opportunities for spontaneous mutations to arise. Identifying spontaneous mutations relies on the detection of phenotypes segregating independently of targeted alleles, and having a broad estimate of the level of mutations generated by intensive breeding programmes is difficult given that many phenotypes are easy to miss if not specifically looked for. Here we present data from a large, targeted knockout programme in which mice were analysed through a phenotyping pipeline. Such spontaneous mutations segregating within mutant lines may confound phenotypic analyses, highlighting the importance of record-keeping and maintaining correct pedigrees. RESULTS: Twenty-five lines out of 1311 displayed different deafness phenotypes that did not segregate with the targeted allele. We observed a variety of phenotypes by Auditory Brainstem Response (ABR) and behavioural assessment and isolated eight lines showing early-onset severe progressive hearing loss, later-onset progressive hearing loss, low frequency hearing loss, or complete deafness, with vestibular dysfunction. The causative mutations identified include deletions, insertions, and point mutations, some of which involve new genes not previously associated with deafness while others are new alleles of genes known to underlie hearing loss. Two of the latter show a phenotype much reduced in severity compared to other mutant alleles of the same gene. We investigated the ES cells from which these lines were derived and determined that only one of the 8 mutations could have arisen in the ES cell, and in that case, only after targeting. Instead, most of the non-segregating mutations appear to have occurred during breeding of mutant mice. In one case, the mutation arose within the wildtype colony used for expanding mutant lines. CONCLUSIONS: Our data show that spontaneous mutations with observable effects on phenotype are a common side effect of intensive breeding programmes, including those underlying targeted mutation programmes. Such spontaneous mutations segregating within mutant lines may confound phenotypic analyses, highlighting the importance of record-keeping and maintaining correct pedigrees.
Assuntos
Surdez , Perda Auditiva , Alelos , Animais , Surdez/genética , Perda Auditiva/genética , Camundongos , Mutagênese , MutaçãoRESUMO
Norrie disease is caused by mutation of the NDP gene, presenting as congenital blindness followed by later onset of hearing loss. Protecting patients from hearing loss is critical for maintaining their quality of life. This study aimed to understand the onset of pathology in cochlear structure and function. By investigating patients and juvenile Ndp-mutant mice, we elucidated the sequence of onset of physiological changes (in auditory brainstem responses, distortion product otoacoustic emissions, endocochlear potential, blood-labyrinth barrier integrity) and determined the cellular, histological, and ultrastructural events leading to hearing loss. We found that cochlear vascular pathology occurs earlier than previously reported and precedes sensorineural hearing loss. The work defines a disease mechanism whereby early malformation of the cochlear microvasculature precedes loss of vessel integrity and decline of endocochlear potential, leading to hearing loss and hair cell death while sparing spiral ganglion cells. This provides essential information on events defining the optimal therapeutic window and indicates that early intervention is needed. In an era of advancing gene therapy and small-molecule technologies, this study establishes Ndp-mutant mice as a platform to test such interventions and has important implications for understanding the progression of hearing loss in Norrie disease.
Assuntos
Cegueira/congênito , Gerenciamento Clínico , Potenciais Evocados Auditivos do Tronco Encefálico/fisiologia , Previsões , Doenças Genéticas Ligadas ao Cromossomo X/fisiopatologia , Perda Auditiva Neurossensorial/fisiopatologia , Audição/fisiologia , Doenças do Sistema Nervoso/fisiopatologia , Degeneração Retiniana/fisiopatologia , Espasmos Infantis/fisiopatologia , Adolescente , Adulto , Animais , Cegueira/complicações , Cegueira/fisiopatologia , Cegueira/terapia , Criança , Pré-Escolar , Modelos Animais de Doenças , Feminino , Seguimentos , Doenças Genéticas Ligadas ao Cromossomo X/complicações , Doenças Genéticas Ligadas ao Cromossomo X/terapia , Perda Auditiva Neurossensorial/diagnóstico , Perda Auditiva Neurossensorial/etiologia , Humanos , Masculino , Camundongos , Camundongos Mutantes , Doenças do Sistema Nervoso/complicações , Doenças do Sistema Nervoso/terapia , Degeneração Retiniana/complicações , Degeneração Retiniana/terapia , Espasmos Infantis/complicações , Espasmos Infantis/terapia , Adulto JovemRESUMO
Age-related hearing loss in humans (presbycusis) typically involves impairment of high frequency sensitivity before becoming progressively more severe at lower frequencies. Pathologies initially affecting lower frequency regions of hearing are less common. Here we describe a progressive, predominantly low-frequency recessive hearing impairment in two mutant mouse lines carrying different mutant alleles of the Klhl18 gene: a spontaneous missense mutation (Klhl18lowf) and a targeted mutation (Klhl18tm1a(KOMP)Wtsi). Both males and females were studied, and the two mutant lines showed similar phenotypes. Threshold for auditory brainstem responses (ABR; a measure of auditory nerve and brainstem neural activity) were normal at 3 weeks old but showed progressive increases from 4 weeks onwards. In contrast, distortion product otoacoustic emission (DPOAE) sensitivity and amplitudes (a reflection of cochlear outer hair cell function) remained normal in mutants. Electrophysiological recordings from the round window of Klhl18lowf mutants at 6 weeks old revealed 1) raised compound action potential thresholds that were similar to ABR thresholds, 2) cochlear microphonic potentials that were normal compared with wildtype and heterozygous control mice and 3) summating potentials that were reduced in amplitude compared to control mice. Scanning electron microscopy showed that Klhl18lowf mutant mice had abnormally tapering of the tips of inner hair cell stereocilia in the apical half of the cochlea while their synapses appeared normal. These results suggest that Klhl18 is necessary to maintain inner hair cell stereocilia and normal inner hair cell function at low frequencies.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas de Ciclo Celular/genética , Células Ciliadas Auditivas Internas/patologia , Perda Auditiva/genética , Presbiacusia/genética , Animais , Cóclea/patologia , Modelos Animais de Doenças , Potenciais Evocados Auditivos do Tronco Encefálico/fisiologia , Células Ciliadas Auditivas Internas/metabolismo , Perda Auditiva/patologia , Humanos , Camundongos , Mutação de Sentido Incorreto/genética , Presbiacusia/patologiaRESUMO
The microRNA miR-96 is important for hearing, as point mutations in humans and mice result in dominant progressive hearing loss. Mir96 is expressed in sensory cells along with Mir182 and Mir183, but the roles of these closely-linked microRNAs are as yet unknown. Here we analyse mice carrying null alleles of Mir182, and of Mir183 and Mir96 together to investigate their roles in hearing. We found that Mir183/96 heterozygous mice had normal hearing and homozygotes were completely deaf with abnormal hair cell stereocilia bundles and reduced numbers of inner hair cell synapses at four weeks old. Mir182 knockout mice developed normal hearing then exhibited progressive hearing loss. Our transcriptional analyses revealed significant changes in a range of other genes, but surprisingly there were fewer genes with altered expression in the organ of Corti of Mir183/96 null mice compared with our previous findings in Mir96 Dmdo mutants, which have a point mutation in the miR-96 seed region. This suggests the more severe phenotype of Mir96 Dmdo mutants compared with Mir183/96 mutants, including progressive hearing loss in Mir96 Dmdo heterozygotes, is likely to be mediated by the gain of novel target genes in addition to the loss of its normal targets. We propose three mechanisms of action of mutant miRNAs; loss of targets that are normally completely repressed, loss of targets whose transcription is normally buffered by the miRNA, and gain of novel targets. Any of these mechanisms could lead to a partial loss of a robust cellular identity and consequent dysfunction.
RESUMO
Progressive hearing loss is very common in the human population but we know little about the underlying molecular mechanisms. Synaptojanin2 (Synj2) has been reported to be involved, as a mouse mutation led to a progressive increase in auditory thresholds with age. Synaptojanin2 is a phosphatidylinositol (PI) phosphatase that removes the five-position phosphates from phosphoinositides, such as PIP2 and PIP3, and is a key enzyme in clathrin-mediated endocytosis. To investigate the mechanisms underlying progressive hearing loss, we have studied a different mutation of mouse Synj2 to look for any evidence of involvement of vesicle trafficking particularly affecting the synapses of sensory hair cells. Auditory brainstem responses (ABR) developed normally at first but started to decline between 3 and 4 weeks of age in Synj2tm1b mutants. At 6 weeks old, some evidence of outer hair cell (OHC) stereocilia fusion and degeneration was observed, but this was only seen in the extreme basal turn so cannot explain the raised ABR thresholds that correspond to more apical regions of the cochlear duct. We found no evidence of any defect in inner hair cell (IHC) exocytosis or endocytosis using single hair cell recordings, nor any sign of hair cell synaptic abnormalities. Endocochlear potentials (EP) were normal. The mechanism underlying progressive hearing loss in these mutants remains elusive, but our findings of raised distortion product otoacoustic emission (DPOAE) thresholds and signs of OHC degeneration both suggest an OHC origin for the hearing loss. Synaptojanin2 is not required for normal development of hearing but it is important for its maintenance.
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The underlying causes of age-related hearing loss (ARHL) are not well understood, but it is clear from heritability estimates that genetics plays a role in addition to environmental factors. Genome-wide association studies (GWAS) in human populations can point to candidate genes that may be involved in ARHL, but follow-up analysis is needed to assess the role of these genes in the disease process. Some genetic variants may contribute a small amount to a disease, while other variants may have a large effect size, but the genetic architecture of ARHL is not yet well-defined. In this study, we asked if a set of 17 candidate genes highlighted by early GWAS reports of ARHL have detectable effects on hearing by knocking down expression levels of each gene in the mouse and analysing auditory function. We found two of the genes have an impact on hearing. Mutation of Dclk1 led to late-onset progressive increase in ABR thresholds and the A430005L14Rik (C1orf174) mutants showed worse recovery from noise-induced damage than controls. We did not detect any abnormal responses in the remaining 15 mutant lines either in thresholds or from our battery of suprathreshold ABR tests, and we discuss the possible reasons for this.
Assuntos
Percepção Auditiva/genética , Variação Genética , Perda Auditiva Provocada por Ruído/genética , Audição/genética , Presbiacusia/genética , Fatores Etários , Animais , Quinases Semelhantes a Duplacortina , Potenciais Evocados Auditivos do Tronco Encefálico/genética , Feminino , Predisposição Genética para Doença , Estudo de Associação Genômica Ampla , Perda Auditiva Provocada por Ruído/fisiopatologia , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Masculino , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Camundongos Transgênicos , Fenótipo , Presbiacusia/fisiopatologia , Proteínas Serina-Treonina Quinases/genética , Medição de Risco , Fatores de RiscoRESUMO
Adult-onset hearing loss is very common, but we know little about the underlying molecular pathogenesis impeding the development of therapies. We took a genetic approach to identify new molecules involved in hearing loss by screening a large cohort of newly generated mouse mutants using a sensitive electrophysiological test, the auditory brainstem response (ABR). We review here the findings from this screen. Thirty-eight unexpected genes associated with raised thresholds were detected from our unbiased sample of 1,211 genes tested, suggesting extreme genetic heterogeneity. A wide range of auditory pathophysiologies was found, and some mutant lines showed normal development followed by deterioration of responses, revealing new molecular pathways involved in progressive hearing loss. Several of the genes were associated with the range of hearing thresholds in the human population and one, SPNS2, was involved in childhood deafness. The new pathways required for maintenance of hearing discovered by this screen present new therapeutic opportunities.
Assuntos
Percepção Auditiva/genética , Potenciais Evocados Auditivos do Tronco Encefálico/genética , Perda Auditiva/genética , Estimulação Acústica/métodos , Adulto , Animais , Proteínas de Transporte de Ânions/genética , Criança , Fenômenos Eletrofisiológicos/genética , Potenciais Evocados Auditivos do Tronco Encefálico/fisiologia , Feminino , Estudos de Associação Genética , Audição/genética , Perda Auditiva/metabolismo , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BLRESUMO
Hearing loss is a common sensory deficiency suffered by millions worldwide. It is a heterogeneous condition and genetics plays a critical role in its etiology. Gene variants can fundamentally alter hearing function, or predispose the auditory system towards loss of function resulting from other factors. In mouse studies of hearing loss and gene function, an evoked potential electrophysiological recording, the auditory brainstem response (ABR), is now considered the optimal way to screen large numbers of individuals, either with normal hearing sensitivity or with hearing impairment. Other routinely used methods to assess hearing function (such as acoustic startle responses, or otoacoustic emissions) do not allow assessment of the same broad spectrum of dysfunction nor readily allow the threshold sensitivity of the neural output of the cochlea to be assessed and are less ideal. An optimized recording system to rapidly and reproducibly record high-quality ABRs from mutant mice as part of a high-throughput phenotyping pipeline was developed. Click-evoked ABRs and ABRs evoked by pure-tone frequencies over a range of sound levels from 0 dB to 95 dB, sound pressure levels (SPL) are recorded. This takes approximately 15-20 min per mouse (with 5 tone frequencies), allowing a large number of mutant mice to be screened. This method has been used to measure ABRs on a high-throughput mutant mouse phenotyping pipeline and in laboratory tests to follow-up the hearing loss phenotypes identified on that pipeline.
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The developmental and physiological complexity of the auditory system is likely reflected in the underlying set of genes involved in auditory function. In humans, over 150 non-syndromic loci have been identified, and there are more than 400 human genetic syndromes with a hearing loss component. Over 100 non-syndromic hearing loss genes have been identified in mouse and human, but we remain ignorant of the full extent of the genetic landscape involved in auditory dysfunction. As part of the International Mouse Phenotyping Consortium, we undertook a hearing loss screen in a cohort of 3006 mouse knockout strains. In total, we identify 67 candidate hearing loss genes. We detect known hearing loss genes, but the vast majority, 52, of the candidate genes were novel. Our analysis reveals a large and unexplored genetic landscape involved with auditory function.The full extent of the genetic basis for hearing impairment is unknown. Here, as part of the International Mouse Phenotyping Consortium, the authors perform a hearing loss screen in 3006 mouse knockout strains and identify 52 new candidate genes for genetic hearing loss.
Assuntos
Perda Auditiva/genética , Mapas de Interação de Proteínas/genética , Animais , Conjuntos de Dados como Assunto , Testes Genéticos , Perda Auditiva/epidemiologia , Testes Auditivos , Camundongos , Camundongos Knockout , FenótipoRESUMO
Recent findings suggest that the manipulation of the EphA/ephrinA system can improve hearing threshold sensitivity in the auditory system (Yates et al., 2014). These results appear to open-up the possibility that pharmacological manipulation of this system could lead to the development of treatments to cure some types of hearing loss. As a first step towards this goal, we have performed a further series of auditory brainstem evoked potential recordings on ephrinA2 homozygous knockout mice and their wildtype littermates in order to replicate the previously reported findings. However, we found that ephrinA2 knockout mice had auditory threshold sensitivity for click and 3-42 kHz tone pip frequencies comparable to that of their wildtype littermates. Evoked potential wave amplitudes, latencies and inter-peak intervals were also comparable between ephrinA2 knockout mice and wild type control littermates. Thus in our experiments we could not replicate the findings of Yates et al. (2014). Whilst the EphA/ephrinA system may therefore play a role in the development of innervation of the cochlea and neural circuitry of the auditory brainstem, there appears to be a functional redundancy between members of this family such that loss of ephrinA2 function alone is insufficient to alter auditory function in the mouse.
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Vias Auditivas/metabolismo , Percepção Auditiva , Efrina-A2/metabolismo , Audição , Estimulação Acústica , Animais , Limiar Auditivo , Efrina-A2/deficiência , Efrina-A2/genética , Potenciais Evocados Auditivos do Tronco Encefálico , Feminino , Genótipo , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fenótipo , Fatores de TempoRESUMO
Progressive hearing loss is very common in the population but we still know little about the underlying pathology. A new spontaneous mouse mutation (stonedeaf, stdf ) leading to recessive, early-onset progressive hearing loss was detected and exome sequencing revealed a Thr289Arg substitution in Sphingosine-1-Phosphate Receptor-2 (S1pr2). Mutants aged 2 weeks had normal hearing sensitivity, but at 4 weeks most showed variable degrees of hearing impairment, which became severe or profound in all mutants by 14 weeks. Endocochlear potential (EP) was normal at 2 weeks old but was reduced by 4 and 8 weeks old in mutants, and the stria vascularis, which generates the EP, showed degenerative changes. Three independent mouse knockout alleles of S1pr2 have been described previously, but this is the first time that a reduced EP has been reported. Genomic markers close to the human S1PR2 gene were significantly associated with auditory thresholds in the 1958 British Birth Cohort (n = 6099), suggesting involvement of S1P signalling in human hearing loss. The finding of early onset loss of EP gives new mechanistic insight into the disease process and suggests that therapies for humans with hearing loss due to S1P signalling defects need to target strial function.
Assuntos
Substituição de Aminoácidos , Perda Auditiva Neurossensorial/genética , Receptores de Lisoesfingolipídeo/genética , Animais , Limiar Auditivo , Modelos Animais de Doenças , Potenciais Evocados Auditivos , Perda Auditiva Neurossensorial/fisiopatologia , Humanos , Camundongos , Pessoa de Meia-Idade , Receptores de Lisoesfingolipídeo/química , Receptores de Esfingosina-1-Fosfato , Estria Vascular/fisiologia , Sequenciamento do ExomaRESUMO
WHRN (DFNB31) mutations cause diverse hearing disorders: profound deafness (DFNB31) or variable hearing loss in Usher syndrome type II. The known role of WHRN in stereocilia elongation does not explain these different pathophysiologies. Using spontaneous and targeted Whrn mutants, we show that the major long (WHRN-L) and short (WHRN-S) isoforms of WHRN have distinct localizations within stereocilia and also across hair cell types. Lack of both isoforms causes abnormally short stereocilia and profound deafness and vestibular dysfunction. WHRN-S expression, however, is sufficient to maintain stereocilia bundle morphology and function in a subset of hair cells, resulting in some auditory response and no overt vestibular dysfunction. WHRN-S interacts with EPS8, and both are required at stereocilia tips for normal length regulation. WHRN-L localizes midway along the shorter stereocilia, at the level of inter-stereociliary links. We propose that differential isoform expression underlies the variable auditory and vestibular phenotypes associated with WHRN mutations.
Assuntos
Processamento Alternativo/genética , Células Ciliadas Auditivas/metabolismo , Mecanotransdução Celular , Proteínas de Membrana/genética , Estereocílios/metabolismo , Animais , Fenômenos Eletrofisiológicos , Células Ciliadas Auditivas/ultraestrutura , Proteínas de Membrana/metabolismo , Camundongos , Fenótipo , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Estereocílios/ultraestrutura , Vestíbulo do Labirinto/fisiologiaRESUMO
A neuron׳s response to a sound can be suppressed by the presentation of a preceding sound. It has been suggested that this suppression is a direct correlate of the psychophysical phenomenon of forward masking, however, forward suppression, as measured in the responses of the auditory nerve, was insufficient to account for behavioural performance. In contrast the neural suppression seen in the inferior colliculus and auditory cortex was much closer to psychophysical performance. In anaesthetised guinea-pigs, using a physiological two-interval forced-choice threshold tracking algorithm to estimate suppressed (masked) thresholds, we examine whether the enhancement of suppression can occur at an earlier stage of the auditory pathway, the ventral cochlear nucleus (VCN). We also compare these responses with the responses from the central nucleus of the inferior colliculus (ICc) using the same preparation. In both nuclei, onset-type neurons showed the greatest amounts of suppression (16.9-33.5dB) and, in the VCN, these recovered with the fastest time constants (14.1-19.9ms). Neurons with sustained discharge demonstrated reduced masking (8.9-12.1dB) and recovery time constants of 27.2-55.6ms. In the VCN the decrease in growth of suppression with increasing suppressor level was largest for chopper units and smallest for onset-type units. The threshold elevations recorded for most unit types are insufficient to account for the magnitude of forward masking as measured behaviourally, however, onset responders, in both the cochlear nucleus and inferior colliculus demonstrate a wide dynamic range of suppression, similar to that observed in human psychophysics.
Assuntos
Limiar Auditivo/fisiologia , Núcleo Coclear/fisiologia , Neurônios/fisiologia , Estimulação Acústica , Potenciais de Ação , Algoritmos , Animais , Vias Auditivas/fisiologia , Comportamento de Escolha/fisiologia , Nervo Coclear/fisiologia , Cobaias , Colículos Inferiores/fisiologia , Microeletrodos , Processamento de Sinais Assistido por ComputadorRESUMO
WBP2 encodes the WW domain-binding protein 2 that acts as a transcriptional coactivator for estrogen receptor α (ESR1) and progesterone receptor (PGR). We reported that the loss of Wbp2 expression leads to progressive high-frequency hearing loss in mouse, as well as in two deaf children, each carrying two different variants in the WBP2 gene. The earliest abnormality we detect in Wbp2-deficient mice is a primary defect at inner hair cell afferent synapses. This study defines a new gene involved in the molecular pathway linking hearing impairment to hormonal signalling and provides new therapeutic targets.