RESUMEN
The inner ear, like all organs, interacts with the systemic immune system via lymphatic drainage and vascular circulation to protect itself from infections and stress such as acoustic trauma. The adult mammalian inner ear including the endolymphatic sac is populated with bone-marrow derived resident macrophages. Circulating macrophages continually renew the resident macrophage population. Cells within the endolymphatic sac participate in and affect inner ear immune responses, but specific mechanisms for the interactions are unknown. Resident macrophages are present within the cochlear modiolus, spiral ligament, stria vascularis, on the scala tympani surface of the basilar membrane and in the vestibular ganglia and connective tissue of the vestibular sensory epithelia. In general, the mammalian organ of Corti, on the other hand, does not contain resident macrophages. Although repair of the epithelium following hair cell death is performed by adjacent supporting cells, macrophages in the osseous spiral lamina have been seen to extend processes into the organ of Corti below the inner hair cells where they may assist in reducing synaptopathy. Systemic and middle ear bacterial infections, experimentally simulated by lipopolysaccharide (LPS) injections, cause circulating inflammatory cells to enter the inner ear from venules in the spiral ligament and modiolus. Presumably, this is a surveillance mechanism, and in the absence of cochlear infection, no action is taken, but if noise trauma or ototoxic drug exposure occurs simultaneously, a more aggressive immune response is mounted. Acoustic trauma alone induces influx of circulating immune cells. Vigorous immune responses to pathogens within the cochlea result in fibrotic tissue and osteoid formation within the fluid-filled inner ear spaces. Many of the signals for recruiting and activating immune cells have been identified, but little is known about exactly what the activated cells do, how they interact with resident macrophages and what signals terminate their activity.
Asunto(s)
Saco Endolinfático , Pérdida Auditiva Provocada por Ruido , Animales , Cóclea/metabolismo , Saco Endolinfático/metabolismo , Pérdida Auditiva Provocada por Ruido/metabolismo , Mamíferos , Rampa Timpánica , Estría VascularRESUMEN
In 2000, we reported that human cytomegalovirus (HCMV) induced specific damage on chromosome 1. The capacity of the virus to induce DNA breaks indicated potent interaction between viral proteins and these loci. We have fine mapped the 1q42 breaksite. Transcriptional analysis of genes encoded in close proximity revealed virus-induced downregulation of a single gene, nidogen 1 (NID1). Beginning between 12 and 24 hours postinfection (hpi) and continuing throughout infection, steady-state (ss) NID1 protein levels were decreased in whole-cell lysates and secreted supernatants of human foreskin fibroblasts. Addition of the proteasomal inhibitor MG132 to culture medium stabilized NID1 in virus-infected cells, implicating infection-activated proteasomal degradation of NID1. Targeting of NID1 via two separate pathways highlighted the virus' emphasis on NID1 elimination. NID1 is an important basement membrane protein secreted by many cell types, including the endothelial cells (ECs) lining the vasculature. We found that ss NID1 was also reduced in infected ECs and hypothesized that virus-induced removal of NID1 might offer HCMV a means of increased distribution throughout the host. Supporting this idea, transmigration assays of THP-1 cells seeded onto NID1-knockout (KO) EC monolayers demonstrated increased transmigration. NID1 is expressed widely in the developing fetal central and peripheral nervous systems (CNS and PNS) and is important for neuronal migration and neural network excitability and plasticity and regulates Schwann cell proliferation, migration, and myelin production. We found that NID1 expression was dramatically decreased in clinical samples of infected temporal bones. While potentially beneficial for virus dissemination, HCMV-induced elimination of NID1 may underlie negative ramifications to the infected fetus.IMPORTANCE We have found that HCMV infection promotes the elimination of the developmentally important basement membrane protein nidogen 1 (NID1) from its host. The virus both decreased transcription and induced degradation of expressed protein. Endothelial cell (EC) secretion of basement membrane proteins is critical for vascular wall integrity, and infection equivalently affected NID1 protein levels in these cells. We found that the absence of NID1 in an EC monolayer allowed increased transmigration of monocytes equivalent to that observed after infection of ECs. The importance of NID1 in development has been well documented. We found that NID1 protein was dramatically reduced in infected inner ear clinical samples. We believe that HCMV's attack on host NID1 favors viral dissemination at the cost of negative developmental ramifications in the infected fetus.
Asunto(s)
Membrana Basal/metabolismo , Infecciones por Citomegalovirus/metabolismo , Infecciones por Citomegalovirus/virología , Citomegalovirus/fisiología , Endotelio Vascular/metabolismo , Fibroblastos/metabolismo , Glicoproteínas de Membrana/metabolismo , Movimiento Celular , Infecciones por Citomegalovirus/patología , Endotelio Vascular/virología , Fibroblastos/virología , Humanos , Glicoproteínas de Membrana/antagonistas & inhibidores , Glicoproteínas de Membrana/genética , Transducción de Señal , Internalización del VirusRESUMEN
Presbycusis, or age-related hearing loss (ARHL), occurs in most mammals with variations in the age of onset, rate of decline, and magnitude of degeneration in the central nervous system and inner ear. The affected cochlear structures include the stria vascularis and its vasculature, spiral ligament, sensory hair cells and auditory neurons. Dysfunction of the stria vascularis results in a reduced endocochlear potential. Without this potential, the cochlear amplification provided by the electro-motility of the outer hair cells is insufficient, and a high-frequency hearing-loss results. Degeneration of the sensory cells, especially the outer hair cells also leads to hearing loss due to lack of amplification. Neuronal degeneration, another hallmark of ARHL, most likely underlies difficulties with speech discrimination, especially in noisy environments. Noise exposure is a major cause of ARHL. It is well-known to cause sensory cell degeneration, especially the outer hair cells at the high frequency end of the cochlea. Even loud, but not uncomfortable, sound levels can lead to synaptopathy and ultimately neuronal degeneration. Even in the absence of a noisy environment, aged cells degenerate. This pathology most likely results from damage to mitochondria and contributes to degenerative changes in the stria vascularis, hair cells, and neurons. The genetic underpinnings of ARHL are still unknown and most likely involve various combinations of genes. At present, the only effective strategy for reducing ARHL is prevention of noise exposure. If future strategies can improve mitochondrial activity and reduce oxidative damage in old age, these should also bring relief.
Asunto(s)
Cóclea/patología , Audición/fisiología , Presbiacusia/patología , Presbiacusia/fisiopatología , Envejecimiento/fisiología , Animales , Células Ciliadas Auditivas/patología , HumanosRESUMEN
Exposure to intense sound or noise can result in purely temporary threshold shift (TTS), or leave a residual permanent threshold shift (PTS) along with alterations in growth functions of auditory nerve output. Recent research has revealed a number of mechanisms that contribute to noise-induced hearing loss (NIHL). The principle cause of NIHL is damage to cochlear hair cells and associated synaptopathy. Contributions to TTS include reversible damage to hair cell (HC) stereocilia or synapses, while moderate TTS reflects protective purinergic hearing adaptation. PTS represents permanent damage to or loss of HCs and synapses. While the substrates of HC damage are complex, they include the accumulation of reactive oxygen species and the active stimulation of intracellular stress pathways, leading to programmed and/or necrotic cell death. Permanent damage to cochlear neurons can also contribute to the effects of NIHL, in addition to HC damage. These mechanisms have translational potential for pharmacological intervention and provide multiple opportunities to prevent HC damage or to rescue HCs and spiral ganglion neurons that have suffered injury. This paper reviews advances in our understanding of cellular mechanisms that contribute to NIHL and their potential for therapeutic manipulation.
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Células Ciliadas Auditivas/patología , Pérdida Auditiva Provocada por Ruido/patología , Audición , Ruido/efectos adversos , Animales , Apoptosis , Fatiga Auditiva , Señalización del Calcio , Células Ciliadas Auditivas/efectos de los fármacos , Células Ciliadas Auditivas/metabolismo , Audición/efectos de los fármacos , Pérdida Auditiva Provocada por Ruido/tratamiento farmacológico , Pérdida Auditiva Provocada por Ruido/metabolismo , Pérdida Auditiva Provocada por Ruido/fisiopatología , Humanos , Necrosis , Estrés OxidativoRESUMEN
Many protein-coding genes identified by genome sequencing remain without functional annotation or biological context. Here we define a novel protein-coding gene, Nmf9, based on a forward genetic screen for neurological function. ENU-induced and genome-edited null mutations in mice produce deficits in vestibular function, fear learning and circadian behavior, which correlated with Nmf9 expression in inner ear, amygdala, and suprachiasmatic nuclei. Homologous genes from unicellular organisms and invertebrate animals predict interactions with small GTPases, but the corresponding domains are absent in mammalian Nmf9. Intriguingly, homozygotes for null mutations in the Drosophila homolog, CG45058, show profound locomotor defects and premature death, while heterozygotes show striking effects on sleep and activity phenotypes. These results link a novel gene orthology group to discrete neurological functions, and show conserved requirement across wide phylogenetic distance and domain level structural changes.
Asunto(s)
Péptidos y Proteínas de Señalización del Ritmo Circadiano/genética , Ritmo Circadiano/fisiología , Proteínas de Drosophila/genética , Miedo/fisiología , Proteínas del Tejido Nervioso/genética , Vestíbulo del Laberinto/patología , Amígdala del Cerebelo/metabolismo , Animales , Secuencia de Bases , Conducta Animal/fisiología , Drosophila melanogaster/genética , Femenino , Eliminación de Gen , Locomoción/genética , Masculino , Ratones , Ratones Endogámicos AKR , Ratones Endogámicos BALB C , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Ratones Endogámicos DBA , Ratones Transgénicos , Análisis de Secuencia de ADN , Factores Sexuales , Sueño/genética , Sueño/fisiología , Núcleo Supraquiasmático/metabolismo , Pruebas de Función Vestibular , Vestíbulo del Laberinto/fisiologíaRESUMEN
Age-related hearing loss is a multi-factorial process involving genetic and environmental factors, including exposure to noise and ototoxic agents, as well as pathological processes. Among these is the accumulation of mitochondrial DNA mutations and deletions. The creation of a transgenic mouse with a loss-of-function deletion of the nuclear gene that encodes the polymerase required to repair damaged mitochondrial DNA (PolgA) enabled evaluation of age-related cochlear pathology associated with random mitochondrial DNA deletions that accrue over the lifespan of the mouse. In comparison with their wild-type or heterozygous counterparts, animals with mutated DNA polymerase gamma developed hearing loss most rapidly. Any loss of mitochondrial DNA polymerase function however, resulted in detrimental effects, as evidenced by hearing tests and histological investigation of transgenic heterozygotes. Cochlear pathology in transgenic animals at 10 months of age included loss of neurons and clumping of surviving neurons in the apical turn of the spiral ganglion. Mitochondrial mutations in young animals, on the other hand, were protective against the development of temporary threshold shift in response to relatively low level noise exposure. This supports the idea that temporary threshold shifts are the result of an active process involving mitochondria and respiratory chain activity. Our results indicate that mitochondrial mutation and deletion can certainly contribute to the development of an aging phenotype, specifically age-related hearing loss.
Asunto(s)
Envejecimiento/genética , Envejecimiento/patología , Cóclea/patología , ADN Mitocondrial/genética , Audición/genética , Mutación/genética , Envejecimiento/fisiología , Animales , Cóclea/fisiopatología , ADN Polimerasa gamma , ADN Polimerasa Dirigida por ADN/genética , ADN Polimerasa Dirigida por ADN/fisiología , Complejo IV de Transporte de Electrones/fisiología , Femenino , Audición/fisiología , Masculino , Ratones , Ratones Transgénicos , Modelos Animales , Presbiacusia/genética , Presbiacusia/patología , Presbiacusia/fisiopatología , Ganglio Espiral de la Cóclea/patología , Ganglio Espiral de la Cóclea/fisiopatologíaRESUMEN
The thermo-reversible triblock copolymer poloxamer 407 was investigated as a drug delivery vehicle for micronized dexamethasone into the middle and inner ears of guinea pigs. The study characterized the gelation and in vitro release kinetics of poloxamer formulations. In vivo, the pharmacokinetic profile of formulations containing varying concentrations of poloxamer and dexamethasone was examined following intratympanic administration. Significant drug levels within the perilymph were observed for at least 10 days, while systemic exposure was minimal. The sustained-release kinetics profile could be significantly modulated by varying the concentrations of both poloxamer and dexamethasone. Assessment of auditory function revealed a small transient shift in hearing threshold, most probably of conductive nature, which resolved itself within a week. No significant histological changes of the round window membrane or cochlea could be noted. Poloxamer 407 thus represents an effective and safe delivery system to achieve sustained release of dexamethasone to the inner ear.
Asunto(s)
Dexametasona/administración & dosificación , Dexametasona/farmacocinética , Portadores de Fármacos/administración & dosificación , Portadores de Fármacos/farmacocinética , Perilinfa/efectos de los fármacos , Membrana Timpánica/efectos de los fármacos , Análisis de Varianza , Animales , Cóclea/efectos de los fármacos , Preparaciones de Acción Retardada/administración & dosificación , Preparaciones de Acción Retardada/farmacocinética , Relación Dosis-Respuesta a Droga , Vías de Administración de Medicamentos , Electrofisiología , Potenciales Evocados Auditivos del Tronco Encefálico/fisiología , Femenino , Cobayas , Audición/efectos de los fármacos , Pruebas Auditivas , Poloxámero/administración & dosificación , Poloxámero/farmacocinéticaRESUMEN
OBJECTIVES/HYPOTHESIS: To test whether noise-exposure, which activates a cochlear immune response with cytokine expression and infiltration of circulating leukocytes could augment the response to antigen (Ag). STUDY DESIGN: Randomized, prospective, mice. METHODS: We sensitized mice to an Ag, injected it intrathecally, and subsequently exposed the mice to noise (8-16 kHz, 90, 100, or 118 dB for 2 hours). Control mice received either noise exposure alone (100 or 118 dB), Ag challenge alone, intrathecal surgery and phosphate-buffered saline injection or no treatment. Four hours or 7 days later the mice were killed and cochlear sections were evaluated immunohistochemically for CD45, ICAM-1, and phospho-nuclear transcription factor-kappaB expression. RESULTS: Intrathecal Ag injection caused no hearing loss, but did result in a small immune response. Loud noise (118 dB) caused severe hearing loss and slight inflammation. The number of CD45-positive cells was significantly greater in the Ag plus-118 dB noise group relative to the Ag-alone group or 118 dB noise-exposure group. ICAM expression was seen in the lower part of the spiral ligament and small vessels within the normal cochlea. The amount of expression increased after Ag injection and acoustic trauma. Activated nuclear transcription factor-kappaB occurred in the nuclei of hair cells, supporting cells, spiral ligament fibrocytes, and neurons 4 hours after noise exposure. CONCLUSIONS: It seems that noise exposure can activate a cochlear immune response, which in the presence of Ag, allows for greater recruitment of inflammatory cells than occurred in response to Ag alone.
Asunto(s)
Cóclea/inmunología , Pérdida Auditiva Provocada por Ruido/inmunología , Hemocianinas/inmunología , Animales , Cóclea/patología , Potenciales Evocados Auditivos del Tronco Encefálico , Femenino , Pérdida Auditiva Provocada por Ruido/patología , Pérdida Auditiva Provocada por Ruido/fisiopatología , Inmunidad Innata , Inmunización , Inmunohistoquímica , Molécula 1 de Adhesión Intercelular/análisis , Antígenos Comunes de Leucocito/análisis , Leucocitos/patología , Ratones , Ratones Endogámicos , FN-kappa B/análisisRESUMEN
HYPOTHESIS: Leukocyte recruitment to the cochlea can be induced by tumor necrosis factor alpha (TNF-alpha) at concentrations that are not cytotoxic to sensory cells in the organ of Corti. BACKGROUND: Leukocytes participating in inflammation enter the inner ear via the spiral modiolar vein and its tributaries. Many of the infiltrated leukocytes express TNF-alpha 3 hours after cochlear antigen challenge of systemically antigen-sensitized animals. Competitive inhibition of TNF-alpha receptors reduces inflammation and hearing loss in experimentally induced labyrinthitis in guinea pigs and mice. However, TNF-alpha is also potentially cytotoxic, acting through the external apoptotic pathway and TNF-alpha transmembrane, cell surface receptors. It may therefore also participate in the sensory cell degeneration resulting from inflammation. METHODS: To test for recruitment potential, TNF-alpha or phosphate-buffered saline was infused into the guinea pig inner ear for 2 to 4 days through a cochleostomy using an osmotic pump (0.2 or 2.0 microg/mL; 1 microL/h) or a bolus injection (50 microg/mL; 10 microL). Auditory evoked brainstem response thresholds were measured before and after challenge, and cochleas were evaluated for the presence of leukocytes. To test for toxicity, organ of Corti explants were subjected to 3 concentrations of TNF-alpha (0.1, 10, and 1,000 ng/mL) for 96 hours, and the number of hair cell places was counted. RESULTS: Tumor necrosis factor alpha infused into the guinea pig cochlear scala tympani resulted in infiltration of leukocytes around the venules and within scala tympani. There was no associated hearing loss as measured with a click stimulus. Tumor necrosis factor alpha applied directly to organ of Corti explants caused minimal hair cell death at concentrations used in the in vivo experiments. At higher concentrations, there was 15 to 20% loss of cells. CONCLUSION: Tumor necrosis factor alpha is sufficient to recruit inflammatory cells to the cochlea but is not likely to be directly responsible for the hearing loss that follows immune-mediated labyrinthitis.
Asunto(s)
Cóclea/efectos de los fármacos , Leucocitos/efectos de los fármacos , Factor de Necrosis Tumoral alfa/farmacología , Animales , Animales Recién Nacidos , Células Ciliadas Auditivas/efectos de los fármacos , RatonesRESUMEN
OBJECTIVES/HYPOTHESIS: This study investigated the otoprotective properties of AM-111, an inhibitor of c-Jun N-terminal kinase-mediated apoptosis and inflammation. STUDY DESIGN: A controlled, prospective animal study using a guinea pig model of acute labyrinthitis. METHODS: Acute labyrinthitis was generated by injection of antigen into the scala tympani of sensitized guinea pigs. Treatment groups received 100 microL of AM-111 at concentrations of 100 micromol/L, 10 micromol/L, and 1 micromol/L in a hyaluronic acid gel formulation delivered over the round window niche within 1 hour of antigen challenge. Cochlear function was monitored over 21 days with serial auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) measurements followed by histologic analysis. RESULTS: The ABR results on day 21 demonstrated that untreated control ears for acute labyrinthitis had a mean hearing loss (HL) of 68 +/- 12 dB. In contrast, ears treated with AM-111 (100 micromol/L) had a mean HL of 39 +/- 31 dB. These two groups were statistically different (one-way analysis of variance, P = .03). Secondary outcomes, including DPOAE shift, inner hair cell survival, inflammatory cell counts, and spiral ganglion density, were also statistically significant in favor of an otoprotective effect of AM-111. Lower doses of AM-111 did not produce a statistically significant reduction in HL over controls. CONCLUSION: AM-111 delivered over the round window membrane in a 100 microL hyaluronic acid formulation at a 100 micromol/L concentration immediately after induction of acute labyrinthitis in the guinea pig cochlea protects hearing, reduces hair cell loss, and reduces the number of inflammatory cells at 21 days after treatment.
Asunto(s)
Pérdida Auditiva/prevención & control , Laberintitis/tratamiento farmacológico , Péptidos/uso terapéutico , Animales , Apoptosis/efectos de los fármacos , Recuento de Células , Modelos Animales de Enfermedad , Potenciales Evocados Auditivos del Tronco Encefálico/efectos de los fármacos , Femenino , Estudios de Seguimiento , Cobayas , Pérdida Auditiva/etiología , Pérdida Auditiva/fisiopatología , Laberintitis/complicaciones , Laberintitis/patología , Estudios Prospectivos , Ganglio Espiral de la Cóclea/efectos de los fármacos , Ganglio Espiral de la Cóclea/patología , Resultado del TratamientoRESUMEN
Age-related cochlear structural changes include the degeneration of sensory, neural cells and the stria vascularis. The hypothesis that cellular degeneration results from exposure to oxidative products of respiration was tested by supplementing aged dogs with a diet high in antioxidants and mitochondrial metabolites and by genetically modifying the expression level of the antioxidant, manganese superoxide dismutase (SOD2) in mice. Aged dogs received either a high antioxidant diet or a normal, control diet for the last 3 years of their life. Cellular measures were compared among the two aged groups (10-15 years) and young dogs. Both aged groups had cellular degeneration relative to young dogs, but the animals fed the antioxidant diet showed less degeneration at the base and apex than the control-diet group. Transgenic mice, heterozygous null for SOD2, produce only half as much enzyme as a normal mouse. These mice showed no increase in the amount of hearing loss relative to the background strain. A diet containing antioxidants reduced the magnitude of cochlear degeneration. Genetic reduction of one antioxidant, however, did not increase the magnitude of hearing loss in aging mice. A reduction in one enzyme seems to be compensated while the addition of a complex of factors is effective.
Asunto(s)
Envejecimiento/metabolismo , Antioxidantes/farmacología , Oído Interno/efectos de los fármacos , Envejecimiento/patología , Animales , Nervio Coclear/patología , Dieta , Perros , Oído Interno/metabolismo , Oído Interno/patología , Potenciales Evocados Auditivos del Tronco Encefálico , Ratones , Ratones Transgénicos , Presbiacusia/metabolismo , Presbiacusia/patología , Presbiacusia/prevención & control , Estría Vascular/patología , Superóxido Dismutasa/genética , Superóxido Dismutasa/metabolismoRESUMEN
Acoustic trauma induces cochlear inflammation. We hypothesized that chemokines are involved in the recruitment of leukocytes as part of a wound healing response. The cochleas of NIH-Swiss mice, exposed to octave-band noise (8-16 kHz, at 118 dB) for 2h, were examined after the termination of exposure. Leukocytes were identified immunohistochemically with antibodies to CD45 and F4/80. Gene array analysis followed by RT-PCR was performed on cochlear tissue to identify up-regulation of chemokine and adhesion molecule mRNA. The expression of the adhesion molecule ICAM-1 was also investigated immunohistochemically. Few CD45- or F4/80-positive leukocytes were observed in the non-exposed cochlea. Following acoustic trauma however, the number of CD45-positive cells was dramatically increased especially after 2 and 4 days, after which time the numbers decreased. F4/80-positive cells also increased in number over the course of a week. Gene array analysis indicated increased expression of monocyte chemoattractant protein 5 (MCP-5), monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein-1beta (MIP-1beta) and ICAM-1. RT-PCR, performed using primers for the individual mRNA sequences, confirmed the increased expression of MCP-1, MCP-5, MIP-1beta, and ICAM-1 relative to non-exposed mice. In the normal cochlea, ICAM-1 immunohistochemical expression was observed in venules, spiral ligament fibrocytes and in endosteal cells of the scala tympani. Expression increased to include more of the spiral ligament and endosteal cells after acoustic trauma. A cochlear inflammatory response is initiated in response to acoustic trauma and involves the recruitment of circulating leukocytes to the inner ear.
Asunto(s)
Pérdida Auditiva Provocada por Ruido/fisiopatología , Sistema Inmunológico/fisiopatología , Animales , Antígenos de Diferenciación/metabolismo , Umbral Auditivo , Quimiocina CCL2/metabolismo , Quimiocina CCL4 , Quimiocinas CC/metabolismo , Cóclea/inmunología , Cóclea/metabolismo , Cóclea/patología , Femenino , Pérdida Auditiva Provocada por Ruido/patología , Sistema Inmunológico/patología , Inmunohistoquímica , Molécula 1 de Adhesión Intercelular/metabolismo , Antígenos Comunes de Leucocito/metabolismo , Ratones , Proteínas Quimioatrayentes de Monocitos/metabolismo , Análisis de Secuencia por Matrices de Oligonucleótidos , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Distribución Tisular , Regulación hacia ArribaRESUMEN
OBJECTIVES: The involvement of transforming growth factor beta (TGF-beta), a strong mediator of fibrogenesis, during cochlear immune responses was investigated. METHODS: An inner ear adaptive immune response to antigen was created in mice that were painlessly sacrificed 3 to 48 hours and 7 days after initiation of the immune response. The cochleas were assayed by immunocytochemistry for TGF-beta and latency-associated peptide (LAP). RESULTS: We found LAP expressed in normal cochleas and the endolymphatic sac, in the small round cells in the cochlear scalae and the mesothelial cells under the basilar membrane, and in the endolymphatic sac perisaccular area. We found TGF-beta expressed in infiltrated, inflammatory cells in the scalae and the endolymphatic sac lumen 3 hours after cochlear antigen challenge. At this time, LAP immunoreactivity was decreased. This rapid shift in immunoreactivity provides evidence for activation of TGF-beta during an immune response. This reversal of expression persisted for 48 hours, but conditions reverted to normal after 7 days. Surgical controls did not show TGF-beta expression. CONCLUSIONS: We conclude that TGF-beta activation occurs in the early phase of a cochlear adaptive immune response and is down-regulated as the response resolves. This finding suggests that the process of cochlear fibrosis starts early and that proper treatment could prevent cochlear fibrosis.
Asunto(s)
Cóclea/inmunología , Laberintitis/metabolismo , Factor de Crecimiento Transformador beta/biosíntesis , Animales , Biomarcadores/metabolismo , Cóclea/metabolismo , Modelos Animales de Enfermedad , Femenino , Estudios de Seguimiento , Inmunohistoquímica , Laberintitis/inmunología , RatonesRESUMEN
Mice, in which the genetics can be manipulated and the life span is relatively short, enable evaluation of the effects of specific gene expression on cochlear degeneration over time. Antioxidant enzymes such as Cu/Zn superoxide dismutase (SOD1) protect cells from toxic, reactive oxygen species and may be involved in age-related degeneration. The effects of SOD1 deletion and over-expression on the cochlea were examined in Sod1-null mice, Sod1 transgenic mice and in age- and genetics-matched controls. Auditory brainstem responses (ABR) were measured and cochleae were histologically examined. The absence of SOD1 resulted in hearing loss at an earlier age than in wildtype or heterozygous mice. The cochleae of the null mice had severe spiral ganglion cell degeneration at 7-9 months of age. The stria vascularis in the aged, null mice was thinner than in the heterozygous or wildtype mice. Over-expression of SOD1 did not protect against hearing loss except at 24 months of age. In conclusion, SOD1 seems important for survival of cochlear neurons and the stria vascularis, however even half the amount is sufficient and an over abundance does not provide much protection from age-related hearing loss.
Asunto(s)
Envejecimiento/metabolismo , Pérdida Auditiva/enzimología , Superóxido Dismutasa/deficiencia , Superóxido Dismutasa/genética , Envejecimiento/patología , Análisis de Varianza , Animales , Tronco Encefálico/fisiología , Cóclea/enzimología , Cóclea/metabolismo , Cóclea/patología , Femenino , Expresión Génica , Pérdida Auditiva/patología , Masculino , Ratones , Ratones Noqueados , Ratones Transgénicos , Órgano Espiral/enzimología , Órgano Espiral/metabolismo , Órgano Espiral/patología , Presbiacusia/fisiopatología , Ganglio Espiral de la Cóclea/enzimología , Ganglio Espiral de la Cóclea/metabolismo , Ganglio Espiral de la Cóclea/patología , Estría Vascular/enzimología , Estría Vascular/metabolismo , Estría Vascular/patología , Superóxido Dismutasa-1RESUMEN
Cell fate specification during inner ear development is dependent upon regional gene expression within the otic vesicle. One of the earliest cell fate determination steps in this system is the specification of neural precursors, and regulators of this process include the Atonal-related basic helix-loop-helix genes, Ngn1 and NeuroD and the T-box gene, Tbx1. In this study we demonstrate that Eya1 signaling is critical to the normal expression patterns of Tbx1, Ngn1, and NeuroD in the developing mouse otocyst. We discuss a potential mechanism for the absence of neural precursors in the Eya1-/- inner ears and the primary and secondary mechanisms for the loss of cochleovestibular ganglion cells in the Eya1bor/bor hypomorphic mutant.
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Cóclea/embriología , Regulación del Desarrollo de la Expresión Génica , Proteínas del Tejido Nervioso/fisiología , Neurotrofina 3/fisiología , Proteínas de Dominio T Box/fisiología , Transactivadores/fisiología , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Muerte Celular , Linaje de la Célula , Genotipo , Inmunohistoquímica , Hibridación in Situ , Etiquetado Corte-Fin in Situ , Péptidos y Proteínas de Señalización Intracelular , Ratones , Ratones Transgénicos , Mutación , Proteínas del Tejido Nervioso/biosíntesis , Neuronas/metabolismo , Neurotrofina 3/biosíntesis , Proteínas Nucleares , Sondas de Oligonucleótidos/química , Fenotipo , Proteínas Tirosina Fosfatasas , Proteínas de Dominio T Box/biosíntesis , Factores de Tiempo , Transactivadores/biosíntesis , Factores de Transcripción/biosíntesis , Factores de Transcripción/fisiologíaRESUMEN
HYPOTHESIS: Cochlear microperfusion will be a useful treatment of severe sensorineural hearing loss caused by inflammation. BACKGROUND: Viruses, bacteria, and autoimmunity can initiate inflammation in the inner ear. The acute phase is associated with elevations in cytokines, nitrous oxide, and cellular infiltrates and the breakdown of the blood-labyrinthine barrier. The chronic phase leads to irreversible ossification of the labyrinth. METHODS: The authors developed cochlear microperfusion to facilitate removal of inflammatory cells and their byproducts during the acute phase of inflammation. Using a ventral approach to the guinea pig cochlea, the authors displaced resident perilymph by delivering perfusate into the scala vestibuli and collecting the effluent from the scala tympani. The authors evaluated the benefit of the procedure in an animal model of severe hearing loss caused by inflammation. RESULTS: Healthy controls undergoing cochlear microperfusion with phosphate-buffered saline incurred a mean hearing loss of 16 dB (n=4). This hearing loss was associated with the creation of two cochleostomies and not the perfusion itself. Sterile labyrinthitis (n=5) generated by perfusion of the cochlea with antigen consistently produced severe hearing loss over the initial 48 hours, and this hearing loss persisted for the subsequent 7 days. Therapeutic cochlear microperfusion, performed within the first 24 hours of developing severe hearing loss (n=9), immediately restored on average 24 dB (p <0.007) of hearing. CONCLUSION: Cochlear microperfusion is a promising new technique for treating severe deafness caused by inflammation. The benefit may be sustained when combined with local delivery of immunosuppressive agents to the inner ear.
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Cóclea , Modelos Animales de Enfermedad , Pérdida Auditiva Sensorineural/terapia , Laberintitis/terapia , Perfusión/métodos , Animales , Umbral Auditivo/fisiología , Supervivencia Celular/fisiología , Cóclea/inmunología , Cóclea/patología , Femenino , Cobayas , Pérdida Auditiva Sensorineural/inmunología , Pérdida Auditiva Sensorineural/patología , Hemocianinas , Mediadores de Inflamación/metabolismo , Laberintitis/inmunología , Laberintitis/patología , Leucocitos , Fagocitos/inmunología , Rampa Timpánica/inmunología , Rampa Timpánica/patologíaRESUMEN
Inner ear immune responses mediated by antigen-specific processes are thought to contribute to hearing loss in humans. Systemic activation of innate immunity contributes to immune responses in the central nervous system. We hypothesized that activation of innate immunity can prime the inner ear for adaptive immune responses and exacerbate disease. Mice were systemically immunized with antigen. Three weeks after initial antigen exposure, the antigen was injected intrathecally coincident with systemic injection of lipopolysaccharide (LPS), an activator of innate immunity. Responses were measured by quantifying the leukocyte infiltrate and cochlear IL-1beta expression. LPS stimulation markedly amplified the adaptive immune response to exogenous antigen in the inner ear. These data indicate that the cochlea is activated by systemic events that stimulate innate immunity and when antigen is present in the inner ear, a robust cochlear adaptive response is generated. If true in humans, this implies that priming may be an important component in the development of immune-mediated hearing loss.
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Enfermedades Autoinmunes del Sistema Nervioso/inmunología , Cóclea/inmunología , Pérdida Auditiva Sensorineural/inmunología , Inmunidad Innata/inmunología , Adyuvantes Inmunológicos/farmacología , Análisis de Varianza , Animales , Antígenos/inmunología , Oído Interno/inmunología , Femenino , Hemocianinas/farmacología , Inmunidad Innata/efectos de los fármacos , Inmunohistoquímica , Interleucina-1/genética , Interleucina-1/metabolismo , Lipopolisacáridos/farmacología , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , Ratones , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , Receptores Toll-LikeRESUMEN
C57BL/6 (B6) mice experience hearing loss and cochlear degeneration beginning about mid-life, whereas CAST/Ei (CAST) mice retain normal hearing until old age. A locus contributing to the hearing loss of B6 mice, named age-related hearing loss (ahl), was mapped to Chromosome 10. A homozygous, congenic strain of mice (B6.CAST-+ahl ), generated by crossing B6 (ahl/ahl) and CAST (+ahl/+ahl) mice has the same genomic material as the B6 mice except in the region of the ahl locus, which is derived from CAST. In this study, we have determined the extent of the CAST-derived region of Chromosome 10 in the congenic strain and have examined mice of all three strains for hearing loss and cochlear morphology between 9 and 25 months of age. Results for B6 mice were similar to those described previously. CAST mice showed no detectable hearing loss even at 24 months of age; however, they had a small amount of ganglion cell degeneration. B6.CAST-+ahl mice were protected from early onset hearing loss and basal turn degeneration, but older animals did show some hearing loss and ganglion cell degeneration. We conclude that loci in addition to ahl contribute to the differences in hearing loss between B6 and CAST mice. These results illustrate the complex inheritance of age-related hearing loss in mice and may have implications for the study of human presbycusis.
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Envejecimiento/genética , Envejecimiento/fisiología , Cóclea/patología , Presbiacusia/genética , Presbiacusia/fisiopatología , Envejecimiento/patología , Análisis de Varianza , Animales , Umbral Auditivo/fisiología , Potenciales Evocados Auditivos del Tronco Encefálico , Genotipo , Heterocigoto , Homocigoto , Humanos , Inmunohistoquímica , Ratones , Ratones Endogámicos C57BL , Órgano Espiral/patología , Presbiacusia/patología , Ganglio Espiral de la Cóclea/patologíaRESUMEN
Endogenous retroviruses have shaped the evolution of mammalian genomes. Host genes that control the effects of retrovirus insertions are therefore of great interest. The modifier-of-vibrator-1 locus (Mvb1) controls levels of correctly processed mRNA from genes mutated by endogenous retrovirus insertions into introns, including the Pitpn(vb) tremor mutation and the Eya1(BOR) model of human branchiootorenal syndrome. Positional complementation cloning identifies Mvb1 as the nuclear export factor Nxf1, providing an unexpected link between the mRNA export receptor and pre-mRNA processing. Population structure of the suppressive allele in wild Mus musculus castaneus suggests selective advantage. A congenic Mvb1(CAST) allele is a useful tool for modifying gene expression from existing mutations and could be used to manipulate engineered mutations containing retroviral elements.
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Alelos , Proteínas de Unión al ADN/genética , Retrovirus Endógenos/genética , Secuencia de Aminoácidos , Animales , Prueba de Complementación Genética , Humanos , Intrones , Ratones , Ratones Mutantes , Datos de Secuencia Molecular , Mutagénesis Insercional , Proteínas Represoras , Homología de Secuencia de Aminoácido , Factores de Transcripción , TransgenesRESUMEN
The inner ear is capable of rapidly mounting an immune response that can ultimately lead to cochlear degeneration and permanent hearing loss. The role of the endolymphatic sac in this immune process is not clear. In order to investigate the cytokine expression of cells within the endolymphatic sac, a secondary inner ear immune response to keyhole limpet hemocyanin (KLH) was created in mice. The animals were sacrificed 3-48 h and 7 days following initiation of the immune response. The cochleas and endolymphatic sacs were assayed by immunocytochemistry for IL-1beta, TNFalpha, and IL-6. Three hours after KLH challenge of the scala tympani, the perisaccular tissue of the endolymphatic sac contained more inflammatory cells than the scala tympani or endolymphatic sac lumen. Only a few of these cells, however, expressed the proinflammatory cytokines IL-1beta and TNFalpha between 3 and 12 h after KLH injection. On the other hand, TNFalpha, which plays an important role in the cochlear secondary immune response, was expressed in cells in the endolymphatic sac lumen. The maximum percentage of cells expressing TNFalpha was seen later than in the scala tympani. Animals treated with systemic injection of the TNF blocker, etanercept, showed a reduction in the number of cells in the endolymphatic sac lumen. It is concluded that the cells in the endolymphatic sac lumen contribute to the amplification of the adaptive immune response by expressing TNFalpha, while the infiltration of cells into the perisaccular connective tissue is part of the nonspecific, innate, cochlear immune response.