Live imaging the phagocytic activity of inner ear supporting cells in response to hair cell death

Hearing loss and balance disorders affect millions of people worldwide. Sensory transduction in the inner ear requires both mechanosensory hair cells (HCs) and surrounding glia-like supporting cells (SCs). HCs are susceptible to death from aging, noise overexposure, and treatment with therapeutic drugs that have ototoxic side effects; these ototoxic drugs include the aminoglycoside antibiotics and the antineoplastic drug cisplatin. Although both classes of drugs are known to kill HCs, their effects on SCs are less well understood. Recent data indicate that SCs sense and respond to HC stress, and that their responses can influence HC death, survival, and phagocytosis. These responses to HC stress and death are critical to the health of the inner ear. Here we have used live confocal imaging of the adult mouse utricle, to examine the SC responses to HC death caused by aminoglycosides or cisplatin. Our data indicate that when HCs are killed by aminoglycosides, SCs efficiently remove HC corpses from the sensory epithelium in a process that includes constricting the apical portion of the HC after loss of membrane integrity. SCs then form a phagosome, which can completely engulf the remaining HC body, a phenomenon not previously reported in mammals. In contrast, cisplatin treatment results in accumulation of dead HCs in the sensory epithelium, accompanied by an increase in SC death. The surviving SCs constrict fewer HCs and display impaired phagocytosis. These data are supported by in vivo experiments, in which cochlear SCs show reduced capacity for scar formation in cisplatin-treated mice compared with those treated with aminoglycosides. Together, these data point to a broader defect in the ability of the cisplatin-treated SCs, to preserve tissue health in the mature mammalian inner ear.

Clinical implications of aging

Figure summarizes the major changes of aging and some key ways these changes affect pages. Though many changes occur with aging, under normal or resting conditions, there is usually very little functionally that is diminished solely on the basis of aging. The net effects are reductions in reserve capacity and placing geriatric patients at higher risk for adverse consequences related to medications and diseases. Interactions between lifestyle factors, such as exercise, diet, and environmental exposures, have a large impact on aging and lead to great individual variability. The interplay between these environmental factors, aging, and development of chronic diseases multiply the amount of variation seen as individual's age.

Long-term omega-3 fatty acid supplementation prevents expression changes in cochlear homocysteine metabolism and ameliorates progressive hearing loss in C57BL/6J mice

Omega-3 polyunsaturated fatty acids (PUFAs) are essential nutrients well known for their beneficial effects, among others on cognitive development and maintenance, inflammation and oxidative stress. Previous studies have shown an inverse association between high plasma levels of PUFAs and age-related hearing loss, and the relationship between low serum folate and elevated plasma homocysteine levels and hearing loss. Therefore, we used C57BL/6J mice and long-term omega-3 supplementation to evaluate the impact on hearing by analyzing their auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) thresholds. The omega-3 group showed significantly lower ABR hearing thresholds (~25 dB sound pressure level) and higher DPOAE amplitudes in mid-high frequencies when compared to the control group. These changes did not correlate with alterations between groups in plasma homocysteine or serum folate levels as measured by high-performance liquid chromatography and a microbiological method, respectively. Aging in the control group was associated with imbalanced cytokine expression toward increased proinflammatory cytokines as determined by quantitative reverse transcriptase polymerase chain reaction; these changes were prevented by omega-3 supplementation. Genes involved in homocysteine metabolism showed decreased expression during aging of control animals, and only alterations in Bhmt and Cbs were significantly prevented by omega-3 feeding. Western blotting showed that omega-3 supplementation precluded the CBS protein increase detected in 10-month-old controls but also produced an increase in BHMT protein levels. Altogether, the results obtained suggest a long-term protective role of omega-3 supplementation on cochlear metabolism and progression of hearing loss.

Age-related shifts in distortion product otoacoustic emissions peak-ratios and amplitude modulation spectra

Amplitude modulation (AM) is an important temporal cue for precise speech and complex sound recognition. However, functional decline of the auditory periphery as well as degradation of central auditory processing due to aging can reduce the salience and resolution of temporal cues. Age-related deficits in central temporal processing have previously been observed at more rapid AM frequencies and various AM depths. These centrally observed changes result from cochlear changes compounded with changes along the ascending auditory pathway. In fact, a decrease in ability to detect temporally modulated sounds accurately could originate from changes in cochlear filtering properties and in cochlear mechanics due to aging. Nonetheless, few studies have examined cochlear mechanisms in AM detection. To assess integrity of the mechanical properties of the auditory periphery, distortion product otoacoustic emissions (DPOAEs) are a tool commonly used in clinics and in research. In this study, we measured DPOAEs to reveal age-related changes in peak f2/f1 ratio and degradation in AM detection by basilar membrane vibration. Two tones (f1 and f2, f2 > f1) at various f2/f1 ratios and simultaneous presentation of one AM and one pure tone were used as stimuli to evoke DPOAEs. In addition of observing reduced DPOAE amplitudes and steeper slopes in the input-output DPOAE functions, higher peak f2/f1 ratios and broader f2/f1 tuning were also observed in aged animals. Aged animals generally had lower distortion product (DP) and first sideband (SB 1) responses evoked by an f1 pure tone and an f2 AM tone, regardless of whether the AM frequency was 45 Hz or 128 Hz. SB 1 thresholds, which corresponds to the smallest stimulus AM depth that can induce cochlear vibrations at the DP generator locus, were higher in aged animals as well. The results suggest that age-related changes in peak f2/f1 ratio and AM detection by basilar membrane vibration are consistent with a reduction in endocochlear potential and reduced prestin activity but with preserved hair cell bundle function. SB 1 responses evoked by f2 AM/f1 pure tone with various AM depths could serve as an estimate for cochlear AM detection. The sidebands of DP could also serve as additional physiological cues for detection of AM in the presence of other tone(s), even at typical conversational levels in speech.

Impaired unfolded protein response in the degeneration of cochlea cells in a mouse model of age-related hearing loss

Endoplasmic reticulum (ER) stress triggers the unfolded protein response (UPR) to prevent the accumulation of proteins in an aberrant conformation. The UPR can restore homeostasis by upregulating ER chaperones, such as glucose-regulated protein 78kD (GRP78), to refold the incorrectly handled protein, and by degrading the misfolded proteins via the ubiquitin-proteasome and autophagy-lysosome system. ER stress was recently demonstrated to be involved in the pathogenesis of age-related diseases. In this study, we measured the expression levels of GRP78 and ubiquitinated proteins in the cochleae of young C57BL/6 mice and aged mice to assess the capacity of the UPR. The lower expression of GRP78 and the increased number of ubiquitinated proteins observed in the cochleae of aged mice suggested that the capacity of the UPR was impaired and that the cell death pathway was activated. We found a markedly increased expression of the ER-related pro-apoptotic factor C/EBP homologous protein (CHOP) in the cochleae of aged mice, whereas the level of cleaved caspase-12 did not differ between the two groups. In addition, the cleavage of caspase-9, caspase-3 and poly [ADP-ribose] polymerase 1 was significantly increased in the aged cochleae, suggesting the activation of apoptosis in the cochleae resulting from the cross-talk between the ER and mitochondria through CHOP. These results indicated that impaired UPR in the cochleae of aged C57BL/6 mice resulting in ER stress may lead to apoptosis that is dependent on the mitochondrial pathway and that ER stress induced apoptosis may not be mediated by caspase-12.

Association Between Hearing Impairment and Risk of Hospitalization in Older Adults

OBJECTIVES

To determine the association between hearing impairment (HI) and risk and duration of hospitalization in community-dwelling older adults in the United States.

DESIGN

Prospective observational study.

SETTING

Health, Aging and Body Composition Study.

PARTICIPANTS

Well-functioning community-dwelling white and black Medicare beneficiaries aged 70 to 79 at study enrollment in 1997-98 were followed for a median of 12 years.

MEASUREMENTS

Incidence, annual rate, and duration of hospitalization were the primary outcomes. Hearing was defined as the pure-tone average (PTA) of hearing thresholds in decibels re: hearing level (dB HL) at octave frequencies from 0.5 to 4.0 kHz. Mild HI was defined as a PTA from 25 to 40 dB HL, and moderate or greater HI was defined as a PTA greater than 40 dB HL.

RESULTS

Of the 2,148 participants included in the analysis, 1,801 (83.5%) experienced one or more hospitalizations, with 7,007 adjudicated hospitalization events occurring during the study period. Eight hundred eighty-two (41.1%) participants had normal hearing, 818 (38.1%) had mild HI, and 448 (20.9%) had moderate or greater HI. After adjusting for demographic characteristics and cardiovascular comorbidities, persons with mild HI experienced a 16% (hazard ratio (HR) = 1.16, 95% confidence interval (CI) = 1.04-1.29) greater risk of incident hospitalization and a 17% (incidence rate ratio (IRR) = 1.17, 95% CI = 1.04-1.32) greater annual rate of hospitalization, and those with moderate or greater HI experienced a 21% (HR = 1.21, 95% CI = 1.06-1.38) greater risk of incident hospitalization and a 19% (IRR = 1.19, 95% CI = 1.04-1.38) greater annual rate of hospitalization than persons with normal hearing. There was no significant association between HI and mean duration of hospitalization.

CONCLUSION

Hearing-impaired older adults experience a greater incidence and annual rate of hospitalization than those with normal hearing. Investigating whether rehabilitative therapies could affect the risk of hospitalization in older adults requires further study.

Distúrbios fonoaudiológicos autodeclarados e fatores associados em idosos

OBJETIVO: identificar os distúrbios fonoaudiológicos e fatores associados autodeclarados em uma população de idosos. MÉTODOS: estudo transversal a partir de visitas domiciliares com uma amostra de 44 idosos com idade igual ou superior a 60 anos. A amostragem foi aleatória por múltiplos estágios. Utilizou-se um roteiro previamente estruturado com questões relacionadas a: aspectos sócio demográficos de saúde geral e uso de serviços de saúde; comunicação oral; motricidade e funções orofaciais; audição e equilíbrio segundo auto-percepção. Perguntou-se ainda sobre a existência ou não de tontura, zumbido uso de prótese dentária, dentição precária, diagnóstico de doenças sistêmicas, uso de cigarro ou assemelhados e manutenção de acompanhamento médico sistemático. Os dados foram registrados em banco de dados e as análises estatísticas realizadas por meio do programa EpiInfo versão 7.0. Foram verificadas as frequências das variáveis e sua distribuição na amostra estudada. RESULTADOS: 44 idosos com idades entre 60-80 anos (média de 66,04 anos; DP=4,8). Destes, 52,3% eram do sexo masculino e 47,4% do sexo feminino. 11,4% dos sujeitos da amostra referiram alteração de fala; 09,1% alteração de voz; 11,4% alteração de motricidade orofacial sendo que 27,3% fazia uso de prótese dentária e 18,2% apresentava dentição precária; 6,8% citaram audição e equilíbrio ruins sendo que 40,9% relataram tontura; 54,5% mencionaram serem portadores de doença sistêmica; 18,2% declararam-se fumantes e 70,4% disseram manter acompanhamento médico periódico. CONCLUSÃO: as queixas fonoaudiológicas mais frequentes na população entrevistada estão relacionadas à motricidade orofacial, audição e equilíbrio, sendo que ter doença sistêmica está mais comumente associado às queixas fonoaudiológicas.

Relationships among hearing loss, cognition and balance ability in community-dwelling older adults

[Purpose] The purpose of this study was to determine the relationships among hearing loss, cognition, and balance ability in elderly individuals. [Subjects and Methods] In total, 46 elderly individuals over 65 years of age who were attending senior welfare centers participated in this study. Through a hearing test, the speech frequency pure tone average in the better ear was checked. We set a criterion of hearing loss if the better ear hearing level (BEHL) value was 25 dB or more. Cognition ability was evaluated using the Korean mini-mental state examination (K-MMSE). Dynamic balance ability was evaluated by the timed up and go (TUG) test, and static balance ability was tested using a one-leg stance test (OLST). [Results] The ages of the subjects were all related to BEHL, TUG, K-MMSE, and OLST. BEHL had a negative correlation with OLST, whereas it had no correlation with K-MMSE or TUG. The hearing loss group had a significantly shorter OLST time than the normal hearing group. [Conclusion] As elderly individuals get older, their hearing and cognition, as well as their balance abilities deteriorate. The results of this study indicate there is a significant correlation between hearing loss and static balance.

Molecular basis of hair cell loss

Mechanisms that lead to the death of hair cells are reviewed. Exposure to noise, the use of ototoxic drugs that damage the cochlea and old age are accompanied by hair cell death. Outer hair cells are often more susceptible than inner hair cells, partly because of an intrinsically greater susceptibility; high frequency cells are also more vulnerable. A common factor in hair cell loss following age-related changes and exposure to ototoxic drugs or high noise levels is the generation of reactive oxygen species, which can trigger intrinsic apoptosis (the mitochondrial pathway). However, hair cell death is sometimes produced via an extracellular signal pathway triggering extrinsic apoptosis. Necrosis and necroptosis also play a role and, in various situations in which cochlear damage occurs, a balance exists between these possible routes of cell death, with no one mechanism being exclusively activated. Finally, the numerous studies on these mechanisms of hair cell death have led to the identification of many potential therapeutic agents, some of which have been used to attempt to treat people exposed to damaging events, although clinical trials are not yet conclusive. Continued work in this area is likely to lead to clinical treatments that could be used to prevent or ameliorate hearing loss.

Folic acid deficiency induces premature hearing loss through mechanisms involving cochlear oxidative stress and impairment of homocysteine metabolism

Nutritional imbalance is emerging as a causative factor of hearing loss. Epidemiologic studies have linked hearing loss to elevated plasma total homocysteine (tHcy) and folate deficiency, and have shown that folate supplementation lowers tHcy levels potentially ameliorating age-related hearing loss. The purpose of this study was to address the impact of folate deficiency on hearing loss and to examine the underlying mechanisms. For this purpose, 2-mo-old C57BL/6J mice (Animalia Chordata Mus musculus) were randomly divided into 2 groups (n = 65 each) that were fed folate-deficient (FD) or standard diets for 8 wk. HPLC analysis demonstrated a 7-fold decline in serum folate and a 3-fold increase in tHcy levels. FD mice exhibited severe hearing loss measured by auditory brainstem recordings and TUNEL-positive-apoptotic cochlear cells. RT-quantitative PCR and Western blotting showed reduced levels of enzymes catalyzing homocysteine (Hcy) production and recycling, together with a 30% increase in protein homocysteinylation. Redox stress was demonstrated by decreased expression of catalase, glutathione peroxidase 4, and glutathione synthetase genes, increased levels of manganese superoxide dismutase, and NADPH oxidase-complex adaptor cytochrome b-245, α-polypeptide (p22phox) proteins, and elevated concentrations of glutathione species. Altogether, our findings demonstrate, for the first time, that the relationship between hyperhomocysteinemia induced by folate deficiency and premature hearing loss involves impairment of cochlear Hcy metabolism and associated oxidative stress.

Subclinical hearing loss, longer sleep duration, and cardiometabolic risk factors in Japanese general population

Hearing loss leads to impaired social functioning and quality of life. Hearing loss is also associated with sleeping disorders and cardiometabolic risk factors. Here, we determined whether subclinical hearing loss is associated with sleep duration and cardiometabolic risk factors in a cross-sectional and longitudinal study of healthy Japanese general population. 48,091 men and women aged 20–79 years who underwent medical checkups were included in a cross-sectional study, and 6,674 were included in an 8-year longitudinal study. The prevalence of audiometrically determined hearing loss (>25 dB) at 4000 and 1000 Hz increased significantly with increasing sleep duration in any age strata. Logistic regression analysis showed that compared with reference sleep duration (6 h) longer sleep duration (≥8 h) was significantly associated with hearing loss, even after adjusting for potential confounding factors. Simultaneously, hearing loss was significantly associated with male sex, diabetes, and no habitual exercise. In the longitudinal study, the risk of longer sleep duration (≥8 h) after 8 years was significantly greater in subjects with hearing loss at 4000 Hz at baseline. In conclusion, current results suggest a potential association of subclinical hearing loss with longer sleep duration and cardiometabolic risk factors in a Japanese general population.

Sensitivity and specificity of portable hearing screening in middle-aged and older adults

Introduction Hearing screening allows the identification of individuals with hearing loss. Aim To determine the sensitivity and specificity of a portable hearing screening device in middle-aged and older adults using the manufacturer scoring and a scoring system proposed by the researchers. Methods In this transversal study, participants underwent anamnesis, otoscopy, and hearing screening using portable equipment. After this, a pure tone audiometry was performed, with participants classified into two groups: with and without hearing loss. The sensitivity and specificity of the hearing screening were calculated for the right and left ears using two methods of interpretation: the original method recommended by the manufacturer (criteria 1) and the method proposed by researchers (criteria 2). Results The sample consisted of 55 individuals, 83.6% (n = 46) of whom were women. Per criteria 1, the sensitivities were 26.3 (right ear) and 21.4% (left ear). The specificity was 100% for both ears. Using criteria 2, the sensitivity was 94.7 (right ear) and 100% (left ear). The specificity was 74.3 (right ear) and 65.9% (left ear). Conclusion This study showed that the criteria proposed by the manufacturer presented low sensitivity in the hearing screening. The criteria proposed by the researchers to achieve a more efficient performance reached high and balanced values for sensitivity and specificity.

Improving the safety of aging road users: a mini-review

Older drivers are at greatest risk for injury or death as a result of a car crash. In this mini-review, we outline the normative age-related changes to perceptual, cognitive, and motor abilities that contribute to increased crash risk and decreased comfort with driving, and highlight specific driving scenarios and conditions that are particularly challenging for aging road users. Adopting a person-environment fit framework, we discuss how the roadway environment can be modified to better match the abilities of the aging driver. We also review evidence for the efficacy of training interventions that aim to change the abilities and strategies of the aging driver to better match the demands of the driving environment. Evidence suggests that specific changes to the roadway and driver training strategies can bring the abilities of the older driver back into alignment with the demands of the driving task. A focus on both approaches will help ensure the safety of all road users as the number of aging drivers greatly increases over the next few decades.

Improving the safety of aging road users: a mini-review

Older drivers are at greatest risk for injury or death as a result of a car crash. In this mini-review, we outline the normative age-related changes to perceptual, cognitive, and motor abilities that contribute to increased crash risk and decreased comfort with driving, and highlight specific driving scenarios and conditions that are particularly challenging for aging road users. Adopting a person-environment fit framework, we discuss how the roadway environment can be modified to better match the abilities of the aging driver. We also review evidence for the efficacy of training interventions that aim to change the abilities and strategies of the aging driver to better match the demands of the driving environment. Evidence suggests that specific changes to the roadway and driver training strategies can bring the abilities of the older driver back into alignment with the demands of the driving task. A focus on both approaches will help ensure the safety of all road users as the number of aging drivers greatly increases over the next few decades.

Severe vision and hearing impairment and successful aging: a multidimensional view

PURPOSE

Previous research on psychosocial adaptation of sensory-impaired older adults has focused mainly on only one sensory modality and on a limited number of successful aging outcomes. We considered a broad range of successful aging indicators and compared older adults with vision impairment, hearing impairment, and dual sensory impairments and without sensory impairment.

DESIGN AND METHODS

Data came from samples of severely visually impaired (VI; N = 121), severely hearing-impaired (HI; N = 116), dual sensory-impaired (DI; N = 43), and sensory-unimpaired older adults (UI; N = 150). Participants underwent a wide-ranging assessment, covering everyday competence, cognitive functioning, social resources, self-regulation strategies, cognitive and affective well-being, and 4-year survival status (except the DI group).

RESULTS

The most pronounced difference among groups was in the area of everyday competence (lowest in VI and DI). Multigroup comparisons in latent space revealed both similar and differing relationship strengths among health, everyday competence, social resources, self-regulation, and overall well-being, depending on sensory status. After 4 years, mortality in VI (29%) and HI (30%) was significantly higher than in UI (20%) at the bivariate level, but not after controlling for confounders in a multivariate analysis.

IMPLICATIONS

A multidimensional approach to the understanding of sensory impairment and psychosocial adaptation in old age reveals a complex picture of loss and maintenance.

Lead roles for supporting actors: critical functions of inner ear supporting cells

Many studies that aim to investigate the underlying mechanisms of hearing loss or balance disorders focus on the hair cells and spiral ganglion neurons of the inner ear. Fewer studies have examined the supporting cells that contact both of these cell types in the cochlea and vestibular end organs. While the roles of supporting cells are still being elucidated, emerging evidence indicates that they serve many functions vital to maintaining healthy populations of hair cells and spiral ganglion neurons. Here we review recent studies that highlight the critical roles supporting cells play in the development, function, survival, death, phagocytosis, and regeneration of other cell types within the inner ear. Many of these roles have also been described for glial cells in other parts of the nervous system, and lessons from these other systems continue to inform our understanding of supporting cell functions. This article is part of a Special Issue entitled "Annual Reviews 2013".

Age effects on sensory-processing abilities and their impact on handwriting

Background.

Sensory-processing abilities are known to deteriorate in the elderly. As a result, daily activities such as handwriting may be impaired. Yet, knowledge about sensory-processing involvement in handwriting characteristics among older persons is limited.

Purpose

To examine how age influences sensory-processing abilities and the impact on handwriting as a daily performance.

Method.

The study participants were 118 healthy, independently functioning adults divided into four age groups: 31–45, 46–60, 61–75 and 76+ years. All participants completed the Adolescent/Adult Sensory Profile (AASP). Handwriting process was documented using the Computerized Handwriting Penmanship Evaluation Tool (ComPET).

Findings.

Age significantly affects sensory processing and handwriting pressure as well as temporal and spatial measures. Both handwriting time and spatial organization of the written product were predicted by sensory seeking. When examining age contribution to the prediction of handwriting by sensory processing, sensory seeking showed a tendency for predicting handwriting pressure (p = .06), while sensory sensitivity significantly predicted handwriting velocity.

Implications.

Age appears to influence sensory-processing abilities and affect daily performance tasks, such as handwriting, for which sensitivity and seeking for sensations are essential. Awareness of clinicians to sensory-processing deficits among older adults and examining their impact on broader daily activities are essential to improve daily performance and quality of life.