Loss of osteoprotegerin expression in the inner ear causes degeneration of the cochlear nerve and sensorineural hearing loss

Human otic progenitor cell models of congenital hearing loss reveal potential pathophysiologic mechanisms of Zika virus and cytomegalovirus infections

Congenital hearing loss is a common chronic condition affecting children in both developed and developing nations. Viruses correlated with congenital hearing loss include human cytomegalovirus (HCMV) and Zika virus (ZIKV), which causes congenital Zika syndrome. The mechanisms by which HCMV and ZIKV infections cause hearing loss are poorly understood. It is challenging to study human inner ear cells because they are encased in bone and also scarce as autopsy samples. Recent advances in culturing human stem cell-derived otic progenitor cells (OPCs) have allowed us herein to describe successful in vitro infection of OPCs with HCMV and ZIKV, and also to propose potential mechanisms by which each viral infection could affect hearing. We find that ZIKV infection rapidly and significantly induces the expression of type I interferon and interferon-stimulated genes, while OPC viability declines, at least in part, from apoptosis. In contrast, HCMV infection did not appear to upregulate interferons or cause a reduction in cell viability, and instead disrupted expression of key genes and pathways associated with inner ear development and function, including Cochlin, nerve growth factor receptor, SRY-box transcription factor 11, and transforming growth factor-beta signaling. These findings suggest that ZIKV and HCMV infections cause congenital hearing loss through distinct pathways, that is, by inducing progenitor cell death in the case of ZIKV infection, and by disruption of critical developmental pathways in the case of HCMV infection.

IMPORTANCE

Congenital virus infections inflict substantial morbidity and devastating disease in neonates worldwide, and hearing loss is a common outcome. It has been difficult to study viral infections of the human hearing apparatus because it is embedded in the temporal bone of the skull. Recent technological advances permit the differentiation of otic progenitor cells (OPCs) from human-induced pluripotent stem cells. This paper is important for demonstrating that inner ear virus infections can be modeled in vitro using OPCs. We infected OPCs with two viruses associated with congenital hearing loss: human cytomegalovirus (HCMV), a DNA virus, or Zika virus (ZIKV), an RNA virus. An important result is that the gene expression and cytokine production profiles of HCMV/ZIKV-infected OPCs are markedly dissimilar, suggesting that mechanisms of hearing loss are also distinct. The specific molecular regulatory pathways identified in this work could suggest important targets for therapeutics.

Genome-wide screen of otosclerosis in population biobanks: 27 loci and shared associations with skeletal structure

Otosclerosis is one of the most common causes of conductive hearing loss, affecting 0.3% of the population. It typically presents in adulthood and half of the patients have a positive family history. The pathophysiology of otosclerosis is poorly understood. A previous genome-wide association study (GWAS) identified a single association locus in an intronic region of RELN. Here, we report a meta-analysis of GWAS studies of otosclerosis in three population-based biobanks comprising 3504 cases and 861,198 controls. We identify 23 novel risk loci (p < 5 × 10^-8) and report an association in RELN and three previously reported candidate gene or linkage regions (TGFB1, MEPE, and OTSC7). We demonstrate developmental stage-dependent immunostaining patterns of MEPE and RUNX2 in mouse otic capsules. In most association loci, the nearest protein-coding genes are implicated in bone remodelling, mineralization or severe skeletal disorders. We highlight multiple genes involved in transforming growth factor beta signalling for follow-up studies.

Toward Personalized Diagnosis and Therapy for Hearing Loss: Insights From Cochlear Implants

ABSTRACT

Sensorineural hearing loss (SNHL) is the most common sensory deficit, disabling nearly half a billion people worldwide. The cochlear implant (CI) has transformed the treatment of patients with SNHL, having restored hearing to more than 800,000 people. The success of CIs has inspired multidisciplinary efforts to address the unmet need for personalized, cellular-level diagnosis, and treatment of patients with SNHL. Current limitations include an inability to safely and accurately image at high resolution and biopsy the inner ear, precluding the use of key structural and molecular information during diagnostic and treatment decisions. Furthermore, there remains a lack of pharmacological therapies for hearing loss, which can partially be attributed to challenges associated with new drug development. We highlight advances in diagnostic and therapeutic strategies for SNHL that will help accelerate the push toward precision medicine. In addition, we discuss technological improvements for the CI that will further enhance its functionality for future patients. This report highlights work that was originally presented by Dr. Stankovic as part of the Dr. John Niparko Memorial Lecture during the 2021 American Cochlear Implant Alliance annual meeting.

Bone-turnover biomarkers as potential prognostic factors in sudden sensorineural hearing loss: A prospective cohort study

Objectives

This study aims to explore the relationship between bone-turnover biomarkers and the recovery of SSNHL to provide clues for further improvements in etiological research and predictors.

Methods

The medical history, hearing thresholds, biomarkers of bone-turnover, and related hormones of 117 SSNHL patients were collected prospectively between August 2018 and December 2021. Linear correlation and logistic regression models were applied to examine the association between bone-turnover biomarkers and the prognosis of SSNHL.

Results

Age, the incidence of vertigo, pure tone average of the impaired frequencies (PTAimpairedfre), and the levels of bone turnover [including alkaline phosphatase (ALP), β-carboxy terminal crosslinked telopeptide of type 1 collagen (β-CTX), and N-terminal-midfragment of osteocalcin (N-MID)] were higher in the nonresponders than responders (P &lt; 0.05). Logistic regression showed that the age (OR = 1.035, P = 0.027), time to treatment (OR = 1.157, P = 0.038), PTAimpairedfre (OR = 1.031, P = 0.008), and β-CTX (OR = 1.004, P = 0.001) were independent risk factors for the prognosis of SSNHL. In the women SSNHL subgroup, age, postmenopause percentage, PTAimpairedfre, the activity of ALP, levels of β-CTX, and N-MID were significantly higher in the nonresponders than the responders (P &lt; 0.05). Compared to the men SSNHL subgroup, β-CTX has a higher correlation coefficient and predictive efficiency in the women SSNHL subgroup, and logistic regression showed that β-CTX (OR = 1.004, P = 0.004) was an independent risk factor for the women SSNHL.

Conclusions

Bone-turnover biomarkers are risk factors for poor prognosis in SSNHL, especially β-CTX. The differences were significant in women SSNHL, which may be related to the rapid regression of estrogen after menopause that leads to the occurrence of osteoporosis with a high conversion rate.

Correlation of blast-induced tympanic membrane perforation with peripheral cochlear synaptopathy

The auditory organs, including the tympanic membrane, cochlea, and central auditory pathway, are the most fragile components of the human body when exposed to blast overpressure. Tympanic membrane perforation (TMP) is the most frequent symptom in blast-exposed patients. However, the impact of TMP on the inner ear and central auditory system is not fully understood. We aimed to analyze the effect of blast-induced TMP on the auditory pathophysiological changes in mice after blast exposure. Mice aged 7 weeks were exposed to blast overpressure to induce TMP and allowed to survive for 2 months. All TMP cases had spontaneously healed by week 3 following the blast exposure. Compared to controls, blast-exposed mice exhibited a significant elevation in hearing thresholds and an apparent disruption of stereocilia in the outer hair cells, regardless of the occurrence or absence of TMP. The reduction in synapses in the inner hair cells, which is known as the most frequent pathology in blast-exposed cochleae, was significantly more severe in mice without TMP. However, a decrease in the number of excitatory central synapses labeled by VGLUT-1 in the cochlear nucleus was observed regardless of the absence or presence of TMP. Our findings suggest that blast-induced TMP mitigates peripheral cochlear synaptic disruption but leaves the central auditory synapses unaffected, indicating that central synaptic disruption is independent of TMP and peripheral cochlear synaptic disruption. Synaptic deterioration in the peripheral and central auditory systems can contribute to the promotion of blast-induced hearing impairment, including abnormal auditory perception.

A pathogenic deletion in Forkhead Box L1 (FOXL1) identifies the first otosclerosis (OTSC) gene

Otosclerosis is a bone disorder of the otic capsule and common form of late-onset hearing impairment. Considered a complex disease, little is known about its pathogenesis. Over the past 20 years, ten autosomal dominant loci (OTSC1-10) have been mapped but no genes identified. Herein, we map a new OTSC locus to a 9.96 Mb region within the FOX gene cluster on 16q24.1 and identify a 15 bp coding deletion in Forkhead Box L1 co-segregating with otosclerosis in a Caucasian family. Pre-operative phenotype ranges from moderate to severe hearing loss to profound sensorineural loss requiring a cochlear implant. Mutant FOXL1 is both transcribed and translated and correctly locates to the cell nucleus. However, the deletion of 5 residues in the C-terminus of mutant FOXL1 causes a complete loss of transcriptional activity due to loss of secondary (alpha helix) structure. FOXL1 (rs764026385) was identified in a second unrelated case on a shared background. We conclude that FOXL1 (rs764026385) is pathogenic and causes autosomal dominant otosclerosis and propose a key inhibitory role for wildtype Foxl1 in bone remodelling in the otic capsule. New insights into the molecular pathology of otosclerosis from this study provide molecular targets for non-invasive therapeutic interventions.

Brain microstructural changes in mice persist in adulthood and are modulated by the palmitoyl acyltransferase ZDHHC7

For a long time, mice have been classified as adults with completely mature brains at 8 weeks of age, but recent research suggests that developmental brain changes occur for up to 6 months. In particular, adolescence coincides with dramatic changes of neuronal structure and function in the brain that influence the connectivity between areas like hippocampus and medial prefrontal cortex (mPFC). Neuronal development and plasticity are regulated in part by the palmitoyl acyltransferase ZDHHC7, which modulates structural connectivity between hippocampus and mPFC. The aim of the current study was to investigate whether developmental changes take place in hippocampus and mPFC microstructure even after 8 weeks of age and whether deficiency of ZDHHC7 impacts such age-dependent alterations. Altogether, 46 mice at 11, 14 or 17 weeks of age with a genetic Zdhhc7 knockout (KO) or wild type (WT) were analysed with neuroimaging and diffusion tensor-based fibre tractography. The hippocampus and mPFC regions were compared regarding fibre metrics, supplemented by volumetric and immunohistological analyses of the hippocampus. In WT animals, we identified age-dependent changes in hippocampal fibre lengths that followed a U-shaped pattern, whereas in mPFC, changes were linear. In Zdhhc7-deficient animals, the fibre statistics were reduced in both regions, whereas the hippocampus volume and the intensities of myelin and neurofilament were higher in 11-week-old KO mice compared to WTs. Our results confirmed ongoing changes of microstructure in mice up to 17 weeks old and demonstrate that deleting the Zdhhc7 gene impairs fibre development, suggesting that palmitoylation is important in this process.

Osteoporosis, bisphosphonate use, and risk of moderate or worse hearing loss in women

BACKGROUND

Osteoporosis and low bone density (LBD) may be associated with higher risk of hearing loss, but findings are inconsistent and longitudinal data are scarce. Bisphosphonates may influence risk, but the relation has not been studied in humans. We longitudinally investigated associations of osteoporosis and LBD, bisphosphonate use, vertebral fracture (VF), hip fracture (HF), and risk of self-reported moderate or worse hearing loss.

DESIGN

Longitudinal cohort study.

SETTING

The Nurses' Health Study (NHS) (1982-2016) and Nurses' Health Study II (NHS II) (1995-2017).

PARTICIPANTS

Participants included 60,821 NHS women, aged 36-61 years at baseline, and 83,078 NHS II women, aged 31-48 years at baseline (total n = 143,899).

MEASUREMENTS

Information on osteoporosis, LBD, bisphosphonate use, VF, HF, and hearing status was obtained from validated biennial questionnaires. In a subcohort (n = 3749), objective hearing thresholds were obtained by audiometry. Multivariable-adjusted Cox proportional hazards models were used to examine independent associations between osteoporosis (NHS), osteoporosis/LBD (NHS II), and risk of hearing loss.

RESULTS

The multivariable-adjusted relative risk (MVRR, 95% confidence interval) of moderate or worse hearing loss was higher among women with osteoporosis or LBD in both cohorts. In NHS, compared with women without osteoporosis, the MVRR was 1.14 (1.09, 1.19) among women with osteoporosis; in NHS II, the MVRR was 1.30 (1.21, 1.40) among women with osteoporosis/LBD. The magnitude of the elevated risk was similar among women who did and did not use bisphosphonates. VF was associated with higher risk (NHS: 1.31 [1.16, 1.49]; NHS II: 1.39 [1.13, 1.71]), but HF was not (NHS: 1.00 [0.86, 1.16];NHS II: 1.15 [0.75,1.74]). Among participants with audiometric measurements, compared with women without osteoporosis/LBD, the mean multivariable-adjusted hearing thresholds were higher (i.e., worse) among those with osteoporosis/LBD who used bisphosphonates.

CONCLUSION

Osteoporosis and LBD may be important contributors to aging-related hearing loss. Among women with osteoporosis, the risk of hearing loss was not influenced by bisphosphonate use.

Postnatal expression and possible function of RANK and RANKL in the murine inner ear

The bone encasing the inner ear, known as the otic capsule, is unique because it remodels little postnatally compared to other bones in the body. Previous studies established that osteoprotegerin (OPG) in the inner ear inhibits otic capsule remodeling. OPG acts as a decoy receptor of receptor activator of nuclear factor κB ligand (RANKL) to disrupt the interaction between RANKL and RANK, the primary regulators of bone metabolism. Here we studied the expression and function of RANK and RANKL in the murine cochlea. Using a combination of in situ hybridization, real-time quantitative RT-PCR, and western blot, we demonstrate that Rankl and Rank genes and their protein products are expressed in the intracochlear soft tissues and the otic capsule in a developmentally regulated manner. Using a culture of neonatal murine cochlear neurons, we show that the interaction between RANK and RANKL inhibits neurite outgrowth in these neurons, and is associated with upregulation of NOGO-A expression. Taken together, our results suggest that, in addition to regulating otic capsule bone remodeling, RANK and RANKL expressed by intracochlear soft tissues may also regulate spiral ganglion neuron function by affecting neurite outgrowth.

CCDC154 Mutant Caused Abnormal Remodeling of the Otic Capsule and Hearing Loss in Mice

Osteopetrosis is a rare inherited bone disease characterized by dysfunction of osteoclasts, causing impaired bone resorption and remodeling, which ultimately leads to increased bone mass and density. Hearing loss is one of the most common complications of osteopetrosis. However, the etiology and pathogenesis of auditory damage still need to be explored. In this study, we found that a spontaneous mutation of coiled-coil domain-containing 154 (CCDC154) gene, a new osteopetrosis-related gene, induced congenital deafness in mice. Homozygous mutant mice showed moderate to severe hearing loss, while heterozygous or wild-type (WT) littermates displayed normal hearing. Pathological observation showed that abnormal bony remodeling of the otic capsule, characterized by increased vascularization and multiple cavitary lesions, was found in homozygous mutant mice. Normal structure of the organ of Corti and no substantial hair cell or spiral ganglion neuron loss was observed in homozygous mutant mice. Our results indicate that mutation of the osteopetrosis-related gene CCDC154 can induce syndromic hereditary deafness in mice. Bony remodeling disorders of the auditory ossicles and otic capsule are involved in the hearing loss caused by CDCC154 mutation.

ENT Manifestations of Celiac Disease: A Scholarly Review

OBJECTIVES

Celiac disease is a common multisystemic autoimmune disorder. It is now increasingly recognized that it may present with extraintestinal manifestations which contribute to the difficulty in its diagnosis. The objective of this scholarly review was to examine the extraintestinal ENT manifestations of celiac disease and its pathophysiology and management, in order to highlight that some patients with celiac disease may present initially to the otolaryngologist. Improving awareness of celiac disease among otolaryngologists may aid in the correct diagnosis and correct management plan.

METHODS

A literature review was conducted using the PubMed database to identify original articles related to celiac disease and ENT manifestations between the years 2000 and 2020. The search was performed using the search string: ("coeliac disease" OR "celiac disease") AND ("ENT manifestations" OR "hearing loss" OR "epistaxis" OR "nasal septal perforation" OR "obstructive sleep apnoea" OR "vertigo" OR "tonsillitis" OR "sinusitis"). Only articles written in English were reviewed.

RESULTS

A total of 17 papers met the inclusion criteria. Extraintestinal ENT manifestations of celiac disease include sensorineural hearing loss, obstructive sleep apnea, nasal septal perforation, epistaxis, and vertigo with nystagmus. Sensorineural hearing loss, obstructive sleep apnea, nasal septal perforation, vertigo, and nystagmus are thought to result from immunologically mediated mechanisms, with intestinal malabsorption resulting in epistaxis.

CONCLUSIONS

Celiac disease can cause extraintestinal ENT manifestations and requires a high index of suspicion from the otolaryngologist to diagnose and suitably manage. A gluten-free diet may result in sufficient symptom resolution for most manifestations. Sensorineural hearing loss due to celiac disease appears to be progressive and permanent and may require frequent audiological monitoring.

Identifying three otopathologies in humans

OBJECTIVES

Hearing-in-noise (HIN) is a primary complaint of both the hearing impaired and the hearing aid user. Both auditory nerve (AN) function and outer hair cell (OHC) function are thought to contribute to HIN, but their relative contributions are still being elucidated. OHCs play a critical role in HIN by fine tuning the motion of the basilar membrane. Further, animal studies suggest that cochlear (auditory) synaptopathy, which is the loss of synaptic contact between hair cells and the AN, may be another cause of HIN difficulty. While there is evidence that cochlear synaptopathy occurs in animal models, there is debate as to whether cochlear synaptopathy is clinically significant in humans, which may be due to disparate methods of measuring noise exposure in humans and our high variability in susceptibility to noise damage. Rather than use self-reported noise exposure to define synaptopathic groups, this paper assumes that the general population exhibits a range of noise exposures and resulting otopathologies and defines cochlear synaptopathy "operationally" as low CAP amplitude accompanied by normal DPOAE levels in persons with low pure tone averages. The first question is whether the standard audiogram detects AN dysfunction and OHC dysfunction? The second question is whether HIN performance is primarily dependent on AN function, OHC function, or both functions?

DESIGN

Adult subjects have been recruited to participate in an ongoing study and variables such as age, self-reported gender, pure tone audiometry (0.25-20 kHz), subjective perception of HIN difficulty, Quick Speech-in Noise (QuickSIN) test, 45% time compressed word recognition (WR) in 10% reverberation and WR in the presence of ipsilateral speech-weighted noise have been collected. These variables were correlated with OHC function measured by distortion-product otoacoustic emission (DPOAE) signal to-noise-ratio (SNR), and AN function measured by compound action potential (CAP) peak amplitude and ratio to summating potential measured using electrocochleography.

RESULTS

Synaptopathy, by this operational definition, may be present in as many as 30% of individuals with normal hearing. Persons hearing within normal limits may exhibit HIN difficulties, and persons with hearing within normal limits may exhibit two distinct types of otopathologies undetected by the standard audiogram (a.k.a. hidden hearing loss) namely operational cochlear synaptopathy and OHC dysfunction. AN untuning secondary to OHC dysfunction is a third otopathology that occurs in subjects with a Mild-Moderate sensorineural hearing loss (SNHL). Clinical norms for each of these otopathologies are presented. Finally, the data show that operational cochlear synaptopathy does not correlate with HIN dysfunction. Rather, HIN performance is primarily governed by OHC function, while AN untuning also plays a lesser but statistically significant role.

CONCLUSIONS

The results of this study suggest the following: (1) persons hearing within normal limits may exhibit HIN difficulties; (2) persons hearing within normal limits may exhibit undetected otopathologies, namely AN dysfunction and OHC dysfunction; (3) AN untuning secondary to OHC dysfunction occurs in subjects with Mild-Moderate SNHL; (4) HIN performance is primarily governed by OHC function rather than AN function.

Regeneration of Cochlear Synapses by Systemic Administration of a Bisphosphonate

Sensorineural hearing loss (SNHL) caused by noise exposure and attendant loss of glutamatergic synapses between cochlear spiral ganglion neurons (SGNs) and hair cells is the most common sensory deficit worldwide. We show here that systemic administration of a bisphosphonate to mice 24 h after synaptopathic noise exposure regenerated synapses between inner hair cells and SGNs and restored cochlear function. We further demonstrate that this effect is mediated by inhibition of the mevalonate pathway. These results are highly significant because they suggest that bisphosphonates could reverse cochlear synaptopathy for the treatment of SNHL.

Evolutionary Basis of High-Frequency Hearing in the Cochleae of Echolocators Revealed by Comparative Genomics

High-frequency hearing is important for the survival of both echolocating bats and whales, but our understanding of its genetic basis is scattered and segmented. In this study, we combined RNA-Seq and comparative genomic analyses to obtain insights into the comprehensive gene expression profile of the cochlea and the adaptive evolution of hearing-related genes. A total of 144 genes were found to have been under positive selection in various species of echolocating bats and toothed whales, 34 of which were identified to be related to hearing behavior or auditory processes. Subsequently, multiple physiological processes associated with those genes were found to have adaptively evolved in echolocating bats and toothed whales, including cochlear bony development, antioxidant activity, ion balance, and homeostatic processes, along with signal transduction. In addition, abundant convergent/parallel genes and sites were detected between different pairs of echolocator species; however, no specific hearing-related physiological pathways were enriched by them and almost all of the convergent/parallel signals were selectively neutral, as previously reported. Notably, two adaptive parallel evolved sites in TECPR2 were shown to have been under positive selection, indicating their functional importance for the evolution of echolocation and high-frequency hearing in laryngeal echolocating bats. This study deepens our understanding of the genetic bases underlying high-frequency hearing in the cochlea of echolocating bats and toothed whales.

Increased Risk of Sudden Sensory Neural Hearing Loss in Osteoporosis: A Longitudinal Follow-Up Study

CONTEXT

The results of a previous population cohort study suggested an association between osteoporosis and sudden sensory neural hearing loss (SSNHL).

OBJECTIVES

To use a nationwide cohort in the Korean population to investigate the risk of SSNHL in patients with osteoporosis.

DESIGN, SETTING, AND PARTICIPANTS

Data entered from 2002 to 2013 were collected from the Korean National Health Insurance Service-National Sample Cohort. A total of 68,241 patients with osteoporosis aged ≥50 years were matched with 68,241 control individuals. The crude (simple) and adjusted hazard ratios (HRs) of SSNHL in those with osteoporosis were analyzed using the Cox proportional hazard model. A subgroup analysis was performed according to age and sex.

RESULTS

The risk of SSNHL was greater in the osteoporosis group than in the control group (adjusted HR, 1.56; 95% CI, 1.37 to 1.78; P < 0.001). The risk of SSNHL in those with osteoporosis was greater in patients aged <60 years, regardless of sex. Women aged ≥60 years had a higher HR for SSNHL in the presence of osteoporosis (women aged 60 to 69 years: adjusted HR, 1.67; 95% CI, 1.34 to 2.08; P < 0.001; women aged ≥70 years: adjusted HR, 1.90; 95% CI, 1.29 to 2.79; P < 0.001).

CONCLUSIONS

The risk of SSNHL was greater for patients with osteoporosis aged ≥50 years. Middle-age adults, as well as the elderly, are at an increased risk of SSNHL in the presence of osteoporosis.

Loss of the Hematopoietic Stem Cell Factor GATA2 in the Osteogenic Lineage Impairs Trabecularization and Mechanical Strength of Bone

The transcription factor GATA2 is required for expansion and differentiation of hematopoietic stem cells (HSCs). In mesenchymal stem cells (MSCs), GATA2 blocks adipogenesis, but its biological relevance and underlying genomic events are unknown. We report a dual function of GATA2 in bone homeostasis. GATA2 in MSCs binds near genes involved in skeletal system development and colocalizes with motifs for FOX and HOX transcription factors, known regulators of skeletal development. Ectopic GATA2 blocks osteoblastogenesis by interfering with SMAD1/5/8 activation. MSC-specific deletion of GATA2 in mice increases the numbers and differentiation capacity of bone-derived precursors, resulting in elevated bone formation. Surprisingly, MSC-specific GATA2 deficiency impairs the trabecularization and mechanical strength of bone, involving reduced MSC expression of the osteoclast inhibitor osteoprotegerin and increased osteoclast numbers. Thus, GATA2 affects bone turnover via MSC-autonomous and indirect effects. By regulating bone trabecularization, GATA2 expression in the osteogenic lineage may contribute to the anatomical and cellular microenvironment of the HSC niche required for hematopoiesis.

Juvenile Paget disease

Juvenile Paget disease (JPD) is a rare disorder, mainly caused by mutations in the gene TNFRSF11B that encodes osteoprotegerin (OPG). Loss of OPG action causes generalized, extremely rapid bone turnover. The clinical manifestations are both skeletal - progressive skeletal deformity that develops in childhood - and extra-skeletal, including hearing loss, retinopathy, vascular calcification and internal carotid artery aneurysm formation. The severity of the phenotype seems to be related to the severity of TNFRSF11B gene deactivation. JPD is characterized biochemically by very high alkaline phosphatase activity, as well as other bone turnover markers. Bisphosphonates are commonly used to reduce the greatly accelerated bone turnover and can ameliorate the skeletal phenotype, if started early enough in childhood and continued at least until growth is complete. Limited evidence from patients treated with recombinant OPG or denosumab also provided favorable results. Recombinant OPG would represent a replacement treatment, but it is unavailable for clinical use. It seems that life-long treatment with anti-resorptives is required, since the disease is reactivated after treatment discontinuation. An international collaborating network for the continuous registration and follow-up of JPD patients could be helpful in the future.

Bisphosphonate-Linked TrkB Agonist: Cochlea-Targeted Delivery of a Neurotrophic Agent as a Strategy for the Treatment of Hearing Loss

Hearing loss affects more than two-thirds of the elderly population, and more than 17% of all adults in the U.S. Sensorineural hearing loss related to noise exposure or aging is associated with loss of inner ear sensory hair cells (HCs), cochlear spiral ganglion neurons (SGNs), and ribbon synapses between HCs and SGNs, stimulating intense interest in therapies to regenerate synaptic function. 7,8-Dihydroxyflavone (DHF) is a selective and potent agonist of tropomyosin receptor kinase B (TrkB) and protects the neuron from apoptosis. Despite evidence that TrkB agonists can promote survival of SGNs, local delivery of drugs such as DHF to the inner ear remains a challenge. We previously demonstrated in an animal model that a fluorescently labeled bisphosphonate, 6-FAM-Zol, administered to the round window membrane penetrated the membrane and diffused throughout the cochlea. Given their affinity for bone mineral, including cochlear bone, bisphosphonates offer an intriguing modality for targeted delivery of neurotrophic agents to the SGNs to promote survival, neurite outgrowth, and, potentially, regeneration of synapses between HCs and SGNs. The design and synthesis of a bisphosphonate conjugate of DHF (Ris-DHF) is presented, with a preliminary evaluation of its neurotrophic activity. Ris-DHF increases neurite outgrowth in vitro, maintains this ability after binding to hydroxyapatite, and regenerates synapses in kainic acid-damaged cochlear organ of Corti explants dissected in vitro with attached SGNs. The results suggest that bisphosphonate-TrkB agonist conjugates have promise as a novel approach to targeted delivery of drugs to treat sensorineural hearing loss.

Third-generation bisphosphonates for cochlear otosclerosis stabilizes sensorineural hearing loss in long-term follow-up

Objective

To assess long‐term hearing outcomes in patients treated with third‐generation bisphosphonates for otosclerosis‐related progressive sensorineural hearing loss (SNHL).

Study Design

Retrospective case series review

Methods

We performed a retrospective case series review of patients with otosclerosis and progressive SNHL. Patients were treated with either risedronate or zoledronate after a diagnosis of otosclerosis with a significant SNHL component. Bone conduction pure tone threshold averages (BC‐PTAs) and word recognition scores (WRS) before and after bisphosphonate administration in long‐term follow‐up was analyzed. Significant change in BC‐PTA was defined as greater than 10dB or between 4% and 18% in WRS based on binomial variance.

Results

Seven patients were identified and 14 ears met inclusion criteria. Three patients were female and the mean age was 48.3 ± 10.3 years. The mean duration between treatment with bisphosphonate administration and long‐term post‐treatment follow‐up audiometry was 87.6 ± 18.3 months, with a range of 61.6 to 109.1 months and median of 89.2 months. Analysis using BC‐PTA and WRS demonstrated that 11 ears remained stable while 2 improved and 1 worsened. No patient experienced any major complication as the result of bisphosphonate therapy.

Conclusion

Treatment with third‐generation bisphosphonates is associated with stability in otosclerosis‐related sensorineural hearing over 5‐ to 9‐year period. These results suggest that such medications may prevent the progression of SNHL in patients with otosclerosis.

Level of Evidence

4 (Case series).

Long-term Incidence and Degree of Sensorineural Hearing Loss in Otosclerosis

OBJECTIVES

1) To evaluate the long-term incidence and degree of the sensorineural component of hearing loss (SNHL) in patients with otosclerosis after accounting for expected age-related hearing loss. 2) To identify variables that might predict development of sensorineural hearing loss due to otosclerosis.

STUDY DESIGN

Retrospective audiometric database and chart review.

SETTING

Tertiary referral center.

PATIENTS

Consecutive patients with otosclerosis observed between 1994 and 2004, with ≥10 years follow-up, excluding patients with postoperative hearing loss or surgery before the initial audiogram.

INTERVENTION

Bone conduction (BC) thresholds at 0.5, 1, 2, and 4 kHz and Word Recognition.

MAIN OUTCOME MEASURE

BC threshold change (BCTC) over ≥10 years minus estimated age-related threshold change (ARTC) specific to age and sex for each patient (based on ISO 7029 reference population).

RESULTS

Three-hundred fifty-seven ears (290 patients) met study criteria, including 217 ears that had undergone stapedectomy during the study period. Mean follow-up was 14.0 years. The average BCTC after subtracting estimated ARTC was 4.6, 2.6, 3, and 2.7 dB for 0.5, 1, 2, and 4 kHz frequencies, respectively. However, 34% of ears (122 ears) had clinically significant progression of SNHL during the study period (>10 dB BCTC beyond expected ARTC at ≥2 frequencies). Multivariate analysis demonstrated that the probability of developing clinically significant SNHL was higher for women (odds ratio 1.86, p = 0.018) and lower for operated patients (odds ratio 0.46, p = 0.002).

CONCLUSION

The average long-term sensorineural hearing loss due to otosclerosis was statistically significantly more than for age alone at each frequency, but these average values (from 2.6 to 4.6 dB for tested frequencies) were clinically insignificant. Approximately one-third of patients with otosclerosis demonstrated a clinically significant progression of the sensorineural component of hearing loss, with the average BCTC above expected age-related changes ranging from 10.2 to 14.6 dB for tested frequencies among this subgroup.

Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

While there have been remarkable advances in hearing research over the past few decades, there is still no cure for Sensorineural Hearing Loss (SNHL), a condition that typically involves damage to or loss of the delicate mechanosensory structures of the inner ear. Sophisticated in vitro and ex vivo assays have emerged in recent years, enabling the screening of an increasing number of potentially therapeutic compounds while minimizing resources and accelerating efforts to develop cures for SNHL. Though homogenous cultures of certain cell types continue to play an important role in current research, many scientists now rely on more complex organotypic cultures of murine inner ears, also known as cochlear explants. The preservation of organized cellular structures within the inner ear facilitates the in situ evaluation of various components of the cochlear infrastructure, including inner and outer hair cells, spiral ganglion neurons, neurites, and supporting cells. Here we present the preparation, culture, treatment, and immunostaining of neonatal murine cochlear explants. The careful preparation of these explants facilitates the identification of mechanisms that contribute to SNHL and constitutes a valuable tool for the hearing research community.

Loss of Functional Osteoprotegerin: More Than a Skeletal Problem

INTRODUCTION

Juvenile Paget's disease (JPD), an ultra-rare, debilitating bone disease due to loss of functional osteoprotegerin (OPG), is caused by recessive mutations in TNFRFSF11B. A genotype-phenotype correlation spanning from mild to very severe forms is described.

AIM

This study aimed to describe the complexity of the human phenotype of OPG deficiency in more detail and to investigate heterozygous mutation carriers for clinical signs of JPD.

PATIENTS

We investigated 3 children with JPD from families of Turkish, German, and Pakistani descent and 19 family members (14 heterozygous).

RESULTS

A new disease-causing 4 bp-duplication in exon 1 was detected in the German patient, and a microdeletion including TNFRFSF11B in the Pakistani patient. Skeletal abnormalities in all affected children included bowing deformities and fractures, contractures, short stature and skull involvement. Complex malformation of the inner ear and vestibular structures (2 patients) resulted in early deafness. Patients were found to be growth hormone deficient (2), displayed nephrocalcinosis (1), and gross motor (3) and mental (1) retardation. Heterozygous family members displayed low OPG levels (12), elevated bone turnover markers (7), and osteopenia (6). Short stature (1), visual impairment (2), and hearing impairment (1) were also present.

CONCLUSION

Diminished OPG levels cause complex changes affecting multiple organ systems, including pituitary function, in children with JPD and may cause osteopenia in heterozygous family members. Diagnostic and therapeutic measures should aim to address the complex phenotype.

Parallel mechanisms suppress cochlear bone remodeling to protect hearing

Bone remodeling, a combination of bone resorption and formation, requires precise regulation of cellular and molecular signaling to maintain proper bone quality. Whereas osteoblasts deposit and osteoclasts resorb bone matrix, osteocytes both dynamically resorb and replace perilacunar bone matrix. Osteocytes secrete proteases like matrix metalloproteinase-13 (MMP13) to maintain the material quality of bone matrix through perilacunar remodeling (PLR). Deregulated bone remodeling impairs bone quality and can compromise hearing since the auditory transduction mechanism is within bone. Understanding the mechanisms regulating cochlear bone provides unique ways to assess bone quality independent of other aspects that contribute to bone mechanical behavior. Cochlear bone is singular in its regulation of remodeling by expressing high levels of osteoprotegerin. Since cochlear bone expresses a key PLR enzyme, MMP13, we examined whether cochlear bone relies on, or is protected from, osteocyte-mediated PLR to maintain hearing and bone quality using a mouse model lacking MMP13 (MMP13(-/-)). We investigated the canalicular network, collagen organization, lacunar volume via micro-computed tomography, and dynamic histomorphometry. Despite finding defects in these hallmarks of PLR in MMP13(-/-) long bones, cochlear bone revealed no differences in these markers, nor hearing loss as measured by auditory brainstem response (ABR) or distortion product oto-acoustic emissions (DPOAEs), between wild type and MMP13(-/-) mice. Dynamic histomorphometry revealed abundant PLR by tibial osteocytes, but near absence in cochlear bone. Cochlear suppression of PLR corresponds to repression of several key PLR genes in the cochlea relative to long bones. These data suggest that cochlear bone uniquely maintains bone quality and hearing independent of MMP13-mediated osteocytic PLR. Furthermore, the cochlea employs parallel mechanisms to inhibit remodeling by osteoclasts and osteoblasts, and by osteocytes, to protect hearing. Understanding the cellular and molecular mechanisms that confer site-specific control of bone remodeling has the potential to elucidate new pathways that are deregulated in skeletal disease.

Extracellular vesicles derived from human vestibular schwannomas associated with poor hearing damage cochlear cells

BACKGROUND

Vestibular schwannoma (VS) is a tumor of the vestibular nerve that transmits balance information from the inner ear to the brain. Sensorineural hearing loss occurs in 95% of patients with these tumors, but the cause of this loss is not well understood. We posit a role of VS-secreted extracellular vesicles (EVs) as a major contributing factor in cochlear nerve damage.

METHODS

Using differential centrifugation, we isolated EVs from VS cell line HEI-193 and primary cultured human VS cells from patients with good hearing or poor hearing. The EVs were characterized using a Nanosight device and transmission electron microscopy and by extracting their RNA content. The EVs' effects on cultured murine spiral ganglion cells and organotypic cochlear cultures were studied using a transwell dual-culture system and by direct labeling of EVs with PKH-67 dye. EV-induced changes in cochlear cells were quantified using confocal immunohistochemistry. Transfection of VS cells with a green fluorescent protein-containing plasmid was confirmed with reverse transcription PCR.

RESULTS

Human VS cells, from patients with poor hearing, produced EVs that could damage both cultured murine cochlear sensory cells and neurons. In contrast, EVs derived from VS cells from patients with good hearing did not damage the cultured cochlear cells.

CONCLUSIONS

This is the first report on EVs derived from VSs and on the capacity of EVs from VSs from patients with hearing loss to selectively damage cochlear cells, thereby identifying a potential novel mechanism of VS-associated sensorineural hearing loss.

Hepatocyte nuclear factor-4 alpha in noise-induced cochlear neuropathy

Noise-induced hearing loss (NIHL) is a problem of profound clinical significance and growing magnitude. Alarmingly, even moderate noise levels, previously assumed to cause only temporary shifts in auditory thresholds ("temporary" NIHL), are now known to cause cochlear synaptopathy and subsequent neuropathy. To uncover molecular mechanisms of this neuropathy, a network analysis of genes reported to have significantly altered expression after temporary threshold shift-inducing noise exposure was performed. The transcription factor Hepatocyte Nuclear Factor-4 alpha (HNF4α), which had not previously been studied in the context of cochlear response to noise, was identified as a hub of a top-ranking network. Hnf4α expression and localization using quantitative RT-PCR and in situ hybridization, respectively, were described in adolescent and adult mice exposed to neuropathic noise levels in adolescence. Isoforms α3 and α12 in the cochlea were also identified. At every age examined, Hnf4α mRNA expression in the cochlear apex was similar to expression in the base. Hnf4α expression was evident in select cochlear cells, including spiral ganglion neurons (SGNs) and hair cells, and was significantly upregulated from 6 to 70 weeks of age, especially in SGNs. This age-related Hnf4α upregulation was inhibited by neuropathic noise exposure in adolescence. Hnf4α silencing with shRNA transfection into auditory neuroblast cells (VOT-33) reduced cell viability, as measured with the MTT assay, suggesting that Hnf4α may be involved in SGN survival. Our results motivate future studies of HNF4α in cochlear pathophysiology, especially because HNF4α mutations and polymorphisms are associated with human diseases that may include hearing loss. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1374-1386, 2016.

Xenograft of human umbilical mesenchymal stem cells from Wharton's jelly as a potential therapy for rat pilocarpine-induced epilepsy

We evaluated the effects of intra-hippocampal transplantation of human umbilical mesenchymal stem cells (HUMSCs) on pilocarpine-treated rats. Sprague-Dawley rats were divided into the following three groups: (1) a normal group of rats receiving only PBS, (2) a status epilepticus (SE) group of rats with pilocarpine-induced SE and PBS injected into the hippocampi, and (3) a SE+HUMSC group of SE rats with HUMSC transplantation. Spontaneous recurrent motor seizures (SRMS) were monitored using simultaneous video and electroencephalographic recordings at two to four weeks after SE induction. The results showed that the number of SRMS within two to four weeks after SE was significantly decreased in SE+HUMSCs rats compared with SE rats. All of the rats were sacrificed on Day 29 after SE. Hippocampal morphology and volume were evaluated using Nissl staining and magnetic resonance imaging. The results showed that the volume of the dorsal hippocampus was smaller in SE rats compared with normal and SE+HUMSCs rats. The pyramidal neuron loss in CA1 and CA3 regions was more severe in the SE rats than in normal and SE+HUMSCs rats. No significant differences were found in the hippocampal neuronal loss or in the number of dentate GABAergic neurons between normal and SE+HUMSCs rats. Compared with the SE rats, the SE+HUMSCs rats exhibited a suppression of astrocyte activity and aberrant mossy fiber sprouting. Implanted HUMSCs survived in the hippocampus and released cytokines, including FGF-6, amphiregulin, glucocorticoid-induced tumor necrosis factors receptor (GITR), MIP-3β, and osteoprotegerin. In an in vitro study, exposure of cortical neurons to glutamate showed a significant decrease in cell viability, which was preventable by co-culturing with HUMSCs. Above all, the expression of human osteoprotegerin and amphiregulin were significantly increased in the media of the co-culture of neurons and HUMSCs. Our results demonstrate the therapeutic benefits of HUMSC transplantation for the development of epilepsy, which are likely due to the ability of the cells to produce neuroprotective and anti-inflammatory cytokines. Thus, HUMSC transplantation may be an effective therapy in the future.

Activation of TRAIL-DR5 pathway promotes sensorineural degeneration in the inner ear

Tumor necrosis factor (TNF) family cytokines are important mediators of inflammation. Elevated levels of serum TNF‐α are associated with human sensorineural hearing loss via poorly understood mechanisms. We demonstrate, for the first time, expression of TNF‐related apoptosis‐inducing ligand (TRAIL) and its signaling death receptor 5 (DR5) in the murine inner ear and show that exogenous TRAIL can trigger hair cell and neuronal degeneration, which can be partly prevented with DR5‐blocking antibodies.

Transactivation of human osteoprotegerin promoter by GATA-3

Osteoprotegerin (OPG) is a key regulator of bone remodeling. Mutations in OPG are involved in a variety of human diseases. We have shown that cochlear spiral ganglion cells secrete OPG at high levels and lack of OPG causes sensorineural hearing loss in addition to the previously described conductive hearing loss. In order to study the regulation of OPG expression, we conducted a database search on regulatory elements in the promoter region of the OPG gene, and identified two potential GATA-3 binding sites. Using luciferase assays and site directed mutagenesis, we demonstrate that these two elements are GATA-3 responsive and support GATA-3 transactivation in human HEK and HeLa cells. The expression of wild type GATA-3 activated OPG mRNA and protein expression, while the expression of a dominant negative mutant of GATA-3 or a GATA-3 shRNA construct reduced OPG mRNA and protein levels. GATA-3 deficient cells generated by expressing a GATA-3 shRNA construct were sensitive to apoptosis induced by etoposide and TNF-α. This apoptotic effect could be partly prevented by the co-treatment with exogenous OPG. Our results suggest new approaches to rescue diseases due to GATA-3 deficiency – such as in hypoparathyroidism, sensorineural deafness, and renal (HDR) syndrome – by OPG therapy.

Disrupted bone remodeling leads to cochlear overgrowth and hearing loss in a mouse model of fibrous dysplasia

Normal hearing requires exquisite cooperation between bony and sensorineural structures within the cochlea. For example, the inner ear secretes proteins such as osteoprotegrin (OPG) that can prevent cochlear bone remodeling. Accordingly, diseases that affect bone regulation can also result in hearing loss. Patients with fibrous dysplasia develop trabecular bone overgrowth resulting in hearing loss if the lesions affect the temporal bones. Unfortunately, the mechanisms responsible for this hearing loss, which could be sensorineural and/or conductive, remain unclear. In this study, we used a unique transgenic mouse model of increased G_s G-protein coupled receptor (GPCR) signaling induced by expression of an engineered receptor, Rs1, in osteoblastic cells. These ColI(2.3)⁺/Rs1⁺ mice showed dramatic bone lesions that histologically and radiologically resembled fibrous dysplasia. We found that ColI(2.3)⁺/Rs1⁺ mice showed progressive and severe conductive hearing loss. Ossicular chain impingement increased with the size and number of dysplastic lesions. While sensorineural structures were unaffected, ColI(2.3)⁺/Rs1⁺ cochleae had abnormally high osteoclast activity, together with elevated tartrate resistant acid phosphatase (TRAP) activity and receptor activator of nuclear factor kappa-B ligand (Rankl) mRNA expression. ColI(2.3)⁺/Rs1⁺ cochleae also showed decreased expression of Sclerostin (Sost), an antagonist of the Wnt signaling pathway that normally increases bone formation. The osteocyte canalicular networks of ColI(2.3)⁺/Rs1⁺ cochleae were disrupted and showed abnormal osteocyte morphology. The osteocytes in the ColI(2.3)⁺/Rs1⁺ cochleae showed increased expression of matrix metalloproteinase 13 (MMP-13) and TRAP, both of which can support osteocyte-mediated peri-lacunar remodeling. Thus, while the ossicular chain impingement is sufficient to account for the progressive hearing loss in fibrous dysplasia, the deregulation of bone remodeling extends to the cochlea as well. Our findings suggest that factors regulating bone remodeling, including peri-lacunar remodeling by osteocytes, may be useful targets for treating the bony overgrowths and hearing changes of fibrous dysplasia and other bony pathologies.