Matrix recruitment and calcium sequestration for spatial specific otoconia development

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Cross-species analysis and comparison of the inner ear between chickens and mice

The inner ear of mammals includes the cochlea and vestibule, which house specialized hair cells that are responsible for hearing and balance, respectively. While cochlear hair cells fail to regenerate following damage, those of the utricle, which is part of the vestibular apparatus, show partial regeneration. In birds, the macula lagena, a unique ear structure in this clade, has the ability to regenerate hair cells similarly to the utricle. Many studies have sought to explain regeneration in terms of evolution and species differences. However, it remains unclear what the cellular and molecular basis is behind the differences in inner ear structures and between avians and mammals. In the present study, we first investigated the anatomical structures of the inner ear of both chickens and rodents. We then performed RNA sequencing (RNA-Seq) and made cross-species analyses of the expression of homologous genes obtained from the inner ear tissue from both chickens and mice. Finally, we focused on the lagena, the basilar papilla, and the utricle in chickens and identified differentially expressed genes between tissues and determined the expression patterns of genes involved in inner ear structure formation by single-cell RNA sequencing and bulk RNA-Seq. We concluded that the cellular and molecular composition of the lagena is more similar to that of the utricle than the cochlea. Taken together, our study provides a valuable resource for the study of inner ear evolution and development.

Correlation between serum vitamin D level and benign paroxysmal positional vertigo recurrence

OBJECTIVE

Benign paroxysmal positional vertigo (BPPV) is the most common cause of dizziness in the general population. BPPV is known to be closely related to the serum vitamin D level. This study aimed to examine the relationship between serum vitamin D levels and BPPV recurrence.

METHODS

A retrospective chart review was conducted on 50 patients diagnosed with posterior and lateral canal BPPV. The diagnosis of BPPV was based on the finding of vertigo and nystagmus induced by certain head positions (The Dix-Hallpike maneuver and head roll tests). The patients were classified into BPPV recurrence (Group A) and non-recurrence groups (Group B). Otolith function was assessed by cervical vestibular evoked myogenic potential (cVEMP) and ocular vestibular evoked myogenic potential (oVEMP), and their association with vitamin D levels was evaluated.

RESULTS

There were 19 subjects in Group A and 31 in Group B. There were no significant differences in age, sex, cVEMP, and oVEMP between the two groups. The average vitamin D level was 12.9 ± 8.0 ng/mL for Group A and 19.2 ± 8.2 ng/mL for Group B, and the difference between the groups was significant (p = 0.011). In the receiver operating characteristic curve analysis for BPPV recurrence with the best sensitivity and specificity, the optimal cut-off value of total serum vitamin D was determined as 12.74 ng/mL. Furthermore, reclassifying the patients based on the cut-off value showed a significantly higher recurrence rate in the group with a lower serum vitamin D level (70.5% vs. 22.5%, p = 0.007).

CONCLUSION

This complex finding highlights the importance of measuring serum vitamin D levels to monitor and evaluate patients at risk of BPPV recurrence.

Injectable thermosensitive chitosan/gelatin hydrogel for dental pulp stem cells proliferation and differentiation

Introduction: Biocompatible and biodegradable scaffolds based on natural polymers such as gelatin and chitosan (CS) provide suitable microenvironments in dental tissue engineering. In the present study, we report on the synthesis of injectable thermosensitive hydrogel (PNIPAAm-g-CS copolymer/gelatin hybrid hydrogel) for osteogenic differentiation of human dental pulp stem cells (hDPSCs). Methods: The CS-g-PNIPAAm was synthesized using the reaction of carboxyl terminated PNIPAAm with CS, which was then mixed with various amounts of gelatin solution in the presence of genipin as a chemical crosslinker to gain a homogenous solution. The chemical composition and microstructures of the fabricated hydrogels were confirmed by FT-IR and SEM analysis, respectively. To evaluate the mechanical properties (e.g., storage and loss modulus of the gels), the rheological analysis was considered. Calcium deposition and ALP activity of DPSCs were carried out using alizarin red staining and ALP test. While the live/dead assay was performed to study its toxicity, the real-time PCR was conducted to investigate the osteogenic differentiation of hDPSCs cultured on prepared hydrogels. Results: The hydrogels with higher gelatin incorporation showed a slightly looser network compared to the other ones. The hydrogel with less gelatin indicates a rather higher value of G', indicating a higher elasticity due to more crosslinking reaction of amine groups of CS via a covalent bond with genipin. All the hydrogels contained viable cells with negligible dead cells, indicating the high biocompatibility of the prepared hydrogels for hDPSCs. The quantitative results of alizarin red staining displayed a significant rise in calcium deposition in hDPSCs cultured on prepared hydrogels after 21 days. Further, hDPSCs cultured on hydrogel with more gelatin displayed the most ALP activity. The expression of late osteogenic genes such as OCN and BMP-2 were respectively 6 and 4 times higher on the hydrogel with more gelatin than the control group after 21 days. Conclusion: The prepared PNIPAAm-g-CS copolymer/gelatin hybrid hydrogel presented great features (e.g., porous structure, suitable rheological behavior, and improved cell viability), and resulted in osteogenic differentiation necessary for dental tissue engineering.

The heterogeneity of mammalian utricular cells over the course of development

BACKGROUND

The inner ear organ is a delicate tissue consisting of hair cells (HCs) and supporting cells (SCs).The mammalian inner ear HCs are terminally differentiated cells that cannot spontaneously regenerate in adults. Epithelial non-hair cells (ENHCs) in the utricle include HC progenitors and SCs, and the progenitors share similar characteristics with SCs in the neonatal inner ear.

METHODS

We applied single-cell sequencing to whole mouse utricles from the neonatal period to adulthood, including samples from postnatal day (P)2, P7 and P30 mice. Furthermore, using transgenic mice and immunostaining, we traced the source of new HC generation.

RESULTS

We identified several sensory epithelial cell clusters and further found that new HCs arose mainly through differentiation from Sox9+ progenitor cells and that only a few cells were produced by mitotic proliferation in both neonatal and adult mouse utricles. In addition, we identified the proliferative cells using the marker UbcH10 and demonstrated that in adulthood the mitotically generated HCs were primarily found in the extrastriola. Moreover, we observed that not only Type II, but also Type I HCs could be regenerated by either mitotic cell proliferation or progenitor cell differentiation.

CONCLUSIONS

Overall, our findings expand our understanding of ENHC cell fate and the characteristics of the vestibular organs in mammals over the course of development.

Low 25-Hydroxyvitamin D Levels Are Associated With Residual Dizziness After Successful Treatment of Benign Paroxysmal Positional Vertigo

Objective:

Vitamin D (Vit D) regulates calcium and phosphate metabolism and helps to maintain otolith organ function. Residual dizziness (RD) is one of the most common complications after the successful treatment of benign paroxysmal positional vertigo (BPPV). Various theories have been suggested to explain the cause of RD, and otolith organ disorder is the most evident cause of RD. This study aimed to investigate the association between serum levels of Vit D and the occurrence of RD after the successful treatment of BPPV.

Methods

A prospective study including patients who were diagnosed with de novo posterior semicircular canal-type BPPV (PC-BPPV) was conducted at our institution from May 2017 to May 2019. All the patients underwent canalith repositioning procedures and were followed up. Univariate and multivariate analyses were performed to investigate the relationship between serum 25-hydroxy vitamin D (25(OH)D) levels and RD occurrence after successful BPPV treatment.

Results

In total, 123 patients with PC-BPPV were enrolled, and 41.5% (51/123) experienced RD. The serum level of 25(OH)D was significantly lower in PC-BPPV patients with RD [median 16.2 ng/ml (IQR 12.9–22.1)] than in patients without RD [median 20.5 ng/ml (IQR 16.5–26.5)] (P = 0.001). In multivariate models comparing the prevalence of RD in the insufficient group [25(OH)D ≥ 20 to <30 ng/ml], deficient group [25(OH)D < 20 ng/ml] and normal group [25(OH)D ≥ 30 ng/ml], the 25(OH)D levels in the deficient group were associated with the occurrence of RD (odds ratio = 5.48, 95% confidence interval = 1.08–27.71; P = 0.04).

Conclusion

Low 25(OH)D levels are associated with the development of RD in patients with PC-BPPV after successful treatment. Further efforts to validate and elucidate the mechanism are needed.

Association of Serum Calcium and Vitamin D with Benign Paroxysmal Positional Vertigo

Introduction  Benign paroxysmal positional vertigo (BPPV) is one of the common disorders of the peripheral vestibular system. The prevalence of BPPV is found to be higher among middle-aged women.

Objectives  To estimate the serum levels of calcium and vitamin D in patients with BPPV, and to study their association.

Methods  The present is a hospital-based prospective case-control study. Venous blood samples of the 49 patients with BPPV and an equal number of age- and gender-matched individuals were recruited and submitted to an analysis of the serum levels of calcium and vitamin D.

Results  Among the cases, 67.3% were found to be females, and 32.7% were males. Most of the 30 cases (61.3%) were aged > 40 years. The mean age of the cases was 44.39 years. The mean serum level of vitamin D in the cases was of 21.26 ng/ml compared with 17.59 ng/ml in the controls. The mean serum level of calcium was of 9.33 mg/dl in the cases, compared with 8.95 mg/dl in the controls. There was no significant difference in the serum levels of vitamin D and calcium between cases and controls.

Conclusion  We could not establish any correlation between the serum levels of calcium and vitamin D with BPPV. However, a negative relationship was found between the serum levels of vitamin D and the number of episodes of BPPV ( p  = 0.012).

Whole-Genome Sequencing and Genome-Wide Studies of Spiny Head Croaker (Collichthys lucidus) Reveals Potential Insights for Well-Developed Otoliths in the Family Sciaenidae

Spiny head croaker (Collichthys lucidus), belonging to the family Sciaenidae, is a small economic fish with a main distribution in the coastal waters of Northwestern Pacific. Here, we constructed a nonredundant chromosome-level genome assembly of spiny head croaker and also made genome-wide investigations on genome evolution and gene families related to otolith development. A primary genome assembly of 811.23 Mb, with a contig N50 of 74.92 kb, was generated by a combination of 49.12-Gb Illumina clean reads and 35.24 Gb of PacBio long reads. Contigs of this draft assembly were further anchored into chromosomes by integration with additional 185.33-Gb Hi-C data, resulting in a high-quality chromosome-level genome assembly of 817.24 Mb, with an improved scaffold N50 of 26.58 Mb. Based on our phylogenetic analysis, we observed that C. lucidus is much closer to Larimichthys crocea than Miichthys miiuy. We also predicted that many gene families were significantly expanded (p-value <0.05) in spiny head croaker; among them, some are associated with "calcium signaling pathway" and potential "inner ear functions." In addition, we identified some otolith-related genes (such as otol1a that encodes Otolin-1a) with critical deletions or mutations, suggesting possible molecular mechanisms for well-developed otoliths in the family Sciaenidae.

Otoconia Structure After Short- and Long-Duration Exposure to Altered Gravity

Vertebrates use weight-lending otoconia in the inner ear otolith organs to enable detection of their translation during self or imposed movements and a change in their orientation with respect to gravity. In spaceflight, otoconia are near weightless. It has been hypothesized that otoconia undergo structural remodeling after exposure to weightlessness to restore normal sensation. A structural remodeling is reasoned to occur for hypergravity but in the opposite sense. We explored these hypotheses in several strains of mice within a Biospecimen Sharing Program in separate space- and ground-based projects. Mice were housed 90 days on the International Space Station, 13 days on two Shuttle Orbiter missions, or exposed to 90 days of hindlimb unloading or net 2.38 g via centrifugation. Corresponding flight habitat and standard cage vivarium controls were used. Utricular otoliths were visually analyzed using scanning electron microscopy and in selected samples before and after focused ion beam (FIB) milling. Results suggest a possible mass addition to the otoconia outer shell might occur after exposure to longer-duration spaceflight, but not short ones or hindlimb unloading. A destructive process is clearly seen after centrifugation: an ablation or thinning of the outer shell and cavitation of the inner core. This study provides a purely descriptive account of otoconia remodeling after exposures to altered gravity. The mechanism(s) underlying these processes must be identified and quantitatively validated to develop countermeasures to altered gravity levels during exploration missions.

Development and evolution of the vestibular apparatuses of the inner ear

The vertebrate inner ear is a labyrinthine sensory organ responsible for perceiving sound and body motion. While a great deal of research has been invested in understanding the auditory system, a growing body of work has begun to delineate the complex developmental program behind the apparatuses of the inner ear involved with vestibular function. These animal studies have helped identify genes involved in inner ear development and model syndromes known to include vestibular dysfunction, paving the way for generating treatments for people suffering from these disorders. This review will provide an overview of known inner ear anatomy and function and summarize the exciting discoveries behind inner ear development and the evolution of its vestibular apparatuses.

Natural Mutations Affect Structure and Function of gC1q Domain of Otolin-1

Otolin-1 is a scaffold protein of otoliths and otoconia, calcium carbonate biominerals from the inner ear. It contains a gC1q domain responsible for trimerization and binding of Ca²⁺. Knowledge of a structure-function relationship of gC1q domain of otolin-1 is crucial for understanding the biology of balance sensing. Here, we show how natural variants alter the structure of gC1q otolin-1 and how Ca²⁺ are able to revert some effects of the mutations. We discovered that natural substitutions: R339S, R342W and R402P negatively affect the stability of apo-gC1q otolin-1, and that Q426R has a stabilizing effect. In the presence of Ca²⁺, R342W and Q426R were stabilized at higher Ca²⁺ concentrations than the wild-type form, and R402P was completely insensitive to Ca²⁺. The mutations affected the self-association of gC1q otolin-1 by inducing detrimental aggregation (R342W) or disabling the trimerization (R402P) of the protein. Our results indicate that the natural variants of gC1q otolin-1 may have a potential to cause pathological changes in otoconia and otoconial membrane, which could affect sensing of balance and increase the probability of occurrence of benign paroxysmal positional vertigo (BPPV).

Relation between vitamin D deficiency and benign paroxysmal positional vertigo

Benign paroxysmal positional vertigo (BPPV) is the most common cause of positional vertigo. Vitamin D deficiency may be one of the causes of its development. To assess the relation between recurrent attacks BPPV and Vitamin D deficiency. A case control study in which 40 patients were clinically diagnosed as posterior canal BPPV, Serum 25(OH) D was measured at 1st visit. Patients were divided into two groups; group A (20 patients) received Vitamin D supplementation in addition to canal repositioning maneuver and group B (20 patients) treated by canal repositioning maneuver only. Follow up of all patients for 6 months, neuro-otological assessment was repeated and recurrent attacks were recorded. Serum vitamin D was repeated after 6 month. This study included 14 males and 26 females age ranged from 35 to 61 years, Average serum of 25 (OH) D at the first visit was (12.4 ± 2 ng/ml) for group A, and (12.2 ± 1.7 ng/ml) for group B, all patients had low serum level of 25(OH) D (below 20 ng/ml). Recurrent BPPV episodes, were significantly lower in group A than that of group B. There is a relation between BPPV recurrence and low serum Vitamin D.

Molecular Mediators of Estrogen Reduction-induced Otolith Shedding

OBJECTIVE

Previous study suggested that estradiol (E2) plays an important role in otolith shedding by regulating the expression of otoconin 90 (OC90). The purpose of this article is to provide further data on the effect and mechanism of E2 on the morphology of otolith.

METHODS

The rats receiving bilateral ovariectomy (OVX) were used as animal models. Co-immunoprecipitation was used to observe the relationship between estrogen receptor (ER) and estrogen-related receptor α (ERRα). The morphology of otolith was observed under the scanning electron microscopy. Western blotting and qPCR were used for quantitative analysis of the roles of ER and ERRα in regulating OC90 expression.

RESULTS

The looser otoliths were observed in rats receiving bilateral OVX, which could be reversed by supplementation with E2. The level of ERRα was decreased in bilateral OVX rats. ER and ERRα interacted with each other on the regulation of the expression of OC90.

CONCLUSION

Our results suggest ER and ERRα are both important downstream receptors involved in regulating OC90 expression in utricles of rats, and ERRα probably functions by interacting with ER. This provides evidence for the mechanism of otolith shedding. And it may be significant for future studies of targeted prevention and therapies for benign paroxysmal positional vertigo.

Prestin and otolin-1 proteins in the hearing loss of adults chronically exposed to lead

BACKGROUND

Some studies in animal models and humans suggest that exposure to lead is associated with hearing loss. Lead can reach the inner ear through the blood circulation; evidence suggests that lead could accumulate in the inner ear, causing inner ear damage.

AIM

To evaluate prestin and otolin-1 protein levels and their relationship with an increased hearing threshold in participants exposed to lead.

METHODS

We conducted a cross-sectional study with 315 participants from Tlaxcala, Mexico. Blood lead levels (BPb) were evaluated by graphite furnace atomic absorption spectrometry. Serum prestin and otolin-1 were quantified using ELISA. Auditory function at frequencies of 0.125 to 8 kHz was evaluated in a soundproof chamber.

RESULTS

Participants were classified according to BPb: group I (<10 μg/dL) had a median BPb of 6 μg/dL and prestin levels of 11.06 ng/mL. While participants in group II (≥10 μg/dL) had a median of BPb 20.7 μg/dL (p < 0.05) and prestin levels of 0.15 ng/mL (p < 0.001). Participants in both groups showed a normal hearing. Otolin-1 levels were higher for participants with normal hearing and lower for participants with hearing loss in both groups, p > 0.05. Multiple linear regression models predict an average decrease of 0.17 to 0.26 ng/mL in prestin levels per decibel increase for the frequencies evaluated.

CONCLUSIONS

Participants with high BPb showed an increase in hearing threshold, and prestin levels decreased proportionally to the hearing threshold increase. This is the first study to evaluate prestin as a potential biomarker for hearing damage, evaluated by audiometry, in participants with lead exposure.

Molecular mechanism of calcium induced trimerization of C1q-like domain of otolin-1 from human and zebrafish

The C1q superfamily includes proteins involved in innate immunity, insulin sensitivity, biomineralization and more. Among these proteins is otolin-1, which is a collagen-like protein that forms a scaffold for the biomineralization of inner ear stones in vertebrates. The globular C1q-like domain (gC1q), which is the most conserved part of otolin-1, binds Ca²⁺ and stabilizes its collagen-like triple helix. The molecular details of the assembly of gC1q otolin-1 trimers are not known. Here, we substituted putative Ca²⁺-binding acidic residues of gC1q otolin-1 with alanine to analyse how alanine influences the formation of gC1q trimers. We used human and zebrafish gC1q otolin-1 to assess how evolutionary changes affected the function of the protein. Surprisingly, the mutated forms of gC1q otolin-1 trimerized even in the absence of Ca²⁺, although they were less stable than native proteins saturated with Ca²⁺. We also found that the zebrafish gC1q domain was less stable than the human homologue under all tested conditions and became stabilized at higher concentrations of Ca²⁺, which showed that specific interactions leading to the neutralization of the negative charge at the axis of a gC1q trimer by Ca²⁺ are required for the trimers to form. Moreover, human gC1q otolin-1 seems to be optimized to function at lower concentrations of Ca²⁺, which is consistent with reported Ca²⁺ concentrations in the endolymphs of fish and mammals. Our results allow us to explain the molecular mechanism of assembly of proteins from the C1q superfamily, the modulating role of Ca²⁺ and expand the knowledge of biomineralization of vertebrate inner ear stones: otoliths and otoconia.

An evaluation of serum Otolin-1 & Vitamin-D in benign paroxysmal positional vertigo

BACKGROUND

Serum otolin-1 is an inner ear protein exclusively expressed in otoconia and cells of vestibule and cochlea. Serum otolin-1 is found to be quantifiable in patients with BPPV. Low Vitamin-D is associated with pathogenesis of BPPV. Since otoconia degeneration contributes to BPPV, lack of Vitamin-D may impact otoconia structure and integrity.

OBJECTIVE

We aimed at studying the s.otolin-1 as biomarker and significance of vit-D in BPPV.

MATERIAL AND METHOD

23 patients in test and control groups respectively were chosen within the age of 20 to 65 years. All the patients were diagnosed using Dix Hallpike menouver and head roll test, patients were treated with appropriate Canal Reposition Menouver (CRM).

RESULTS

Serum Otolin-1 levels among the test ranged from 366 to 882 pg/mL with mean of 585.17 pg/mL whereas in control group ranged from 223 to 462 pg/mL with mean of 335.26 pg/mL. Mean Vitamin-D levels among the test group was 22.67 ng/mL (Range = 6.3-68.4) and that of control 15.43 pg/mL (Range = 5.4-27.7) respectively. The relationship between the serum Otolin-1 and Vitamin-D was not statistically significant.

CONCLUSION

Otolin-1 levels is increased in BPPV patients and is sensitive in BPPV, specificity needs to be validated. Role of vitamin-D with respect to inner ear proteins needs further investigation.

Functional cooperation between two otoconial proteins Oc90 and Nox3

BACKGROUND

Otoconia-related vertigo and balance deficits are common in humans, but the molecular etiology is unknown at present.

OBJECTIVE

In order to study mechanisms of otoconia formation and maintenance, we have investigated whether otoconin-90 (Oc90), the predominant otoconial constituent protein, and the NADPH oxidase Nox3, an essential regulatory protein for otoconia formation, are functionally interlinked.

METHODS

We performed balance behavioral, electrophysiological, morphological and molecular cellular analyses.

RESULTS

Double heterozygous mutant mice for Oc90 and Nox3 show severe imbalance, albeit less profound than double null mutants. In contrast, single heterozygous mutant mice have normal balance. Double heterozygous mice have otoconia defects and double null mice have no otoconia. In addition, some hair bundles in the latter mice go through accelerated degeneration. In vitro calcification analysis in cells stably expressing these proteins singly and doubly shows much more intense calcification in the double transfectants.

CONCLUSIONS

Oc90 and Nox3 augment each other's function, which is not only critical for otoconia formation but also for hair bundle maintenance.

Otoliths-composed gelatin/sodium alginate scaffolds for bone regeneration

Evidence that otoliths, mineral-rich limestone concrescences present in the inner ear of bone fishes, can accelerate bone formation in vivo has been previously reported. The goal of this work was the development, characterization, and evaluation of the cytocompatibility of otoliths-incorporated sodium alginate and gelatin scaffolds. Cynoscion acoupa-derived otoliths were characterized by X-ray fluorescence spectrometry (FRX), particle size, free lime, and weight loss by calcination. Furthermore, otoliths were incorporated into sodium alginate (ALG/OTL-s) or gelatin (GEL/OTL-s) scaffolds, previously developed by freeze-drying. Then, the scaffolds were characterized by thermogravimetric analysis (TGA/DTG), differential scanning calorimetry (DSC), infrared spectroscopy with Fourier transform (FTIR), swelling tests, and scanning electron microscopy (SEM). Cytotoxicity assays were run against J774.G8 macrophages and MC3T3-E1 osteoblasts. Data obtained from TGA/DTG, DSC, and FTIR analyses confirmed the interaction between otoliths and the polymeric scaffolds. SEM showed the homogeneous porous 3D structure rich in otolith micro-fragments in both scaffolds. Swelling of the GEL/OTL-s (63.54 ± 3.0%) was greater than of ALG/OTL-s (13.36 ± 9.9%) (p < 0.001). The viability of J774.G8 macrophages treated with both scaffolds was statistically similar to the group treated with DMEM only (p > 0.05) and significantly higher than that treated with Triton-X (p < 0.01) at 72 h. Both scaffolds showed approximately 100% growth of MC3T3-E1 osteoblasts by 24 h, similarly to control (p > 0.05). However, by 48 h, only ALG/OTL-s showed growth similar to control (p > 0.05), whereas GEL/OTL showed a significantly lower growth index (p < 0.05). In conclusion, the physicochemical profiles suggest proper interaction between the otoliths and the two developed polymeric 3D scaffolds. Moreover, both materials showed cytocompatibility with J774.G8 macrophages but the growth of MC3T3-E1 osteoblasts was higher when exposed to ALG/OTL-s. These data suggest that sodium alginate/otoliths scaffolds are potential biomaterials to be used in bone regeneration applications. Graphical abstract.

Evaluation of the structure of the otoconial layer using micro-computed tomography

OBJECTIVE

Estrogen deficiency caused by bilateral ovariectomy (OVX) has been reported to lead to morphological changes in otoconia. Thus, we examined the morphological changes in the otoconial layer after OVX. We also investigated whether micro-computed tomography (µCT) is useful for the detection of morphological changes in the otoconial layer.

METHODS

The otic capsules of C57BL/6 J mice were removed and evaluated using histological techniques and µCT at 2, 4, and 8 weeks after OVX or sham surgery. The volume of the utricle otoconial layer was measured and compared between the OVX and sham groups. The µCT scan and histological study results were also compared.

RESULTS

The volume of the utricle otoconial layer was significantly increased 4 weeks after OVX compared to the sham group in both histological and µCT studies (p < 0.05). The volume of the otoconial layer measured using µCT was significantly correlated with the histological study results (p < 0.05).

CONCLUSION

The volume of the utricle otoconial layer increased after OVX. These morphological changes could be detected by µCT.

A Relationship Between Blood Levels of Otolin-1 and Vitamin D

OBJECTIVE

Low vitamin D levels have been associated with and could play a role in the pathogenesis of idiopathic benign paroxysmal positional vertigo (iBPPV). Since otoconia degeneration contributes to iBPPV and a lack of vitamin D may impact otoconia structure and integrity, we proposed a negative association between vitamin D levels and levels of a proposed circulatory biomarker for otolithic degeneration, otolin-1.

STUDY DESIGN

Cross-sectional clinical study.

SETTING

Clinical research center.

PATIENTS

Seventy-nine men and women ranging in age from 22 to 95 years old without known vertigo.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Blood levels of 25-OH vitamin D and otolin-1.

RESULTS

Previously, we had reported higher otolin-1 levels in older age groups. The majority of the subjects (83%) had vitamin D levels that were below 40 ng/ml. Vitamin D level was lowest in the young and increased with age before declining in subjects 70 years of age and older (p = 0.005). There was a negative correlation between vitamin D and otolin-1 levels of subjects over 70 (r = -0.36, p = 0.036).

CONCLUSION

Our results demonstrate a relationship between vitamin D and otolin-1. The majority of our subjects had abnormally low vitamin D levels, but only those over 70 years of age showed a negative correlation with high otolin-1 levels. We postulate that a seasonal drop in vitamin D may not be sufficient for otoconia fragmentation and ultimately iBPPV, rather, chronically low vitamin D maybe required to induce otoconia degeneration.

Otopetrin-2 Immunolocalization in the Human Macula Utricle

BACKGROUND

In the present study, we investigated the localization of otopetrin-2-a member of the otopetrin family that encodes proton-selective ion channels-in the human macula utricle using immunohistochemistry.

METHODS

Macula utricle were acquired at surgery from patients who required transmastoid labyrinthectomy for intractable vertigo due to Meniere's disease (MD; n = 3) and/or vestibular drops attacks (VDA; n = 2) and from temporal bones (n = 2) acquired at autopsy from individuals with no balance disorders. Immunofluorescence staining with otopetrin-2 (rabbit affinity purified polyclonal antibody) and GFAP (mouse monoclonal antibody) to identify vestibular supporting cells was made in formalin fixed cryostat sections or whole microdissected utricle (for flat mount preparations). Secondary antibodies against rabbit and mouse were used for the identification of both proteins. Digital fluorescent images were obtained using a high-resolution laser confocal microscope.

RESULTS

Using cryostat sections and flat mount preparations otopetrin-2 immunofluorescence was seen as punctated signal throughout the supporting cells cytoplasm. GFAP immunofluorescence was present in the supporting cell cytoplasm. The distribution of otopetrin-2 was similar in the macula utricle obtained from MD, VDA, or autopsy normative patients.

CONCLUSIONS

Otopetrin-2 was localized in supporting cells in a similar fashion that otopetrin-1 previously reported in the mouse macula utricle. The differential expression of otopetrin-2 in the supporting cells of the human macula utricle suggest an important role in the vestibular sensory periphery homeostasis and otolith maintenance.

Zebrafish otolith biomineralization requires polyketide synthase

Deflecting biomineralized crystals attached to vestibular hair cells are necessary for maintaining balance. Zebrafish (Danio rerio) are useful organisms to study these biomineralized crystals called otoliths, as many required genes are homologous to human otoconial development. We sought to identify and characterize the causative gene in a trio of homozygous recessive mutants, no content (nco) and corkscrew (csr), and vanished (vns), which fail to develop otoliths during early ear development. We show that nco, csr, and vns have potentially deleterious mutations in polyketide synthase (pks1), a multi-modular protein that has been previously implicated in biomineralization events in chordates and echinoderms. We found that Otoconin-90 (Oc90) expression within the otocyst is diffuse in nco and csr; therefore, it is not sufficient for otolith biomineralization in zebrafish. Similarly, normal localization of Otogelin, a protein required for otolith tethering in the otolithic membrane, is not sufficient for Oc90 attachment. Furthermore, eNOS signaling and Endothelin-1 signaling were the most up- and down-regulated pathways during otolith agenesis in nco, respectively. Our results demonstrate distinct processes for otolith nucleation and biomineralization in vertebrates and will be a starting point for models that are independent of Oc90-mediated seeding. This study will serve as a basis for investigating the role of eNOS signaling and Endothelin-1 signaling during otolith formation.

Destabilised human transthyretin shapes the morphology of calcium carbonate crystals

Human transthyretin (TTR) is a homotetramer that transports thyroid hormones and retinol in the serum and cerebrospinal fluid. TTR is also an intracellular protein found in tissues such as those in the brain, eye and pancreas. TTR is a nutrition marker, reflecting the health of the organism, and TTR levels are linked to the normal and diseased states of the body. The switch from a protective to a pathological role is attributed to the destabilisation of the TTR structure, which leads to tetramer dissociation and amyloid formation. Native and destabilised TTR have been associated with osteoarthritis and bone density in humans. Moreover, TTR is present in eggshell mammillary cones; therefore, we verified the putative TTR engagement in the process of mineral formation. Using an in vitro assay, we found that TTR affected calcium carbonate crystal growth and morphology, producing asymmetric crystals with a complex nanocrystalline composition. The crystals possessed rounded edges and corners and irregular etch pits, suggesting the selective inhibition of crystal growth and/or dissolution imposed by TTR. The occurrence of many porosities, fibrillary inclusions and amorphous precipitates suggested that destabilisation of the TTR structure is an important factor involved in the mineralisation process. Crystals grown in the presence of TTR exhibited the characteristic features of crystals controlled by biomineralisation-active proteins, suggesting novel functions of TTR in the mineral formation process.

25 (OH) D3 levels, incidence and recurrence of different clinical forms of benig paroxysmal positional vertigo

Introduction

Objectives

Methods

Results

Conclusions

Mechanism Underlying the Effects of Estrogen Deficiency on Otoconia

Otoconia-related vertigo and balance deficits, particularly benign paroxysmal positional vertigo (BPPV), are common. Our recent studies in humans show that, while BPPV prevalence greatly increases with age in both genders, peri-menopausal women are especially susceptible. In the present study, we show that bilateral ovariectomized (OVX) mice have significant balance behavioral deficits, and that estrogen deficiency compromises otoconia maintenance and anchoring by reducing the expression of otoconial component and anchoring proteins. There is ectopic debris formation in the ampulla under estrogen deficiency due to aberrant matrix protein expression. Furthermore, phytoestrogen is effective in rescuing the otoconia abnormalities. By comparing the expression levels of known estrogen receptor (Esr) subtypes, and by examining the otoconia phenotypes of null mice for selected receptors, we postulate that Esr2 may be critical in mediating the effects of estrogen in otoconia maintenance.

Age-Related Increase in Blood Levels of Otolin-1 in Humans

OBJECTIVE

To test the hypothesis that age-related demineralization of otoconia will result in an age-related increase in blood levels of otoconia matrix protein, otolin-1.

STUDY DESIGN

Cross-sectional observational clinical trial.

SETTING

Clinical research center.

PATIENTS

Seventy nine men and women ranging in age from 22 to 95 years old.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Blood levels of otolin-1 in relation to age.

RESULTS

Levels of otolin-1 of subjects divided into four age groups (1: 20-30 [n = 20], 2: 50-65 [n = 20], 3: 66-80 [n = 20], 4: 81-95 [n = 19] years old) demonstrated an increasing trend with age. The difference between otolin levels of groups 2 and 3, as well as, (p = 0.04) and 2 and 4 (p = 0.031) were statistically significant, but there was no significant difference between the two oldest groups.

CONCLUSIONS

Otolin-1 blood levels are significantly higher in patients older than 65 years of age. This is consistent with previous scanning electron microscopy findings of age-related otoconia degeneration and increased prevalence of benign paroxysmal positional vertigo (BPPV) with age. Normative data provided here can serve as important reference values against which levels from BPPV patients can be compared with further evaluate otolin-1 as a circulatory biomarker for otoconia degeneration.

Estradiol deficiency is a risk factor for idiopathic benign paroxysmal positional vertigo in postmenopausal female patients

OBJECTIVES/HYPOTHESIS

Although it is generally considered that benign paroxysmal positional vertigo (BPPV) is associated with changes in female sex hormone levels, no direct data have been reported until now. The purpose of this article was to provide direct data showing the distinct relationship between female sex hormone fluctuations and BPPV in postmenopausal female patients.

STUDY DESIGN

Prospective analysis in humans and basic research in animals.

METHODS

Blood samples were analyzed to determine the levels of estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone in 50- to 80-year-old postmenopausal female patients newly diagnosed with idiopathic BPPV based on history compatible with BPPV and positive provocative maneuvers. Animal models of bilateral ovariectomy and female sex hormone replacement therapy were used to further confirm the relationship between BPPV and female sex hormone levels by determining the expression levels of otoconin 90, the protein suggested as essential in the dislocation of otoconia.

RESULTS

Statistically significant differences between the estradiol level of BPPV patients and the control group were found (P < .001). Moreover, in bilateral ovariectomy in rats, 17β-estradiol replacement reversed the decrease of otoconin 90 levels.

CONCLUSIONS

Our results suggest that estradiol deficiency may be an important risk factor for idiopathic benign paroxysmal positional vertigo in postmenopausal female patients.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:948-953, 2018.

Spatiotemporal differences in otoconial gene expression

Otoconia are minute biocrystals composed of glycoproteins, proteoglycans, and CaCO₃ , and are indispensable for sensory processing in the utricle and saccule. Otoconia abnormalities and degeneration can cause or facilitate crystal dislocation to the ampulla, leading to vertigo and imbalance in humans. In order to better understand the molecular mechanism controlling otoconia formation and maintenance, we have examined the spatial and temporal expression differences of otoconial genes in the mouse inner ear at developmental, mature and aging stages using whole transcriptome sequencing (RNA-Seq) and quantitative RT-PCR. We show that the expression levels of most otoconial genes are much higher in the utricle and saccule compared with other inner ear tissues before postnatal stages in C57Bl/6J mice, and the expression of a few of these genes is restricted to the embryonic utricle and saccule. After the early postnatal stages, expression of all otoconial genes in the utricle and saccule is drastically reduced, while a few genes gain expression dominance in the aging ampulla, indicating a potential for ectopic debris formation in the latter tissue at old ages. The data suggest that the expression of otoconial genes is tightly regulated spatially and temporally during developmental stages and can become unregulated at aging stages. Birth Defects Research (Part A) 106:613-625, 2016. © 2016 Wiley Periodicals, Inc.

Preliminary Report on the Investigation of the Association Between BPPV and Osteoporosis Using Biomarkers

OBJECTIVE

To test the hypothesis that levels of a BPPV biomarker, otolin-1, correlate with those of osteoporosis markers, aminoterminal propeptide of protocollagen type I (P1NP), and aminoterminal telopeptides of collagen (NTX), thus further supporting a link between the two diseases.

STUDY DESIGN

Prospective pilot clinical trial (Level of Evidence: 2b).

PATIENTS

Postmenopausal women with BPPV.

INTERVENTIONS

Diagnostic.

MAIN OUTCOME MEASURES

Serum levels of otolin-1, P1NP, NTX, vitamin D, and calcium were examined in relation to each other, age, and DEXA scan T-scores.

RESULTS

There was a strong, negative correlation between T-scores and otolin-1 levels. Although P1NP and NTX levels were strongly correlated, neither had statistical correlations with otolin-1.

CONCLUSIONS

Despite a strong correlation between DEXA scan results and otolin-1 levels, there were no significant correlations between otolin-1 and P1NP or NTX. This suggests that the association between osteoporosis and BPPV is complex, but not likely to be causal. Although more work is needed to elucidate these relationships, this preliminary finding has important practical implications for BPPV in that proactive management of osteoporosis, per se, would not be expected to have benefits in management of BPPV.

QTL Mapping of Endocochlear Potential Differences between C57BL/6J and BALB/cJ mice

We reported earlier that the endocochlear potential (EP) differs between C57BL/6J (B6) and BALB/cJ (BALB) mice, being lower in BALBs by about 10 mV (Ohlemiller et al. Hear Res 220: 10-26, 2006). This difference corresponds to strain differences with respect to the density of marginal cells in cochlear stria vascularis. After about 1 year of age, BALB mice also tend toward EP reduction that correlates with further marginal cell loss. We therefore suggested that early sub-clinical features of the BALB stria vascularis may predispose these mice to a condition modeling Schuknecht's strial presbycusis. We further reported (Ohlemiller et al. J Assoc Res Otolaryngol 12: 45-58, 2011) that the acute effects of a 2-h 110 dB SPL noise exposure differ between B6 and BALB mice, such that the EP remains unchanged in B6 mice, but is reduced by 40-50 mV in BALBs. In about 25 % of BALBs, the EP does not completely recover, so that permanent EP reduction may contribute to noise-induced permanent threshold shifts in BALBs. To identify genes and alleles that may promote natural EP variation as well as noise-related EP reduction in BALB mice, we have mapped related quantitative trait loci (QTLs) using 12 recombinant inbred (RI) strains formed from B6 and BALB (CxB1-CxB12). EP and strial marginal cell density were measured in B6 mice, BALB mice, their F1 hybrids, and RI mice without noise exposure, and 1-3 h after broadband noise (4-45 kHz, 110 dB SPL, 2 h). For unexposed mice, the strain distribution patterns for EP and marginal cell density were used to generate preliminary QTL maps for both EP and marginal cell density. Six QTL regions were at least statistically suggestive, including a significant QTL for marginal cell density on chromosome 12 that overlapped a weak QTL for EP variation. This region, termed Maced (Marginal cell density QTL) supports the notion of marginal cell density as a genetically influenced contributor to natural EP variation. Candidate genes for Maced notably include Foxg1, Foxa1, Akap6, Nkx2-1, and Pax9. Noise exposure produced significant EP reductions in two RI strains as well as significant EP increases in two RI strains. QTL mapping of the EP in noise-exposed RI mice yielded four suggestive regions. Two of these overlapped with QTL regions we previously identified for noise-related EP reduction in CBA/J mice (Ohlemiller et al. Hear Res 260: 47-53, 2010) on chromosomes 5 and 18 (Nirep). The present map may narrow the Nirep interval to a ~10-Mb region of proximal Chr. 18 that includes Zeb1, Arhgap12, Mpp7, and Gjd4. This study marks the first exploration of natural gene variants that modulate the EP. Their orthologs may underlie some human hearing loss that originates in the lateral wall.

Reduction of recurrence rate of benign paroxysmal positional vertigo by treatment of severe vitamin D deficiency

OBJECTIVE

Several studies correlated between vitamin D deficiency and the development, and the recurrence of benign positional paroxysmal vertigo (BPPV), but none of them proved that treatment of vitamin D deficiency would reduce the recurrence rate of BPPV. This study aims to detect the effect of treatment of severe vitamin D deficiency on the recurrence rate of BPPV.

METHODS

The inclusion criteria of the study group were: (1) Unilateral, idiopathic, posterior canal BPPV with no history suggestive of secondary BPPV and (2) 25-hydroxyvitamin D3 level ≤10 ng/ml. All subjects enrolled in the current study underwent detailed clinical history, audiovestibular evaluation consisting of pure-tone audiometry, Immittancemetry, Videonystugmography, serum 25-hydroxyvitamin D3 assessment, and Dual-energy X-ray absorptiometry (DXA). Vitamin D therapy was prescribed for the study group. Serum 25-hydroxyvitamin D3 level was evaluated twice, on recruitment into the study group and 3 months after commencing vitamin D therapy. According to the results of the second evaluation of serum 25-hydroxyvitamin D3, the study group was subdivided into two subgroups: Subgroup (I): including 28 subjects who disclosed elevation of serum 25-hydroxyvitamin D3 level; improvement ≥10 ng/ml. Subgroup (II): including 65 patients who disclosed elevation of serum 25-hydroxyvitamin D3 levels <10 ng/ml. The study group was followed up for 18 months in order to observe the recurrence of BPPV.

RESULTS

The differences between both study subgroups (I) & (II) regarding age, sex distribution, and bone mineral density were insignificant. The number of subjects who had recurrence of BPPV in subgroup (I) was 4 (14%) versus 28 subjects (43%) in subgroup (II). The mean values for recurrent attacks/subject in subgroups (I) & (II) were 0.18, and 0.66 attack/subject respectively; these differences between both subgroups were of high statistical significance (p<0.01). The Odds Ratio for development of recurrence of BPPV in subjects with severe vitamin D deficiency was 4.54 (95% CI: 1.41-14.58, p<0.01). The relapse attacks of BPPV affected both ears irrespective of the ear showing the original BPPV attack.

CONCLUSION

The present study indicates that improvement of serum 25-hydroxyvitamin D3 levels is associated with substantial decrease in recurrence of BPPV.

Effect of Otoconial Proteins Fetuin A, Osteopontin, and Otoconin 90 on the Nucleation and Growth of Calcite

We investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on calcite surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on crystal morphology. All three proteins were found to be potent inhibitors of calcite growth, although fetuin A promoted growth at concentrations below about 40 nM and only became an inhibitor at higher concentrations. We then used in situ optical microscopy to observe calcite nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the calcite nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous calcite nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution-substrate interfacial energy.

Intrinsically disordered and pliable Starmaker-like protein from medaka (Oryzias latipes) controls the formation of calcium carbonate crystals

Fish otoliths, biominerals composed of calcium carbonate with a small amount of organic matrix, are involved in the functioning of the inner ear. Starmaker (Stm) from zebrafish (Danio rerio) was the first protein found to be capable of controlling the formation of otoliths. Recently, a gene was identified encoding the Starmaker-like (Stm-l) protein from medaka (Oryzias latipes), a putative homologue of Stm and human dentine sialophosphoprotein. Although there is no sequence similarity between Stm-l and Stm, Stm-l was suggested to be involved in the biomineralization of otoliths, as had been observed for Stm even before. The molecular properties and functioning of Stm-l as a putative regulatory protein in otolith formation have not been characterized yet. A comprehensive biochemical and biophysical analysis of recombinant Stm-l, along with in silico examinations, indicated that Stm-l exhibits properties of a coil-like intrinsically disordered protein. Stm-l possesses an elongated and pliable structure that is able to adopt a more ordered and rigid conformation under the influence of different factors. An in vitro assay of the biomineralization activity of Stm-l indicated that Stm-l affected the size, shape and number of calcium carbonate crystals. The functional significance of intrinsically disordered properties of Stm-l and the possible role of this protein in controlling the formation of calcium carbonate crystals is discussed.

Mechanisms of otoconia and otolith development

BACKGROUND

Otoconia are bio-crystals that couple mechanic forces to the sensory hair cells in the utricle and saccule, a process essential for us to sense linear acceleration and gravity for the purpose of maintaining bodily balance. In fish, structurally similar bio-crystals called otoliths mediate both balance and hearing. Otoconia abnormalities are common and can cause vertigo and imbalance in humans. However, the molecular etiology of these illnesses is unknown, as investigators have only begun to identify genes important for otoconia formation in recent years.

RESULTS

To date, in-depth studies of selected mouse otoconial proteins have been performed, and about 75 zebrafish genes have been identified to be important for otolith development.

CONCLUSIONS

This review will summarize recent findings as well as compare otoconia and otolith development. It will provide an updated brief review of otoconial proteins along with an overview of the cells and cellular processes involved. While continued efforts are needed to thoroughly understand the molecular mechanisms underlying otoconia and otolith development, it is clear that the process involves a series of temporally and spatially specific events that are tightly coordinated by numerous proteins. Such knowledge will serve as the foundation to uncover the molecular causes of human otoconia-related disorders.

Mechanisms of otoconia and otolith development

BACKGROUND

Otoconia are bio-crystals that couple mechanic forces to the sensory hair cells in the utricle and saccule, a process essential for us to sense linear acceleration and gravity for the purpose of maintaining bodily balance. In fish, structurally similar bio-crystals called otoliths mediate both balance and hearing. Otoconia abnormalities are common and can cause vertigo and imbalance in humans. However, the molecular etiology of these illnesses is unknown, as investigators have only begun to identify genes important for otoconia formation in recent years.

RESULTS

To date, in-depth studies of selected mouse otoconial proteins have been performed, and about 75 zebrafish genes have been identified to be important for otolith development.

CONCLUSIONS

This review will summarize recent findings as well as compare otoconia and otolith development. It will provide an updated brief review of otoconial proteins along with an overview of the cells and cellular processes involved. While continued efforts are needed to thoroughly understand the molecular mechanisms underlying otoconia and otolith development, it is clear that the process involves a series of temporally and spatially specific events that are tightly coordinated by numerous proteins. Such knowledge will serve as the foundation to uncover the molecular causes of human otoconia-related disorders.

Inner Ear Protein as a Biomarker in Circulation?

Serum biomarkers detect the earliest events in disease, monitor management, and provide insight into disease pathogenesis. At this time, there are no biomarkers available for otologic disorders. Otolin-1 is a scaffolding protein exclusively expressed in otoconia and cells of the vestibule and the cochlea; therefore, it may be a biomarker candidate for assessing the health of the inner ear. As a proof of concept, we used serum samples from controls without otologic history and subjects with a history of benign paroxysmal positional vertigo (BPPV), performed enzyme-linked immunosorbent assay for otolin-1, and measured the optical density of the substrate. Otolin-1 was detectable and quantifiable in all subjects, indicating that this inner ear protein crosses the blood-labyrinthine barrier. Furthermore, subjects with BPPV had significantly higher levels, with about one-third being above the control range. This promising preliminary result suggests that inner ear–specific proteins have the potential to serve as biomarkers for otologic disease processes.

Benign Paroxysmal Positional Vertigo: An Integrated Perspective

Benign paroxysmal positional vertigo (BPPV), the most common cause of dizziness, occurs in all age groups. It presents with vertigo on head movement, but in older patients presentation may be typical and thus accounting for a low recognition rate in the primary care setting. It may be recurrent in up to 50% of cases. BPPV is associated with displacement of fragments of utricular otoconia into the semicircular canals, most commonly the posterior semicircular canal. Otoconia are composed of otoconin and otolin forming the organic matrix on which calcium carbonate mineralizes. Otoconia may fragment with trauma, age, or changes in the physiology of endolymph (e.g., pH and calcium concentration). Presentation varied because otoconia fragments can be displaced into any of the semicircular canals on either (or both) side and may be free floating (canalolithiasis) or attached to the cupula (cupulolithiasis). Most cases of BPPV are idiopathic, but head trauma, otologic disorders, and systemic disease appear to be contributory in a subset. Positional maneuvers are used to diagnose and treat the majority of cases. In rare intractable cases surgical management may be considered. A strong association with osteoporosis suggests that idiopathic BPPV may have diagnostic and management implications beyond that of a purely otologic condition.

In vitro calcite crystal morphology is modulated by otoconial proteins otolin-1 and otoconin-90

Otoconia are formed embryonically and are instrumental in detecting linear acceleration and gravity. Degeneration and fragmentation of otoconia in elderly patients leads to imbalance resulting in higher frequency of falls that are positively correlated with the incidence of bone fractures and death. In this work we investigate the roles otoconial proteins Otolin-1 and Otoconin 90 (OC90) perform in the formation of otoconia. We demonstrate by rotary shadowing and atomic force microscopy (AFM) experiments that Otolin-1 forms homomeric protein complexes and self-assembled networks supporting the hypothesis that Otolin-1 serves as a scaffold protein of otoconia. Our calcium carbonate crystal growth data demonstrate that Otolin-1 and OC90 modulate in vitro calcite crystal morphology but neither protein is sufficient to produce the shape of otoconia. Coadministration of these proteins produces synergistic effects on crystal morphology that contribute to morphology resembling otoconia.

Vitamin D deficiency and benign paroxysmal positioning vertigo

Benign paroxysmal positional vertigo is a common cause of disabling vertigo with a high rate of recurrence. Although connections between vitamin D deficiency and osteoporosis, as well as between osteoporosis and benign paroxysmal positional vertigo have been suggested respectively in the literature, we are not aware of any publication linking vitamin D and benign paroxysmal positional vertigo. As a hypothesis, we suggest that there is a relation between insufficient vitamin D level and benign paroxysmal positional vertigo. In order to test this hypothesis, in a small retrospective pilot study, 25-hydroxyvitamin D levels in serum of patients with benign paroxysmal positional vertigo and frequency of recurrence after correction of serum level were assessed retrospectively. Patients with idiopathic positional vertigo had a low average serum level of 25-hydroxyvitamin D (23ng/mL) similar to that of the general Austrian population, which has a high prevalence of hypovitaminosis D. In 4 cases with chronically recurrent severe vertigo episodes, average levels of serum 25-hydroxyvitamin D were even significantly lower than in the other vertigo patients, who had their first episode. Vertigo attacks did not recur after supplementation with vitamin D. We raise the possibility that patients with benign paroxysmal positional vertigo who have low vitamin D levels may benefit from supplementation and suggest further epidemiological investigations to determine the effect of correcting vitamin D deficiency on the recurrence of vertigo. Given the many known benefits of vitamin D, the authors recommend the measurement of vitamin D in patients with benign paroxysmal positional vertigo and supplementation if necessary.

Immunogold TEM of otoconin 90 and otolin - relevance to mineralization of otoconia, and pathogenesis of benign positional vertigo

Implementation of the deep-etch technique enabled unprecedented definition of substructural elements of otoconia, including the fibrillar meshwork of the inner core with its globular attachments. Subsequently the effects of the principal soluble otoconial protein, otoconin 90, upon calcite crystal growth in vitro were determined, including an increased rate of nucleation, inhibition of growth kinetics and significant morphologic changes. The logical next step, ultrastructural localization of otoconin 90, by means of immunogold TEM in young mature mice, demonstrated a high density of gold particles in the inner core in spite of a relatively low level of mineralization. Here gold particles are typically arranged in oval patterns implying that otoconin 90 is attached to a scaffold consisting of the hexagonal fibrillar meshwork, characteristic of otolin. The level of mineralization is much higher in the outer cortex where mineralized fiber bundles are arranged parallel to the surface. Following decalcification, gold particles, as well as matrix fibrils, presumed to consist of a linear structural phenotype of otolin, are aligned in identical direction, suggesting that they serve as scaffold to guide mineralization mediated by otoconin 90. In the faceted tips, the level of mineralization is highest, even though the density of gold particles is relatively low, conceivably due to the displacement by the dense mineral phase. TEM shows that individual crystallites assemble into iso-oriented columns. Columns are arranged in parallel lamellae which convert into mineralized blocks for hierarchical assembly into the complex otoconial mosaic. Another set of experiments based on immunogold TEM in young mice demonstrates that the fibrils interconnecting otoconia consist of the short chain collagen otolin. By two years of age the superficial layer of mouse otoconia (corresponding to mid-life human) has become demineralized resulting in weakening or loss of anchoring of the fibrils interconnecting otoconia. Consequently, otoconia detached from each other may be released into the endolymphatic space by minor mechanical disturbances. In humans, benign positional vertigo (BPV) is believed to result from translocation of otoconia from the endolymphatic space into the semi-circular canals rendering their receptors susceptible to stimulation by gravity causing severe attacks of vertigo. The combinations of these observations in humans, together with the presented animal experiments, provide a tentative pathogenetic basis of the early stage of BPV.