Effect of calcium ions on structure and stability of the C1q-like domain of otolin-1 from human and zebrafish

Deciphering the molecular toolkit: regulatory elements governing shell biomineralization in marine molluscs

The intricate process of shell biomineralization in marine molluscs is governed by a complex interplay of regulatory elements, encompassing secretomes, transporters, and noncoding RNA. This review delves into recent advancements in understanding these regulatory mechanisms, emphasizing their significance in elucidating the functions and evolutionary dynamics of the molluscan shell biomineralization process. Central to this intricate orchestration are secretomes with diverse functional domains, selectively exported to the extrapallial space, which directly regulate crystal growth and morphology. Transporters are crucial for substrate transportation in the calcification and maintenance of cellular homeostasis. Beyond proteins and transporters, noncoding RNA molecules are integral components influencing shell biomineralization. This review underscores the nonnegligible roles played by these genetic elements at the molecular level. To comprehend the complexity of biomineralization in mollusc, we explore the origin and evolutionary history of regulatory elements, primarily secretomes. While some elements have recently evolved, others are ancient genes that have been co-opted into the biomineralization toolkit. These elements undergo structural and functional evolution through rapidly evolving repetitive low-complexity domains and domain gain/loss/rearrangements, ultimately shaping a distinctive set of secretomes characterized by both conserved features and evolutionary innovations. This comprehensive review enhances our understanding of molluscan biomineralization at the molecular and genetic levels.

The relevance of calcium-binding domains to promoting activities of annexin A2 in calcium oxalate stone formation

Annexin A2 (ANXA2) is a Ca2+-binding protein involved in kidney stone disease (KSD) but with unclear mechanism. Herein, five Ca2+-binding domains of ANXA2 were mutated by substituting glutamic acid (E) at positions 53rd (domain I), 96th (domain II) and 247th (domain IV), and aspartic acid (D) at positions 162nd (domain III) and 322nd (domain V) with alanine (A). Recombinant ANXA2 wide type (WT) and mutants (E53A, E96A, D162A, E247A and D322A) were constructed, produced, purified and subjected to multiple crystal and functional assays. Crystal assays revealed that ANXA2 WT increased calcium oxalate monohydrate (COM) crystal size during crystallization and enhanced growth and crystal-cell adhesion phases compared with blank and negative controls. However, crystals exposed to all ANXA2 mutants had comparable or slightly lower parameters compared with controls. Although ANXA2 WT did not affect crystal aggregation, its mutants still showed a lower degree of crystal aggregation. Immunofluorescence staining and Ca2+-binding assay demonstrated that ANXA2 WT had the greatest affinity to COM crystals and free Ca2+ ions, whereas all the mutants showed lower affinity. Taken together, all five Ca2+-binding domains are relevant to the promoting activities of ANXA2 in COM stone formation by interacting with COM crystal surfaces and free Ca2+ ions.

Double-Edged Sword: Exploring the Mitochondria-Complement Bidirectional Connection in Cellular Response and Disease

Mitochondria serve an ultimate purpose that seeks to balance the life and death of cells, a role that extends well beyond the tissue and organ systems to impact not only normal physiology but also the pathogenesis of diverse diseases. Theorized to have originated from ancient proto-bacteria, mitochondria share similarities with bacterial cells, including their own circular DNA, double-membrane structures, and fission dynamics. It is no surprise, then, that mitochondria interact with a bacterium-targeting immune pathway known as a complement system. The complement system is an ancient and sophisticated arm of the immune response that serves as the body's first line of defense against microbial invaders. It operates through a complex cascade of protein activations, rapidly identifying and neutralizing pathogens, and even aiding in the clearance of damaged cells and immune complexes. This dynamic system, intertwining innate and adaptive immunity, holds secrets to understanding numerous diseases. In this review, we explore the bidirectional interplay between mitochondrial dysfunction and the complement system through the release of mitochondrial damage-associated molecular patterns. Additionally, we explore several mitochondria- and complement-related diseases and the potential for new therapeutic strategies.

Context-dependent design of induced-fit enzymes using deep learning generates well-expressed, thermally stable and active enzymes

The potential of engineered enzymes in industrial applications is often limited by their expression levels, thermal stability, and catalytic diversity. De novo enzyme design faces challenges due to the complexity of enzymatic catalysis. An alternative approach involves expanding natural enzyme capabilities for new substrates and parameters. Here, we introduce CoSaNN (Conformation Sampling using Neural Network), an enzyme design strategy using deep learning for structure prediction and sequence optimization. CoSaNN controls enzyme conformations to expand chemical space beyond simple mutagenesis. It employs a context-dependent approach for generating enzyme designs, considering non-linear relationships in sequence and structure space. We also developed SolvIT, a graph NN predicting protein solubility in Escherichia coli, optimizing enzyme expression selection from larger design sets. Using this method, we engineered enzymes with superior expression levels, with 54% expressed in E. coli, and increased thermal stability, with over 30% having higher Tm than the template, with no high-throughput screening. Our research underscores AI's transformative role in protein design, capturing high-order interactions and preserving allosteric mechanisms in extensively modified enzymes, and notably enhancing expression success rates. This method's ease of use and efficiency streamlines enzyme design, opening broad avenues for biotechnological applications and broadening field accessibility.

Calcium carbonate polymorph selection in fish otoliths: A key role of phosphorylation of Starmaker-like protein

Fish otoliths are calcium carbonate biominerals found in the inner ear commonly used for tracking fish biochronologies and as a model system for biomineralization. The process of fish otolith formation is biologically controlled by numerous biomacromolecules which not only affect crystal size, shape, mechanical properties, but also selection of calcium carbonate polymorph (e.g., aragonite, vaterite). The proteinaceous control over calcium carbonate polymorph selection occurs in many other species (e.g., corals, mollusks, echinoderms) but the exact mechanism of protein interactions with calcium and carbonate ions - constituents of CaCO3 - are not fully elucidated. Herein, we focus on a native Starmaker-like protein isolated from vaterite asteriscus otoliths from Cyprinus carpio. The proteomic studies show the presence of the phosphorylated protein in vaterite otoliths. In a series of in vitro mineralization experiments with Starmaker-like, we show that native phosphorylation is a crucial determinant for the selection of a crystal's polymorphic form. This is the first report showing that the switch in calcium carbonate phase depends on the phosphorylation pattern of a single isolated protein. STATEMENT OF SIGNIFICANCE: Calcium carbonate has numerous applications in industry and medicine. However, we still do not understand the mechanism of biologically driven polymorph selection which results in specific biomineral properties. Previous work on calcium carbonate biominerals showed that either several macromolecular factors or high magnesium concentration (non-physiological) are required for proper polymorph selection (e.g., in mollusk shells, corals and otoliths). In this work, we showed for the first time that protein phosphorylation is a crucial factor for controlling the calcium carbonate crystal phase. This is important because a single protein from the otolith organic matrix could switch between polymorphs depending on the phosphorylation level. It seems that protein post-translational modifications (native, not artificial) are more important for biomolecular control of crystal growth than previously considered.

Otolin-1, an otolith- and otoconia-related protein, controls calcium carbonate bioinspired mineralization

BACKGROUND

Otoliths and otoconia are calcium carbonate biomineral structures that form in the inner ear of fish and humans, respectively. The formation of these structures is tightly linked to the formation of an organic matrix framework with otolin-1, a short collagen-like protein from the C1q family as one of its major constituents.

METHODS

In this study, we examined the activity of recombinant otolin-1 originating from Danio rerio and Homo sapiens on calcium carbonate bioinspired mineralization with slow-diffusion method and performed crystals characterization with scanning electron microscopy, two-photon excited fluorescence microscopy, confocal laser scanning microscopy and micro-Raman spectroscopy.

RESULTS

We show that both proteins are embedded in the core of CaCO₃ crystals that form through the slow-diffusion mineralization method. Both of them influence the morphology but do not change the polymorphic mineral phase. D.rerio otolin-1 also closely adheres to the crystal surface.

GENERAL SIGNIFICANCE

The results suggest, that otolin-1 is not a passive scaffold, but is directly involved in regulating the morphology of the resulting calcium carbonate biocrystals.

First paleoproteome study of fossil fish otoliths and the pristine preservation of the biomineral crystal host

Otoliths are calcium carbonate components of the stato-acoustical organ responsible for hearing and maintenance of the body balance in teleost fish. During their formation, control over, e.g., morphology and carbonate polymorph is influenced by complex insoluble collagen-like protein and soluble non-collagenous protein assemblages; many of these proteins are incorporated into their aragonite crystal structure. However, in the fossil record these proteins are considered lost through diagenetic processes, hampering studies of past biomineralization mechanisms. Here we report the presence of 11 fish-specific proteins (and several isoforms) in Miocene (ca. 14.8-14.6 Ma) phycid hake otoliths. These fossil otoliths were preserved in water-impermeable clays and exhibit microscopic and crystallographic features indistinguishable from modern representatives, consistent with an exceptionally pristine state of preservation. Indeed, these fossil otoliths retain ca. 10% of the proteins sequenced from modern counterparts, including proteins specific to inner ear development, such as otolin-1-like proteins involved in the arrangement of the otoliths into the sensory epithelium and otogelin/otogelin-like proteins that are located in the acellular membranes of the inner ear in modern fish. The specificity of these proteins excludes the possibility of external contamination. Identification of a fraction of identical proteins in modern and fossil phycid hake otoliths implies a highly conserved inner ear biomineralization process through time.

The Role of Intrinsically Disordered Proteins in Liquid–Liquid Phase Separation during Calcium Carbonate Biomineralization

Some animal organs contain mineralized tissues. These so-called hard tissues are mostly deposits of calcium salts, usually in the form of calcium phosphate or calcium carbonate. Examples of this include fish otoliths and mammalian otoconia, which are found in the inner ear, and they are an essential part of the sensory system that maintains body balance. The composition of ear stones is quite well known, but the role of individual components in the nucleation and growth of these biominerals is enigmatic. It is sure that intrinsically disordered proteins (IDPs) play an important role in this aspect. They have an impact on the shape and size of otoliths. It seems probable that IDPs, with their inherent ability to phase separate, also play a role in nucleation processes. This review discusses the major theories on the mechanisms of biomineral nucleation with a focus on the importance of protein-driven liquid–liquid phase separation (LLPS). It also presents the current understanding of the role of IDPs in the formation of calcium carbonate biominerals and predicts their potential ability to drive LLPS.

Advances in otolith-related protein research

Otoliths are biological crystals formed by a layer of calcium carbonate crystal that adhere to the ciliary surface of the utricular and saccular receptors in the vestibule of all vertebrates inner ear, enabling the utricle and saccule to better perceive the changes in linear and gravitational acceleration. However, the molecular etiology of otolith related diseases is still unclear. In this review, we have summarized the recent findings and provided an overview of the proteins that play important roles in otolith formation and maintenance (Otoconin-90, Otolin-1, Otolith Matrix Protein-1, Cochlin, Otogelin, α-Tectorin, β-Tectorin, Otopetrin-1, and Otopetrin-2, PMCA2, etc.), providing new insight for the prevention and management of benign paroxysmal positional vertigo (BPPV) with basis for otolith-related proteins as potential biomarkers of vestibular disease.

N'-terminal- and Ca2+-induced stabilization of high-order oligomers of full-length Danio rerio and Homo sapiens otolin-1

Otolin-1 is a C1q family member and a major component of the organic matrix of fish otoliths and human otoconia. To date, the protein molecular properties have not been characterized. In this work, we describe biochemical characterization and comparative studies on saccular-specific otolin-1 derived from Danio rerio and Homo sapiens. Due to the low abundance of proteins in the otoconial matrix, we developed a production and purification method for both recombinant homologues of otolin-1. Danio rerio and Homo sapiens otolin-1 forms higher-order oligomers that can be partially disrupted under reducing conditions. The presence of Ca²⁺ stabilizes the oligomers and significantly increases the thermal stability of the proteins. Despite the high sequence coverage, the oligomerization of Danio rerio otolin-1 is more affected by the reducing conditions and presence of Ca²⁺ than the human homologue. The results show differences in molecular behaviour, which may be reflected in Danio rerio and Homo sapiens otolin-1 role in otolith and otoconia formation.

High Serum Levels of Otolin-1 in Patients With Benign Paroxysmal Positional Vertigo Predict Recurrence

Background

Otolin-1 is an inner ear-specific protein that is exclusively expressed in otoconia and vestibule and cochlea cells. Recent investigations reported that otolin-1 can cross the blood-labyrinthine barrier and that the levels in serum well-reflected otolith status. Serum otolin-1 levels in patients with benign paroxysmal positional vertigo (BPPV) are significantly elevated compared with healthy controls. We aimed to explore whether otolin-1 can also serve as a biomarker for predicting BPPV recurrence.

Method

Patients at our institution with new-onset of idiopathic BPPV between May, 2017 and May, 2018 were recruited and followed up for 2 years. All demographic data of the patients were collected, and serum levels of otolin-1 and other laboratory indicators were measured and compared according to the recurrence status.

Results

A total of 74 patients, who met the inclusion criteria were enrolled in this study, of which 27 (36.5%) patients had suffered one or more episodes of recurrence after undergoing canal repositioning treatments during the study. The serum levels of otolin-1 in patients with recurrent BPPV were significantly higher than those in patients without recurrent BPPV (363.9 vs. 309.8 pg/ml, p = 0.001). In multivariate analysis comparing the second to fourth quartiles (Q2–Q4) against the first quartile (Q1) of otolin-1, the level of otolin-1 in Q4 could significantly predict BPPV recurrence, and the odds ratio (OR) was elevated by approximately 812% (OR = 9.12; 95% confidence interval [CI]: 1.44–57.9; p = 0.019).

Conclusion

High serum levels of otolin-1 were associated with an increased risk of BPPV recurrence, and further investigation is required to confirm this association and clarify the exact mechanism.

Transcriptomic, Proteomic, and Functional Assays Underline the Dual Role of Extrapallial Hemocytes in Immunity and Biomineralization in the Hard Clam Mercenaria mercenaria

Circulating hemocytes in the hemolymph represent the backbone of innate immunity in bivalves. Hemocytes are also found in the extrapallial fluid (EPF), the space delimited between the shell and the mantle, which is the site of shell biomineralization. This study investigated the transcriptome, proteome, and function of EPF and hemolymph in the hard clam Mercenaria mercenaria. Total and differential hemocyte counts were similar between EPF and hemolymph. Overexpressed genes in the EPF were found to have domains previously identified as being part of the "biomineralization toolkit" and involved in bivalve shell formation. Biomineralization related genes included chitin-metabolism genes, carbonic anhydrase, perlucin, and insoluble shell matrix protein genes. Overexpressed genes in the EPF encoded proteins present at higher abundances in the EPF proteome, specifically those related to shell formation such as carbonic anhydrase and insoluble shell matrix proteins. Genes coding for bicarbonate and ion transporters were also overexpressed, suggesting that EPF hemocytes are involved in regulating the availability of ions critical for biomineralization. Functional assays also showed that Ca2+ content of hemocytes in the EPF were significantly higher than those in hemolymph, supporting the idea that hemocytes serve as a source of Ca2+ during biomineralization. Overexpressed genes and proteins also contained domains such as C1q that have dual functions in biomineralization and immune response. The percent of phagocytic granulocytes was not significantly different between EPF and hemolymph. Together, these findings suggest that hemocytes in EPF play a central role in both biomineralization and immunity.

Characteristics of bone metabolism in postmenopausal female patients with different types of idiopathic benign paroxysmal positional vertigo: A single-centre retrospective study

OBJECTIVE

The association between benign paroxysmal positional vertigo (BPPV) and impaired calcium metabolism has attracted widespread interest. Several studies have suggested that decreased bone mineral density (BMD) and serum 25-hydroxyvitamin D (25(OH)D) level are related to the occurrence and/or recurrence of BPPV; however, the characteristics of bone metabolism in patients with BPPV subtypes have not been fully investigated, and conclusions have been controversial. This study aimed to evaluate BMD and serum levels of 25(OH)D and bone turnover markers to clarify the characteristics of bone metabolism in patients with different types of BPPV.

METHOD

We retrospectively analysed the data of new-onset idiopathic postmenopausal female patients with BPPV at our institution from January 2016 to January 2020. The patients' demographic data including age, medication history, concomitant diseases, onset time, clinical form, laboratory indicators, such as serum levels of 25(OH)D, bone formation markers, namely, amino-terminal propeptide of type I procollagen (PINP) and osteocalcin (OC), bone resorption marker, namely, β-isomerized carboxy-terminal telopeptide of type I collagen (β-CTX), and BMD were collected and analysed.

RESULTS

This study included 201 consecutive postmenopausal female patients with BPPV. Among them, 138 were diagnosed with posterior semicircular canal BPPV, 42 were diagnosed with lateral semicircular canal canalolithiasis, and 21 were diagnosed with lateral semicircular canal cupulolithiasis. There were no significant differences in age distribution, body mass index, clinical history, levels of albumin, globulin, uric acid, creatinine, or blood urea nitrogen, lipid profiles (except high-density lipoprotein cholesterol) and routine blood parameters among these groups (P > 0.05). There were no significant differences in the mean T-score and BMD values of different sites or in the serum levels of 25(OH)D and bone turnover markers (PINP, OC and β-CTX) among the subgroups (P > 0.05). The proportion of reduction in BMD (T-score < -1 SD) and decreased serum vitamin D level (< 20 ng/ml) were not significantly different between the subgroups (P > 0.05).

CONCLUSION

There were no significant differences in bone metabolism in postmenopausal female patients with different types of idiopathic BPPV.

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.

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).

Serum otolin-1 as a biomarker for benign paroxysmal positional vertigo: a case-control study

OBJECTIVES

This study aimed to evaluate serum otolin-1 levels in patients with benign paroxysmal positional vertigo and to compare these levels with healthy individuals.

METHOD

This was a case-control study. After obtaining institutional ethical committee clearance, the serum level of otolin-1 was calculated in adult individuals (18-75 years old) who were divided into group 1 (patients presenting with benign paroxysmal positional vertigo) and group 2 (healthy patients without benign paroxysmal positional vertigo as the control group). Data analysis was carried out to compare the serum levels in the cases and controls. A p-value less than 0.05 was considered significant.

RESULTS

A total of 70 age-matched individuals (cases, n = 40; controls, n = 30) were included in the study. The mean serum level of otolin-1 was 636.8 pg/ml (range, 259-981 pg/ml) in the group of patients with benign paroxysmal positional vertigo and 236.2 pg/ml (range, 189-370 pg/ml) in the control group. The difference was statistically significant (p = 0.0000).

CONCLUSION

The serum levels of otolin-1 in patients with benign paroxysmal positional vertigo are significantly higher compared with individuals without benign paroxysmal positional vertigo.

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.

A bivalve biomineralization toolbox

Mollusc shells are a result of the deposition of crystalline and amorphous calcite catalysed by enzymes and shell matrix proteins. Developing a detailed understanding of bivalve mollusc biomineralization pathways is complicated not only by the multiplicity of shell forms and microstructures in this class, but also by the evolution of associated proteins by domain co-option and domain shuffling. In spite of this, a minimal biomineralization toolbox comprising proteins and protein domains critical for shell production across species has been identified. Using a matched pair design to reduce experimental noise from inter-individual variation, combined with damage-repair experiments and a database of biomineralization shell matrix proteins (SMP) derived from published works, proteins were identified that are likely to be involved in shell calcification. Eighteen new, shared proteins likely to be involved in the processes related to the calcification of shells were identified by analysis of genes expressed during repair in Crassostrea gigas, Mytilus edulis and Pecten maximus. Genes involved in ion transport were also identified as potentially involved in calcification either via the maintenance of cell acid-base balance or transport of critical ions to the extrapallial space, the site of shell assembly. These data expand the number of candidate biomineralization proteins in bivalve molluscs for future functional studies and define a minimal functional protein domain set required to produce solid microstructures from soluble calcium carbonate. This is important for understanding molluscan shell evolution, the likely impacts of environmental change on biomineralization processes, materials science, and biomimicry research.

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.

Kcnb1 plays a role in development of the inner ear

The function of the inner ear depends on the maintenance of high concentrations of K⁺ ions. The slow-inactivating delayed rectifier Kv2.1/KCNB1 channel works in the inner ear in mammals. The kcnb1 gene is expressed in the otic vesicle of developing zebrafish, suggesting its role in development of the inner ear. In the present study, we found that a Kcnb1 loss-of-function mutation affected development of the inner ear at multiple levels, including otic vesicle expansion, otolith formation, and the proliferation and differentiation of mechanosensory cells. This resulted in defects of kinocilia and stereocilia and abnormal function of the inner ear detected by behavioral assays. The quantitative transcriptional analysis of 75 genes demonstrated that the kcnb1 mutation affected the transcription of genes that are involved in K⁺ metabolism, cell proliferation, cilia development, and intracellular protein trafficking. These results demonstrate a role for Kv2.1/Kcnb1 channels in development of the inner ear in zebrafish.

Increased Otolin-1 in Serum as a Potential Biomarker for Idiopathic Benign Paroxysmal Positional Vertigo Episodes

Objective: Otolin-1, a main specific otoconia matrix protein, passes through the labyrinth-blood barrier and is detectable in peripheral blood. Serum otolin-1 levels differ between patients with benign paroxysmal positional vertigo (BPPV) and healthy controls and are significantly age-related, increasing in healthy controls with age, suggesting that serum otolin-1 levels reflect otolith status. The aim of this study was to determine whether otolin-1 levels change during vertigo episodes in patients with BPPV and whether any change is specific and sensitive enough for BPPV episodes.

Method: Patients diagnosed with de novo idiopathic BPPV during an acute episode were included in the study from May 2017 to May 2018. Blood samples were drawn before patients were treated with canalith-repositioning maneuvers. Serum otolin-1 levels were compared between 78 patients and 121 age- and sex-matched healthy individuals.

Results: There were no significant differences between the groups in the age distribution, sex ratio, body mass index, clinical history, routine blood parameters, or total protein, albumin, uric acid, creatinine, blood urea nitrogen and lipid profiles (P > 0.05). Serum levels of otolin-1 were significantly higher in BPPV patients than in healthy controls (P < 0.001). Receiver operating characteristic analysis revealed that a serum otolin-1 value of 299.45 pg/ml was the optimal cut-off value to discriminate patients with BPPV from healthy controls (area under the curve 0.757, 95% CI 0.687~0.826) with a sensitivity of 67.9% and a specificity of 72.7%.

Conclusion: Serum levels of otolin-1 may be a potential biomarker for BPPV episodes.

Functional derivatives of human dentin matrix protein 1 modulate morphology of calcium carbonate crystals

Dentin matrix protein 1 (DMP1) is an acidic, extracellular matrix protein essential for biomineralization of calcium phosphate, in bone and dentin. It is proteolytically processed into two fragments, 44K and 56K. Recently, the presence of DMP1 was noticed in inner ear, specifically in otoconia, which are calcium carbonate biominerals involved in sensing of balance. In this study, the solution structure and biomineralization activity of otoconial 44K and 56K fragments toward calcium carbonate were investigated. The results of analytical ultracentrifugation, circular dichroism, and gel filtration indicated that DMP1 fragments are disordered in solution. Notably, 56K formed oligomers in the presence of calcium ions. It was also observed that both fragments influenced the crystal growth by in vitro biomineralization assay and scanning electron microscopy. In addition, they sequester the calcium ions during the calcite formation. Calcium carbonate crystals precipitated in vitro changed their size and shape in the presence of DMP1 fragments. Oligomerization propensity of 56K may significantly enhance this function. Our study indicates that intrinsically disordered DMP1 has a previously unknown regulatory function for biomineralization of otoconia.

In situ 3D visualization of biomineralization matrix proteins

Calcium biominerals occur in all major animal phyla, and through biomolecular control, exhibit such diverse structures as exoskeletons, shells, bones, teeth and earstones (otoliths). Determining the three-dimensional expression of key biomineral proteins, however, has proven challenging as typical protein identification methods either lose spatial resolution during dissolution of the mineral phase or are costly and limited to two-dimensional expression of high abundance proteins. Here we present a modification of the CLARITY and ACT-PRESTO protocols to visualize and confirm, for the first time, the timing of expression and function of two key regulators of biomineralization.