Pathogenesis Of Otosclerosis Research Articles

Background Otosclerosis is a common ear disease that causes fixation of the stapes and conductive hearing impairment. However, the pathogenesis of otosclerosis is still unknown. Otosclerosis could be associated with the unique bony environment found in the otic capsule. Normal bone remodelling is almost completely absent around the inner ear after birth allowing degenerative changes and dead osteocytes to accumulate. High levels of inner ear anti resorptive osteoprotegerin (OPG) is most likely responsible for this capsular configuration. Studies have demonstrated how osteocyte lifespan variation creates occasional clusters of dead osteocytes, so-called cellular voids, at otosclerotic predilection sites in the human otic capsule. These cellular voids have been suggested as possible starting points of otosclerosis. Aim To describe the cellular viability in otosclerotic lesions and compare it to that of cellular voids. Materials and Methods The study was based on unbiased stereological quantifications in undecalcified human temporal bones with otosclerosis. Results Osteocyte viability was found to vary within the otosclerotic lesions. Furthermore, the results presented here illustrate that inactive otosclerotic lesions consist of mainly dead interstitial bone, much like cellular voids. Conclusions and significance Focal degeneration in the otic capsule may play an important role in the pathogenesis of otosclerosis.

Otosclerosis is one of the most common causes of progressive hearing loss, in particular in people of working age. The effectiveness of stapedial surgery largely determines the interest in studying the problems and prospects for the development of technologies, namely, the improvement of prostheses, surgical techniques, and assistance during interventions. It is worth noting that the main attention in the scientific literature is paid to the description of the clinic, the diagnosis of otosclerosis, as well as the methods of stapedoplasty. However, the question of the etiology and pathogenesis of this disease remains relevant and open for discussion, despite the many domestic and foreign works in this field. The emergence of new research methods, including molecular-genetic ones, contributed to the transition of research to a new level and the development of several new theories. Modern understanding of the pathogenesis of otosclerosis considers this disease as a multifactorial condition, in which many processes are involved, for example, genetic, hormonal, biochemical, and immunological. Likely, further study of the theory and hypothesis of the development of otosclerosis will find their justification, which will help answer many questions. The purpose of this article is to analyze and systematize data concerning various theories of the etiopathogenesis of the otosclerosis process, based on the study of modern domestic and foreign literature.

耳硬化症是影响听软骨囊内稳态的主要疾病，是导致获得性听力损失的最常见原因之一。其病因复杂，目前多认为由遗传和环境因素共同引起。研究表明遗传因素在耳硬化症的发生及发展过程中起着重要的作用，涉及多种分子途径，包括骨重塑、免疫途径、炎症及内分泌与代谢途径。本文回顾目前对耳硬化症病因及发病机制的认识，并总结一些已被证明有助于耳硬化症发展的环境和遗传因素。.

Otosclerosis is a focal lesion of the inner ear. The role of genetic factors in the pathogenesis of otosclerosis has received increasing attention. We analyzed the clinical manifestations, inheritance pattern, and pathogenic genes in a family with otosclerosis. We collected clinical data and generated a family pedigree. High-throughput second-generation sequencing technology was used to identify candidate genes by performing whole-exome sequencing of 7 members of the family, and Sanger sequencing was performed to validate candidate gene mutations in the 7 family members. Otosclerosis was characterized by autosomal dominant inheritance in this family. Whole-exome sequencing did not reveal mutation sites in known deafness-related genes. However, a c.2209A > G (p.T737A) mutation was detected in exon 6 of the SP1 gene, which is associated with the COL1A1 gene. This mutation was a pathogenic mutation, and Sanger sequencing confirmed that this mutation cosegregated with the clinical phenotype among the family members. The pattern of otosclerosis in this family is consistent with autosomal dominant inheritance, and the SP1 gene, harboring the c.2209A > G (p.T737A) mutation in exon 6, may be the causative gene of otosclerosis in this family.

Otosclerosis can be found exclusively in the human otic capsule of the temporal bone. Its etiology is still unknown. In the past decades, several potential etiopathogenetic factors have been revealed, however, most studies were based on otosclerotic patients diagnosed by clinical symptoms only. The current experience indicates that one third of this group suffer from non-otosclerotic stapes fixation. In our experimental series, we have diagnosed and classified otosclerotic patients based on histologic examination, and analyzed also the pathogenetic factors. Recent data demonstrate that measles virus and rs1800472 SNP of transforming growth factor beta 1 (TGFβ1) gene are marked obvious etiologic factors, which have no therapeutic consequences so far. Furthermore, we summarize the genetic and environmental factors to be found in the literature, which may play a fundamental role in the pathogenesis of otosclerosis. Orv Hetil. 2018; 159(30): 1215-1220.

Otosclerosis (OTSC) is defined by abnormal bone remodeling in the otic capsule of middle ear which leads to conductive hearing loss. In our previous study, we have identified a de novo heterozygous mutation −832G > A in the promoter of TGFB1 in an otosclerosis patient. In the present study, we progressively screened this mutation in a cohort of 254 cases and 262 controls. The family members of the patient positive for −832G > A variation were also screened and found inheritance of this variation only to her daughter. Interestingly, this variation is associated with a decreased level of the TGFB1 transcript in the patient compared to her parents and controls. In silico analysis of this mutation predicted the altered binding of two transcription factors v-Myb and MZF1 in the mutated promoter sequence. Further, functional analysis of this mutation using in vitro luciferase and electrophoretic mobility shift assays revealed that this variation is associated with decreased gene expression. In conclusion, this study established the fact that TGFB1 mutation −832G > A altered the TGFB1 promoter activity, which could affect the susceptibility to otosclerosis development. Further, systemic analysis of TGFB1 gene sequence and expression analysis of this gene might reveal its precise role in the pathogenesis of otosclerosis.

Otosclerosis (OTSC) is a late-onset hearing disorder characterized by increased bone turnover in the otic capsule. Disturbed osteoprotegerin expression has been found in the otosclerotic foci which may have an important role in the pathogenesis of OTSC. To identify the genetic risk factors, we sequenced the coding region and exon-intron boundaries of the OPG gene in 254 OTSC patients and 262 controls. Sequence analysis identified five known polymorphisms c.9C>G, c.30+15C>T, c.400+4C>T, c.768A>G, and c.817+8A>C. Testing of these SNPs revealed sex specific association with c.9C>G in males and c.30+15C>T in females after multiple correction. Furthermore, meta-analysis provided evidence of association of the c.9C>G polymorphism with OTSC. In secondary analysis, we investigated the mRNA expression of OPG and associated genes RANK and RANKL in otosclerotic tissues compared to controls. Expression analysis revealed significantly missing/reduced OPG expression only in otosclerotic tissues. However, the signal sequence polymorphism c.9C>G has shown no effect on OPG mRNA expression. In conclusion, our results suggest that the risk of OTSC is influenced by variations in the OPG gene along with other factors which might regulate its altered expression in otosclerotic tissues. Further research is warranted to elucidate the mechanisms underlying these observations.

In Ethiopians, like in other Africans, the incidence of otosclerosis is lower than in Western and Asian populations. Unfortunately, due to the lack of available otorhinolaryngology specialists many patients are not treated and suffer the progression of the disease and severe hearing loss. This program of the Global ENT Outreach Organization (GEO) together with the Ethiopian partners was done to help some of these patients and in parallel to evaluate the presence of the oxidative stress bioactive marker 4-hydroxynonenal (HNE), which is known as major lipid peroxidation product and the second messenger of free radicals, in the otosclerotic bone specimens. Namely, we described recently that as HNE acts as a bone growth regulator associated with pathogenesis of otosclerosis. The prospective study conducted at the ENT Department of the Migbare Senay General Hospital, Addis Ababa, Ethiopia in June 2012, under the auspices of the Global ENT Outreach Organization, USA. Altogether 36 patients (male = 12, female = 24) underwent surgery due to the previous otosclerosis diagnosis based on the clinical and audiometric findings. The bone samples were harvested from patients with intraoperatively confirmed otosclerosis diagnosis. Immunohistochemistry for HNE-modified proteins was carried out on formalin-fixed paraffin-embedded specimens. The presence of HNE was found in almost all bone samples analyzed, without particular difference in the HNE distribution pattern between the otosclerotic and respective control bone specimens. Although there was no significant association between the HNE appearance and otosclerotic bone outgrowth observed, several cases have shown tendency of higher HNE expression in patients with more severe hearing loss. The results of the present study are in contrast with our previous findings obtained on European patients most likely due to the differences between studied population groups.

Persistent measles virus infections play a crucial role in the pathomechanism of otosclerosis. The study was undertaken to investigate the role of tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β) and osteoprotegerin (OPG) in otosclerotic bone remodeling and to assess the relation of TNF-α, OPG and IL-1β expression levels in otosclerotic stape footplates to the occurrence of measles virus infection. 61 patients with otosclerosis were treated surgically. Thirty-one stapes obtained from cadavers of people, who had died from a sudden cause were used as a control group. The presence of measles virus RNA and the expression levels of TNF-α, IL-1β and OPG in otosclerotic foci were assessed using one-step RT-PCR. The presence of measles virus RNA was noted in 80.3 % of otosclerotic stapes (49 out of 61) and 9.7 % of normal tissues (3 out of 31). Transcript of TNF-α, IL-1β and OPG was detected in 40, 46 and 18 virus-positive stapes, respectively. The transcript level of TNF-α and IL-1β was significantly higher in otosclerotic tissues comparing to normal tissue. The OPG expression level was significantly lower in otosclerotic tissues comparing to controls. The presence of measles virus RNA in the stapes may indicate its role in the pathogenesis of otosclerosis. The presence of TNF-α and IL-1β mRNA in the virus-positive stapes could be the result of viral antigen stimulation and may be a marker of inflammation the otosclerotic focus. The lack of OPG mRNA and the presence of TNF-α and IL-1β mRNA in the majority of otosclerotic tissues reflect the bone remodeling process occurring in the stapes.

Recent studies have reported genetic associations between with single nucleotide polymorphism (SNP) of the several genes of the renin-angiotensin-aldosterone (RAA) system in otosclerosis without the confirmation of RAA system expression in human stapes footplates. There are conflicting results. These results are conflicting because RAA system expression has been attributed exclusively to neural, vascular, and renal tissues, exclusively. Ankylotic stapes footplates (n = 20), cortical bone fragments (n = 10), and human kidney tissue specimens (n = 10) were processed to hematoxylin-eosin (HE) staining and RAA system-specific immunofluorescent assay (IFA), respectively. Histologic diagnosis of otosclerosis was established in all ankylotic stapes footplates. Histologically active- (n = 13) and inactive (n = 7) foci of otosclerosis were consequently characterized by negative immunoreactions for renin, angiotensin converting enzyme (ACE), angiotensin-II (AT-II), and angiotensin-II receptor (AT-IIR), consequently. In cortical bones, a considerable RAA system expression was observed confirmed in the perivascular bone marrow progenitor cells. Kidney specimens, applied as positive controls, showed intense RAA system-specific immunoreactions. Concerning current observations, the 4 studied members of RAA system that did not display active expression were not expressed at protein level in otosclerotic stapes footplates. This phenomenon was independent from the histologic activity of otosclerosis. Between these conditions, the etiologic role of RAA system is questionable in the pathogenesis of otosclerosis.

Association of COL1A1 polymorphism in Turkish patients with otosclerosis

Conclusion: This study is the first to establish that bone morphogenetic protein 5 (BMP5) plays a role in the pathogenesis of otosclerosis. These results confirm that elevated expression levels of BMPs, members of the transforming growth factor (TGF)-β superfamily, contribute to the pathologically increased bone turnover in early, active stages of otosclerosis. Objectives: Otosclerosis is a complex bone remodeling disorder of the otic capsule, which might be characterized by increased expression of different types of BMPs. TGF-β and BMP are both members of the TGF-β superfamily and play a critical role in bone resorption and new bone formation. It has been suggested that BMP and its receptors may be involved in the pathologically increased bone turnover observed in otosclerosis. Methods: Fifty-one otosclerotic and 16 non-otosclerotic ankylotic stapes footplates were histologically analyzed: conventional hematoxylin-eosin staining and BMP2, 4, 5, and 7specific immunofluorescent assays were performed. Cortical bone fragments (n = 35) and incus specimens (n = 6) were used as negative controls. Results: Active otosclerosis (n = 39) was characterized by increased expression of BMP2, 4, 5, and 7. Inactive cases of otosclerosis (n = 12) were characterized by negative immunoreaction for BMPs. Non-otosclerotic stapes specimens (n = 16) and negative controls (n = 41) showed negligible BMP expression. The BMP expression pattern showed a strong correlation with the histological activity of otosclerosis.

This paper is a review of our most recent findings concerning the osteo-dynamics of the bony otic capsule and pathogenesis of otosclerosis. By exploring the spatial relationship between normal perilabyrinthine bone remodeling, the viability and spatial distribution of labyrinthine osteocytes, and the location of otosclerosis, a unique spatial pattern emerged. Bone remodeling is highly inhibited around the inner ear space. Most likely, inner ear anti-resorptive signals enter the bony otic capsule through the lacuno-canalicular porosity. The patency of this signaling pathway depends on the viability of individual osteocytes. In the young otic capsule the density of viable osteocytes is high and centripetally distributed. This arrangement may sustain a life-long osseus pathway for anti-resorptive signals even within a bone where a considerable loss of viable osteocytes must be expected, as demonstrated by a centripetal accumulation of dead osteocytes with age. The spatial distribution of dead osteocytes follows the same general pattern as otosclerosis. We suggest that clustering of dead osteocytes may impede the transmission of anti-resorptive signals locally, leaving such ghost regions susceptible to focal bone remodeling as in human otosclerosis. The preserved network of viable osteocytes around the depleted ghost regions may contain the process and distort the structure of bone remodeling into an abnormal otosclerotic pattern.

Several studies have reported a potential genetic association between disease-specific single nucleotide polymorphism (SNPs) of RELN and otosclerosis and confirmed RELN expression in human stapes footplates. These are conflicting results, since RELN expression has been attributed exclusively to neural tissues and to odontoblasts. Otosclerosis is a disease of complex bone remodeling disorder, which is limited to the human otic capsule. Genetic predisposition has long been suspected, however, the pathogenesis remained unclear. Ankylotic stapes footplates (n = 85), cortical bone fragments (n = 4), hearing ossicles (n = 2) and human brain tissue specimens (n = 4) were processed to RELN-specific RT-PCR and reelin-specific immunofluorescent assay (IFA). The first group of ankylotic stapes footplates (n = 22) showed a consistent positive reaction against reelin by IFA; however, RELN-specific mRNA could not be detected in the second, RT-PCR group (n = 63). Brain specimens were characterized by robust expression of reelin (n = 2) and RELN-specific mRNA (n = 2). In case of bone-specific controls (n = 6), reelin/RELN expression was excluded obviously. Concerning current observations, RELN gene does not show active expression in adult stapes footplates. Since, the otic capsule surrounds a special neural structure (membranous labyrinth), reelin might play a coordinative role in the early embryonic stage of development. As being a part of the otic capsule, stapes footplate might be characterized by persisting reelin detectability without mRNA expression. Between these conditions, the etiologic role of RELN is questionable in the pathogenesis of otosclerosis.

The objectives of our study was to review our current knowledge of the etiopathogenesis of otosclerotic bone remodeling including genetics, viral infection, autoimmunity and inflammation and to discuss disease pathogenesis with relevance to pharmacotherapy. Relevant publications on the etiopathogenesis, molecular biology, genetics and histopathology of otosclerosis from 1984 to 2009 were analyzed. Otosclerosis is a bone remodeling disorder of the human otic capsule; however, the etiopathogenesis remains unclear. Genetic predisposition, disturbed bone metabolism, persistent measles virus infection, autoimmunity, and hormonal and environmental factors also may play contributing roles in the pathogenesis of otosclerosis. Since diagnosis of otosclerosis is still based on histopathological examination of the removed stapes footplate, systemic prospective studies based on comprehensive histopathological and molecular biological analysis are necessary to obtain further information on the background of the disease.

Otosclerosis is a major cause of acquired hearing loss in adult life affecting exclusively the human temporal bone. Until recently, the etiopathogenesis of otosclerosis was still a matter of debate. Genetic research, however, has evolved enormously the last years and unveiled important clues regarding the cause of otosclerosis. The objective of this article is to review the genetics of otosclerosis with special attention for the links to the bone homeostasis of the otic capsule. A detailed literature study was performed focusing on the recent genetic findings in otosclerosis and the special bone turnover of the otic capsule. A PubMed search and own research data were used to bring the relevant information for this review together. Unlike all other bones in the human skeleton, the otic capsule undergoes very little remodeling after development, possibly due to local inner ear factors. Otosclerosis is a process of pathologic increased bone turnover in the otic capsule, which in most cases leads to stapes fixation, resulting in a conductive hearing loss. Although environmental factors such as estrogens, fluoride, and viral infection have been implicated, it is clear that genetic factors play a significant role in the manifestation of otosclerosis. From a genetic viewpoint, otosclerosis is considered to be a complex disease with rare autosomal dominant forms caused by a single gene. Already, 7 monogenic loci have been published, but none of the genes involved have been identified. For the complex form of otosclerosis, caused by an interaction between genetic and environmental factors, the first susceptibility genes were identified by case-control association studies. All 3 replicated genes, TGFB1, BMP2, and BMP4, are a part of the transforming growth factor-beta1 pathway. Data from both genetic association studies and gene expression analysis of otosclerotic bone showed that the TGF-beta1 pathway is most likely an important factor in the pathogenesis of otosclerosis.

Otosclerosis is a common form of hearing loss characterized by abnormal bone remodeling in the otic capsule. It is considered a complex disease caused by both genetic and environmental factors. In a previous study, we identified a region on chr7q22.1 located in the RELN gene that is associated with otosclerosis in Belgian-Dutch and French populations. Evidence for allelic heterogeneity was found in this chromosomal region in the form of two independent signals. To confirm this finding, we have completed a replication study that includes four additional populations from Europe (1,141 total samples). Several SNPs in this region replicated in these populations separately. While the power to detect significant association in each population is small, when all four populations are combined, six of seven SNPs replicate and show an effect in the same direction as in the previous populations. We also confirmed the presence of allelic heterogeneity in this region. These data further implicate RELN in the pathogenesis of otosclerosis. Functional research is warranted to determine the pathways through which RELN acts in the pathogenesis of otosclerosis.

A Genome-wide Analysis Identifies Genetic Variants in the RELN Gene Associated with Otosclerosis

To the Editor: The last issue of the journal (Otology & Neurotology, 28:301-3) published a paper titled "Otosclerosis of the Incus." Escada et al. (1) describes a bony lesion in the incus that is considered to be otosclerotic upon hematoxylin-eosin staining and a single light microscopic histological examination (1). A series of articles have been published during the last 3 years about the pathogenesis of otosclerosis (Karosi et al. 2-4). These reports clearly call the attention to the fact that all histologically otosclerotic stapes fixations are associated with the presence of measles virus genomic RNA. Otosclerotic stapes fixations are, however, only two thirds of the stapes fixations in a series of more than 300 stapes footplates consecutively operated on during the last 4 years (3,4). Similar histological lesions and/or presence of measles virus in the stapes superstructure or other bones are not found. Those ankylotic stapes that do not represent otosclerosis show heterogeneous histological pattern of localized hemosiderosis, lymphocytic-plasmocytic infiltration with thickened stapedial mucosal layer, globular fibrosis, or annular calcification (3,4). The otic capsule shows inevitable affinity to persisting measles virus infection and replication, which coincides with the organ-specific localization of otosclerotic foci. The subsequent inflammatory process is characterized by pseudovascular, irregular, and hypercellular absorption lacunae bordered by numerous osteoclasts and multi-nucleated giant cells in the active stage. In contrast, the inactive phase of otosclerosis is featured by almost total absence of bone-derived cells with woven and mosaiclike pattern of cement lines. In these cases, the osteoid substance represents homogeneous eosinophilia. Nevertheless, cement lines cannot be visualized without polarizing light microscopic analysis (3,4), and cement line pattern is a structure of inorganic bony material that is not identical with the osteoid rings bordered by osteocytes. The presented histological section of the incus in the cited article shows no sign of the aforementioned histological features; rather, it shows regular vascular cross sections and Haversian lacunae (1). The section shows normal cellularity and concentric disposition of regular osteocytes. No osteoclasts or giant cells can be identified. The osteoid substance is eosinophilic, only the bulky perivascular connective tissue and vascular endothelial cells are characterized by basophilia. It does not represent information about the pattern of osteoid cement lines. It would be helpful to identify the sectioned part of the incus because intraosseal vascular network is different in the long process and in the body. In addition, the serological diagnosis of otosclerosis is based upon the antimeasles immunoglobulin G low concentration (<12 IU/mL) in the sera of these patients versus healthy immunized individuals' high titer (>100 IU/mL) (5). The specificity and sensitivity of this test for otosclerosis in conductive hearing loss are around 95% (5). Today, we do think, that the diagnosis of otosclerosis cannot be established without detecting low antimeasles immunoglobulin G in the serum and/or detecting measles virus RNA in the affected bone specimen. István Sziklai, M.D., D.Sc. Tamás Karosi, M.D., Ph.D. Department of Otolaryngology- Head and Neck Surgery University Medical School of Debrecen Debrecen, Hungary

The aim of this article is to summarize and put into historical perspective current advances in research in otosclerosis, a disorder of the human temporal bone with a hereditary predisposition that is among the most common causes of acquired hearing loss. Genetic studies have revealed that otosclerosis is heterogeneous, with evidence for defects in at least seven genes associated with six distinct chromosomal loci. Measurements of high levels of osteoprotegerin expression in the normal otic capsule and soft tissues of the cochlea provide the first molecular insight as to why the normal otic capsule remodels minimally, if at all. Osteoprotegerin knockout mice provide the best available animal model to date to study abnormal otic capsule remodeling that closely resembles otosclerosis. There is mounting evidence that the measles virus plays an important role in pathogenesis of otosclerosis although the mechanisms by which the virus results in otosclerosis remain unknown. Quantitative measures of angiogenesis can reliably distinguish between clinical and histological otosclerosis. Advances in the emerging field of osteoimmunology will likely impact and benefit from the research in otosclerosis. Insights into molecular mechanisms that inhibit extensive remodeling in the normal otic capsule, and understanding of how these mechanisms are dysregulated in otosclerosis will allow future design of rational treatment strategies for otosclerosis.