The coding polymorphism T263I in TGF-β1 is associated with otosclerosis in two independent populations

Dynamic Molecular Markers of Otosclerosis in the Human Cochlea

OBJECTIVE

To investigate the role and distribution of various molecular markers using immunohistochemistry and immunofluorescence to further elucidate and understand the pathogenesis of otosclerosis.

METHODS

Archival celloidin formalin-fixed 20-micron thick histologic sections from 7 patients diagnosed with otosclerosis were studied and compared to controls. Sections in the mid-modiolar region were immunoreacted with rabbit polyclonal antibodies against nidogen-1, β2-laminin, collagen-IX, BSP, and monoclonal antibodies against TGF β-1 and ubiquitin. Digital images were acquired using a high-resolution light and laser confocal microscope.

RESULTS

Nidogen-1, BSP, and collagen-IX were expressed in the otospongiotic regions, and to lesser extent, in the otosclerotic regions, the latter previously believed to be inactive. β2-laminin and ubiquitin were uniformly expressed in both otospongiotic and otosclerotic regions. There was a basal level of expression of all of these markers in the normal hearing and sensorineural hearing loss specimens utilized as control. TGF β -1, however, though present in the otosclerosis bones, was absent in the normal hearing and sensorineural hearing loss controls.

CONCLUSIONS

Our results propose that the activity and function of TGF-1 may play a key role in the development and pathogenesis of otosclerosis. Further studies utilizing a higher number of temporal bone specimens will be helpful for future analysis and to help decipher its role as a potential target in therapeutic interventions.

SMARCA4 mutation causes human otosclerosis and a similar phenotype in mice

BACKGROUND

Otosclerosis is a common cause of adult-onset progressive hearing loss, affecting 0.3%-0.4% of the population. It results from dysregulation of bone homeostasis in the otic capsule, most commonly leading to fixation of the stapes bone, impairing sound conduction through the middle ear. Otosclerosis has a well-known genetic predisposition including familial cases with apparent autosomal dominant mode of inheritance. While linkage analysis and genome-wide association studies suggested an association with several genomic loci and with genes encoding structural proteins involved in bone formation or metabolism, the molecular genetic pathophysiology of human otosclerosis is yet mostly unknown.

METHODS

Whole-exome sequencing, linkage analysis, generation of CRISPR mutant mice, hearing tests and micro-CT.

RESULTS

Through genetic studies of kindred with seven individuals affected by apparent autosomal dominant otosclerosis, we identified a disease-causing variant in SMARCA4, encoding a key component of the PBAF chromatin remodelling complex. We generated CRISPR-Cas9 transgenic mice carrying the human mutation in the mouse SMARCA4 orthologue. Mutant Smarca4+/E1548K mice exhibited marked hearing impairment demonstrated through acoustic startle response and auditory brainstem response tests. Isolated ossicles of the auditory bullae of mutant mice exhibited a highly irregular structure of the incus bone, and their in situ micro-CT studies demonstrated the anomalous structure of the incus bone, causing disruption in the ossicular chain.

CONCLUSION

We demonstrate that otosclerosis can be caused by a variant in SMARCA4, with a similar phenotype of hearing impairment and abnormal bone formation in the auditory bullae in transgenic mice carrying the human mutation in the mouse SMARCA4 orthologue.

Targeted Resequencing of Otosclerosis Patients from Different Populations Replicates Results from a Previous Genome-Wide Association Study

Otosclerosis is one of the most common causes of hearing loss in young adults. It has a prevalence of 0.3-0.4% in the European population. Clinical symptoms usually occur between the second and fifth decade of life. Different studies have been performed to unravel the genetic architecture of the disease. Recently, a genome-wide association study (GWAS) identified 15 novel risk loci and replicated the regions of three previously reported candidate genes. In this study, seven candidate genes from the GWAS were resequenced using single molecule molecular inversion probes (smMIPs). smMIPs were used to capture the exonic regions and the 3' and 5' untranslated regions (UTR). Discovered variants were tested for association with the disease using single variant and gene-based association analysis. The single variant results showed that 13 significant variants were associated with otosclerosis. Associated variants were found in five of the seven genes studied here, including AHSG, LINC01482, MARK3, SUPT3H and RELN. Conversely, burden testing did not show a major role of rare variants in the disease. In conclusion, this study was able to replicate five out of seven candidate genes reported in the previous GWAS. This association is likely mainly driven by common variants.

The risks of RELN polymorphisms and its expression in the development of otosclerosis

Otosclerosis (OTSC) is the primary form of conductive hearing loss characterized by abnormal bone remodelling within the otic capsule of the human middle ear. A genetic association of the RELN SNP rs3914132 with OTSC has been identified in European population. Previously, we showed a trend towards association of this polymorphism with OTSC and identified a rare variant rs74503667 in a familial case. Here, we genotyped these variants in an Indian cohort composed of 254 OTSC cases and 262 controls. We detected a significant association of rs3914132 with OTSC (OR = 0.569, 95%CI = 0.386–0.838, p = 0.0041). To confirm this finding, we completed a meta-analysis which revealed a significant association of the rs3914132 polymorphism with OTSC (Z = 6.707, p<0.0001) across different ethnic populations. Linkage analysis found the evidence of linkage at RELN locus (LOD score 2.1059) in the OTSC family which has shown the transmission of rare variant rs74503667 in the affected individuals. To understand the role of RELN and its receptors in the development of OTSC, we went further to perform a functional analysis of RELN/reelin. Here we detected a reduced RELN (p = 0.0068) and VLDLR (p = 0.0348) mRNA levels in the otosclerotic stapes tissues. Furthermore, a reduced reelin protein expression by immunohistochemistry was confirmed in the otosclerotic tissues. Electrophoretic mobility shift assays for rs3914132 and rs74503667 variants revealed an altered binding of transcription factors in the mutated sequences which indicates the regulatory role of these variations in the RELN gene regulation. Subsequently, we showed by scanning electron microscopy a change in stapes bone morphology of otosclerotic patients. In conclusion, this study evidenced that the rare variation rs74503667 and the common polymorphism rs3914132 in the RELN gene and its reduced expressions that were associated with OTSC.

Genetics of otosclerosis: finally catching up with other complex traits?

Otosclerosis is a relatively common cause of hearing impairment, characterized by abnormal bone remodeling of the middle and inner ear. In about 50-60% of the patients, the disease is present in a familial form. In most of these families, otosclerosis seems to be caused by a small number of genetic factors (oligogenic) while only in a small number of families the disease seems to be truly monogenic. In the remaining patients a complex genetic form of otosclerosis is present. Several studies have aimed to identify the genetic factors underlying otosclerosis, which has led to the identification of eight published loci for monogenic otosclerosis, as well as several genes and one chromosomal region (11q13.1) with a clear association with otosclerosis. Implementation of next-generation sequencing (NGS) in otosclerosis research has led to the identification of pathogenic variants in MEPE, ACAN and SERPINF1, although the pathogenic role of the latter is under debate. In addition, a recent GWAS can be considered a breakthrough for otosclerosis as it identified several strong associations with otosclerosis and suggested new potential candidate genes. These recent findings are important for unraveling the genetic architecture of otosclerosis. More future studies will help to understand the complete pathogenesis of the disease.

Personalized Proteomics for Precision Diagnostics in Hearing Loss: Disease-Specific Analysis of Human Perilymph by Mass Spectrometry

Despite a vast amount of data generated by proteomic analysis on cochlear fluid, novel clinically applicable biomarkers of inner ear diseases have not been identified hitherto. The aim of the present study was to analyze the proteome of human perilymph from cochlear implant patients, thereby identifying putative changes of the composition of the cochlear fluid perilymph due to specific diseases. Sampling of human perilymph was performed during cochlear implantation from patients with clinically or radiologically defined inner ear diseases like enlarged vestibular aqueduct (EVA; n = 14), otosclerosis (n = 10), and Ménière's disease (n = 12). Individual proteins were identified by a shotgun proteomics approach and data-dependent acquisition, thereby revealing 895 different proteins in all samples. Based on quantification values, a disease-specific protein distribution in the perilymph was demonstrated. The proteins short-chain dehydrogenase/reductase family 9C member 7 and esterase D were detected in nearly all samples of Ménière's disease patients, but not in samples of patients suffering from EVA and otosclerosis. The presence of both proteins in the inner ear tissue of adult mice and neonatal rats was validated by immunohistochemistry. Whether these proteins have the potential for a biomarker in the perilymph of Ménière's disease patients remains to be elucidated.

A wide range of protective and predisposing variants in aggrecan influence the susceptibility for otosclerosis

In this study, we investigated the association of ACAN variants with otosclerosis, a frequent cause of hearing loss among young adults. We sequenced the coding, 5'-UTR and 3'-UTR regions of ACAN in 1497 unrelated otosclerosis cases and 1437 matched controls from six different subpopulations. The association between variants in ACAN and the disease risk was tested through single variant and gene-based association tests. After correction for multiple testing, 14 variants were significantly associated with otosclerosis, ten of which represented independent association signals. Eight variants showed a consistent association across all subpopulations. Allelic odds ratios of the variants identified four predisposing and ten protective variants. Gene-based tests showed an association of very rare variants in the 3'-UTR with the phenotype. The associated exonic variants are all located in the CS domain of ACAN and include both protective and predisposing variants with a broad spectrum of effect sizes and population frequencies. This includes variants with strong effect size and low frequency, typical for monogenic diseases, to low effect size variants with high frequency, characteristic for common complex traits. This single-gene allelic spectrum with both protective and predisposing alleles is unique in the field of complex diseases. In conclusion, these findings are a significant advancement to the understanding of the etiology of otosclerosis.

Clinical utility of TGFB1 and its receptors (TGFBR1 and TGFBR2) in thyroid nodules: evaluation based on single nucleotide polymorphisms and mRNA analysis

Objective

Abnormalities involving the TGFB1 gene and its receptors are common in several types of cancer and often related to tumor progression. We investigated the role of single nucleotide polymorphisms (SNP) in the susceptibility to cancer, their impact on its features, as well as the role of mRNA expression of these genes in thyroid malignancy.

Methods

We genotyped TGFB1, TGFBR1, and TGFBR2 SNPs in 157 papillary thyroid cancer (PTC) patients and 200 healthy controls. Further, we investigated RNA samples of 47 PTC and 80 benign nodules, searching for differential mRNA expression.

Results

SNPs rs1800472 and rs1800469 were associated with characteristics of PTC aggressiveness. Effect predictor software analysis of nonsynonymous SNP rs1800472 indicated increasing protein stability and post-translational changes. TGFB1 mRNA expression was upregulated in PTC and downregulated in benign samples, differentiating malignant from benign nodules (p<0.0001); PTC from goiter (p<0.0001); and PTC from FA (p<0.0001). TGFBR1 mRNA expression was upregulated in goiter and PTC, but downregulated in FA, distinguishing PTC from goiter (p=0.0049); PTC from FA (p<0.0001); and goiter from FA (p=0.0267). On the other hand, TGFBR2 was downregulated in all histological types analyzed and was not able to differentiate thyroid nodules.

Conclusion

TGFB1 polymorphism rs1800472 may confer greater activity to TGF-β1 in the tumor microenvironment, favoring PTC aggressiveness. Evaluation of TGFB1 and TGFBR1 mRNA levels may be useful to identify malignancy in thyroid nodules.

Otosclerosis and Measles: Do Measles Have a Role in Otosclerosis? A Review Article

Otosclerosis is a common cause of conductive hearing loss which is an autoimmune inflammatory disorder related to abnormal bone remodeling of the human otic capsule that has complex etiopathogenesis attributed to genetics, autoimmunity, viral infection, inflammation, hormonal factor, environmental factor, and disturbed bone metabolism. It has a prevalence of 0.3%-0.4% in Caucasians, which makes up 5-9% of all hearing loss and 18-22% of all conductive hearing loss. This review article aims to study the postulated role of sustained measles virus infection in the etiopathogenesis of otosclerosis, among others. A PubMed search of the related topic identified 97,990 articles. After we applied the inclusion and exclusion criteria, it was determined that 52 articles were relevant, which included 38 observational studies, 13 review articles, and a systematic review. Among them, 33 observational studies, 13 review articles and a systematic review spotted a positive association between persistent measles virus infection and otosclerosis. On the contrary, five observational studies reported no evidence of the association. The majority of the current literature supported the presence of the measles virus component in the otosclerotic stapes samples and its role in the etiopathogenesis of otosclerosis. Measles virus infection may have the amplitude to initiate a pathological process, which in the presence of other factors like autoimmunity and genes plays a significant role in causing otosclerosis. However, other studies have failed to show the presence of the measles virus component in otosclerotic stapes. So, more studies are needed to probe the role of persistent measles virus infection in the etiopathogenesis of otosclerosis.

Evaluation of Gene Variants in TGFB1, SERPINF1 and MEPE in a Spanish Family Affected by Otosclerosis and Tinnitus

Otosclerosis (OTSC) is a common type of deafness affecting up to 0.4 % of Caucasians. Its familial form is inherited in an autosomal dominant fashion, although to this date, no definitive cause for OTSC has been found. In the development of OTSC, three recent genetic association studies have suggested the participation of particular point mutations and small indels in the TGFB1, SERPINF1, and MEPE genes. Consequently, replicative studies are needed to confirm the role of the proposed mutations in OTSC patients. The goal of this study was to test the presence of the candidate variants described in the genes TGFB1, SERPINF1, and MEPE in a new case of familial OTSC with seven affected individuals. DNA was extracted from saliva samples of a Spanish family with several members affected by OTSC. PCR amplified target regions of some candidate genes, and the products were purified, Sanger-sequenced, and analyzed in silico. The family subject of the study did not carry the candidate variants for OTSC described in the genes TGFB1, SERPINF1, and MEPE, although it cannot be ruled out the involvement of other mutations in genes related to their same signaling pathways. This result highlights the importance of performing replicative studies for complex diseases, such as OTCS, in families of diverse origins. Additionally, a significant association of subjective tinnitus with OTSC has been found in this family, although the link between the two pathologies should be studied further.

Insufficient evidence for a role of SERPINF1 in otosclerosis

Otosclerosis is a common form of hearing loss (HL) due to abnormal remodeling of the otic capsule. The genetic causes of otosclerosis remain largely unidentified. Only mutations in a single gene, SERPINF1, were previously published in patients with familial otosclerosis. To unravel the contribution of genetic variation in this gene to otosclerosis, this gene was re-sequenced in a large population of otosclerosis patients and controls. Resequencing of the 5' and 3' UTRs, coding regions, and exon-intron boundaries of SERPINF1 was performed in 1604 unrelated otosclerosis patients and 1538 unscreened controls, and in 62 large otosclerosis families. Our study showed no enrichment of rare variants, stratified by type, in SERPINF1 in patients versus controls. Furthermore, the c.392C > A (p.Ala131Asp) variant, previously reported as pathogenic, was identified in three patients and four controls, not replicating its pathogenic nature. We could also not find evidence for a pathogenic role in otosclerosis for 5' UTR variants in the SERPINF1-012 transcript (ENST00000573763), described as the major transcript in human stapes. Furthermore, no rare variants were identified in the otosclerosis families. This study does not support a pathogenic role for variants in SERPINF1 as a cause of otosclerosis. Therefore, the etiology of the disease remains largely unknown and will undoubtedly be the focus of future studies.

Evidence of distinct RELN and TGFB1 genetic associations in familial and non-familial otosclerosis in a British population

Otosclerosis is a common form of hearing loss which typically presents in young adults. The disease has a familial, monogenic form and a non-familial form with a more complex aetiology. A previous genome wide association study identified evidence that variants within RELN are associated with the condition. Other genes in which an association has been reported include BMP2, COL1A1, FGF2, PPP2R5B and TGFB1. However, follow up studies have often failed to replicate initial positive results. The aim of this study was to establish if an association exists between eight single nucleotide polymorphisms (SNPs) in these six previously implicated genes and otosclerosis in a British case–control cohort (n = 748). Evidence of an association between rs1800472 in TGFB1 and otosclerosis was found (p = 0.034), this association was strongest amongst non-familial cases (p = 0.011). No evidence of an association was detected with variants in COL1A1, FGF2, BMP2, and PPP2R5B. No association between variation in RELN and otosclerosis was observed in the whole cohort. However, a significant association (p = 0.0057) was detected between one RELN SNP (rs39399) and otosclerosis in familial patients. Additionally, we identify expression of one RELN transcript in 51 of 81 human stapes tested, clarifying previous conflicting data as to whether RELN is expressed in the affected tissue. Our findings strengthen the association of TGFB1 (rs1800472) with otosclerosis and support a relationship between RELN and familial otosclerosis only, which may explain previous variable replications.

Single nucleotide polymorphisms in the TGF-β1 gene are associated with polycystic ovary syndrome susceptibility and characteristics: a study in Korean women

PURPOSE

Although many hypotheses regarding the pathogenesis of polycystic ovary syndrome (PCOS) have been generated, genetic studies have not identified specific genes that play a role in PCOS etiopathogenesis. This study aimed to investigate the relationship between TGF-β1 gene polymorphism and PCOS in Koreans.

METHOD

A total of 51 Korean women with PCOS and 69 healthy women were enrolled. We analyzed 4 single nucleotide polymorphisms (SNPs) of the TGF-β1 gene (rs11466313, rs1800469, rs2317130, and rs4803457). We also analyzed laboratory measurements, such as free testosterone, glucose, and cholesterol.

RESULTS

The frequencies of rs1800469T allele negativity, rs4803457T allele negativity, the rs1800469CC genotype, and the rs4803457CC genotype showed positive associations with PCOS (P = 0.003, P = 0.027, P = 0.009, and P=0.031, respectively), whereas the haplotypes rs1800469C-rs4803457T and rs1800469T-rs4803457T showed negative associations with PCOS. A strong protective effect of the "rs1800469CT-rs4803457TT" combination (OR = 0.09) and a strong risk effect of "rs1800469CC-rs4803457CC" (OR = 6.23) for PCOS were observed. The rs1800469C/T and rs2317130C/T SNPs exhibited associations with several laboratory measurements with various levels of significance.

CONCLUSION

The results demonstrated an association of TGF-β1 gene polymorphisms with the development and/or characteristics of PCOS in the Korean population.

The TGF-β Signalling Network in Muscle Development, Adaptation and Disease

Skeletal muscle possesses remarkable ability to change its size and force-producing capacity in response to physiological stimuli. Impairment of the cellular processes that govern these attributes also affects muscle mass and function in pathological conditions. Myostatin, a member of the TGF-β family, has been identified as a key regulator of muscle development, and adaptation in adulthood. In muscle, myostatin binds to its type I (ALK4/5) and type II (ActRIIA/B) receptors to initiate Smad2/3 signalling and the regulation of target genes that co-ordinate the balance between protein synthesis and degradation. Interestingly, evidence is emerging that other TGF-β proteins act in concert with myostatin to regulate the growth and remodelling of skeletal muscle. Consequently, dysregulation of TGF-β proteins and their associated signalling components is increasingly being implicated in muscle wasting associated with chronic illness, ageing, and inactivity. The growing understanding of TGF-β biology in muscle, and its potential to advance the development of therapeutics for muscle-related conditions is reviewed here.

Otosclerosis Associated with a De Novo Mutation -832G > A in the TGFB1 Gene Promoter Causing a Decreased Expression Level

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.

Mutations and altered expression of SERPINF1 in patients with familial otosclerosis

Otosclerosis is a relatively common heterogenous condition, characterized by abnormal bone remodelling in the otic capsule leading to fixation of the stapedial footplate and an associated conductive hearing loss. Although familial linkage and candidate gene association studies have been performed in recent years, little progress has been made in identifying disease-causing genes. Here, we used whole-exome sequencing in four families exhibiting dominantly inherited otosclerosis to identify 23 candidate variants (reduced to 9 after segregation analysis) for further investigation in a secondary cohort of 84 familial cases. Multiple mutations were found in the SERPINF1 (Serpin Peptidase Inhibitor, Clade F) gene which encodes PEDF (pigment epithelium-derived factor), a potent inhibitor of angiogenesis and known regulator of bone density. Six rare heterozygous SERPINF1 variants were found in seven patients in our familial otosclerosis cohort; three are missense mutations predicted to be deleterious to protein function. The other three variants are all located in the 5′-untranslated region (UTR) of an alternative spliced transcript SERPINF1-012. RNA-seq analysis demonstrated that this is the major SERPINF1 transcript in human stapes bone. Analysis of stapes from two patients with the 5′-UTR mutations showed that they had reduced expression of SERPINF1-012. All three 5′-UTR mutations are predicted to occur within transcription factor binding sites and reporter gene assays confirmed that they affect gene expression levels. Furthermore, RT-qPCR analysis of stapes bone cDNA showed that SERPINF1-012 expression is reduced in otosclerosis patients with and without SERPINF1 mutations, suggesting that it may be a common pathogenic pathway in the disease.

Identification of target proteins involved in cochlear otosclerosis

HYPOTHESIS

Investigation of differential protein expression will provide clues to pathophysiology in otosclerosis.

BACKGROUND

Otosclerosis is a bone remodeling disorder limited to the endochondral layer of the otic capsule within the temporal bone. Some authors have suggested an inflammatory etiology for otosclerosis resulting from persistent measles virus infection involving the otic capsule. Despite numerous genetic studies, implication of candidate genes in the otosclerotic process remains elusive. We employed liquid chromatography-mass spectrometry (LC-MS) analysis on formalin-fixed celloidin-embedded temporal bone tissues for postmortem investigation of otosclerosis.

METHODS

Proteomic analysis was performed using human temporal bones from a patient with severe otosclerosis and a control temporal bone. Sections were dissected under microscopy to remove otosclerotic lesions and normal otic capsule for proteomic analysis. Tandem 2D chromatography mass spectrometry was employed. Data analysis and peptide matching to FASTA human databases was done using SEQUEST and proteome discoverer software.

RESULTS

TGFβ1 was identified in otosclerosis but not in the normal control temporal bone specimen. Aside from TGFβ1, many proteins and predicted cDNA-encoded proteins were observed, with implications in cell death and/or proliferation pathways, suggesting a possible role in otosclerotic bone remodeling. Immunostaining using TGFβ1 monoclonal revealed marked staining of the spongiotic otosclerotic lesions.

CONCLUSIONS

Mechanisms involved in cochlear extension of otosclerosis are still unclear, but the implication of TGFβ1 is supported by the present proteomic data and immunostaining results. The established role of TGFβ1 in the chondrogenesis process supports the theory of a reaction targeting the globulae interossei within the otic capsule.

Genetic association and altered gene expression of osteoprotegerin in otosclerosis patients

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.

Genetic association analysis in a clinically and histologically confirmed otosclerosis population confirms association with the TGFB1 gene but suggests an association of the RELN gene with a clinically indistinguishable otosclerosis-like phenotype

BACKGROUND/HYPOTHESIS

Otosclerosis is a frequent cause of hearing impairment characterized by abnormal resorption and deposition of bone in the human otic capsule. It is a disease of complex etiopathogenesis that is caused by both environmental and genetic factors. The goal of this study is to replicate association for genes that were previously reported to be associated with otosclerosis. However, in this study, patients were used in which the presence of otosclerotic foci was confirmed by histologic investigation, in contrast to previous studies, that did not use histologic confirmation.

METHODS

Case-control association study using 153 cases and 300 controls. Thirteen single nucleotide polymorphisms (SNPs) in 6 genes (COL1A1, TGFB1, BMP2, BMP4, AGT, and RELN) were genotyped.

RESULTS

An association between TGFB1 (rs1800472) and otosclerosis was detected, confirming several previous reports. It is surprising that no association was found between RELN and otosclerosis because the current analysis had very reasonable power and the RELN association has been published before in different articles using several independent populations.

CONCLUSION

Our findings strengthen the association of TGFB1 (rs1800472) with otosclerosis. The fact that other genes did not replicate could be due to different reasons like lack of power (BMP2 and BMP4) and possible false-positive initial association (COL1A1 and AGT). A plausible explanation for the lack of association for RELN is that RELN could be associated with a specific otosclerosis-like phenotype that is different from the histologically confirmed phenotype of the patients in this study, and that is clinically not distinguishable.

Rare variants in BMP2 and BMP4 found in otosclerosis patients reduce Smad signaling

HYPOTHESIS

Genetic variation in BMP2 and BMP4 found in otosclerosis patients result in altered Smad signaling.

BACKGROUND

Otosclerosis is a common form of adult-onset conductive hearing loss resulting from abnormal bone remodeling of the bony labyrinth that surrounds the inner ear. Both genetic and environmental factors are implicated in the disease, yet very little is known about its pathogenesis. The evidence for a genetic component has been established through family-based linkage and population-based association studies. Previously, members of the TGF-β superfamily of genes have been associated with otosclerosis.

METHODS

Sequencing of BMP2 and BMP4 coding regions was performed to identify common and rare variation in German otosclerosis patients compared with controls. Functional analyses of rare variation in the patient cohort were conducted by exposing an osteosarcoma cell line to conditioned media containing either wild type or variant forms of BMP2 or BMP4 and analyzing Smad1/5/8 phosphorylation.

RESULTS

Although no significant association with common variation in these 2 genes was detected, there were 8 singleton variants identified in the German population. Of the 4 coding variants found solely in otosclerosis patients, two--BMP4(N150K) and BMP2(K357-R396del)--were found to decrease Smad1/5/8 signaling.

CONCLUSION

Rare variants in BMP2 and BMP4 are not a major genetic component in the otosclerosis population. However, those with functional affect showed decreased Smad signaling. Further analysis of Smad signaling molecules should be performed to determine if these pathways in combination are a major contributor to otosclerosis, which could lead to additional treatment options for otosclerosis patients.

A comprehensive network and pathway analysis of human deafness genes

OBJECTIVE

To perform comprehensive network and pathway analyses of the genes known to cause genetic hearing loss.

STUDY DESIGN

In silico analysis of deafness genes using ingenuity pathway analysis (IPA).

METHODS

Genes relevant for hearing and deafness were identified through PubMed literature searches and the Hereditary Hearing Loss Homepage. The genes were assembled into 3 groups: 63 genes that cause nonsyndromic deafness, 107 genes that cause nonsyndromic or syndromic sensorineural deafness, and 112 genes associated with otic capsule development and malformations. Each group of genes was analyzed using IPA to discover the most interconnected, that is, "nodal" molecules, within the most statistically significant networks (p < 10).

RESULTS

The number of networks that met our criterion for significance was 1 for Group 1 and 2 for Groups 2 and 3. Nodal molecules of these networks were as follows: transforming growth factor beta1 (TGFB1) for Group 1, MAPK3/MAPK1 MAP kinase (ERK 1/2) and the G protein coupled receptors (GPCR) for Group 2, and TGFB1 and hepatocyte nuclear factor 4 alpha (HNF4A) for Group 3. The nodal molecules included not only those known to be associated with deafness (GPCR), or with predisposition to otosclerosis (TGFB1), but also novel genes that have not been described in the cochlea (HNF4A) and signaling kinases (ERK 1/2).

CONCLUSION

A number of molecules that are likely to be key mediators of genetic hearing loss were identified through three different network and pathway analyses. The molecules included new candidate genes for deafness. Therapies targeting these molecules may be useful to treat deafness.

Exclusion of TNFRSF11B as Candidate Gene for Otosclerosis in Campania Population

The etiology of otosclerosis is unknown. The etiopathogenesis of otosclerosis seems similar to that occurring in Paget's disease of bone, for which mutations or polymorphisms in several genes have been identified. Among these, TNFRSF11B gene encoding the osteoprotegerin is produced at high levels in the normal inner ear and at low level in active otosclerotic stapes footplates. The aim of this work was to verify the presence of a correlation between the rs2073618 (N3K) polymorphism in the TNFRSF11B gene and otosclerosis. Mutational screening in the TNFRSF11B gene was performed by direct sequencing. SNPs analysis was performed by PCR and by specific restriction enzyme assay with HpaI. The significance of the association was analyzed by statistical specific software. No causative mutation has been identified but the data suggested a strong correlation between the rs2073618 (N3K) polymorphism and otosclerosis. This correlation, however, has been excluded in a case-control study. This study excluded the association between the N3K polymorphism and otosclerosis in Campania region population.

TheTGFB1 functional polymorphism rs1800469 and susceptibility to atrial fibrillation in two Chinese Han populations

Transforming growth factor-β1 (TGF-β1) is related to the degree of atrial fibrosis and plays critical roles in the induction and perpetuation of atrial fibrillation (AF). To investigate the association of the common promoter polymorphism rs1800469 in the TGF-β1 gene (TGFB1) with the risk of AF in Chinese Han population, we carried out a case-control study of two hospital-based independent populations: Southeast Chinese population (581 patients with AF and 723 controls), and Northeast Chinese population (308 AF patients and 292 controls). Two hundred and seventy-eight cases of AF were lone AF and 334 cases of AF were diagnosed as paroxysmal AF. In both populations, AF patients had larger left atrial diameters than the controls did. The rs1800469 genotypes in the TGFB1 gene were determined by polymerase chain reaction-restriction fragment length polymorphism. The genotype and allele frequencies of rs1800469 were not different between AF patients and controls of the Southeast Chinese population, Northeast Chinese population, and total Study Population. After adjustment for age, sex, hypertension and LAD, there was no association between the rs1800469 polymorphism and the risk of AF under the dominant, recessive and additive genetic models. Similar results were obtained from subanalysis of the lone and paroxymal AF subgroups. Our results do not support the role of the TGFB1 rs1800469 functional gene variant in the development of AF in the Chinese Han population.

Genetic association and gene expression profiles of TGFB1 and the contribution of TGFB1 to otosclerosis susceptibility

Otosclerosis (OTSC) is a common form of acquired hearing loss resulting from disturbed bone remodeling in the otic capsule of the middle ear. Transforming growth factor-beta1 (TGFB1) produced by osteoblasts is the most abundant growth factor in human bone. Previous studies have shown the contribution of single-nucleotide polymorphisms (SNPs) in TGFB1 toward the risk of developing OTSC in some ethnic populations. The present study was aimed at investigating the genetic association and expression profiles of TGFB1 in OTSC patients. Two SNPs (c.-800G > A and c.-509C > T) in the promoter region and three SNPs (c.29T > C, c.74G > C, and c.788C > T) in the coding region were genotyped in 170 cases and 170 controls. The genetic association analysis revealed the significant association between c.-509C > T (p = 0.0067; odds ratio [OR] = 1.562; 95% confidence interval [CI], 1.140-2.139) and OTSC. The increased minor allele "T" frequency in cases (0.42) compared to controls (0.31) indicates its possible role in the etiology of the disease. The minor allele frequencies for the SNPs c.-800G > A, c.29T > C, and c.74G >C were similar among the cases (0.04, 0.47, and 0.08, respectively) and controls (0.05, 0.42, 0.07, respectively). We found that c.788C > T was monomorphic in this population. Interestingly, a four-locus haplotype (G-T-T-G) from these SNPs was found to be significantly associated with OTSC (p = 0.0077). We identified a de novo heterozygous mutation c.-832G > A in the promoter region of TGFB1 in 1 patient. In a secondary analysis, we investigated the possibility of abnormal TGFB1 expression and irregular bone growth in OTSC by expression analysis of TGFB1 mRNA in disease tissue compared to control. We found relatively increased expression of TGFB1 mRNA in the stapes tissues of cases compared to controls (p = 0.0057). In conclusion, this study identified a risk variant c.-509C > T and a risk haplotype G-T-T-G in the TGFB1 gene that contribute toward the susceptibility to OTSC.

Detection of otosclerosis-specific measles virus receptor (cd46) protein isoforms

Genetic predisposition of otosclerosis has long been suspected, but unclarified. Unique coexpression pattern of measles virus receptor (CD46) splicing isoforms in the human otic capsule is assumed, since otosclerosis is a measles virus-associated organ-specific disease. In order to identify CD46 involved in the pathogenesis of otosclerosis, we used representative groups of histologically diagnosed otosclerotic, nonotosclerotic, and normal stapes footplates (n = 109). Consecutive histopathological examinations and CD46-specific Western blot analysis were performed. Normal and nonotosclerotic stapes footplates showed consistent expression of the conventional c, d, e, f, and l CD46 isoforms. In contrast, four novel isoforms (os1–4) translated as intact proteins were additionally detected in each otosclerotic specimen. The study herein presented provides evidence for the otosclerosis-associated expression pattern of CD46. This finding might explain the organ-specific, virus-associated and autoimmune-inflammatory pathogenesis of otosclerosis. Regarding our current knowledge, this is the first report that confirms the presence of four new disease-specific protein variants of CD46.

No evidence for the expression of renin-angiotensin-aldosterone system in otosclerotic stapes footplates

INTRODUCTION

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

Expression of bone morphogenetic protein 2, 4, 5, and 7 correlates with histological activity of otosclerotic foci

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.

COL1A1 association and otosclerosis: a meta-analysis

Otosclerosis is a disease of abnormal bone remodeling in the human otic capsule that can lead to progressive hearing loss. Little of the underlying disease etiology has been elucidated thus far, although several studies have suggested that COL1A1 may play a role based on its importance in bone metabolism and other diseases like osteoporosis and osteogenesis imperfecta. Genetic association studies between COL1A1 and otosclerosis, however, have been contradictory. To resolve this issue, we studied a large Belgian-Dutch and a Swiss population for a genetic association between COL1A1 and otosclerosis and additionally performed a meta-analysis to investigate the overall genetic effect of COL1A1 on all otosclerosis populations studied to date. We found a significant association both in the Belgian-Dutch population and in the meta-analysis. In aggregate, our analysis supports evidence for an association between COL1A1 and otosclerosis although effect sizes of the variants reported in the initial studies are likely to be an overestimate of true effect sizes.

The etiology of otosclerosis: a combination of genes and environment

Otosclerosis is a common form of hearing loss characterized by abnormal bone remodeling in the otic capsule. It is a complex genetic disease, caused by a combination of genetic and environmental factors. During the past decade, several attempts have been made to identify factors for otosclerosis. This review provides an overview of the current understanding of the etiology of otosclerosis and describes the genetic and environmental factors that have been implicated in the disease. Environmental factors include fluoride and viral factors, particularly measles. Genetic association studies for otosclerosis have reported several associations of genetic variants that influence the risk of disease, mainly involving bone remodeling pathways, although their individual risk contributions are small. Rare monogenic forms of otosclerosis also exist, which are caused by a mutation in a single gene leading to a clear familial segregation of the disease. Linkage analysis of large otosclerosis families has led to the identification of seven loci, and recently evidence was found that T cell receptor beta is a gene responsible for familial otosclerosis, suggesting an underlying immunological pathway. However, this might also represent an autoimmune process, a hypothesis that is supported by other data as well. In conclusion, a variety of pathways have been identified to be involved in the development of otosclerosis, showing that distinct mechanisms involving both genetic and environmental risk factors can influence and contribute to a similar disease outcome.

Differences in gene expression between the otic capsule and other bones

Our long term goal is to understand the molecular pathology of otosclerosis and to develop better forms of therapy. Toward this goal, the current study focused on characterizing the molecular factors responsible for the unique biological features of the otic capsule: its minimal rate of remodeling, and lack of healing capacity when fractured. We compared expression levels of 62 genes involved in bone metabolism between the adult murine otic capsule and the tibia and parietal bones; the latter exemplify bones formed by endochondral and intramembranous ossification, respectively. Gene expression levels were measured using real-time quantitative RT-PCR and analyzed using tools of bioinformatics. Expression patterns of key genes were verified with in situ hybridization. The molecular profile of the otic capsule was distinctly different from that of the tibia and parietal bone. Genes found to be most characteristic of the otic capsule were: osteoprotegerin (opg), bone morphogenetic protein receptor 1b (bmpr1b) and bone morphogenetic protein 3 (bmp3). Expression levels were high for opg and bmpr1b, and minimal for bmp3 within the otic capsule. We concluded that opg and bmpr1b likely play important roles in inhibition of remodeling within the otic capsule.

Involvement of T-cell receptor-beta alterations in the development of otosclerosis linked to OTSC2

Otosclerosis is a common form of hearing loss, characterized by disordered bone remodeling in the otic capsule. Within the otosclerotic foci, several immunocompetent cells and immune-modulating factors can be found. Different etiological theories involving the immune system have been suggested. However, a genetic component is clearly present. In large otosclerosis families, seven autosomal-dominant loci have been found, but none of the disease-causing genes has been identified. This study focused on the exploration of the second otosclerosis locus on chromosome 7q34-36 (OTSC2), holding the T-cell receptor beta locus (TRB locus). A significantly lower T-cell receptor-beta (TCR-beta) mRNA expression and percentage of blood circulating TCR-alphabeta(+) T cells was detected in OTSC2 patients compared with controls and patients with the complex form of the disease. Further analysis illustrated more significant disturbances in specific T-cell subsets, including an increased CD28(null) cell population, suggesting a disturbed T-cell development and ageing in OTSC2 patients. These disturbances could be associated with otosclerotic bone remodeling, given the known effects of immunocompetent cells on bone physiology. These data implicate the TRB locus as the causative gene in the OTSC2 region and represent an important finding in the elucidation of the disease pathology.

Genetics of otosclerosis

OBJECTIVES

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.

DATA SOURCES

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.

CONCLUSION

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.