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Gut microbiota plays an important role in the regulation of bone homeostasis and bone health. Recent studies showed that these effects could be mediated through microbial metabolites released by the microbiota like short-chain fatty acids, metabolism of endogenous molecules such as bile acids, or a complex interplay between microbiota, the endocrine system, and the immune system. Importantly, some studies showed a reciprocal relationship between the endocrine system and gut microbiota. For instance, postmenopausal estrogen deficiency could lead to dysbiosis of the gut microbiota, which could in turn affect various immune response and bone remodeling. In addition, evidence showed that shift in the indigenous gut microbiota caused by antibiotics treatment may also impact normal skeletal growth and maturation. In this mini-review, we describe recent findings on the role of microbiome in bone homeostasis, with a particular focus on molecular mechanisms and their interactions with the endocrine and immune system. We will also discuss the recent findings on estrogen deficiency and microbiota dysbiosis, and the clinical implications for the development of new therapeutic strategies for osteoporosis and other bone disorders., (Published by Oxford University Press on behalf of the Endocrine Society 2024.)

Otosclerosis (OTSC) is a focal and diffuse bone disorder of the human middle ear characterized by abnormal bone growth and deposition at the stapes' footplate. This hinders the transmission of acoustic waves to the inner ear leading to subsequent conductive hearing loss. The plausible convections for the disease are genetic and environmental factors with yet an unraveled root cause. Recently, exome sequencing of European individuals with OTSC revealed rare pathogenic variants in the Serpin Peptidase Inhibitor, Clade F (SERPINF1) gene. Here, we sought to investigate the causal variants of SERPINF1 in the Indian population. The gene and protein expression was also evaluated in otosclerotic stapes to ameliorate our understanding of the potential effect of this gene in OTSC. A total of 230 OTSC patients and 230 healthy controls were genotyped by single-strand conformational polymorphism and Sanger sequencing methods. By comparing the case controls, we identified five rare variants (c.72 C > T, c.151 G > A, c.242 C > G, c.823 A > T, and c.826 T > A) only in patients. Four variants c.390 T > C (p = 0.048), c.440-39 C > T (p = 0.007), c.643 + 9 G > A (p = 0.035), and c.643 + 82 T > C (p = 0.005) were found to be significantly associated with the disease. Down-regulation of SERPINF1 transcript level in otosclerotic stapes was quantified by qRT-PCR, ddPCR and further validated by in situ hybridization. Similarly, reduced protein expression was observed by immunohistochemistry and immunofluorescence in otosclerotic stapes that corroborate with immunoblotting of patients' plasma samples. Our findings identified that SERPINF1 variants are associated with the disease. Furthermore, reduced expression of SERPINF1 in otosclerotic stapes might contribute to OTSC pathophysiology., (© 2023. The Author(s), under exclusive licence to The Japan Society of Human Genetics.)

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., Competing Interests: The authors have declared that no competing interests exist.

Otosclerosis (OTSC) is a complex bone disorder of the otic capsule, which causes conductive hearing impairment in human adults. The dysregulation of the signaling axis mediated by the receptor activator of nuclear factor-kappa-B (RANK), RANK ligand (RANKL), and osteoprotegerin has been widely attributed to the context of metabolic bone disorders. While genetic associations and epigenetic alterations in the TNFSF11 gene (RANKL) have been well-linked to metabolic bone diseases of the skeleton, particularly osteoporosis, they have never been addressed in OTSC. This study aimed to assess whether the genetic association of rs1021188 polymorphism in the upstream of TNFSF11 and the DNA methylation changes in its promoter CpG-region reveal the susceptibility of OTSC. Peripheral blood DNA samples were collected from unrelated Tunisian-North African subjects for genotyping (109 cases and 120 controls) and for DNA methylation analysis (40 cases and 40 controls). The gender-stratified analysis showed that the TNFSF11 rs1021188 C/T was associated with OTSC in men ( p = 0.023), but not in women ( p = 0.458). Individuals with CC genotype were more susceptible to OTSC, suggesting an increased risk to disease development. Using publicly available data, the rs1021188 was within a cluster grouping the subpopulations with African ethnicity. Moreover, 26 loci in the TNFSF11 gene were in linkage disequilibrium with rs1021188, revealing relative similarities between different populations. Significant differences in both DNA methylation and unmethylation status were detected with 4.53- and 4.83-fold decreases in the global DNA methylation levels in female and male OTSC groups, respectively. These changes could contribute to an increased risk of OTSC development. Bioinformatic analyses indicated that each of the rs1021188 variations and the DNA methylation changes in the promoter CpG-sites within TNFSF11 may play an important role in its transcription regulation. To our knowledge, this is the first study that investigates an independent effect of the rs1021188 polymorphism and DNA hypomethylation of TNFSF11 promoter in OTSC. Genetic and epigenetic changes in the regulatory regions of TNFSF11 could offer new molecular insights into the understanding of the complexity of OTSC., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Bouzid, Chelly, Tekari, Singh, Hansdah, Achour, Ben Ayed, Jbeli, Charfeddine, Ramchander, Hamoudi and Masmoudi.)

Background: Otosclerosis (OTSC) is among the most common causes of a late-onset hearing loss in adults and is characterized by an abnormal bone growth in the otic capsule. Alteration in the osteoprotegerin (OPG) expression has been suggested in the implication of OTSC pathogenesis., Methods: A case-control association study of rs2228568, rs7844539, rs3102734 and rs2073618 single nucleotide polymorphisms (SNPs) in the OPG gene was performed in a Tunisian-North African population composed of 183 unrelated OTSC patients and 177 healthy subjects. In addition, a multilocus association and a meta-analysis of existing studies were conducted., Results: Rs3102734 (p = 0.013) and rs2073618 (p = 0.007) were significantly associated with OTSC, which were predominantly detected in females after multiple corrections. Among the OPG studied SNPs, the haplotypes A-A-C-G (p = 0.0001) and A-A-C-C (p = 0.0004) were significantly associated with OTSC in females. Multilocus association revealed that the SNPs: rs2073618 in OPG, rs1800472 in TGFβ1, rs39335, rs39350 and rs39374 in RELN, and rs494252 in chromosome 11 showed significant OTSC-associated alleles in Tunisian individuals. In addition, meta-analysis of the rs2073618 SNP in Tunisian, Indian and Italian populations revealed evidence of an association with OTSC (OR of 0.826, 95% CI [0.691-0.987], p = 0.035)., Conclusions: Our findings suggest that rs3102734 and rs2073618 variants are associated with OTSC in North African ethnic Tunisian population. Meta-analysis of the rs2073618 in three different ethnic population groups indicated an association with OTSC.

Background: Otosclerosis (OTSC) is a genetically heterogeneous disorder, characterized by abnormal bone growth in the middle ear, affecting the stapes bone. Previous studies have shown that single nucleotide polymorphisms (SNPs) of the COL1A1, BMP2, and BMP4 genes are linked to susceptibility of OTSC, musculoskeletal degenerative diseases, and bone remodeling. Aims : To evaluate the genetic association and expression levels of COL1A1 , BMP2 , and BMP4 genes with OTSC in the Indian population. Methods : A total of 320 otosclerotic and 320 control samples were screened for four SNPs (rs1107946, rs11327935, rs2269336, and rs1800012) of the COL1A1 gene; rs3178250 of the BMP2 gene; and rs17563 of the BMP4 gene using single-strand conformation polymorphism analysis, and restriction fragment length polymorphism analyses. Genotypic, haplotypic, and linkage disequilibrium analyses were performed to assess the potential associations of these SNPs with OTSC. COL1A1 , BMP2 , and BMP4 mRNA expression levels were analyzed by semiquantitative RT-PCR and real-time PCR. Results : Genotypes of two SNPs, rs1800012 and rs17563, were found to be associated with OTSC (the rs1800012 GT genotype, p  = 0.0022, OR = 0.481; and the rs17563 TC genotype, p  = 0.0225, OR = 1.471). Haplotypic analyses revealed that the COL1A1 haplotype G-T-C-T ( p  = 0.021) was significantly increased among controls. Functional studies revealed an unexpected decrease in mRNA expression of COL1A1 but an increased expression of the BMP2 and BMP4 genes in otosclerotic stapes tissues. Conclusions : Our findings suggest that OTSC is a heterogeneous disorder, but that the GT genotype of the rs1800012 locus is protective and that the TC genotype at the rs17563 locus is a risk factor. In addition, our studies indicate that changes in the expression of the COL1A1 , BMP2 , and BMP4 genes may contribute to the genetic susceptibility of OTSC by regulating their mRNA levels.

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.