Postnatal expression and possible function of RANK and RANKL in the murine inner ear.

The bone encasing the inner ear, known as the otic capsule, is unique because it remodels little postnatally compared to other bones in the body. Previous studies established that osteoprotegerin (OPG) in the inner ear inhibits otic capsule remodeling. OPG acts as a decoy receptor of receptor activator of nuclear factor κB ligand (RANKL) to disrupt the interaction between RANKL and RANK, the primary regulators of bone metabolism.

Activation of TRAIL-DR5 pathway promotes sensorineural degeneration in the inner ear.

Tumor necrosis factor (TNF) family cytokines are important mediators of inflammation. Elevated levels of serum TNF-α are associated with human sensorineural hearing loss via poorly understood mechanisms. We demonstrate, for the first time, expression of TNF-related apoptosis-inducing ligand (TRAIL) and its signaling death receptor 5 (DR5) in the murine inner ear and show that exogenous TRAIL can trigger hair cell and neuronal degeneration, which can be partly prevented with DR5-blocking antibodies.

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.

Studies of otic capsule morphology and gene expression in the Mov13 mouse--an animal model of type I osteogenesis imperfecta.

Type I osteogenesis imperfecta (OI) is a disorder of skeletal bones characterized by bone fragility and blue sclera, which can result from mutations in genes encoding for type I collagen--the COL1A1 and COL1A2 genes. Fifty percent of patients with type I OI develop hearing loss and associated histopathological changes in the otic capsule that are indistinguishable from otosclerosis, a major cause of acquired hearing loss. In an attempt to elucidate molecular and cellular mechanisms of hearing loss in type I OI, we have studied the Mov13 mouse, which has served as an animal model of type I OI by virtue of exhibiting variable transcriptional block of the COL1A1 gene.

Molecular biology of otosclerosis.

Otosclerosis is a bone disease of the human otic capsule, which is among the most common causes of acquired hearing loss. The pathologic process is characterized by a wave of abnormal bone remodeling in specific sites of predilection within the endochondral layer of the temporal bone. Although the cause of otosclerosis remains uncertain, there is a clear genetic predisposition with half of all cases occurring in families with more than one affected member.

Osteoprotegrin knockout mice demonstrate abnormal remodeling of the otic capsule and progressive hearing loss.

Objectives: The otic capsule, when compared with other bones in the body, is unique in that it undergoes no significant remodeling of bone after development. We previously demonstrated that osteoprotegerin (OPG), which inhibits formation and function of osteoclasts, is produced at high levels in the inner ear of normal mice and secreted into the perilymph from where it diffuses into the surrounding otic capsule bone through a lacunocanalicular system. To test our hypothesis that the high level of OPG may be important in the inhibition of otic capsule remodeling, we studied the light microscopic histology of the otic capsule in OPG knockout mice for evidence of abnormal remodeling of bone.

Distribution of type IV collagen in the cochlea in Alport syndrome.

Objective: To determine the distribution of alpha1, alpha3, and alpha5 chains of type IV collagen in the cochlea in Alport syndrome.

Design: Case-control study.

Patients: Two patients with sensorineural hearing loss due to Alport syndrome.

Osteoprotegerin in the inner ear may inhibit bone remodeling in the otic capsule.

Objectives: To elucidate factors that may be responsible for the inhibition of remodeling of bone within the otic capsule.

Methods: Expression of osteoprotegerin (OPG), receptor activator of nuclear factor kappa B (RANK), and RANK ligand (RANKL) were assayed in samples of bone obtained from the otic capsule, calvarium, and femur, and from the soft tissue within the cochlea using semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) in mice. Immunostaining was used for histologic localization of the gene products.

Association of otosclerosis with Sp1 binding site polymorphism in COL1A1 gene: evidence for a shared genetic etiology with osteoporosis.

Hypothesis: There is an association between otosclerosis and osteoporosis.

Background: Both osteoporosis and otosclerosis are common bone diseases to which relatively large portions of the population are genetically predisposed. Recently, a strong association has been described between osteoporosis and an Sp1 binding site of putative functional significance in the first intron of the COL1A1 gene.

Deoxyribonucleic acid contamination in archival human temporal bones: a potentially significant problem.

Hypothesis: Contamination of archival human temporal bones with extraneous deoxyribonucleic acid may represent a potentially significant problem in the analysis of nucleic acids isolated from archival specimens.

Background: During the past decade, there has been growing interest in the development of molecular biologic techniques that can be applied to the investigation of pathologic changes in archival human temporal bones. The impetus for the development of these techniques is in part related to the fact that the temporal bone collections represent a repository of archival material compiled over decades, which is not available from living patients.

Similar COL1A1 expression in fibroblasts from some patients with clinical otosclerosis and those with type I osteogenesis imperfecta.

Because of the clinical and histopathologic similarities between otosclerosis and type I osteogenesis imperfecta, we examined COL1A1 messenger RNA (mRNA) expression in cultured fibroblasts from patients with clinical otosclerosis to determine whether abnormalities of expression of COL1A1 were present, as has been reported in type I osteogenesis imperfecta. Type I osteogenesis imperfecta has been found to result from mutations in the COL1A1 gene that result in null expression of the mutant allele. Patients with clinical otosclerosis were genotyped for the presence of an expressed 4 base-pair insertion polymorphism in the 3' region of the COL1A1 gene.