Fine morphology of bony dysplasia of the murine ear: comparisons with otosclerosis

Immunohistochemical analysis of Otic Capsule Osteogenesis in the Palmerston North Autoimmune Mouse

Autoimmunity and the immune complex disease associated with it have been hypothesized to be the cause of several idiopathic diseases of the inner ear—including the new bone formation associated with otic capsule osteogenesis and otosclerosis. The Palmerston North (PN) autoimmune mouse strain, which exhibits both spontaneous systemic autoimmune disease and otic capsule bone formation, has been proposed as a model relating these two disease processes. To investigate the potential role of immunopathologic processes in PN otic capsule lesion formation, inner ears from PN mice were immunostained for the presence of IgG and complement (C3), two immunologic markers involved in the development of the vascular and perivascular changes associated with immune complex deposition. Both systemic autoimmune disease and otic capsule bony lesions were confirmed in all animals. However, immunohistochemical analyses did not establish a direct relationship between the two conditions as complement was absent in all lesions and IgG stained positive in only one instance. These results suggest that immune complex deposition is not directly involved in the otic capsule lesions of the PN mouse, and alternate mechanisms relating autoimmune disease and otic capsule osteogenesis must be explored.

Differences in Otosclerotic and Normal Human Stapedial Osteoblast Properties Are Normalized by Alendronate in Vitro

Objective

Identify and compare phenotypic properties of osteoblasts from patients with otosclerosis (OSO), normal bones (HOB), and normal stapes (NSO) to determine a possible cause for OSO hypermineralization and assess any effects of the bisphosphonate, alendronate.

Study Design

OSO (n = 11), NSO (n = 4), and HOB (n = 13) cultures were assayed for proliferation, adhesion, mineralization, and gene expression with and without 10–10M-10–8M alendronate.

Setting

Academic hospital.

Methods

Cultures were matched for age, sex, and passage number. Cell attachment and proliferation + alendronate were determined by Coulter counting cells and assaying tritiated thymidine uptake, respectively. At 7, 14, and 21 days of culture + alendronate, calcium content and gene expression by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were determined.

Results

OSO had significantly more cells adhere but less proliferation than NSO or HOB. Calcification was significantly increased in OSO compared to HOB and NSO. NSO and HOB had similar cell adhesion and proliferation rates. A dose-dependent effect of alendronate on OSO adhesion, proliferation, and mineralization was found, resulting in levels equal to NSO and HOB. All cultures expressed osteoblast-specific genes such as RUNX2, alkaline phosphatase, type I collagen, and osteocalcin. However, osteopontin was dramatically reduced, 9.4-fold at 14 days, in OSO compared to NSO. Receptor activator of nuclear factor κB ligand/osteoprotegerin (RANKL/OPG), important in bone resorption, was elevated in OSO with decreased levels of OPG levels. Alendronate had little effect on gene expression in HOB but in OSO increased osteopontin levels and decreased RANKL/OPG.

Conclusions

OSO cultures displayed properties of hypermineralization due to decreased osteopontin (OPN) and also had increased RANKL/OPG, which were normalized by alendronate.

Fine structure histopathology of labyrinthitis ossificans in the gerbil model

Labyrinthitis ossificans (LO) is the pathological deposition of new bone within the lumen of the cochlea and labyrinth. This process occurs most commonly as a result of infection or inflammation affecting the otic capsule. Trauma and vascular compromise can also lead to neo-ossification within the otic capsule. The mechanism that regulates this process remains unestablished. This study details the end-stage histopathology in high-resolution plastic thin sections. Twenty Mongolian gerbils were infected by intrathecal injection of Streptococcus pneumoniae type 3 followed by subcutaneous penicillin G procaine (8 days) and were painlessly sacrificed 3 months later. The cochleas were serially divided and sectioned for light and electron microscopy. Sixteen of 20 animals (27 of 40 cochleas) demonstrated LO. Cochlear damage was most extensive in the vestibule and basal turn and decreased toward the apex, which often appeared normal. The histopathologic findings consisted of 1) new bone, calcospherites, osteoid, and fibrosis without dense connective tissue or osteoblasts extending from the endosteal wall into the lumen of the vestibule and scala tympani; 2) areas of dense connective tissue and osteoid enclosed by epithelial cells conjoined with the organ of Corti, stria vascularis, spiral ligament, and vestibular (Reissner's) membrane; and 3) partial to complete loss of the organ of Corti, spiral ligament cell bodies, stria vascularis, and spiral ganglion cells. Osteoblastic activity was not demonstrated in end-stage ossification in LO in the gerbil model. Neo-ossification appears to occur by calcospherite deposition along collagen-like fibrils within osteoid. The destruction of the organ of Corti, spiral ganglion cells, stria vascularis, and cells of Reissner's membrane and the spiral ligament occurs even in the absence of ossification of the cochlear duct.

Ultrastructure of otic capsule sclerosis in Palmerston North autoimmune mice

PURPOSE

Numerous temporal bone studies have reported a correlation between systemic autoimmune disease and osteogenic lesions within the inner ear. However, little is known of the cellular mechanisms that relate these two disease processes. The Palmerston North (PN) autoimmune strain mouse exhibits both spontaneous systemic autoimmune disease and otic capsule sclerotic lesions that are similar in many ways to those reported in humans. This suggests the PN mouse is a potential model in which to study the cellular events responsible for immune-related otic capsule lesions. Therefore, an evaluation of the fine structure of the PN modiolus was conducted to better understand these matrix changes of the inner ear.

MATERIALS AND METHODS

Inner ears were collected from 15 PN mice at ages from 17 to 24 months and prepared for electron microscopy. The ears were ultrastructurally evaluated to characterize the lesions and their associated cytoarchitecture.

RESULTS

The sclerotic lesions consisted of an electron-dense mass that appeared lobulated or layered, usually adjacent to the modiolar bone and blood vessels. Immediately surrounding the lesions were activated fibroblasts and fine fibrillar material in the extracellular space between them. The sclerotic foci often were apposed to normal modiolar bone that never appeared degraded.

CONCLUSIONS

The similarities between these bony lesions and known human otic capsule diseases suggests parallel processes are involved. Thus, further study of the PN inner ear may provide insight into the cellular events that underlie otic capsule and other temporal bone alterations in systemic autoimmune diseases.

Dexamethasone inhibition of the development of dysplastic bony lesions in LP/J mice

Inbred LP/J mice have been observed to spontaneously develop abnormal bony lesions of the ossicles and otic capsule that progress throughout the life of the animals. This genetically inherited murine disorder produces bony lesions that share some gross and histologic features with bony lesions seen in human tympanosclerosis. Previous studies on LP/J mice have demonstrated evidence of immunologically mediated injury in the progression of the newly forming bony lesions. This study was designed to examine the effects of dexamethasone on the development of the bony lesions in LP/J mice. The purpose was to attempt to elucidate the relationship of the immunologic injury observed in earlier studies and the progression of the dysplastic bony lesions. The results show that LP/J mice treated with dexamethasone developed significantly fewer dysplastic bony lesions compared to the age-matched, saline-treated controls. There was also a statistically significant difference in the quantity and cellularity of the middle ear effusions between the experimental and control animals.

Otic capsule bony lesions in the Palmerston North autoimmune mouse

Otosclerosis is an otic capsule disorder of unknown etiology. While autoimmunity has been proposed as part of the etiopathogenesis of otosclerosis, no spontaneous autoimmune disease animal model has been identified. In the Palmerston North mouse, a model for systemic lupus erythematosus, sclerotic lesions consistently develop within the modiolus that are correlated with systemic autoimmune disease symptoms. No lesions were seen in 2-month-old mice, which is before autoimmune disease onset at 4 months. Lesions were first seen in mice at 6 to 8 months of age and increased in size and frequency thereafter. By 20 months, all ears examined had the otic capsule lesions, which were primarily perivascular in location and composed of both noncellular and cellular elements. The noncellular material was globular to fibrillar in arrangement and stained positively for calcium. The associated cells appeared to be metabolically active fibroblasts. It is proposed that the Palmerston North mouse may serve as a model to further investigate the role of autoimmunity in otosclerosis and other forms of otic capsule osteogenesis.

Early ossification within the human fetal otic capsule: morphological and microanalytical findings

Besides the use of conventional techniques such as light and polarization microscopy, the present paper proposes the combined use of transmission electron microscopy, secondary and backscattered electron imaging, energy dispersive X-ray analysis and computed tomography for the diagnostic evaluation of ear pathology in the human fetus. These methods were used to revisit the primary calcification front of the fetal otic capsule between 16 and 23 weeks gestational age. Ultramicroscopic evaluation demonstrates similar fetal bone formation to that found in other bones of the human fetus. The formation of the endosteal and periosteal layers is a typical example of early intra-membranous ossification. The enchondral layer is made up of fibrillar bone, laid down around the calcified cartilage remnants. Microchemical analysis indicates a significantly higher Ca/P ratio in the endochondral layer with respect to the endosteum and periosteum. The consequences of a lower Ca/P ratio in the endosteal layer are discussed in view of calcium homeostasis and inner ear function.

Thirty years of stapes surgery

The modern stapedectomy with prosthesis insertion and living oval window seal, like the modern cataract extraction with lens replacement, is now performed, very much the same, throughout the world. I have reviewed the evolution of stapes surgery during these last thirty years and tried to gain some agreement for several important facts about otosclerosis and several basic principals of stapes surgery. While a well-performed stapedectomy can eliminate the conductive component, the sensorineural hearing loss continues and, in about one-third, will progress till the patient, after age 65, must return to a hearing aid. A piston prosthesis gives the best hearing results: 0.6 mm diameter, when half the footplate is removed and a living oval window seal interposed, and 0.6 mm diameter when a small opening is made in the footplate obliterated by otosclerosis. I prefer a teflon prosthesis to stainless steel because it can be altered by the surgeon at operation, and vein as an oval window seal. I have presented a rare group of patients who develop facial palsy 5-1/2 days after uncomplicated stapedectomy, of whom all recover quickly and completely. I am confident that progress will continue to be made in the understanding of otosclerosis, and the performance of stapes surgery, but in these last thirty years we have made a good beginning.

The possible role of immunologic injury in the dysplastic bony lesion in LP/J mice

An immunohistologic study was performed on temporal bones from 30 LP/J mice and 17 CBA/J mice to assess the role of immunologic injury in the pathogenesis of dysplastic bony lesions in LP/J mice. Temporal bones were harvested from animals aged 2 to 31 months to evaluate the progression of the disease. As early as 2 months of age, before the onset of bony lesions, the tympanic cavities frequently contained small effusions coating the ossicles and otic capsules that were demonstrated to contain immunoglobulins and pockets of macrophages. Later in the course of the disease, bony lesions grossly and histologically similar to human otosclerosis developed, which stained for immunoglobulins. No similar bony lesions, effusions, cellular infiltrates, or staining for immunoglobulins was detected in the control animals, even in the presence of acute otitis media. This study suggests a role of immunologic injury in the pathogenesis of dysplastic bony lesions in LP/J mice.