Abnormal cochlear connective tissue mineralization in the palmerston north autoimmune mouse

Inner ear fibrosis and osteogenesis are common features of human autoimmune disease, although the cellular mechanisms are unknown. The Palmerston North (PN) autoimmune strain mouse has been shown to develop modiolar sclerotic lesions with progression of its systemic disease. Therefore, lesion development was studied in the cochleas of PN mice to gain insight into potential autoimmune osteogenic processes in the human ear. Cochleas from PN mice were examined with electron microscopy to characterize the cellular and extracellular matrix changes that lead to abnormal mineralization. Initially, activated fibroblasts produced extracellular matrix fibers, ranging in size from fine fibrils to larger collagen-like fibers. These proliferating fibers appeared to 'seed' the mineralizing lesions by serving as the framework for mineral deposition. As mineralization continued, the foci grew in size and fused to form large sclerotic masses within the connective tissue. However, the lesions never invaded nor degraded the normal modiolar bone. These observations of abnormal mineralization of cochlear connective tissue fibers show some parallels with human cochlear autoimmune osteogenesis, suggesting similar molecular processes may be involved.