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. We studied the morphometry of the Mov13 otic capsule and compared expression levels of 60 genes in the otic capsule with those in the tibia and parietal bone of the Mov13 and wild-type mice. The degree of transcriptional block of the COL1A1 gene and its downstream effects differed significantly between the bones examined. We found that expression levels of bone morphogenetic protein 3 and nuclear factor kappa-B1 best distinguished Mov13 otic capsule from wild-type otic capsule, and that osteoprotegerin, caspase recruitment domain containing protein 1, and partitioning defective protein 3 best distinguished Mov13 otic capsule from Mov13 tibia and parietal bone. Although the Mov13 mouse did not demonstrate evidence of active abnormal otic capsule remodeling as seen in type I OI and otosclerosis, studying gene expression in the Mov13 mouse has provided evidence that osteocytes of the otic capsule differ from osteocytes in other bones.