To examine the mechanism by which the Arg-->Cys 519 mutation causes the clinical phenotype employing transgenic mice that express the mutated human COL2A1.
A DNA construct under the control of a COL2A1 specific promoter was prepared from genomic DNA isolated from fibroblasts from the proband with primary generalized osteoarthritis (OA) associated with a mild chondrodysplasia. Transgenic mice were obtained by injection of the constructs into pro-nuclei of fertilized eggs from the FVB/N inbred mouse strain. Transgenic mice harboring two alleles of the mutated human COL2A1 were examined for morphological abnormalities and for alterations of their skeletal development. Ultrastructural examination was performed to identify changes in the organization and density of collagen II fibrils in articular cartilage of the transgenic mice.
Transgenic mice harboring two alleles of the mutated human collagen gene were smaller than their normal littermates, had a cleft palate, and disorganized growth plate. Electron microscopy of articular cartilage showed a decreased density of collagen II fibrils and revealed chondrocytes with dilated Golgi cysternae.
Expression of a COL2A1 with an Arg-->Cys 519 substitution in transgenic mice causes retardation of skeletal development and ultrastructural alterations in articular cartilage with a profound reduction of the density of the collagen II fibrils in the tissue. These alterations may be responsible for the phenotype of precocious generalized OA and chondrodysplasia displayed by patients harboring this COL2A1 mutation.