INCREASED TYPE-XI COLLAGEN EXPRESSION IN THE SPINAL HYPEROSTOTIC MOUSE (TWY TWY)

The twy (tiptoe walking Yoshimura) mouse is a mutant manifesting spinal hyperostosis that resembles human ankylosing spinal hyperostosis. To clarify the pathogenic mechanisms of the hyperostotic change, collagen type distributions in twy mouse spine were examined immunohisto-chemically. In the process of the spinal hyperostosis, the intervertebral disc was seen to protrude laterally and the vertebral ligament was thickened, becoming like periosteal fibrous tissue; it was gradually replaced by bony tissue which finally formed an osseous bridge over the protruded disc, whereas ossification never occurred in the protruded disc region. Immunohistochemical studies using anti-type XI collagen antibodies showed an intense staining of the growth cartilage of the vertebral endplate. Although this staining for type XI decreased with age in controls, the growth cartilage in mature twy mice was still intensely stained with anti-type XI collagen antibodies. In the transitional region from vertebral body to thickened ligament of mature twy mice, proliferation of round-shaped cells was observed and matrices around these cells were well stained with anti-type II and type XI collagen antibodies as well as with anti-type I collagen antibodies, in contrast to those of control mice, where only the presence of type I collagen was demonstrated. These results indicate that continous expression of type XI collagen in growth cartilage and cartilaginous metaplasia of ligament cells accompanied by type XI collagen expression seem to be closely related to the onset and progression of spinal hyperostosis in twy mice.