ORTHOTOPIC OSSIFICATION OF THE SPINAL LIGAMENTS OF ZUCKER FATTY RATS - A POSSIBLE ANIMAL-MODEL FOR OSSIFICATION OF THE HUMAN POSTERIOR LONGITUDINAL LIGAMENT

Ossification of the posterior longitudinal ligament is a human genetic disease in which pathological ectopic ossification of the spinal liga ments develops. This leads to myelopathy or radiculopathy due to compr ession of the spinal cord. In this study, we investigated the histolog ical features of orthotopic ossification of the spinal ligaments of se nile Zucker fatty rats. A remarkably high incidence of orthotopic ossi fication was observed mainly in the thoracic spinal ligaments as compa red with controls The histopathological findings were similar to those for ossification of the human posterior longitudinal ligament. Bone m orphogenetic proteins and activins, which exert their effects by way o f specific type-I and type-II serine/threonine kinase receptors. play important roles in the formation of bone and cartilage. In the spinal ligaments of Zucker fatty rats, bone morphogenetic protein receptors a nd activin receptors were immunohistochemically detected around the os sified foci in a manner similar to that previously shown for the ossif ied tissue from patients who had ossification of the posterior longitu dinal ligament. Thus, bone morphogenetic proteins and activin receptor s might play important roles in orthotopic ossification of the spinal ligaments of Zucker fatty rats as well as in ossification of the poste rior longitudinal ligament of humans. In addition, bone morphogenetic protein-receptor-IA was expressed in the nonossified ligament, suggest ing that the spinal ligaments of the rats may have a predisposition to orthotopic ossification. In the controls, no expression of bone morph ogenetic protein receptors or of activin receptors was observed. In co nclusion, there is a great degree of similarity between orthotopic oss ification of the spinal ligaments of Zucker fatty rats and ossificatio n of the posterior longitudinal ligament of humans. Thus, the rats pro vide a useful animal model for the study of ossification of the human posterior longitudinal ligament.