Immunohistochemical Examination of Epiphyseal Growth Plates of Japanese Brown Cattle with Chondrodysplasia

SummaryA new type of inherited chondrodysplasia is described in Japanese Brown cattle, but the basic defects of the epiphyseal growth plate (EGP) in the limb long bones, and proliferation and differentiation of the chondrocytes in the EGP, are not yet understood. In the present study, the EGPs of the limb long bones in eight cases of chondrodysplasia and four normal (control) cattle were examined histologically and immunohistochemically. In the control cattle, proliferative chondrocytes (PCs) and hypertrophic chondrocytes (HCs) were arranged in columns parallel to the long axis of the bone, and HCs were situated on the metaphyseal side of the EGP. In all the affected cattle, many chondrocytes with a hypertrophic appearance were detected in the inner areas of the central portion of the EGP. The PC columns were short and arranged irregularly. Bone tissue and small blood vessels were found frequently in these areas. Six affected cattle showed complete EGP-closure. Backscattered electron (BSE) imaging showed that the calcified cartilage matrix was restricted to the lower region of the hypertrophic zone (HZ) of the EGP in the control cattle, while the calcified cartilage matrix and bone tissue were scattered in the inner areas of the EGP in all the chondrodysplastic cattle. Immunohistochemistry revealed type X collagen in the HCs and cartilage matrix of the HZ in the control cattle. In all the affected cattle, type X collagen was detected in apparently hypertrophic chondrocytes in the inner areas of the EGP. Type II collagen was detected in the entire EGP in all the affected cattle, as in the controls. BrdU (5-bromo-2’-deoxyuridine), injected intravenously 1 h before euthanasia was detected in many PCs in the EGP in the control cattle; none, however, was detected in the central portion of the EGP in any affected animal. These observations indicate that differentiation into HCs and calcification of cartilage matrix occur in the inner areas of the central portion of the EGP in chondrodysplasia of Japanese Brown cattle. Differentiation into the HCs at this abnormal site may be caused by the inadequate proliferation and disorganization of the PCs. Premature EGP-closure, observed commonly in chondrodysplasia of Japanese Brown cattle, was thought to be caused by replacement of the calcified cartilage in the inner areas of the EGP by bone tissue.