Title: Cell-molecular interactions at the border of articular cartilage and subchondral bone
Abstract: It has been proven that subchondral bone and articular cartilage are structurally and metabolically related. The molecular triad OPG/RANK/RANKL controls the differentiation and biological function of osteoclasts. It was established that the level of expression of these molecules by chondrocytes depends on the stage of pathological changes. Objective: to study the expression of RANKL and OPG in the cells of the articular cartilage and subchondral bone obtained after hip replacement of 56 patients with hip joint arthritis and in an animal experiment. Methods: сhanges in articular cartilage and bone tissue were induced in animals by ovariectomy. Clinical and experimental material was studied by histological methods using scanning microscopy, immunohistochemical evaluation of RANKL and OPG. Results: OPG and RANKL expression in early arthritic disorders was detected in rats, mainly in the superficial area of articular cartilage. In clinical material, RANKL expression was noted only in individual chondrocytes of preserved articular cartilage. The color intensity was low. An increased expression of RANKL by osteocytes was found in the osteochondral junction zone. The most pronounced immunoreactivity was noted in chondrocytes, especially in isogenic groups, throughout the preserved articular cartilage. Osteocytes and single osteoblasts located on the marginal surface of bone trabeculae were expressed in OPG bone tissue. In the intertrabecular spaces, an intense reaction is fixed in the cells around the vessels. Conclusions: an increase in the RANKL/OPG ratio was noted in chondrocytes of articular cartilage already in the early stages of arthrosis. Significant changes in the subchondral bone microarchitecture with the presence of immunopositive cells indicate active remodeling processes, which are a reflection of the abnormal expression of RANKL/OPG by cells of bone and cartilage tissue under conditions of arthritis against a background of reduced bone mineral density.