An experimental study of COMP (cartilage oligomeric matrix protein) in the rabbit menisci

Abstract

Secondary knee osteoarthritis (OA) is currently associated with meniscal injuries, but the pathogenesis is unclear. We analyzed the distribution of cells and cartilage oligomeric matrix protein (COMP) and its changes in the early stages of degeneration in meniscus. Ten New Zealand rabbits underwent anterior cruciate ligament (ACL)-transection of the right knee-joint. Left knee-joints were used as controls. The animals were killed at 4 and 12weeks. Gross injuries in meniscus and articular cartilage were scored. Meniscal tissues were immunostained with a specific antibody against COMP, with Ki-67, using TUNEL-assay and alcian blue stain. The number of cells was counted. At 4weeks post-ACL-transection, 2/5 of the operated knees showed articular damages and medial menisci tears. Menisci showed a weak increase of cells, higher in cells under division and an increase of apoptosis, COMP and proteoglycans. At 12weeks, 5/5 of the medial menisci and 2/5 of lateral menisci presented tears, and osteoarthritic changes were seen in the cartilage of all the operated knees. Meniscal cells reverted to normal number, while active cell division decreased below normal, apoptotic events were still high, COMP remained elevated, and glycosaminoglycans were even more elevated. Extracellular matrix changes and altered cell distribution occur early in the degenerative meniscus. There is a close relationship between changes in the articular cartilage and the menisci at the onset of secondary OA.