Vascular invasion of cartilage: Correlation of morphology with lysozyme, glycosaminoglycans, protease, and protease-inhibitory activity during endochondral bone development

Abstract

Changes in the levels of lysozyme, patterns of glycosaminoglycans, and activities of proteases and protease inhibitors were studied during matrix-induced cartilage, bone, and bone marrow development. The morphological transitions were correlated with the biochemical parameters. There was a peak in lysozyme content on Day 3, during mesenchymal cell proliferation, followed by a decline during endochondral bone formation. The lysozyme levels increased again and attained maximal values during hematopoiesis on Day 21. Protease-inhibitory activity was maximal during chondrogenesis and diminished during osteogenesis. Protease activity was maximal on Day 3 during mesenchymal cell proliferation and was apparently present as an enzyme-inhibitor complex. Vascularization and bone formation were accompanied by an increase in protease activity. Chondroitin-4-sulfate was the predominant glycosaminoglycan detected in the matrix-induced cartilage and bone.