Fig. 5.

Overview of the experimental model design and results. Cortical bone, articular cartilage and an osteochondral matrix, consisting of subchondral bone and calcified cartilage, were isolated from bovine femoral diaphyses and femoral condyles, and fixated in 70% ethanol. The articular cartilage and the osteochondral matrix were metabolically inactivated by immersion in liquid nitrogen. The osteochondral matrix was crushed to generate a homogeneous osteochondral extracellular matrix (ECM) for culture. Human osteoclasts derived from CD14⁺ monocytes were cultured on the different matrices in the presence of vacuolar-type H⁺-ATPase, matrix metalloproteinase (MMP) and cathepsin K inhibitors. The contributions of hydrochloric acid, MMPs and cathepsin K in degrading the ECMs were assessed by measuring biomarkers of ECM degradation in the culture supernatants. CTX-I, C-terminal type I collagen