The loss of aggrecan from articular cartilage may lead to the development of osteoarthritis (OA). Degradation products of human aggrecan, generated in vivo by enzymatic cleavages, have been identified in synovial fluid of patients with rheumatoid arthritis and OA. One matrix metalloproteinase (MMP), stromelysin (MMP-3), and an unidentified proteinase called "aggrecanase" are believed to generate these products in pathologic conditions. Thus far, only one proteinase, neutrophil collagenase (MMP-8), has been shown in vitro to be capable of cleavage of the aggrecan molecule at the "aggrecanase" site. In this study, we compare the presence and distribution of MMP-3 and MMP-8 in cartilages from two different joints of normal human donors. We determined whether mRNA for MMP-8 is expressed in normal human articular cartilage from different joints. In addition, we compared differences in MMP-8 and MMP-3 gene expression between human ankle and knee cartilage after in vitro stimulation by interleukin (IL)-1 beta. These two joints were chosen because the incidence of symptomatic and radiographic OA varies between the different joints. The knee is the most frequently involved joint, whereas the ankle (talocrural) joint is relatively rarely affected. Message for MMP-8 was detected in untreated cartilage from normal knee joints, but not in untreated cartilage of normal ankle joints. Message for MMP-3 was detectable in most of the knee and ankle cartilages. Messenger RNA expression for both MMPs could be up-regulated by IL-1 beta. The highest doses of IL-1 beta appeared to be most effective in stimulation of mRNA for MMP-3, whereas MMP-8 expression was more sensitive to lower doses of IL-1 beta. The fact that ankle cartilage with a low incidence of OA does not express MMP-8, whereas knee cartilage with a high incidence of OA does not express MMP-8, whereas knee cartilage with a high incidence of OA does constitutively express MMP-8, suggests that MMP-8 might be one of the key enzymes in the pathogenesis of osteoarthritis. This is further supported by our finding that the earliest signs of cartilage degradation were very similar to those found in IL-1 beta-treated explants.