Degradation of cartilage matrix components by the cysteine proteinases, cathepsins B and L.

Rat chondrosarcoma chondrocytes are able to secrete both the precursor and mature forms of cathepsins B and L. When these two cysteine proteinases were added to a native cartilaginous matrix near neutral pH they were found to release and degrade both the proteoglycan and collagen components. One cleavage site in the proteoglycan monomer was found to be near the amino terminal globular domain. Collagen types II, IX, and XI in the matrix were also released and partially degraded. Ultimately these proteinases act as matrix depolymerases as they attacked the regions which are involved in collagen crosslinking. We conclude that these enzymes may play a role in matrix destruction as seen in arthritis.