TEMPORAL PATTERN OF CYSTEINE ENDOPEPTIDASE (CATHEPSIN-B) EXPRESSION IN CARTILAGE AND SYNOVIUM FROM RABBIT KNEES WITH EXPERIMENTAL OSTEOARTHRITIS - GENE-EXPRESSION IN CHONDROCYTES IN RESPONSE TO INTERLEUKIN-1 AND MATRIX DEPLETION

Objective-To determine the temporal pattern of expression of cathepsin -B in chondrocytes and synovium in experimental osteoarthritis, and to determine possible mechanisms for upregulation and secretion of cathe psin-B from chondrocytes. Methods-Experimental osteoarthritis was indu ced with partial medial meniscectomy (PM); sham operated (SH) and norm al (N) rabbits were used as controls. Cathepsin-B mRNA expression was assessed with northern blotting with a P-32 labelled cDNA probe. Cathe psin-B was measured in conditioned media or cell extracts using a fluo rogenic substrate Z-Arg-Arg-AMC. Chondrocyte monolayers were used to d etermine cathepsin-B expression in response to interleukin-1 beta (IL- 1 beta). Cartilage explants were used to test the effect of matrix dep letion on cathepsin-B release. Results-Chondrocytes obtained from expe rimental osteoarthritis knees did not show cathepsin-B mRNA upregulati on. However, isolated chondrocytes secreted cathepsin-B into the cultu re medium. Enzyme release was significantly higher at 8 weeks relative to controls, but not at 12 weeks or 4 weeks. Enzyme released from syn ovium was significantly higher in PM group compared with SH group at 4 and 8 weeks. IL-1 beta was ineffective in upregulating steady state c athepsin-B mRNA in chondrocytes; however, it upregulated the intracell ular enzyme, and this was blocked with cycloheximide. Enzymatic deplet ion of cartilage matrix after exposure of explants to IL-1 resulted in release of significantly higher amounts of cathepsin-B into the mediu m by matrix depleted chondrocytes compared with intact explants. Concl usions-In experimental osteoarthritis, cathepsin-B is upregulated in s ynovial tissue during the early degenerative phase. Progression of exp erimental osteoarthritis is accompanied by upregulation of cathepsin-B in cartilage. Cartilage and synovial cathepsin-B levels decline as ex perimental osteoarthritis advances to more degenerative states. IL-1 u pregulates intracellular cathepsin-B by increasing cathepsin-B protein synthesis; it is not an effective stimulus for enzyme secretion. Depl etion of cartilage matrix during progression of experimental osteoarth ritis may contribute to secretion of cathepsin-B and perpetuation of c artilage destruction.