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 cathepsin-B from chondrocytes.


METHODS
Experimental osteoarthritis was induced with partial medial meniscectomy (PM); sham operated (SH) and normal (N) rabbits were used as controls. Cathepsin-B mRNA expression was assessed with northern blotting with a 32P labelled cDNA probe. Cathepsin-B was measured in conditioned media or cell extracts using a fluorogenic substrate Z-Arg-Arg-AMC. Chondrocyte monolayers were used to determine cathepsin-B expression in response to interleukin-1 beta (IL-1 beta). Cartilage explants were used to test the effect of matrix depletion on cathepsin-B release.


RESULTS
Chondrocytes obtained from experimental osteoarthritis knees did not show cathepsin-B mRNA upregulation. However, isolated chondrocytes secreted cathepsin-B into the culture medium. Enzyme release was significantly higher at 8 weeks relative to controls, but not at 12 weeks or 4 weeks. Enzyme released from synovium was significantly higher in PM group compared with SH group at 4 and 8 weeks. IL-1 beta was ineffective in upregulating steady state cathepsin-B mRNA in chondrocytes; however, it upregulated the intracellular enzyme, and this was blocked with cycloheximide. Enzymatic depletion of cartilage matrix after exposure of explants to IL-1 resulted in release of significantly higher amounts of cathepsin-B into the medium by matrix depleted chondrocytes compared with intact explants.


CONCLUSIONS
In experimental osteoarthritis, cathepsin-B is upregulated in synovial tissue during the early degenerative phase. Progression of experimental osteoarthritis is accompanied by upregulation of cathepsin-B in cartilage. Cartilage and synovial cathepsin-B levels decline as experimental osteoarthritis advances to more degenerative states. IL-1 upregulates intracellular cathepsin-B by increasing cathepsin-B protein synthesis; it is not an effective stimulus for enzyme secretion. Depletion of cartilage matrix during progression of experimental osteoarthritis may contribute to secretion of cathepsin-B and perpetuation of cartilage destruction.
Mehraban
F
F
Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
Tindal
M H
MH
Proffitt
M M
MM
Moskowitz
R W
RW
D000818:Animals; D015152:Blotting, Northern; D002358:Cartilage, Articular / Q000201:enzymology*; D002401:Cathepsin B / Q000235:genetics / Q000378:metabolism*; D046508:Culture Techniques; D018450:Disease Progression; D005109:Extracellular Matrix / Q000502:physiology; D005260:Female; D007375:Interleukin-1 / Q000494:pharmacology; D007719:Knee Joint / Q000201:enzymology*; D010003:Osteoarthritis / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D013583:Synovial Membrane / Q000201:enzymology*; D015854:Up-Regulation
D007375:Interleukin-1; D012333:RNA, Messenger; D002401:Cathepsin B