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.
Ann Rheum Dis 1997;
56:108-15. [PMID:
9068283 PMCID:
PMC1752324 DOI:
10.1136/ard.56.2.108]
[Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
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.
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