Matrix metalloproteinase and proinflammatory cytokine production by chondrocytes of human osteoarthritic cartilage - Associations with degenerative changes

Objective. To examine by immunohistochemistry the relative distributions of 6 matrix metalloproteinases (MMPs 1, 2, 3, 8, 9, and 13) and the 2 proinfl ammatory cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) in osteoarthritic (OA) cartilage compared with normal, a ge-matched articular cartilage. Methods. Articular cartilage samples were obtained from the tibial plateau of OA knees removed at arthroplasty and from normal, nonarthritic, knees ob tained at autopsy. Specimens were promptly fixed in Carnoy's fixative, proc essed, embedded in paraffin, sectioned, and examined by immunohistochemistr y for MMP and cytokine production. In addition, human articular chondrocyte s (HAC) were treated in vitro with either IL-1 beta, TNF alpha, or phorbol myristate acetate (PMA) to assess their potential to produce each of the MM Ps, as determined by Western blotting and gelatin zymography. Results. Immunodetection of the collagenases (MMPs 1, 8, and 13) and strome lysin 1 (MMP-3) was demonstrated in a proportion of chondrocytes in the sup erficial zone of almost all of the OA specimens that had degenerative matri x changes. The gelatinases (MMPs 2 and 9) were also demonstrated by immunoh istochemistry but were not so prominent. IL-1 beta- and TNF alpha -positive chondrocytes were also observed in a proportion of cells in the superficia l zones of OA specimens. Much less immunostaining for MMPs and cytokines wa s observed in the deep zone of all OA specimens, where the cartilage matrix and chondrocyte morphology appeared normal. In contrast, full-thickness no rmal cartilage specimens showed virtually no immunostaining for these MMPs or cytokines. Confirmation that chondrocytes can produce these 6 MMPs was o btained from RAC cultures treated with either IL-1 beta, TNF alpha, or PMA; conditioned medium from activated RAC contained all the MMPs demonstrated by immunohistochemistry. Dual immunolocalization studies of OA cartilage sp ecimens demonstrated the coexpression of IL-1 with MMP-8 by individual chon drocytes in situ. Conclusion. These results indicate that the superficial zone of OA cartilag e specimens, which is characterized by fibrillations, chondrocyte clusters, and degenerative matrix changes, contains a variable proportion of cells t hat immunostain for IL-1 beta, TNF alpha, and 6 different MMPs. These obser vations support the concept that cytokine-MMP associations reflect a modifi ed chondrocyte phenotype and an intrinsic process of cartilage degradation in OA.