Cartilage damaging activities of fibronectin fragments derived from cartilage and synovial fluid

Objective: To investigate whether fibronectin fragments (Fn-fs), shown to damage cultured cartilage, can be found in cartilage from patients with osteoarthritis (OA) or rheumatoid arthritis, or can be generated from fibronectin (Fn) within synovial fluids or from Fn in the matrix of cultured cartilage. To also determine whether cartilage or synovial fluid Fn-fs are active and, thus, could contribute to cartilage damage in vivo. Methods: Fn-fs were immunochemically identified in cartilage extracts from patients with OA or rheumatoid arthritis or in bovine cartilage cultured with IL-1 alpha or in bovine synovial fluids treated with stromelysin-1 (MMP-3). The effect of removal of Fn-fs were OA synovial fluids was tested by passing fluids over an anti-Fn column and adding the resultant fluids to bovine cartilage cultures to measure proteoglycan (PCT) degradation. Gelatin-Sepharose purified Fns from bovine plasma, synovial fluid or cartilage were digested with MMP-3 and the Fn-fs tested for degradation of PG; in cultured cartilage. Results: Extracts of cartilage from patients with rheumatoid arthritis or with OA contained a range of Fn-fs. Removal of Fn-fs from OA synovial fluids significantly reduced the resultant damage when the fluids were added to cultured cartilage. Addition of IL-1 alpha to cultured cartilage or of MMP-3 to synovial fluids enhanced generation of Fn-fs. Fn-fs, whether derived from bovine plasma or synovial fluid or cartilage Fns, damaged cartilage. Conclusions: These data demonstrate that although Fn-fs could be generated in vivo within synovial fluids and Fn-fs found in OA synovial fluid may contribute to cartilage damage in vivo, Fn-fs could also be generated within cartilage and amplify cartilage damage. Thus, Fn-fs may be both autocrine and paracrine regulators of cartilage metabolism.