Lack of tissue inhibitor of metalloproteinases-3 results in an enhanced inflammatory response in antigen-induced arthritis

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is known to inhibit matrix metalloproteinases, aggre-canases, and tumor necrosis factor (TNF)-alpha-converting enzyme (TACE, ADAM17). These metalloproteases participate in different aspects of joint destruction in inflammatory arthritis. To determine the relative importance of this inhibitor in joint pathology, wildtype and Timp3(-/-) mice were immunized with methylated bovine serum albumin followed by arthritis induction by intra-articular injection of the same antigen. Animals were monitored for up to 14 days after challenge, and joint tissues were analyzed by routine and Safranin 0 staining and for the presence of aggrecan neoepitopes produced by metalloprotease cleavage. Serum TNF-alpha was measured by immunoassay. Compared to wild-type animals, Timp3(-/-) mice showed a dramatic increase in the initial inflammatory response to intra-articular antigen injection, and serum TNF-a levels were greatly elevated in the Timp3(-/-) animals after immunization. However, these differences in clinical features disappeared by days 7 to 14. No difference in Safranin 0 staining or aggrecan cleavage site neoepitope abundance was seen. Thus, in inflammatory joint disease TIMP-3 likely dampens the inflammatory response of TNF-a by reducing ADAM17 activity.