Matrix metalloproteinases (MMPs), such as stromelysin, have been linked the degradation of articular cartilage in normal and pathologic tissue. Elevated levels of MMP production and mRNA expression have been detected in patients with rheumatoid arthritis, osteoarthritis and traumatic joint injury as well as in developing tissue and normal growth plate cartilage. While MMPs have been shown to degrade purified matrix macromolecules in vitro, their action against the matrix of intact cartilage has not been well established. The objectives of this thesis were threefold:​ (1) to characterize the ability of MMPs to degrade cartilage matrix constituents of intact cartilage;​ (2) to quantify the effects of this degradation on the functional biophysical properties of cartilage;​ and (3) to evaluate the ability of synthetic and natural MMP inhibitors to modulate these changes in composition and biophysical properties.

Bovine cartilage explants were treated with recombinant human stromelysin-1 and changes in biochemical, biomechanical, and physicochemical properties as well as histological appearance were assessed. Stromelysin treatment resulted in a time and dose dependent loss of proteoglycan fragments from the explants, increased degradation and loss of type IX collagen, and a concomitant swelling of the tissue. Histological examination demonstrated that proteoglycan loss proceeded inward from the exposed tissue surfaces, with a marked boundary between degraded and undegraded tissue. Stromelysin treatment resulted in marked decreases in equilibrium modulus and dynamic stiffness and a substantial increase in hydraulic permeability after three days in culture. Measurement of dynamic streaming potential showed that changes due to stromelysin treatment were strongly dependent on compression frequency, with dramatic decreases seen at high frequency prior to changes in mechanical properties, and little initial change seen at low frequency.

Cartilage from rabbit stifle joints which were exposed to stromelysin for 1 hour in vivo showed little difference in proteoglycan content from cartilage from contralateral control joints, while synovial fluid proteoglycan content from stromelysin treated joints was significantly higher than that of controls. Histological examination revealed that loss of proteoglycan, as indicated by both toluidine blue and FVDIPEN antibody staining, occurred primarily in a narrow region of the tissue near the articular surface. Consequently, the mechanical properties, such as equilibrium modulus and dynamic stiffness, of cartilage samples from treated joints did not differ significantly from those of control joints, while electromechanical properties, such as streaming potential and electrokinetic coupling coefficient, of cartilage from treated joints were degraded significantly compared to controls. Systemic administration of a synthetic MMP inhibitor signficantly decreased release of proteoglycan fragments to synovial fluid, inhibited loss of proteoglycan as indicated by toluidine blue and FVDIPEN antibody staining, and prevented changes in cartilage electromechanical properties due to intraarticular injection of stromelysin.

The degradation of cartilage matrix by endogenous MMPs was characterized by treatment of explants with 4-aminophenylmercuric acetate (APMA) to activate native MMPs or by treatment with interleukin- 10 (IL- 10) or retinoic acid (RA), which upregulate production of MMPs by chondrocytes, and may increase levels of other endogenous proteinases. Treatment with APMA resulted in significant loss of proteoglycan by 1 day in culture and in significant swelling response by 3 days in culture. Matrix degradation was manifest in changes in sample mechanical and electromechanical properties. Both a synthetic MMP inhibitor and the native MMP inhibitor, TIMP, significantly inhibited proteoglycan loss, swelling response, and changes in physical properties due to APMA treatment. Treatment with IL-1 /3 and RA induced significant loss of proteoglycan after 4 days in culture. Treatment with IL-10 resulted in an increased swelling response after 8 days in culture, while RA treatment did not. Both IL-1/3 and RA treatments resulted in significant changes in tissue mechanical and electromechanical properties which were partially modulated by addition of TIMP to the culture media. Use of synthetic inhibitors also partially modulated proteoglycan loss from IL-10 and RA treated tissue. Analysis of fragments in the culture media from these samples indicated that cleavage of proteoglycan did not occur at the VDIPEN-FFGV site associated with MMP activity, but rather at the NITEGE-ARGSVL site on the aggrecan core protein. This was the only proteinase activity observed against aggrecan in this system, and it was partially inhibited by the addition of a synthetic MMP inhibitor to the culture media.