AGGRECAN IS DEGRADED BY MATRIX METALLOPROTEINASES IN HUMAN ARTHRITIS - EVIDENCE THAT MATRIX METALLOPROTEINASE AND AGGRECANASE ACTIVITIES CAN BE INDEPENDENT

Proteolytic degradation of aggrecan is a hallmark of the pathology of arthritis, yet the identity of the enzyme(s) in cartilage responsible for this degradation is unknown, Previous studies have suggested that the matrix metalloproteinases (MMPs) may be involved but there has bee n no definitive evidence for their direct action in the proteolysis of aggrecan in human arthritis, We now show unequivocally that aggrecan fragments derived from the specific action of MMPs can be detected in synovial fluids from patients with both inflammatory and noninflammato ry arthritis, with a neoepitope monoclonal antibody AF-28 that detects the NH2-terminal sequence F(342)FGVG.... The synovial fluid MMP fragm ents were of low buoyant density and distributed exclusively at the to p of cesium chloride density gradients, suggesting that these fragment s lacked chondroitin sulfate chains, AF-28 immunoblotting of synovial fluid aggrecan fragments revealed a population of small AF-28 fragment s of 30-50 kD. Based on their size relative to characterized products of an MMP-8 digest (Fosang, A.J., K. Last, P. Gardiner, D.C. Jackson, and L. Brown. 1995, Biochem. J. 310:337-343), these AF-28 fragments we re derived from proteinase cleavage at, or near, the... ITEGE(373) dow n arrow ARGSV... aggrecanase site. Immunodetection with polyclonal ant i-ITEGE antiserum revealed that these fragments lacked the... ITEGE(37 4) COOH terminus and were not therefore products of aggrecanase action , The same fluid samples contained a broad 68-90-kD G1 fragment that c ontained the COOH-terminal ...ITEGE(374) neoepitope. The results sugge st that in some circumstances, despite extensive proteolysis of the co re protein, aggrecan molecules may be cleaved by MMPs or aggrecanase i n the interglobular domain, but not both.