Localization and expression of cartilage oligomeric matrix protein by human rheumatoid and osteoarthritic synovium and cartilage

Synovium and cartilage from patients with osteoarthritis or rheumatoid arth ritis were analyzed for expression of cartilage oligomeric matrix protein. Immunostaining of synovium with antiserum to cartilage oligomeric matrix pr otein demonstrated positive staining in both diseases. In osteoarthritis, t here was positive staining within the synovial cells and immediately subjac ent connective tissue, with less intense staining in the deeper connective tissue. In rheumatoid arthritis, there was less intense staining within the synovial cells and marked intense staining in the deeper connective tissue . In Situ hybridization performed with an antisense digoxigenin-labeled rib oprobe to human cartilage oligomeric matrix protein confirmed the presence of cartilage oligomeric matrix protein mRNA in the cells of the synovial li ning in both types of synovium. Quantitative polymerase chain reaction with a cartilage oligomeric matrix protein MIMIC demonstrated increased cartila ge oligomeric matrix protein mRNA in rheumatoid cartilage and synovium as c ompared with osteoarthritic cartilage and synovium, respectively; mRNA leve ls in rheumatoid synovium were similar to those from osteoarthritic chondro cytes. As a result of the high expression of cartilage oligomeric matrix pr otein from rheumatoid synovium, inflammatory synovium should be considered as a potential tissue source of cartilage oligomeric matrix protein in any investigation of biological markers of cartilage metabolism. The upregulate d expression of cartilage oligomeric matrix protein in inflammatory tissues suggests its in vivo regulation by cytokines.