SERPINE1 and rheumatoid arthritis: Synovial cells express membrane u-PAR, and cultured RA synoviocytes display a higher production of plasminogen activator inhibitor (PAI)-1 than in osteoarthritis and normal synoviocytes [13], suggesting that the plasminogen activator/plasminutes system is involved in the inflammatory remodeling of connective tissues occurring in arthritic joints.