CHARACTERIZATION OF THE PLASMINOGEN ACTIVATORS AND PLASMINOGEN-ACTIVATOR INHIBITORS EXPRESSED BY CELLS ISOLATED FROM RABBIT LIGAMENT AND SYNOVIAL TISSUES - EVIDENCE FOR UNIQUE CELL-POPULATIONS

Fibroblasts derived from rabbit anterior cruciate and medial collateral ligaments were found to constitutively produce and secrete a plasminogen activator (PA). The PA was identified as urokinase-like using biochemical, immunological, and molecular techniques. These fibroblasts also produced and secreted low levels of a plasminogen activator inhibitor (PAI). The inhibitor was identified as PAI-1 by biochemical and molecular techniques. The expression of both PA and PAI activity in the rabbit ligament fibroblasts increased upon addition of phorbol myristate acetate (PMA). To determine the relationship of the ligament flbroblast population to synovial fibroblasts, comparison of the biochemical characteristics of the cell types was performed. It was determined that synovial fibroblasts differed from ligament fibroblasts with respect to PA/PAI profile, type of collagen secreted, and the amount of hyaluronic acid secreted. More specifically, stimulation of synovial fibroblasls with PMA resulted in the detection of a fibrinolytic activity which was not detected in the conditioned medium from PMA-treated ligament fibroblasts. It was also shown that synovial fibroblasts secreted fourfold more hyaluronic acid than ligament fibroblasts. In addition, it was also determined that synovial fibroblasts secrete more type III collagen than do cells isolated from either the ACL or either MCL. These results support the conclusion that the cells derived from these tissues maintain distinct phenotypes in vitro. © 1993 Academic Press, Inc.