Fibronectin and Fibronectin Fragments Modulate the Expression of Proteinases and Proteinase Inhibitors in Human Periodontal Ligament Cells

Fragments of the matrix molecule fibronectin (FN) have been shown to modulate tissue remodeling activity by inducing matrix metalloproteinases (MMPs) in synovial fibroblasts. These molecules could contribute to the tissue degradation that occurs during periodontal disease if they also modulate the expression of proteinases in cells of the periodontal ligament (PDL). We tested the hypothesis that FN and specific FN fragments induce the expression of specific proteinases in PDL cells. Using substrate zymograms, reverse zymograms and Western immunoblots, we found that PDL cells constitutively express 72 kDa gelatinase, urokinase-type plasminogen activator (uPA) and at least three inhibitors whose molecular masses correspond to those of the tissue inhibitors of metalloproteinases (TIMPs). A fourth, previously uncharacterized, proteinase inhibitor of approximately 22 kDa was also observed in some cell isolates. PDL cells, when exposed to a 120 kDa proteolytic FN fragment containing the cell-binding domain, were induced to express collagenase and stromelysin and also demonstrated an increased secretion of the serine proteinase uPA. Expression of collagenase increased with increasing concentrations (0.001 microM-1 microM) of the 120 kDa FN fragment. This fragment also induced the expression of a 20 kDa inhibitor, but not of the higher-molecular-mass inhibitors, in PDL cells. The observed alterations in proteinases were associated specifically with the 120 kDa FN fragment, since similar responses were not seen when PDL cells were exposed to either a 60 kDa heparin-binding FN fragment or a 45 kDa collagen/gelatin-binding FN fragment. PDL cells exposed to intact FN did not express the proteinases induced by the 120 kDa fragment but did express 92 kDa gelatinase and the 20 kDa proteinase inhibitor. These data suggest that FN and specific FN fragments can differentially induce the expression of proteinases in PDL cells. Thus, functional regions of FN may modulate many of the functions of PDL cells that contribute to periodontal disease, wound healing and maintenance of extracellular matrix in periodontal tissues.