The expression of plasminogen activator system in a rat model of periodontal wound healing

Background: The plasminogen activator system has been proposed to play a ro le in proteolytic degradation of extracellular matrices in tissue remodelin g, including wound healing. The aim of this study was to elucidate the pres ence of components of the plasminogen activator system during different sta ges of periodontal wound healing. Methods: Periodontal wounds were created around the molars of adult rats an d healing was followed for 28 days. Immunohistochemical analyses of the hea ling tissues and an analysis of the periodontal wound healing fluid by ELIS A were carried out for the detection of tissue-type plasminogen activator ( t-PA), urokinase-type plasminogen activator (u-PA), and 2 plasminogen activ ator inhibitors (PAI-1 and PAI-2). Results: During the early stages (days 1 to 3) of periodontal wound healing , PAI-1 and PAI-2 were found to be closely associated with the deposition o f a fibrin clot in the gingival sulcus. These components were strongly asso ciated with the infiltrating inflammatory cells around the fibrin clot. Dur ing days 3 to 7, u-PA, PAI-1, and PAI-2 were associated with cells (particu larly monocytes/macrophages, fibroblasts, and endothelial cells) in the new ly formed granulation tissue. During days 7 to 14, a new attachment apparat us was formed during which PAI-1, PAI-2, and u-PA were localized in both pe riodontal ligament fibroblasts (PDL) and epithelial cells at sites where th ese cells were attaching to the root surface. In the periodontal wound heal ing fluid, the concentration for t-PA increased and peaked during the first week. PAI-2 had a similar expression to t-PA, but at a lower level over th e entire wound-healing period. Conclusions: These findings indicate that the plasminogen activator system is involved in the entire process of periodontal wound healing, in particul ar with the formation of fibrin matrix on the root surface and its replacem ent by granulation tissue, as well as the subsequent formation of the attac hment of soft tissue to the root surface during the later stages of wound r epair.