Stimulation of Phagocytic Activity in Cultured Human Corneal Fibroblasts by Plasminogen.
Plasminogen has been detected in the corneal stroma after tissue injury and interacts with corneal fibroblasts during wound healing. We examined the effect of plasminogen on phagocytic activity of corneal fibroblasts. Cultured human corneal fibroblasts were exposed to plasminogen and then incubated with fluorescent microparticles before measurement of phagocytic activity by confocal microscopy or flow cytometry. The binding of corneal fibroblasts to immobilized plasminogen was quantitated with a real-time biomolecular interaction assay. The production of urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs), and IL-1β by corneal fibroblasts was measured by fibrin zymography, by immunoblot analysis or gelatin zymography, or with an enzyme-linked immunosorbent assay, respectively. Plasminogen increased phagocytic activity of corneal fibroblasts in a concentration- and time-dependent manner, with the maximal effect apparent at 30 μg/mL and 24 hours. Corneal fibroblasts bound to immobilized plasminogen in a manner dependent on time and cell number, and the stimulatory effect of plasminogen on phagocytic activity was blocked in the presence of epsilon-aminocaproic acid, an inhibitor of plasminogen binding to cell surface receptors. Plasminogen-induced phagocytic activity was not associated with changes in the production of uPA, MMPs, or IL-1β by corneal fibroblasts. Plasminogen induced phagocytic activity in corneal fibroblasts in a manner dependent on its binding to the cell surface. This effect was not associated with increased production of proteases or IL-1β. Thus, plasminogen may promote the clearance of foreign particles or damaged tissue components by corneal fibroblasts early after tissue injury.