PLASMINOGEN ACTIVATORS IN HUMAN CORNEAL FIBROBLASTS - SECRETION, CELLULAR-LOCALIZATION, AND REGULATION

Plasminogen activators (PA) play an important role not only in fibrino lysis but also in a variety of processes including tissue remodelling. The stroma of the cornea is a dense connective tissue characterized b y its transparency. Healing, degenerative, and inflammatory processes lead to corneal opacification. In an attempt to determine the role of PA in corneal physiology, we have analysed the secretion of PA and pla sminogen activator inhibitor (PAI-1) by corneal fibroblasts in vitro. We show that in contrast to other adult fibroblasts, corneal fibroblas ts secrete both tissue-type plasminogen activator (t-PA) and urokinase -plasminogen activator (u-PA). Epithelial growth factor and basic fibr oblast growth factor stimulated t-PA secretion whereas transforming gr owth factor-beta decreased t-PA and increased PAI-1 secretion. t-PA wa s secreted in the surrounding medium while u-PA remained mostly associ ated to the cell surface. The production and secretion of t-PA are cha racteristic of corneal fibroblasts and could be implicated in matrix r emodelling and the maintenance of corneal transparency.