Thrombin is a potent inducer of connective tissue growth factor productionvia proteolytic activation of protease-activated receptor-1

The coagulation protease thrombin plays a critical role in hemostasis and e xerts pro-inflammatory and profibrotic: effects via proteolytic activation of the major thrombin receptor, protease-activated receptor-1 (PAR-1), Conn ective tissue growth factor (CTGF) is a novel fibroblast mitogen and also p romotes extracellular matrix protein production. It is selectively induced by transforming growth factor beta (TGF-beta) and is thought to be the auto crine agent responsible for mediating its pro-fibrotic effects. CTGF is up- regulated during tissue repair and in fibrotic conditions associated with a ctivation of the coagulation cascade. We therefore hypothesized that coagul ation proteases promote the production of CTGF by cells at sites of tissue injury, To begin to address this hypothesis, we assessed the effect of coag ulation proteases on fibroblast CTGF expression in vitro, and we show that thrombin, at physiological concentrations, up-regulated CTGF mRNA levels 5- fold relative to base line (p < 0.01) in fetal fibroblasts and 7-fold in pr imary adult fibroblasts (p < 0.01), These effects were cycloheximide-insens itive and were not blocked with a pan-specific TGF-beta -neutralizing antib ody. They were further paralleled by a concomitant increase in CTGF protein production and could be mimicked with selective PAR-1 agonists, In additio n, fibroblasts derived from PAR-1 knockout mice were unresponsive to thromb in but responded normally to TGF-beta (1) Finally, factor Xa, which is resp onsible for activating prothrombin during blood coagulation, exerted simila r stimulatory effects. We propose that coagulation proteases and PAR-1 may play a role in promoting connective tissue formation during normal tissue r epair and the development of fibrosis by up-regulating fibroblast CTGF expr ession.