Thrombin Inhibits the Migration of Human Liver Myofibroblasts

Abstract

Liver myofibroblasts are the key cells of liver fibrogenesis. Recent data show that the serine proteinase thrombin is involved in fibrogenesis through a mitogenic effect on myofibroblasts. The aim of this study was to evaluate the effects of thrombin on the migration of human liver myofibroblasts; another major parameter in fibrogenesis.In a Boyden chamber assay, thrombin dose‐dependently (10−10–10−7 M) decreased spontaneous myofibroblast migration down to 49 ± 1% of control values (p = 5.10−10) without affecting cell adhesion or viability. Thrombin effect was blocked by its specific catalytic inhibitor hirudin and could be reproduced by using the proteinase‐activated receptor‐1 (PAR‐1) agonist SFLLRNP. Thrombin also completely inhibited migration when induced by the chemotactic agent platelet‐derived growth factor‐BB. We then investigated the signaling mechanisms involved. The COX‐2 inhibitor NS398 dose‐dependently (2.5–10 μM) blunted the inhibitory effect of thrombin on spontaneous migration. However, NS398 did not reverse the inhibitory effect of thrombin on PDGF‐BB‐induced migration. Phosphatidylinositol 3‐kinase (PI3‐K) is a major determinant of chemotaxis induced by PDGF. Whereas thrombin did not itself induce PI3‐K activity, as shown by the lack of detectable phosphorylation of Akt‐1, it inhibited PDGF‐BB‐induced Akt‐1 phosphorylation. This effect was dependent of the Rho/ROCK pathway since it was abolished in the presence of the ROCK inhibitor Y‐27632.In summary, thrombin, acting via a proteinase‐activated receptor, inhibits human liver myofibroblasts migration. Inhibition of basal migration is dependent on COX‐2, while inhibition of PDGF‐BB‐induced migration involves decreased PI3‐K activation via a Rho/ROCK mechanism. We suggest that thrombin could thus stabilize activated myofibroblasts on the site of active fibrogenesis.