Altered factor VII activating protease expression in murine hepatic fibrosis and its influence on hepatic stellate cells

Background: Platelet‐derived growth factor‐BB (PDGF‐BB) is a profibrotic factor in liver fibrosis through its ability to stimulate hepatic stellate cells (HSC). The liver‐derived serine protease factor VII activating protease (FSAP) regulates the activities of PDGF‐BB in a cell‐specific manner. Aims: Our aim was to determine the influence of FSAP on the activation of HSC and to analyse the regulation of FSAP in hepatic fibrogenesis. Methods: The effect of FSAP on PDGF‐stimulated p42/p44 mitogen‐activated protein kinase (MAPK) activation in primary rat HSC was determined by Western blotting. Migration and proliferation of HSC was evaluated in Boyden chamber experiments and ³H‐thymidine incorporation assays respectively. Expression of FSAP was analysed in a CCl₄ mouse model of liver fibrosis by Western blot, quantitative real‐time polymerase chain reaction and immunohistochemistry. Results: FSAP inhibited PDGF‐BB‐stimulated p42/p44 MAPK phosphorylation, proliferation and migration of HSC. FSAP mRNA expression level was increased 3 h after CCl₄ application and decreased after 18 h and, in established fibrosis, after chronic CCl₄ administration. In parallel, there was a decrease in the circulating FSAP protein in chronic fibrosis. Concurrently, the homogenous hepatic expression pattern of FSAP was disturbed. Immunohistochemistry revealed a decrease of FSAP in hepatocytes in inflammatory and fibrotic lesions. Conclusions: Our results demonstrate an inhibitory effect of FSAP on PDGF‐mediated activation of HSC. In addition, FSAP expression is transiently increased in acute‐phase reaction but decreased during chronic fibrogenesis, which in turn may influence PDGF‐BB availability and myofibroblast activity.