PDGF-Mediated Chemoattraction of Hepatic Stellate Cells by Bile Duct Segments in Cholestatic Liver Injury

Abstract

The accumulation of myofibroblasts and fibrosis around proliferating bile ducts in cholestatic liver disease has been attributed to the proliferation and phenotypic modulation of portal fibroblasts, whereas the contribution of hepatic stellate cells remains uncertain. There is increasing evidence to indicate that bile ducts may stimulate chemoattraction of hepatic stellate cells (HSC). In the present study, we undertook dynamic tests to examine such a possibility and to investigate the role of two potential mediators: platelet-derived growth factor-BB (PDGF-BB) and endothelin-1. Cholestasis was induced by bile duct ligation in rats. HSC were isolated from normal rats and culture activated into myofibroblasts expressing PDGF-β receptors. Migration of myofibroblastic HSC was investigated in a Transwell chemotaxis filter assay. As compared with basal conditions, PDGF-BB (100 μg/l) and endothelin-1 (10−8m) induced a 3-fold and 1.7-fold increase in HSC migration, respectively. Bile duct segments isolated from cholestatic rats triggered a 3-fold increase in migration. This stimulation was significantly more potent than that observed in the presence of normal bile ducts. It was inhibited by neutralizing anti-PDGF antibodies and by STI571 PDGF receptor tyrosine kinase inhibitor, by 60% and 85%, respectively, whereas Bosentan, an endothelin receptor antagonist, had no significant inhibiting effect. In bile duct segments from cholestatic rats PDGF-B chain mRNA was detected at higher levels than in controls, whereas PDGF-BB was immunolocalized in bile duct epithelial cells. The results indicate that chemotaxis of HSC towards bile duct structures may contribute to the development of periductular fibrosis in cholestatic disorders, and that PDGF-BB is the major mediator in this process. In addition, anti-liver fibrogenic properties of STI571 are suggested by potent inhibition of myofibroblastic HSC function.