Signalling pathways involved in isoprostane-induced fibrogenic effects in hepatic stellate cells

INTRODUCTION: We have previously shown that the levels of plasma F2-Isoprostanes (F2-Iso) are maintained elevated in the model of chronic CCl4 intoxication leading to fibrosis and cirrhosis, and correlated to the increased hepatic collagen. F2-Iso can also potentially mediate some of the adverse effects of oxidant injury. We demonstrated that in hepatic stellate cells (HSC) some fibrogenic events (such as cell proliferation and collagen synthesis) are induced by F2-Iso through the activation of receptors analogous to those for tromboxane A2 (TP receptor), but how isoprostanes act to initiate these events remains unclear. METHODS: HSC were isolated from rat liver and treated with 8-epi-PGF2the most represented isomer). Inositol-3-phosphate (IP3) and cAMP levels were determined by commercial kits. Activation of MAPK and cyclin D1 was assessed by Western blotting. Cell proliferation and collagen production were determined by measuring the incorporation of 3H-thymidine and 3H-proline, respectively. RESULTS: A transient increase of cAMP was observed. 8-epi-PGF2also increased IP3 levels and activated ERK and p38 MAPK which have been shown to influence cell proliferation and collagen gene expression, as well as cyclin D1 expression. Collagen synthesis and cell proliferation induced by 8-epi-PGF2 were completely reversed by PD98059, a specific inhibitor of ERK activation. CONCLUSIONS: The data obtained suggest that one of the pathways activated by 8-epi-PGF2 is that of Gq/PKC. The binding of isoprostanes to TP receptor in HSC could stimulate downstream MAPK activation, leading to an increased collagen production. Furthermore the ability of ERK to increase cyclin D1 expression can stimulate cell proliferation.