Prostaglandin D2 induces contraction via thromboxane A2 receptor in rat liver myofibroblasts

Increased intrahepatic resistance is one of the major characteristics of cirrhotic liver, in which extravascular cells including liver myofibroblasts (MFs) abnormally contract. Although several studies provided evidence that various prostaglandins (PG) are involved in liver cirrhosis, the role of PGD2 remains unknown. In this study, we investigated the effect of PGD2 on the contractile properties of liver MFs. Cultured rat liver MFs were used at passages 4–7. A collagen gel contraction assay was used for the evaluation of the MFs contraction. mRNA expression was assessed by semi-quantitative RT-PCR. Intracellular Ca2+ concentrations ([Ca2+]i) were measured by monitoring the fluorescence intensity of fura-2. PGD2 (1–10 μM) induced liver MF contraction in a dose-dependent manner with [Ca2+]i elevation. Pretreatment with 300 nM LaCl3, a nonselective Ca2+ channel blocker abolished the 10 μM PGD2-induced MFs contraction. RT-PCR revealed that three distinct PGD2 responsive receptors, prostanoid DP receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) and thromboxane A2 receptor (prostanoid TP receptor), were expressed in liver MFs. While prostanoid DP receptor agonist and CRTH2 agonist didn't induce contraction, 0.01–1 μM U46619 (11α, 9α-epoxymethano-PGH2, prostanoid TP receptor agonist) caused robust contraction with [Ca2+]i elevation. Furthermore, pretreatment with prostanoid TP receptor antagonists ramatroban (1 μM) or SQ29548 ([1S-[1α, 2α(Z), 3α, 4α]]-7-[3-[[2-[(phenyl amino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid, 1 μM) completely suppressed PGD2-induced contraction and [Ca2+]i elevation. Additionally, we observed that BW245C (1–10 μM) decreased basal MF contraction. These results suggest that PGD2 induces rat liver MF contraction with an increase in [Ca2+]i through prostanoid TP receptor.