Prostaglandin E2 induces contraction of liver myofibroblasts by activating EP3 and FP prostanoid receptors

Background and purpose: Increased portal pressure in liver injury results from hypercontraction of perivascular non-parenchymal cells including liver myofibroblasts (MFs). Prostaglandin E-2 (PGE(2)) is the major eicosanoid which is released around the venous system during liver injury, but little is known about their contractile effect on MFs. Experimental approach: Contraction of primary rat liver MFs was measured by a collagen gel contraction assay. Expression of E prostanoid (EP) receptor subtypes was assessed by reverse transcription-polymerase chain reaction. Fura-2 fluorescence was used to determine intracellular Ca2+ concentration ([Ca2+](i)). Phosphorylation of protein kinase C (PKC) was detected by Western blot analysis. Key results: Liver MFs expressed mRNAs for all four EP receptors. PGE(2) induced contraction in a dose- and time-dependent manner, and slightly increased [Ca2+](i) only at high concentrations (10 mu mol.L-1). An agonist selective for EP3 receptors, ONO-AE-248, dose-dependently induced MF contraction but did not increase [Ca2+](i). Pretreatment with rottlerin (a specific novel PKC inhibitor) and Ro 31-8425 (a general PKC inhibitor) significantly reduced 1 mu mol.L-1 PGE(2)- or ONO-AE-248-induced contractions. Furthermore, 1 mu mol.L-1 PGE(2) stimulated phosphorylation of PKC isoforms PKC delta and PKC epsilon. The F prostanoid (FP) receptor antagonist AL8810 abolished the [Ca2+](i) elevation and the rapid contraction induced by 10 mu mol.L-1 PGE(2). Conclusions and implications: Lower concentrations up to 1 mu mol.L-1 of PGE(2) induce liver MF contraction via a [Ca2+](i)-independent PKC-mediated pathway through the EP3 receptor, while higher concentrations have an additional pathway leading to Ca2+-dependent contraction through activating the FP receptor.