Prostaglandin E 2 induces contraction of liver myofibroblasts by activating EP 3 and FP prostanoid receptors

Abstract

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 Ca 2+ concentration ([Ca 2+] 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 [Ca 2+] i only at high concentrations (10 μmol·L -1). An agonist selective for EP 3 receptors, ONO-AE-248, dose-dependently induced MF contraction but did not increase [Ca 2+] i. Pretreatment with rottlerin (a specific novel PKC inhibitor) and Ro 31-8425 (a general PKC inhibitor) significantly reduced 1 μmol·L -1 PGE 2- or ONO-AE-248-induced contractions. Furthermore, 1 μmol·L -1 PGE 2 stimulated phosphorylation of PKC isoforms PKCδ and PKCη. The F prostanoid (FP) receptor antagonist AL8810 abolished the [Ca 2+] i elevation and the rapid contraction induced by 10 μmol·L -1 PGE 2. Conclusions and implications: Lower concentrations up to 1 μmol·L -1 of PGE 2 induce liver MF contraction via a [Ca 2+] i-independent PKC-mediated pathway through the EP 3 receptor, while higher concentrations have an additional pathway leading to Ca 2+-dependent contraction through activating the FP receptor. © 2009 The British Pharmacological Society.