Hennenberg Martin, Trebicka Jonel, Biecker Erwin, Schepke Michael, Sauerbruch Tilman, Heller Jörg
Department of Internal Medicine I, University of Bonn, Bonn, Germany.
Hepatology. 2007 Feb;45(2):495-506. doi: 10.1002/hep.21502.
In cirrhosis, vascular hypocontractility leads to vasodilation and contributes to portal hypertension. Impaired activation of contractile pathways contributes to vascular hypocontractility. Angiotensin II type 1 receptors (AT1-Rs) are coupled to the contraction-mediating RhoA/Rho-kinase pathway and may be desensitized by phosphorylation through G-protein-coupled receptor kinases (GRKs) and binding of beta-arrestin-2. In the present study, we analyzed vascular hypocontractility to angiotensin II in cirrhosis. Human hepatic arteries were obtained during liver transplantation. In rats, cirrhosis was induced by bile duct ligation (BDL). Contractility of rat aortic rings was measured myographically. Protein expression and phosphorylation were analyzed by Western blot analysis. Immunoprecipitation was performed with protein A-coupled Sepharose beads. Myosin light chain (MLC) phosphatase activity was assessed as dephosphorylation of MLCs. Aortas from BDL rats were hyporeactive to angiotensin II and extracellular Ca2+. Expression of AT1-R and Galphaq/11,12,13 remained unchanged in hypocontractile rat and human vessels, whereas GRK-2 and beta-arrestin-2 were up-regulated. The binding of beta-arrestin-2 to the AT1-R was increased in hypocontractile rat and human vessels. Inhibition of angiotensin II-induced aortic contraction by the Rho-kinase inhibitor Y-27632 was pronounced in BDL rats. Basal phosphorylation of the ROK-2 substrate moesin was reduced in vessels from rats and patients with cirrhosis. Analysis of the expression and phosphorylation of Ca(2+)-sensitizing proteins (MYPT1 and CPI-17) in vessels from rats and patients with cirrhosis suggested decreased Ca2+ sensitivity. Angiotensin II-stimulated moesin phosphorylation was decreased in aortas from BDL rats. MLC phosphatase activity was elevated in aortas from BDL rats.
Vascular hypocontractility to angiotensin II in cirrhosis does not result from changes in expression of AT1-Rs or G-proteins. Our data suggest that in cirrhosis-induced vasodilation, the AT1-R is desensitized by GRK-2 and beta-arrestin-2 and that changed patterns of phosphorylated Ca(2+) sensitizing proteins decrease Ca(2+) sensitivity.
在肝硬化中，血管收缩功能减退导致血管舒张并促成门静脉高压。收缩途径的激活受损促成了血管收缩功能减退。1型血管紧张素II受体（AT1-Rs）与介导收缩的RhoA/Rho激酶途径偶联，可能通过G蛋白偶联受体激酶（GRKs）磷酸化和β-抑制蛋白2的结合而脱敏。在本研究中，我们分析了肝硬化中血管对血管紧张素II的收缩功能减退情况。在肝移植过程中获取人肝动脉。在大鼠中，通过胆管结扎（BDL）诱导肝硬化。用肌动描记法测量大鼠主动脉环的收缩性。通过蛋白质印迹分析来分析蛋白质表达和磷酸化情况。用蛋白A偶联的琼脂糖珠进行免疫沉淀。肌球蛋白轻链（MLC）磷酸酶活性通过MLC的去磷酸化来评估。BDL大鼠的主动脉对血管紧张素II和细胞外Ca2+反应性降低。在收缩功能减退的大鼠和人血管中，AT1-R和Gαq/11、12、13的表达保持不变，而GRK-2和β-抑制蛋白2上调。在收缩功能减退的大鼠和人血管中，β-抑制蛋白2与AT1-R的结合增加。Rho激酶抑制剂Y-27632对血管紧张素II诱导的主动脉收缩的抑制在BDL大鼠中很明显。肝硬化大鼠和患者血管中ROK-2底物埃兹蛋白的基础磷酸化降低。对肝硬化大鼠和患者血管中Ca(2+)敏化蛋白（MYPT1和CPI-17）的表达和磷酸化分析表明Ca2+敏感性降低。BDL大鼠主动脉中血管紧张素II刺激的埃兹蛋白磷酸化降低。BDL大鼠主动脉中MLC磷酸酶活性升高。
肝硬化中血管对血管紧张素II的收缩功能减退并非由AT1-Rs或G蛋白表达变化所致。我们的数据表明，在肝硬化诱导的血管舒张中，AT1-R被GRK-2和β-抑制蛋白2脱敏，并且磷酸化的Ca(2+)敏化蛋白模式改变降低了Ca(2+)敏感性。
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