Vascular dysfunction in human and rat cirrhosis: role of receptor-desensitizing and calcium-sensitizing proteins.
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.


CONCLUSIONS
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.
Hennenberg
Martin
M
Department of Internal Medicine I, University of Bonn, Bonn, Germany. Martin.Hennenberg@ukb.uni-bonn.de
Trebicka
Jonel
J
Biecker
Erwin
E
Schepke
Michael
M
Sauerbruch
Tilman
T
Heller
Jörg
J
D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D001011:Aorta / Q000503:physiopathology; D019390:Arrestins / Q000378:metabolism; D002118:Calcium / Q000502:physiology*; D054769:G-Protein-Coupled Receptor Kinase 2; D019204:GTP-Binding Proteins / Q000502:physiology*; D006499:Hepatic Artery / Q000503:physiopathology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology; D008103:Liver Cirrhosis / Q000503:physiopathology*; D008297:Male; D008840:Microfilament Proteins / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1 / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology; D051552:beta-Adrenergic Receptor Kinases / Q000378:metabolism; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D054460:rho-Associated Kinases
C000605254:ARRB2 protein, human; C000605257:Arrb2 protein, rat; D019390:Arrestins; D047908:Intracellular Signaling Peptides and Proteins; D008840:Microfilament Proteins; D044140:Receptor, Angiotensin, Type 1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D000804:Angiotensin II; C071058:moesin; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; C496569:Grk2 protein, rat; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D043263:Myosin-Light-Chain Phosphatase; D019204:GTP-Binding Proteins; D002118:Calcium