Phosphorylation of eNOS initiates excessive NO production in early phases of portal hypertension

Yasuko Iwakiri, Ming Hung Tsai, Timothy J. McCabe, Jean Philippe Gratton, David Fulton, Roberto J. Groszmann, William C. Sessa

Research output: Contribution to journalArticle

69 Citations (Scopus)

Abstract

Akt, also known as protein kinase B, is a serine/threonine kinase. Akt becomes active when phosphorylated by the activation of receptor tyrosine kinases, G protein-coupled receptors, and mechanical forces such as shear stress. Studies in vitro have shown that Akt can directly phosphorylate endothelial nitric oxide (NO) synthase (eNOS) and activate the enzyme, leading to NO production. The aim of this study was to test the hypothesis that the phosphorylation of eNOS plays a role in the enhanced NO production observed in early portal hypertension. Male Sprague-Dawley rats were subjected to either sham or portal vein ligation (PVL), and mesenteric arterial beds were used for ex vivo perfusion studies., Mesenteric arterial beds from PVL rats had an approximately 60-70% decrease in response to methoxamine (an α 1-agonist and vasoconstrictor) compared with the sham group (P < 0.01). When N G-monomethyl-L-arginine (a NOS inhibitor) was added to the perfusion, the difference in perfusion pressure between the two groups was abolished, suggesting that enhanced NO production in the PVL group blunted the response to the vasoconstrictor. The reduced responsiveness in PVL was not due to changes in eNOS expression but was due to an increase in enzyme-specific activity, suggesting posttranslational modification of eNOS. The phosphorylation of eNOS at Ser 1176 was significantly increased by twofold (P < 0.05) in the PVL group. Furthermore, PVL significantly increased Akt phosphorylation (an active form of Akt) by threefold (P < 0.05). When vessels were treated with wortmannin (10 nM) to block the phosphatidylinositol-3-OH-kinase/Akt pathway, NO-induced vasodilatation was significantly reduced. These results suggest that the phosphorylation of eNOS by Akt activates the enzyme and may be the first step leading to an initial increase in NO production in portal hypertension.

Original languageEnglish (US)
Pages (from-to)H2084-H2090
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume282
Issue number6 51-6
StatePublished - Jul 2 2002

Fingerprint

Portal Hypertension
Portal Vein
Ligation
Nitric Oxide
Phosphorylation
Perfusion
Vasoconstrictor Agents
Enzymes
Phosphatidylinositol 3-Kinase
Methoxamine
Proto-Oncogene Proteins c-akt
Nitric Oxide Synthase Type III
Protein-Serine-Threonine Kinases
Receptor Protein-Tyrosine Kinases
Post Translational Protein Processing
G-Protein-Coupled Receptors
Vasodilation
Sprague Dawley Rats
Arginine
Pressure

Keywords

  • Akt
  • In vivo
  • Portal vein ligation
  • Superior mesenteric artery

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

Cite this

Iwakiri, Y., Tsai, M. H., McCabe, T. J., Gratton, J. P., Fulton, D., Groszmann, R. J., & Sessa, W. C. (2002). Phosphorylation of eNOS initiates excessive NO production in early phases of portal hypertension. American Journal of Physiology - Heart and Circulatory Physiology, 282(6 51-6), H2084-H2090.

Phosphorylation of eNOS initiates excessive NO production in early phases of portal hypertension. / Iwakiri, Yasuko; Tsai, Ming Hung; McCabe, Timothy J.; Gratton, Jean Philippe; Fulton, David; Groszmann, Roberto J.; Sessa, William C.

In: American Journal of Physiology - Heart and Circulatory Physiology, Vol. 282, No. 6 51-6, 02.07.2002, p. H2084-H2090.

Research output: Contribution to journalArticle

Iwakiri, Y, Tsai, MH, McCabe, TJ, Gratton, JP, Fulton, D, Groszmann, RJ & Sessa, WC 2002, 'Phosphorylation of eNOS initiates excessive NO production in early phases of portal hypertension', American Journal of Physiology - Heart and Circulatory Physiology, vol. 282, no. 6 51-6, pp. H2084-H2090.
Iwakiri, Yasuko ; Tsai, Ming Hung ; McCabe, Timothy J. ; Gratton, Jean Philippe ; Fulton, David ; Groszmann, Roberto J. ; Sessa, William C. / Phosphorylation of eNOS initiates excessive NO production in early phases of portal hypertension. In: American Journal of Physiology - Heart and Circulatory Physiology. 2002 ; Vol. 282, No. 6 51-6. pp. H2084-H2090.
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abstract = "Akt, also known as protein kinase B, is a serine/threonine kinase. Akt becomes active when phosphorylated by the activation of receptor tyrosine kinases, G protein-coupled receptors, and mechanical forces such as shear stress. Studies in vitro have shown that Akt can directly phosphorylate endothelial nitric oxide (NO) synthase (eNOS) and activate the enzyme, leading to NO production. The aim of this study was to test the hypothesis that the phosphorylation of eNOS plays a role in the enhanced NO production observed in early portal hypertension. Male Sprague-Dawley rats were subjected to either sham or portal vein ligation (PVL), and mesenteric arterial beds were used for ex vivo perfusion studies., Mesenteric arterial beds from PVL rats had an approximately 60-70{\%} decrease in response to methoxamine (an α 1-agonist and vasoconstrictor) compared with the sham group (P < 0.01). When N G-monomethyl-L-arginine (a NOS inhibitor) was added to the perfusion, the difference in perfusion pressure between the two groups was abolished, suggesting that enhanced NO production in the PVL group blunted the response to the vasoconstrictor. The reduced responsiveness in PVL was not due to changes in eNOS expression but was due to an increase in enzyme-specific activity, suggesting posttranslational modification of eNOS. The phosphorylation of eNOS at Ser 1176 was significantly increased by twofold (P < 0.05) in the PVL group. Furthermore, PVL significantly increased Akt phosphorylation (an active form of Akt) by threefold (P < 0.05). When vessels were treated with wortmannin (10 nM) to block the phosphatidylinositol-3-OH-kinase/Akt pathway, NO-induced vasodilatation was significantly reduced. These results suggest that the phosphorylation of eNOS by Akt activates the enzyme and may be the first step leading to an initial increase in NO production in portal hypertension.",
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