Key Event Overview
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AOPs Including This Key Event
|AOP Name||Event Type||Essentiality|
|Oxidative Stress Leading to Hypertension||KE||Strong|
|Homo sapiens||Homo sapiens||NCBI|
|Bos taurus||Bos taurus||NCBI|
|Mus musculus||Mus musculus||NCBI|
Level of Biological Organization
How this Key Event works
Endothelial nitric oxide synthase (eNOS) is responsible for the generation of nitric oxide (NO), which is an important regulator of vascular homeostasis. The activity of eNOS can be regulated through calmodulin-mediated dimerization, tetrahydrobiopterin-mediated conversion of L-arginine to L-citrulline, protein-protein interactions with heat shock protein 90 and caveolin, S-nitrosylation, acetylation and phosphorylation (Atochin et al., 2007; Qian and Fulton, 2013). eNOS has been shown to be phosphorylated at multiple sites including tyrosine (Y), serine (Ser) and threonine (Thr) residues. Serine-threonine protein kinase Akt, a multifunctional regulator of cellular processes like glucose metabolism and proliferation, can directly phosphorylate eNOS at Ser1177/Ser1179, leading to increased eNOS enzymatic activity and subsequent NO production (Dimmeler et al., 1999; Fulton et al., 1999). Inhibition of the Akt or a mutation of Akt site on eNOS attenuates eNOS phosphorylation and its activity, resulting in decreased NO bioavailability and endothelial dysfunction.
How it is Measured or Detected
Western blot analysis can be performed to determine the expression levels of phosphorylated eNOS, phosphorylated Akt, total Akt and total eNOS proteins using the appropriate anti-phospho-eNOS, anti-phospho-Akt, anti-eNOS, and anti-Akt antibodies. Alternatively, eNOS activity can be measured using the conversion of L-arginine to L-citrulline assay.
Evidence Supporting Taxonomic Applicability
Decreased Akt and eNOS activity was observed in humans, cows, and mice.
Atochin, D.N., Wang, A., Liu, V.W.T., Critchlow, J.D., Dantas, A.P.V., Looft-Wilson, R., Murata, T., Salomone, S., Shin, H.K., Ayata, C., et al. (2007). The phosphorylation state of eNOS modulates vascular reactivity and outcome of cerebral ischemia in vivo. J. Clin. Invest. 117, 1961–1967.
Dimmeler, S., Fleming, I., Fisslthaler, B., Hermann, C., Busse, R., and Zeiher, A.M. (1999). Activation of nitric oxide synthase in endothelial cells by Akt-dependent phosphorylation. Nature 399, 601–605.
Fulton, D., Gratton, J.P., McCabe, T.J., Fontana, J., Fujio, Y., Walsh, K., Franke, T.F., Papapetropoulos, A., and Sessa, W.C. (1999). Regulation of endothelium-derived nitric oxide production by the protein kinase Akt. Nature 399, 597–601.
Qian, J., and Fulton, D. (2013). Post-translational regulation of endothelial nitric oxide synthase in vascular endothelium. Oxid. Physiol. 4, 347.