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Relationship: 988


A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Decrease, AKT/eNOS activity leads to Depletion, Nitric Oxide

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes. Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Peptide Oxidation Leading to Hypertension adjacent High High Frazer Lowe (send email) Not under active development Under Development

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER.  More help
Term Scientific Term Evidence Link
Homo sapiens Homo sapiens High NCBI
Bos taurus Bos taurus High NCBI
Rattus norvegicus Rattus norvegicus High NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help
Sex Evidence
Unspecific High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER.  More help
Term Evidence
All life stages High

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

AKT can phosphorylate eNOS which leads to increased eNOS enzymatic activity and subsequent NO production (Dimmeler et al., 1999; Fulton et al., 1999). Inhibition of AKT attenuates eNOS phosphorylation and its activity, resulting in decreased NO bioavailability and endothelial dysfunction.

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER.  For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings.  Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help
Biological Plausibility
Addresses the biological rationale for a connection between KEupstream and KEdownstream.  This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured.   More help

Two studies demonstrated that AKT can directly phosphorylate eNOS at Ser1177/Ser1179, leading to increased eNOS enzymatic activity and subsequent NO production in COS cells (Dimmeler et al., 1999; Fulton et al., 1999). Expressing active AKT in bovine microvascular endothelial cells also induced NO release (Fulton et al., 1999). Inhibition of Akt or a mutation of eNOS at AKT-sensitive sites attenuated eNOS phosphorylation and its activity, resulting in decreased NO bioavailability and endothelial dysfunction (Dimmeler et al., 1999; Fulton et al., 1999; Uruno et al., 2005). Treatment of BAECs with SIN-1 resulted in a reduction in both eNOS activity and NO production (Das et al., 2014). Cigarette smoke extract (CSE) treatment inhibited AKT and eNOS and NO release in VEGF-stimulated HUVECs (Michaud et al., 2006), and methylglyoxal and high glucose reduced eNOS bradykinin-stimulated eNOS activity and NO production in HUVECs (Dhar et al., 2010). Overall, the biological plausibility for decreased AKT/eNOS activity leading to NO depletion is strong.

Uncertainties and Inconsistencies
Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

In the context of this AOP, decreased activity of AKT is likely due to proteasomal degradation following exposure to a (oxidative) stressor (Abdehghany et al. 2017).  However, decreased eNOS activity could be due to multiple causes, highlighted in this AOP.  Firstly, if AKT expression levels are reduced, it follows that eNOS phosphorylation will be reduced.  Secondly, similar to AKT, eNOS itself has been shown to be susceptible to proteasomal degradation (Abdehghany et al. 2017).  Thirdly, depletion of BH4 and/or S-glutathionylation has been shown to uncouple eNOS, leading to reduced NO levels and increased superoxide levels.  The relative contribution of each of these eNOS perturbation routes to NO depletion is currently unknown.

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references.  More help
Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help
Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help
Known Feedforward/Feedback loops influencing this KER
Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

The relationship between decreased AKT/eNOS activity and NO depletion is supported by studies performed in humans, cows, and rats.


List of the literature that was cited for this KER description. More help

AbdelGhany, T., Ismail, R., Elmahdy, M., Mansoor F, Zweier J, Lowe, F., and Zweier, JL. (2017). Cigarette Smoke Constituents Cause Endothelial Nitric Oxide Synthase Dysfunction and Uncoupling due to Depletion of Tetrahydrobiopterin with Degradation of GTP Cyclohydrolase.  Nitric Oxide (Under review).

Choi, Y.-J., Yoon, Y., Lee, K.-Y., Hien, T.T., Kang, K.W., Kim, K.-C., Lee, J., Lee, M.-Y., Lee, S.M., Kang, D.-H., et al. (2014). Uric acid induces endothelial dysfunction by vascular insulin resistance associated with the impairment of nitric oxide synthesis. FASEB J. 28, 3197–3204.

Choi, Y.-J., Yoon, Y., Lee, K.-Y., Kang, Y.-P., Lim, D.K., Kwon, S.W., Kang, K.-W., Lee, S.-M., and Lee, B.-H. (2015). Orotic Acid Induces Hypertension Associated with Impaired Endothelial Nitric Oxide Synthesis. Toxicol. Sci. 144, 307–317.

Das, A., Gopalakrishnan, B., Druhan, L.J., Wang, T.-Y., De Pascali, F., Rockenbauer, A., Racoma, I., Varadharaj, S., Zweier, J.L., Cardounel, A.J., et al. (2014). Reversal of SIN-1-induced eNOS dysfunction by the spin trap, DMPO, in bovine aortic endothelial cells via eNOS phosphorylation. Br. J. Pharmacol. 171, 2321–2334.

Dhar, A., Dhar, I., Desai, K.M., and Wu, L. (2010). Methylglyoxal scavengers attenuate endothelial dysfunction induced by methylglyoxal and high concentrations of glucose. Br. J. Pharmacol. 161, 1843–1856.

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.

Dumitrescu, C., Biondi, R., Xia, Y., Cardounel, A.J., Druhan, L.J., Ambrosio, G., and Zweier, J.L. (2007). Myocardial ischemia results in tetrahydrobiopterin (BH4) oxidation with impaired endothelial function ameliorated by BH4. Proc. Natl. Acad. Sci. U. S. A. 104, 15081–15086.

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.

Michaud, S.E., Dussault, S., Groleau, J., Haddad, P., and Rivard, A. (2006). Cigarette smoke exposure impairs VEGF-induced endothelial cell migration: role of NO and reactive oxygen species. J. Mol. Cell. Cardiol. 41, 275–284.

Song, P., Wu, Y., Xu, J., Xie, Z., Dong, Y., Zhang, M., and Zou, M.-H. (2007). Reactive nitrogen species induced by hyperglycemia suppresses Akt signaling and triggers apoptosis by upregulating phosphatase PTEN (phosphatase and tensin homologue deleted on chromosome 10) in an LKB1-dependent manner. Circulation 116, 1585–1595.

Song, P., Xie, Z., Wu, Y., Xu, J., Dong, Y., and Zou, M.-H. (2008). Protein kinase Czeta-dependent LKB1 serine 428 phosphorylation increases LKB1 nucleus export and apoptosis in endothelial cells. J. Biol. Chem. 283, 12446–12455.

Uruno, A., Sugawara, A., Kanatsuka, H., Kagechika, H., Saito, A., Sato, K., Kudo, M., Takeuchi, K., and Ito, S. (2005). Upregulation of nitric oxide production in vascular endothelial cells by all-trans retinoic acid through the phosphoinositide 3-kinase/Akt pathway. Circulation 112, 727–736.

Zou, M.-H., Hou, X.-Y., Shi, C.-M., Nagata, D., Walsh, K., and Cohen, R.A. (2002). Modulation by peroxynitrite of Akt- and AMP-activated kinase-dependent Ser1179 phosphorylation of endothelial nitric oxide synthase. J. Biol. Chem. 277, 32552–32557.