Dexamethasone, tetrahydrobiopterin and uncoupling of endothelial nitric oxide synthase.

Content Provider	Europe PMC
Author	Tobias, Silke Habermeier, Alice Siuda, Daniel Reifenberg, Gisela Xia, Ning Closs, Ellen I Förstermann, Ulrich Li, Huige
Copyright Year	2015
Abstract	ObjectiveTo find out whether dexamethasone induces an uncoupling of the endothelial nitric oxide synthase (eNOS).Methods & ResultsA major cause of eNOS uncoupling is a deficiency of its cofactor tetrahydrobiopterin (BH4). Treatment of human EA.hy 926 endothelial cells with dexamethasone decreased mRNA and protein expression of both BH4-synthesizing enzymes: GTP cyclohydrolase I and dihydrofolate reductase. Consistently, a concentration- and time-dependent reduction of BH4, dihydrobiopterin (BH2) as well as BH4: BH2 ratio was observed in dexamethasone-treated cells. Surprisingly, no evidence for eNOS uncoupling was found. We then analyzed the expression and phosphorylation of the eNOS enzyme. Dexamethasone treatment led to a down-regulation of eNOS protein and a reduction of eNOS phosphorylation at serine 1177. A reduction of eNOS expression may lead to a relatively normal BH4: eNOS molar ratio in dexamethasone-treated cells. Because the BH4-eNOS stoichiometry rather than the absolute BH4 amount is the key determinant of eNOS functionality (i.e., coupled or uncoupled), the down-regulation of eNOS may represent an explanation for the absence of eNOS uncoupling. Phosphorylation of eNOS at serine 1177 is needed for both the NO-producing activity of the coupled eNOS and the superoxide-producing activity of the uncoupled eNOS. Thus, a reduction of serine 1177 phosphorylation may render a potentially uncoupled eNOS hardly detectable.ConclusionsAlthough dexamethasone reduces BH4 levels in endothelial cells, eNOS uncoupling is not evident. The reduction of NO production in dexamethasone-treated endothelial cells is mainly attributable to reduced eNOS expression and decreased eNOS phosphorylation at serine 1177.
ISSN	16715411
Journal	Journal of Geriatric Cardiology : JGC
Volume Number	12
PubMed Central reference number	PMC4605949
Issue Number	5
PubMed reference number	26512245
DOI	10.11909/j.issn.1671-5411.2015.05.013
Language	English
Publisher	Science Press
Publisher Date	2015-09-01
Access Restriction	Open
Rights License	This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License, which allows readers to alter, transform, or build upon the article and then distribute the resulting work under the same or similar license to this one. The work must be attributed back to the original author and commercial use is not permitted without specific permission. Institute of Geriatric Cardiology
Subject Keyword	Dexamethasone Endothelial cells eNOS uncoupling Nitric oxide synthase Reactive oxygen species Tetrahydrobiopterin
Content Type	Text
Resource Type	Article
Subject	Geriatrics and Gerontology Cardiology and Cardiovascular Medicine