Dexamethasone, tetrahydrobiopterin and uncoupling of endothelial nitric oxide synthase  

作　　者：Silke Tobias Alice Habermeier Daniel Siuda Gisela Reifenberg Ning Xia Ellen I Closs Ulrich Forstermann Huige Li 

机构地区：[1]Department of Pharmacology, Johannes Gutenberg University Medical Center, Mainz, Germany

出　　处：《Journal of Geriatric Cardiology》2015年第5期528-539,共12页老年心脏病学杂志（英文版）

摘　　要：Objective To find out whether dexamethasone induces an uncoupling of the endothelial nitric oxide synthase （eNOS）. Methods ＆ Results A 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 cyclobydrolase 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. Conclusions Although 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.

关 键 词：DEXAMETHASONE Endothelial cells eNOS uncoupling Nitric oxide synthase Reactive oxygen species TETRAHYDROBIOPTERIN 

分 类 号：Q55[生物学—生物化学] TQ460.31[化学工程—制药化工]