title: Inhibition of proteasome-mediated glucocorticoid receptor degradation restores nitric oxide bioavailability in myocardial endothelial cells in vitro.
abstract: BACKGROUND
  Glucocorticoids (GCs), including the synthetic GC derivate dexamethasone, are widely used as immunomodulators. One of the numerous side effects of dexamethasone therapy is hypertension arising from reduced release of the endothelium-derived vasodilator nitric oxide (NO).
  
  
  RESULTS
  Herein, we described the role of dexamethasone and its glucocorticoid receptor (GR) in the regulation of NO synthesis in vitro using the mouse myocardial microvascular endothelial cell line, MyEND. GC treatment caused a firm decrease of extracellular NO levels, whereas the expression of endothelial NO synthase (eNOS) was not affected. However, GC application induced an impairment of tetrahydrobiopterin (BH4 ) concentrations as well as GTP cyclohydrolase-1 (GTPCH-1) expression, both essential factors for NO production upstream of eNOS. Moreover, dexamethasone stimulation resulted in a substantially decreased GR gene and protein expression in MyEND cells. Importantly, inhibition of proteasome-mediated proteolysis of the GR or overexpression of an ubiquitination-defective GR construct improved the bioavailability of BH4 and strengthened GTPCH-1 expression and eNOS activity.
  
  
  CONCLUSIONS
  Summarising our results, we propose a new mechanism involved in the regulation of NO signalling by GCs in myocardial endothelial cells. We suggest that a sufficient GR protein expression plays a crucial role for the management of GC-induced harmful adverse effects, including deregulations of vasorelaxation arising from disturbed NO biosynthesis.
authors.affiliation: University of Würzburg, Department of Anaesthesia and Critical Care, Würzburg, 97080, Germany.
authors.forename: Kinga G
authors.initials: KG
authors.lastname: Blecharz
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Burek
authors.forename: Johann
authors.initials: J
authors.lastname: Bauersachs
authors.forename: Thomas
authors.initials: T
authors.lastname: Thum
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Tsikas
authors.forename: Julian
authors.initials: J
authors.lastname: Widder
authors.forename: Norbert
authors.initials: N
authors.lastname: Roewer
authors.forename: Carola Y
authors.initials: CY
authors.lastname: Förster
mesh_terms: D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000378:metabolism; D002460:Cell Line; D003331:Coronary Vessels / Q000378:metabolism; D003907:Dexamethasone / Q000378:metabolism / Q000494:pharmacology*; D042783:Endothelial Cells / Q000378:metabolism*; D006136:GTP Cyclohydrolase / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology; D051379:Mice; D052250:Nitric Oxide Synthase Type III / Q000096:biosynthesis*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*
chemical_list: D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; D001708:Biopterins; D003907:Dexamethasone; D052250:Nitric Oxide Synthase Type III; D046988:Proteasome Endopeptidase Complex; D006136:GTP Cyclohydrolase; C003402:sapropterin
keywords: Glucocorticoid receptor; Glucocorticoids; Microvascular endothelial cells; Nitric oxide; Proteasome