Rapid nontranscriptional activation of endothelial nitric oxide synthase mediates increased cerebral blood flow and stroke protection by corticosteroids.
Many cellular responses to corticosteroids involve the transcriptional modulation of target genes by the glucocorticoid receptor (GR). A rapid, non-nuclear effect of GR was found to mediate neuroprotection. High-dose corticosteroids (20 mg/kg intraperitoneally), given within 2 hours of transient cerebral ischemia, acutely increased endothelial nitric oxide synthase (eNOS) activity, augmented regional cerebral blood flow (CBF) by 40% to 50%, and reduced cerebral infarct size by 32%. These neuroprotective effects of corticosteroids were abolished by the GR antagonist RU486 and by inhibition of phosphatidylinositol 3-kinase (PI3K), and were absent in eNOS(-/-) mice. To determine the mechanism by which GR activated eNOS, we measured the effect of corticosteroids on PI3K and the protein kinase Akt. In a ligand-dependent manner, GR activated PI3K and Akt in vitro and in vivo caused NO-dependent vasodilation, which was blocked by cotreatment with RU486 or the PI3K inhibitor LY294002 but not by transcriptional inhibitors. Indeed, a mutant GR, which cannot dimerize and bind to DNA, still activated PI3K and Akt in response to corticosteroids. These findings indicate that non-nuclear GR rapidly activates eNOS through the PI3K/Akt pathway and suggest that this mechanism mediates the acute neuroprotective effects of corticosteroids through augmentation of CBF.
Limbourg
Florian P
FP
Cardiovascular Division, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
Huang
Zhihong
Z
Plumier
Jean-Christophe
JC
Simoncini
Tommaso
T
Fujioka
Masayuki
M
Tuckermann
Jan
J
Schütz
Günther
G
Moskowitz
Michael A
MA
Liao
James K
JK
D000305:Adrenal Cortex Hormones / Q000627:therapeutic use*; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002417:Cattle; D002478:Cells, Cultured; D002544:Cerebral Infarction / Q000517:prevention & control*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002522:Chlorocebus aethiops; D017931:DNA Primers; D004730:Endothelium, Vascular / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D006801:Humans; D002546:Ischemic Attack, Transient / Q000201:enzymology / Q000503:physiopathology; D051379:Mice; D008815:Mice, Inbred Strains; D018696:Neuroprotective Agents; D019001:Nitric Oxide Synthase / Q000235:genetics*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011965:Receptors, Glucocorticoid / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D020521:Stroke / Q000517:prevention & control*; D014162:Transfection
D000305:Adrenal Cortex Hormones; D017931:DNA Primers; D018696:Neuroprotective Agents; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D019869:Phosphatidylinositol 3-Kinases; D011965:Receptors, Glucocorticoid; D011994:Recombinant Proteins; C496314:NOS3 protein, human; C496315:Nos3 protein, mouse