Inhibitory signaling of 17β-estradiol in platelet activation: the pivotal role of cyclic AMP-mediated nitric oxide synthase activation.
Arterial thromboses are mostly composed of platelets adherent to ruptured endothelial surfaces. Platelets are anucleated cells; therefore, they represent an excellent and unique model to selectively investigate the signaling pathways mediating the nongenomic effects of estrogen. The aim of this study was to examine the signal transduction pathways of 17β-estradiol in preventing platelet activation. In this study, 17β-estradiol (5~10 μM) exhibited more-potent activity of inhibiting platelet aggregation stimulated by collagen than other agonists (i.e., thrombin). 17β-Estradiol-inhibited collagen-stimulated platelet activation accompanied by [Ca(2+)]i mobilization, thromboxane A₂ (TxA₂) formation, and phospholipase C (PLC)γ2, protein kinase C (PKC), and p38 mitogen-activated protein kinase (MAPK) phosphorylation. 17β-Estradiol markedly increased cyclic AMP and cyclic GMP levels, nitric oxide (NO) release, vasodilator-stimulated phosphoprotein (VASP) phosphorylation, and endothelial nitric oxide synthase (eNOS) expression. SQ 22536, an inhibitor of adenylate cyclase, markedly reversed the 17β-estradiol-mediated effects (i.e., platelet aggregation, and PLCγ2, VASP, and eNOS phosphorylation). Furthermore, ICI 182,780, a pure estrogen receptor antagonist, also reversed the 17β-estradiol-mediated effects on platelet aggregation and eNOS activation. In conclusion, the most important findings of this study demonstrate for the first time that the inhibitory effect of 17β-estradiol in platelet activation involves activation of the cyclic AMP-eNOS/NO-cyclic GMP pathway, resulting in inhibition of PLCγ2 and p38 MAPK activation, which may lower the incidence of cardiovascular events in postmenopausal women.
Wu
Gong-Jhe
GJ
Department of Anesthesiology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan.
Lee
Jie-Jen
JJ
Chou
Duen-Suey
DS
Jayakumar
Thanasekaran
T
Hsiao
George
G
Chen
Wei-Fan
WF
Sheu
Joen-Rong
JR
D000067956:Adenylyl Cyclase Inhibitors; D000328:Adult; D002318:Cardiovascular Diseases / Q000517:prevention & control; D003094:Collagen / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D004965:Estrogen Antagonists / Q000494:pharmacology; D005260:Female; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D009994:Osmolar Concentration; D015539:Platelet Activation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects*; D055815:Young Adult
D000067956:Adenylyl Cyclase Inhibitors; D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D010975:Platelet Aggregation Inhibitors; D009569:Nitric Oxide; D004958:Estradiol; D003094:Collagen; D000242:Cyclic AMP; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III