Control of platelet activation by cyclic AMP turnover and cyclic nucleotide phosphodiesterase type-3.
Prostaglandin-induced cAMP elevation restrains key signaling pathways in platelet activation including Ca(2+) mobilization and integrin alphaIIbbeta3 affinity regulation. We investigated how cAMP turnover by cyclic nucleotide phosphodiesterases (PDEs) regulates platelet activation. In washed human platelets, inhibition of all PDEs and also specific inhibition of PDE3 but not of PDE5 suppressed thrombin-induced Ca(2+) responses. The effect of general PDE or PDE3 inhibition was accompanied by an increase in cAMP, and potentiated by Gs stimulation with prostaglandin E(1). In platelet-rich plasma, general or PDE3 inhibition blocked platelet aggregation, integrin activation, secretion and thrombin generation. In contrast, inhibition of PDE5 increased the cGMP level, but without significant influence on aggregation, alphaIIbbeta3 activation, secretion or procoagulant activity. Nitroprusside (nitric oxide) potentiated the effect of PDE5 inhibition in elevating cGMP. Nitroprusside inhibited platelet responses, but this was accompanied by elevation of cAMP. Together, these results indicate that cAMP is persistently formed in platelets, independently of agonist-induced Gs stimulation. PDE3 thus functions to keep cAMP at a low equilibrium level and reduce the cAMP-regulated threshold for platelet activation. This crucial role of PDE3, but not of PDE5, extends to all major processes in thrombus formation: assembly of platelets into aggregates, secretion of autocrine products, and procoagulant activity.
Feijge
Marion A H
MA
Department of Biochemistry, University of Maastricht, P.O. Box 616, Maastricht, MD 6200, The Netherlands. jwm.heemskerk@bioch.unimaas.nl
Ansink
Karin
K
Vanschoonbeek
Kristof
K
Heemskerk
Johan W M
JW
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000704:Analysis of Variance; D001777:Blood Coagulation / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D006801:Humans; D066298:In Vitro Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015539:Platelet Activation; D010974:Platelet Aggregation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism
D010726:Phosphodiesterase Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517381:PDE5A protein, human; D013917:Thrombin; D006152:Cyclic GMP; D002118:Calcium