title: Regulators of platelet cAMP levels: clinical and therapeutic implications.
abstract: Platelets are indispensable for primary haemostasis, but their function needs to be tightly regulated to prevent excessive platelet activity, possibly leading to atherothrombotic events. An important mediator of the platelet activity is cyclic AMP (cAMP), which inhibits platelet aggregation. Intracellular cAMP levels are regulated via the Gs and Gi alpha subunits of heterotrimeric G proteins, which couple to adenylyl cyclase to respectively stimulate or inhibit cAMP production. Binding of a ligand to its G protein-coupled seven-transmembrane receptor activates these G proteins. In this review, we discuss a Gs-coupled receptor on platelets, VPAC1, and 2 important Gi-coupled receptors, the ADP receptor P2Y(12) and the prostaglandin E(2) receptor EP3. The regulation of platelet cAMP levels at the level of the receptors themselves or the G proteins coupled to them is analyzed. Alterations in Gsα and Giα function are associated with altered platelet reactivity. An increase in Gs function, or alternatively a defective Gi signaling, can be a risk factor for bleeding, while a loss of Gs function can result in a prothrombotic state. Regulator of G protein signaling (RGS) proteins accelerate the rate of inactivation of G protein-mediated signaling. One of the RGS proteins, RGS2, inhibits Gs signaling by interacting directly with adenylyl cyclase. The thienopyridine class of antiplatelet agents is based on cAMP-mediated regulation of platelet function through modification of the P2Y(12) receptor. Clopidogrel and some other novel cAMP regulators are discussed. Secondly, we review the use of prostacyclin derivatives to treat pulmonary arterial hypertension.
authors.affiliation: Center for Molecular and Vascular Biology, University of Leuven, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Noé
authors.forename: K
authors.initials: K
authors.lastname: Peeters
authors.forename: B
authors.initials: B
authors.lastname: Izzi
authors.forename: C
authors.initials: C
authors.lastname: Van Geet
authors.forename: K
authors.initials: K
authors.lastname: Freson
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism*; D000077144:Clopidogrel; D000242:Cyclic AMP / Q000097:blood / Q000378:metabolism*; D065627:Familial Primary Pulmonary Hypertension; D006801:Humans; D006976:Hypertension, Pulmonary / Q000188:drug therapy; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use*; D058921:Purinergic P2Y Receptor Antagonists / Q000737:chemistry / Q000494:pharmacology* / Q000627:therapeutic use*; D058925:Receptors, Purinergic P2Y12 / Q000378:metabolism; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013988:Ticlopidine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology
chemical_list: C548576:P2RY12 protein, human; D010975:Platelet Aggregation Inhibitors; D058921:Purinergic P2Y Receptor Antagonists; D058925:Receptors, Purinergic P2Y12; D051238:Receptors, Vasoactive Intestinal Polypeptide, Type I; D000077144:Clopidogrel; D000242:Cyclic AMP; D013988:Ticlopidine