title: Irreversible platelet activation requires protease-activated receptor 1-mediated signaling to phosphatidylinositol phosphates.
abstract: Thrombin induces platelet activation through an early, reversible stage of platelet aggregation, which is followed by a later, irreversible stage of platelet aggregation. Without intervention, events leading to pathological platelet activation can result in vessel occlusion, acute coronary syndrome, and stroke. Therefore, a better understanding of events leading to platelet-mediated clot formation may provide insight into new therapeutic targets. Once activated, protease activated receptors (PARs) are essential in regulating events leading to platelet aggregation. We have determined a signaling cascade through PAR1, which involves phosphatidylinositol (PI) kinases, phosphatidylinositol bisphosphate (PIP(2)), and Rap1 activation (independent of P2Y12) in the formation of a stable platelet aggregate. The putative phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002 was found to reduce basal and PAR-stimulated PIP(2) levels by mass spectrometry and to inhibit PAR1-mediated stable platelet aggregation. Rap1 activation in platelets (during time points corresponding to the late, irreversible phase of aggregation) was found to require the PI signaling pathway. Perturbation of PI3K signaling by isoform-selective inhibitors had differential effects on Rap1 activation through PAR1 and PAR4. Hence, it is possible to disrupt lipid signaling pathways involved in stable clot formation without inhibiting early clot formation, offering a new potential target for antiplatelet therapy.
authors.affiliation: Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232-6600, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Holinstat
authors.forename: Anita M
authors.initials: AM
authors.lastname: Preininger
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Milne
authors.forename: W James
authors.initials: WJ
authors.lastname: Hudson
authors.forename: H Alex
authors.initials: HA
authors.lastname: Brown
authors.forename: Heidi E
authors.initials: HE
authors.lastname: Hamm
mesh_terms: D001792:Blood Platelets / Q000187:drug effects*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D044463:Receptor, PAR-1 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D018129:Phosphatidylinositol Phosphates; D044463:Receptor, PAR-1; D019869:Phosphatidylinositol 3-Kinases; D020827:rap1 GTP-Binding Proteins