title: Role of the PAR4 thrombin receptor in stabilizing platelet-platelet aggregates as revealed by a patient with Hermansky-Pudlak syndrome.
abstract: Individuals with Hermansky-Pudlak Syndrome (HPS) lack platelet dense granules and have no ADP-autocrine response. Despite these platelet deficiencies, HPS patients exhibit a surprisingly mild bleeding phenotype. We hypothesize that activation of the PAR4 thrombin receptor compensates for the lack of an ADP-autocrine response by the P2Y12 ADP receptor in individuals with HPS. Here, we determine that PAR4 activation by thrombin occurs well after ADP release from dense granules in normal individuals. However, the signal from PAR4 stabilizes platelet-platelet aggregate formation in the absence of P2Y12 activation by ADP. Thus, the strong signal emanating from PAR4 during platelet aggregation would provide an explanation for the mild bleeding diathesis of HPS.
authors: Division of Hematology/Oncology, Molecular Cardiology Research Institute, New England Medical Center, Boston, Massachusetts 02111, USA.
authors: Lidija
authors: L
authors: Covic
authors: Christopher
authors: C
authors: Singh
authors: Hedy
authors: H
authors: Smith
authors: Athan
authors: A
authors: Kuliopulos
mesh_terms: D000249:Adenosine Monophosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000328:Adult; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D005260:Female; D022861:Hermanski-Pudlak Syndrome / Q000097:blood* / Q000235:genetics; D006801:Humans; D008565:Membrane Proteins; D008954:Models, Biological; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D011647:Puerto Rico / Q000453:epidemiology; D058919:Purinergic P2 Receptor Antagonists; D044463:Receptor, PAR-1; D018048:Receptors, Purinergic P2 / Q000502:physiology; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D018179:Receptors, Thrombin / Q000502:physiology*; D013917:Thrombin / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D008565:Membrane Proteins; D009842:Oligopeptides; C546382:P2RY1 protein, human; C548576:P2RY12 protein, human; D010446:Peptide Fragments; D058919:Purinergic P2 Receptor Antagonists; D044463:Receptor, PAR-1; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D018179:Receptors, Thrombin; C455901:alanyl-tyrosyl-prolyl-glycyl-lysyl-phenylalanine; C082835:thrombin receptor peptide (42-47); D000249:Adenosine Monophosphate; C117446:cangrelor; D013917:Thrombin; C112908:protease-activated receptor 4