title: Modulation and pre-amplification of PAR1 signaling by ADP acting via the P2Y12 receptor during platelet subpopulation formation.
abstract: BACKGROUND
  Two major soluble blood platelet activators are thrombin and ADP. Of these two, only thrombin can induce mitochondrial collapse and programmed cell death leading to phosphatidylserine (PS) exposure required for blood clotting reactions acceleration. Thrombin can also greatly potentiate collagen-induced PS exposure. However, ADP acting through the P2Y12 receptor was shown to increase the PS-exposing (PS+) platelets fraction produced by thrombin or thrombin-plus-collagen via an unknown mechanism.
  
  
  METHODS
  We developed a comprehensive multicompartmental computational model of platelet PAR1-and-P2Y12 calcium signal transduction that included cytoplasmic signaling, dense tubular system and mitochondria. To test model predictions, flow cytometry experiments with washed, annexin V-labeled platelets were performed.
  
  
  RESULTS
  Stimulation of thrombin receptor PAR1 in the model induced cytoplasmic calcium oscillations, calcium uptake by mitochondria, opening of the permeability transition pore and collapse of the mitochondrial membrane potential. ADP stimulation of P2Y12 led to cAMP decrease that, in turn, caused changes in phospholipase C phosphorylation by protein kinase A, increase in cytoplasmic calcium level and, consequently, PS+ platelet formation. ADP addition before stimulation of PAR1 produced much greater increase of the PS+ fraction because cAMP concentration had time to go down prior to calcium oscillations; this prediction was also tested and confirmed experimentally.
  
  
  CONCLUSIONS
  These results suggest a mechanism of ADP-dependent PS exposure regulation and show a likely mode of action that could be important for the PS exposure regulation in thrombi, where ADP is released before thrombin formation.
authors.affiliation: Faculty of Physics, Lomonosov Moscow State University, 1-2 Leninskie Gory, GSP-1, Moscow 119991, Rusia. Electronic address: shakhidzhanov.s@yandex.ru.
authors.forename: S S
authors.initials: SS
authors.lastname: Shakhidzhanov
authors.affiliation: Faculty of Physics, Lomonosov Moscow State University, 1-2 Leninskie Gory, GSP-1, Moscow 119991, Rusia. Electronic address: msuff@mail.ru.
authors.forename: V I
authors.initials: VI
authors.lastname: Shaturny
authors.affiliation: Faculty of Physics, Lomonosov Moscow State University, 1-2 Leninskie Gory, GSP-1, Moscow 119991, Rusia; Federal Research and Clinical Center of Pediatric Hematology, Oncology and Immunology, 1 Samory Mashela St, Moscow 117198, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, 4 Kosygina St, Moscow 119991, Russia; Faculty of Biological and Medical Physics, Moscow Institute of Physics and Technology, 9 Institutskii per., Dolgoprudnyi, 141700, Russia. Electronic address: mapanteleev@yandex.ru.
authors.forename: M A
authors.initials: MA
authors.lastname: Panteleev
authors.affiliation: Faculty of Physics, Lomonosov Moscow State University, 1-2 Leninskie Gory, GSP-1, Moscow 119991, Rusia; Federal Research and Clinical Center of Pediatric Hematology, Oncology and Immunology, 1 Samory Mashela St, Moscow 117198, Russia; Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, 4 Kosygina St, Moscow 119991, Russia. Electronic address: agolomy@gmail.com.
authors.forename: A N
authors.initials: AN
authors.lastname: Sveshnikova
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D001792:Blood Platelets / Q000166:cytology*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D044463:Receptor, PAR-1 / Q000378:metabolism*; D058925:Receptors, Purinergic P2Y12 / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D044463:Receptor, PAR-1; D058925:Receptors, Purinergic P2Y12; D000244:Adenosine Diphosphate; D002118:Calcium
keywords: Adenylyl cyclase; Calcium signaling; Cyclic AMP; Differential equations; Mitochondria; Phospholipase C