title: The effects of an inhibitor of diglyceride lipase on collagen-induced platelet activation.
abstract: Human platelet activation by collagen occurs in a dose-dependent manner. High concentrations of collagen bind to a pair of receptors, the α2β1 integrin and glycoprotein (GP)VI/Fc-receptor γ-chain (FcRγ), which stimulate a cascade of events including Syk, LAT, Btk, Gads, and phospholipase Cγ2, leading to calcium release and protein kinase C (PKC) activation. Calcium and PKC are responsible for a range of platelet responses including exocytosis and aggregation, as well as the cytosolic phospholipase A2 (cPLA2)-mediated release of arachidonic acid, which is converted to thromboxane (Tx)A2. In contrast, low concentrations of collagen are acutely aspirin-sensitive, and calcium release and aggregation are TxA2-dependent. Under these conditions, cPLA2 is not involved and it has been suggested that phospholipase C generates 1,2-diacylglycerol (DG) from which arachidonic acid is liberated by diglyceride lipase (DGL). Here a novel DGL blocker (OMDM-188) inhibited collagen-, but not arachidonic acid-induced aggregation and TxA2 synthesis. Furthermore, OMDM-188 inhibited collagen-induced arachidonic acid release. Finally OMDM-188 inhibited collagen-induced p38(MAPK) phosphorylation, but not extracellular signal-regulated kinase (ERK) phosphorylation, with no effect on the phosphorylation of either enzyme in response to arachidonic acid. Taken together, these data suggest a role for a pathway involving phospholipase C liberating DG from membrane phospholipids in response to minimally activating concentrations of collagen. The DG serves as a substrate for DGL, potentially under the regulations of p38(MAPK), to release arachidonic acid, which is subsequently converted to TxA2, which mediates the final platelet response.
authors.affiliation: Department of Oral Biology (E.C.G.J., A.M.) and Pharmacology and Therapeutics (A.M.), University of Manitoba, Winnipeg, Manitoba, Canada; and Dipartimento di Chimica e Tecnologie del Farmaco Università di Roma 'Sapienza', Roma, Italy (G.O.).
authors.forename: Elke C G
authors.initials: EC
authors.lastname: Jackson
authors.forename: Giorgio
authors.initials: G
authors.lastname: Ortar
authors.forename: Archie
authors.initials: A
authors.lastname: McNicol
mesh_terms: D016718:Arachidonic Acid / Q000378:metabolism; D001241:Aspirin / Q000494:pharmacology; D015153:Blotting, Western; D003094:Collagen / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007532:Isoleucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D007783:Lactones / Q000494:pharmacology*; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D013931:Thromboxanes / Q000096:biosynthesis; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D007783:Lactones; C585831:N-formyl-isoleucine-1-((3-hexyl-4-oxo-2-oxetanyl)methyl)dodecyl ester; D013931:Thromboxanes; D007532:Isoleucine; D016718:Arachidonic Acid; D003094:Collagen; D048051:p38 Mitogen-Activated Protein Kinases; D008071:Lipoprotein Lipase; D001241:Aspirin