title: Thrombin-induced lysosomal exocytosis in human platelets is dependent on secondary activation by ADP and regulated by endothelial-derived substances.
abstract: Exocytosis of lysosomal contents from platelets has been speculated to participate in clearance of thrombi and vessel wall remodelling. The mechanisms that regulate lysosomal exocytosis in platelets are, however, still unclear. The aim of this study was to identify the pathways underlying platelet lysosomal secretion and elucidate how this process is controlled by platelet inhibitors. We found that high concentrations of thrombin induced partial lysosomal exocytosis as assessed by analysis of the activity of released N-acetyl-β-glucosaminidase (NAG) and by identifying the fraction of platelets exposing the lysosomal-associated membrane protein (LAMP)-1 on the cell surface by flow cytometry. Stimulation of thrombin receptors PAR1 or PAR4 with specific peptides was equally effective in inducing LAMP-1 surface expression. Notably, lysosomal exocytosis in response to thrombin was significantly reduced if the secondary activation by ADP was inhibited by the P2Y12 antagonist cangrelor, while inhibition of thromboxane A2 formation by treatment with acetylsalicylic acid was of minor importance in this regard. Moreover, the NO-releasing drug S-nitroso-N-acetyl penicillamine (SNAP) or the cyclic AMP-elevating eicosanoid prostaglandin I2 (PGI2) significantly suppressed lysosomal exocytosis. We conclude that platelet inhibitors that mimic functional endothelium such as PGI2 or NO efficiently counteract lysosomal exocytosis. Furthermore, we suggest that secondary release of ADP and concomitant signaling via PAR1/4- and P2Y12 receptors is important for efficient platelet lysosomal exocytosis by thrombin.
authors.affiliation: a Department of Clinical and Experimental Medicine, Faculty of Health Sciences , Linköping University , Linköping , Sweden .
authors.forename: Anna L
authors.initials: AL
authors.lastname: Södergren
authors.affiliation: a Department of Clinical and Experimental Medicine, Faculty of Health Sciences , Linköping University , Linköping , Sweden .
authors.forename: Ann-Charlotte B
authors.initials: AC
authors.lastname: Svensson Holm
authors.affiliation: a Department of Clinical and Experimental Medicine, Faculty of Health Sciences , Linköping University , Linköping , Sweden .
authors.forename: Sofia
authors.initials: S
authors.lastname: Ramström
authors.affiliation: b Department of Medical and Health Sciences, Faculty of Health Sciences , Linköping University , Linköping , Sweden , and.
authors.forename: Eva G
authors.initials: EG
authors.lastname: Lindström
authors.affiliation: b Department of Medical and Health Sciences, Faculty of Health Sciences , Linköping University , Linköping , Sweden , and.|c Department of Clinical Medicine , School of Health Sciences, Örebro University , Örebro , Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Grenegård
authors.affiliation: a Department of Clinical and Experimental Medicine, Faculty of Health Sciences , Linköping University , Linköping , Sweden .
authors.forename: Karin
authors.initials: K
authors.lastname: Öllinger
mesh_terms: D000118:Acetylglucosaminidase / Q000097:blood; D000244:Adenosine Diphosphate / Q000097:blood* / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D011464:Epoprostenol / Q000097:blood; D005089:Exocytosis / Q000187:drug effects; D006801:Humans; D051907:Lysosomal Membrane Proteins / Q000096:biosynthesis / Q000097:blood; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D058921:Purinergic P2Y Receptor Antagonists / Q000494:pharmacology; D044463:Receptor, PAR-1 / Q000097:blood; D013917:Thrombin / Q000494:pharmacology; D052118:Lysosomal-Associated Membrane Protein 1
chemical_list: D000118:Acetylglucosaminidase; D000244:Adenosine Diphosphate; D000249:Adenosine Monophosphate; D011464:Epoprostenol; D051907:Lysosomal Membrane Proteins; D058921:Purinergic P2Y Receptor Antagonists; D044463:Receptor, PAR-1; D013917:Thrombin; C489116:LAMP1 protein, human; D052118:Lysosomal-Associated Membrane Protein 1; C117446:cangrelor
keywords: ADP receptors; endothelium; exocytosis; lysosome; platelet physiology; protease activated receptors (PAR); thrombin