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Platelet activation and adhesion resulting in thrombus growth is essential for normal hemostasis, but can lead to irreversible, life-threatening vessel occlusion. In the current study, the contribution of platelet integrins, activation receptors and the contact system of blood coagulation in such pathological conditions was investigated in mice. / Plättchenaktivierung, -adhäsion und nachfolgende Thrombusbildung ist ein für die Hämostase essentieller Prozess, der jedoch zu irreversiblem lebensbedrohlichen Gefäßverschluss führen kann. In der vorliegenden Arbeit wurde die Rolle von Thrombozyten-Integrinen, aktivierenden Rezeptoren, sowie dem Kontaktsystem der Koagulation unter pathologischen Bedingungen im Maussystem untersucht.

by Chu, Pui-ya. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 115-126. / ACKNOWLEDGEMENT / LIST OF ABBREVIATIONS / ABSTRACT --- p.1 / Chapter CHAPTER 1 --- INTRODUCTION / Chapter 1.1 --- PLATELET-ACTIVATING FACTOR (PAF) --- p.4 / Chapter 1.1.1 --- Metabolism of PAF --- p.4 / Chapter 1.1.1.1 --- Biosynthesis of PAF --- p.4 / Chapter 1.1.1.2 --- Degradation of PAF --- p.9 / Chapter 1.1.2 --- Systemic effects of PAF --- p.12 / Chapter 1.1.3 --- Structure - activity relationship of PAF --- p.16 / Chapter 1.2 --- PAF RECEPTORS --- p.19 / Chapter 1.2.1 --- PAF receptor on platelets --- p.19 / Chapter 1.2.2 --- PAF receptor on leukocytes --- p.20 / Chapter 1.2.3 --- PAF receptor on macrophages --- p.20 / Chapter 1.2.4 --- Antagonists of PAF --- p.20 / Chapter 1.2.4.1 --- Nonspecific inhibitors of PAF --- p.21 / Chapter 1.2.4.2 --- Specific antagonists of PAF --- p.21 / Chapter 1.3 --- SECOND MESSENGER SYSTEMS OF PAF --- p.22 / Chapter 1.3.1 --- Adenylate cyclase - cyclic adenosine mono- phosphate system --- p.26 / Chapter 1.3.2 --- Phospholipase C - phosphatidylinositol system --- p.28 / Chapter 1.3.3 --- Intracellular calcium --- p.29 / Chapter 1.3.4 --- The role of prostaglandins and leukotrienes --- p.30 / Chapter 1.3.5 --- Protein kinase C --- p.30 / Chapter 1.3.5.1 --- Dual action of PKC --- p.31 / Chapter 1.3.5.2 --- Down regulation of PKC --- p.33 / Chapter 1.4 --- THE FUNCTION OF MACROPHAGES --- p.33 / Chapter 1.4.1 --- Phagocytosis --- p.34 / Chapter 1.4.2 --- Antigen presentation --- p.34 / Chapter 1.4.3 --- Release of cytokines --- p.34 / Chapter 1.4.4 --- Respiratory burst --- p.35 / Chapter CHAPTER 2 --- METHODS / Chapter 2.1 --- PREPARATION OF PERITONEAL MACROPHAGES --- p.37 / Chapter 2.1.1 --- Preparation of reagents --- p.37 / Chapter 2.1.2 --- Preparation of peritoneal macrophages --- p.37 / Chapter 2.2 --- RADIOLIGAND BINDING ASSAY --- p.38 / Chapter 2.2.1 --- Reagents --- p.38 / Chapter 2.2.2 --- [3H]-PAF binding to TG-PEC --- p.39 / Chapter 2.2.2.1 --- Preparation of thioglycollate-elicited peritoneal macrophages --- p.39 / Chapter 2.2.2.2 --- Preparation of working solutions --- p.39 / Chapter 2.2.2.3 --- Assay of [3H]-PAF binding --- p.40 / Chapter 2.2.3 --- [3H]-PAF binding to resident PEC --- p.40 / Chapter 2.2.3.1 --- Preparation of resident peritoneal mcrophages --- p.41 / Chapter 2.2.3.2 --- Preparation of working solutions --- p.41 / Chapter 2.2.3.3 --- Assay of [3H]-PAF binding --- p.41 / Chapter 2.2.4 --- Preparation of drugs --- p.41 / Chapter 2.2.5 --- Data analysis --- p.42 / Chapter 2.3 --- MEASUREMENT OF INOSITOL PHOSPHATES --- p.42 / Chapter 2.3.1 --- Preparation of reagents --- p.42 / Chapter 2.3.2 --- Dowex column preparation --- p.43 / Chapter 2.3.3 --- Cell plating in 24 - well plastic trays --- p.44 / Chapter 2.3.4 --- Determination of total inositol phosphates --- p.44 / Chapter 2.3.5 --- Column separation --- p.45 / Chapter 2.3.6 --- Determination of inositol trisphosphate (IP3) --- p.46 / Chapter 2.4 --- MEASUREMENT OF INOSITOL PHOSPHATES ACCUMULATION AFTER PROLONGED PMA PRETREATMENT --- p.46 / Chapter 2.4.1 --- Preparation of phorbol-12-myristate-13-acetate (PMA) solutions --- p.47 / Chapter 2.4.2 --- Preparation of cells with PMA --- p.47 / Chapter 2.5 --- DETERMINATION OF SUPEROXIDE ANION PRODUCTION --- p.47 / Chapter 2.5.1 --- Preparation of drugs --- p.47 / Chapter 2.5.2 --- Assay of superoxide anion production --- p.48 / Chapter 2.5.3 --- Data analysis --- p.48 / Chapter 2.6 --- STATISTICAL METHOD --- p.48 / Chapter CHAPTER 3 --- RESULTS / Chapter 3.1 --- [3H]-PAF BINDING TO TG-PEC --- p.50 / Chapter 3.1.1 --- General properties --- p.50 / Chapter 3.1.2 --- Stereospecific of PAF receptor --- p.57 / Chapter 3.1.3 --- Comparison of [3H]-PAF binding to TG-PEC and TG-PMΦ from Balb/c mice --- p.57 / Chapter 3.1.4 --- Inhibition of specific binding of [3H]-PAF to murine and guinea pig TG-PEC by PAF --- p.57 / Chapter 3.1.5 --- Effects of PAF antagonists on the binding of [3H]- PAF to TG-PEC from Balb/c mice and guinea pigs --- p.60 / Chapter 3.1.6 --- Scatchard analysis of [3H]-PAF binding to murine and guinea pig TG-PMΦ --- p.65 / Chapter 3.2 --- SUPEROXIDE ANION PRODUCTION IN PERITONEAL MACROPHAGES --- p.69 / Chapter 3.2.1 --- Superoxide anion production induced by PAFin murine and guinea pig TG-PMΦ --- p.69 / Chapter 3.2.2 --- Effect of PMA on superoxide anion production in murine and guinea pig TG-PMΦ --- p.69 / Chapter 3.2.3 --- Effect of calcium ionophore on superoxide anion production in murine and guinea pig TG-PMΦ --- p.75 / Chapter 3.2.4 --- Effect of PAF antagonists on PAF - induced superoxide anion production in guinea pig TG-PMΦ --- p.75 / Chapter 3.3 --- PHOSPHOLIPASE C - PHOSPHATIDYLINOSITOL SYSTEM IN PERITONEAL MACROPHAGES --- p.79 / Chapter 3.3.1 --- Effect of PAF on the accumulation of inositol phosphates in the absence of LiCl --- p.79 / Chapter 3.3.2 --- Effect of PAF on the accumulation of inositol phosphates in the presence of LiCl --- p.79 / Chapter 3.3.2.1 --- Time course of [3H]-inositol phosphates accumulation induced by PAF in TG-PMΦ --- p.86 / Chapter 3.3.2.2 --- Effect of PAF on the accumulation of [3H]-IPs in TG- PMΦ from Balb/c mice and guinea pigs --- p.86 / Chapter 3.3.2.3 --- Effect of PAF antagonists on PAF-induced [3H]-IPs accumulation in TG-PMΦ from Balb/c mice and guinea pigs --- p.86 / Chapter 3.3.2.4 --- Effect of PMA on PAF-induced [3H]-IPs formation in TG-PMΦ from Balb/c mice and guinea pigs --- p.90 / Chapter 3.3.2.5 --- Effect of prolonged PMA pretreatment on PAF and PMA-induced [3H]-IPs accumulation in murine and guinea pig TG-PMΦ --- p.90 / Chapter 3.4 --- STUDIES OF RESIDENT PEC FROM Balb/c MICE --- p.96 / Chapter 3.4.1 --- Binding of 2nM [3H]-PAF to Balb/c mice resident PEC --- p.96 / Chapter 3.4.2 --- PAF-induced [3H]-IPs accumulation in murine resident PMΦ --- p.100 / Chapter 3.4.3 --- Binding of 0.2 nM [3H]-PAF to Balb/c mice resident PEC --- p.100 / Chapter 3.4.4 --- Superoxide anion production induced by PAF and PMA in murine resident PMΦ --- p.104 / Chapter CHAPTER 4 --- DISCUSSIONS / Chapter 4.1 --- PAF RECEPTOR ON PERITONEAL MACROPHAGES --- p.125 / Chapter 4.1.1 --- [3H]-PAF binding to peritoneal macrophages --- p.105 / Chapter 4.1.2 --- Expression of PAF receptor on Balb/c mice peritoneal macrophages --- p.107 / Chapter 4.2 --- SUPEROXIDE ANION PRODUCTION IN PERITONEAL MACROPHAGES --- p.108 / Chapter 4.3 --- PAF RECEPTOR AND POLYPHOSPHATIDYLINOSITOL SYSTEM IN PERITONEAL MACROPHAGES --- p.109 / Chapter CHAPTER 5 --- CONCLUSIONS --- p.112 / REFERENCES --- p.115

Platelet activation and aggregation are essential to limit posttraumatic blood loss at sites of vascular injury, but also contribute to arterial thrombosis, leading to myocardial infarction and stroke. Thrombus formation is the result of well-defined molecular events, including agonist-induced elevation of intracellular calcium ([Ca2+]i) and series of cytoskeletal rearrangements. With the help of genetically modified mice, the work presented in this thesis identified novel mechanisms underlying the process of platelet activation in hemostasis and thrombosis. Store-operated calcium entry (SOCE) through Orai1 was previously shown to be the main Ca2+ influx pathway in murine platelets. The residual Ca2+ entry in the Orai1 deficient platelets suggested a role for additional non-store-operated Ca2+ (non-SOC) and receptor operated Ca2+ entry (ROCE) in maintaining platelet calcium homeostasis. Canonical transient receptor potential channel 6 (TRPC6), which is expressed in both human and murine platelets, has been attributed to be involved in SOCE as well as in diacylglycerol (DAG)-triggered ROCE. In the first part of the study, the function of TRPC6 in platelet Ca2+ signaling and activation was analyzed by using the TRPC6 knockout mice. In vitro agonist induced Ca2+ responses and in vivo platelet function were unaltered in Trpc6-/- mice. However, Trpc6-/- mice displayed a completely abolished DAG mediated Ca2+-influx but a normal SOCE. These findings identified TRPC6 as the major DAG operated ROC channel in murine platelets, but DAG mediated ROCE has no major functional relevance for hemostasis and thrombosis. In the second part of the thesis, the involvement of the PDLIM family member CLP36 in the signaling pathway of the major platelet collagen receptor glycoprotein (GP) VI was investigated. The GPVI/FcR-chain complex initiates platelet activation through a series of tyrosine phosphorylation events downstream of the FcR-chain-associated immunoreceptor tyrosine-based activation motif (ITAM). GPVI signaling has to be tightly regulated to prevent uncontrolled intravascular platelet activation, but the underlying mechanisms are not fully understood. The present study reports the adaptor protein CLP36 as a major inhibitor of GPVI-ITAM signaling in platelets. Platelets from mice expressing a truncated form of CLP36, (Clp36ΔLIM) and platelets from mice lacking the entire protein (Clp36-/-) displayed profound hyper-activation in response to GPVI-specific agonists, whereas GPCR signaling pathways remained unaffected. These alterations translated into accelerated thrombus formation and enhanced pro-coagulant activity of Clp36ΔLIM platelets and a pro-thrombotic phenotype in vivo. These studies revealed an unexpected inhibitory function of CLP36 in GPVI-ITAM signaling and established it as a key regulator of arterial thrombosis. / Die Aktivierung und die Aggregation von Thrombozyten (Blutplättchen) sind essentielle Prozesse, um Blutverluste nach Verletzungen zu begrenzen, sie spielen jedoch auch eine Rolle bei der arteriellen Thrombose, die zu Herzinfarkt und Schlaganfall führen kann. Die Thrombusbildung ist das Ergebnis wohldefinierter molekularer Vorgänge, die die Agonisten-induzierte Konzentrationserhöhung von intrazellulärem Kalzium ([Ca2+]i) und eine Reihe von Umlagerungen des Zytoskeletts mit einschließen. Die Ergebnisse dieser Arbeit, die mit Hilfe genetisch veränderter Mauslinien erzielt wurden, decken neue Mechanismen der Thrombozytenaktivierung in Thrombose und Hämostase auf. Es wurde bereits gezeigt, dass der durch Orai1 vermittelte Store-operated calcium entry (SOCE) den Haupteintrittsweg für Ca2+ in Mausthrombozyten darstellt. Der verbleibende Ca2+ Einstrom führte zur Annahme, dass zusätzlich non-store-operated Ca2+ (non-SOC) und receptor operated Ca2+ entry (ROCE) eine Rolle in der Aufrechterhaltung der Ca2+ Homöostase spielen. Dem Canonical transient receptor potential channel 6 (TRPC6), der in Thrombozyten des Menschen als auch der Maus exprimiert wird, wurde eine Rolle in dem SOCE und diacylglycerol (DAG)-vermitteltem ROCE zugeschrieben. Im ersten Teil dieser Arbeit wurde die Funktion von TRPC6 im Ca2+ Signaling und der Aktivierung von Thrombozyten mit Hilfe der TRPC6 defizienten Mauslinie untersucht. Die Funktion der Trpc6-/- Thrombozyten waren in vitro (z.B. Agonisten-induzierte Ca2+-Antworten) als auch in vivo unverändert. Jedoch zeigten Thrombozyten von Trpc6-/- Mäusen einen komplett fehlenden DAG vermittelten Kalziumeinstrom, aber normalen SOCE. Diese Ergebnisse identifizierten TRPC6 als den Haupt-DAG-aktivierten ROC Kanal in Mausthrombozyten. Jedoch hatte diese DAG vermittelte ROCE keine größere funktionelle Relevanz für Thrombose und Hämostase. Im zweiten Teil dieser Arbeit wurde die Rolle von CLP36, einem Mitglied der PDLIM Proteinfamilie, im Signalweg des Haupt-Kollagenrezeptors, Glykoprotein (GP) VI, auf Thrombozyten untersucht. Der GPVI/FcRKette Komplex initiiert die Thrombozytenaktivierung durch eine Reihe von Tyrosinphosphorylierungen, die dem FcR-Kette-assoziiertem immunoreceptor tyrosine based activation motif (ITAM) nachgeschaltet sind. GPVI-vermittelte Signale müssen sorgfältig reguliert sein, um eine unkontrollierte intravaskuläre Thrombozytenaktivierung zu verhindern. Jedoch sind die zugrunde liegenden Mechanismen nicht komplett verstanden. Die vorliegende Arbeit zeigt, dass das Adapterprotein CLP36 als ein wichtiger Inhibitor des GPVI-ITAM Signalwegs wirkt. Thrombozyten von Mäusen, welche eine trunkierte Form von CLP36 exprimieren, der die LIM-Domäne fehlt (Clp36ΔLIM), als auch von Mäusen, denen das komplette Protein fehlt (Clp36-/-), zeigten eine deutlich verstärkte Aktivierung als Antwort auf GPVI-spezifische Agonisten. Andere Signalwege aber waren nicht beeinflusst. Diese Veränderungen resultierten in einer schnelleren Thrombusbildung und erhöhten prokoagulatorischen Aktivität von Clp36ΔLIM Thrombozyten, welche sich letztendlich als prothrombotischer Phänotyp in vivo bemerkbar machten. Diese Ergebnisse deckten eine unerwartete inhibitorische Funktion von CLP36 im GPVI-ITAM Signalweg auf und etablierten CLP36 als einen wichtigen Regulator der arteriellen Thrombose.

Thesis (Ph. D.)--University of Oregon, 2001. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 90-98). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 262-280). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 262-280). Also available online.

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

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