Acid Sphingomyelinase Regulates Platelet Cell Membrane Scrambling, Secretion, and Thrombus Formation

Objective-Platelet activation is essential for primary hemostasis and acute thrombotic vascular occlusions. On activation, platelets release their prothrombotic granules and expose phosphatidylserine, thus fostering thrombin generation and thrombus formation. In other cell types, both degranulation and phosphatidylserine exposure are modified by sphingomyelinase-dependent formation of ceramide. The present study thus explored whether acid sphingomyelinase participates in the regulation of platelet secretion, phosphatidylserine exposure, and thrombus formation. Approach and Results-Collagen-related peptide-induced or thrombin-induced ATP release and P-selectin exposure were significantly blunted in platelets from Asm-deficient mice (Smpd1(-/-)) when compared with platelets from wild-type mice (Smpd1(+/+)). Moreover, phosphatidylserine exposure and thrombin generation were significantly less pronounced in Smpd1(-/-) platelets than in Smpd1(+/+) platelets. In contrast, platelet integrin alpha(IIb)beta(3) activation and aggregation, as well as activation-dependent Ca2+ flux, were not significantly different between Smpd1(-/-) and Smpd1(+/+) platelets. In vitro thrombus formation at shear rates of 1700 s(-1) and in vivo thrombus formation after FeCl3 injury were significantly blunted in Smpd1(-/-) mice while bleeding time was unaffected. Asm-deficient platelets showed significantly reduced activation-dependent ceramide formation, whereas exogenous ceramide rescued diminished platelet secretion and thrombus formation caused by Asm deficiency. Treatment of Smpd1(+/+) platelets with bacterial sphingomyelinase (0.01 U/mL) increased, whereas treatment with functional acid sphingomyelinase-inhibitors, amitriptyline or fluoxetine (5 mu mol/L), blunted activation-dependent platelet degranulation, phosphatidylserine exposure, and thrombus formation. Impaired degranulation and thrombus formation of Smpd1(-/-) platelets were again overcome by exogenous bacterial sphingomyelinase. Conclusions-Acid sphingomyelinase is a completely novel element in the regulation of platelet plasma membrane properties, secretion, and thrombus formation

Copyright: Elsevier

A novel role for phospholipase D as a

Epithets Characterizing Heroes in Homer's “Odyssey”

Bakalaura darba „Epiteti varoņu raksturojumam Homēra Odisejā” mērķis ir izpētīt epitetu lietojumu varoņu atainojumam. Bakalaura darba teorētisko bāzi viedo gan antīkie avoti un antīko teorētiķu atziņas par epitetu, episko stilu un varoni episkā tekstā, gan mūsdienu zinātnieku pētījumu materiāli. Tēmas izpētē izmantotas arī vārdnīcas un Homēra Odisejas orģinālteksts. Klasificējot un analizējot tēmai atbilstošus varoņu epitetus, izdalītas galvenās trīs varoņu epitetu tematiskās grupas, kuras veido statusu un ietekmes, garīgo un morālo, kā arī fizisko kvalitāšu atainojoši epiteti. Atrasto un analizēto varoņu epitetu lielais skaits un dažādās lietojumu nozīmes norāda uz šī mākslinieciskās izteiksmes līdzekļa nenoliedzamo lomu spilgtākā varoņa attēlošanā episkajā tekstā. Atslēgvārdi: Homērs, Odiseja, varonis, epitets, episkais stils.The object of the bachelor’s thesis “Epithets Characterizing Heroes in Homer's Odyssey” is to research epithets that describe heroes. The theoretical basis of this bachelor’s thesis are works of ancient authors, who have gave adjudgments on epithet, epic style and hero in an epic text, as well as research materials of modern literature scientists. In the process of object’s study there had been used dictionaries and the original text of Homer’s Odyssey. By classification and analysis of hero epithets, three main thematic groups had been educed. These groups consist of epithets that describe mental and moral, status and authority as well as physical qualities. The large amount of found and analysed hero epithets together with differential meanings of use, indicate the evidentiary role of this artistic expression tool in describing the hero more brightly. Keywords: Homer, Odyssey, hero, epithet, epic style

A novel role for phospholipase D as an endogenous negative regulator of platelet sensitivity

Platelet aggregation, secretion and thrombus formation play a critical role in primary hemostasis to prevent excessive blood loss. On the other hand, uncontrolled platelet activation leads to pathological thrombus formation resulting in myocardial infarction or stroke. Stimulation of heterotrimeric G-proteins by soluble agonists or immunoreceptor tyrosine based activation motif-coupled receptors that interact with immobilized ligands such as the collagen receptor glycoprotein (GP) VI lead to the activation of phospholipases that cleave membrane phospholipids to generate soluble second messengers. Platelets contain the phospholipases (PL) D1 and D2 which catalyze the hydrolysis of phosphatidylcholine to generate the second messenger phosphatidic acid (PA). The production of PA is abrogated by primary alcohols that have been widely used for the analysis of PLD-mediated processes. However, it is not clear if primary alcohols effectively reduce PA generation or if they induce PLD-independent cellular effects. In the present study we made use of the specific PLD inhibitor 5-fluoro-2-indolyl des-chlorohalopemide (FIPI) and show for the first time, that FIPI enhances platelet dense granule secretion and aggregation of human platelets. Further. FIPI has no effect on cytosolic Ca2+ activity but needs proper Rho kinase signaling to mediate FIPI-induced effects on platelet activation. Upon FIPI treatment the phosphorylation of the PKC substrate pleckstrin was prominently enhanced suggesting that FIPI affects PKC-mediated secretion and aggregation in platelets. Similar effects of FIPI were observed in platelets from mouse wild-type and Pld1(-/-) mice pointing to a new role for PLD2 as a negative regulator of platelet sensitivity