scholarly journals Thrombin-induced platelet activation via PAR4: pivotal role for exosite II

2014 ◽  
Vol 112 (09) ◽  
pp. 558-565 ◽  
Author(s):  
Niklas Boknäs ◽  
Lars Faxälv ◽  
Daniel Sanchez Centellas ◽  
Maria Wallstedt ◽  
Sofia Ramström ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Active Site ◽  
Pivotal Role ◽  
Underlying Mechanisms

SummaryThrombin-induced platelet activation via PAR1 and PAR4 is an important event in haemostasis. Although the underlying mechanisms responsible for ensuring efficient PAR1 activation by thrombin have been extensively studied, the potential involvement of recognitions sites outside the active site of the protease in thrombin-induced PAR4 activation is largely unknown. In this study, we developed a new assay to assess the importance of exosite I and II for PAR4 activation with α- and γ-thrombin. Surprisingly, we found that exosite II is critical for activation of PAR4. We also show that this dependency on exosite II likely represents a new mechanism, as it is unaffected by blockage of the previously known interaction between thrombin and glycoprotein Ibα.

scholarly journals IκB kinase 2 is not essential for platelet activation

2020 ◽  
Vol 4 (4) ◽  
pp. 638-643
Author(s):  
Manuel Salzmann ◽  
Sonja Bleichert ◽  
Bernhard Moser ◽  
Marion Mussbacher ◽  
Mildred Haase ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Active Site ◽  
Bleeding Time ◽  
Thrombus Formation ◽  
Human Platelets ◽  
Iκb Kinase ◽  
Specific Deletion

Abstract Platelets are small anucleate cells that release a plethora of molecules to ensure functional hemostasis. It has been reported that IκB kinase 2 (IKK2), the central enzyme of the inflammatory NF-κB pathway, is involved in platelet activation, because megakaryocyte/platelet-specific deletion of exons 6 and 7 of IKK2 resulted in platelet degranulation defects and prolonged bleeding. We aimed to investigate the role of IKK2 in platelet physiology in more detail, using a platelet-specific IKK2 knockout via excision of exon 3, which makes up the active site of the enzyme. We verified the deletion on genomic and transcriptional levels in megakaryocytes and were not able to detect any residual IKK2 protein; however, platelets from these mice did not show any functional impairment in vivo or in vitro. Bleeding time and thrombus formation were not affected in platelet-specific IKK2-knockout mice. Moreover, platelet aggregation, glycoprotein GPIIb/IIIa activation, and degranulation were unaltered. These observations were confirmed by pharmacological inhibition of IKK2 with TPCA-1 and BMS-345541, which did not affect activation of murine or human platelets over a wide concentration range. Altogether, our results imply that IKK2 is not essential for platelet function.

scholarly journals Perceiving the Classical Cadence

2012 ◽  
Vol 31 (5) ◽  
pp. 397-417 ◽  
Author(s):  
David Sears ◽  
William E. Caplin ◽  
Stephen McAdams
Keyword(s):  
Music Theory ◽  
Empirical Support ◽  
Pivotal Role ◽  
Formal Context ◽  
Experimental Setting ◽  
Tonal Music ◽  
Classical Style ◽  
Keyboard Sonatas ◽  
Rhetorical Features ◽  
Underlying Mechanisms

This study explores the underlying mechanisms responsible for the perception of cadential closure in Mozart’s keyboard sonatas. Previous investigations into the experience of closure have typically relied upon the use of abstract harmonic formulæ as stimuli. However, these formulæ often misrepresent the ways in which composers articulate phrase endings in tonal music. This study, on the contrary, examines a wide variety of cadential types typically found in the classical style, including evaded cadences, which have yet to be examined in an experimental setting. The present findings reveal that cadential categories play a pivotal role in the perception of closure, and for musicians especially, ratings of the cadential categories provide empirical support for a model of cadential strength proposed in music theory. A number of rhetorical features also affect participants' ratings of closure, such as formal context, the presence of a melodic dissonance at the cadential arrival, and the use of a trill within the penultimate dominant. Finally, the results indicate that expertise modulates attention, with musicians privileging bass-line motion and nonmusicians attending primarily to the soprano voice.

Abstract 140: Electronegative LDL and Beta-Amyloid Synergistically Induce Platelet Activation that Can Be Inhibited by Novel MicroRNA-145 and NF-κB Decoys

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Ming-Yi Shen ◽  
Joen-Rong Sheu ◽  
Fang-Yu Chen ◽  
Richard AF Dixon ◽  
Chu-Huang Chen
Keyword(s):  
Platelet Aggregation ◽  
Platelet Activation ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Human Platelets ◽  
Iκb Kinase ◽  
Platelet Receptor ◽  
Amyloid Aβ ◽  
Underlying Mechanisms ◽  
Iκbα Degradation

Background: In addition to its role in Alzheimer’s disease, β-amyloid (Aβ) stimulates platelet aggregation by activating NF-κB. L5, a highly electronegative atherogenic subfraction of low-density lipoprotein (LDL), also induces platelet activation. Our preliminary experiments showed that Aβ and L5 function synergistically; thus, we examined the underlying mechanisms and tested a novel therapeutic approach using oligodeoxynucleotide (ODN) decoys. Methods and Results: Human plasma LDL was separated into 5 subfractions, L1-L5, with increasing electronegativity. L5, but not L1-L4, induced human platelets to release Aβ from α-granules. By phosphorylating IκB kinase β (IKKβ), both L5 and Aβ induced degradation of kappa B inhibitor (IκBα) to activate NF-κB. This led to, by way of c-Jun N-terminal kinase (JNK), the activation of platelet receptor GPIIbIIIa and platelet aggregation. L5- and Aβ-induced IκBα degradation was inhibited by ubiquitin-specific peptidase 31 through deubiquitination, which was in turn inhibited by microRNA (miR)-145. However, a specific miR-145 decoy ODN prevented IκBα degradation by inhibiting miR-145 (Figure), whereas scramble ODN had no effect. Furthermore, a specific NF-κB decoy prevented NF-κB-mediated GPIIbIIIa activation (Figure). Compared to L1, L5 injected into C57/BL6 mice (5 mg/kg of each twice a week for 6 weeks) shortened tail-bleeding time by 38% (n=6; P <0.05), which was prevented by NF-κB decoy but not scramble ODN. Conclusions: Atherogenic L5 LDL potentiates Aβ-mediated platelet activation and aggregation. Novel miR-145 and NF-κB decoys effectively blocked the synergistic effect of L5 and Aβ and may reduce the risk for thrombotic stroke.

scholarly journals Critical role of peroxisome proliferator-activated receptor α in promoting platelet hyperreactivity and thrombosis under hyperlipidemia

Haematologica ◽  
2021 ◽  
Author(s):  
Li Li ◽  
Jiawei Zhou ◽  
Shuai Wang ◽  
Lei Jiang ◽  
Xiaoyan Chen ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Thrombus Formation ◽  
Critical Role ◽  
Dense Granule ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Important Regulator ◽  
Dense Granule Secretion ◽  
Granule Secretion ◽  
Underlying Mechanisms

Platelet hyperreactivity and increased atherothrombotic risk are specifically associated with dyslipidemia. Peroxisome proliferator-activated receptor alpha (PPARα) is an important regulator of lipid metabolism. It was suggested to affect both thrombosis and hemostasis, yet the underlying mechanisms are not well understood. In this study, the role and mechanism of PPARα in platelet activation and thrombosis related to dyslipidemia were examined. Employing mice with deletion of PPARα (Pparα -/-), we demonstrated that PPARα is required for platelet activation and thrombus formation. The effect of PPARα is critically dependent on platelet dense granule secretion, and is contributed by p38MAPK/Akt, fatty acid β- oxidation, and NAD(P)H oxidase (NOX) pathways. Importantly, PPARα and the associated pathways mediated a prothrombotic state induced by high-fat diet (HFD) and platelet hyperactivity provoked by oxidized low density lipoproteins (oxLDL). Platelet reactivities were positively correlated with the expression levels of PPARα, as revealed by data from wild-type (WT), chimeric (Pparα +/-), and Pparα -/- mice. This positive correlation was recapitulated in platelets from hyperlipidemic patients. In a lipid-treated megakaryocytic cell line, lipid-induced reactive oxygen species (ROS)-NF-κB pathway was revealed to upregulate platelet PPARα in hyperlipidemia. These data suggested platelet PPARα critically mediates platelet activation and contributes to prothrombotic status under hyperlipidemia.

Abstract P551: Platelet Activation is Associated with Pulmonary Edema and Renal Injury in a Rat Model of Polymicrobial Sepsis

Hypertension ◽  
2017 ◽  
Vol 70 (suppl_1) ◽  
Author(s):  
Jeanne Ishimwe ◽  
Maggie L McCalmon ◽  
Corbin A Shields ◽  
Ashley Gnam ◽  
Jan M Williams ◽  
...  
Keyword(s):  
Renal Function ◽  
Pulmonary Edema ◽  
Organ Dysfunction ◽  
Platelet Activation ◽  
Rat Model ◽  
Renal Injury ◽  
Cecal Ligation ◽  
Cecal Ligation And Puncture ◽  
Activated Platelets ◽  
Underlying Mechanisms

Sepsis, life-threatening organ dysfunction due to a dysregulated host response to infection, is positively correlated with platelet activation. Furthermore, clinical studies have also shown that platelet activation is associated with sepsis severity, suggesting a role for platelets in sepsis pathophysiology. Despite this correlation, the underlying mechanisms by which activated platelets contribute to sepsis are under investigated. In preliminary studies, we set out to determine if platelet activation is associated with multi-organ dysfunction and injury in a rat model of chronic polymicrobial abdominal sepsis. Sepsis was induced via cecal ligation and puncture (CLP) followed by cecum removal 24 hours post-CLP. At 72 hours post-CLP, blood, urine, and tissues were collected for analysis. Platelet activation was measured via flow cytometry. Lung wet/dry ratio and plasma creatinine were measured to assess lung edema and renal injury, respectively. Platelet activation doubled in CLP rats versus Sham rats. Activated platelets increased from 3.8±1.7% of the gated population in Sham animals (n=5) to 9.2±1.9% of the gated population in CLP animals (n=5; p=0.07). Lung wet/dry ratio significantly increased from 3.9±0.2 in Sham (n=8) to 6.7±1 in CLP rats (n=8; p<0.05). Furthermore, plasma creatinine increased by 33% from 0.55±0.3 mg/dL in Sham animals (n=6) to 0.73±0.06 mg/dL in CLP rats (n=8; p<0.05), indicating a decrease in renal function. These data demonstrate, for the first time, an increase in platelet activation in response to CLP, and identifies an association of activated platelets with pulmonary edema and reduced renal function in the cecal ligation and puncture rat model of abdominal polymicrobial sepsis. Future studies will investigate the underlying mechanisms by which activated platelets contribute to multi-organ dysfunction and injury in sepsis.

Transformation of Cellular Factor XIII into an Active Zymogen Transglutaminase in Thrombin-Stimulated Platelets

1995 ◽  
Vol 73 (04) ◽  
pp. 702-705 ◽  
Author(s):  
László Muszbek ◽  
Gizella Haramura ◽  
János Polgár
Keyword(s):  
Blood Coagulation ◽  
Platelet Activation ◽  
Active Site ◽  
Factor Xiii ◽  
Coagulation Factor ◽  
Transglutaminase Activity ◽  
Activated Platelets ◽  
Monocytes And Macrophages ◽  
Stimulation Of

SummaryThe cellular form of blood coagulation factor XIII (FXIII) is present in platelets, monocytes and macrophages. During long-term stimulation of platelets by thrombin cellular FXIII becomes activated and crosslinks proteins, however, the mechanism of its activation has not been elucidated. It was shown that, contrary to plasma FXIII, the intracellular activation of platelet FXIII does not involve proteolysis. FXIII remained intact in thrombin-activated platelets, i.e., the activation peptide was not removed from the molecule. Part of the zymogen FXIII molecules, however, assumed an active configuration as was demonstrated both by the measurement of transglutaminase activity and by active-site-SH titration. These findings clearly indicate that during platelet activation, when intracellular Ca2+ concentration is raised, a slow non-proteolytic transformation of FXIII zymogen into an active transglutaminase occurs.

scholarly journals Nix-mediated mitophagy regulates platelet activation and life span

2019 ◽  
Vol 3 (15) ◽  
pp. 2342-2354 ◽  
Author(s):  
Weilin Zhang ◽  
Qi Ma ◽  
Sami Siraj ◽  
Paul A. Ney ◽  
Junling Liu ◽  
...  
Keyword(s):  
Life Span ◽  
Platelet Activation ◽  
Platelet Function ◽  
Bone Marrow Cells ◽  
Mitochondrial Protein ◽  
Genetic Ablation ◽  
Underlying Mechanisms ◽  
Adenosine Triphosphate Production ◽  
And Control

Abstract Platelet activation requires fully functional mitochondria, which provide a vital energy source and control the life span of platelets. Previous reports have shown that both general autophagy and selective mitophagy are critical for platelet function. However, the underlying mechanisms remain incompletely understood. Here, we show that Nix, a previously characterized mitophagy receptor that plays a role in red blood cell maturation, also mediates mitophagy in platelets. Genetic ablation of Nix impairs mitochondrial quality, platelet activation, and FeCl3-induced carotid arterial thrombosis without affecting the expression of platelet glycoproteins (GPs) such as GPIb, GPVI, and αIIbβ3. Metabolic analysis revealed decreased mitochondrial membrane potential, enhanced mitochondrial reactive oxygen species level, diminished oxygen consumption rate, and compromised adenosine triphosphate production in Nix−/− platelets. Transplantation of wild-type (WT) bone marrow cells or transfusion of WT platelets into Nix-deficient mice rescued defects in platelet function and thrombosis, suggesting a platelet-autonomous role (acting on platelets, but not other cells) of Nix in platelet activation. Interestingly, loss of Nix increases the life span of platelets in vivo, likely through preventing autophagic degradation of the mitochondrial protein Bcl-xL. Collectively, our findings reveal a novel mechanistic link between Nix-mediated mitophagy, platelet life span, and platelet physiopathology. Our work suggests that targeting platelet mitophagy Nix might provide new antithrombotic strategies.

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