Disaggregation Signals Initiated by Ligand Binding and Platelet Aggregation

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 2196-2196
Author(s):  
Cunji Gao ◽  
Juan Fang ◽  
Huiying Zhi ◽  
David A. Wilcox ◽  
Peter J. Newman
Keyword(s):  
Platelet Aggregation ◽  
Low Dose ◽  
Akt Signaling ◽  
Negative Regulator ◽  
Dependent Manner ◽  
Integrin Activation ◽  
Integrin Αiibβ3 ◽  
Agonist Stimulation ◽  
Platelet Disaggregation ◽  
Platelet Aggregates

Abstract Abstract 2196 Accumulating evidence suggests that activation of the major platelet integrin, αIIbβ3, and subsequent platelet aggregation are intrinsically dynamic and reversible processes, especially when platelets are activated by low-dose agonists like ADP. When aggregation is not robust enough to activate feed-forward autocrine amplification pathways, platelet integrins revert to their inactivated state and fibrinogen dissociates, resulting in platelet disaggregation. Failure to disaggregate following low-dose agonist stimulation has been known for many years to correlate with occlusive arterial disease and diabetes mellitus, however the mechanisms by which integrins become inactivated leading to dissociation of fibrinogen is not well understood. Because phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) signaling is known to be required to maintain integrins in an activated state and to support the formation of stable platelet aggregates, we examined whether the PI3K/Akt signaling might be actively reversed when platelets aggregate in response to ADP. We found that Akt becomes completely dephosphorylated in an aggregation-dependent manner. SHIP-1, a negative regulator of PI3K signaling, also becomes phosphorylated and activated during the early stages of platelet aggregation. These results suggest that fibrinogen binding and platelet aggregation initiate negative feedback through the PI3K/Akt signaling pathway to control unnecessary platelet aggregation responses. To gain further insight into the mechanism of platelet disaggregation, we examined the dynamic interaction of αIIbβ3 with talin – a cytosolic protein whose association with the integrin β3 cytoplasmic domain is required for integrin activation. We found that talin translocates to αIIbβ3 upon ADP stimulation, but dissociates from it during the process of platelet disaggregation. Blocking ADP-induced platelet aggregation with RGDW inhibited dissociation of talin from the integrin, again supporting the notion that that platelet aggregation initiates negative, as well as positive, signals to regulate the extent of agonist-induced platelet aggregation. Finally, we found that platelets missing PLCγ2 or FcγRIIa, each of which plays a positive role downstream of αIIbβ3-mediated outside-in signaling, are less prone to disaggregate following low-dose agonist stimulation than are their wild-type counterparts, although neither of them plays a role in ADP-induced platelet aggregation. Taken together, these data demonstrate that platelet aggregation and integrin αIIbβ3-mediated outside-in signaling not only initiates signals that amplify integrin activation and platelet aggregation, but also guards against inadvertent activation by shifting activated integrin αIIbβ3 back to its resting state, triggering platelet contraction and leading to dissociation of platelet aggregates. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Integrin αIIbβ3-Mediated Outside-in Signaling: Brake or Amplifier of Platelet Activation?

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4161-4161
Author(s):  
Baiyun Dai ◽  
Peng Wu ◽  
Feng Xue ◽  
Renchi Yang ◽  
Ziqiang Yu ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Ligand Binding ◽  
Signaling Pathway ◽  
Platelet Activation ◽  
Low Dose ◽  
Akt Signaling ◽  
Negative Regulator ◽  
Akt Signaling Pathway ◽  
Integrin Αiibβ3 ◽  
Granule Secretion

Abstract αIIbβ3 is the most prominent integrin in platelets, and binding to its ligands, in addition to supporting platelet aggregation, also results in the transmission of so-called αIIbβ3-mediated outside-in signals into the cell interior. While it is well accepted that integrin-mediated outside-in signaling functions as an amplifier of platelet activation, accumulating evidence suggests that outside-in signaling can, under certain conditions, function as an inhibitor of platelet activation. In this regard, previous studies have shown that ligand binding and platelet aggregation activate the inositol phosphatase SHIP-1, a negative regulator of the PI3K/Akt signaling pathway, to shift activated integrins back to their resting state, leading to dissociation of platelet aggregates. Because the PI3K/Akt signaling pathway is also involved in platelet granule secretion, we examined whether ligand binding to αIIbβ3 might transmit inhibitory signals that suppress platelet granule secretion. Interestingly, we found that antagonists of integrin αIIbβ3 promote both platelet dense- and α-granule secretion stimulated by low dose agonists. In support of this finding, both mouse and human platelets lacking expression of αIIbβ3 exhibited increased granule secretion compared to their wild-type counterparts. Conversely, Mn++-induced fibrinogen binding to αIIbβ3 inhibited low-dose agonist-induced platelet granule secretion. Biochemical analysis revealed that blocking ligand binding to, or absence of, αIIbβ3, enhanced agonist-induced Akt phosphorylation, while at the same time prevented the activation of the inhibitory enzyme, SHIP-1. To further investigate the role of SHIP-1 in inhibitory signaling, we examined the effect on platelet secretion of 3AC, a specific inhibitor of SHIP-1. We found that 3AC not only restores ADP-induced platelet granule secretion, but also increases CRP- or TRAP-induced platelet granule secretion. Taken together, these data demonstrate that integrin αIIbβ3-mediated outside-in signaling act as a brake to restrict unnecessary platelet activation that occurs in the presence of low-dose agonist stimulation. Disclosures No relevant conflicts of interest to declare.

The Interaction of Platelet Integrin αIIbβ3 and ICln Is Activation Dependent.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1558-1558
Author(s):  
Deirdre Larkin ◽  
Niamh Moran
Keyword(s):  
Platelet Aggregation ◽  
Low Dose ◽  
Detection System ◽  
Thrombus Formation ◽  
Critical Role ◽  
Specific Interaction ◽  
Regulatory Volume Decrease ◽  
Dependent Manner ◽  
Integrin Αiibβ3 ◽  
Protein Protein Interaction

Abstract The major platelet integrin αIIbβ3 plays a critical role in thrombus formation and has been a major target for anti-thrombotic therapy. The precise molecular mechanism of activation of the platelet integrin αIIbβ3 is not understood although a critical role for the conserved αIIb-integrin cytoplasmic motif, KxGFFKR, has been identified. We have recently shown, using a synthetic KVGFFKR peptide probe, evidence for a direct and specific interaction between the platelet integrin αIIbβ3 and a protein involved in regulatory volume decrease, ICln. ICln is a volume regulating chloride channel protein that is capable of forming a pore structure within the membrane. Previously we demonstrated by surface plasmon resonance that purified αIIbβ3 binds to His-tagged recombinant ICln (His-ICln). We now show that purified αIIbβ3 binds to His-ICln in protein pulldown assays using a western blot detection system. In addition, His-ICln selectively pulls down endogenous αIIbβ3 from platelet lysates, but in an activation dependent manner. These comparisons were carried out in lysates from resting platelets and platelets activated with U46619 (10μM), TRAP (5μM) and thrombin (0.2U/ml) for 3 minutes at 37°C, unstirred. Reduced integrin precipitation was observed in lysates from platelets treated with acyclovir (100μM), a known pharmacological inhibitor of ICln, consistent with an activation dependent interaction. As the channel function of ICln is nucleotide sensitive we set out to further identify if ICln regulates the activation of αIIbβ3 or if the integrin contributes to the activation of ICln. Low dose nucleotides were found to effect platelet function. Gel-filtered platelets treated with ATP (2nM) and apyrase (1U/ml) showed an increase in PAC-1 binding that could be inhibited with acyclovir (1mM). U46619 stimulation caused an increase in PAC-1 binding and enhanced platelet aggregation in the presence of ATP/apyrase that could also be inhibited by acyclovir in a dose-dependent manner (10μM–1mM). Thus, activation of ICln by low dose nucleotides can induce αIIbβ3 activation without further stimulus. However maximum αIIbβ3 activation is observed upon stimulation of both αIIbβ3 and ICln. The presence of an ICln inhibitor, acyclovir, interferes with platelet aggregation and integrin activation with and without specific ICln stimulation, suggesting a co-dependence between αIIbβ3 and ICln to obtain maximum platelet activation. Taken together with results of the protein- protein interaction studies this data suggests an activation-dependent, functional interaction between the volume regulating ICln protein and the platelet integrin αIIbβ3.

Interaction of Red Cell Microparticles (RMP) with Platelets: Potential Role of RMP in Hemostasis and Thrombosis,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3263-3263
Author(s):  
Wenche Jy ◽  
Max E Johansen ◽  
Carlos Bidot ◽  
Powei Chen ◽  
Lawrence L Horstman ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Adhesion ◽  
Low Dose ◽  
Potential Role ◽  
Image Analyzer ◽  
Venous Blood Flow ◽  
Color Flow ◽  
Induce Platelet Aggregation ◽  
Blood Calcium ◽  
Platelet Aggregates

Abstract Abstract 3263 Introduction: We previously reported data indicating that RMP are well suited for use as hemostatic agent for treating bleeding disorders (Jy et al, Hemophilia 17:4, 2011). Previous studies have shown that RMP can contribute to RBC-related thrombotic complications such as sickle cell disease and PNH. Microparticles (MP) derived from platelets (PMP), endothelia (EMP), and leukocytes (LMP) are believed to play a role in hemostasis and thrombosis. They can adhere to blood cells and endothelia, facilitating prothrombotic and proinflammatory reactions. However, less is known about interaction of RMP with cells and their potential role in hemostasis and thrombosis. Here we report evidence of interaction of RMP with platelets resulting in enhanced platelet aggregation and increased size of adherent platelet aggregates induced by shear stress. Methods: (i) RMP were prepared by high-pressure extrusion of washed RBC. (ii) Platelet aggregation was performed in a Chrono-log aggregometer. PRP (490 μL) was mixed with 10 μL of RMP (1 × 108 /mL final conc.) for 5 min, then low-dose activating agent (ADP 0.2 μM, or arachidonic acid (AA) 0.3 mM) was added. (iii) Shear-induced platelet adhesion was measured in a cone-and-well device (Diamed Impact-R). Whole blood was pre-incubated with RMP as above for 10 min, then subjected to various shear rates (900, 1800, 2700 sec−1) for 1 min. The adherent platelets were then washed, stained, and quantitated by image analyzer. (iv) RMP-platelet interaction employed 2-color flow cytometry. RMP-platelet conjugates were identified by co-expression of α-CD41-FITC and α-glycophrin A-PE, in both the free platelet and micro-aggregated platelet populations. Results: (1) Platelet aggregation: Addition of RMP to PRP did not induce platelet aggregation. However, RMP enhanced platelet aggregation induced by low-dose ADP or AA. Low-dose ADP alone induced a transient increase of aggregation peaking at 25–35% followed by slow disaggregation to 0–5% at 10 min; but in presence of RMP, a similar rate (slope) of aggregation was seen but peaking at 50–60% and disaggregation was abolished. Using AA, the RMP also potentiated aggregation from 20–30% to 50–60%. These results were obtained with heparinized PRP. Interestingly, when citrated PRP was used, the RMP effect was negligible. (2) Shear-induced platelet adhesion: At 1800 sec−1 shear rate, which approximates venous blood flow, addition of RMP increases the adhered mean aggregate size from 47 to 53 μm2 (p<0.03) but decreased the number of adhering objects from 1380 to 1242 (p<0.01). At lower (900 sec−1) or higher (2700 sec−1) rate, the RMP effects disappeared. (3) Two-color flow cytomrtry showed that RMP do not conjugate with single platelets but do with platelet micro-aggregates induced by ADP. When platelet micro-aggregates are diluted with PBS (1:10), they usually disaggregate rapidly (t1/2 = 10–15 min) but in presence of RMP, the rate of dissociation was much slower (t1/2 = 30–40 min). Conclusions: These results reveal that RMP can interact with weakly activated platelets to enhance platelet adhesion and aggregation and stabilize platelet aggregates. Since these effects were seen with heparinized but not with citrated blood, calcium may be a cofactor for this interaction. We suggest that RMP-platelet interaction could play a role in hemostasis, and that therapeutic RMP may improve hemostatic abnormality in thrombocytopenia and platelet dysfunction partly by this mechanism, augmenting the limited platelet function. Disclosures: No relevant conflicts of interest to declare.

An Additional Mechanism of Action of Abciximab: Dispersal of Newly Formed Platelet Aggregates

2002 ◽  
Vol 87 (06) ◽  
pp. 1020-1025 ◽  
Author(s):  
Stanley Marciniak ◽  
Mark Furman ◽  
Alan Michelson ◽  
Joseph Jakubowski ◽  
Robert Jordan ◽  
...  
Keyword(s):  
Single Cells ◽  
Dense Granule ◽  
Light Transmittance ◽  
Dependent Manner ◽  
Aggregate Formation ◽  
Fibrinogen Binding ◽  
Platelet Disaggregation ◽  
Platelet Aggregates

SummaryThe ability of abciximab to prevent fibrinogen binding to activated platelets indicates it may also promote dissolution of platelet-rich thrombi. The present study examined the capacity of abciximab to reverse platelet aggregation in vitro. Experiments were performed on blood from healthy non-medicated donors. Platelet aggregate formation and disaggregation were monitored turbidimetrically. Platelet-bound fibrinogen was measured by flow cytometry. For disaggregation studies, platelets were first stimulated with either ADP or the 11-mer thrombin receptor activating peptide (TRAP), then varying amounts of abciximab were added at periodic intervals after agonist addition. Platelet disaggregation was detected by comparing the extent of light transmittance at 4 min after addition of either abciximab or saline to PRP. ATP release was simultaneously monitored by chemi-luminescence. When added 1 min after low concentrations of ADP, abciximab rapidly (<1 min) dispersed platelet aggregates in a dose-dependent manner, with complete disaggregation observed with 6.25 µg/mL of the β3 antagonist. In contrast, equivalent concentrations of abciximab did not induce appreciable disaggregation to platelets stimulated with TRAP (10 µM). Platelet counts of samples that had undergone complete disaggregation, as assessed by aggregometry, were equivalent to baseline, indicating dispersal of aggregates to single cells. Concentrations of abciximab that produced complete disaggregation induced partial displacement of platelet-bound fibrinogen (52 ± 8% inhibition of fibrinogen binding at 12.5 µg/ml abciximab). The disaggregation effectiveness of abciximab decreased as the time between ADP and subsequent abciximab addition widened, and as the amount of both dense granule release and agonist stimulation increased. However, pre-treatment of platelets with acetylsalicylic acid (ASA) did not potentiate platelet disaggregation induced by abciximab.These data indicate that abciximab facilitates the dispersal of newly formed platelet aggregates in vitro, by partially displacing fibrinogen from activated GPIIb/IIIa receptors. In vivo, abciximab may destabilize coronary thrombi by preventing aggregate formation and dispersing mural thrombi.

scholarly journals CIB1 is an endogenous inhibitor of agonist-induced integrin αIIbβ3 activation

2006 ◽  
Vol 172 (2) ◽  
pp. 169-175 ◽  
Author(s):  
Weiping Yuan ◽  
Tina M. Leisner ◽  
Andrew W. McFadden ◽  
Zhengyan Wang ◽  
Mark K. Larson ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Active Conformation ◽  
Endogenous Inhibitor ◽  
Integrin Αiibβ3 ◽  
Binding Partners ◽  
Agonist Stimulation ◽  
Potential Binding ◽  
Normal Hemostasis ◽  
Αiibβ3 Integrin

In response to agonist stimulation, the αIIbβ3 integrin on platelets is converted to an active conformation that binds fibrinogen and mediates platelet aggregation. This process contributes to both normal hemostasis and thrombosis. Activation of αIIbβ3 is believed to occur in part via engagement of the β3 cytoplasmic tail with talin; however, the role of the αIIb tail and its potential binding partners in regulating αIIbβ3 activation is less clear. We report that calcium and integrin binding protein 1 (CIB1), which interacts directly with the αIIb tail, is an endogenous inhibitor of αIIbβ3 activation; overexpression of CIB1 in megakaryocytes blocks agonist-induced αIIbβ3 activation, whereas reduction of endogenous CIB1 via RNA interference enhances activation. CIB1 appears to inhibit integrin activation by competing with talin for binding to αIIbβ3, thus providing a model for tightly controlled regulation of αIIbβ3 activation.

Abstract 54: PSI Domain of ß3 Integrin Has Endogenous Thiol Isomerase Function and is a Novel Antithrombotic Therapeutic Target

2014 ◽  
Vol 34 (suppl_1) ◽  
Author(s):  
Emily C Reddy ◽  
Guangheng Zhu ◽  
Pingguo Chen ◽  
Adili Reheman ◽  
Xi Lei ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Cell Biology ◽  
Human Platelet ◽  
Critical Role ◽  
Rnase A ◽  
Dependent Manner ◽  
Integrin Activation ◽  
Free System ◽  
Integrin Β3 ◽  
Β3 Integrin

Integrin αIIbβ3 plays a critical role in platelet aggregation and adhesion, key events in hemostasis and thrombosis. Integrin activation involves complex signalling events that lead to conformational changes exposing ligand-binding sites; however, mechanisms underlying integrin activation remain poorly understood. The β subunit contains a PSI domain that is highly conserved across integrins and species, though its function is unknown. Integrin β subunits are cysteine-rich and endogenous thiol isomerase activity in integrin β3 has been reported. The PSI domain contains two CXXC sequences, the active site motif of protein disulfide isomerase (PDI). Based on this observation and the location of this domain at the knee region of the integrin, we hypothesized that integrin PSI domain has endogenous thiol isomerase function, which plays a key regulatory role in integrin conformation and function. Targeting the PSI domain may have therapeutic potential. Using reduced, denatured RNase, a recombinant murine integrin β3 PSI domain demonstrated endogenous PDI-like activity. This PDI-like activity was dose-dependently inhibited by the PDI inhibitor, bacitracin. Mutation of either CXXC motif within the integrin β3 PSI domain reduced PDI-like activity, while removal of both CXXC motifs completely abolished this activity. We developed unique mouse anti-mouse/anti-human β3 PSI domain monoclonal antibodies (anti-PSI mAbs) that inhibited the PDI-like activity of both the murine recombinant integrin β3 PSI domain and purified human platelet β3 integrin, in a dose-dependent manner. Interestingly, the anti-PSI mAbs blocked fibrinogen to human platelet β3 integrin in a cell free system. Furthermore, anti-PSI mAbs inhibited murine and human platelet aggregation in vitro and ex vivo and inhibited murine thrombus formation in vivo without significantly changing bleeding time or platelet count. In conclusion, we identified that the PSI domain has PDI function, is a fundamental regulator of platelet β3 integrin activation, and is a potential novel target for anti-thrombotic therapies. Since PSI domain is conserved in all integrin β subunits, our discovery may have broad implications for the role of integrins in cell biology of many human diseases.

Abstract P234: CTMP Negatively Regulates Pathological Cardiac Hypertrophy via Akt-dependent Manner

Hypertension ◽  
2016 ◽  
Vol 68 (suppl_1) ◽  
Author(s):  
Hongliang Li ◽  
Ke-Qiong Deng ◽  
Xiao-Jing Zhang
Keyword(s):  
Cardiac Hypertrophy ◽  
Knockout Mice ◽  
Pressure Overload ◽  
Akt Signaling ◽  
Negative Regulator ◽  
Dependent Manner ◽  
Loss Of Function ◽  
Akt Inhibitor ◽  
Pathological Cardiac Hypertrophy

Pathological cardiac hypertrophy which represents a leading cause of morbidity and mortality worldwide is a pathological process related to multifactorial and multiple molecules and regulated by numerous signaling pathways. Deregulation of AKT signaling is important in cardiac hypertrophy and cardiac dysfunction, but the underlying mechanism is not fully understood. In this study, we identified carboxy-terminal modulator protein (CTMP), an endogenous AKT inhibitor, as a key regulator of cardiac hypertrophy in response to pressure overload. Our results demonstrated that CTMP levels were downregulated by about 40% in aortic banding (AB)–induced hypertrophied mice hearts and 50% in failing human hearts compared to their controls respectively. Mice overexpressing CTMP specifically in the heart were resistant to AB-induced cardiac hypertrophy, whereas cardiac-specific conditional CTMP-knockout mice exhibited an aggravated phenotype induced by pressure overload. Additionally, gain-or-loss of function experiments mediated by adenovirus demonstrated that CTMP also prevented an angiotensin II–induced hypertrophic response in isolated cardiomyocytes in vitro . Mechanistically, we discovered that AKT signaling was significantly activated in AB-treated WT hearts, which was blocked by cardiac overexpression of CTMP, whereas being enhanced by loss of CTMP in response to chronic pressure overload and agonist stimulation. Moreover, rescue-experiments revealed that inhibition of AKT activation through LY294002 ameliorated the cardiac abnormalities in CTMP-knockout mice after AB. Taken together, our present study provides both in vitro and in vivo evidences that CTMP functions as a novel negative regulator factor of pathological cardiac hypertrophy. The underlying mechanisms responsible for CTMP-elicited effects are dependent on the inhibition of AKT signaling. The above-mentioned findings also expand our knowledge of the mechanisms of cardiac hypertrophy and provide potential therapeutic targets for pathological cardiac hypertrophy and heart failure.

scholarly journals Increased Platelet Aggregation due to a Plasmatic Aggregating Activity

1977 ◽  
Author(s):  
G.G. Neri Serneri ◽  
R. Abbate ◽  
G.F. Gensini ◽  
S. Favilla ◽  
C. Mugnaini
Keyword(s):  
Platelet Aggregation ◽  
Morphological Changes ◽  
Cerebrovascular Disorders ◽  
Gel Filtration ◽  
Gel Chromatography ◽  
Factor X ◽  
Elution Volume ◽  
Platelet Disaggregation ◽  
History Of ◽  
Platelet Aggregates

In various clinical states an increased platelet aggregation has been observed, but its mechanism(s) is not yet completely understood. Plasma of some patients with history of myocardial infarction (MIP) or with cerebrovascular disorders (CVP) delays platelet disaggregation after aggregation by ADP (Neri Serneri et al 1974) and induces morphological changes in control platelets (Schatz and Gross 1975). In a group of 27 MIP and 20 CVP we identified 16 MIP and 12 CVP with plasmatic aggregating activity (AA) by cross-matches in a modification of the method of Wu and Hoak (1974) for platelet aggregates. As the AA disappeared after heparin treatment (12,500 U × 2 for 7 days) we investigated whether the AA was related to an activation of clotting processes. At this purpose we measured in these patients and in those without AA the concentration of high molecular weight fibrinogen complexes (HMWFC) by agarose 4% gel-filtration. The patients with AA showed a significantly (P<0.0l) higher HMWFC concentration (9.68±2.15 %) than those without AA (5.41±1.7 %) but the AA was not related to the HMWFC themselves, which on the contrary showed a mild antiaggregating activity. On gel-chromatography of the whole plasma the AA was eluted at an elution volume at which factor X is usually collected.

scholarly journals Inflammatory Cytokine TSLP Stimulates Platelet Secretion and Potentiates Platelet Aggregation via a TSLPR-Dependent PI3K/Akt Signaling Pathway

2015 ◽  
Vol 35 (1) ◽  
pp. 160-174 ◽  
Author(s):  
Jangchuan Dong ◽  
Jing Lin ◽  
Boyuan Wang ◽  
Shaolin He ◽  
Chun Wu ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Platelet Aggregation ◽  
Signaling Pathway ◽  
Platelet Activation ◽  
Inflammatory Cytokine ◽  
Thrombus Formation ◽  
Akt Signaling ◽  
Integrin Αiibβ3 ◽  
Akt Phosphorylation ◽  
Pi3k Inhibitors

Aims: Thymic stromal lymphopoietin (TSLP) plays an important role in inflammatory diseases and is over-expressed in human atherosclerotic artery specimens. The present study investigated the role of TSLP in platelet activation and thrombosis models in vitro and in vivo, as well as the underlying mechanism and signaling pathway. Methods and Results: Western blotting and flow cytometry demonstrated that the TSLP receptor was expressed on murine platelets. According to flow cytometry, platelet stimulation with TSLP induced platelet degranulation and integrin αIIbβ3 activation. A TSLPR deficiency caused defective platelet aggregation, defective platelet secretion and markedly blunted thrombus growth in perfusion chambers at both low and high shear rates. TSLPR KO mice exhibited defective carotid artery thrombus formation after exposure to FeCl3. TSLP increased Akt phosphorylation, an effect that was abrogated by the PI3K inhibitors wortmannin and LY294002. The PI3K inhibitors further diminished TSLP-induced platelet activation. TSLP-mediated platelet degranulation, integrin αIIbβ3 activation and Akt phosphorylation were blunted in platelets that lacked the TSLP receptor. Conclusion: This study demonstrated that the functional TSLPR was surface-expressed on murine platelets. The inflammatory cytokine TSLP triggered platelet activation and thrombus formation via TSLP-dependent PI3K/Akt signaling, which suggests an important role for TSLP in linking vascular inflammation and thrombo-occlusive diseases.

Ticlopidine Facilitates the Deaggregation of Human Platelets Aggregated by Thrombin

1994 ◽  
Vol 71 (01) ◽  
pp. 091-094 ◽  
Author(s):  
M Cattaneo ◽  
B Akkawat ◽  
R L Kinlough-Rathbone ◽  
M A Packham ◽  
C Cimminiello ◽  
...  
Keyword(s):  
Cardiovascular Disease ◽  
Platelet Aggregation ◽  
Prostaglandin E1 ◽  
Human Platelet ◽  
Adenosine Diphosphate ◽  
Human Platelets ◽  
Before And After ◽  
Normal Human ◽  
Platelet Aggregates ◽  
Induced Aggregation

SummaryNormal human platelets aggregated by thrombin undergo the release reaction and are not readily deaggregated by the combination of inhibitors hirudin, prostaglandin E1 (PGE1) and chymotrypsin. Released adenosine diphosphate (ADP) plays an important role in the stabilization of thrombin-induced human platelet aggregates. Since ticlopidine inhibits the platelet responses to ADP, we studied thrombin-induced aggregation and deaggregation of 14C-serotonin-labeled platelets from 12 patients with cardiovascular disease before and 7 days after the oral administration of ticlopidine, 250 mg b.i.d. Before and after ticlopidine, platelets stimulated with 1 U/ml thrombin aggregated, released about 80–90% 14C-serotinin and did not deaggregate spontaneously within 5 min from stimulation. Before ticlopidine, hirudin (5× the activity of thrombin) and PGE1 (10 μmol/1) plus chymotrypsin (10 U/ml) or plasmin (0.06 U/ml), added at the peak of platelet aggregation, caused slight or no platelet deaggregation. After ticlopidine, the extent of platelet deaggregation caused by the same inhibitors was significantly greater than before ticlopidine. The addition of ADP (10 μmol/1) to platelet suspensions 5 s after thrombin did not prevent the deaggregation of ticlopidine-treated platelets. Thus, ticlopidine facilitates the deaggregation of thrombin-induced human platelet aggregates, most probably because it inhibits the effects of ADP on platelets.

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