VAMP-7 Interacts With The Actin Cytoskeleton To Control Platelet Spreading and Mediate α-Granule Exocytosis During Thrombus Formation

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 1058-1058
Author(s):  
Secil Koseoglu ◽  
Jennifer L Fitch-Tewfik ◽  
Christian G. Peters ◽  
Lydia Danglot ◽  
Thierry Galli ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Conflicts Of Interest ◽  
Thrombus Formation ◽  
Surface Expression ◽  
Wild Type ◽  
Granule Exocytosis ◽  
Granule Secretion ◽  
Platelet Spreading

Abstract Platelet granule secretion is important not only for hemostasis and thrombosis, but also for a variety of physiological processes including inflammation, angiogenesis and malignancy. Vesicle Associated Membrane Proteins (VAMPs) are a group of v-SNARE proteins resident on the platelet granule surface that participate in granule secretion. Platelets contain several VAMP isoforms including VAMP-2, VAMP-3, VAMP-7, and VAMP-8. VAMP-7 is unique in that it contains an N-terminal profilin-like longin domain. Previous work by our group demonstrated spatial segregation of granules expressing different VAMPs during platelet spreading. Granules expressing VAMP-3 and VAMP-8 localized to the granulomere of spreading platelets, while those expressing VAMP-7 moved towards the periphery. Based on this observation, we proposed that VAMP-7+ granules move to the periphery of the spreading platelet to add membrane to growing actin structures. To assess this hypothesis, platelets from VAMP-7 null mice were used to analyze the role of VAMP-7 in platelet spreading, aggregation and secretion. VAMP-7 null platelets were normal in size, shape, and number. When compared to wild-type platelets, VAMP-7 null platelets did not show any defects in aggregation upon exposure to increasing doses of the PAR4 agonist peptide, AYPGKF, or collagen. In contrast, the surface area of VAMP-7 null platelets following 15 min of spreading on poly-L-lysine was only 51% that of wild-type of platelets (P < 0.05). To assess mechanisms of the movement of VAMP-7 to the platelet periphery, the association of VAMP-7 to the Triton X-100-insoluble platelet cytoskeleton was evaluated and results showed that VAMP-7 associated with the actin cytoskeleton. Moreover, VAMP-7 null platelets showed impaired P-selectin surface expression and PF4 secretion at low concentrations of AYPGKF. TIMP-2 and VEGF localize to VAMP-7 expressing granules in the periphery of spread platelets. We therefore evaluated the secretion of TIMP-2 and VEGF from VAMP-7 null platelets. Secretion of TIMP-2 and VEGF was reduced even at saturating doses of agonist (300 mM AYPGKF). To examine the role of VAMP-7 in a-granule exocytosis during platelet activation in vivo, PF4 release was monitored following laser-induced injury of cremaster arterioles. Platelet accumulation at sites of laser injury was identical in wild-type and VAMP-7 null mice. In wild-type mice, PF4 was secreted by activated platelets and bound back to activated endothelium and platelets producing a localized concentration of PF4 that accumulated over 15 min following injury. PF4 release from platelets lacking VAMP-7 was decreased to 47% of that of control. These results demonstrate that VAMP-7 interacts with the actin cytoskeleton and functions selectively in a-granule exocytosis. VAMP-7 associates with the actin cytoskeleton and functions during platelet spreading, adding further support to the premise that membrane fusion occurring during granule secretion is an essential component of normal platelet spreading. This VAMP-7 mediated, actin-dependent mechanism of secretion is not important for platelet thrombus formation, but rather functions in the release of particular granular contents, such as PF4, at sites of vascular injury. Disclosures: No relevant conflicts of interest to declare.

C-Cbl Regulates c-Mpl Receptor Trafficking and Its Internalization

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 2388-2388
Author(s):  
Sebastian Jonas Saur ◽  
Melanie Märklin ◽  
Manuela Ganser ◽  
Kyle Hoehn ◽  
James E David ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Plasma Levels ◽  
Thrombus Formation ◽  
Surface Expression ◽  
Mrna Levels ◽  
Wild Type ◽  
Primary Mouse

Abstract Megakaryopoiesis is controlled by a variety of hematopoietic growth factors and cytokines in order to maintain physiological levels of circulating platelets. Thrombopoietin (TPO) signalling via its receptor c-Mpl is a key regulator of megakaryopoiesis driving megakaryocyte differentiation, promoting endomitosis and proplatelet formation. Therefore TPO/c-Mpl signalling needs to be tightly regulated to maintain physiological megakaryopoiesis. One of the most effective mechanisms to permanently disable activated signalling proteins is by targeted degradation via lysosomes or proteasomes. Previous studies have identified c-Cbl as an E3 ligase responsible for the ubiquitination of c-Mpl in cell lines. In this study, we investigated the mechanisms of TPO-mediated c-Mpl degradation in primary mouse cells. In order to determine the potential role of c-Cbl in murine megakaryopoiesis we used a conditional PF4-Cre c-Cbl knockout (ko) mouse model to specifically delete c-Cbl in the megakaryocytic lineage. Megakaryocytes were generated in vitro by culturing bone marrow from WT and PF4-Cre/c-Cbl-floxed (c-Cbl ko) lines for 72 hrs in the presence of rmTPO. C-Cbl ko mice showed significant bone marrow megakaryocyte hyperplasia, however megakaryocyte numbers in the spleen remained unchanged. Platelets counts were significantly elevated as compared to control mice (1.2 x106 vs. 1.7x106 p=0.0001) and in addition, the platelets from the c-Cbl ko mouse strain were of significantly smaller size (43 vs. 38 fL, p=0.0022). Using a method of in vivo double labelling of platelets, we were able to simultaneously follow the survival of both the entire population of platelets and new platelets which were generated during the last 24 hours. There were more new platelets produced within a 24 h period in the c-Cbl ko mice although the half-life of platelets was similar in the both cohorts. Although c-Cbl ko mice exhibited thrombocytosis, they showed a severe defect in thrombus formation using an in vivo thrombus formation model with Fe3Cl. TPO plasma levels, known to be inversely regulated by circulating platelet numbers, were surprisingly increased (250 vs. 420 pg/ml, p=0.005) in the c-Cbl ko mice. There was no difference in liver mRNA levels in the two cohorts. We therefore looked at c-Mpl protein and mRNA expression in megakaryocytes and found c-Cbl ko mice to express more c-Mpl compared with wild type controls. Surprisingly, we found c-Mpl surface expression to be reduced and internalization of the receptor significantly impaired following TPO stimulation in c-Cbl ko mice. Incubating platelets in vitro with TPO for 2 hours to evaluate the TPO uptake capacity of platelets, we found c-Cbl ko platelets to show a severe uptake defect compared with wild type control platelets. Taken together, we have successfully ablated c-Cbl specifically from the megakaryocyte lineage and demonstrated that this has profound effects on platelet counts and size. In addition, we showed that c-Cbl ablation leads to reduced c-Mpl surface expression and impaired internalization, which culminates in increased TPO plasma levels causing increased megakaryopoiesis in the c-Cbl ko mice. In summary, our data enhance our understanding of the regulation of TPO signalling and the physiological role of c-Cbl in the megakaryocytic lineage. Disclosures No relevant conflicts of interest to declare.

Role of Thiol Isomerase ERp5 in Thrombus Formation

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 370-370
Author(s):  
Freda H. Passam ◽  
Lin Lin ◽  
Mingdong Huang ◽  
Jonathan M. Gibbins ◽  
Bruce Furie ◽  
...  
Keyword(s):  
Cho Cells ◽  
Conflicts Of Interest ◽  
Thrombus Formation ◽  
Dependent Manner ◽  
Wild Type ◽  
In Vivo Models ◽  
Platelet Accumulation

Abstract Abstract 370 Protein disulfide isomerase is required for thrombus formation in various in vivo models of thrombosis. Another member of the thiol isomerase family, endoplasmic reticulum protein 5 (ERp5), is released from activated platelets and co-immunoprecipitates with beta 3 integrin (Jordan et al, 2005). We further investigated the association of ERp5 with the platelet fibrinogen receptor alpha IIb beta 3 and the significance of ERp5 release in thrombus formation in vivo. Recombinant purified ERp5 was labeled with Alexa 488 and used in direct binding assays to CHO cells expressing wild type (WT) alpha IIb beta 3, CHO cells expressing mutant alpha IIb beta 3 (containing an Asp119Tyr substitution in the beta 3 subunit) and to control CHO cells. The mutant alpha IIb beta 3 does not bind fibrinogen. ERp5 bound to CHO cells expressing wild type (WT) alpha IIb beta 3 in a dose-dependent manner but did not bind to CHO cells expressing mutant alpha IIb beta 3 or to control CHO cells. The relative increase in the geomean of Alexa 488-labeled ERp5 binding to 0.5 ×106 WT alpha IIb beta 3 CHO cells over that bound to control CHO cells was 20, 45 and 85% for ERp5 concentrations of 80, 160 and 400 nM respectively. Binding of ERp5 (160 nM) to WT alpha IIb beta 3 expressing CHO cells was further increased by 75% when the integrin was activated with 2 mM Mn2+ compared to non-activated WT alpha IIb beta 3 CHO cells. A role for ERp5 in thrombus formation was studied in the laser injury model of thrombosis in mouse cremaster arterioles using a rabbit polyclonal anti-ERp5 antibody, immunoaffinity purified against recombinant ERp5. This antibody detected ERp5 in the releasate of thrombin-activated mouse platelets in vitro by Western blot and on the surface of thrombin-activated mouse platelets by flow cytometry. Dylight 649-labeled anti-CD42b was infused into the mouse circulation to detect platelet accumulation and Alexa 488-labeled anti-ERp5 antibody at 0.05 ug/g, a dose that does not inhibit thrombus formation, was infused to detect ERp5. The fluorescent anti-ERp5 signal detected at the thrombus site was compared to the signal produced by a non-specific IgG labeled with Alexa 488 infused into a control mouse. Anti-ERp5 fluorescence was detected in the thrombus with kinetics that followed platelet accumulation whereas there was minimal signal from the control IgG. We examined whether higher doses of anti-ERp5 affect thrombus formation. Platelet and fibrin accumulation were detected using fluorescently labeled anti-CD42b antibody and monoclonal anti-fibrin-specific antibody respectively before or after the injection of unlabeled anti-ERp5 antibody or pre-immune IgG at 2.5 ug/g. Platelet and fibrin accumulation, expressed as area under the curve of the median integrated fluorescence over time, was obtained from 14 thrombi in 6 mice formed before infusion of antibody, 18 thrombi in 2 mice formed after infusion of control IgG and 29 thrombi in 3 mice formed after infusion of anti-ERp5. Anti-ERp5 infusion caused a 70% decrease in the deposition of platelets and a 62% decrease in fibrin accumulation compared to infusion of control antibody (p<0.01). There was no difference in platelet and fibrin accumulation before infusion of antibody and after infusion of control antibody. These results provide evidence for a role of a second thiol isomerase, ERp5, in thrombus formation, a function which may be mediated through its association with alpha IIb beta 3. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Characterization of TNF receptor subtype expression and signaling on pulmonary endothelial cells in mice

2011 ◽  
Vol 300 (5) ◽  
pp. L781-L789 ◽  
Author(s):  
Szabolcs Bertok ◽  
Michael R. Wilson ◽  
Anthony D. Dorr ◽  
Justina O. Dokpesi ◽  
Kieran P. O'Dea ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Adhesion Molecules ◽  
Surface Expression ◽  
Tnf Receptor ◽  
Wild Type ◽  
Tnf Receptors ◽  
Pulmonary Endothelial Cells ◽  
Microvascular Inflammation

TNF plays a crucial role in the pathogenesis of acute lung injury. However, the expression profile of its two receptors, p55 and p75, on pulmonary endothelium and their influence on TNF signaling during lung microvascular inflammation remain uncertain. Using flow cytometry, we characterized the expression profile of TNF receptors on the surface of freshly harvested pulmonary endothelial cells (PECs) from mice and found expression of both receptors with dominance of p55. To investigate the impact of stimulating individual TNF receptors, we treated wild-type and TNF receptor knockout mice with intravenous TNF and determined surface expression of adhesion molecules (E-selectin, VCAM-1, ICAM-1) on PECs by flow cytometry. TNF-induced upregulation of all adhesion molecules was substantially attenuated by absence of p55, whereas lack of p75 had a similar but smaller effect that varied between adhesion molecules. Selective blockade of individual TNF receptors by specific antibodies in wild-type primary PEC culture confirmed that the in vivo findings were due to direct effects of TNF receptor inhibition on endothelium and not other cells (e.g., circulating leukocytes). Finally, we found that PEC surface expression of p55 dramatically decreased in the early stages of endotoxemia following intravenous LPS, while no change in p75 expression was detected. These data demonstrate a crucial in vivo role of p55 and an auxiliary role of p75 in TNF-mediated adhesion molecule upregulation on PECs. It is possible that the importance of the individual receptors varies at different stages of pulmonary microvascular inflammation following changes in their relative expression.

Endobrevin/VAMP-8-Mediated Dense Granule Release Is Required for Efficient Thrombus Formation in Vivo.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1836-1836
Author(s):  
Price S. Blair ◽  
Qiansheng Ren ◽  
Gwenda J. Graham ◽  
James R. Dilks ◽  
Sidney W. Whiteheart ◽  
...  
Keyword(s):  
Vascular Injury ◽  
Thrombus Formation ◽  
Dense Granule ◽  
Wild Type ◽  
Platelet Accumulation ◽  
Induced Aggregation ◽  
Kinetics Of ◽  
Granule Release

Abstract Individuals whose platelets lack dense core or alpha-granules suffer varying degrees of abnormal bleeding, implying that granule cargo contributes to hemostasis. Despite these clinical observations, little is known regarding the effects of impaired platelet granule secretion on thrombus formation in vivo. The release of cargo from platelet granules requires a group of membrane proteins called SNAREs (Soluble NSF Attachment Protein Receptors) that mediate fusion of granule membranes to the plasma membrane and open canalicular system. Endobrevin/VAMP-8 is the primary vesicular-SNARE (v-SNARE) responsible for efficient release of dense core and a-granule contents. To evaluate the importance of VAMP-8-mediated secretion on the kinetics of thrombus formation in vivo, we measured platelet accumulation following laser-induced vascular injury in VAMP-8−/− mice. Three different phases of thrombus formation - initiation, maximal accumulation, and stabilized platelet accumulation - were tested. Analysis of initial thrombus formation from wild-type and VAMP-8−/− mice showed that average platelet accumulation in VAMP- 8−/− mice was 23% of accumulation in wild-type mice (P=0.009) at 30 sec following injury. There was a trend towards smaller maximal thrombus size in VAMP-8−/− mice, but the difference was not statistically significant (P=0.1). Average stabilized platelet accumulation at 180 sec in VAMP-8−/− mice was 40% of wild-type mice (P=0.05). Thus, thrombus formation is delayed and decreased in VAMP-8−/− mice, but not absent. Dense granule release occurs more rapidly than alpha-granule release, which does not occur for 2–3 min following laser-induced vascular injury. Agonist-induced dense granule release from VAMP-8−/− platelets is defective. To directly evaluate the role of dense granule release on the kinetics of thrombus formation, we assessed thrombus formation in the mouse model of Hermansky-Pudlak syndrome, ruby-eye, which lack dense granules. Thrombus formation following laser-induced vascular injury was nearly abolished in ruby-eye mice such that maximal platelet accumulation was 15% that of wild-type mice. In vitro, the thrombin doses required to induce irreversible aggregation in wild-type, VAMP-8−/−, and ruby-eye platelets were 25 mU, 50 mU, and 150 mU, respectively. Incubation with apyrase had little effect on thrombin-induced aggregation of VAMP-8−/− or ruby-eye platelets. In contrast, incubation of wild-type platelets with apyrase reduced their thrombin sensitivity compared to that of ruby-eye platelets. Supplementation with a substimulatory ADP concentration reversed the thrombin-induced aggregation defect in VAMP-8−/− and ruby-eye mice. Thus, defective ADP release is the primary abnormality leading to impaired aggregation in VAMP-8−/− and ruby-eye mice. Tail bleeding times were assessed in VAMP- 8−/− mice to evaluate the role of VAMP-8 in hemostasis. In contrast to ruby-eye mice, which have a markedly prolonged bleeding time, tail bleeding times in VAMP-8−/− mice were not significantly prolonged compared to those in wild-type mice. These results demonstrate the importance of VAMP-8 and dense granule release in the initial phases of thrombus formation and validate the distal platelet secretory machinery as a potential target for anti-platelet therapies.

Modulation of Mesenchymal Stem Cell MHC-I Complex Increases Engraftment In Vivo.

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 1457-1457
Author(s):  
Melisa Soland ◽  
Evan J Colletti ◽  
Mariana Bego ◽  
Chad Sanada ◽  
Christopher D Porada ◽  
...  
Keyword(s):  
Nk Cells ◽  
Conflicts Of Interest ◽  
Surface Expression ◽  
Large Animal ◽  
Specific Lysis ◽  
Fetal Sheep ◽  
Mhc I ◽  
Npt Ii

Abstract Abstract 1457 Mesenchymal stem cells (MSC) are good candidates for cell therapies due to their immunomodulatory properties, ability to home to/engraft damaged tissues, and potential to differentiate into different cell types. However, when transplanted (Tx) in an allogeneic setting, MSC can elicit an immune response, activating the recipient's cytotoxic T lymphocytes (CTL) and Natural Killer (NK) cells, resulting in rejection of the Tx cells and reduced therapeutic efficacy. Human cytomegalovirus (HCMV, has developed several strategies to evade CTL and NK cell recognition. HCMV avoids CTL attack by producing proteins that downregulate MHC-I surface expression. These proteins are coded for by the unique short regions (US) 2, 3, 6 and 11 of HCMV's genome. We have previously shown that when MSC are transduced with retroviral vectors encoding each one of these US proteins, US6 and US11 were the most effective in reducing MSC's HLA-I surface expression and allogeneic CTL recognition and proliferation. However, HLA-I downregulation may render MSC transduced with US6 (MSC-US6) and US11 (MSC-US11) more susceptible to NK killing, undermining MSC's inherent ability to inhibit function of allogeneic NK cells. Here, we first investigated the role of US6 or US11 on MSC allorecognition by NK cells, and on MSC in vivo engraftment capability. NK killing assays demonstrated that US11 generated the most protective effect at the highest NK concentration (E:T ratio 20:1) (% specific lysis for MSC-US6: 60.4 ± 5.7 %; MSC-US11: 45.5 ± 2.4 % vs. MSC: 88.5 ± 3.4 % respectively). However, at an E:T ratio of 10:1 and 5:1 US11 produced the same degree of protection as US6 (E:T ratio of 10:1; % specific lysis for MSC-US6: 30.1 ± 5.6 %; MSC-US11: 26.3 ± 1.9 % vs. MSC: 54.7 ± 1.9 %); (E:T ratio 5:1; % specific lysis for MSC-US6: 11.9 ± 4.2; MSC-US11: 13.4 ± 2.3; vs. MSC: 25.5 ± 4 respectively). Only at an E:T ratio of 1:1 were US6 and US11 similar to untransduced MSCs (% specific lysis for MSC-US6: 4.7 ± 1.6; MSC-US11: 2.1 ± 0.5; vs. MSC: 4.9 ± 1.8; respectively) in terms of inhibition of NK killing. We also studied the role of US6 and 11 on the expression of beta-2-microglobulin (b2m) and other HLA-I molecules, and we found that US6 reduced b2m by 87± 2 % and HLA-G1 by 44±4.7 %, while US11 reduced b2m by 70± 0.6 % but increased HLA-G1 expression by 176.6±1.9 %. Therefore, the increase in HLA-G1 expression induced by US11 may explain the decrease in NK killing observed in the MSC-US11 cells. Furthermore, we investigated whether US6 or US11 could play a role in mediating complement resistance. While US6 increased the expression of CD59 in transduced cells (Mean fluorescence intensity (MFI) increased by 123.3±1), US11 increased the number of cells expressing CD59 by 121.4 ± 0.8 %, but did not modify their MFI. We next compared the in vivo engraftment potential of MSC, MSC-US6 and MSC-US11 by Tx 5.6×10^4 of each cell population into fetal sheep at 60 days of gestation (n=6). Since we have previously reported the ability of MSC to generate liver cells, we first investigated whether the expression of US6 and 11 would allow higher levels of liver engraftment and hepatocyte formation when compared to MSC (MSC-E) transduced with a retroviral vector encoding only NPT-II. Two months after Tx, liver tissues were collected and stained with NPT-II antibody. This revealed that US6 and US11 increased engraftment efficiency by 241% for MSC-US6 and 277% for MSC-US11 (MSC-E: 5.3 ± 0.4 %, MSC-US6: 12.8 ± 0.9 % and MSC-US:11 14.7 ± 0.8 %). Despite the higher level of liver engraftment seen with MSC-US6 and MSC-US11, co-expression of NPT-II and albumin (MSC-US6: 57% MSC-US1: 50% MSC-E: 75%) or NPT-II and Ov-6 was found at significantly lower levels in MSC-US11 and MSC-US6 Tx animals than in those Tx with MSC-E. Nevertheless, similar numbers of NPT-II/CD34 double-positive cells were found in the liver of MSC-US6 and MSC-US11 Tx animals when compared to MSC-E alone. In conclusion, engineering MSC to over-express US6 or US11 is an effective way to reduce CTL proliferation, NK killing and destruction of engrafted cells by the complement membrane attack complex. In agreement with the in vitro studies, transplantation of these cells into a large animal sheep model resulted in significantly higher levels of overall cell engraftment, but not differentiation towards a hepatocytic phenotype. Studies are underway to determine the mechanism by which HCMV proteins are interfering with MSC differentiation. Disclosures: No relevant conflicts of interest to declare.

Rhog Regulates GPVI/FcRγ-Mediated Platelet Activation and Thrombus Formation

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 1060-1060
Author(s):  
Soochong Kim ◽  
Carol Dangelmaier ◽  
Dheeraj Bhavanasi ◽  
Shu Meng ◽  
Hong Wang ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Western Blotting ◽  
Thrombus Formation ◽  
Human Platelets ◽  
Wild Type ◽  
Thrombosis Model ◽  
Significant Difference ◽  
Granule Secretion ◽  
Time Required

Abstract We investigated the mechanism of activation and functional role of a hitherto uncharacterized signaling molecule, RhoG, in platelets. RhoG is a ubiquitously expressed member of the Rho Family of GTPases. We demonstrated for the first time the expression [Fig 1A] and activation of RhoG [Fig 1B] in platelets. Platelet aggregation and dense-granule secretion in response to glycoprotein VI (GPVI) agonists, collagen-related peptide (CRP) and convulxin were significantly inhibited in RhoG-deficient platelets compared to wild type murine platelets [Fig 1C]. Integrin αIIbβ3 activation and α-granule secretion as measured by flow cytometry were also significantly inhibited in RhoG-deficient murine platelets downstream of GPVI agonists. In contrast, 2-MeSADP- and AYPGKF-induced platelet aggregation and secretion [Fig 1D] were minimally affected in RhoG deficient platelets, indicating that the function of RhoG in platelets is GPVI-specific.Figure 1(A): Increasing amounts of human platelet lysate (in μg) were separated by SDS-PAGE, Western blotted, and probed with anti-RhoG antibody. (B) RhoG activation was measured upon stimulation of washed human platelets with 5μg/ml CRP for various times. Washed platelets were lysed and active GTP-bound RhoG was determined by pull-down analysis using bacterially expressed GST-ELMO. (C) Washed platelets from RhoG -/- mice and RhoG +/+ littermates were stimulated with GPVI agonists, 2.5 μg/ml CRP and 100 ng/ml convulxin and (D) G protein coupled receptor agonists, 30 nM 2MeSADP and 100 μM AYPGKF for 3.5 min under stirring conditions. Platelet aggregation and ATP secretion were measured by aggregometry.Figure 1. (A): Increasing amounts of human platelet lysate (in μg) were separated by SDS-PAGE, Western blotted, and probed with anti-RhoG antibody. (B) RhoG activation was measured upon stimulation of washed human platelets with 5μg/ml CRP for various times. Washed platelets were lysed and active GTP-bound RhoG was determined by pull-down analysis using bacterially expressed GST-ELMO. (C) Washed platelets from RhoG -/- mice and RhoG +/+ littermates were stimulated with GPVI agonists, 2.5 μg/ml CRP and 100 ng/ml convulxin and (D) G protein coupled receptor agonists, 30 nM 2MeSADP and 100 μM AYPGKF for 3.5 min under stirring conditions. Platelet aggregation and ATP secretion were measured by aggregometry. CRP-induced phosphorylations of Syk, Akt and ERK, but not Src family kinases (SFKs), were significantly reduced in RhoG-deficient platelets compared to those of wild type [Fig 2A]. Consistently, CRP-induced RhoG activation was abolished by pan-SFK inhibitor but not by Syk or PI 3-kinase inhibitors [Fig 2B]. Interestingly, unlike CRP, platelet aggregation and Syk phosphorylation induced by fucoidan, a CLEC-2 agonist, were unaffected in RhoG deficient platelets [Fig 2C].Figure 2(A): Washed platelets from RhoG -/- mice and RhoG +/+ littermates were stimulated with 2.5 μg/ml CRP and at 37 °C for 2 min and probed with anti-phospho-Syk (Tyr525/526), anti-phospho-Src (Tyr416), anti-phospho-Akt (Ser473), anti-phospho-ERK, or anti-β-actin (lane loading control) antibodies by western blotting. (B): RhoG activation induced by 5μg/ml CRP for 60 sec was evaluated in the presence and absence of 10 μM PP2, 2 μM OXSI-2, or 100nM wortmannin. (C): Wild type and RhoG-deficient platelets were stimulated with 100 μg/ml fucoidan and probed with anti-phospho-Syk (Tyr525/526), anti-phospho-Akt (Ser473), or anti-β-actin (lane loading control) antibodies by western blotting.Figure 2. (A): Washed platelets from RhoG -/- mice and RhoG +/+ littermates were stimulated with 2.5 μg/ml CRP and at 37 °C for 2 min and probed with anti-phospho-Syk (Tyr525/526), anti-phospho-Src (Tyr416), anti-phospho-Akt (Ser473), anti-phospho-ERK, or anti-β-actin (lane loading control) antibodies by western blotting. (B): RhoG activation induced by 5μg/ml CRP for 60 sec was evaluated in the presence and absence of 10 μM PP2, 2 μM OXSI-2, or 100nM wortmannin. (C): Wild type and RhoG-deficient platelets were stimulated with 100 μg/ml fucoidan and probed with anti-phospho-Syk (Tyr525/526), anti-phospho-Akt (Ser473), or anti-β-actin (lane loading control) antibodies by western blotting. Finally, RhoG -/- mice had a significant delay in time to thrombotic occlusion in cremaster arterioles compared to wild type littermates [Fig 3A and 3B], indicating the important in vivo functional role of RhoG in platelets.Figure 3(A): Time required for occlusion of cremaster arterioles in RhoG +/+ and RhoG -/- mice was measured using microvascular thrombosis model with light/dye-induced injury. 5 mice of each genotype were used, and statistical analysis revealed a significant difference between the 2 genotypes of mice (*, P < .01). (B) Representative images of cremaster arterioles were taken from RhoG +/+ and RhoG -/- mice 30 min after the injury. As seen with the outline (arrows) of the thrombus formed, thrombus formation was inhibited in RhoG -/- mice.Figure 3. (A): Time required for occlusion of cremaster arterioles in RhoG +/+ and RhoG -/- mice was measured using microvascular thrombosis model with light/dye-induced injury. 5 mice of each genotype were used, and statistical analysis revealed a significant difference between the 2 genotypes of mice (*, P < .01). (B) Representative images of cremaster arterioles were taken from RhoG +/+ and RhoG -/- mice 30 min after the injury. As seen with the outline (arrows) of the thrombus formed, thrombus formation was inhibited in RhoG -/- mice. In conclusion, we show for the first time that RhoG is expressed and activated in platelets, plays an important role in GPVI/FcRγ-mediated platelet activation and is critical for thrombus formation in vivo. Disclosures: No relevant conflicts of interest to declare.

Platelet JNK1 is involved in secretion and thrombus formation

Blood ◽  
2010 ◽  
Vol 115 (20) ◽  
pp. 4083-4092 ◽  
Author(s):  
Frédéric Adam ◽  
Alexandre Kauskot ◽  
Paquita Nurden ◽  
Eric Sulpice ◽  
Marc F. Hoylaerts ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Thrombus Formation ◽  
Blood Perfusion ◽  
Collagen Matrix ◽  
In Vivo Model ◽  
Wild Type ◽  
Platelet Secretion

Abstract The role of c-Jun NH2-terminal kinase 1 (JNK1) in hemostasis and thrombosis remains unclear. We show here, with JNK1-deficient (JNK1−/−) mice, that JNK1 plays an important role in platelet biology and thrombus formation. In tail-bleeding assays, JNK1−/− mice exhibited longer bleeding times than wild-type mice (396 ± 39 seconds vs 245 ± 32 seconds). We also carried out in vitro whole-blood perfusion assays on a collagen matrix under arterial shear conditions. Thrombus formation was significantly reduced for JNK1−/− platelets (51%). In an in vivo model of thrombosis induced by photochemical injury to cecum vessels, occlusion times were 4.3 times longer in JNK1−/− arterioles than in wild-type arterioles. Moreover, in vitro studies carried out in platelet aggregation conditions demonstrated that, at low doses of agonists, platelet secretion was impaired in JNK1−/− platelets, leading to altered integrin αIIbβ3 activation and reduced platelet aggregation, via a mechanism involving protein kinase C. JNK1 thus appears to be essential for platelet secretion in vitro, consistent with its role in thrombus growth in vivo. Finally, we showed that ERK2 and another isoform of JNK affect platelet aggregation through 2 pathways, one dependent and another independent of JNK1.

scholarly journals Impaired Platelet Responses to Thromboxane a2 and Thrombin in Mice Lacking Receptor-Interacting Protein Kinase 3

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2762-2762
Author(s):  
Yiwen Zhang ◽  
Jian Zhang ◽  
Rong Yan ◽  
Jie Zhang ◽  
Mengxing Chen ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Protein Kinase ◽  
Conflicts Of Interest ◽  
Thrombus Formation ◽  
Thromboxane A2 ◽  
Dense Granule ◽  
In Vivo Model ◽  
Interacting Protein ◽  
Granule Secretion

Abstract Objective: Receptor-interacting protein 3 (RIP3) is a member of RIP family with a Ser/Thr protein kinase domain in its amino-terminus which is essential for kinase activity and autophosphorylation. The roles of RIP3 in embryonic development and different disease pathologies, such as inflammation and infections, have been reported in recent years. However, the role of RIP3 in thrombosis and hemostasis remains unknown. Methods: Hematologic analysis was performed and tail bleeding time was monitored. Mouse platelets were isolated from anti-coagulated whole blood. Platelet aggregation and secretion were recorded at real time. Platelet P-selectin exposure and specific fibrinogen binding were detected by flow cytometry. TXA2 generation was measured with enzyme immunoassay (EIA) kit. Protein phosphorylations were detected by western blotting. Result: RIP3-/- mice had tail-bleeding times that were significantly prolonged compared with their wild type littermates. In an in vivo model of mesenteric arteriole thrombosis, mice lacking RIP3 exhibited delayed thrombus formation, fewer accumulated platelets, smaller thrombi, and prolonged occlusion times. RIP3 was expressed in both human and mouse platelets. Deletion of RIP3 in mouse platelets caused a marked defect in aggregation and attenuated dense granule secretion in response to low doses of thrombin or a thromboxane A2 (TXA2) analogue, U46619. The defect in ADP secretion appears responsible for the impaired platelet aggregation, because addition of exogenous ADP rescued the reduced platelet aggregation. Although TXA2 generation and α-granule secretion were not impaired, integrin αIIbβ3 activation was attenuated in RIP3-/- platelets. Moreover, phosphorylation of Akt induced by U46619 or thrombin was markedly reduced in the absence of RIP3. Activation of Akt signaling restored the impaired aggregation of RIP3-/- platelets. ERK and p38 phosphorylation elicited by either U46619 or thrombin was attenuated in RIP3-/- platelets. In contrast, U46619- and thrombin-induced activation of PTEN, PDK1, or Src was not impaired in RIP3-/- platelets. Conclusion: Our data demonstrate a novel role for RIP3 in amplifying U46619- and thrombin-induced platelet activation by mediating Akt-dependent ADP secretion, and in supporting hemostasis and thrombus formation in vivo. RIP3 may represent a novel target to modulate PARs and TP signaling and a potential new target for antithrombotic strategy. Disclosures No relevant conflicts of interest to declare.

The Role of the VWF A1 and A2 Domains in Murine Models of TTP and Thrombosis.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3060-3060
Author(s):  
Jennifer Barr ◽  
Justin Barr ◽  
David Motto
Keyword(s):  
Thrombus Formation ◽  
Platelet Glycoprotein ◽  
Cysteine Residues ◽  
Wild Type ◽  
Domain Sequence ◽  
Initial Adhesion ◽  
A1 Domain ◽  
A2 Domain

Abstract Abstract 3060 Poster Board II-1036 von Willebrand Factor (VWF) is a large multimeric plasma glycoprotein synthesized in endothelial cells and megakaryocytes. In humans and mice, VWF dysfunction is associated both with defects in hemostasis, and with the systemic blood clotting disease thrombotic thrombocytopenic purpura (TTP). The initial adhesion of platelets to sites of vascular injury in large part involves binding of the VWF A1 domain to the platelet glycoprotein receptor GPIb alpha. This VWF A1-GPIb alpha interaction, along with deficiency of the ADAMTS13 plasma metalloprotease, is thought to be required for the pathogenesis of TTP. Deficiency of ADAMTS13 results in the failure to cleave the Y1605-M1606 sissile bond within the A2 domain of VWF. The structure of VWF is strongly influenced by its high content of cysteine residues, all of which are involved in inter-or intra-chain disulfide bonds. The location of these cysteine residues within the A domains leads to the formation of disulfide loops within the A1 (Cys 1272-1458) and A3 (Cys 1686-1872) domains, but not within the A2 domain. The lack of a disulfide loop allows the A2 domain to assume a “flexible” conformation that is thought to “open” in response to fluid shear stress, exposing the Y1605-M1606 bond to cleavage by ADAMTS13. To investigate specifically the role of the VWF A1-Gp1b alpha interaction in the context of otherwise functional VWF in vivo, we generated a chimeric murine VWF expression construct in which the murine A1 domain sequence is replaced with the corresponding sequence from human VWF (the human VWF A1 domain is known to not interact appreciably with murine GPIb alpha). Additionally, we engineered a VWF construct in which paired cysteine residues analogous to those in the A1 and A3 domains were introduced into the A2 domain sequence, with the goal being to “lock” the A2 domain closed and prevent cleavage by ADAMTS13. Hydrodynamic tail vein injection of both the VWF-hA1 and the VWF-A2 lock constructs into VWF-deficient mice resulted in plasma VWF levels up to 20-fold higher than observed in wild-type mice, dependent on the amount of plasmid injected. Importantly, the degree of VWF multimerization appeared nearly identical both to that observed in wild-type mice, and to mice injected with wild-type murine VWF, and expression persisted for approximately 30 days. Functionally, unlike WT murine VWF, expression of VWF-hA1 failed to restore thrombus formation in a ferric chloride-induced injury model, demonstrating the crucial importance of the VWF A1-GP1b apha interaction in thrombus formation. Currently we are investigating whether expression of VWF-hA1 can support disease pathogenesis in a mouse model of TTP. Similarly, we are determining whether expression of VWF-A2 lock leads to development of TTP, even in the presence of ADAMTS13. The ultimate goal of these studies is to completely “humanize” the VWF A1-GP1b alpha interaction in mice by replacing the murine GP1b alpha sequence with that from humans. These resulting animals will be used to further investigate the role of the VWF A1 domain-GPIb alpha interaction in vivo, and should prove useful for identifying compounds to effectively inhibit this interaction in humans. In addition, the expression of a VWF construct that is unable to be cleaved by ADAMTS13 should help to elucidate the role of VWF cleavage in TTP pathogenesis. Disclosures No relevant conflicts of interest to declare.

Biphasic Roles for the Soluble Guanylyl Cyclase (sGC) In Platelet Activation In Mice

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 486-486
Author(s):  
Guoying Zhang ◽  
Binggang Xiang ◽  
Radek C. Skoda ◽  
Susan S. Smyth ◽  
Xiaoping Du ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Guanylyl Cyclase ◽  
Conflicts Of Interest ◽  
Soluble Guanylyl Cyclase ◽  
Wild Type ◽  
No Donor ◽  
Cgmp Production ◽  
Deficient Mice

Abstract Abstract 486 The role of intracellular secondary messenger cGMP in platelet activation has been controversial, with both stimulatory and inhibitory roles reported. The platelet cGMP is believed to be predominantly synthesized by soluble guanylyl cyclase (sGC), which is activated by nitric oxide (NO). To specifically determine the role of sGC-dependent cGMP synthesis in platelet function and in vivo thrombosis and hemostasis, we produced mice harboring a “floxed” sGC beta1 allele. In the “floxed” sGC beta1 mice (sGC beta1fl/fl), the exons 7 and 8 of sGC beta1 gene and an inserted Neo cassette were flanked with three LoxP sites. Platelet-specific deletion of sGC beta1fl/fl allele was accomplished through breeding of the sGC beta1fl/fl mice with pf4-Cre recombinase transgenic mice. Immunoblotting showed the complete absence of this protein in sGC beta1fl/fl/Cre platelets. Mice lacking sGC beta1 in platelets appeared to develop normally and had normal blood counts, including platelets. Blood pressure of platelet-specific sGC deficient mice was comparable to that of wild-type littermates. Inactivating the sGC beta1 gene in platelets abolished cGMP production induced by either NO donors or platelet agonists that are known to activate endogenous NO synthesis, confirming that both the platelet agonist-induced and NO donor-induced platelet cGMP production are predominantly mediated by sGC. Platelets lacking sGC exhibit a marked defect in aggregation and secretion in response to low doses of platelet agonists, collagen and thrombin. Importantly, tail-bleeding times were significantly prolonged in the platelet-specific sGC deficient mice compared with the wild-type littermates. In a FeCl3-induced carotid artery thrombosis model, time to occlusive thrombosis was prolonged in the platelet-specific sGC deficient mice, compared to wild type littermates. Thus, the agonist-stimulated sGC activation is important in promoting platelet granule secretion and aggregation. On the other hand, NO donor SNP-induced inhibition of platelet activation was abolished in sGC-deficient platelets. However, at high concentrations (>100μM), SNP inhibited platelet activation in both wild type and sGC deficient mice, indicating that both cGMP-dependent and -independent mechanisms are involved in NO donor-induced inhibition of platelet activation. Together, our data demonstrate that sGC contributes to both agonist-induced platelet activation and NO donor-induced platelet inhibition. Disclosures: No relevant conflicts of interest to declare.

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