Study of blood platelet adhesion and activation mechanisms to identify safer antithrombotic targets

L’adhérence, l’activation et l’agrégation des plaquettes sanguines sont essentielles à l’hémostase mais peuvent également conduire à la thrombose artérielle sur plaque d’athérosclérose, aujourd’hui première cause de mortalité dans le monde. Les anti-thrombotiques actuels, dirigés contre l’activation et l’agrégation plaquettaires, ont une efficacité reconnue mais ont pour inconvénient d’augmenter le risque de saignement. L’objectif de cette thèse a été d’explorer de nouvelles stratégies réduisant la thrombose tout en préservant l’hémostase. L’utilisation de souris modifiées génétiquement a mis en évidence que l’intégrine alpha6 beta1, impliquée dans l’adhérence des plaquettes aux laminines, joue un rôle critique en thrombose expérimentale mais pas en hémostase. De plus, nous avons montré dans un système de perfusion de sang qu’une protéine préférentiellement exprimée dans les plaques d’athérosclérose, la ténascine-C, permet l’adhérence et l’activation des plaquettes. En revanche, la beta-arrestine-1, une protéine de signalisation, ne contribue que modestement aux fonctions plaquettaires et à la thrombose. En conclusion, ce travail a permis de dégager deux nouvelles pistes anti-thrombotiques potentiellement capables de préserver l’hémostase, basées sur le ciblage de l’intégrine alpha6 beta1 ou de l’interaction plaquette/ténascine-C.Following vascular injury, blood platelet adhesion, activation and aggregation are essential for hemostasis but can also lead to arterial thrombosis, which is a leading cause of death worldwide. Current antithrombotic drugs impede platelet activation and aggregation, thereby considerably reducing cardiovascular mortality, but their use is linked to an increased bleeding risk. This thesis aimed to explore more selective strategies causing minimal perturbation of hemostasis. The use of genetically-modified mice has revealed an unsuspected important contribution of integrin alpha6 beta1, which mediates platelet adhesion to laminins, to experimental arterial thrombosis but not hemostasis. In addition, we showed that tenascin-C, an extracellular matrix protein overexpressed in atherosclerotic plaques, can support platelet adhesion and activation under flow. In contrast, the signaling protein beta-arrestin-1 does not play a major role in platelet function, hemostasis and thrombosis. In conclusion, this work provides two interesting candidates, namely integrin alpha6 beta1 and tenascin-C, to put into practice the concept of targeting thrombosis while minimally impairing hemostasis

Etude des mécanismes d'adhérence et d'activation des plaquettes sanguines appliquée à l'identification de nouvelles cibles anti-thrombotiques plus sûres

Following vascular injury, blood platelet adhesion, activation and aggregation are essential for hemostasis but can also lead to arterial thrombosis, which is a leading cause of death worldwide. Current antithrombotic drugs impede platelet activation and aggregation, thereby considerably reducing cardiovascular mortality, but their use is linked to an increased bleeding risk. This thesis aimed to explore more selective strategies causing minimal perturbation of hemostasis. The use of genetically-modified mice has revealed an unsuspected important contribution of integrin alpha6 beta1, which mediates platelet adhesion to laminins, to experimental arterial thrombosis but not hemostasis. In addition, we showed that tenascin-C, an extracellular matrix protein overexpressed in atherosclerotic plaques, can support platelet adhesion and activation under flow. In contrast, the signaling protein beta-arrestin-1 does not play a major role in platelet function, hemostasis and thrombosis. In conclusion, this work provides two interesting candidates, namely integrin alpha6 beta1 and tenascin-C, to put into practice the concept of targeting thrombosis while minimally impairing hemostasis.L’adhérence, l’activation et l’agrégation des plaquettes sanguines sont essentielles à l’hémostase mais peuvent également conduire à la thrombose artérielle sur plaque d’athérosclérose, aujourd’hui première cause de mortalité dans le monde. Les anti-thrombotiques actuels, dirigés contre l’activation et l’agrégation plaquettaires, ont une efficacité reconnue mais ont pour inconvénient d’augmenter le risque de saignement. L’objectif de cette thèse a été d’explorer de nouvelles stratégies réduisant la thrombose tout en préservant l’hémostase. L’utilisation de souris modifiées génétiquement a mis en évidence que l’intégrine alpha6 beta1, impliquée dans l’adhérence des plaquettes aux laminines, joue un rôle critique en thrombose expérimentale mais pas en hémostase. De plus, nous avons montré dans un système de perfusion de sang qu’une protéine préférentiellement exprimée dans les plaques d’athérosclérose, la ténascine-C, permet l’adhérence et l’activation des plaquettes. En revanche, la beta-arrestine-1, une protéine de signalisation, ne contribue que modestement aux fonctions plaquettaires et à la thrombose. En conclusion, ce travail a permis de dégager deux nouvelles pistes anti-thrombotiques potentiellement capables de préserver l’hémostase, basées sur le ciblage de l’intégrine alpha6 beta1 ou de l’interaction plaquette/ténascine-C

Les anti-plaquettaires sans risque de saignement : nouvelles cibles et stratégies

Les médicaments anti-plaquettaires comme l’aspirine, le clopidogrel et les antagonistes de l’intégrine αIIbβ3 ont permis de réduire grandement la morbidité et la mortalité associées à la thrombose artérielle. Une limite majeure de ces agents est qu’ils augmentent le risque de saignement. Au cours des dernières années, plusieurs stratégies anti-thrombotiques innovantes, qui ne prolongeraient pas le temps de saignement, ont été proposées. Ces approches ciblent l’interaction entre la glycoprotéine (GP) VI et le collagène ou l’axe GPIb/facteur de von Willebrand, le récepteur PAR-1 de la thrombine, la forme activée d’αIIbβ3 ou le récepteur P2Y1 de l’ADP. Si un antagoniste de PAR-1 a récemment été commercialisé, les preuves cliniques de l’efficacité et de la sûreté des autres agents restent encore à´etablir. Cette revue examine ces nouvelles approches anti-plaquettaires potentiellement plus sûres

Platelet Integrins in Tumor Metastasis: Do They Represent a Therapeutic Target?

Platelets are small anucleated cell fragments that ensure the arrest of bleeding after a vessel wall injury. They are also involved in non-hemostatic function such as development, immunity, inflammation, and in the hematogeneous phase of metastasis. While the role of platelets in tumor metastasis has been recognized for 60 years, the molecular mechanism underlying this process remains largely unclear. Platelets physically and functionally interact with various tumor cells through surface receptors including integrins. Platelets express five integrins at their surface, namely α2β1, α5β1, α6β1, αvβ3, and αIIbβ3, which bind preferentially to collagen, fibronectin, laminin, vitronectin, and fibrinogen, respectively. The main role of platelet integrins is to ensure platelet adhesion and aggregation at sites of vascular injury. Two of these, α6β1 and αIIbβ3, were proposed to participate in platelet–tumor cell interaction and in tumor metastasis. It has also been reported that pharmacological agents targeting both integrins efficiently reduce experimental metastasis, suggesting that platelet integrins may represent new anti-metastatic targets. This review focuses on the role of platelet integrins in tumor metastasis and discusses whether these receptors may represent new potential targets for novel anti-metastatic approaches

β-arrestin-1 participates in thrombosis and regulates integrin aIIbβ3 signalling without affecting P2Y receptors desensitisation and function.: Role of β-arrestins in platelet function

International audienceβ-arrestin-1 (β-arr1) and β-arrestin-2 (β-arr2) are cytosolic proteins well-known to participate in G protein-coupled receptor desensitisation and signalling. We used genetically-inactivated mice to evaluate the role of β-arr1 or β-arr2 in platelet function, P2Y receptor desensitisation, haemostasis and thrombosis. Platelet aggregation, soluble fibrinogen binding and P-selectin exposure induced by various agonists were near normal in β-arr1-/- and β-arr2-/- platelets. In addition, deficiency in β-arr1 or β-arr2 was not critical for P2Y receptors desensitisation. A functional redundancy between β-arr1 and β-arr2 may explain these unchanged platelet responses. Interestingly, β-arr1-/- but not β-arr2-/- mice were protected against laser- and FeCl3-induced thrombosis. The tail bleeding times, number of rebleeds and volume of blood loss were unchanged in β-arr1-/- and β-arr2-/- mice, suggesting no defect in haemostasis. β-arr1-/- platelet activation upon adhesion to immobilised fibrinogen was inhibited, as attested by a 37 ± 5% (n = 3, p<0.0001) decrease in filopodia extension, suggesting defective signalling through integrin αIIbβ3. β-arr1 appeared to be located downstream of Src family kinases and to regulate αIIbβ3 signalling by increasing Akt phosphorylation. Overall, this study supports a role for β-arr1 in promoting thrombus formation, in part through its participation in αIIbβ3 signalling, and no role of β-arr1 and β-arr2 in agonist-induced platelet activation and P2Y receptors desensitisation

Diagnosis and management of hepatic focal nodular hyperplasia

Focal nodular hyperplasia (FNH) is the second most common benign tumor of the liver, after hemangioma. It is generally found incidentally and is most common in reproductive-aged women, but it also affects males and can be diagnosed at any age. Patients are rarely symptomatic, but FNH sometimes causes epigastric or right upper quadrant pain. The main clinical task is to differentiate it from other hypervascular hepatic lesions such as hepatic adenoma, hepatocellular carcinoma, or hypervascular metastases, but invasive diagnostic procedures can generally be avoided with the appropriate use of imaging techniques. Magnetic resonance (MR) imaging is more sensitive and specific than conventional ultrasonography (US) or computed tomography (CT), but Doppler US and contrast-enhanced US (CEUS) can greatly improve the accuracy in the diagnosis of FNH. Once a correct diagnosis has been made, in most cases there is no indication for surgery, and treatment includes conservative clinical follow-up in asymptomatic patients. \ua9 2007 Elsevier Masson. All rights reserved