A031 Développement d’un peptido-mimétique de la glycorpotein VI plaquettaire comme outil d’imagerie de la fibrose

ObjectifLa glycoprotéine VI est le récepteur d’activation des plaquettes par les collagènes de type I et de type III. Nous avons émis l’hypothèse que nous pourrions développer une sonde spécifique du collagène basée sur la spécificité de GPVI et que cette sonde permettrait de visualiser la fibrose in vivo par une méthode non invasive.MéthodesUn anticorps bloquant la liaison de GPVI au collagène a été utilisé pour cribler une banque peptidique permettant d’identifier un motif peptidique cyclique. La capacité du peptide à mimer la GPVI a été analysée par des études de liaison et de compétition en phase solide. La liaison au collagène tissulaire a été analysée par histochimie. L’imagerie in vivo a été réalisée par injection du peptide-marqué au Tc-99m dans un modèle de fibrose cicatricielle sur infarctus du myocarde chez le rat, scintigraphie et autoradiographieRésultatsLe peptide, nommé collagelin, se lie de manière spécifique à l’anticorps anti GPVI 9O12.2 et aux collagènes I et III in vitro et la liaison est inhibée par GPVI indiquant que le peptide mime GPVI. Cependant le collagelin n’inhibe pas l’agrégation des plaquettes induite par le collagène. Les études d’histochimie montrent que le collagelin se lie au collagène tissulaire sur coupe d’aorte et de queue de rat indiquant que le collagelin se comporte comme un traceur du collagène. Dans le modèle d’infarctus cicatriciel, une accumulation du collagelin radiomarqué est observée dans la zone cardiaque par scintigraphie planaire et tomographie chez les animaux avec MI mais pas chez les animaux contrôles ni avec un peptide contrôle. L’accumulation du traceur dans les zones de fibrose a été mise en évidence ex vivo par superposition des images d’autoradiographies et d’histologie sur coupes congelées.ConclusionNous avons produit un peptide qui mime en partie le site de liaison de GPVI au collagène. Ce peptide se comporte comme un traceur spécifique du collagène in vitro et in vivo. Nous proposons que ce traceur pourrait être utile pour le diagnostic et le suivi évolutif de la fibrose dans un grand nombre de pathologies

Coagulation factor XIIIa and activated protein C activate platelets via GPVI and PAR1

Platelet and coagulation activation are highly reciprocal processes. Activated platelets secrete several coagulation factors and expose phosphatidylserine, which supports the activation of coagulation factors. On the other hand, the coagulation cascade generates known ligands for platelet receptors, such as thrombin and fibrin. Coagulation factor (F)Xa, (F)XIIIa and activated protein C (APC) can also bind to platelets, but the functional consequences are unclear. Here, we investigated the effects of the activated (anti)coagulation factors on platelets, other than thrombin. Multicolor flow cytometry and aggregation experiments revealed that the ‘supernatant of (hirudin-treated) coagulated plasma’ (SCP) enhanced CRP-XL-induced platelet responses, i.e., integrin αIIbβ3 activation, P-selectin exposure and aggregate formation. We demonstrated that FXIIIa in combination with APC enhanced platelet activation in solution, and separately immobilized FXIIIa and APC resulted in platelet spreading. Platelet activation by FXIIIa was inhibited by blockade of glycoprotein VI (GPVI) or Syk kinase. In contrast, platelet spreading on immobilized APC was inhibited by PAR1 blockade. Immobilized, but not soluble, FXIIIa and APC also enhanced in vitro adhesion and aggregation under flow. In conclusion, in coagulation, factors other than thrombin or fibrin can induce platelet activation via GPVI and PAR receptors

Non-Invasive Molecular Imaging of Fibrosis Using a Collagen-Targeted Peptidomimetic of the Platelet Collagen Receptor Glycoprotein VI

Background: Fibrosis, which is characterized by the pathological accumulation of collagen, is recognized as an important feature of many chronic diseases, and as such, constitutes an enormous health burden. We need non-invasive specific methods for the early diagnosis and follow-up of fibrosis in various disorders. Collagen targeting molecules are therefore of interest for potential in vivo imaging of fibrosis. In this study, we developed a collagen-specific probe using a new approach that takes advantage of the inherent specificity of Glycoprotein VI (GPVI), the main platelet receptor for collagens I and III. Methodology/Principal: Findings An anti-GPVI antibody that neutralizes collagen-binding was used to screen a bacterial random peptide library. A cyclic motif was identified, and the corresponding peptide (designated collagelin) was synthesized. Solid-phase binding assays and histochemical analysis showed that collagelin specifically bound to collagen (Kd 10−7 M) in vitro, and labelled collagen fibers ex vivo on sections of rat aorta and rat tail. Collagelin is therefore a new specific probe for collagen. The suitability of collagelin as an in vivo probe was tested in a rat model of healed myocardial infarctions (MI). Injecting Tc-99m-labelled collagelin and scintigraphic imaging showed that uptake of the probe occurred in the cardiac area of rats with MI, but not in controls. Post mortem autoradiography and histological analysis of heart sections showed that the labeled areas coincided with fibrosis. Scintigraphic molecular imaging with collagelin provides high resolution, and good contrast between the fibrotic scars and healthy tissues. The capacity of collagelin to image fibrosis in vivo was confirmed in a mouse model of lung fibrosis. Conclusion/Significance: Collagelin is a new collagen-targeting agent which may be useful for non-invasive detection of fibrosis in a broad spectrum of diseases.Psycholog

Phosphorothioate backbone modifications of nucleotide-based drugs are potent platelet activators

Nucleotide-based drug candidates such as antisense oligonucleotides, aptamers, immunoreceptor-activating nucleotides, or (anti)microRNAs hold great therapeutic promise for many human diseases. Phosphorothioate (PS) backbone modification of nucleotide-based drugs is common practice to protect these promising drug candidates from rapid degradation by plasma and intracellular nucleases. Effects of the changes in physicochemical properties associated with PS modification on platelets have not been elucidated so far. Here we report the unexpected binding of PS-modified oligonucleotides to platelets eliciting strong platelet activation, signaling, reactive oxygen species generation, adhesion, spreading, aggregation, and thrombus formation in vitro and in vivo. Mechanistically, the platelet-specific receptor glycoprotein VI (GPVI) mediates these platelet-activating effects. Notably, platelets from GPVI function-deficient patients do not exhibit binding of PS-modified oligonucleotides, and platelet activation is fully abolished. Our data demonstrate a novel, unexpected, PS backbone-dependent, platelet-activating effect of nucleotide-based drug candidates mediated by GPVI. This unforeseen effect should be considered in the ongoing development programs for the broad range of upcoming and promising DNA/RNA therapeutics