Involvement of platelet αIIbβ3 integrin and downstream signalling pathways in release of extracellular vesicles, CXCL4 and CCL5

• Published in: Journal of extracellular vesicles 2018-01, Vol.7, p.164-164
• Main Authors: Heinzmann, Alexandra C A, Vajen, Tanja, Meulendijks, Nicole M M, Suylen, Dennis P L, Cosemans, Judith M E M, Heemskerk, Johan W M, Hackeng, Tilman M, Koenen, Rory R
• Format: Article
• Language: English
• Subjects: Calpain; Chemokines; Collagen; Cytoskeleton; Extracellular vesicles; Inflammation; Nanoparticles; Platelets; Prothrombinase; Signal transduction; Src protein; Thrombin; Thrombin receptors; Thrombosis; Ultracentrifugation
• ISSN: 2001-3078

Background: Platelets play essential roles in haemostasis and thrombosis, and are important in inflammation and immunity. These functions are mediated by the presence of bioactive molecules in platelet interior, which are secreted upon activation. Chemokines CCL5 and CXCL4 are stored in platelet a-granules, and become released by stimulation of thrombin or collagen receptors. During prolonged storage and after activation, platelets can also shed extracellular vesicles (EVs), which modulate haemostatic and inflammatory processes. The aim of this study was to compare the release mechanisms of EVs and chemokines in activated platelets. Methods: Isolated platelets were activated with convulxin or thrombin for 30 min at 37°C. Isolation of EVs was performed with ultracentrifugation at 20,000 g for 1 h at 4°C. Chemokines were found in the supernatant and EVs were present in the pellet. Release of chemokines was measured by immunoassays, while release of EVs was quantified by measuring their phosphotidylserine content (prothrombinase assay) and nanoparticle tracking analysis. Investigation of different aspects of aIIbß3 integrin and associated outside-in signalling was performed by treatment of platelets prior to activation with different inhibitors. Results: Stimulation of collagen and/or thrombin receptors with convulxin and thrombin resulted in a robust release of EVs and CCL5 and CXCL4. Release of EVs, but not of chemokines, was abrogated by inhibiting cytoskeletal rearrangement and blocking integrin aIIbß3 with eptifibatide. Whereas blockade of c-Src only weakly affected EV release, it could be inhibited by blockade of Ga13. Neither blockade of cSrc nor of Ga13 influenced release of chemokines. To further investigate aIIbß3-associated signalling, calpain and PTPN1 were blocked upon platelet activation. Inhibition of calpain significantly reduced EV release, yet increased chemokine secretion. In addition, PTPN1 inhibitor also resulted in decreased EV release, yet showed only minor effects on chemokine release. Summary/Conclusion: This study set out to examine the involvement of aIIbß3 integrin and outside-in signalling events in platelet EV and chemokine release. The current data highlight the importance of aIIbß3 integrin in EV release by activated platelets, while chemokine secretion appears to be governed by the inside-out signalling pathway.