Background: Atherosclerosis is characterized as inflammation of the endothelial vessel wall leading to plaque formation and eventually causing cardiovascular complications. Platelet-derived extracellular vesicles (PEVs) and chemokines are known to upregulate the inflammatory state, leading to an acceleration of plaque formation. PEVs and chemokines can mediate communication and interactions between endothelial and immune cells, which implies direct interactions of PEVs and even uptake by these cells. However, the molecular mechanisms of adhesion and uptake and their functional consequences of the recipient cells remain unclear.

Aims: The characterisation of the uptake of PEVs and chemokines by endothelial cells and the functional consequences.

Methods: PEVs were isolated by centrifugation from platelet concentrates. Chemokines CCL5 and CXCL4 were expressed and purified from E. coli. PEV internalisation of Alexa-Fluor 488 anti-CD41 labelled PEVs was assessed during incubation of HUVECS for 12 hours and imaged by multicolour fluorescence microscopy. Changes in cytosolic [Ca2+] in Fluo-4-loaded HUVECs were recorded for 10 min, using a Zeiss LSM 510 confocal microscope. Monocyte adhesion was performed with Syto-13-labelled THP-1 cells and perfused over differently treated HUVECs.

Results: HUVEC cells appeared to take-up PEVs, which was increased when F-actin polymerisation was inhibited. Interestingly, PEV uptake was not affected after dynamin endocytosis was inhibited. PEVs or chemokines caused repetitive oscillatory transients in cytosolic Ca²⁺ signalling of HUVECs, in agreement with G-protein coupled receptor signalling. In addition, monocyte adhesion on TNF-α treated HUVECS was increased and further significantly stimulated by addition of PEVs or chemokines.

Conclusions: PEV uptake by endothelial cells is regulated via a cytoskeletal mechanism and might not be controlled by dynamin.
Monocyte adhesion and intracellular calcium responses of endothelial cells are increased by PEV and chemokines.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/mechanisms-and-functional-consequences-of-platelet-derived-extracellular-vesicle-and-chemokine-internalisation-by-endothelial-cells/