Browsing by Subject "platelets"

Extracellular vesicles (EVs) are phospholipid bilayer-enclosed nanoparticles that are secreted by eukaryotic and prokaryotic cells. EVs carry macromolecules and signalling molecules to adjacent cells and play an important role in intercellular communication under both pathologic and homeostatic conditions. Therefore, they have become of significant interest for their therapeutic, diagnostic and prognostic potential. EVs are small and highly heterogeneous in size, shape, cargo and membrane composition, posing several challenges for establishing analytical and clinical guidelines. Therefore, EV research requires standardized and robust methods for their separation and characterization. In this study physical and immunochemical methods were employed to characterize human platelet-derived EVs (pEVs) generated from platelets activated with different external biochemical stimuli. The platelet-activating effect of the pro-inflammatory S100A8/A9 protein complex and a combination of thrombin and collagen were studied with nano flow cytometry. The size distribution of pEVs was studied with nanoparticle tracking analysis (NTA) and asymmetrical flow field-flow fractionation (AF4), which represents a newly emerging method on the EV field. Finally, fluorescent labelling and co-localization analysis were employed to characterize membrane marker composition of pEVs and assess its usefulness as an analytic tool for EV research. We succeeded in providing new hints towards meaningful discoveries in platelet biology by characterizing the way platelets respond to inflammatory and hemostatic signals by shedding pEVs. When platelet activation markers are characterized with flow cytometry, the S100A8/A9 protein appeared to cause a shift in membrane activation markers when compared to the thrombin- collagen mix and the baseline control. Increased TLT-1 translocation and decreased integrin αIIbβ3 expression on pEV surfaces suggests that S100A8/A9 induced pEV secretion through differently packed platelet α-granules, rather than from the plasma membrane. An increase in TLT-1 expression compared to decreased P-selectin and αIIbβ3 suggests that S100A8/A9 stimulation shifts platelet phenotype towards secretion rather than aggregation. A protocol for small pEV separation with AF4-MALS was set up. With this method, subtle differences between small pEV populations were seen that were not distinguishable with NTA or flow cytometry. When investigated with AF4-MALS, S100A8/A9 induced pEVs appeared larger than those produced with thrombin- collagen activation. The mean particle sizes of the pEV populations obtained from activated platelets were generally also larger than those produced without an activator. We tested novel methods to detect subtle differences in small EV population sizes that are easily missed with conventional methods due to their technical limitations. A well-optimised AF4 protocol can detect different pEV subpopulations and is a promising tool for EV. In the future, when AF4 is combined with a MALS detector and a fraction collector, nanoimaging of fluorescently labelled EVs could be combined with it as a downstream application to obtain information on their versatile biological functions.