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Activation Mechanism Dependent Surface Exposure of Cellular FXIII on Platelets and Platelet Microparticles: Immunofluorescence and Immune Electron Microscopic Study

L. Somodi1, H. Bárdos2, I. Beke Debreceni3, G. Kis4, J. Kappelmayer3, M. Antal4, L. Muszbek1

1University of Debrecen, Faculty of Medicine/Department of Laboratory Medicine, Division of Clinical Laboratory Science, Debrecen, Hungary, 2University of Debrecen, Faculty of Medicine, Department of Public Health and Epidemiology, Debrecen, Hungary, 3University of Debrecen, Faculty of Medicine/Department of Laboratory Medicine, Debrecen, Hungary, 4University of Debrecen, Faculty of Medicine/Department of Anatomy, Histology and Embryology, Debrecen, Hungary

Abstract Number: LPB0017

Meeting: ISTH 2021 Congress

Theme: Fibrinogen, Fibrinolysis and Proteolysis » Fibrinogen and Factor XIII

Background: The cellular form of coagulation factor XIII (cFXIII) is a dimer of two potentially active A subunits (FXIII-A2). cFXIII is of cytoplasmic localization and amounts to 3% of the total platelet protein. Coinciding activation of platelet collagen and the PAR1 receptor by convulxin (CVX) and thrombin (THR) transpose cFXIII (Mitchell et al. Blood 2014;124:3982-90) and phosphatidylserine (PS) to the surface of activated platelets.

Aims: To compare the surface exposure of cFXIII and PS on platelets undergoing receptor-mediated (CVX+THR) and non-receptor-mediated (Ca2+-ionophore) activation and on platelet microparticles shed from activated cells.

Methods: Gel-filtered platelets were stimulated by CVX+THR or Ca2+-ionophore (A23187). Platelets and platelet derived MPs were identified by anti-CD41a antibodies. In immunfluorescent studies FXIII-A was labeled by rabbit anti-human FXIII-A and DyLight 488-labeled horse anti-rabbit IgG, annexin V was conjugated to Alexa Fluor 568. For double immunogold labeling rabbit anti-FXIII-A and mouse anti-CD41a were followed by goat-anti-rabbit IgG conjugated to 15 nm gold particles and goat-anti-mouse IgG conjugated to 10 nm gold particles.

Results: Following activation by CVX+THR in over half of platelets and platelet MPs PS and cFXIII became transposed to the outer membrane surface. The majority of PS-positive MPs also showed FXIII-A positivity. Most of the surface exposed cFXIII accumulated in a cap-like structure. Larger microparticle with intact CD41a positive membrane showed weak FXIII positivity while smaller particles were CD41a negative and strongly labeled for cFXIII. Non-receptor mediated activation triggered by Ca2+-ionophore resulted PS positive platelets and MPs, however neither the cells nor the formed MPs expressed FXIII-A on their surface.

Conclusions: Surface exposure of PS and cFXIII on both platelets and microparticles was induced by receptor-mediated activation. Transposition of PS and cFXIII to the membrane surface requires different mechanisms. Elevation of intracellular Ca2+concentration is sufficient for PS transposition but insufficient to expose cFXIII.

To cite this abstract in AMA style:

Somodi L, Bárdos H, Beke Debreceni I, Kis G, Kappelmayer J, Antal M, Muszbek L. Activation Mechanism Dependent Surface Exposure of Cellular FXIII on Platelets and Platelet Microparticles: Immunofluorescence and Immune Electron Microscopic Study [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/activation-mechanism-dependent-surface-exposure-of-cellular-fxiii-on-platelets-and-platelet-microparticles-immunofluorescence-and-immune-electron-microscopic-study/. Accessed October 1, 2023.

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