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 December 8, 2021.« Back to ISTH 2021 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/activation-mechanism-dependent-surface-exposure-of-cellular-fxiii-on-platelets-and-platelet-microparticles-immunofluorescence-and-immune-electron-microscopic-study/