Related Experiment Videos
Platelet-derived microparticle formation involves glycoprotein IIb-IIIa. Inhibition by RGDS and a Glanzmann's
C H Gemmell1, M V Sefton, E L Yeo
1Department of Medicine, University of Toronto.
Abstract:
While the physiologic role of platelet microparticles may include a stable, physical dispersion of concentrated surface procoagulant activity the mechanism(s) of platelet vesiculation remains unknown. We demonstrate using flow cytometric methods a central role for the beta 3 integrin glycoprotein (GP) IIb-IIIa complex and its ligand tetrapeptide Arg-Gly-Asp-Ser (RGDS) binding site in platelet vesiculation. Time- and calcium-dependent vesiculation of platelets in response to ADP, collagen, thrombin, phorbol myristate acetate, and the thrombin peptide SFLLRN were dramatically inhibited, in a concentration-dependent manner, by monoclonal antibodies to GPIIb-IIIa (A2A9, 7E3, PAC1) and RGDS. Complete inhibition with A2A9 and RGDS occurred at 7.5 micrograms/ml and 75 microM, respectively, while control antibodies and a mock peptide had no effect. Platelet vesiculation requires intact GPIIb-IIIa and is fully supported by the intracellular pool of GPIIb-IIIa alone since de-complexing of this heterodimer by calcium chelation completely abolished microparticle formation in response to collagen (no alpha-granule release) but not to thrombin or SFLLRN. A central role for GPIIb-IIIa is supported by the near total inability of Glanzmann's thrombasthenic (type I) platelets to vesiculate in response to thrombin, ADP, collagen, and phorbol 12-myristate 13-acetate. This extends the biologic roles of GPIIb-IIIa to include platelet vesiculation and suggests that one or all of its binding ligands play a role.
Insights
Platelet vesiculation, the formation of microparticles, is crucial for blood clotting. This study reveals that the glycoprotein (GP) IIb-IIIa complex and its binding site are central to this process.
Area of Science:
- Hematology
- Cell Biology
- Biochemistry
Background:
- Platelet microparticles are implicated in hemostasis and thrombosis.
- The precise mechanisms driving platelet vesiculation remain poorly understood.
Purpose of the Study:
- To elucidate the role of the glycoprotein (GP) IIb-IIIa complex and its ligand binding site in platelet vesiculation.
Main Methods:
- Flow cytometry was employed to assess platelet vesiculation.
- Inhibition studies utilized monoclonal antibodies against GPIIb-IIIa and the tetrapeptide Arg-Gly-Asp-Ser (RGDS).
- Experiments included calcium chelation and analysis of Glanzmann's thrombasthenic platelets.
Main Results:
- Platelet vesiculation induced by various agonists (ADP, collagen, thrombin, PMA, SFLLRN) was significantly inhibited by anti-GPIIb-IIIa antibodies and RGDS.
- Complete inhibition of vesiculation was observed with specific concentrations of A2A9 and RGDS.
- Calcium chelation abolished collagen-induced vesiculation, while thrombin/SFLLRN-induced vesiculation was less affected, indicating reliance on intact GPIIb-IIIa.
- Glanzmann's thrombasthenic platelets exhibited a near-complete inability to vesiculate.
Conclusions:
- The glycoprotein (GP) IIb-IIIa complex and its ligand binding site play a central role in platelet vesiculation.
- Intact GPIIb-IIIa is essential for microparticle formation, with contributions from both surface and intracellular pools.
- These findings expand the known functions of GPIIb-IIIa and suggest ligand involvement in platelet vesiculation.