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Increased thrombin responsiveness in platelets from mice lacking glycoprotein V.
V Ramakrishnan1, P S Reeves, F DeGuzman
1COR Therapeutics, Inc., South San Francisco, CA, USA.
Summary
Glycoprotein V (GPV) normally inhibits platelet activation. Mice lacking GPV show enhanced responses to thrombin, indicating GPV acts as a negative regulator of platelet function.
Area of Science:
- Hematology
- Molecular Biology
- Biochemistry
Background:
- Glycoprotein (GP)V's role in platelet function is debated, with proposed roles in thrombin cleavage and GP Ib-IX expression.
- Previous studies suggested GPV involvement in platelet activation and GP Ib-IX surface expression.
Purpose of the Study:
- To investigate the function of GPV in platelet activation and GP Ib-IX expression.
- To determine the role of GPV in thrombin-induced platelet responses using a knockout mouse model.
Main Methods:
- Generation of GPV null mice (GPV -/-).
- Analysis of platelet size, GP Ib-IX expression, and von Willebrand factor binding in GPV -/- platelets.
- In vitro assessment of GPV -/- platelet aggregation and fibrinogen binding in response to thrombin.
- Evaluation of bleeding time in GPV -/- mice.
Main Results:
- GPV -/- platelets exhibited normal size and functional GP Ib-IX expression.
- GPV -/- platelets showed hyperresponsiveness to thrombin, with increased fibrinogen binding and aggregation.
- GPV -/- mice displayed a shorter bleeding time compared to wild-type mice.
- Absence of GPV defects in Bernard-Soulier syndrome was explained by normal GP Ib-IX-V function.
Conclusions:
- GPV acts as a negative modulator of platelet activation.
- Thrombin enhances platelet responsiveness through a mechanism independent of classical G-protein-coupled receptors.
- These findings reveal a novel regulatory pathway in platelet activation.