Related Experiment Videos
Megakaryocyte hyperplasia and enhanced agonist-induced platelet activation in vasodilator-stimulated phosphoprotein
W Hauser1, K P Knobeloch, M Eigenthaler
1Institut für Klinische Biochemie und Pathobiochemie und, Josef-Schneider Strasse 2, 97080 Würzburg, Germany.
Abstract:
Vasodilator-stimulated phosphoprotein (VASP), a substrate of cAMP- and cGMP-dependent protein kinases, is associated with focal adhesions, cell-cell contacts, microfilaments, and highly dynamic membrane regions. VASP, which is expressed in most cell types and in particularly high levels in human platelets, binds to profilin, zyxin, vinculin, F-actin, and the Listeria monocytogenes surface protein ActA. VASP is a member of the enabled (Ena)/VASP protein family and is thought to be involved in actin filament formation and integrin alphaIIbbeta3 inhibition in human platelets. To gain further insight into the in vivo function of this protein, VASP-deficient mice were generated by homologous recombination. VASP-/- mice demonstrated hyperplasia of megakaryocytes in bone marrow and spleen but exhibited no other macroscopic or microscopic abnormalities. Activation of platelets with thrombin induced a more than 2-fold higher surface expression of P-selectin and fibrinogen binding in VASP-deficient platelets in comparison to wild type. These data support the concept that VASP is a negative modulator of platelet and integrin alphaIIbbeta3 activation. Although the limited phenotypic differences between wild-type and VASP-/- mice suggested functional compensation of VASP by members of the Ena/VASP family, alterations in the expression levels of mammalian enabled (Mena) and Ena-VASP-like (Evl) protein were not detected. VASP-deficient mice may provide an interesting model system for diseases in which enhanced platelet activation plays a major role.
Insights
Vasodilator-stimulated phosphoprotein (VASP) negatively regulates platelet activation. VASP-deficient mice show enhanced platelet responses, suggesting VASP
Area of Science:
- Molecular biology
- Cell biology
- Hematology
Background:
- Vasodilator-stimulated phosphoprotein (VASP) is a key protein involved in actin dynamics and cell adhesion.
- VASP interacts with various proteins, including actin and integrins, and is highly expressed in human platelets.
- The precise in vivo function of VASP, particularly in platelet activation, remains incompletely understood.
Purpose of the Study:
- To investigate the in vivo role of VASP in platelet function and overall physiology.
- To characterize the phenotype of VASP-deficient mice and their platelets.
Main Methods:
- Generation of VASP-deficient (VASP-/-) mice using homologous recombination.
- Analysis of VASP-/- mice for macroscopic and microscopic abnormalities.
- Assessment of platelet activation markers (P-selectin and fibrinogen binding) in VASP-/- platelets compared to wild-type.
Main Results:
- VASP-/- mice exhibited megakaryocyte hyperplasia in bone marrow and spleen without other apparent abnormalities.
- VASP-deficient platelets showed significantly increased P-selectin surface expression and fibrinogen binding upon thrombin activation.
- No alterations in the expression of related Ena/VASP family proteins (Mena, Evl) were detected in VASP-/- mice.
Conclusions:
- VASP acts as a negative modulator of platelet activation and integrin alphaIIbbeta3 activity.
- VASP-deficient mice represent a valuable model for studying diseases characterized by heightened platelet responsiveness.
- Functional compensation by other Ena/VASP family members does not appear to fully account for the observed platelet phenotype in VASP deficiency.