BACKGROUND:
Human platelets contain matrix metalloproteinases (MMPs) that are secreted during platelet activation. Platelet MMPs have been implicated in the regulation of cellular activation and aggregation. Although the proaggregatory effect of MMP-2 has been demonstrated, the functional mechanism is not clearly understood.
OBJECTIVES:
This work was carried out in order to elucidate the biochemical mechanism of MMP-2-associated platelet activation and aggregation.
METHODS:
MMP-2 binding to the platelet surface was analyzed by flow cytometry. The cell surface target of MMP-2 was identified in thrombin receptor-activating peptide-stimulated platelets by immunoprecipitation, Western blotting and fluorescence microscopy. A recombinant hemopexin-like domain was used to characterize the nature of MMP-2 binding to the platelet surface. The functional significance of MMP-2 in platelet activation was investigated by quantitative measurements of the activation markers P-selectin (CD62P) and active alpha(IIb)beta(3). The role of MMP-2 in platelet aggregation was analyzed with an aggregometer.
RESULTS:
ProMMP-2 binds to integrin alpha(IIb)beta(3) in stimulated platelets in which proMMP-2 is converted into MMP-2. Fibrinogen was able to replace the alpha(IIb)beta(3)-bound MMP-2. The molecular interaction of MMP-2 and integrin alpha(IIb)beta(3) was abrogated by the recombinant human hemopexin-like domain of MMP-2, leading to reduced cell surface expression of activation markers CD62P and active alpha(IIb)beta(3), and resulting in suppressed platelet aggregation.
CONCLUSION:
This work clearly demonstrates that platelet activation and aggregation is regulated by MMP-2 that specifically interacts with integrin alpha(IIb)beta(3). The C-terminal hemopexin-like domain of MMP-2 is an essential element for binding to alpha(IIb)beta(3).
