Inhibition of collagen-induced platelet reactivity by DGEA peptide

Direct interactions between collagen, the most thrombogenic component of the extracellular matrix, and platelet surface membrane receptors mediate platelet adhesion and induce platelet activation and aggregation. In this process two glycoproteins are crucial: integrin alpha2beta1, an adhesive receptor, and GPVI, which is especially responsible for signal transduction. Specific antagonists of the collagen receptors are useful tools for investigating the complexity of platelet-collagen interactions. In this work we assessed the usefulness of DGEA peptide (Asp-Gly-Glu-Ala), the shortest collagen type I-derived motif recognised by the collagen-binding integrin alpha2beta1, as a potential antagonist of collagen receptors. We examined platelet function using several methods including platelet adhesion under static conditions, platelet function analyser PFA-100TM, whole blood electric impedance aggregometry (WBEA) and flow cytometry. We found that DGEA significantly inhibited adhesion, aggregation and release reaction of collagen activated blood platelets. The inhibitory effect of DGEA on static platelet adhesion reached sub-maximal values at millimolar inhibitor concentrations, whereas the specific blocker of alpha2beta1 - monoclonal antibodies Gi9, when used at saturating concentrations, had only a moderate inhibitory effect on platelet adhesion. Considering that 25-30% of total collagen binding to alpha2beta1 is specific, we conclude that DGEA is a strong antagonist interfering with a variety of collagen-platelet interactions, and it can be recognised not only by the primary platelet adhesion receptor alpha2beta1 but also by other collagen receptors.