Novel Function of Tenascin-C, a Matrix Protein Relevant to Atherosclerosis, in Platelet Recruitment and Activation Under Flow

Abstract

OBJECTIVE: The identification of platelet-reactive proteins exclusively present in atherosclerotic plaques could provide interesting targets for effective and safe antithrombotic strategies. In this context, we explored platelet adhesion and activation to tenascin-C (TN-C), a matrix protein preferentially found within atheroma. METHODS AND RESULTS: We show that platelets efficiently adhere to TN-C under both static and flow conditions. Videomicroscopy revealed a unique behavior under flow, with platelets exhibiting stationary adhesion to TN-C; in contrast, platelets rolled over von Willebrand factor and detached from fibrinogen. Platelet interaction with TN-C was predominantly supported by integrin α(2)β(1) under static conditions, whereas under high shear, it was dependent on both the α(2)β(1) integrin and the glycoprotein Ib-IX complex. Integrin α(IIb)β(3) appeared to play a secondary role but only at low shear rates. The glycoprotein Ib-IX-dependent interaction was indirect, relying on von Willebrand factor, and increased as a function of wall shear rate. Von Willebrand factor bound directly to TN-C, as shown by ELISA and coimmunoprecipitation, suggesting that it acts as a bridge between TN-C and platelets. The adhesion of platelets to TN-C triggered their activation, as demonstrated by a shape change and increases in intracellular calcium level. CONCLUSIONS: This study provides evidence that TN-C serves as a novel adhesive matrix for platelets in a context that is relevant to atherothrombosis.