Abstract EN:

Under high shear rate conditions, the binding of the platelet GPIb-V-IX complex to the von Willebrand Factor (vWF) ensures platelet adhesion and initiation of activation at sites of vascular lesion. This interaction triggers an intracellular signaling leading to platelet shape change (filopodia extensions) and integrin GPIIb-IIIa activation necessary for stable adhesion and platelet aggregation. This activation pathway is not fully characterized but it is likely to involve adaptor proteins associated to the cytoplasmic domains of the complex. In order to establish a functional map of the GPIb-V-IX intracellular regions, two approaches were followed: i) the effects, in intact platelets, of peptides corresponding to the cytoplasmic part of the GPIba subunit coupled to a Cell-Penetrating-Peptide were studied. The GPIba 557-559 region was found to be important for platelet adhesion and filopodia emission on a vWF matrix; ii) experiments in CHO cells transfected with a GPIb-V-IX complex containing mutation of the GPIba or GPIbb intracellular domains identified the GPIbb 150-170 segment as an important region for GPIb-mediated signaling responsible for filopodia production on vWF. Finally, an immunoprecipitation strategy coupled to mass spectrometry analysis identified of cyclophilin A as a new intracellular partner of the GPIb-V-IX complex. In conclusion, this work points to two functional regions within the GPIba and GPIbb cytoplasmic regions and identified a new intracellular partner. These three elements are potential targets to prevent activation induced by the binding of vWF to the GPIb-V-IX complex.