The contribution of glycoprotein VI to stable platelet adhesion and thrombus formation illustrated by targeted gene deletion Running head: A Platelet GP VI Knockout

Platelet interaction with exposed adhesive ligands at sites of vascular injury is required to initiate a normal hemostatic response and may become a pathogenic factor in arterial diseases leading to thrombosis. We report a targeted disruption in a key receptor for collagen-induced platelet activation, glycoprotein (GP) VI. The breeding of mice with heterozygous GP VI alleles produced the expected frequency of wild-type, heterozygous and homozygous genotypes, indicating that these animals had no reproductive problems and normal viability. GP VI platelets failed to aggregate in response to type I fibrillar collagen or convulxin, a snake venom protein and known platelet agonist of GP VI. Nevertheless, tail bleeding time measurements revealed no severe bleeding tendency as a consequence of GP VI deficiency. Ex vivo platelet thrombus formation on type I collagen fibrils was abolished using blood from either GP VI or FcR-γnull animals. Reflection interference contrast microscopy revealed that the lack of thrombus formation by GP VI platelets could be linked to a defective platelet activation following normal initial tethering to the surface, visualized as lack of spreading and less stable adhesion. These results illustrate the role of GP VI in post-adhesion events leading to the development of platelet thrombi on collagen fibrils. For personal use only. on April 13, 2017. by guest www.bloodjournal.org From