CLEC-2 contributes to hemostasis independently of classical hemITAM signaling in mice

C-type lectin-like receptor 2 (CLEC-2) is a platelet receptor that is critical during development in blood-lymph separation and implicated in thrombus stability in thrombosis and hemostasis. It is the only known platelet activatory receptor that participates in both of these aspects of platelet function, and it is the only one to signal through a hemi-immunoreceptor tyrosine-based activation motif (hemITAM). Current investigations into the function of CLEC-2 in vivo have focused on knockout (KO) studies in which both the receptor and its signaling are deleted, making it impossible to explore the possible signaling-independent functions of the receptor, which are indicated by its only known physiological ligand, podoplanin, being an integral membrane protein. In this report, we present a novel knockin mouse model that maintains the expression of a CLEC-2 receptor that cannot signal through its hemITAM (Y7A KI). Remarkably, this mouse phenocopies the blood-lymphatic mixing and lethality of CLEC-2 KO models, but not their hemostatic/thrombotic defect. However, treatment of Y7A KI mice with Fab' fragments of the function-blocking anti-CLEC-2 antibody, INU1, resulted in a thrombus formation defect in vivo and ex vivo, revealing a hemITAM signaling-independent role for CLEC-2 in hemostasis and thrombosis.