The Adhesive Epidermal Growth Factor (EGF) Repeats of Platelet SCUBE1 Are Critical for Thrombus Formation

SCUBE1 (signal peptide‐CUB‐EGF domain‐containing protein 1) is the founding member of a secreted and member‐tethered SCUBE protein family. SCUBEs are composed of ~ 1,000 amino acids with 5 domains: an NH 2 ‐terminal signal peptide sequence, 9 tandem repeats of EGF‐like motifs, a large N‐glycosylated spacer region followed by 3 cysteine‐rich repeats and one CUB domain at the COOH terminus. We previously showed that SCUBE1, a plasma and platelet‐associated protein, might be involved in platelet‐platelet and platelet‐subendothelial matrix interactions through its adhesive EGF‐like motifs in vitro (Cardiovasc Res., 71:486–95, 2006), and genetic ablation of plasma SCUBE1 protected mice against thrombosis (Arterioscler Thromb Vasc Biol., 34:1390–8, 2014). However, whether the adhesive module of the EGF‐like repeats present in platelet SCUBE is essential for platelet adhesion and thrombosis remains largely unknown in vivo . Here, we generated a new mutant (Δ2) mice lacking the EGF‐like repeats to evaluate its functional importance in platelet biology in vivo . While the Δ2‐deficient mice had normal hematological parameters and expression of major platelet receptors, the Δ2 animals showed impaired platelet aggregation induced by ADP, collagen, and thrombin and protected against lethal thromboembolism. In flow chamber assay, washed Δ2 platelets showed marked decrease in its adhesion, aggregation and thrombus formation on collagen‐coated surface under arterial shear conditions. Most importantly, hematopoietic reconstitution of +/+ bone marrow into Δ2/Δ2 mice restore the platelet adhesive function and thrombus formation in vivo . Together, our data demonstrate for the first time that the platelet‐derived SCUBE1 plays a critical role in arterial thrombosis via its adhesive EGF‐like module in vivo , and suggest targeting these adhesive domains of SCUBE1 as potential anti‐thrombotic strategy.