Defining the Role of Platelet ABO(H) Blood Group Antigens in Hemostasis and Thrombosis

Brigham And Women'S Hospital, Boston MA

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT Approximately one in three deaths results from hemorrhage (bleeding) or thrombosis (blood clots). ABO blood type is a major risk factor for hemorrhage or thrombosis. Type O individuals are at higher risk for bleeding than those with non-O blood types. Conversely, non-O individuals are at higher risk of thrombosis. The reason that blood type O is associated with a higher risk of bleeding and lower risk of thrombosis is incompletely understood. Several recent publications have suggested that differences in platelet function contribute to the increased bleeding risk in type O vs non-O individuals. Despite the clinical importance of ABO type as a risk factor for thrombosis and hemorrhage, the mechanism by which platelet ABO(H) blood group antigens impact hemostasis and thrombosis remains uncharacterized. Our central hypothesis is that ABO(H) antigens on functionally relevant platelet membrane glycoproteins impacts their binding to ligands. I will test this hypothesis via the following aims: AIM 1. Define the impact of ABO(H) glycans on platelet binding to Von Willebrand Factor (VWF). Our working hypothesis is that GPIb⍺ that is decorated with A or B antigen containing O-glycans will exhibit enhanced binding to VWF compared with type O(H) GPIb⍺. We will use enzyme-linked immunosorbent assays (ELISA) and surface plasmon resonance to quantify the binding kinetics of VWF to platelets of blood types O, A, B, and AB. AIM 2. Identify ABO(H) antigen carrying glycoproteins on platelets using a click chemistry enrichment strategy and mass spectrometry proteomics. Our working hypothesis is that there are dozens of functionally relevant platelet glycoproteins that carry the ABO(H) blood group antigens. We will use an innovative click chemistry strategy to selectively enrich H antigen carrying glycoproteins from platelet lysates, and identify these proteins using mass spectrometry proteomics. We will validate these hits using western blot, glycomics, and glycoproteomics. The successful completion of this project will provide mechanistic insight into how platelet ABO blood type affects binding to VWF and a comprehensive inventory of the glycoproteins and glycans on the platelet surface that carry ABO(H) antigens. This will provide unprecedented insight into platelet-intrinsic mechanisms underlying the well-known epidemiologic association between ABO blood type and risk of bleeding and clotting. This work will fill a critical knowledge gap in our understanding of why ABO blood type is associated with risk of bleeding and clotting, and provide a molecular framework that will facilitate future development of diagnostic tests and therapies to better predict, prevent, and manage thromboembolic disease and hemorrhage.