Type 2B VWD substitutions trigger enhanced macrophage-mediated clearance that is attenuated by the BT200 aptamer

Abstract

Type 2B von Willebrand disease (VWD) is characterized by missense variants in exon 28 of the von Willebrand factor (VWF) gene that encodes the VWF-A1 domain. These missense mutations result in single amino acid residue substitutions that cause activation of VWF-A1 and promote spontaneous interaction with platelet GPIba;. Importantly, enhanced VWF clearance has been shown to play a key pathogenic role in >90% patients with Type 2B VWD. Although this VWF clearance occurs via mechanisms that are independent of VWF-platelet complex formation, the biological mechanisms responsible for the increased clearance of type 2B VWD variants remain poorly understood. In this study, we investigated a series of different type 2B amino acid substitutions within the VWF-A1 domain (R1306W, R1308C, W1313C and R1379L). We demonstrate that these variants all exhibit significantly increased macrophage binding. In part, the enhanced macrophage interactions are mediated via increased binding of type 2B VWD variants to LRP1 extracellular cluster II and IV. Our findings further demonstrate that the K1405-K1408 lysine cluster in the VWF-A1 domain plays a key role in enabling enhanced LRP1 interactions for type 2B VWD variants. In addition, we show that type 2B VWF variants demonstrate significantly enhanced interaction with the macrophage MGL receptor. Finally, and importantly from a clinical perspective, we demonstrate that the increase in macrophage binding for type 2B variants is significantly attenuated in the presence of BT200. Collectively, our findings have direct translational relevance with respect to the clinical heterogeneity and treatment of type 2B VWD.