R1205H (Vicenza) causes conformational changes in the von Willebrand factor D′D3 domains and enhances von Willebrand factor binding to clearance receptors LRP1 and SR-AI

Backgroundvon Willebrand factor (VWF)-R1205H variant (Vicenza) results in markedly enhanced VWF clearance in humans that has been shown to be largely macrophage-mediated. However, the biological mechanisms underlying this enhanced clearance remain poorly understood.ObjectivesThis study aimed to investigate the roles of (i) specific VWF domains and (ii) different macrophage receptors in regulating enhanced VWF-R1205H clearance.MethodsIn vivo clearance of full-length and truncated wild-type (WT)-VWF and VWF with R1205 substitutions was investigated in VWF−/− mice. Plate-binding assays were employed to characterize VWF binding to purified scavenger receptor class A member 1 (SR-AI), low-density lipoprotein receptor–related protein-1 (LRP1) cluster II or cluster IV receptors, and macrophage galactose-type lectin.ResultsIn full-length VWF missing the A1 domain, introduction of R1205H led to significantly enhanced clearance in VWF−/− mice compared with WT-VWF missing the A1 domain. Importantly, R1205H in a truncated VWF-D′D3 fragment also triggered increased clearance compared with WT-VWF-D′D3. Additional in vivo studies demonstrated that VWF-R1205K (which preserves the positive charge at 1205) exhibited normal clearance, whereas VWF-R1205E (which results in loss of the positive charge) caused significantly enhanced clearance, pinpointing the importance of the positive charge at VWF-R1205. In vitro plate-binding studies confirmed increased VWF-R1205H interaction with SR-AI compared with WT-VWF. Furthermore, significantly enhanced VWF-R1205H binding to LRP1 cluster IV (P < .001) and less marked enhanced binding to LRP1 cluster II (P = .034) was observed. In contrast, VWF-R1205H and WT-VWF demonstrated no difference in binding affinity to macrophage galactose-type lectin.ConclusionDisruption of the positive charge at amino acid R1205 causes conformational changes in the VWF-D′D3 domains and triggers enhanced LRP1-mediated and SR-AI–mediated clearance.