Role of glycans in VWF biology and VWD pathogenesis

PROJECT SUMMARY: PROJECT 4 Partial quantitative deficiency of VWF accounts for approximately 70% of all cases of VWD. Previous studies have demonstrated that reduced plasma VWF levels (particularly mild to moderate reductions in the 30-50 IU/dL range) are commonly independent of the VWF gene on chromosome 12. Importantly, GWAS studies have also highlighted significant associations between plasma VWF-FVIII levels and a number of glyco-related genes. Critically however, although complex N- and O-linked carbohydrate determinants have been shown to influence multiple aspects of VWF biology (including biosynthesis, activation, proteolysis and clearance), the mechanisms through which specific glycans modulate these effects and contribute to VWD pathogenesis remain poorly understood. This project will investigate the role of VWF glycans in regulating VWF biology using a series of parallel strategies underpinned by unique clinical and genomic resources assembled through the previous Zimmerman PPG. Aim 1 will investigate the mechanisms through which N- and O-glycans regulate VWF biosynthesis and/or secretory pathways. Importantly, our preliminary studies suggest that alterations in both N-linked and O-linked glycans differentially modulate VWF biosynthesis within EC. In collaboration with clinical and genomic cores, we will specifically address the hypothesis that abnormalities in VWF glycosylation machinery play causal roles in VWD pathogenesis. In Aim 2, we will characterize the roles of glycans in regulating VWF activation and its functional properties. In particular, we will investigate the concept that O-glycans flanking the A1 domain within the recently described autoinhibitory module (AIM) region play important roles in regulating VWF activation and thereby influence functional activity and clearance. Finally, Aim 3 will focus on defining the mechanisms through which VWF glycosylation and activation influence its clearance through specific lectin and scavenger receptors. In addition, the importance of aberrant VWF glycosylation in the pathogenesis of VWD will also be investigated.