von Willebrand factor sialylation—A critical regulator of biological function

Authors: Soracha Ward | Jamie M. O’Sullivan | James S. O’Donnell

Published : J Thromb Haemost. April 2019;17:1018–1029.

Abstract: von Willebrand factor (VWF) undergoes complex post‐translational modification prior to its secretion into the plasma. Consequently, VWF monomers contain complex N‐glycan and O‐glycan structures that, together, account for approximately 20% of the final monomeric mass. An increasing body of evidence has confirmed that these carbohydrate determinants play critical roles in regulating multiple aspects of VWF biology. In particular, studies have demonstrated that terminal ABO blood group has an important effect on plasma VWF levels. This effect is interesting, given that only 15% of the N‐glycans and 1% of the O‐glycans of VWF actually express terminal ABO(H) determinants. In contrast, the vast majority of the N‐glycans and O‐glycans on human VWF are capped by terminal negatively charged sialic acid residues. Recent data suggest that sialylation significantly regulates VWF functional activity, susceptibility to proteolysis, and clearance, through a number of independent pathways. These findings are of direct clinical relevence, in that quantitative and qualitative variations in VWF sialylation have been described in patients with VWD, as well as in patients with a number of other physiologic and pathologic conditions. Moreover, platelet‐derived VWF is significantly hyposialylated as compared with plasma‐derived VWF, whereas the recently licensed recombinant VWF therapeutic is hypersialylated. In this review, we examine the evidence supporting the hypothesis that VWF sialylation plays multiple biological roles. In addition, we consider data suggesting that quantitative and qualitative variations in VWF sialylation may play specific roles in the pathogenesis of VWD, and that sialic acid expression on VWF may also differ across a number of other physiologic and pathologic conditions.