Variations in glycosylation of von Willebrand factor with O-linked sialylated T antigen are associated with its plasma levels

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Abstract
The glycosylation profile of von Willebrand factor (VWF) is known to strongly influence its plasma levels. VWF contains several carbohydrate structures, including O-linked glycans that primarily consist of sialylated T antigen (NeuAc(α2-3)Gal-(β1-3)-[NeuAc(α2-6)]GalNAc). It is not yet known whether O-linked carbohydrates affect VWF levels. We developed an immunosorbent assay based on neuraminidase incubation allowing subsequent binding of peanut agglutinin (PNA) to desialylated O-linked T antigen on VWF. An inverse relation was found between PNA binding and VWF antigen levels in healthy individuals (n = 111; Pearson rank = −0.43; P < .001). A similar inverse association was observed in randomly selected plasma samples from our diagnostic laboratory: 252% ± 125% for VWF levels less than 0.5 U/mL (n = 15); 131% ± 36% for VWF levels between 0.5 and 1.5 U/mL (n = 32); and 92% ± 40% for VWF levels more than 1.5 U/mL (n = 19). Reduced or increased PNA binding was also observed in patients with increased (liver cirrhosis) or reduced (von Willebrand disease [VWD] type 1) VWF antigen levels, respectively. VWD type 1 patients further displayed increased ratios of propeptide over mature VWF antigen levels (0.38 ± 0.18 versus 0.17 ± 0.03 for patients and controls, respectively; P < .001), which is indicative of reduced VWF survival in these patients. Of interest, a linear relation between PNA binding and propeptide/VWF ratio was observed (Spearman rank = 0.47), suggesting a potential association between O-linked glycosylation and VWF survival. Finally, we detected a marked decrease in PNA binding in post-DDAVP (1-deamino-8-D-arginine vasopressin) samples from various patients, indicating that the O-linked glycosylation profile of VWF stored in endothelial storage organelles may differ from circulating VWF.