Fut2^−/− (Non-Secretor) Mice Exhibit High Vwf Levels.

Abstract 2184

Levels of the critical adhesive glycoprotein von Willebrand Factor (VWF) are widely variable in human populations. Two-thirds of VWF variation is heritable, of which one-third is due to the carbohydrate blood group ABO. Another closely related carbohydrate blood group, Secretor (FUT2), has also been reported to influence VWF levels, but this association is controversial. In humans, FUT2 nonsense mutations are common and result in the loss of FUT2 enzyme activity and the absence of Lewis and ABH sugars in mucosal secretions, hence the designation of FUT2 null individuals as “non-Secretors”. The FUT2 (Secretor) fucosyltransferase makes H antigen (fucalpha1à2betagal) in mucosal tissues, which can subsequently be fucosylated by other Lewis enzymes (FUT3, FUT6, etc.) to generate the variations within the Lewis blood groups system, or serve as a substrate for the ABO glycosyltransferase to generate ABH structures. To investigate the hypothesis that Secretor influences VWF, we examined Vwf levels in Fut2 knock-out (non-Secretor) mice. The Fut2 knock-out mouse line backcrossed >20 generations to C57BL6/J was recovered from cryopreserved stock at the Jackson Laboratory. Eight to 12 week old male mice were selected for study to avoid the potential effects of estrous and aging on Vwf levels. Platelet-poor plasma was obtained from Fut2^−/− (non-Secretor, n=7) and their Fut2^+/+ (Secretor, n=5) littermates and assayed for Vwf antigen (Vwf:Ag) by sandwich ELISA using polyclonal anti-VWF antibodies [rabbit anti-human VWF (Dako); sheep anti-human VWF (Abcam)] and a pooled C57BL6/J plasma standard. Non-Secretor (Fut2^−/−) animals exhibited Vwf:Ag levels nearly double those of their Secretor (Fut2^+/+) littermates (p<0.01, Table 1). These data show that Secretor (Fut2) plays a significant role in VWF homeostasis in mice, consistent with previous reports suggesting that human Secretors have lower VWF levels than non-Secretors. We speculate that the large effect size of Fut2 on Vwf:Ag observed in this study is due to the absence of the confounding effects of variation in ABO and vascular H expression common amongst humans. Though Fut2 is expressed primarily at mucosal surfaces, FUT2-derived H antigen is thought to be transferred to red cells via adsorption of glycolipids. This work offers new clues into the complexities of VWF homeostasis by implicating carbohydrate-dependent mechanisms other than those of classical intracellular ER-golgi post-translational glycosylation as a means to influence VWF.