Abstract Number: PB0920
Meeting: ISTH 2021 Congress
Background: In our cohort of von Willebrand disease (VWD) patients, we found four missense substitutions located either in the A1 domain linker (p.Cys1227Arg), A1 region (p.Leu1288Arg and p.Leu1340Arg), or A2 domain (p.Val1524Gly).
Aims: This study aimed to characterize the impact of these missense variants on VWF conformations, biosynthesis, and functions.
Methods: The full-length wild-type (wt) or mutant VWF cDNA were expressed in HEK293T cells. Quantitative and qualitative assessments (GPIbα binding and multimer analysis) of the VWF secreted into the medium were performed. The structural impact of the VWF variants was assessed by homology modeling.
Results: Homozygous expression of the p.Cys1227Arg and p.Val1288Arg demonstrated a substantial reduction in VWF secretion, 18.7% and 33.5% of wt, respectively, with loss of large multimers. The co-transfection of the p.Cys1227Arg/wt improved the expression but still showed reduced secretion and loss of large multimers. However, co-transfection of the p.Leu1288Arg/wt corrected secretion and multimer profile but still showed diminished binding to GPIbα. The homozygous and heterozygous expression of the variant p.Leu1340Arg showed only a slight reduction in VWF secretion, 77% and 81% of wt, respectively, but impaired binding to GPIbα severely. Interestingly, the p.Val1524Gly did not affect VWF secretion in both single and co-expression studies but showed multimers with triplet structures (and loss of large multimers), which could be cleaved by endogenously produced ADAMTS13 in HEK293T. Homology modeling showed that p.Val1524G, result in easier access of the ADAMTS13 cleavage site by facilitating the unfolding of the A2 domain.
Conclusions: We demonstrated that variants p.Cys1227Arg and p.Val1288Arg affected the multimerization and secretion, besides interfering with platelet binding, whereas variant p.Leu1340Arg impaired the binding to GPIbα, but did not affect the multimerization markedly. Furthermore, we showed the gain of function variant p.Val1524Gly in the A2 domain caused a structural alignment that leads to the accessibility of the ADAMTs13 cleavage site.
To cite this abstract in AMA style:Yadegari H, Biswas A, Sadangi S, Oldenburg J. Investigating Pathomolecular Mechanisms von Willebrand Disease Variants Located in a Domains of the von Willebrand Factor [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 1). https://abstracts.isth.org/abstract/investigating-pathomolecular-mechanisms-von-willebrand-disease-variants-located-in-a-domains-of-the-von-willebrand-factor/. Accessed September 24, 2021.
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