Enhanced VWF biosynthesis and elevated plasma VWF due to a natural variant in the murine Vwf gene

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• The D9D3 domains of VWF are sufficient to stabilize FVIII in vivo.• The prolongation of VWF D9D3 survival in vivo by Fc fusion elevates FVIII levels in the setting of VWF but not FVIII deficiency.Plasma factor VIII (FVIII) and von Willebrand factor (VWF) circulate together as a complex. We identify VWF fragments sufficient for FVIII stabilization in vivo and show that hepatic expression of the VWF D9D3 domains (S764-P1247), either as a monomer or a dimer, is sufficient to raise FVIII levels in Vwf 2/2 mice from a baseline of ∼5% to 10%, to ∼50% to 100%. These results demonstrate that a fragment containing only ∼20% of the VWF sequence is sufficient to support FVIII stability in vivo. Expression of the VWF D9D3 fragment fused at its C terminus to the Fc segment of immunoglobulin G1 results in markedly enhanced survival in the circulation (t 1/2 > 7 days), concomitant with elevated plasma FVIII levels (>25% at 7 days) in Vwf 2/2 mice. Although the VWF D9D3-Fc chimera also exhibits markedly prolonged survival when transfused into FVIII-deficient mice, the cotransfused FVIII is rapidly cleared. Kinetic binding studies show that VWF propeptide processing of VWF D9D3 fragments is required for optimal FVIII affinity. The reduced affinity of VWF D9D3 and VWF D9D3-Fc for FVIII suggests that the shortened FVIII survival in FVIII-deficient mice transfused with FVIII and VWF D9D3/D9D3-Fc is due to ineffective competition of these fragments with endogenous VWF for FVIII binding. (Blood. 2014; 124(3):445-452)

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

A von Willebrand factor fragment containing the D′D3 domains is sufficient to stabilize coagulation factor VIII in mice

Yee

Gildersleeve

et al. 2014

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“…22 Considerable variability in VWF levels has been noted in various strains of mice. 25 In contrast, strain-dependent variation of ADAMTS13 has not been described. In our effort to develop animal models for investigation of ADAMTS13 function in vivo, we discovered that mouse strains differed markedly in their plasma ADAMTS13 activity levels.…”

Section: Introductionmentioning

confidence: 99%

“…25,34 Nevertheless, variability in VWF levels does not correlate with the risk of thrombosis in mice with ADAMTS13 deficiency. 35 The present study reveals that mouse strains also differ considerably in their ADAMTS13 activity levels.…”

Section: Iap Retrotransposon In Mouse Adamts13 Gene 891mentioning

confidence: 99%

An IAP retrotransposon in the mouse ADAMTS13 gene creates ADAMTS13 variant proteins that are less effective in cleaving von Willebrand factor multimers

Zhou

Bouhassira

Tsai

2007

Severe deficiency of ADAMTS13, a von Willebrand factor (VWF)-cleaving metalloprotease, causes thrombotic thrombocytopenic purpura. When analyzed with VWF multimers, but not with an abbreviated VWF peptide (VWF73) as the substrate, the plasma ADAMTS13 activity levels of mouse strains segregated into a high and a low group that differed by approximately 10 fold. Low ADAMTS13 activity was detected in mice containing 2 alleles of intracisternal A-type particle (

“…This represents a greater level of divergence between B6 and WSB, 2 strains that are thought to be primarily mus musculus domesticus in origin, versus A/J and CASA/RkJ (the strains used to identify Mvwf2-4), which are mus musculus domesticus and mus musculus castaneus, respectively. 17 To evaluate potential cis-regulatory differences in mRNA expression or stability, lung mRNA was isolated from (B6 ϫ WSB) F1 mice and subjected to RT-PCR for Vwf mRNA, followed by primer extension analysis that distinguishes the B6 and WSB alleles because of an exonic SNP ( Figure 5A). A similar approach has been successful in distinguishing expression from maternal and paternal alleles in cases of human VWD.…”

mentioning

confidence: 99%

Modifiers of von Willebrand factor identified by natural variation in inbred strains of mice

Shavit

Manichaikul

Lemmerhirt³

et al. 2009

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Type 1 von Willebrand disease (VWD) is the most common inherited human bleeding disorder. However, diagnosis is complicated by incomplete penetrance and variable expressivity, as well as wide variation in von Willebrand factor (VWF) levels among the normal population. Previous work has exploited the highly variable plasma VWF levels among inbred strains of mice to identify 2 major regulators, Mvwf1 and Mvwf2 (modifier of VWF).Mvwf1 is a glycosyltransferase and Mvwf2 is a natural variant in Vwf that alters biosynthesis. We report the identification of an additional alteration at the Vwf locus (Mvwf5), as well as 2 loci unlinked to Vwf (Mvwf6-7) using a backcross approach with the inbred mouse strains WSB/EiJ and C57BL/6J. Through positional cloning, we show that Mvwf5 is a cis-regulatory variant that alters Vwf mRNA expression. A similar mechanism could potentially explain a significant percentage of human VWD cases, especially those with no detectable mutation in the VWF coding sequence. Mvwf6 displays conservation of synteny with potential VWF modifier loci identified in human pedigrees, suggesting that its ortholog may modify VWF in human populations. Introductionvon Willebrand factor (VWF) is a central component of hemostasis, serving as the adhesive link between platelets and the injured blood vessel wall, as well as the carrier for factor VIII. Deficiencies in VWF result in von Willebrand disease (VWD), the most common inherited bleeding disorder in humans. Elevated VWF levels may also be an important risk factor for thrombosis, both through a direct role in platelet adhesion, 1 as well as indirectly by causing elevated levels of factor VIII. [2][3][4] Diagnosis of VWD is elusive in many cases because of its variable expressivity and incomplete penetrance 5 and the nonspecific nature of bleeding symptoms. 6 VWF plasma protein levels also display a broad distribution in the normal human population. Thus, it is often difficult to determine whether a person has VWD and is at risk for pathologic hemorrhage or simply has VWF levels in the low range of normal.Levels of plasma VWF have been shown to be largely determined by genetic factors, with estimates of heritability in humans ranging from 25% to 32% by pedigree analysis, 7,8 to 66% to 75% in twin studies. 9,10 ABO blood group is responsible for one-third of the genetic variability in VWF plasma levels. 11 However, the loci responsible for the remaining two-thirds of this genetic component are unknown. Recent evidence from European and Canadian cooperative studies on type 1 VWD have found that disease diagnosis does not segregate with VWF genotype in approximately 50% of families, supporting the existence of additional genetic factors. [12][13][14][15][16] Laboratory mice display wide variation in VWF levels with 65% heritability in a cross between the strains A/J and CASA/RkJ, 17 strikingly similar to the estimates for humans derived from twin studies. 9,10 This variability among inbred mouse strains has been used to identify genetic loci modifying VWF level...