Normal cleavage of von Willebrand factor by ADAMTS-13 in the absence of factor VIII in patients with severe hemophilia A

Dynamic and functional linkage between von Willebrand factor and ADAMTS-13 with aging: an Atherosclerosis Risk in Community study

BACKGROUND

von Willebrand factor (VWF) is a multimeric glycoprotein critically involved in hemostasis, thrombosis, and inflammation. VWF function is regulated by its antigen levels, multimeric structures, and the state of enzymatic cleavage. Population studies in the past have focused almost exclusively on VWF antigen levels in cross-sectional study designs.

OBJECTIVE

To identify subjects in the Atherosclerosis Risk in Community study who had persistently low and high VWF antigen over 10 years and to quantify longitudinal changes in the biological activities and cleavage of VWF in these subjects.

METHODS

We measured VWF antigen, propeptide, adhesive activities, and cleavage by ADAMTS-13 quantified using a mass spectrometry method that detected the cleaved VWF peptide EQAPNLVY, as well as coagulation factor VIII activity.

RESULTS

We determined the mean subject-specific increase in VWF to be 22.0 International Units (IU)/dL over 10 years, with 95% between -0.3 and 59.7 IU/dL. This aging-related increase was also detected in VWF propeptide levels, ristocetin cofactor activity, and VWF binding to collagen. We identified 4.1% and 25.0% of subjects as having persistently low (<50 IU/dL) and high (>200 IU/dL) VWF antigen, respectively. Subjects with persistently low VWF had enhanced ristocetin cofactor activity, whereas those with persistently high VWF had elevated levels of ADAMTS-13, resulting in a comparable rate of VWF cleavage between the 2 groups.

CONCLUSIONS

These results provide new information about the effects of aging on VWF antigens and adhesive activity and identify a functional coordination between VWF and the rate of its cleavage by ADAMTS-13.

Coagulation factor VIII regulates von Willebrand factor homeostasis invivo

BACKGROUND

Coagulation factor VIII (FVIII) and von Willebrand factor (VWF) circulate as a noncovalent complex, but each has its distinct functions. Binding of FVIII to VWF results in a prolongation of FVIII's half-life in circulation and modulates FVIII's immunogenicity during hemophilia therapy. However, the biological effect of FVIII and VWF interaction on VWF homeostasis is not fully understood.

OBJECTIVES

To determine the effect of FVIII in VWF proteolysis and homeostasis in vivo.

METHODS

Mouse models, recombinant FVIII infusion, and patients with hemophilia A on a high dose FVIII for immune tolerance induction therapy or emicizumab for bleeding symptoms were included to address this question.

RESULTS

An intravenous infusion of a recombinant B-domain less FVIII (BDD-FVIII) (40 and 160 μg/kg) into wild-type mice significantly reduced plasma VWF multimer sizes and its antigen levels; an infusion of a high but not low dose of BDD-FVIII into Adamts13+/- and Adamts13-/- mice also significantly reduced the size of VWF multimers. However, plasma levels of VWF antigen remained unchanged following administration of any dose BDD-FVIII into Adamts13-/- mice, suggesting partial ADAMTS-13 dependency in FVIII-augmented VWF degradation. Moreover, persistent expression of BDD-FVIII at ∼50 to 250 U/dL via AAV8 vector in hemophilia A mice also resulted in a significant reduction of plasma VWF multimer sizes and antigen levels. Finally, the sizes of plasma VWF multimers were significantly reduced in patients with hemophilia A who received a dose of recombinant or plasma-derived FVIII for immune tolerance induction therapy.

CONCLUSION

Our results demonstrate the pivotal role of FVIII as a cofactor regulating VWF proteolysis and homeostasis under various (patho)physiological conditions.

Looking for a partner: ceruloplasmin in protein-protein interactions

Ceruloplasmin (CP) is a mammalian blood plasma ferroxidase. More than 95% of the copper found in plasma is carried by this protein, which is a member of the multicopper oxidase family. Proteins from this group are able to oxidize substrates through the transfer of four electrons to oxygen. The essential role of CP in iron metabolism in humans is particularly evident in the case of loss-of-function mutations in the CP gene resulting in a neurodegenerative syndrome known as aceruloplasminaemia. However, the functions of CP are not limited to the oxidation of ferrous iron to ferric iron, which allows loading of the ferric iron into transferrin and prevents the deleterious reactions of Fenton chemistry. In recent years, a number of novel CP functions have been reported, and many of these functions depend on the ability of CP to form stable complexes with a number of proteins.

A Disintegrin and Metalloproteinase with Thrombospondin Motifs 18 Deficiency Leads to Visceral Adiposity and Associated Metabolic Syndrome in Mice

Visceral adiposity is of greater risk than obesity in s.c. adipose tissue for diabetes and cardiovascular disease. Its pathogenesis remains unclear, but it is associated with extracellular matrix (ECM) remodeling. A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs) are a family of secreted zinc-dependent metalloproteinases that play crucial roles in development and various diseases because of their ECM remodeling activity. ADAMTS18 is an orphan ADAMTS whose function and substrate remain unclear. Herein, we showed that Adamts18 mRNA was abundantly expressed in visceral (gonadal) white adipose tissue (vWAT) during the early stage of development after birth. Adamts18 knockout (KO) mice showed increased body fat percentage and larger adipocyte size in vWAT relative to wild-type littermates. These findings may be partly attributed to ECM remodeling, especially increased expression of laminin 1 and adipokine thrombospondin 1 in vWAT. Attenuated extracellular signal-regulated kinase 1 and 2 activity, along with increased expression of adipocyte-specific transcription factors peroxisome proliferator-activated receptor-γ, CCAAT/enhancer binding protein β, and marker gene Fabp4, was detected in vWAT of Adamts18 KO mice. Furthermore, Adamts18 KO mice showed early metabolic syndrome, including hyperlipidemia, blood glucose metabolic disorder, and hypertension. ADAMTS18 deficiency promotes atherosclerosis in apolipoprotein E-deficient mice. These results indicate a novel function of ADAMTS18 in vWAT development and associated metabolic disorders.