Von Willebrand factor propeptide in vascular disorders

Von Willebrand factor (VWF) is a multifunctional plasma protein that plays a prominent role in haemostasis. In endothelial cells, processing of its precursor pro-VWF results in the formation of two large polypeptides, mature VWF and a propeptide. These proteins are co-secreted on an equimolar basis but are cleared from the circulation at different rates. VWF levels are frequently elevated in response to vascular disorders. Similarly, propeptide levels are increased under these conditions, although primarily in fulminant vascular disease, such as thrombotic thrombocytopenic purpura and septicemia. In chronic vascular disease, e.g. diabetes or peripheral vascular disease, propeptide levels are much less elevated. The differential response of VWF and propeptide levels to vascular disease could provide a means to assess the extent and time course of endothelial cell activation. After secretion, the propeptide may play a role in modulating cellular adhesion processes. Thus, enhanced propeptide secretion seems not to be of merely diagnostic significance.     

von Willebrand factor: an emerging target in stroke therapy

Thrombus formation is of paramount importance in the pathophysiology of acute ischemic stroke. Current antithrombotics used to treat or prevent cerebral ischemia are only moderately effective or bear an increased risk of severe bleeding. von Willebrand factor (VWF) has long been known to be a key player in thrombus formation at sites of vascular damage. While the association between VWF and coronary heart disease has been well studied, knowledge about the role of VWF in stroke is much more limited. However, in recent years, an increasing amount of clinical and preclinical evidence has revealed the critical involvement of VWF in stroke development. This review summarizes the latest insights into the pathophysiologic role of VWF-related processes in ischemic brain injury under experimental conditions and in humans. Potential clinical merits of novel inhibitors of VWF-mediated platelet adhesion and activation as powerful and safe tools to combat thromboembolic disorders including ischemic stroke are discussed. Preclinical and clinical evidence illustrates an important role of VWF in ischemic stroke, suggesting that VWF could become a promising target in stroke therapy.     

Changes in plasma von Willebrand factor and ADAMTS13 levels associated with left atrial remodeling in atrial fibrillation

Introduction

Previous studies have shown raised plasma von Willebrand factor (VWF) levels in patients with atrial fibrillation (AF). However, little is known about changes of VWF associated with VWF-cleaving protease (ADAMTS13) in AF. The aim of this study was to examine the relationship between changes in plasma VWF and ADAMTS13 levels, and left atrial remodeling in AF patients.

Materials and Methods

We measured plasma VWF and ADAMTS13 antigen levels in 70 paroxysmal AF (PAF) patients, 56 chronic AF (CAF) patients, and 55 control subjects.

Results

Plasma VWF levels (mU/ml) were significantly higher in CAF and PAF patients compared with the controls (2103 ± 743, 1930 ± 676, 1532 ± 555, respectively, P < 0.0001 in CAF vs. controls, P = 0.001 in PAF vs. control), while ADAMTS13 levels (mU/ml) were significantly lower in CAF and PAF patients compared with the controls (795 ± 169, 860 ± 221, 932 ± 173, respectively, P = 0.0002 in CAF vs. controls, P = 0.04 in PAF vs. control). The VWF/ADAMTS13 ratio was significantly higher in patients with CAF than PAF or controls (2.81 ± 1.30, 2.34 ± 0.92, 1.73 ± 0.83, respectively; P = 0.01 in CAF vs. PAF, P < 0.0001 in CAF vs. controls). There was a significant correlation between the VWF/ADAMTS13 ratio and left atrial diameter (positive correlation; r = 0.275, P = 0.0002) and left atrial appendage flow velocity (negative correlation; r = - 0.345, P = 0.0018).

Conclusions

These findings suggest that the imbalance between plasma VWF and ADAMTS13 levels caused by left atrial remodeling might be closely associated with intra-atrial thrombus formation in AF patients.     

Heregulin and forskolin-induced cyclin D3 expression in Schwann cells: role of a CCAAT promoter element and CCAAT enhancer binding protein

Heregulin, a polypeptide growth factor, and forskolin, an adenylyl cyclase activator, synergistically stimulate expression of cyclin D3 and cell division in Schwann cells. Heregulin induces expression in Schwann cells of a luciferase reporter gene linked to the cyclin D3 promoter. Forskolin markedly augments reporter expression in the presence of heregulin. Deletion analysis identified several promoter sites that contribute to high-level reporter expression in heregulin- and forskolin-treated Schwann cells. A promoter fragment that contains 103 bp of 5'-flanking sequence produced significant reporter expression in heregulin- and forskolin-stimulated cells. Deletion of a consensus CCAAT site within this promoter fragment caused a nearly complete loss of reporter expression. Similar results were obtained when CCAAT site mutations were introduced into the promoter. Heregulin and forskolin increased steady-state levels of CCAAT/enhancer binding protein-beta (C/EBPbeta) in Schwann cells. Mobility shift assays identified proteins in Schwann cell nuclear extracts that formed stable complexes with the cyclin D3 CCAAT promoter element and were disrupted by anti-C/EBPbeta antibody. Transfection of Schwann cells with C/EBPbeta cDNA increased cyclin D3 reporter expression. In contrast to these results, mutation of a cAMP response element in the cyclin D3 promoter had only a modest effect on heregulin- and forskolin-stimulated reporter expression. These findings demonstrate that C/EBPbeta plays a key role in the heregulin and cAMP-dependent regulation of cyclin D3 expression in Schwann cells.     

The factor VIII/von Willebrand factor ratio discriminates between reduced synthesis and increased clearance of von Willebrand factor

It is often stated that a decrease in Von Willebrand factor (VWF), the carrier protein of factor VIII, results in a concordant change in factor VIII. Clinical data suggest that this is not always the case and we hypothesized that the ratio between factor VIII and VWF depends on the genetic defect that causes the VWF deficiency. We have analyzed the ratio between plasma factor VIII and VWF in several subtypes of Von Willebrand Disease and we show that the ratio is increased when VWF synthesis is reduced, but that the ratio remains one when VWF clearance is increased. These observations could be of clinical importance as an increased factor VIII/VWF ratio in combination with a borderline VWF level may indicate the presence of a true genetic defect, possibly a VWF null allele.     

Von Willebrand factor promoter targets the expression of amyloid beta protein precursor to brain vascular endothelial cells of transgenic mice

Dysfunction of brain vascular endothelial cells may be associated with the pathogenesis of several diseases including cerebral amyloid angiopathy, hemorrhagic stroke and Alzheimer disease. New model systems are necessary to examine the contribution of brain endothelial cells in these disorders. The Von Willebrand factor gene promoter fragment that spans sequences -487 to +247 targets the expression of LacZ marker gene in transgenic mice specifically to brain vascular endothelial cells. Transgenic mice have been prepared that express human amyloid beta protein precursor protein (AbetaPP) isoforms 695 and 751 (wild-type and Dutch variant mutations) under the regulation of this VWF promoter sequence. These AbetaPP transgenes are specifically expressed in brain vascular endothelial cells. The VWF promoter is a valuable tool for targeting gene expression to brain vascular endothelial cells to provide a model to directly examine endothelial cell placement of genes and their contribution to cerebral vascular disease.