Insights from von Willebrand disease animal models

138

182

Activated platelets release their granule content in a concentrated fashion at sites of injury. We examined whether ectopically expressed factor VIII in developing megakaryocytes would be stored in ␣-granules and whether its release from circulating platelets would effectively ameliorate bleeding in a factor VIII null mice model. Using the proximal glycoprotein 1b␣ promoter to drive expression of a human factor VIII cDNA construct, transgenic lines were established. One line had detectable human factor VIII that colocalizes with von Willebrand factor in platelets. These animals had platelet factor VIII levels equivalent to 3% to 9% plasma levels, although there was no concurrent plasma human factor VIII detectable. When crossed onto a factor VIII null background, whole blood clotting time was partially corrected, equivalent to a 3% correction level. In a cuticular bleeding time study, these animals also had only a partial correction, but in an FeCl 3 carotid artery, thrombosis assay correction was equivalent to a 50% to 100% level. These studies show that factor VIII can be expressed and stored in platelet ␣-granules. Our studies also suggest that plateletreleased factor VIII is at least as potent as an equivalent plasma level and perhaps even more potent in an arterial thrombosis model. (Blood. 2003;102:4006-4013)

Section: Discussionmentioning

confidence: 99%

Factor VIII ectopically expressed in platelets: efficacy in hemophilia A treatment

Yarovoi

Kufrin

Eslin

et al. 2003

138

182

“…While canine hemophilia and von Willebrand disease are common, a variety of clotting factor deficiencies and platelet function defects caused by surface glycoprotein abnormalities, storage pool defects, and failure of signal transduction occur in this species. [44][45][46] Comprehensive testing of the GSDs described in this report revealed a new canine hemostatic defect with features comparable to Scott syndrome of human beings. The affected dogs experienced a mild to moderate bleeding tendency but had normal in vitro coagulation and normal response to tests of platelet adhesion, aggregation, and secretion.…”

Section: Discussionmentioning

confidence: 99%

A hereditary bleeding disorder of dogs caused by a lack of platelet procoagulant activity

Brooks

Catalfamo

Brown

et al. 2002

We have discovered a novel canine hereditary bleeding disorder with the characteristic features of Scott syndrome, a rare defect of platelet procoagulant activity. Affected dogs were from a single, inbred colony and experienced clinical signs of epistaxis, hyphema, intramuscular hematoma, and prolonged bleeding with cutaneous bruising after surgery. The hemostatic abnormalities identified were restricted to tests of platelet procoagulant activity, whereas platelet count, platelet morphology under light microscopy, bleeding time, clot retraction, and platelet aggregation and secretion in response to thrombin, collagen, and adenosine diphosphate stimulation were all within normal limits. Washed platelets from the affected dogs demonstrated approximately twice normal clotting times in a platelet factor 3 availability assay and, in a prothrombinase assay, generated only background levels of thrombin in response to calcium ionophore, thrombin, or combined thrombin plus collagen stimulation. While platelet phospholipid content was normal, flow cytometric analyses revealed diminished phosphatidylserine exposure and a failure of microvesiculation in response to calcium ionophore, thrombin, and collagen stimulation. Pedigree studies indicate a likely homozygous recessive inheritance pattern of the defect. These findings confirm the importance of platelet procoagulant activity for in vivo hemostasis and provide a large animal model for studying agonist-induced signal transduction, calcium mobilization, and effector pathways involved in the late platelet response of transmembrane phospholipid movement and membrane vesiculation. (Blood. 2002; 99:2434-2441)

“…The importance of VWF for the hemostatic system is illustrated by the severe bleeding tendency associated with its functional deficiency, both in patients and in animal models. 10,11 Interestingly, studies using VWF-deficient mice revealed that VWF might also participate in inflammatory processes. For instance, when VWF Ϫ/Ϫ mice were stimulated in a cytokine-induced meningitis model (which represents a model for acute inflammation), reduced neutrophil infiltration compared with control mice was observed.…”

Section: Introductionmentioning

confidence: 99%

P-selectin glycoprotein ligand 1 and β2-integrins cooperate in the adhesion of leukocytes to von Willebrand factor

Pendu

Terraube

Olivier

et al. 2006

161

159

Von Willebrand factor (VWF) is an essential component of hemostasis. However, animal studies using VWF-deficient mice suggest that VWF may also contribute to inflammation. In the present study, we demonstrate that VWF was able to interact with polymorphonuclear leukocytes (PMNs) and monocytes under static and flow conditions. Adhesion under flow was dominated by short-lasting contact with resting PMNs, whereas adhesion of phorbol-12-myristate-13-acetate (PMA)-stimulated PMNs was characterized by firm adhesion. Transient binding of PMNs to VWF appeared to be mediated by P-selectin glycoprotein ligand-1 (PSGL-1). Moreover, recombinant PSGL-1 protein and cell surface-expressed PSGL-1 directly interacted with VWF. As for stable adhesion by PMA-stimulated PMNs, we observed that static adhesion and adhesion under flow were strongly inhibited (greater than 75%) by neutrophilinhibitory factor, an inhibitor of ␤2-integrin function. In addition, the isolated I-domain of ␣M␤2 bound to VWF, and cell lines expressing ␣L␤2 or ␣X␤2 adhered efficiently to VWF. Taken together, our data showed that VWF can function as an adhesive surface for various leukocyte subsets (monocytes, PMNs). Analogous to VWF-platelet interaction, VWF provided binding sites for leukocyte receptors involved in rolling (PSGL-1) and stable (␤2-integrins) adhesion. VWF is unique in its intrinsic capacity to combine the rolling and the stable adhesion step in the interaction with leukocytes. IntroductionRecruiting leukocytes to sites of infection or tissue damage is a key element in the inflammatory response. However, these inflammatory cells are in a resting, low-adhesive state while circulating in blood or lymphatic vessels. Stimulatory signals are therefore required to promote the migration of leukocytes through the endothelial layer. This migration involves a complex process that distinguishes a number of distinct steps, including initial rolling to slow down the leukocytes and firm adhesion to allow transendothelial migration. 1 Several endothelial and leukocyte receptors have been identified that contribute to these processes. For instance, leukocyte rolling over the endothelial layer is predominantly mediated through interactions between selectins that are exposed on the stimulated endothelial cell and the P-selectin glycoprotein ligand-1 (PSGL-1) on the leukocyte surface. 2 These interactions result not only in the deceleration of cells but in the activation of signaling pathways that bring these leukocytes into the highadhesive state required for stable adhesion. 3 Important players in the stable adhesion step are the ␤2-integrins. This leukocytespecific integrin family consists of 4 isotypes (␣L␤2, ␣M␤2, ␣D␤2, and ␣X␤2), each of which has the intrinsic capacity to mediate stable adhesion. 4 The major counterreceptors for the ␤2-integrin isotypes are the intercellular adhesion molecules (ICAMs). 4 It has become clear, however, that many other proteins have the capacity to interact with this integrin family, including fibrinogen, vitronectin, juncti...