P-selectin anchors newly released ultralarge von Willebrand factor multimers to the endothelial cell surface

Abstract

von Willebrand factor (VWF) released from endothelium is ultralarge (UL) and hyperreactive. If released directly into plasma, it can spontaneously aggregate platelets, resulting in systemic thrombosis. This disastrous consequence is prevented by the ADAMTS13 (A Disintegrin and Metalloprotease with ThromboSpondin motif) cleavage of ULVWF into smaller, less active forms. We previously showed that ULVWF, on release, forms extremely long stringlike structures. ADAMTS13 cleaves these strings under flow significantly faster than it does under static conditions. As ULVWF tethering to endothelium is important for its rapid proteolysis, we investigated 2 molecules for their potential to anchor the ULVWF strings: Pselectin and integrin ␣ v ␤ 3 . We demonstrated that P-selectin anchors ULVWF to endothelium by several means. First, Chinese hamster ovary (CHO) cells expressing P-selectin specifically adhered to immobilized ULVWF and ULVWF-coated beads to immobilized P-selectin. Second, an anti-VWF antibody coimmunoprecipitates P-selectin from the histamine-activated endothelial cells. Third, P-selectin antibody or soluble P-selectin, but not a ␣ v ␤ 3 antibody, RGDS peptide, or heparin, blocked the formation of ULVWF strings. Fourth, P-selectin expression was in clusters predominantly along the ULVWF strings. Finally, the strength of the minimal ULVWF-P-selectin bond was measured to be 7.2 pN. We, therefore, conclude that P-selectin may anchor ULVWF strings to endothelial cells and facilitate their cleavage by ADAMTS13. (Blood.

Differential regulation of endothelial exocytosis of P-selectin and von Willebrand factor by protease-activated receptors and cAMP

“…22 More recently P-selectin has been shown to mediate the attachment of ultralarge VWF multimers to the endothelial surface on release. 23 VWF is released after fusion with the plasma membrane in response to agents that result in elevated intracellular Ca 2ϩ , such as thrombin, histamine, or calcium inonophore. 24 In addition, agents that elevate intracellular cAMP such as vasopressin receptor agonists, purine nucleotides, epinephrine, and forskolin can also trigger the release of VWF.…”

Thrombocytopenia in critically ill patients due to vascular microthrombotic disease: pathogenesis based on “two activation theory of the endothelium”

“…On the other hand, the activation of microthrombotic pathway is initiated by activated platelets and excessively exocytosed ULVWF that are anchored to ECs as long elongated strings [46,47]. If protease ADAMTS13, which cleaves ULVWF to smaller molecular weight VWF, is under expressed [36,48], activated platelets under shear stress of blood flow are recruited to the uncleaved ULVWF strings.…”

“…If protease ADAMTS13, which cleaves ULVWF to smaller molecular weight VWF, is under expressed [36,48], activated platelets under shear stress of blood flow are recruited to the uncleaved ULVWF strings. This microthrombogenesis generates intravascular microthrombi consisting of platelet-ULVWF complexes at ECs [46,47]. This process sets off DIT and could lead to multiple clinical syndromes.…”

“…In the former, microthrombogenesis occurs in the circulation and formed microthrombi become lodged in microvasculatures [49], predominantly in the brain and kidneys. But in the latter, it occurs at ECs-anchored long elongated ULVWF strings [46,47] in smaller and larger vasculatures, commonly involving the lungs (i.e., ARDS), kidneys (i.e., acute renal failure, hemolytic-uremic syndrome), liver (i.e., acute hepatic necrosis syndrome), intestines (i.e., gastroenteritis), pancreas (i.e., acute pancreatitis), muscles (i.e., rhabdomyolysis), heart (i.e., acute myocardial ischemia), skin (i.e., purpura fulminans), and others.…”

ADAMTS13, la protéase spécifique du clivage du facteur von Willebrand

“…Ainsi, seul le dépliement du VWF induit soit par les forces de cisaillement élevées du flux sanguin dans les microvaisseaux in vivo, soit par des agents dénaturants (urée, hydrochlorure de guanidine), ou son immobilisation sur une surface plastique [13] in vitro, permet l'exposition de ce pont peptidique et le rend donc accessible au clivage par ADAMTS13. De plus, cet accès est facilité par la liaison du VWF à certains ligands comme la P-sélectine (qui intervient dans la fixation du VWF à la surface des cellules endothéliales à la phase initiale de sa sécrétion dans le plasma [14]) ou la glycoprotéine Ib plaquettaire (qui permet la liaison du VWF aux plaquettes au sein du clou plaquettaire formé pour réparer une brèche vasculaire [15]). Ceci explique pourquoi le rôle d'ADAMTS13 dans la régulation de la taille des multimères du VWF est prédominant dès l'étape de sécrétion du VWF par les cellules endothéliales (limitation immédiate de la taille des multimères avant la mise en circulation du VWF dans le plasma) et aussi au sein du clou plaquettaire (résorption du clou plaquettaire une fois la brèche vasculaire réparée) (Figure 3) [14,15].…”