von Willebrand factor multimerization and the polarity of secretory pathways in endothelial cells

Abstract

Key Points• The 3 endothelial secretory pathways-constitutive, basal, and regulated-release VWF in different multimeric states.• Apical-and basolaterallyreleased VWF follow different secretory pathways, thus releasing differentially multimerized protein.The von Willebrand factor (VWF) synthesized and secreted by endothelial cells is central to hemostasis and thrombosis, providing a multifunctional adhesive platform that brings together components needed for these processes. VWF secretion can occur from both apical and basolateral sides of endothelial cells, and from constitutive, basal, and regulated secretory pathways, the latter two via Weibel-Palade bodies (WPB). Although the amount and structure of VWF is crucial to its function, the extent of VWF release, multimerization, and polarity of the 3 secretory pathways have only been addressed separately, and with conflicting results. We set out to clarify these relationships using polarized human umbilical vein endothelial cells (HUVECs) grown on Transwell membranes. We found that regulated secretion of ultra-large (UL)-molecular-weight VWF predominantly occurred apically, consistent with a role in localized platelet capture in the vessel lumen. We found that constitutive secretion of low-molecular-weight (LMW) VWF is targeted basolaterally, toward the subendothelial matrix, using the adaptor protein complex 1 (AP-1), where it may provide the bulk of collagen-bound subendothelial VWF. We also found that basally-secreted VWF is composed of UL-VWF, released continuously from WPBs in the absence of stimuli, and occurs predominantly apically, suggesting this could be the main source of circulating plasma VWF. Together, we provide a unified dataset reporting the amount and multimeric state of VWF secreted from the constitutive, basal, and regulated pathways in polarized HUVECs, and have established a new role for AP-1 in the basolateral constitutive secretion of VWF. (Blood. 2016;128(2):277-285)

Abnormal platelet activity in dogs and cats – impact and measurement

“…Endothelial cells constitutively secrete small multimers into the subendothelial matrix and large multimers into the plasma (Lopes da Silva and Cutler ). Here, vWF circulates with factor VIII.…”

A sticky proposition: The endothelial glycocalyx and von Willebrand factor

“…EC‐derived VWF can be released via three pathways: regulated, constitutive, or basal. During regulated VWF secretion, agonists such as histamine and epinephrine can stimulate acute WPB exocytosis through calcium‐ or cyclic adenosine monophosphate‐dependent mechanisms, respectively . In contrast, constitutive VWF secretion is mediated by premature WPBs and occurs predominantly on the basolateral aspect of ECs .…”

“…During regulated VWF secretion, agonists such as histamine and epinephrine can stimulate acute WPB exocytosis through calcium‐ or cyclic adenosine monophosphate‐dependent mechanisms, respectively . In contrast, constitutive VWF secretion is mediated by premature WPBs and occurs predominantly on the basolateral aspect of ECs . Last, continuous basal VWF secretion from WPBs into the vessel lumen is recognized to be the principal determinant of an individual's baseline plasma VWF levels .…”

“…1,2 In contrast, constitutive VWF secretion is mediated by premature WPBs and occurs predominantly on the basolateral aspect of ECs. 1 Last, continuous basal VWF secretion from WPBs into the vessel lumen is recognized to be the principal determinant of an individual's baseline plasma VWF levels. 1 As an extension of these observations, fluid shear has been shown to induce VWF release proportionate to the magnitude of the shear stress by modulating intracellular levels of calcium.…”

Subsequent Response of VWF and ADAMTS13 to Aortic Valve Replacement

“…This polypeptide dimerizes in the endoplasmic reticulum through intermonomer disulfide bonds in the C-terminal regions, and the dimers are transported to the Golgi apparatus, where inter-dimer disulfide bonds in the N-terminal regions produce linear multimers 2) . In endothelial cells, the huge multimers of VWF are packaged into rod-shaped vesicles called Weibel – Palade bodies and are constantly secreted into the circulation or released in response to physiological and pathophysiological stimuli 3) . The largest circulating multimers have a mass of at least 20,000 kDa (> 80 subunits).…”