PB0349 - Shear stress regulates Weibel-Palade Body size and von Willebrand factor release

Background: Weibel-Palade bodies (WPBs) are endothelial specific storage organelles necessary for vascular haemostasis. The multimerisation of the pro-thrombotic glycoprotein von Willebrand Factor (vWF) drives WPB biosynthesis and determines their size and potential function. WPBs display plasticity in their biogenesis, where longer WPBs produce longer vWF strings that confer a greater propensity to pro-thrombotic behaviour. Vascular function is regulated by shear stress (SS) generated by blood flow. High laminar shear stress (HSS) is atheroprotecive, promoting healthy vasculature function with low levels of plasma vWF. Low oscillatory shear stress (LOSS) occurs at areas of vessel curvature and branching and is pathogenic, promoting secretion of pro-thrombotic and inflammatory factors from ECs including vWF. Previous literature focuses on static cultured cells, missing vital environmental cues. I propose therefore that flow impacts the biogenesis of WPBs and this has an effect on WPB function.

Aims: As a LOSS microenvironment is aligned with exocytosis of cargo stored in WPBs, we assessed the effects of different SS on the formation and function of WPBs and release of vWF.

Methods: An in vitro model of SS was devised. ECs from varied vascular beds cultured under LOSS or HSS conditions for 48hrs were stimulated with an agonist to induce vWF exocytosis from WPBs. vWF strings were exposed to activated platelets under SS to assess functionality. T-tests were used to assess significance.

Results: LOSS has no impact of vWF expression, however, it does create a more pro-thrombotic environment with increased WPB size (Fig.1) and subsequent exocytosed platelet-decorated vWF strings (Fig.2).

Conclusion(s): SS has the ability to manipulate WPB biogenesis resulting in pathogenic alterations to function. The resulting LOSS microenvironment has a higher thrombotic capacity with larger WPBs releasing longer vWF strings with a higher affinity for platelets than HSS. This increases the likelihood of atherosclerotic plaque formation and progression of cardiovascular disease (CVD).