Endothelial PIEZO1 regulates Weibel-Palade body exocytosis

Endothelial cells (ECs) rapidly alter their phenotype to support haemostasis and inflammation through the exocytosis of specialized storage organelles, known as Weibel-Palade bodies (WPBs). This exocytic response is stimulated by a variety of physiological and pathological triggers which act through well-described transmembrane receptors. However, the influence of mechanical forces and how this shapes this fundamental endothelial response remains relatively unexplored. Here we demonstrate that the opening of a mechanosensitive cation channel PIEZO1 on the EC surface triggers rapid WPB exocytosis. The dynamics and mechanisms were investigated using the PIEZO1 agonist (Yoda1) and by modelling mechanical opening through interaction with THP-1 cells or anti-ICAM-1 mAb coated beads under low shear fluid flow. In vitro, spatially restricted Ca2+ flux and von Willebrand Factor (VWF) secretion occurred proximal to THP-1 adhesion and ICAM-1 ligation sites, suggesting a reciprocity of finely tuned VWF release alongside leukocyte capture. In vivo, Yoda1 stimulation of tissues resulted in a dramatic increase in leukocyte and platelet adhesion to postcapillary venular walls, which aligned spatially with cargo release (VWF). We also introduce the first intravital imaging model to study WPB dynamics in a live animal through application of an EGFP-Rab27a mouse. Together these data reveal a previously unrecognised instigator of WPB exocytosis and a mechanosensitive molecular pathway coupling inflammation with haemostasis.