Clathrin-mediated post-fusion membrane retrieval influences the exocytic mode of endothelial Weibel-Palade bodies

Abstract

Weibel Palade bodies (WPB), the storage organelles of endothelial cells, are essential to normal haemostatic and inflammatory responses. Their major content protein is Von Willebrands factor (VWF) that, following secretagogue-stimulation, is released into the blood vessel lumen as large platelet-catching strings. This exocytosis changes the protein composition of the cell surface and also results in a net increase in the amount of plasma membrane. Compensatory endocytosis is thought to limit changes in cell size and retrieve fusion machinery and other misplaced integral membrane proteins following exocytosis, however little is known about the extent, timing, mechanism and precise function of compensatory endocytosis in endothelial cells. Using biochemical assays, live cell imaging and correlative spinning disk microscopy and transmission electron microscopy assays we provide the first in-depth high-resolution characterisation of this process. We provide a model of compensatory endocytosis based on rapid clathrin and dynamin mediated retrieval. Inhibition of this process results in a change of exocytic mode: WPB then fuse with previously fused WPB rather than the plasma membrane, leading in turn to formation of structurally-impaired tangled VWF strings.