Endothelial secretion of von Willebrand factor (VWF) from intracellular organelles known as Weibel-Palade bodies (WPBs) is required for platelet adhesion to the injured vessel wall. Here we demonstrate that WPBs are often found near or within autophagosomes and that endothelial autophagosomes contain abundant VWF protein. Pharmacological inhibitors of autophagy or knockdown of the essential autophagy genes Atg5 or Atg7 inhibits the in vitro secretion of VWF. Furthermore, although mice with endothelial-specific deletion of Atg7 have normal vessel architecture and capillary density, they exhibit impaired epinephrine-stimulated VWF release, reduced levels of high-molecular weight VWF multimers and a corresponding prolongation of bleeding times. Endothelial-specific deletion of Atg5 or pharmacological inhibition of autophagic flux results in a similar in vivo alteration of hemostasis. Thus, autophagy regulates endothelial VWF secretion, and transient pharmacological inhibition of autophagic flux may be a useful strategy to prevent thrombotic events.
Bibliographical noteFunding Information:
We are grateful to S. Gutkind (NIH) for help with primary endothelial cell isolation, T. Carter for the gift of the VWF monomeric GFP plasmid (VWF-mGFP), J. Lippincott-Schwartz (NIH) for the LC3-mCherry plasmid and Y. Fitz (NIH) for help with coagulation measurements. We thank B. Zinselmeyer (NIH) for assistance with the spot cluster analysis and C.A. Brantner (NIH) for help performing cryo-immunogold electron microscopy. This work was supported by NIH Intramural Funds. T.T. is a recipient of a Japan Society for the Promotion of Science Research Fellowship in Biomedical and Behavioral Research at the NIH.