Immunofluorescence staining of cultured human umbilical vein endothelial cells has shown the presence of von Willebrand protein in the perinuclear region, in small rodlike structures through the cytoplasm, and on filaments of the extracellular matrix. Nonendothelial cells showed no staining with anti-von Willebrand protein antiserum. At the light microscope level, immunoperoxidase treatment of endothelial cells revealed the same pattern and antibody specificity as the fluorescence staining. Thin sections of the peroxidase-stained cells showed decorated filaments close to the substratum and also specific deposits in the endoplasmic reticulum and WeibeI-Palade bodies. Control antisera against other selected proteins in endothelial cells failed to stain the WeibeI-Palade bodies. These data suggest that the WeibeI-Palade bodies of endothelial cells are storage and/or processing organelles for von Willebrand protein.Von Willebrand protein is a large glycoprotein of complex multimeric structure (1, 2) that mediates attachment ofplatelets to the subendothelium after vascular injury (3). It is synthesized by megakaryocytes (4), which assure its presence in platelets in granulelike storage compartments (5, 6). After activation, platelets bind both von Willebrand protein released from internal storage sites and protein recruited from plasma to their surface membrane (7). Endothelial cells also synthesize von Willebrand protein (8) and the low concentration present in plasma and the subendothelium is probably derived from this source. We studied the distribution of von Willebrand protein in endothelial cells, in an attempt to detect and identify a storage compartment which would allow rapid release of this protein upon appropriate stimulus or physiologic demand. Using indirect immunofluorescence and immunoelectron microscopy, we determined that von Willebrand protein is concentrated in Weibel-Palade bodies. These are membrane-bound, elongate vesicles of 0.1 x 2-3 #In size that contain regularly spaced tubular structures aligned parallel to the longitudinal axis (9). Our data suggest that Weibel-Palade bodies serve as storage and/or processing vesicles for this protein and provide the first demonstration of unique function for these endothelial cell-specific organelles. MATERIALS AND METHODS Cells and Culture ConditionsEndothelial cells were obtained from human umbilical vein using a modification of the method described by Gimbrone et al.(10). Mild proteolytic digestion was carried out with 5 mg/ml of pronase (Calbiochem-Behring,

No abstract

No abstract

No abstract

No abstract