Regulation of von Willebrand factor of human endothelial cells exposed to laminar flows: an in vitro study

The effect of laminar flow on the regulation of von Willebrand Factor (vWF) of cultured human umbilical vein endothelial cells (HUVECs) was studied. C onfluent endothelial monolayers were exposed to shear stresses (0.2 and 1.0 Pa) from 2 to 24 h. VWF was labelled with indirect immunofluorescence meth od and observed with 3D fluorescence microscopy. The distribution of VWF an d the cytoskeleton organization were observed simultaneously by double fluo rescence labelling. More actin stress fibers and an increased release of VW F appeared in the cells exposed to how at the same time. The qualitative an d quantitative results showed that there was not only a shear-dependent reg ulation but also a time-dependent modification. For a short-time shear stim ulation, both 0.2 Pa and 1.0 Pa shear stresses induced a release of VWF fro m the endothelial cells. In contrast, after 24 h exposure to 1.0 Pa shear d ow, vWFs were much more in the cells than that in the cells exposed to 0.2 Pa for 24 h (p < 0.01) or that in the control cells (p < 0.05). TNF-alpha c aused a decrease of VWF and Weibel-Palade bodies in the cells.