Effect of laminar shear stress on the distribution of Weibel-Palade bodies in endothelial cells

Background: Vascular endothelial cells (ECs) provide a highly interactive barrier between blood and the underlying tissues. It is well established that ECs exposed to laminar flow align in the direction of flow and also arrange their actin stress fibers in a parallel manner in the direction of flow. Also the organization of the microtubule network is altered in response to flow with repositioning of the microtubule-organizing centre (MTOC) in the direction of flow. Weibel-Palade bodies (WPBs) are endothelial cell specific storage organelles that contain a number of important homeostatic and inflammatory components. Dynamics of WPBs are controlled by microtubules and the actin cytoskeleton. Objectives: Here, we monitored flow-induced changes in distribution of WPBs. Methods: ECs were exposed for five days to laminar shear stress of 10 dyne/cm(2). Subsequently we measured the distance of individual WPBs with respect to the centre of the nucleus using Image Pro Plus. Results: ECs aligned in the direction of flow under these conditions. After 5 days the MTOC was positioned downstream of the nucleus in the direction of the flow. The number of WPBs per cell was slightly reduced as a result of the application of flow. Unexpectedly, only minor differences in the distribution of WPBs in ECs cultured under laminar flow were observed when compared to that of cells grown under static conditions. Conclusions: Our findings suggest that laminar flow does not induce major changes in number and distribution of WPBs in ECs.