Abstract 1909: Primary Cilia Function in Endothelial Mechanosensing
Primary cilia are microtubule containing membrane protrusions which have been associated with fluid sensing capacities of e.g. vascular endothelial cells (EC). We showed that ciliated EC are present at atherosclerotic predilection sites in adult mice under athero-prone flow conditions, but not in athero-protected areas. Upon plaque formation in Apoe−/− mice, as well as after experimental induction of flow disturbance in the carotid artery by use of a flow restricting cast, the number of ciliated EC is increased. The aim of this study was to relate the presence of a primary cilium on EC to the flow profile to which these cells are exposed to, in vitro and in vivo, and to decipher its role in the mechanosensor for shear stress. We analyzed EC under steady, pulsatile and oscillatory flow and show that ciliation is indeed induced by the oscillatory nature of fluid flow. EC which are exposed to fluid shear stress respond with an acute intracellular calcium transient and release of vasoactive substances, and with a prolonged change in gene expression. The latter is mediated through the microtubular part of the cytoskeleton to which the primary cilium is connected. Targeting the cytoskeletal microtubules with colchicine, or experimental deciliation of EC, largely abolishes the shear response as measured by expression of the shear stress dependent gene Krüppel-like factor-2 (KLF2). In addition, stabilization by taxol enhances induction of KLF2 by shear stress. This shows that the primary cilium sensitizes EC for fluid shear stress. From these studies we conclude that disturbed or oscillatory flow in atherogenic areas induces a ciliated endothelial phenotype. In athero-protected areas cells are non-ciliated and rely on conformational changes of the microtubular cytoskeleton to sense shear stress. The mechanosensor for shear forces facilitates a two step response in endothelial cells: (1) an acute and transient increase in calcium and release of stored vasoactive substances, and (2) a prolonged phenotypic adaptation which is reflected by altered morphology and gene expression. This sheds new light in the epigenetic pathogenesis of atherosclerosis.