Figure 7. Model for the role of primary cilia in shear response of EC.

Depending on the flow pattern EC can be ciliated or not. The center picture shows a scanning electron micrograph of an endothelial cilium. When ciliated EC (+) are exposed to shear stress they show induction of Klf2 and Klf4 and retain a cobblestone endothelial phenotype (green arrow). However, when non-ciliated cells (-) are exposed to flow they fail to induce Klf2 and downregulate Klf4. They lose their endothelial characteristics and acquire a mesenchymal or transition phenotype (red arrow/cells) in a Tgfβ/Alk5 dependent manner. This potentially pathological transition can be prevented by e.g. blocking Tgfß signaling or by inducing Klf4 expression.