Sensing Fluid-Shear Stress in the Endothelial System with a Special Emphasis on the Primary Cilium

Abstract

Fluid shear stress (FSS) is able to generate phenotypic changes in the cells in direct contact with the strain force. In order to detect and transduce FSS into intracellular pathways, biological systems use a specific set of sensors, called mechanosensors. The process involves the conversion of the mechanical force into a chemical or electrical signal. Primary cilium is a non-motile organelle that emanates from the cell surface of most mam- malian cell types that act as a mechanosensor. Increasing evidence suggests that primary cilia are key coordinators of signaling pathways in tissue homeostasis and when defective may cause human diseases and developmental disorders. Here, we will describe the endothelial primary cilium as a mechanotransductory organelle sensing FSS. To fulfill this function, primary cilium requires the localization of mechanoproteins, polycystin-1 and 2, in their membrane and the structural gene product, polaris. Physiologically, deflection of primary cilium increases the intracellular calcium concentration triggering a signaling pathway that leads to nitric oxide (NO) formation and vasodilation. Additionally, ciliopathies, such as polycystic kidney disease and atherosclerosis, will also be discussed. We also analyze available information regarding a trio of membrane receptors involved in FSS sensing and transducing such as vascular endothelial growth factor receptors (VEGFRs) and its coreceptor neuropilin (NRP), as well as purinergic receptors (P2Y2). Whether or not they modulate, the primary cilium role in sensing FSS is poorly under-stood. This chapter highlights the main relevance of primary cilium in sensing blood flow, although exact mechanisms are not fully known yet.