Fluid Shear Stress on Endothelial Cells Modulates Mechanical Tension across VE-Cadherin and PECAM-1

Abstract

Summary Fluid shear stress (FSS) from blood flow acting on the endothelium critically regulates vascular morphogenesis, blood pressure and atherosclerosis [1]. FSS applied to endothelial cells (EC) triggers signaling events including opening of ion channels, activation of signaling pathways and changes in gene expression. Elucidating how ECs sense flow important for understanding both normal vascular function and disease. EC responses to FSS are mediated in part by a junctional mechanosensory complex consisting of VE-cadherin, PECAM-1, and VEGFR2 [2]. Previous work suggested that flow increases force on PECAM-1, which initiates signaling [2–4]. Deletion of PECAM-1 blocks responses to flow in vitro and flow-dependent vascular remodeling in vivo [2, 5]. To understand this process, we developed and validated FRET-based tension sensors for VE-cadherin and PECAM-1 using our previously developed FRET tension biosensor [6]. FRET measurements showed that in static culture, VE-cadherin in cell-cell junctions bears significant myosin-dependent tension, whereas there was no detectable tension on VE-cadherin outside of junctions. Onset of shear stress triggered a rapid (<30 sec) decrease in tension across VE-cadherin, which paralleled a decrease in total cell-cell junctional tension. Flow triggered a simultaneous increase in tension across junctional PECAM-1, while non-junctional PECAM-1 was unaffected. Tension on PECAM-1 was mediated by flow-stimulated association with vimentin. These data confirm the prediction that shear increases force on PECAM-1. However, they also argue against the current model of passive transfer of force through the cytoskeleton to the junctions [7], showing instead that flow triggers cytoskeletal remodeling, which alters forces across the junctional receptors.

Endothelial basement membrane laminin 511 is essential for shear stress response

“…In contrast to PECAM‐1, tension across VE‐cadherin does not increase under flow but VE‐cadherin is nevertheless essential for shear response (Conway et al , 2013). The role of VE‐cadherin is not clear but it most likely regulates the strength of adhesion between individual cells (Daneshjou et al , 2015).…”

Intramembrane binding of VE-cadherin to VEGFR2 and VEGFR3 assembles the endothelial mechanosensory complex

“…It is dispensable for embryonic development but is required for flow induced vessel remodeling and contributes to inflammatory ac tivation at regions of disturbed flow and atherosclerosis (Goel et al, 2008;Harry et al, 2008;Stevens et al, 2008). Develop ment of a molecular force sensor showed that application of flow to ECs induces piconewton force across PECAM 1 (Conway et al, 2013), while direct application of force to PECAM 1 triggers some of the same pathways that are activated by flow (Osawa et al, 2002;Tzima et al, 2005). Thus, PECAM 1 ap pears to be a true mechanotransducer for fluid shear stress.…”

“…It is also essential for ligand independent activation of VEGFR2 by flow, though the nature of this requirement is poorly understood (Tzima et al, 2005). VEcad does not show any increase in tension after flow (Conway et al, 2013), does not activate relevant pathways when tension is applied through magnetic beads (Tzima et al, 2005), and thus does not directly transduce mechanical forces. The VEcad TMD confers binding to…”

Shear-induced force transmission in a multicomponent, multicell model of the endothelium

“…The transmission of FSS to cell-cell junctions has been suggested in previous studies, where PECAM-1 has been identified as a mechanosensor [71,81]. New findings indicate that shear stress triggers the association of PECAM-1 with vimentin, which transmits myosin-generated forces to PECAM-1 [71,81]. The magnitude of the force produced by a single myosin molecule falls in the range of 0.4-4 pN [3,76].…”