Adaptive reorientation of endothelial collectives in response to strain

Abstract

Mature epithelial monolayers share the ability to coherently respond to external mechanical stimuli. Tissue remodeling requires cell shape changes and coordinated movements. Human endothelia provide an exquisite example of such emerging collective activities. As part of their function in maintaining body homeostasis under variable hemodynamic loadings, endothelial ensembles must dynamically adapt to wall shear stress and cyclic deformation. While the alignment of several types of cells, including fibroblasts, osteoblasts and epithelial tissues, in response to various flow conditions or wall shear stress levels has been described in detail, less is known about collective endothelial remodeling under pure wall deformation. Here, using a custom-developed bioreactor, we exposed mature human endothelia to two distinct physiological levels of cyclic loading, generating overlapping gradients of strain. Endothelial cells remodeled depending on the level of imposed strain yielding local variations of cell density. In particular, a collective cell orientation orthogonal to the main direction of strain was observed at low levels of wall deformation, while cells reoriented parallel to the main direction of strain at high levels of wall deformation. The tissue adaptation depended on the establishment of mature adherens junctions, which were reinforced by the polarized recruitment of the adaptor protein vinculin. The pivotal role of cell-to-cell junctions was confirmed by the biochemical inhibition of vascular endothelial cadherin homotypic contacts, which impaired the collective remodeling. Together, our data establish wall deformation as an independent determinant of endothelial architecture with direct implications in vascular physiopathology.

Integration of substrate- and flow-derived stresses in endothelial cell mechanobiology

“…Large physiological strains (~10%), induce a final orientation that is closer to the "minimum strain direction" 228,247,255 , reduced orientation dispersion 220 , and accelerated dynamics 252 relative to smaller strains (~5%). For pathological strains, above 15%, the results are less clear, with reports of both orthogonal 252,256 and longitudinal alignment 250 . Possible explanations are differences in cell type (venous vs. arterial ECs) or in stretching profiles (free uniaxial vs. biaxial).…”

“…Cell confluency also modulates the response to strain amplitudes, suggesting an important role for cell-cell junctions 259 . The previously described switch of endothelial orientation from orthogonal to parallel to the stretch direction under pathological strain levels is lost when cell-cell junction formation is inhibited via blocking antibodies 250 . This collective orientation switch is hypothesized to be key for preserving monolayer integrity, which can be damaged under pathological strains 260 .…”

“…These platforms are mostly used to investigate functional responses to stretch, such as cell proliferation or changes in gene expression. Inflation of circular membranes generates equiaxial strain at the center, where cells are seen to be randomly oriented, and a gradient of anisotropic biaxial strain in the peripheral areas which complicates interpretation of cell orientation responses 249,250 . In contrast, radial stretching of circular membranes leads to uniform equiaxial strains 248 .…”

Non-pharmacological interventions for vascular health and the role of the endothelium

“…Cyclic strain in isolation has been shown to activate a number of mechanosensory pathways, through stretch-activated ion channels, ECM-cell adhesions (via the activation of integrins), and cell-cell interactions [via the VE-cadherin-PECAM-1-VEGFR2/3 mechanosensory complex (Jufri et al 2015)]. Collectively, these mechanisms enable cyclic strain to induce significant signalling responses and have been shown to induce changes in cell morphology and orientation in the absence of shear stress (Bernardi et al 2018). When investigated in combination with shear stress, the two haemodynamic forces have an additive effect on mechanosensory signalling pathways, although this response is not fully synergistic in nature, most likely due to the overlap in the pathways responsible for detecting shear and strain (Meza et al 2019).…”

Biofabrication Strategies and Engineered In Vitro Systems for Vascular Mechanobiology

“…[ 140 ] In addition, 3D microenvironments require considerations of strain propagation between endothelial branches in complex networks, as contracting vessels could potentially change the effective stiffness of the surrounding hydrogel. [ 170–172 ] Separating relative contributions of vessel contractility and fluid pressure will be key to accurately measuring cell‐generated forces in vascularized tissue constructs.…”