Effects of substrate mechanics on angiogenic capacity and nitric oxide release in human endothelial cells.

Loss of vascular elasticity results from progressive degeneration of the extracellular matrix of elastic arteries under the effect of aging and certain diseases, including atherosclerosis. To investigate the influence of vessel wall stiffening on endothelial cell (EC) function, we seeded human umbilical vein ECs onto variably compliant polydimethylsiloxane substrates. When plated on the more compliant substrate, ECs assembled into capillary-like structures. By contrast, they failed to form a network on stiff substrates, even in the presence of vascular endothelial growth factor (VEGF). Cell proliferation and migration increased with stiffness, while ECs released more nitric oxide (NO) on the soft substrate. Treatment with VEGF increased migration and NO release in a stiffness-dependent manner. Atomic force microscopy measurement of cell elasticity along with actin fiber analysis revealed that ECs plated on the more compliant surface were mechanically softer, with mostly diffuse actin arrangement. Our results demonstrate that matrix stiffening induces actin reorganizations, reflected by cortical stiffening in ECs, which may lead to a decrease in their angiogenic capacity and NO release. Hence, the mechanical properties of ECs display a prognostic and therapeutic potential and might serve as a reliable biomarker of vascular function.

Cytoskeletal remodeling induced by substrate rigidity regulates rheological behaviors in endothelial cells.

Altered microenvrionmental mechanical cues induce cytoskeletal remodeling in cells and have a profound impact on their functions as well as rheological properties. This article is aimed to characterize the viscoelastic behavior of endothelial cells, cultivated on variably compliant substrates. Synthetic tunable poly(dimethylsyloxane) substrates, with elastic moduli ranging from 1.5 MPa to 3 kPa, were used to trigger cytoskeletal remodeling of endothelial cells, verified by morphological analysis and actin fluorescent labeling. Elasticity and stress relaxation tests were conducted using an AFM, resulting in a wide range of data. To account for this heterogeneity, fuzzy c-means clustering algorithm was applied to partition elastic data into biologically meaningful groups, representative of different regions in cells. Nanocharacterization of biomechanical properties, along with cytoskeletal studies, proved a significant correlation between substrate flexibility and viscoelasticity of the cells. Regardless of the viscoelastic model applied, increasing substrate rigidity was related to an overall increase in cell stiffness and apparent viscosity (2.95 ± 1.56 kPa and 921.45 ± 102.46 Pa.s for the stiff substrate; 2.17 ± 1.30 kPa and 557.37 ± 494.11 Pa.s for the intermediate substrate), associated with an organized actin cytoskeleton. Conversely, cells on soft substrate were more deformable (1.84 ± 1.3 kPa) and less viscous (327.13 ± 124.25 Pa.s), exhibiting an increased actin disorganization. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 71-80, 2019.