Effects of Morphology vs. Cell–Cell Interactions on Endothelial Cell Stiffness

Abstract

Biological processes such as atherogenesis, wound healing, cancer cell metastasis, and immune cell transmigration rely on a delicate balance between Cell-Cell and cell-substrate adhesion. Cell mechanics have been shown to depend on substrate factors such as stiffness and ligand presentation, while the effects of Cell-Cell interactions on the mechanical properties of cells has received little attention. Here, we use atomic force microscopy to measure the Young's modulus of live human umbilical vein endothelial cells (HUVECs). In varying the degree of Cell-Cell contact in HUVECs (single cells, groups, and monolayers), we observe that increased cell stiffness correlates with an increase in cell area. Further, we observe that HUVECs stiffen as they spread onto a glass substrate. When we weaken Cell-Cell junctions (i.e., through a low dose of cytochalasin B or treatment with a VE-cadherin antibody), we observe that cell-substrate adhesion increases, as measured by focal adhesion size and density, and the stiffness of cells within the monolayer approaches that of single cells. Our results suggest that while morphology can roughly be used to predict cell stiffness, Cell-Cell interactions may play a significant role in determining the mechanical properties of individual cells in tissues by careful maintenance of cell tension homeostasis.

Regulation of Endothelial Cell Adherence and Elastic Modulus by Substrate Stiffness

“…Vascular endothelial cells are supported by their underlying basement membrane which plays major roles in their normal function. Alterations in different characteristics of such extracellular environment including its stiffness have been observed in the case of some vascular diseases (Baluk et al 2003;Liliensiek et al 2009;Stroka & Aranda-Espinoza 2011a;Yeh et al 2012). Such changes in the stiffness of the underlying substrate of endothelial cells can affect their function.…”

“…Therefore to assess cellular responses, previous studies have used different elastic moduli of substrates (for instance, 42 Pa-280 kPa (Stroka & Aranda-Espinoza 2011a) and 10 Pa-10 kPa (Saha et al 2008)). The choice of substrate stiffness depends on the substrate material, too.…”

“…While numerous studies have confirmed the importance of surface chemistry in cell-substrate interaction for successful performance of implants or tissue engineered constructs, the impact of mechanical parameters of substrate, such as stiffness on cellular functions has only been studied in the past 10 years Yeung et al 2005;Saha et al 2008;Byfield et al 2009;Stroka & Aranda-Espinoza 2011a;Yeh et al 2012;Huang et al 2013;Ataollahi et al 2015).…”

“…Some studies have examined cellular responses to the stiffness of different substrates, such as polyacrylamide (PAAM) (Lo et al 2000;Wang et al 2000;Engler et al 2004a;Stroka & Aranda-Espinoza 2011a;Galie et al 2015), Polydimethylsiloxane (PDMS) (Sarkar et al 2005;Ataollahi et al 2015) or alginate (Huang et al 2013), as such materials are biocompatible and can be fabricated using suitable methods to achieve desired stiffness values.…”

Nano-biomechanical investigation of living endothelial cells

“…It might be age dependent (Lieber et al 2004), nevertheless, on this time scale, direct connections cannot be made. Spreading HUVEC cells were reported to have morphology correlated stiffness (Stroka and Aranda-Espinoza 2011). Unfortunately, based on this study, it is difficult to draw valuable conclusions regarding our case, as in their experiments the cells were gently fixed.…”