Distinct impacts of substrate elasticity and ligand affinity on traction force evolution

Abstract

Cell adhesion is regulated by the mechanical characteristics of the cell environment. The influences of different parameters of the adhesive substrates are convoluted in the cell response leading to questions on the underlying mechanisms, like biochemical signaling on the level of adhesion molecules, or viscoelastic properties of substrates and cell. By a time-resolved analysis of traction force generation during early cell adhesion, we wanted to elucidate the contributions of substrate mechanics to the adhesion process, in particular the impact of substrate elasticity and the molecular friction of adhesion ligands on the substrate surface. Both parameters were independently adjusted by (i) an elastic polyacrylamide hydrogel of variable crosslinking degree and (ii) a thin polymer coating of the hydrogel surface controlling the affinity (and the correlated substrate-ligand friction) of the adhesion ligand fibronectin. Our analysis showed two sequential regimes of considerable force generation, whose occurrence was found to be independent of substrate properties. The first regime is characterized by spreading of the cell and a succeeding force increase. After spreading cells enter the second regime with saturated forces. Substrate elasticity and viscosity, namely hydrogel elasticity and ligand affinity, were both found to affect the kinetics and absolute levels of traction force quantities. A faster increase and a higher saturation level of traction forces were observed for a higher substrate stiffness and a higher ligand affinity. The results complement recent modeling approaches on the evolution of forces in cell spreading and contribute to a better understanding of the dynamics of cell adhesion on viscoelastic substrates.

Behavioral remodeling of normal and cancerous epithelial cell lines with differing invasion potential induced by substrate elastic modulus

“…The expression of adhesion markers, ITGB1, CADH1, which regulate adhesion of cells to the substrate and neighbouring cells was gradually enhanced by substrate stiffening (Figure 4). This is probably related to higher spreading which elevates the number of cell-substrate adhesion bonds, and increased cell traction forces that together enhance cell adhesion ability to the substrate [52,53]. Additionally cell-cell tension forces is proportional to cell-ECM traction forces [54].…”

The creatine–phosphagen system is mechanoresponsive in pancreatic adenocarcinoma and fuels invasion and metastasis

“…Nuclei were labelled with NucBlue Live reagent (R37605, Thermo Fisher Scientific) and blebbistatin (B0560; Sigma) treatment (10μM, 60min) was used as a control of relaxed cellular traction forces. Image stacks before and after cell dissociation were processed in Fiji using the StackReg plugin 54 and bead displacements due to cell tractions and cell tractions were calculated with a previously published unconstrained Fourier-transform traction cytometry method 55 . From the displacement field and traction force, the strain energy has been calculated.…”

Collagen: a network for regenerative medicine

“…Ligand density acts independently of matrix stiffness to determine the maximum forces generated by cells during adhesion. 84 The way in which the ligands are anchored in the ECM can also modulate cell expression. A 2.5 fold difference in collagen anchoring density was shown to determine stem cell fate.…”

“…It has been shown that both high substrate elasticity and high ligand affinity increase traction forces exerted by cells and raise the maximum traction force which can be exerted. 84 As integrin bonding is mediated by mechanosensing and ligand density, biological response to scaffolds is altered. 21 Thus, collagen scaffold cross-linking can direct biological responses, such as the differentiation of mesenchymal stem cells.…”