The effect of remodelling and contractility of the actin cytoskeleton on the shear resistance of single cells: a computational and experimental investigation

Abstract

The biomechanisms that govern the response of chondrocytes to mechanical stimuli are poorly understood. In this study, a series of in vitro tests are performed, in which single chondrocytes are subjected to shear deformation by a horizontally moving probe. Dramatically different probe force -indentation curves are obtained for untreated cells and for cells in which the actin cytoskeleton has been disrupted. Untreated cells exhibit a rapid increase in force upon probe contact followed by yielding behaviour. Cells in which the contractile actin cytoskeleton was removed exhibit a linear force -indentation response. In order to investigate the mechanisms underlying this behaviour, a three-dimensional active modelling framework incorporating stress fibre (SF) remodelling and contractility is used to simulate the in vitro tests. Simulations reveal that the characteristic force -indentation curve observed for untreated chondrocytes occurs as a result of two factors: (i) yielding of SFs due to stretching of the cytoplasm near the probe and (ii) dissociation of SFs due to reduced cytoplasm tension at the front of the cell. In contrast, a passive hyperelastic model predicts a linear force -indentation curve similar to that observed for cells in which the actin cytoskeleton has been disrupted. This combined modelling -experimental study offers a novel insight into the role of the active contractility and remodelling of the actin cytoskeleton in the response of chondrocytes to mechanical loading.

A chemo-mechanical free-energy-based approach to model durotaxis and extracellular stiffness-dependent contraction and polarization of cells

“…Motivated by previous experimental and computational work [35], we modelled the steady-state stress developed, s, and the contractility, r, in a cell on a substrate, illustrated in figure 7. The cylindrical substrate and the spherical nucleus are modelled as linear elastic materials with Poisson's ratio 0.3.…”

Cellular contractility and substrate elasticity: a numerical investigation of the actin cytoskeleton and cell adhesion

“…The material parameters used in the current study are based on previous implementations of the current formulation which were used to simulate cells adhered to microposts and cells under direct shear (McGarry et al 2009;Dowling et al 2012). In order to investigate the role of contractility, In order to visualise the resulting 3D SF distributions, two output variables are considered.…”

“…The role of contractility was investigated in the current study by considering three cell phenotypes representing a spectrum of cellular contractility: smooth muscle cells, fibroblasts, and chondrocytes (in order of decreasing contractility). The parameters required to simulate the active contractility of these cells were identified in previous implementations of the material formulation employed here (Dowling et al 2012;McGarry et al 2009). The range of substrate stiffness that has the greatest effect on the substrate-dependent response of each cell type is identified by considering the level of SF formation and average nucleus stress.…”

Computational investigation of in situ chondrocyte deformation and actin cytoskeleton remodelling under physiological loading

“…A recent computational-experimental study by Dowling et al [22] demonstrates the ability of this active framework to accurately simulate the biomechanical response of chondrocytes to applied deformation. In summary, Dowling et al [22] performed a series of in vitro tests in which single bovine chondrocytes were subjected to shear deformation by a horizontally moving probe.…”

“…However, these models of chondrocytes have considered the cell as a passive, homogeneous material. A recent computational-experimental study by Dowling et al [22] has demonstrated that an active modelling framework, based on the bio-chemomechanics of the actin cytoskeleton [23], must be used to elucidate the mechanisms underlying the behaviour of in vitro chondrocytes during shear deformation. Dowling et al [22] also demonstrated that a passive material model captures chondrocyte behaviour only if the actin cytoskeleton is disrupted using cytochalasin-D (further details of this study can be found in Section 2.2).…”