Study of the influence of actin-binding proteins using linear analyses of cell deformability

Abstract

The actin cytoskeleton plays a key role in the deformability of the cell and in mechanosensing. Here we analyze the contributions of three major actin cross-linking proteins, myosin II, α-actinin and filamin, to cell deformability, by using micropipette aspiration of Dictyostelium cells. We examine the applicability of three simple mechanical models: for small deformation, linear viscoelasticity and drop of liquid with a tense cortex; and for large deformation, a Newtonian viscous fluid. For these models, we have derived linearized equations and we provide a novel, straightforward methodology to analyze the experiments. This methodology allowed us to differentiate the effects of the cross-linking proteins in the different regimes of deformation. Our results confirm some previous observations and suggest important relations between the molecular characteristics of the actin-binding proteins and the cell behavior: the effect of myosin is explained in terms of the relation between the lifetime of the bond to actin and the resistive force; the presence of α-actinin obstructs the deformation of the cytoskeleton, presumably mainly due to the higher molecular stiffness and to the lower dissociation rate constants; and filamin contributes critically to the global connectivity of the network, possibly by rapidly turning over cross-links during the remodeling of the cytoskeletal network, thanks to the higher rate constants, flexibility and larger size. The results suggest a sophisticated relationship between the expression levels of actin-binding proteins, deformability and mechanosensing.

Biomechanical analysis of actin cytoskeleton function based on a spring network cell model

“…These results are in good accordance with previous studies, which revealed that the reduction of AFs and ABPs concentrations results in decrease in the cell stiffness. 21–25

Figure 8.(a) Effect of actin concentration enhancement on cell deformation behavior. (b) Effect of actin concentration augmentation on cell stiffness.

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Advances in Micropipette Aspiration: Applications in Cell Biomechanics, Models, and Extended Studies

“…Zhou et al studied the aspiration of a homogeneous neo-Hookean (incompressible) spherical cell (44). From their computed curves, they fitted a nonlinear equation, from which we obtained a linearized version (37):…”

“…5 may be directly used in experiments with constant pressure applied instantaneously at time t ¼ 0. If the pressure varies, the appropriate equation is obtained using the Boltzmann superposition principle (37).…”

“…The deformation behavior of cells, apart from depending on the length scale of observation, is affected by active change and internal structure determined by the state of the cell (36). Hence, the simplest continuum models, commonly used (37,38), do not reflect heterogeneity, anisotropy, and dynamic changes. However, they are very useful to assess mechanical parameters, allowing the comparison of cells in different states or different cells.…”

Probing the effect of tip pressure on fungal growth: Application toAspergillus nidulans

“…The pressure difference between fungal cytoplasm and extracellular medium, i.e., turgor pressure, is balanced by the fungal cell wall, in contrast to the support provided by the contractile actin-myosin cytoskeleton in other eukaryotic cells [32,33]. Considering the fungal wall as a thin membrane of homogenous thickness, the highest value of the stress is found in the circumferential direction of the wall, because this stress is twice the stress in the longitudinal direction and in the semispherical tip of the hypha [34].…”