Mechanical strain increases cell stiffness through cytoskeletal filament reorganization

Abstract

We tested the hypothesis that cytoskeletal reorganization induced by cyclic strain increases cytoskeletal stiffness (G′). G′ was measured by optical magnetic twisting cytometry in control cells and cells that had received mechanical strain for 10–12 days. G′ was measured before and after both contractile and relaxant agonists, and in the strained cells both parallel (Para) and perpendicular (Perp) to the aligned cytoskeleton. Before activation, G′ Para was 24 ± 5% (± SE) greater compared with Perp ( P < 0.05), and 35% ± 6 greater compared with control (Cont, P < 0.01). The difference between strained and control cells was enhanced by KCl, increasing G′ 171 ± 7% Para compared with 125 ± 6% Perp and 129 ± 8% Cont ( P < 10-5 both cases). The decrease in G′ from baseline due to relaxant agonists isoproterenol and dibutyryl cAMP was similar in all groups. Long-term oscillatory loading of airway smooth muscle (ASM) cells caused stiffness to increase and become anisotropic. These findings are consistent with the hypothesis that cytoskeletal reorganization can enhance ASM stiffness and contractility. They imply, furthermore, that oscillatory loading of ASM may contribute to airway narrowing and failure of airway dilation in asthma.

A theoretical model for F-actin remodeling in vascular smooth muscle cells subjected to cyclic stretch

“…Many families of CSK proteins contribute to overall cell stiffness, but F-actin tends to dominate in many cases (Pourati et al, 1998;Wu et al, 1998;Smith et al, 2003;Na et al, 2004;Huang et al, 2005) and thus was the focus herein. There is increasing information available on the elasticity of F-actin, including isolated filaments, networks having different degrees of crosslinks, and stress fibers (e.g., Liu and Pollack, 2002;Gardel et al, 2004;Deguchi et al, 2006).…”

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

“…This can be adapted for acute studies to enable simultaneous assessment of cell morphology and signal transduction events, such as intracellular Ca 2+ flux. Another widely used approach for acute studies is to use magnetic twisting cytometry to apply force and measure stiffness of the underlying cytoskeleton [230,231]. Twisting cytometry, atomic force microscopy and videomicroscopy are currently the most effective approaches with which to assess cell stiffness and shortening in cultured cells.…”

“…These changes depend on strain magnitude and orientation, as discussed in sections below. In several studies, SMITH and coworkers [230,[242][243][244] have demonstrated that a predominantly uniaxial (stretch in one direction) strain of ,10% applied for several days in culture increases proliferation, force generation, expression of contractile proteins, calcium sensitivity and cytoskeletal stiffness with contractile activation. Perhaps the most dramatic changes they have been shown are a doubling in shortening capacity and shortening velocity [245].…”

Mechanotransduction, asthma and airway smooth muscle

“…Force sensing, however, can also induce altered gene regulation [37], and the resulting adaptation processes can go on over the course of days and weeks. For instance, cyclic stretch applied to smooth muscle cells result over a time course of 10-12 days to an alignment of the cells perpendicular to the stretch direction and to an upregulation of contractile protein expression [13].…”

“…Such a force balance need not be static in the sense that the degree of airway constriction reaches a steadystate, and indeed, over the past decade numerous experimental and theoretical studies have shown that airway caliber is equilibrated dynamically rather than statically [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Indeed, the force-length curve of activated smooth muscle is constantly changing as the muscle adapts to its mechanical surroundings, such as the length to which it is stretched or the load against which it must contract.…”