Mapping the cytoskeletal prestress
Dept. of Environmental Health, Harvard School of Public Health, Boston, MA 02115, USA. AJP Cell Physiology
(Impact Factor: 3.78).
02/2010; 298(5):C1245-52. DOI: 10.1152/ajpcell.00417.2009
Cell mechanical properties on a whole cell basis have been widely studied, whereas local intracellular variations have been less well characterized and are poorly understood. To fill this gap, here we provide detailed intracellular maps of regional cytoskeleton (CSK) stiffness, loss tangent, and rate of structural rearrangements, as well as their relationships to the underlying regional F-actin density and the local cytoskeletal prestress. In the human airway smooth muscle cell, we used micropatterning to minimize geometric variation. We measured the local cell stiffness and loss tangent with optical magnetic twisting cytometry and the local rate of CSK remodeling with spontaneous displacements of a CSK-bound bead. We also measured traction distributions with traction microscopy and cell geometry with atomic force microscopy. On the basis of these experimental observations, we used finite element methods to map for the first time the regional distribution of intracellular prestress. Compared with the cell center or edges, cell corners were systematically stiffer and more fluidlike and supported higher traction forces, and at the same time had slower remodeling dynamics. Local remodeling dynamics had a close inverse relationship with local cell stiffness. The principal finding, however, is that systematic regional variations of CSK stiffness correlated only poorly with regional F-actin density but strongly and linearly with the regional prestress. Taken together, these findings in the intact cell comprise the most comprehensive characterization to date of regional variations of cytoskeletal mechanical properties and their determinants.
Available from: Dimitrije Stamenović
- "Therefore, past attempts to map subcellular stiffness and prestress had to rely on a priori assumptions regarding the nature of their distributions (Park et al., 2010; Tambe et al., 2013). "
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ABSTRACT: Local intracellular variations of cell mechanical properties, which are essential for vital cellular functions, have not been well characterized and are poorly understood. Here, we used results from our previous biomechanical imaging study to obtain relationships between intracellular shear modulus and prestress. We found that the subcellular shear modulus vs. prestress relationships exhibited positive linear correlations, consistent with previously observed behaviors at the whole cell and tissue levels. This, in turn, suggests that the prestress may be a unifying factor that determines material properties of living matter at different length scales.
Available from: Masaaki Sato
- "endothelial cells, in which a length change leading to buckling after compression of cells on a membrane sheet was measured. It is likely that the cell prestrain is generated due to the contractile activity of ubiquitous MIIs, resulting in that the intracellular stress-bearing components are physically extended beyond their unloaded length [Stamenovicánd Ingber, 2002; Wang et al., 2002; Paul et al., 2008; Park et al., 2010; Kaunas et al., 2011]. Quantification of prestrain magnitude and its spatial distribution in individual cells is important for accurate understanding of intracellular force transmission triggering mechanical stress-elicited functions. "
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ABSTRACT: It has been proposed that buckling of actin stress fibers (SFs) may be associated with their disassembly. However, much of the detail remains unknown partly because the use of an elastic membrane sheet, conventionally necessary for inducing SF buckling with a mechanical compression to adherent cells, may limit high quality and quick imaging of the dynamic cellular events. Here, we present an alternate approach to induce buckling behavior of SFs on a readily observable glass plate. Actin SFs were extracted from cells, and constituent myosin II (MII) molecules were partially photo-inactivated in contractility. An addition of Mg-ATP allowed actin-myosin cross-bridge cycling and resultant contraction of only thick SFs that still contained active MII in the large volume. Meanwhile, thin SFs with virtually no active motor protein in the small volume had no choice but to buckle with the shortening movement of nearby thick SFs functioning as a compression-inducing element. This novel technique, thus allowing for selective inductions of contraction and buckling of SFs and measurements of the cellular prestress, may be applicable to not only investigations on their disassembly mechanisms but also to measurements of the relative thickness of individual SFs in each cell.
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