Three-dimensional cell body shape dictates the onset of traction force generation and growth of focal adhesions (original) (raw)
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The regulation of traction force in relation to cell shape and focal adhesions
Biomaterials, 2011
Mechanical forces provide critical inputs for proper cellular functions. The interplay between the generation of, and response to, mechanical forces regulate such cellular processes as differentiation, proliferation, and migration. We postulate that adherent cells respond to a number of physical and topographical factors, including cell size and shape, by detecting the magnitude and/or distribution of traction forces under different conditions. To address this possibility we introduce a new simple method for precise micropatterning of hydrogels, and then apply the technique to systematically investigate the relationship between cell geometry, focal adhesions, and traction forces in cells with a series of spread areas and aspect ratios. Contrary to previous findings, we find that traction force is not determined primarily by the cell spreading area but by the distance from cell center to the perimeter. This distance in turn controls traction forces by regulating the size of focal adhesions, such that constraining the size of focal adhesions by micropatterning can override the effect of geometry. We propose that the responses of traction forces to center-periphery distance, possibly through a positive feedback mechanism that regulates focal adhesions, provide the cell with the information on its own shape and size. A similar positive feedback control may allow cells to respond to a variety of physical or topographical signals via a unified mechanism.
Traction forces and rigidity sensing regulate cell functions
Soft Matter, 2008
Increasing evidence suggests that mechanical cues inherent to the extracellular matrix may be as important as its chemical nature in regulating cell behavior. Here, the response of cells to the mechanical properties of the substrate is examined by culturing 3T3 fibroblastic cells and epithelial cells on surfaces composed of a dense array of flexible microfabricated pillars. We focus on the influence of substrate rigidity on the traction forces exerted by cells, and on cell adhesion and migration. We first measure these forces by monitoring the deflection of the pillars. Then, by varying their geometric parameters, we control the substrate stiffness over a large range from 1 to 200 nN mm À1 . We show that the force-rigidity relationship exhibits a similar behavior for both cell types. Two distinct regimes are evidenced: first, a linear increase of the force with the rigidity and then a saturation plateau for the largest rigidities. We observe that the cell spreading area increases with increasing rigidity, as well as the size of focal adhesions. Substrates with an anisotropic rigidity allow us to determine that the migration paths of 3T3 cells are oriented in the stiffest direction in correlation with maximal traction forces. Finally, to compare the force measurements on micro-textured surfaces and continuous flexible gels, we propose an elastic model that estimates the equivalent Young's modulus of a micropillar substrate. This qualitative model gives comparable results for both experimental approaches.
Mechanisms Controlling Cell Size and Shape during Isotropic Cell Spreading
Biophysical Journal, 2010
Cell motility is important for many developmental and physiological processes. Motility arises from interactions between physical forces at the cell surface membrane and the biochemical reactions that control the actin cytoskeleton. To computationally analyze how these factors interact, we built a three-dimensional stochastic model of the experimentally observed isotropic spreading phase of mammalian fibroblasts. The multiscale model is composed at the microscopic levels of three actin filament remodeling reactions that occur stochastically in space and time, and these reactions are regulated by the membrane forces due to membrane surface resistance (load) and bending energy. The macroscopic output of the model (isotropic spreading of the whole cell) occurs due to the movement of the leading edge, resulting solely from membrane force-constrained biochemical reactions. Numerical simulations indicate that our model qualitatively captures the experimentally observed isotropic cell-spreading behavior. The model predicts that increasing the capping protein concentration will lead to a proportional decrease in the spread radius of the cell. This prediction was experimentally confirmed with the use of Cytochalasin D, which caps growing actin filaments. Similarly, the predicted effect of actin monomer concentration was experimentally verified by using Latrunculin A. Parameter variation analyses indicate that membrane physical forces control cell shape during spreading, whereas the biochemical reactions underlying actin cytoskeleton dynamics control cell size (i.e., the rate of spreading). Thus, during cell spreading, a balance between the biochemical and biophysical properties determines the cell size and shape. These mechanistic insights can provide a format for understanding how force and chemical signals together modulate cellular regulatory networks to control cell motility.
Molecular Biology of the Cell, 2015
Mechanical linkage between cell-cell and cell-extracellular matrix (ECM) adhesions regulates cell shape changes during embryonic development and tissue homoeostasis. We examined how the force balance between cell-cell and cell-ECM adhesions changes with cell spread area and aspect ratio in pairs of MDCK cells. We used ECM micropatterning to drive different cytoskeleton strain energy states and cell-generated traction forces and used a Förster resonance energy transfer tension biosensor to ask whether changes in forces across cell-cell junctions correlated with E-cadherin molecular tension. We found that continuous peripheral ECM adhesions resulted in increased cell-cell and cell-ECM forces with increasing spread area. In contrast, confining ECM adhesions to the distal ends of cell-cell pairs resulted in shorter junction lengths and constant cell-cell forces. Of interest, each cell within a cell pair generated higher strain energies than isolated single cells of the same spread area. Surprisingly, E-cadherin molecular tension remained constant regardless of changes in cell-cell forces and was evenly distributed along cell-cell junctions independent of cell spread area and total traction forces. Taken together, our results showed that cell pairs maintained constant E-cadherin molecular tension and regulated total forces relative to cell spread area and shape but independently of total focal adhesion area.
Unleashing shear: Role of intercellular traction and cellular moments in collective cell migration
Biochemical and Biophysical Research Communications
In the field of endothelial biology, the term "shear forces" is tied to the forces exerted by the flowing blood on the quiescent cells. But endothelial cells themselves also exert physical forces on their immediate and distant neighbors. Specific factors of such intrinsic mechanical signals most relevant to immediate neighbors include normal (F n) and shear (F s) components of intercellular tractions, and those factors most relevant to distant neighbors include contractile or dilatational (M c) and shear (M s) components of the moments of cytoskeletal forces. However, for cells within a monolayer, F n , F s , M c , and M s remain inaccessible to experimental evaluation. Here, we present an approach that enables quantitative assessment of these properties. Remarkably, across a collectively migrating sheet of pulmonary microvascular endothelial cells, F s was of the same order of magnitude as F n. Moreover, compared to the normal components (F n , M c) of the mechanical signals, the shear components (F s , M s) were more distinctive in the cells closer to the migration front. Individual cells had an innately collective tendency to migrate along the axis of maximum contractile moment e a collective migratory process we referred to as cellular plithotaxis. Notably, larger F s and M s were associated with stronger plithotaxis, but dilatational moment appeared to disengage plithotactic guidance. Overall, cellular plithotaxis was more strongly associated with the "shear forces" (F s , M s) than with the "normal forces" (F n , M c). Finally, the mechanical state of the cells with fast migration speed and those with highly circular shape were reminiscent of fluid-like and solid-like matter, respectively. The results repeatedly pointed to neighbors imposing shear forces on a cell as a highly significant event, and hence, the term "shear forces" must include not just the forces from flowing fluid but also the forces from the substrate and neighbors. Collectively, these advances set the stage for deeper understanding of mechanical signaling in cellular monolayers.
Current Opinion in Cell Biology, 2018
Biological patterns emerge through specialization of genetically identical cells to take up distinct fates according to their position within the organism. How initial symmetry is broken to give rise to these patterns remains an intriguing open question. Several theories of patterning have been proposed, most prominently Turing's reaction-diffusion model of a slowly diffusing activator and a fast diffusing inhibitor generating periodic patterns. Although these reaction-diffusion systems can generate diverse patterns, it is becoming increasingly evident that cell shape and tension anisotropies, mediated via cell-cell and/or cell-matrix contacts, also facilitate symmetry breaking and subsequent self-organized tissue patterning. This review will highlight recent studies that implicate local changes in adhesion and/or tension as key drivers of cell rearrangements. We will also discuss recent studies on the role of cadherin and integrin adhesive receptors in mediating and responding to local tissue tension asymmetries to coordinate cell fate, position and behavior essential for tissue selforganization and maintenance.
Spatial organization of adhesion: force-dependent regulation and function in tissue morphogenesis
Embo Journal, 2010
Integrin-and cadherin-mediated adhesion is central for cell and tissue morphogenesis, allowing cells and tissues to change shape without loosing integrity. Studies predominantly in cell culture showed that mechanosensation through adhesion structures is achieved by force-mediated modulation of their molecular composition. The specific molecular composition of adhesion sites in turn determines their signalling activity and dynamic reorganization. Here, we will review how adhesion sites respond to mecanical stimuli, and how spatially and temporally regulated signalling from different adhesion sites controls cell migration and tissue morphogenesis.
Cell shape provides global control of focal adhesion assembly
Biochemical and Biophysical Research Communications, 2003
Cell spreading was controlled independently of the amount and density of immobilized integrin ligand by culturing cells on single adhesive islands of different sizes (100-2500 lm 2 ) and shapes (squares, circles, and lines) or on many smaller (3-5 lm diameter) circular islands that were coated with a saturating density of fibronectin and separated by non-adhesive regions. The amount of focal adhesions (FAs) containing vinculin and phosphotyrosine increased in direct proportion to cell spreading under all conditions. FAs localized asymmetrically along the periphery of the small islands that experienced highest tensional stress, and FA staining increased when cytoskeletal tension was stimulated with thrombin, whereas inhibitors of contractility promoted FA disassembly. Thus, these findings demonstrate the existence of an "inside-out" mechanism whereby global cell distortion produces increases in cytoskeletal tension that feed back to drive local changes in FA assembly. This complex interplay between cell morphology, mechanics, and adhesion may be critical to how cells integrate from and function in living tissues.
Physics of cell adhesion: some lessons from cell-mimetic systems
Soft Matter, 2014
Cell adhesion is a paradigm of the ubiquitous interplay of cell signalling, modulation of material properties and biological functions of cells. It is controlled by competition of short range attractive forces, medium range repellant forces and the elastic stresses associated with local and global deformation of the composite cell envelopes. We review the basic physical rules governing the physics of cell adhesion learned by studying cell-mimetic systems and demonstrate the importance of these rules in the context of cellular systems. We review how adhesion induced micro-domains couple to the intracellular actin and microtubule networks allowing cells to generate strong forces with a minimum of attractive cell adhesion molecules (CAMs) and to manipulate other cells through filopodia over micrometer distances. The adhesion strength can be adapted to external force fluctuations within seconds by varying the density of attractive and repellant CAMs through exocytosis and endocytosis or protease-mediated dismantling of the CAM-cytoskeleton link. Adhesion domains form local end global biochemical reaction centres enabling the control of enzymes. Actin-microtubule crosstalk at adhesion foci facilitates the mechanical stabilization of polarized cell shapes. Axon growth in tissue is guided by attractive and repulsive clues controlled by antagonistic signalling pathways.