201
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DiPaolo BC, Lenormand G, Fredberg JJ, Margulies SS. Stretch magnitude and frequency-dependent actin cytoskeleton remodeling in alveolar epithelia. Am J Physiol Cell Physiol 2010; 299:C345-53. [PMID: 20519449 DOI: 10.1152/ajpcell.00379.2009] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Alveolar epithelial cells (AEC) maintain integrity of the blood-gas barrier with gasket-like intercellular tight junctions (TJ) that are anchored internally to the actin cytoskeleton. We hypothesize that stretch rapidly reorganizes actin (<10 min) into a perijunctional actin ring (PJAR) in a manner that is dependent on magnitude and frequency of the stretch, accompanied by spontaneous movement of actin-anchored receptors at the plasma membrane. Primary AEC monolayers were stretched biaxially to create a change in surface area (DeltaSA) of 12%, 25%, or 37% in a cyclic manner at 0.25 Hz for up to 60 min, or held tonic at 25% DeltaSA for up to 60 min, or left unstretched. By 10 min of stretch PJARs were evident in 25% and 37% DeltaSA at 0.25 Hz, but not for 12% DeltaSA at 0.25 Hz, or at tonic 25% DeltaSA, or with no stretch. Treatment with 1 muM jasplakinolide abolished stretch-induced PJAR formation, however. As a rough index of remodeling rate, we measured spontaneous motions of 5-mum microbeads bound to actin focal adhesion complexes on the apical membrane surfaces; within 1 min of exposure to DeltaSA of 25% and 37%, these motions increased substantially, increased with increasing stretch frequency, and were consistent with our mechanistic hypothesis. With a tonic stretch, however, the spontaneous motion of microbeads attenuated back to unstretched levels, whereas PJAR remained unchanged. Stretch did not increase spontaneous microbead motion in human alveolar epithelial adenocarcinoma A549 monolayers, confirming that this actin remodeling response to stretch was a cell-type specific response. In summary, stretch of primary rat AEC monolayers forms PJARs and rapidly reorganized actin binding sites at the plasma membrane in a manner dependent on stretch magnitude and frequency.
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Affiliation(s)
- Brian C DiPaolo
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania19104-6321, USA
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202
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Metzner C, Raupach C, Mierke CT, Fabry B. Fluctuations of cytoskeleton-bound microbeads--the effect of bead-receptor binding dynamics. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:194105. [PMID: 21386432 DOI: 10.1088/0953-8984/22/19/194105] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The cytoskeleton (CSK) of living cells is a crosslinked fiber network, subject to ongoing biochemical remodeling processes that can be visualized by tracking the spontaneous motion of CSK-bound microbeads. The bead motion is characterized by anomalous diffusion with a power-law time evolution of the mean square displacement (MSD), and can be described as a stochastic transport process with apparent diffusivity D and power-law exponent β: MSD ∼ D (t/t(0))(β). Here we studied whether D and β change with the time that has passed after the initial bead-cell contact, and whether they are sensitive to bead coating (fibronectin, integrin antibodies, poly-L-lysine, albumin) and bead size (0.5-4.5 µm). The measurements are interpreted in the framework of a simple model that describes the bead as an overdamped particle coupled to the fluctuating CSK network by an elastic spring. The viscous damping coefficient characterizes the degree of bead internalization into the cell, and the spring constant characterizes the strength of the binding of the bead to the CSK. The model predicts distinctive signatures of the MSD that change with time as the bead couples more tightly to the CSK and becomes internalized. Experimental data show that the transition from the unbound to the tightly bound state occurs in an all-or-nothing manner. The time point of this transition shows considerable variability between individual cells (2-30 min) and depends on the bead size and bead coating. On average, this transition occurs later for smaller beads and beads coated with ligands that trigger the formation of adhesion complexes (fibronectin, integrin antibodies). Once the bead is linked to the CSK, however, the ligand type and bead size have little effect on the MSD. On longer timescales of several hours after bead addition, smaller beads are internalized into the cell more readily, leading to characteristic changes in the MSD that are consistent with increased viscous damping by the cytoplasm and reduced binding strength.
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Affiliation(s)
- C Metzner
- Center for Medical Physics and Technology, University of Erlangen-Nuremberg, Erlangen, Germany
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203
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Park Y, Best CA, Badizadegan K, Dasari RR, Feld MS, Kuriabova T, Henle ML, Levine AJ, Popescu G. Measurement of red blood cell mechanics during morphological changes. Proc Natl Acad Sci U S A 2010; 107:6731-6. [PMID: 20351261 PMCID: PMC2872375 DOI: 10.1073/pnas.0909533107] [Citation(s) in RCA: 236] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The human red blood cell (RBC) membrane, a fluid lipid bilayer tethered to an elastic 2D spectrin network, provides the principal control of the cell's morphology and mechanics. These properties, in turn, influence the ability of RBCs to transport oxygen in circulation. Current mechanical measurements of RBCs rely on external loads. Here we apply a noncontact optical interferometric technique to quantify the thermal fluctuations of RBC membranes with 3 nm accuracy over a broad range of spatial and temporal frequencies. Combining this technique with a new mathematical model describing RBC membrane undulations, we measure the mechanical changes of RBCs as they undergo a transition from the normal discoid shape to the abnormal echinocyte and spherical shapes. These measurements indicate that, coincident with this morphological transition, there is a significant increase in the membrane's shear, area, and bending moduli. This mechanical transition can alter cell circulation and impede oxygen delivery.
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Affiliation(s)
- YongKeun Park
- G. R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Catherine A. Best
- College of Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Kamran Badizadegan
- G. R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
- Department of Pathology, Harvard Medical School and Massachusetts General Hospital, Boston, MA 02114
| | - Ramachandra R. Dasari
- G. R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Michael S. Feld
- G. R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
| | | | - Mark L. Henle
- School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138
| | - Alex J. Levine
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095; and
| | - Gabriel Popescu
- G. R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
- Quantitative Light Imaging Laboratory, Department of Electrical and Computer Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
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204
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In vivo determination of fluctuating forces during endosome trafficking using a combination of active and passive microrheology. PLoS One 2010; 5:e10046. [PMID: 20386607 PMCID: PMC2850365 DOI: 10.1371/journal.pone.0010046] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Accepted: 03/07/2010] [Indexed: 11/19/2022] Open
Abstract
Background Regulation of intracellular trafficking is a central issue in cell biology. The forces acting on intracellular vesicles (endosomes) can be assessed in living cells by using a combination of active and passive microrheology. Methodology/Principal Findings This dual approach is based on endosome labeling with magnetic nanoparticles. The resulting magnetic endosomes act both as probes that can be manipulated with external magnetic fields to infer the viscoelastic modulus of their surrounding microenvironment, and as biological vehicles that are trafficked along the microtubule network by means of forces generated by molecular motors. The intracellular viscoelastic modulus exhibits power law dependence with frequency, which is microtubule and actin-dependent. The mean square displacements of endosomes do not follow the predictions of the fluctuation-dissipation theorem, which offers evidence for active force generation. Microtubule disruption brings the intracellular medium closer to thermal equilibrium: active forces acting on the endosomes depend on microtubule-associated motors. The power spectra of these active forces, deduced through the use of a generalized Langevin equation, show a power law decrease with frequency and reveal an actin-dependent persistence of the force with time. Experimental spectra have been reproduced by a simple model consisting in a series of force steps power-law distributed in time. This model enlightens the role of the cytoskeleton dependent force exerted on endosomes to perform intracellular trafficking. Conclusions/Significance In this work, the influence of cytoskeleton components and molecular motors on intracellular viscoelasticity and transport is addressed. The use of an original probe, the magnetic endosome, allows retrieving the power spectrum of active forces on these organelles thanks to interrelated active and passive measures. Finally a computational model gives estimates of the force itself and hence of the number of the motors pulling on endosomes.
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205
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Head DA, Mizuno D. Nonlocal fluctuation correlations in active gels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:041910. [PMID: 20481756 DOI: 10.1103/physreve.81.041910] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Indexed: 05/29/2023]
Abstract
Many active materials and biological systems are driven far from equilibrium by embedded agents that spontaneously generate forces and distort the surrounding material. Probing and characterizing these athermal fluctuations are essential to understand the properties and behaviors of such systems. Here we present a mathematical procedure to estimate the local action of force-generating agents from the observed fluctuating displacement fields. The active agents are modeled as oriented force dipoles or isotropic compression foci, and the matrix on which they act is assumed to be either a compressible elastic continuum or a coupled network-solvent system. Correlations at a single point and between points separated by an arbitrary distance are obtained, giving a total of three independent fluctuation modes that can be tested with microrheology experiments. Since oriented dipoles and isotropic compression foci give different contributions to these fluctuation modes, ratiometric analysis allows us characterize the force generators. We also predict and experimentally find a high-frequency ballistic regime, arising from individual force-generating events in the form of the slow buildup of stress followed by rapid but finite decay. Finally, we provide a quantitative statistical model to estimate the mean filament tension from these athermal fluctuations, which leads to stiffening of active networks.
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Affiliation(s)
- D A Head
- Institute of Industrial Science, University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan
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206
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Berntsen P, Park CY, Rothen-Rutishauser B, Tsuda A, Sager TM, Molina RM, Donaghey TC, Alencar AM, Kasahara DI, Ericsson T, Millet EJ, Swenson J, Tschumperlin DJ, Butler JP, Brain JD, Fredberg JJ, Gehr P, Zhou EH. Biomechanical effects of environmental and engineered particles on human airway smooth muscle cells. J R Soc Interface 2010; 7 Suppl 3:S331-40. [PMID: 20356875 DOI: 10.1098/rsif.2010.0068.focus] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The past decade has seen significant increases in combustion-generated ambient particles, which contain a nanosized fraction (less than 100 nm), and even greater increases have occurred in engineered nanoparticles (NPs) propelled by the booming nanotechnology industry. Although inhalation of these particulates has become a public health concern, human health effects and mechanisms of action for NPs are not well understood. Focusing on the human airway smooth muscle cell, here we show that the cellular mechanical function is altered by particulate exposure in a manner that is dependent upon particle material, size and dose. We used Alamar Blue assay to measure cell viability and optical magnetic twisting cytometry to measure cell stiffness and agonist-induced contractility. The eight particle species fell into four categories, based on their respective effect on cell viability and on mechanical function. Cell viability was impaired and cell contractility was decreased by (i) zinc oxide (40-100 nm and less than 44 microm) and copper(II) oxide (less than 50 nm); cell contractility was decreased by (ii) fluorescent polystyrene spheres (40 nm), increased by (iii) welding fumes and unchanged by (iv) diesel exhaust particles, titanium dioxide (25 nm) and copper(II) oxide (less than 5 microm), although in none of these cases was cell viability impaired. Treatment with hydrogen peroxide up to 500 microM did not alter viability or cell mechanics, suggesting that the particle effects are unlikely to be mediated by particle-generated reactive oxygen species. Our results highlight the susceptibility of cellular mechanical function to particulate exposures and suggest that direct exposure of the airway smooth muscle cells to particulates may initiate or aggravate respiratory diseases.
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Affiliation(s)
- P Berntsen
- Molecular and Integrative Physiological Sciences, Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA
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207
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Park CY, Tambe D, Alencar AM, Trepat X, Zhou EH, Millet E, Butler JP, Fredberg JJ. Mapping the cytoskeletal prestress. Am J Physiol Cell Physiol 2010; 298:C1245-52. [PMID: 20164383 DOI: 10.1152/ajpcell.00417.2009] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
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.
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Affiliation(s)
- Chan Young Park
- Dept. of Environmental Health, Harvard School of Public Health, Boston, MA 02115, USA
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208
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Abstract
The ability of a eukaryotic cell to resist deformation, to transport intracellular cargo and to change shape during movement depends on the cytoskeleton, an interconnected network of filamentous polymers and regulatory proteins. Recent work has demonstrated that both internal and external physical forces can act through the cytoskeleton to affect local mechanical properties and cellular behaviour. Attention is now focused on how cytoskeletal networks generate, transmit and respond to mechanical signals over both short and long timescales. An important insight emerging from this work is that long-lived cytoskeletal structures may act as epigenetic determinants of cell shape, function and fate.
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Affiliation(s)
- Daniel A Fletcher
- Bioengineering and Biophysics, University of California, Berkeley, California 94720, USA.
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209
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Abstract
A low-cost micro-incubator for imaging dynamic processes in living cells and tissues has been developed. This micro-incubator provides a tunable environment that can be altered to study responses of cell monolayers for several days as well as relatively thick tissue samples and tissue-engineered epithelial tissues in experiments lasting several hours. Samples are contained in a sterile cavity closed by a gas-permeable membrane. The incubator can be positioned in any direction and used on an inverted or upright microscope. Temperature is regulated using a Peltier module controlled by a sensor positioned close to the sample, enabling compensation for any changes in temperature. Rapid changes in a sample's surrounding environment can be achieved due to the fast response of the Peltier module. These features permit monitoring of sample adaptation to induced environmental changes.
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210
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Joo C, Evans CL, Stepinac T, Hasan T, de Boer JF. Diffusive and directional intracellular dynamics measured by field-based dynamic light scattering. OPTICS EXPRESS 2010; 18:2858-71. [PMID: 20174115 PMCID: PMC2839546 DOI: 10.1364/oe.18.002858] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Quantitative measurement of diffusive and directional processes of intracellular structures is not only critical in understanding cell mechanics and functions, but also has many applications, such as investigation of cellular responses to therapeutic agents. We introduce a label-free optical technique that allows non-perturbative characterization of localized intracellular dynamics. The method combines a field-based dynamic light scattering analysis with a confocal interferometric microscope to provide a statistical measure of the diffusive and directional motion of scattering structures inside a microscopic probe volume. To demonstrate the potential of this technique, we examined the localized intracellular dynamics in human epithelial ovarian cancer cells. We observed the distinctive temporal regimes of intracellular dynamics, which transitions from random to directional processes on a timescale of ~0.01 sec. In addition, we observed disrupted directional processes on the timescale of 1 approximately 5 sec by the application of a microtubule polymerization inhibitor, Colchicine, and ATP depletion.
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Affiliation(s)
- Chulmin Joo
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts 02114,
U.S.A.
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,
U.S.A.
| | - Conor L. Evans
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts 02114,
U.S.A.
| | - Thomas Stepinac
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts 02114,
U.S.A.
| | - Tayyaba Hasan
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts 02114,
U.S.A.
| | - Johannes F. de Boer
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts 02114,
U.S.A.
- Department of Physics and Astronomy, VU University, De Boelelaan 1081, 1081 HV Amsterdam,
The Netherlands
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211
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Bonnecaze RT, Cloitre M. Micromechanics of Soft Particle Glasses. HIGH SOLID DISPERSIONS 2010. [DOI: 10.1007/12_2010_90] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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212
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Chowdhury F, Na S, Li D, Poh YC, Tanaka TS, Wang F, Wang N. Material properties of the cell dictate stress-induced spreading and differentiation in embryonic stem cells. NATURE MATERIALS 2010; 9:82-8. [PMID: 19838182 PMCID: PMC2833279 DOI: 10.1038/nmat2563] [Citation(s) in RCA: 412] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2009] [Accepted: 10/01/2009] [Indexed: 05/09/2023]
Abstract
Growing evidence suggests that physical microenvironments and mechanical stresses, in addition to soluble factors, help direct mesenchymal-stem-cell fate. However, biological responses to a local force in embryonic stem cells remain elusive. Here we show that a local cyclic stress through focal adhesions induced spreading in mouse embryonic stem cells but not in mouse embryonic stem-cell-differentiated cells, which were ten times stiffer. This response was dictated by the cell material property (cell softness), suggesting that a threshold cell deformation is the key setpoint for triggering spreading responses. Traction quantification and pharmacological or shRNA intervention revealed that myosin II contractility, F-actin, Src or cdc42 were essential in the spreading response. The applied stress led to oct3/4 gene downregulation in mES cells. Our findings demonstrate that cell softness dictates cellular sensitivity to force, suggesting that local small forces might have far more important roles in early development of soft embryos than previously appreciated.
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Affiliation(s)
- Farhan Chowdhury
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, IL 61801
| | - Sungsoo Na
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, IL 61801
| | - Dong Li
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, IL 61801
| | - Yeh-Chuin Poh
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, IL 61801
| | - Tetsuya S. Tanaka
- Department of Animal Sciences, University of Illinois at Urbana-Champaign, IL 61801
| | - Fei Wang
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, IL 61801
| | - Ning Wang
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, IL 61801
- To whom correspondence should be addressed.
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213
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Abstract
Dynamic regulation of the filamentous actin (F-actin) cytoskeleton is critical to numerous physical cellular processes, including cell adhesion, migration and division. Each of these processes require precise regulation of cell shape and mechanical force generation which, to a large degree, is regulated by the dynamic mechanical behaviors of a diverse assortment of F-actin networks and bundles. In this review, we review the current understanding of the mechanics of F-actin networks and identify areas of further research needed to establish physical models. We first review our understanding of the mechanical behaviors of F-actin networks reconstituted in vitro, with a focus on the nonlinear mechanical response and behavior of "active" F-actin networks. We then explore the types of mechanical response measured of cytoskeletal F-actin networks and bundles formed in living cells and identify how these measurements correspond to those performed on reconstituted F-actin networks formed in vitro. Together, these approaches identify the challenges and opportunities in the study of living cytoskeletal matter.
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214
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Huang R, Grabarek Z, Wang CLA. Differential effects of caldesmon on the intermediate conformational states of polymerizing actin. J Biol Chem 2009; 285:71-9. [PMID: 19889635 DOI: 10.1074/jbc.m109.065078] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The actin-binding protein caldesmon (CaD) reversibly inhibits smooth muscle contraction. In non-muscle cells, a shorter CaD isoform co-exists with microfilaments in the stress fibers at the quiescent state, but the phosphorylated CaD is found at the leading edge of migrating cells where dynamic actin filament remodeling occurs. We have studied the effect of a C-terminal fragment of CaD (H32K) on the kinetics of the in vitro actin polymerization by monitoring the fluorescence of pyrene-labeled actin. Addition of H32K or its phosphorylated form either attenuated or accelerated the pyrene emission enhancement, depending on whether it was added at the early or the late phase of actin polymerization. However, the CaD fragment had no effect on the yield of sedimentable actin, nor did it affect the actin ATPase activity. Our findings can be explained by a model in which nascent actin filaments undergo a maturation process that involves at least two intermediate conformational states. If present at early stages of actin polymerization, CaD stabilizes one of the intermediate states and blocks the subsequent filament maturation. Addition of CaD at a later phase accelerates F-actin formation. The fact that CaD is capable of inhibiting actin filament maturation provides a novel function for CaD and suggests an active role in the dynamic reorganization of the actin cytoskeleton.
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Affiliation(s)
- Renjian Huang
- Boston Biomedical Research Institute, Watertown, Massachusetts 02472, USA
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215
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Tamura K, Mizutani T, Haga H, Kawabata K. Dynamics of leading lamellae of living fibroblasts visualized by high-speed scanning probe microscopy. Histochem Cell Biol 2009; 133:59-67. [PMID: 19816705 DOI: 10.1007/s00418-009-0644-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/21/2009] [Indexed: 10/24/2022]
Abstract
In this study, we aimed at improving the temporal resolution of scanning probe microscopy (SPM) for observing living cells by introducing soft cantilevers, low feedback-gain operations, and cantilever deflection imaging. We achieved visualization of the mechanical architecture in leading lamellae of living fibroblasts at a temporal resolution of around 10 s, which is higher than that of conventional contact-mode SPM. Time-lapse SPM could be used to monitor not only cytoskeletal dynamics but also the dynamics of numerous microgranules. Statistical analysis of microgranular motion revealed that the microgranules have superdiffusive behaviors and significant directional order of motion. We also found that the direction of their motion is correlated with the direction of growing actin stress fibers. The combination of SPM with fluorescence microscopy showed that vinculin, a component of cell-substratum adhesion sites, localizes at the microgranules. Our experimental data provides a new insight into the intracellular mechanical architecture and its structural dynamics, suggesting that high-speed live-cell SPM has great potential for investigating the structural origin of cellular dynamics.
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Affiliation(s)
- Kazushi Tamura
- Division of Biological Sciences, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo, Japan.
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216
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Hoffman BD, Crocker JC. Cell mechanics: dissecting the physical responses of cells to force. Annu Rev Biomed Eng 2009; 11:259-88. [PMID: 19400709 DOI: 10.1146/annurev.bioeng.10.061807.160511] [Citation(s) in RCA: 189] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
It is now widely appreciated that normal tissue morphology and function rely upon cells' ability to sense and generate forces appropriate to their correct tissue context. Although the effects of forces on cells have been studied for decades, our understanding of how those forces propagate through and act on different cell substructures remains at an early stage. The past decade has seen a resurgence of interest, with a variety of different micromechanical methods in current use that probe cells' dynamic deformation in response to a time-varying force. The ability of researchers to carefully measure the mechanical properties of cells subjected to a variety of pharmacological and genetic interventions, however, currently outstrips our ability to quantitatively interpret the data in many cases. Despite these challenges, the stage is now set for the development of detailed models for cell deformability, motility, and mechanosensing that are rooted at the molecular level.
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Affiliation(s)
- Brenton D Hoffman
- Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia 22901, USA.
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217
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Abstract
The integrin lies at the center of our efforts to understand mechanotransduction in the human body. Over the past two decades, a wealth of information has yielded important insights into integrin structure and functioning in biochemical pathways; however, relatively little emphasis has been placed on mechanics. In this article, we review the current knowledge base of integrin mechanobiology by examining the role of integrins in stabilizing tissue structure, the mechanisms of integrin force transfer, the process of cell migration, and the pathology of cancer. In order to successfully address the gaps in cancer and other disease research going forward, future efforts of integrin mechanobiology must focus on examining cells in 3D environments and integrating our current understanding into computational models that predict the behavior of integrins in non-equilibrium interactions.
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Affiliation(s)
- Erin L Baker
- Department of Biomedical Engineering, The University of Texas at Austin, USA
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218
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Picard C, Donald A. The impact of environmental changes upon the microrheological response of adherent cells. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2009; 30:127-134. [PMID: 19551417 DOI: 10.1140/epje/i2009-10473-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2009] [Revised: 05/05/2009] [Accepted: 05/11/2009] [Indexed: 05/28/2023]
Abstract
The mechanical behaviour of adherent cells cultured in vitro is known to be dependent on the mechanical properties of the substrate. We show that this mechanical behaviour is also strongly affected by the cells' environment. We focus here on the impact of temperature and pH. Experiments carried out on individual cells in a tuneable environment reveal that the intra-cellular mechanical behaviour exhibits large and fast changes when the external cell environment is changed. Fast passive microrheometry measurements allow for the precise characterisation of the transient regime observed during a temperature drop. When maintained at a non-physiological temperature, the cells reach a stabilised state distinct from the state observed in physiological conditions. The perturbation can be reversed but exhibits hysteretic behaviour when physiological conditions are restored. The transient regime observed during the recovery process is found to be different from the transient regime observed when leaving physiological conditions. A modified generalized Stokes-Einstein equation taking into account the cell activity through an effective temperature is proposed here to fit the experimental results. Excellent agreement between the model and the measurements is obtained for time lags from 10⁻³ to 1 s considered in this study.
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Affiliation(s)
- C Picard
- Biological and Soft Systems, Cavendish Laboratory, University of Cambridge, Cambridge CB30HE, UK
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219
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Brangwynne CP, Koenderink GH, MacKintosh FC, Weitz DA. Intracellular transport by active diffusion. Trends Cell Biol 2009; 19:423-7. [DOI: 10.1016/j.tcb.2009.04.004] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 04/23/2009] [Accepted: 04/23/2009] [Indexed: 12/31/2022]
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220
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Bruno L, Levi V, Brunstein M, Despósito MA. Transition to superdiffusive behavior in intracellular actin-based transport mediated by molecular motors. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:011912. [PMID: 19658734 DOI: 10.1103/physreve.80.011912] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Revised: 06/03/2009] [Indexed: 05/07/2023]
Abstract
Intracellular transport of large cargoes, such as organelles, vesicles, or large proteins, is a complex dynamical process that involves the interplay of adenosine triphosphate-consuming molecular motors, cytoskeleton filaments, and the viscoelastic cytoplasm. In this work we investigate the motion of pigment organelles (melanosomes) driven by myosin-V motors in Xenopus laevis melanocytes using a high-spatio-temporal resolution tracking technique. By analyzing the obtained trajectories, we show that the melanosomes mean-square displacement undergoes a transition from a subdiffusive to a superdiffusive behavior. A stochastic theoretical model, which explicitly considers the collective action of the molecular motors, is introduced to generalize the interpretation of our data. Starting from a generalized Langevin equation, we derive an analytical expression for the mean square displacement, which also takes into account the experimental noise. By fitting theoretical expressions to experimental data we were able to discriminate the exponents that characterize the passive and active contributions to the dynamics and to estimate the "global" motor forces correctly. Then, our model gives a quantitative description of active transport in living cells with a reduced number of parameters.
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Affiliation(s)
- L Bruno
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina
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221
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Sunyer R, Trepat X, Fredberg JJ, Farré R, Navajas D. The temperature dependence of cell mechanics measured by atomic force microscopy. Phys Biol 2009; 6:025009. [PMID: 19571363 PMCID: PMC3932184 DOI: 10.1088/1478-3975/6/2/025009] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The cytoskeleton is a complex polymer network that regulates the structural stability of living cells. Although the cytoskeleton plays a key role in many important cell functions, the mechanisms that regulate its mechanical behaviour are poorly understood. Potential mechanisms include the entropic elasticity of cytoskeletal filaments, glassy-like inelastic rearrangements of cross-linking proteins and the activity of contractile molecular motors that sets the tensional stress (prestress) borne by the cytoskeleton filaments. The contribution of these mechanisms can be assessed by studying how cell mechanics depends on temperature. The aim of this work was to elucidate the effect of temperature on cell mechanics using atomic force microscopy. We measured the complex shear modulus (G*) of human alveolar epithelial cells over a wide frequency range (0.1-25.6 Hz) at different temperatures (13-37 degrees C). In addition, we probed cell prestress by mapping the contractile forces that cells exert on the substrate by means of traction microscopy. To assess the role of actomyosin contraction in the temperature-induced changes in G* and cell prestress, we inhibited the Rho kinase pathway of the myosin light chain phosphorylation with Y-27632. Our results show that with increasing temperature, cells become stiffer and more solid-like. Cell prestress also increases with temperature. Inhibiting actomyosin contraction attenuated the temperature dependence of G* and prestress. We conclude that the dependence of cell mechanics with temperature is dominated by the contractile activity of molecular motors.
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Affiliation(s)
- R Sunyer
- Unitat de Biofísica i Bioenginyeria, Universitat de Barcelona, 08036 Barcelona, Spain
- Institut de Bioenginyeria de Catalunya, 08028 Barcelona, Spain
- CIBER Enfermedades Respiratorias, 07110 Bunyola, Spain
| | - X Trepat
- Unitat de Biofísica i Bioenginyeria, Universitat de Barcelona, 08036 Barcelona, Spain
- Institut de Bioenginyeria de Catalunya, 08028 Barcelona, Spain
- CIBER Enfermedades Respiratorias, 07110 Bunyola, Spain
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA, USA
| | - J J Fredberg
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA, USA
| | - R Farré
- Unitat de Biofísica i Bioenginyeria, Universitat de Barcelona, 08036 Barcelona, Spain
- CIBER Enfermedades Respiratorias, 07110 Bunyola, Spain
- Institut d’Investigacions Biomèdiques August Pi i Sunyer, 08036 Barcelona, Spain
| | - D Navajas
- Unitat de Biofísica i Bioenginyeria, Universitat de Barcelona, 08036 Barcelona, Spain
- Institut de Bioenginyeria de Catalunya, 08028 Barcelona, Spain
- CIBER Enfermedades Respiratorias, 07110 Bunyola, Spain
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222
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Lau AWC, Lubensky TC. Fluctuating hydrodynamics and microrheology of a dilute suspension of swimming bacteria. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:011917. [PMID: 19658739 DOI: 10.1103/physreve.80.011917] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Indexed: 05/28/2023]
Abstract
A bacterial bath is a model active system consisting of a population of rodlike motile or self-propelled bacteria suspended in a fluid environment. This system can be viewed as an active, nonequilibrium version of a lyotropic liquid crystal or as a generalization of a driven diffusive system. We derive a set of phenomenological equations, which include the effects of internal force generators in the bacteria, describing the hydrodynamic flow, orientational dynamics of the bacteria, and fluctuations induced by both thermal and nonthermal noises. These equations violate the fluctuation dissipation theorem and the Onsager reciprocity relations. We use them to provide a quantitative account of results from recent microrheological experiments on bacterial baths.
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Affiliation(s)
- A W C Lau
- Department of Physics, Florida Atlantic University, Boca Raton, Florida 33431, USA
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223
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Hemmer JD, Nagatomi J, Wood ST, Vertegel AA, Dean D, Laberge M. Role of cytoskeletal components in stress-relaxation behavior of adherent vascular smooth muscle cells. J Biomech Eng 2009; 131:041001. [PMID: 19275430 DOI: 10.1115/1.3049860] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A number of recent studies have demonstrated the effectiveness of atomic force microscopy (AFM) for characterization of cellular stress-relaxation behavior. However, this technique's recent development creates considerable need for exploration of appropriate mechanical models for analysis of the resultant data and of the roles of various cytoskeletal components responsible for governing stress-relaxation behavior. The viscoelastic properties of vascular smooth muscle cells (VSMCs) are of particular interest due to their role in the development of vascular diseases, including atherosclerosis and restenosis. Various cytoskeletal agents, including cytochalasin D, jasplakinolide, paclitaxel, and nocodazole, were used to alter the cytoskeletal architecture of the VSMCs. Stress-relaxation experiments were performed on the VSMCs using AFM. The quasilinear viscoelastic (QLV) reduced-relaxation function, as well as a simple power-law model, and the standard linear solid (SLS) model, were fitted to the resultant stress-relaxation data. Actin depolymerization via cytochalasin D resulted in significant increases in both rate of relaxation and percentage of relaxation; actin stabilization via jasplakinolide did not affect stress-relaxation behavior. Microtubule depolymerization via nocodazole resulted in nonsignificant increases in rate and percentage of relaxation, while microtubule stabilization via paclitaxel caused significant decreases in both rate and percentage of relaxation. Both the QLV reduced-relaxation function and the power-law model provided excellent fits to the data (R(2)=0.98), while the SLS model was less adequate (R(2)=0.91). Data from the current study indicate the important role of not only actin, but also microtubules, in governing VSMC viscoelastic behavior. Excellent fits to the data show potential for future use of both the QLV reduced-relaxation function and power-law models in conjunction with AFM stress-relaxation experiments.
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Affiliation(s)
- Jason D Hemmer
- Department of Bioengineering, 401 Rhodes Engineering Research Center, Clemson University, Clemson, SC 29634, USA.
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224
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Universal behavior of the osmotically compressed cell and its analogy to the colloidal glass transition. Proc Natl Acad Sci U S A 2009; 106:10632-7. [PMID: 19520830 DOI: 10.1073/pnas.0901462106] [Citation(s) in RCA: 164] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mechanical robustness of the cell under different modes of stress and deformation is essential to its survival and function. Under tension, mechanical rigidity is provided by the cytoskeletal network; with increasing stress, this network stiffens, providing increased resistance to deformation. However, a cell must also resist compression, which will inevitably occur whenever cell volume is decreased during such biologically important processes as anhydrobiosis and apoptosis. Under compression, individual filaments can buckle, thereby reducing the stiffness and weakening the cytoskeletal network. However, the intracellular space is crowded with macromolecules and organelles that can resist compression. A simple picture describing their behavior is that of colloidal particles; colloids exhibit a sharp increase in viscosity with increasing volume fraction, ultimately undergoing a glass transition and becoming a solid. We investigate the consequences of these 2 competing effects and show that as a cell is compressed by hyperosmotic stress it becomes progressively more rigid. Although this stiffening behavior depends somewhat on cell type, starting conditions, molecular motors, and cytoskeletal contributions, its dependence on solid volume fraction is exponential in every instance. This universal behavior suggests that compression-induced weakening of the network is overwhelmed by crowding-induced stiffening of the cytoplasm. We also show that compression dramatically slows intracellular relaxation processes. The increase in stiffness, combined with the slowing of relaxation processes, is reminiscent of a glass transition of colloidal suspensions, but only when comprised of deformable particles. Our work provides a means to probe the physical nature of the cytoplasm under compression, and leads to results that are universal across cell type.
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225
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Krishnan R, Park CY, Lin YC, Mead J, Jaspers RT, Trepat X, Lenormand G, Tambe D, Smolensky AV, Knoll AH, Butler JP, Fredberg JJ. Reinforcement versus fluidization in cytoskeletal mechanoresponsiveness. PLoS One 2009; 4:e5486. [PMID: 19424501 PMCID: PMC2675060 DOI: 10.1371/journal.pone.0005486] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Accepted: 04/02/2009] [Indexed: 01/16/2023] Open
Abstract
Every adherent eukaryotic cell exerts appreciable traction forces upon its substrate. Moreover, every resident cell within the heart, great vessels, bladder, gut or lung routinely experiences large periodic stretches. As an acute response to such stretches the cytoskeleton can stiffen, increase traction forces and reinforce, as reported by some, or can soften and fluidize, as reported more recently by our laboratory, but in any given circumstance it remains unknown which response might prevail or why. Using a novel nanotechnology, we show here that in loading conditions expected in most physiological circumstances the localized reinforcement response fails to scale up to the level of homogeneous cell stretch; fluidization trumps reinforcement. Whereas the reinforcement response is known to be mediated by upstream mechanosensing and downstream signaling, results presented here show the fluidization response to be altogether novel: it is a direct physical effect of mechanical force acting upon a structural lattice that is soft and fragile. Cytoskeletal softness and fragility, we argue, is consistent with early evolutionary adaptations of the eukaryotic cell to material properties of a soft inert microenvironment.
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Affiliation(s)
- Ramaswamy Krishnan
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Chan Young Park
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Yu-Chun Lin
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Jere Mead
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Richard T. Jaspers
- Research Institute MOVE, Faculty of Human Movement Sciences, VU University, Amsterdam, The Netherlands
| | - Xavier Trepat
- Unitat de Biofisica i Bioenginyeria, Universitat de Barcelona – IBEC, Barcelona, Spain
| | - Guillaume Lenormand
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Dhananjay Tambe
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Alexander V. Smolensky
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Andrew H. Knoll
- Botanical Museum, Harvard University, Cambridge, Massachusetts, United States of America
| | - James P. Butler
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
| | - Jeffrey J. Fredberg
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, Massachusetts, United States of America
- * E-mail:
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226
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Deng L, Bosse Y, Brown N, Chin LYM, Connolly SC, Fairbank NJ, King GG, Maksym GN, Paré PD, Seow CY, Stephen NL. Stress and strain in the contractile and cytoskeletal filaments of airway smooth muscle. Pulm Pharmacol Ther 2009; 22:407-16. [PMID: 19409505 DOI: 10.1016/j.pupt.2009.04.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2008] [Revised: 04/16/2009] [Accepted: 04/21/2009] [Indexed: 10/20/2022]
Abstract
Stress and strain are omnipresent in the lung due to constant lung volume fluctuation associated with respiration, and they modulate the phenotype and function of all cells residing in the airways including the airway smooth muscle (ASM) cell. There is ample evidence that the ASM cell is very sensitive to its physical environment, and can alter its structure and/or function accordingly, resulting in either desired or undesired consequences. The forces that are either conferred to the ASM cell due to external stretching or generated inside the cell must be borne and transmitted inside the cytoskeleton (CSK). Thus, maintaining appropriate levels of stress and strain within the CSK is essential for maintaining normal function. Despite the importance, the mechanisms regulating/dysregulating ASM cytoskeletal filaments in response to stress and strain remained poorly understood until only recently. For example, it is now understood that ASM length and force are dynamically regulated, and both can adapt over a wide range of length, rendering ASM one of the most malleable living tissues. The malleability reflects the CSK's dynamic mechanical properties and plasticity, both of which strongly interact with the loading on the CSK, and all together ultimately determines airway narrowing in pathology. Here we review the latest advances in our understanding of stress and strain in ASM cells, including the organization of contractile and cytoskeletal filaments, range and adaptation of functional length, structural and functional changes of the cell in response to mechanical perturbation, ASM tone as a mediator of strain-induced responses, and the novel glassy dynamic behaviors of the CSK in relation to asthma pathophysiology.
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Affiliation(s)
- Linhong Deng
- Key Laboratory of Biorheological Science and Technology (Chongqing University), Ministry of Education, and National 985 Project Institute of Biorheology and Gene Regulation, Bioengineering College, Chongqing University, Chongqing, China.
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227
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Duits MHG, Li Y, Vanapalli SA, Mugele F. Mapping of spatiotemporal heterogeneous particle dynamics in living cells. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:051910. [PMID: 19518483 DOI: 10.1103/physreve.79.051910] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Revised: 02/17/2009] [Indexed: 05/27/2023]
Abstract
Colloidal particles embedded in the cytoplasm of living mammalian cells have been found to display remarkable heterogeneity in their amplitude of motion. However, consensus on the significance and origin of this phenomenon is still lacking. We conducted experiments on Hmec-1 cells loaded with about 100 particles to reveal the intracellular particle dynamics as a function of both location and time. Central quantity in our analysis is the amplitude (A) of the individual mean-squared displacement (iMSD), averaged over a short time. Histograms of A were measured, (1) over all particles present at the same time and (2) for individual particles as a function of time. Both distributions showed significant broadening compared to particles in Newtonian liquid, indicating that the particle dynamics varies with both location and time. However, no systematic dependence of A on intracellular location was found. Both the (strong) spatial and (weak) temporal variations were further analyzed by correlation functions of A . Spatial cross correlations were rather weak down to interparticle distances of 1 microm , suggesting that the precise intracellular probe distribution is not crucial for observing a dynamic behavior that is representative for the whole cell. Temporal correlations of A decayed at approximately 10 s , possibly suggesting an intracellular reorganization at this time scale. These findings imply (1) that both individual particle dynamics and the ensemble averaged behavior in a given cell can be measured if there are enough particles per cell and (2) that the amplitude and power-law exponent of iMSDs can be used to reveal local dynamics. We illustrate this by showing how superdiffusive and subdiffusive behaviors may be hidden under an apparently diffusive global dynamics.
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Affiliation(s)
- Michael H G Duits
- Physics of Complex Fluids group, Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
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228
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Sunyer R, Ritort F, Farré R, Navajas D. Thermal activation and ATP dependence of the cytoskeleton remodeling dynamics. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:051920. [PMID: 19518493 DOI: 10.1103/physreve.79.051920] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Revised: 02/12/2009] [Indexed: 05/27/2023]
Abstract
The cytoskeleton (CSK) is a nonequilibrium polymer network that uses hydrolyzable sources of free energy such as adenosine triphosphate (ATP) to remodel its internal structure. As in inert nonequilibrium soft materials, CSK remodeling has been associated with structural rearrangements driven by energy-activated processes. We carry out particle tracking and traction microscopy measurements of alveolar epithelial cells at various temperatures and ATP concentrations. We provide the first experimental evidence that the remodeling dynamics of the CSK is driven by structural rearrangements over free-energy barriers induced by thermally activated forces mediated by ATP. The measured activation energy of these forces is approximately 40k_{B}T_{r} ( k_{B} being the Boltzmann constant and T_{r} being the room temperature). Our experiments provide clues to understand the analogy between the dynamics of the living CSK and that of inert nonequilibrium soft materials.
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Affiliation(s)
- R Sunyer
- Unitat de Biofísica i Bioenginyeria, Universitat de Barcelona and CIBER-Enfermedades Respiratorias, 08036 Barcelona, Spain and Institut de Bioenginyeria de Catalunya, 08028 Barcelona, Spain
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229
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Gao Y, Kilfoil ML. Intermittent and spatially heterogeneous single-particle dynamics close to colloidal gelation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:051406. [PMID: 19518455 DOI: 10.1103/physreve.79.051406] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2008] [Revised: 09/02/2008] [Indexed: 05/27/2023]
Abstract
Dynamical heterogeneities exist ubiquitously in materials near a dynamical arrest transition, such as glass formation or gelation. Among the readily discernible features of heterogeneous dynamics is a non-Gaussian exponential component in the distribution of the constituent particle displacements that is not understood at the single-particle level. We present an experimental study of particle dynamics and self-van Hove functions G_{s}(r,t) in a colloid-polymer system approaching gelation. We show experimental evidence, in the special case of a gelation transition, for exponentially distributed times for anomalously large displacements, and confirm that an exponential tail in G_{s} arises from rare events with associated Poisson statistics. We focus on the role of the anomalous large displacements and analyze their time scales, relating them to other time scales typically used to describe structural relaxation in gels and glasses: the time to cage breakup and the time for re-emergence of Fickian behavior at long times. Furthermore, we search for a structural origin of the dynamical heterogeneity. Various quantities characterizing local structure are examined. We found evidence of a strong correlation between local structure and local dynamics, in contrast to what has been found in supercooled liquids.
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Affiliation(s)
- Yongxiang Gao
- Department of Physics, McGill University, Montréal, Canada H3A 2T8
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230
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Biomechanics: cell research and applications for the next decade. Ann Biomed Eng 2009; 37:847-59. [PMID: 19259817 DOI: 10.1007/s10439-009-9661-x] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2008] [Accepted: 02/21/2009] [Indexed: 12/18/2022]
Abstract
With the recent revolution in Molecular Biology and the deciphering of the Human Genome, understanding of the building blocks that comprise living systems has advanced rapidly. We have yet to understand, however, how the physical forces that animate life affect the synthesis, folding, assembly, and function of these molecular building blocks. We are equally uncertain as to how these building blocks interact dynamically to create coupled regulatory networks from which integrative biological behaviors emerge. Here we review recent advances in the field of biomechanics at the cellular and molecular levels, and set forth challenges confronting the field. Living systems work and move as multi-molecular collectives, and in order to understand key aspects of health and disease we must first be able to explain how physical forces and mechanical structures contribute to the active material properties of living cells and tissues, as well as how these forces impact information processing and cellular decision making. Such insights will no doubt inform basic biology and rational engineering of effective new approaches to clinical therapy.
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231
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Levine AJ, MacKintosh FC. The Mechanics and Fluctuation Spectrum of Active Gels. J Phys Chem B 2009; 113:3820-30. [DOI: 10.1021/jp808192w] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Alex J. Levine
- Department of Chemistry & Biochemistry and The California Nanosystems Institute University of California, Los Angeles, California 90095
| | - F. C. MacKintosh
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, The Netherlands
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232
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Cytoskeletal Deformation at High Strains and the Role of Cross-link Unfolding or Unbinding. Cell Mol Bioeng 2009. [DOI: 10.1007/s12195-009-0048-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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233
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Sakaguchi H. Limit-cycle oscillation of an elastic filament and caterpillar motion. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:026216. [PMID: 19391829 DOI: 10.1103/physreve.79.026216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2008] [Revised: 01/15/2009] [Indexed: 05/27/2023]
Abstract
Soft biological materials can exhibit various active motion such as limit-cycle oscillation. The limit-cycle oscillation of active matter might be used for a mechanism of locomotion. We propose a simple model of an active elastic chain as an extension of the van der Pol equation. The uniform state is unstable, and exhibits a limit cycle of breathing motion. If the breathing motion is mirror symmetric, the elastic chain does not move as a whole. However, the breathing motion becomes a caterpillar motion and a unidirectional motion is induced, if an additional heterogeneity is involved or the chain is set on a spatially periodic sawtooth potential. We also analyze the model equation with coupled mode equations, and try to understand the bifurcation to the collective oscillation and the directional motion.
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Affiliation(s)
- Hidetsugu Sakaguchi
- Department of Applied Science for Electronics and Materials, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
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234
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Vanapalli SA, Duits MHG, Mugele F. Microfluidics as a functional tool for cell mechanics. BIOMICROFLUIDICS 2009; 3:12006. [PMID: 19693387 PMCID: PMC2717604 DOI: 10.1063/1.3067820] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Accepted: 12/15/2008] [Indexed: 05/07/2023]
Abstract
Living cells are a fascinating demonstration of nature's most intricate and well-coordinated micromechanical objects. They crawl, spread, contract, and relax-thus performing a multitude of complex mechanical functions. Alternatively, they also respond to physical and chemical cues that lead to remodeling of the cytoskeleton. To understand this intricate coupling between mechanical properties, mechanical function and force-induced biochemical signaling requires tools that are capable of both controlling and manipulating the cell microenvironment and measuring the resulting mechanical response. In this review, the power of microfluidics as a functional tool for research in cell mechanics is highlighted. In particular, current literature is discussed to show that microfluidics powered by soft lithographic techniques offers the following capabilities that are of significance for understanding the mechanical behavior of cells: (i) Microfluidics enables the creation of in vitro models of physiological environments in which cell mechanics can be probed. (ii) Microfluidics is an excellent means to deliver physical cues that affect cell mechanics, such as cell shape, fluid flow, substrate topography, and stiffness. (iii) Microfluidics can also expose cells to chemical cues, such as growth factors and drugs, which alter their mechanical behavior. Moreover, these chemical cues can be delivered either at the whole cell or subcellular level. (iv) Microfluidic devices offer the possibility of measuring the intrinsic mechanical properties of cells in a high throughput fashion. (v) Finally, microfluidic methods provide exquisite control over drop size, generation, and manipulation. As a result, droplets are being increasingly used to control the physicochemical environment of cells and as biomimetic analogs of living cells. These powerful attributes of microfluidics should further stimulate novel means of investigating the link between physicochemical cues and the biomechanical response of cells. Insights from such studies will have implications in areas such as drug delivery, medicine, tissue engineering, and biomedical diagnostics.
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235
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Comparing the mechanical influence of vinculin, focal adhesion kinase and p53 in mouse embryonic fibroblasts. Biochem Biophys Res Commun 2009; 379:799-801. [PMID: 19126403 DOI: 10.1016/j.bbrc.2008.12.124] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2008] [Accepted: 12/23/2008] [Indexed: 11/21/2022]
Abstract
Cytoskeletal reorganization is an ongoing process when cells adhere, move or invade extracellular substrates. The cellular force generation and transmission are determined by the intactness of the actomyosin-(focal adhesion complex)-integrin connection. We investigated the intracellular course of action in mouse embryonic fibroblasts deficient in the focal adhesion proteins vinculin and focal adhesion kinase (FAK) and the nuclear matrix protein p53 using magnetic tweezer and nanoparticle tracking techniques. Results show that the lack of these proteins decrease cellular stiffness and affect cell rheological behavior. The decrease in cellular binding strength was higher in FAK- to vinculin-deficient cells, whilst p53-deficient cells showed no effect compared to wildtype cells. The intracellular cytoskeletal activity was lowest in wildtype cells, but increased in the following order when cells lacked FAK+p53>p53>vinculin. In summary, cell mechanical processes are differently affected by the focal adhesion proteins vinculin and FAK than by the nuclear matrix protein, p53.
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236
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Mott A, Lenormand G, Costales J, Fredberg JJ, Burleigh BA. Modulation of host cell mechanics by Trypanosoma cruzi. J Cell Physiol 2008; 218:315-22. [PMID: 18853412 DOI: 10.1002/jcp.21606] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To investigate the effects of Trypanosoma cruzi on the mechanical properties of infected host cells, cytoskeletal stiffness and remodeling dynamics were measured in parasite-infected fibroblasts. We find that cell stiffness decreases in a time-dependent fashion in T. cruzi-infected human foreskin fibroblasts without a significant change in the dynamics of cytoskeletal remodeling. In contrast, cells exposed to T. cruzi secreted/released components become significantly stiffer within 2 h of exposure and exhibit increased remodeling dynamics. These findings represent the first direct mechanical data to suggest a physical picture in which an intact, stiff, and rapidly remodeling cytoskeleton facilitates early stages of T. cruzi invasion and parasite retention, followed by subsequent softening and disassembly of the cytoskeleton to accommodate intracellular replication of parasites. We further suggest that these changes occur through protein kinase A and inhibition of the Rho/Rho kinase signaling pathway. In the context of tissue infection, changes in host cell mechanics could adversely affect the function of the infected organs, and may play an important role on the pathophysiology of Chagas' disease.
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Affiliation(s)
- Adam Mott
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, USA
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237
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Purnomo EH, van den Ende D, Vanapalli SA, Mugele F. Glass transition and aging in dense suspensions of thermosensitive microgel particles. PHYSICAL REVIEW LETTERS 2008; 101:238301. [PMID: 19113599 DOI: 10.1103/physrevlett.101.238301] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Indexed: 05/27/2023]
Abstract
We report a thermosensitive microgel suspension that can be tuned reversibly between the glass state at low temperature and the liquid state at high temperature. Unlike hard spheres, we find that the glass transition for these suspensions is governed by both the volume fraction and the softness of the particles, where softer suspensions form a glass at higher effective volume fractions. In the glass state, these suspensions show aging where the relaxation times increase linearly with age, irrespective of the degree of particle softness. This relaxation scaling is in contrast with hard sphere behavior but consistent with the soft glassy rheology model.
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Affiliation(s)
- Eko H Purnomo
- Physics of Complex Fluids, IMPACT, Department of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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238
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Krishnan R, Trepat X, Nguyen TTB, Lenormand G, Oliver M, Fredberg JJ. Airway smooth muscle and bronchospasm: fluctuating, fluidizing, freezing. Respir Physiol Neurobiol 2008; 163:17-24. [PMID: 18514592 PMCID: PMC2591927 DOI: 10.1016/j.resp.2008.04.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2008] [Revised: 04/08/2008] [Accepted: 04/10/2008] [Indexed: 11/24/2022]
Abstract
We review here four recent findings that have altered in a fundamental way our understanding of airways smooth muscle (ASM), its dynamic responses to physiological loading, and their dominant mechanical role in bronchospasm. These findings highlight ASM remodeling processes that are innately out-of-equilibrium and dynamic, and bring to the forefront a striking intersection between topics in condensed matter physics and ASM cytoskeletal biology. By doing so, they place in a new light the role of enhanced ASM mass in airway hyper-responsiveness as well as in the failure of a deep inspiration to relax the asthmatic airway. These findings have established that (i) ASM length is equilibrated dynamically, not statically; (ii) ASM dynamics closely resemble physical features exhibited by so-called soft glassy materials; (iii) static force-length relationships fail to describe dynamically contracted ASM states; (iv) stretch fluidizes the ASM cytoskeleton. Taken together, these observations suggest that at the origin of the bronchodilatory effect of a deep inspiration, and its failure in asthma, may lie glassy dynamics of the ASM cell.
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Affiliation(s)
- Ramaswamy Krishnan
- Program in Molecular and Integrative Physiological Sciences, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, United States
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239
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Kim JS, Sun SX. Continuum modeling of forces in growing viscoelastic cytoskeletal networks. J Theor Biol 2008; 256:596-606. [PMID: 19041329 DOI: 10.1016/j.jtbi.2008.10.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Revised: 09/17/2008] [Accepted: 10/14/2008] [Indexed: 01/29/2023]
Abstract
Mechanical properties of the living cell are important in cell movement, cell division, cancer development and cell signaling. There is considerable interest in measuring local mechanical properties of living materials and the living cytoskeleton using micromechanical techniques. However, living materials are constantly undergoing internal dynamics such as growth and remodeling. A modeling framework that combines mechanical deformations with cytoskeletal growth dynamics is necessary to describe cellular shape changes. The present paper develops a general finite deformation modeling approach that can treat the viscoelastic cytoskeleton. Given the growth dynamics in the cytoskeletal network and the relationship between deformation and stress, the shape of the network is computed in an incremental fashion. The growth dynamics of the cytoskeleton can be modeled as stress dependent. The result is a consistent treatment of overall cell deformation. The framework is applied to a growing 1-d bundle of actin filaments against an elastic cantilever, and a 2-d cell undergoing wave-like protrusion dynamics. In the latter example, mechanical forces on the cell adhesion are examined as a function of the protrusion dynamics.
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Affiliation(s)
- Jin Seob Kim
- Department of Mechanical Engineering, the Johns Hopkins University, Baltimore, MD 21218, USA
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240
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Brangwynne CP, Koenderink GH, MacKintosh FC, Weitz DA. Cytoplasmic diffusion: molecular motors mix it up. ACTA ACUST UNITED AC 2008; 183:583-7. [PMID: 19001127 PMCID: PMC2582900 DOI: 10.1083/jcb.200806149] [Citation(s) in RCA: 152] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Random motion within the cytoplasm gives rise to molecular diffusion; this motion is essential to many biological processes. However, in addition to thermal Brownian motion, the cytoplasm also undergoes constant agitation caused by the activity of molecular motors and other nonequilibrium cellular processes. Here, we discuss recent work that suggests this activity can give rise to cytoplasmic motion that has the appearance of diffusion but is significantly enhanced in its magnitude and which can play an important biological role, particularly in cytoskeletal assembly.
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Affiliation(s)
- Clifford P Brangwynne
- School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
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241
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Rösel D, Brábek J, Tolde O, Mierke CT, Zitterbart DP, Raupach C, Bicanová K, Kollmannsberger P, Panková D, Vesely P, Folk P, Fabry B. Up-regulation of Rho/ROCK signaling in sarcoma cells drives invasion and increased generation of protrusive forces. Mol Cancer Res 2008; 6:1410-20. [PMID: 18819929 DOI: 10.1158/1541-7786.mcr-07-2174] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Tumor cell invasion is the most critical step of metastasis. Determination of the mode of invasion within the particular tumor is critical for effective cancer treatment. Protease-independent amoeboid mode of invasion has been described in carcinoma cells and more recently in sarcoma cells on treatment with protease inhibitors. To analyze invasive behavior, we compared highly metastatic sarcoma cells with parental nonmetastatic cells. The metastatic cells exhibited a functional up-regulation of Rho/ROCK signaling and, similarly to carcinoma cells, an amoeboid mode of invasion. Using confocal and traction force microscopy, we showed that an up-regulation of Rho/ROCK signaling leads to increased cytoskeletal dynamics, myosin light chain localization, and increased tractions at the leading edge of the cells and that all of these contributed to increased cell invasiveness in a three-dimensional collagen matrix. We conclude that cells of mesenchymal origin can use the amoeboid nonmesenchymal mode of invasion as their primary invading mechanism and show the dependence of ROCK-mediated amoeboid mode of invasion on the increased capacity of cells to generate force.
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Affiliation(s)
- Daniel Rösel
- Department of Cell Biology, Faculty of Science, Charles University in Prague, Czech Republic
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242
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Nagayama K, Matsumoto T. Contribution of actin filaments and microtubules to quasi-in situ tensile properties and internal force balance of cultured smooth muscle cells on a substrate. Am J Physiol Cell Physiol 2008; 295:C1569-78. [PMID: 18923059 DOI: 10.1152/ajpcell.00098.2008] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The effects of actin filaments (AFs) and microtubules (MTs) on quasi-in situ tensile properties and intracellular force balance were studied in cultured rat aortic smooth muscle cells (SMCs). A SMC cultured on substrates was held using a pair of micropipettes, gradually detached from the substrate while maintaining in situ cell shape and cytoskeletal integrity, and then stretched up to approximately 15% and unloaded three times at the rate of 1 mum every 5 s. Cell stiffness was approximately 20 nN per percent strain in the untreated case and decreased by approximately 65% and approximately 30% following AF and MT disruption, respectively. MT augmentation did not affect cell stiffness significantly. The roles of AFs and MTs in resisting cell stretching and shortening were assessed using the area retraction of the cell upon noninvasive detachment from thermoresponsive gelatin-coated dishes. The retraction was approximately 40% in untreated cells, while in AF-disrupted cells it was <20%. The retraction increased by approximately 50% and decreased by approximately 30% following MT disruption and augmentation, respectively, suggesting that MTs resist intercellular tension generated by AFs. Three-dimensional measurements of cell morphology using confocal microscopy revealed that the cell volume remained unchanged following drug treatment. A concomitant increase in cell height and decrease in cell area was observed following AF disruption and MT augmentation. In contrast, MT disruption significantly reduced the cell height. These results indicate that both AFs and MTs play crucial roles in maintaining whole cell mechanical properties of SMCs, and that while AFs act as an internal tension generator, MTs act as a tension reducer, and these contribute to intracellular force balance three dimensionally.
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Affiliation(s)
- Kazuaki Nagayama
- Nagoya Institute of Technology Omohi College, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan.
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243
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Is cell rheology governed by nonequilibrium-to-equilibrium transition of noncovalent bonds? Biophys J 2008; 95:5719-27. [PMID: 18835892 DOI: 10.1529/biophysj.108.139832] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
A living cell deforms or flows in response to mechanical stresses. A recent report shows that dynamic mechanics of living cells depends on the timescale of mechanical loading, in contrast to the prevailing view of some authors that cell rheology is timescale-free. Yet the molecular basis that governs this timescale-dependent behavior is elusive. Using molecular dynamics simulations of protein-protein noncovalent interactions, we show that multipower laws originate from a nonequilibrium-to-equilibrium transition: when the loading rate is faster than the transition rate, the power-law exponent alpha(1) is weak; when the loading rate is slower than the transition rate, the exponent alpha(2) is strong. The model predictions are confirmed in both embryonic stem cells and differentiated cells. Embryonic stem cells are less stiff, more fluidlike, and exhibit greater alpha(1) than their differentiated counterparts. By introducing a near-equilibrium frequency f(eq), we show that all data collapse into two power laws separated by f/f(eq), which is unity. These findings suggest that the timescale-dependent rheology in living cells originates from the nonequilibrium-to-equilibrium transition of the dynamic response of distinct, force-driven molecular processes.
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244
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Warren M, Rottler J. Mechanical rejuvenation and overaging in the soft glassy rheology model. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:041502. [PMID: 18999430 DOI: 10.1103/physreve.78.041502] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2008] [Indexed: 05/27/2023]
Abstract
Mechanical rejuvenation and overaging of glasses is investigated through stochastic simulations of the soft glassy rheology (SGR) model. Strain- and stress-controlled deformation cycles for a wide range of loading conditions are analyzed and compared to molecular dynamics simulations of a model polymer glass. Results indicate that deformation causes predominantly rejuvenation, whereas overaging occurs only at very low temperatures, small strains, and for high initial energy states. Although the creep compliance in the SGR model exhibits full aging independent of applied load, large stresses in the nonlinear creep regime cause configurational changes leading to rejuvenation of the relaxation time spectrum probed after a stress cycle. During recovery, however, the rejuvenated state rapidly returns to the original aging trajectory due to collective relaxations of the internal strain.
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Affiliation(s)
- Mya Warren
- Department of Physics and Astronomy, The University of British Columbia, 6224 Agricultural Road, Vancouver, BC, V6T 1Z1, Canada.
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245
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Shlomovitz R, Gov NS. Exciting cytoskeleton-membrane waves. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:041911. [PMID: 18999459 DOI: 10.1103/physreve.78.041911] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Indexed: 05/27/2023]
Abstract
Propagating waves on the surface of cells, over many micrometers, involve active forces. We investigate here the mechanical excitation of such waves when the membrane is perturbed by an external oscillatory force. The external perturbation may trigger the propagation of such waves away from the force application. This scheme is then suggested as a method to probe the properties of the excitable medium of the cell, and learn about the mechanisms that drive the wave propagation. We then apply these ideas to a specific model of active cellular membrane waves, demonstrating how the response of the system to the external perturbation depends on the properties of the model. The most outstanding feature that we find is that the excited waves exhibit a resonance phenomenon at the frequency corresponding to the tendency of the system to develop a linear instability. Mechanical excitation of membrane waves in cells at different frequencies can therefore be used to characterize the properties of the mechanism underlying the existence of these waves.
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Affiliation(s)
- R Shlomovitz
- Department of Chemical Physics, The Weizmann Institute of Science, P. O. Box 26, Rehovot, Israel 76100
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246
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Majumdar A, Suki B, Rosenblatt N, Alencar AM, Stamenović D. Power-law creep behavior of a semiflexible chain. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:041922. [PMID: 18999470 PMCID: PMC6421577 DOI: 10.1103/physreve.78.041922] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2008] [Revised: 09/29/2008] [Indexed: 05/27/2023]
Abstract
Rheological properties of adherent cells are essential for their physiological functions, and microrheological measurements on living cells have shown that their viscoelastic responses follow a weak power law over a wide range of time scales. This power law is also influenced by mechanical prestress borne by the cytoskeleton, suggesting that cytoskeletal prestress determines the cell's viscoelasticity, but the biophysical origins of this behavior are largely unknown. We have recently developed a stochastic two-dimensional model of an elastically joined chain that links the power-law rheology to the prestress. Here we use a similar approach to study the creep response of a prestressed three-dimensional elastically jointed chain as a viscoelastic model of semiflexible polymers that comprise the prestressed cytoskeletal lattice. Using a Monte Carlo based algorithm, we show that numerical simulations of the chain's creep behavior closely correspond to the behavior observed experimentally in living cells. The power-law creep behavior results from a finite-speed propagation of free energy from the chain's end points toward the center of the chain in response to an externally applied stretching force. The property that links the power law to the prestress is the chain's stiffening with increasing prestress, which originates from entropic and enthalpic contributions. These results indicate that the essential features of cellular rheology can be explained by the viscoelastic behaviors of individual semiflexible polymers of the cytoskeleton.
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Affiliation(s)
- Arnab Majumdar
- Department of Biomedical Engineering Boston University Boston, MA 02215, USA
- Department of Physics Boston University Boston, MA 02215, USA
| | - Béla Suki
- Department of Biomedical Engineering Boston University Boston, MA 02215, USA
| | - Noah Rosenblatt
- Department of Kinesiology and Nutrition University of Illinois at Chicago Chicago, IL 60612, USA
| | - Adriano M. Alencar
- Department of Pathology, LIM 05, Medical School University of Sao Paulo Sao Paulo, SP, Brazil
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247
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Abstract
Mechanical cues influence a wide range of cellular behaviors including motility, differentiation, and tumorigenesis. Although previous studies elucidated the role of specific players such as ion channels and focal adhesions as local mechanosensors, the investigation of how mechanical perturbations propagate across the cell is necessary to understand the spatial coordination of cellular processes. Here we quantify the magnitude and timing of intracellular stress propagation, using atomic force microscopy and particle tracking by defocused fluorescence microscopy. The apical cell surface is locally perturbed by atomic force microscopy cantilever indentation, and distal displacements are measured in three dimensions by tracking integrin-bound fluorescent particles. We observe an immediate response and slower equilibration, occurring over times that increase with distance from perturbation. This distance-dependent equilibration occurs over several seconds and can be eliminated by disruption of the actin cytoskeleton. Our experimental results are not explained by traditional viscoelastic models of cell mechanics, but they are consistent with predictions from poroelastic models that include both cytoskeletal deformation and flow of the cytoplasm. Our combined atomic force microscopy-particle tracking measurements provide direct evidence of slow, distance-dependent dissipative stress propagation in response to external mechanical cues and offer new insights into mechanical models and physiological behaviors of adherent cells.
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248
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Reversible disassembly of the actin cytoskeleton improves the survival rate and developmental competence of cryopreserved mouse oocytes. PLoS One 2008; 3:e2787. [PMID: 18665248 PMCID: PMC2467491 DOI: 10.1371/journal.pone.0002787] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Accepted: 06/22/2008] [Indexed: 11/19/2022] Open
Abstract
Effective cryopreservation of oocytes is critically needed in many areas of human reproductive medicine and basic science, such as stem cell research. Currently, oocyte cryopreservation has a low success rate. The goal of this study was to understand the mechanisms associated with oocyte cryopreservation through biophysical means using a mouse model. Specifically, we experimentally investigated the biomechanical properties of the ooplasm prior and after cryopreservation as well as the consequences of reversible dismantling of the F-actin network in mouse oocytes prior to freezing. The study was complemented with the evaluation of post-thaw developmental competence of oocytes after in vitro fertilization. Our results show that the freezing-thawing process markedly alters the physiological viscoelastic properties of the actin cytoskeleton. The reversible depolymerization of the F-actin network prior to freezing preserves normal ooplasm viscoelastic properties, results in high post-thaw survival and significantly improves developmental competence. These findings provide new information on the biophysical characteristics of mammalian oocytes, identify a pathophysiological mechanism underlying cryodamage and suggest a novel cryopreservation method.
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249
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Wilhelm C. Out-of-equilibrium microrheology inside living cells. PHYSICAL REVIEW LETTERS 2008; 101:028101. [PMID: 18764230 DOI: 10.1103/physrevlett.101.028101] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2007] [Indexed: 05/21/2023]
Abstract
Both forced and spontaneous motions of magnetic microbeads engulfed by Dictyostelium cells have served as experimental probes of intracellular dynamics. The complex shear modulus G*(omega), determined from active oscillatory measurements, has a power-law dynamics and increases with the probe size, reflecting intracellular structural complexity. The combined use of passive microrheology allows one to derive the power spectrum of active forces acting on intracellular phagosomes and to test the validity of the fluctuation-dissipation theorem inside living cells.
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Affiliation(s)
- Claire Wilhelm
- Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057, CNRS and University Paris Diderot, Paris, France.
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250
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Bossé Y, Chin LYM, Paré PD, Seow CY. Adaptation of airway smooth muscle to basal tone: relevance to airway hyperresponsiveness. Am J Respir Cell Mol Biol 2008; 40:13-8. [PMID: 18617678 DOI: 10.1165/rcmb.2008-0150oc] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Lung inflammation and airway hyperresponsiveness (AHR) are hallmarks of asthma, but their interrelationship is unclear. Excessive shortening of airway smooth muscle (ASM) in response to bronchoconstrictors is likely an important determinant of AHR. Hypercontractility of ASM could stem from a change in the intrinsic properties of the muscle, or it could be due to extrinsic factors such as chronic exposure of the muscle to inflammatory mediators in the airways. The latter could be the link between lung inflammation and AHR. The present study was designed to examine the influence of chronic exposure to a contractile agonist on the force-generating capacity of ASM. Force generation in response to electric field stimulation (EFS) was measured in ovine trachealis with or without a basal tone induced by acetylcholine (ACh). While the tone was maintained, the EFS-induced force decreased transiently but increased over time to reach a plateau in approximately 50 minutes. The total force (ACh tone + EFS force) increased monotonically and in proportion to ACh concentration. The results indicate that the muscle adapted to the basal tone and regained its contractile ability in response to a second stimulus (EFS) over time. Analysis suggests that this is due to a cytoskeletal transformation that allows the cytoskeleton to bear force, thus freeing up actomyosin crossbridges to generate more force. Force adaptation in ASM as a consequence of prolonged exposure to the many spasmogens found in asthmatic airways could be a mechanism contributing to AHR seen in asthma.
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Affiliation(s)
- Ynuk Bossé
- the James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research/St. Paul's Hospital, Room 166-1081, Burrard Street, Vancouver, BC, V6Z 1Y6 Canada.
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