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Membrane-based actuation for high-speed single molecule force spectroscopy studies using AFM. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2010; 39:1219-27. [DOI: 10.1007/s00249-009-0575-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Revised: 12/01/2009] [Accepted: 12/15/2009] [Indexed: 01/10/2023]
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52
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Carey SP, Charest JM, Reinhart-King CA. Forces During Cell Adhesion and Spreading: Implications for Cellular Homeostasis. CELLULAR AND BIOMOLECULAR MECHANICS AND MECHANOBIOLOGY 2010. [DOI: 10.1007/8415_2010_22] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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53
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Hu M, Chen J, Wang J, Wang X, Ma S, Cai J, Chen CY, Chen ZW. AFM- and NSOM-based force spectroscopy and distribution analysis of CD69 molecules on human CD4+T cell membrane. J Mol Recognit 2009; 22:516-20. [DOI: 10.1002/jmr.976] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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54
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Hosseini BH, Louban I, Djandji D, Wabnitz GH, Deeg J, Bulbuc N, Samstag Y, Gunzer M, Spatz JP, Hämmerling GJ. Immune synapse formation determines interaction forces between T cells and antigen-presenting cells measured by atomic force microscopy. Proc Natl Acad Sci U S A 2009; 106:17852-7. [PMID: 19822763 PMCID: PMC2764924 DOI: 10.1073/pnas.0905384106] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Indexed: 01/21/2023] Open
Abstract
During adaptive immune responses, T lymphocytes recognize antigenic peptides presented by MHC molecules on antigen-presenting cells (APCs). This recognition results in the formation of a so-called immune synapse (IS) at the T-cell/APC interface, which is crucial for T-cell activation. The molecular composition of the IS has been extensively studied, but little is known about the biophysics and interaction forces between T cells and APCs. Here, we report the measurement of interaction forces between T cells and APCs employing atomic force microscopy (AFM). For these investigations, specific T cells were selected that recognize an antigenic peptide presented by MHC-class II molecules on APCs. Dynamic analysis of T-cell/APC interaction by AFM revealed that in the presence of antigen interaction forces increased from 1 to 2 nN at early time-points to a maximum of approximately 14 nN after 30 min and decreased again after 60 min. These data correlate with the kinetics of synapse formation that also reached a maximum after 30 min, as determined by high-throughput multispectral imaging flow cytometry. Because the integrin lymphocyte function antigen-1 (LFA-1) and its counterpart intercellular adhesion molecule-1 (ICAM-1) are prominent members of a mature IS, the effect of a small molecular inhibitor for LFA-1, BIRT377, was investigated. BIRT377 almost completely abolish the interaction forces, emphasizing the importance of LFA-1/ICAM-1-interactions for firm T-cell/APC adhesion. In conclusion, using biophysical measurements, this study provides precise values for the interaction forces between T cells and APCs and demonstrates that these forces develop over time and are highest when synapse formation is maximal.
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Affiliation(s)
- Babak H. Hosseini
- Department of New Materials and Biosystems, Max-Planck-Institute for Metals Research, Stuttgart, Germany, and Department of Biophysical Chemistry, University of Heidelberg, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
| | - Ilia Louban
- Department of New Materials and Biosystems, Max-Planck-Institute for Metals Research, Stuttgart, Germany, and Department of Biophysical Chemistry, University of Heidelberg, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
| | - Dominik Djandji
- Department of Molecular Immunology, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - Guido H. Wabnitz
- Institute for Immunology, University of Heidelberg, Im Neuenheimer Feld 305, D-69120 Heidelberg, Germany; and
| | - Janosch Deeg
- Department of New Materials and Biosystems, Max-Planck-Institute for Metals Research, Stuttgart, Germany, and Department of Biophysical Chemistry, University of Heidelberg, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
| | - Nadja Bulbuc
- Department of Molecular Immunology, German Cancer Research Center, D-69120 Heidelberg, Germany
| | - Yvonne Samstag
- Institute for Immunology, University of Heidelberg, Im Neuenheimer Feld 305, D-69120 Heidelberg, Germany; and
| | - Matthias Gunzer
- Institute of Molecular and Clinical Immunology, Otto-von-Guericke-University-Magdeburg, Leipziger-Strasse 44, D-39120 Magdeburg, Germany
| | - Joachim P. Spatz
- Department of New Materials and Biosystems, Max-Planck-Institute for Metals Research, Stuttgart, Germany, and Department of Biophysical Chemistry, University of Heidelberg, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
| | - Günter J. Hämmerling
- Department of Molecular Immunology, German Cancer Research Center, D-69120 Heidelberg, Germany
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55
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Abdulreda MH, Moy VT. Investigation of SNARE-Mediated Membrane Fusion Mechanism Using Atomic Force Microscopy. JAPANESE JOURNAL OF APPLIED PHYSICS (2008) 2009; 48:8JA03-8JA0310. [PMID: 20228892 PMCID: PMC2836841 DOI: 10.1143/jjap.48.08ja03] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Membrane fusion is driven by specialized proteins that reduce the free energy penalty for the fusion process. In neurons and secretory cells, soluble N-ethylmaleimide-sensitive factor-attachment protein (SNAP) receptors (SNAREs) mediate vesicle fusion with the plasma membrane during vesicular content release. Although, SNAREs have been widely accepted as the minimal machinery for membrane fusion, the specific mechanism for SNARE-mediated membrane fusion remains an active area of research. Here, we summarize recent findings based on force measurements acquired in a novel experimental system that uses atomic force microscope (AFM) force spectroscopy to investigate the mechanism(s) of membrane fusion and the role of SNAREs in facilitating membrane hemifusion during SNARE-mediated fusion. In this system, protein-free and SNARE-reconstituted lipid bilayers are formed on opposite (trans) substrates and the forces required to induce membrane hemifusion and fusion or to unbind single v-/t-SNARE complexes are measured. The obtained results provide evidence for a mechanism by which the pulling force generated by interacting trans-SNAREs provides critical proximity between the membranes and destabilizes the bilayers at fusion sites by broadening the hemifusion energy barrier and consequently making the membranes more prone to fusion.
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56
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Wu Y, Lu H, Cai J, He X, Hu Y, Zhao H, Wang X. Membrane Surface Nanostructures and Adhesion Property of T Lymphocytes Exploited by AFM. NANOSCALE RESEARCH LETTERS 2009; 4:942-7. [PMID: 20596371 PMCID: PMC2894100 DOI: 10.1007/s11671-009-9340-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2009] [Accepted: 05/05/2009] [Indexed: 05/29/2023]
Abstract
The activation of T lymphocytes plays a very important role in T-cell-mediated immune response. Though there are many related literatures, the changes of membrane surface nanostructures and adhesion property of T lymphocytes at different activation stages have not been reported yet. However, these investigations will help us further understand the biophysical and immunologic function of T lymphocytes in the context of activation. In the present study, the membrane architectures of peripheral blood T lymphocytes were obtained by AFM, and adhesion force of the cell membrane were measured by acquiring force-distance curves. The results indicated that the cell volume increased with the increases of activation time, whereas membrane surface adhesion force decreased, even though the local stiffness for resting and activated cells is similar. The results provided complementary and important data to further understand the variation of biophysical properties of T lymphocytes in the context of in vitro activation.
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Affiliation(s)
- Yangzhe Wu
- Chemistry Department, Jinan University, Guangzhou, 510632, Guangdong, People’s Republic of China
| | - Hongsong Lu
- Institution for Tissue Transplantation and Immunology, Jinan University, Guangzhou, 510632, Guangdong, People’s Republic of China
| | - Jiye Cai
- Chemistry Department, Jinan University, Guangzhou, 510632, Guangdong, People’s Republic of China
| | - Xianhui He
- Institution for Tissue Transplantation and Immunology, Jinan University, Guangzhou, 510632, Guangdong, People’s Republic of China
| | - Yi Hu
- Chemistry Department, Jinan University, Guangzhou, 510632, Guangdong, People’s Republic of China
| | - HongXia Zhao
- Faculty of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou, 510090, People’s Republic of China
| | - Xiaoping Wang
- The First Affiliated Hospital, Jinan University, Guangzhou, 510632, Guangdong, People’s Republic of China
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57
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Liu B, Yu Y, Yao DK, Shao JY. A direct micropipette-based calibration method for atomic force microscope cantilevers. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2009; 80:065109. [PMID: 19566228 PMCID: PMC2832057 DOI: 10.1063/1.3152220] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2008] [Accepted: 05/16/2009] [Indexed: 05/23/2023]
Abstract
In this report, we describe a direct method for calibrating atomic force microscope (AFM) cantilevers with the micropipette aspiration technique (MAT). A closely fitting polystyrene bead inside a micropipette is driven by precisely controlled hydrostatic pressures to apply known loads on the sharp tip of AFM cantilevers, thus providing a calibration at the most functionally relevant position. The new method is capable of calibrating cantilevers with spring constants ranging from 0.01 to hundreds of newtons per meter. Under appropriate loading conditions, this new method yields measurement accuracy and precision both within 10%, with higher performance for softer cantilevers. Furthermore, this method may greatly enhance the accuracy and precision of calibration for colloidal probes.
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Affiliation(s)
- Baoyu Liu
- Department of Biomedical Engineering, Washington University, Saint Louis, Missouri 63130, USA
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58
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Abdulreda MH, Bhalla A, Rico F, Berggren PO, Chapman ER, Moy VT. Pulling force generated by interacting SNAREs facilitates membrane hemifusion. Integr Biol (Camb) 2009; 1:301-10. [PMID: 20023730 DOI: 10.1039/b900685k] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In biological systems, membrane fusion is mediated by specialized proteins. Although soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptors (SNAREs) provide the minimal molecular machinery required to drive membrane fusion, the precise mechanism for SNARE-mediated fusion remains to be established. Here, we used atomic force microscope (AFM) spectroscopy to determine whether the pulling force generated by interacting SNAREs is directly coupled to membrane fusion. The mechanical strength of the SNARE binding interaction was determined by single molecule force measurements. It was revealed that the forced unbinding of the SNARE complex formed between opposing (trans) bilayers involves two activation barriers; where the steep inner barrier governs the transition from the bound to an intermediate state and the outer barrier governs the transition between the intermediate and the unbound state. Moreover, truncation of either SNAP-25 or VAMP 2 reduced the slope of the inner barrier significantly and, consequently, reduced the pulling strength of the SNARE complex; thus, suggesting that the inner barrier determines the binding strength of the SNARE complex. In parallel, AFM compression force measurements revealed that truncated SNAREs were less efficient than native SNAREs in facilitating hemifusion of the apposed bilayers. Together, these findings reveal a mechanism by which a pulling force generated by interacting trans-SNAREs reduces the slope of the hemifusion barrier and, subsequently, facilitates hemifusion and makes the membranes more prone to fusion.
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Affiliation(s)
- Midhat H Abdulreda
- University of Miami Miller School of Medicine, Physiology & Biophysics Department, 1600 NW 10th Ave., Miami, FL 33136, USA
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59
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Müller DJ, Krieg M, Alsteens D, Dufrêne YF. New frontiers in atomic force microscopy: analyzing interactions from single-molecules to cells. Curr Opin Biotechnol 2009; 20:4-13. [DOI: 10.1016/j.copbio.2009.02.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Revised: 02/10/2009] [Accepted: 02/11/2009] [Indexed: 10/21/2022]
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60
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Mitchell G, Lamontagne CA, Brouillette E, Grondin G, Talbot BG, Grandbois M, Malouin F. Staphylococcus aureus SigB activity promotes a strong fibronectin-bacterium interaction which may sustain host tissue colonization by small-colony variants isolated from cystic fibrosis patients. Mol Microbiol 2009; 70:1540-55. [PMID: 19007412 DOI: 10.1111/j.1365-2958.2008.06511.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Genes encoding cell-surface proteins regulated by SigB are stably expressed in Staphylococcus aureus small-colony variants (SCVs) isolated from cystic fibrosis (CF) patients. Our hypothesis is that CF-isolated SCVs are locked into a colonization state by sustaining the expression of adhesins such as fibronectin-binding proteins (FnBPs) throughout growth. Force spectroscopy was used to study the fibronectin-FnBPs interaction among strains varying for their SigB activity. The fibronectin-FnBPs interaction was described by a strength of 1000+/-400 pN (pulling rate of 2 microm s(-1)), an energetic barrier width of 0.6+/-0.1 A and an off-rate below 2 x 10(-4) s(-1). A CF-isolated SCV highly expressed fnbA throughout growth and showed a sustained capacity to bind fibronectin, whereas a prototypic strain showed a reduced frequency of fibronectin-binding during the stationary growth phase when its fnbA gene was down-regulated. Reduced expression of fnbA was observed in sigB mutants, which was associated with an overall decrease adhesion to fibronectin. These results suggest that the fibronectin-FnBPs interaction plays a role in the formation of a mechanically resistant adhesion of S. aureus to host tissues and supports the hypothesis that CF-isolated SCVs are locked into a colonization state as a result of a sustained SigB activity.
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Affiliation(s)
- Gabriel Mitchell
- Centre d'Etude et de Valorisation de la Diversité Microbienne, Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada
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61
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Thomas WE. Mechanochemistry of receptor-ligand bonds. Curr Opin Struct Biol 2009; 19:50-5. [PMID: 19157853 DOI: 10.1016/j.sbi.2008.12.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2008] [Accepted: 12/05/2008] [Indexed: 01/21/2023]
Abstract
When cell receptors bind to immobilized ligands, the resulting bond can be subjected to tensile mechanical force. This might be expected to shorten bond lifetimes. However, cells from bacteria to blood cells express receptors that are activated by tensile force to form longer-lived bonds, referred to as catch bonds. The process of catch bond activation involves non-equilibrium processes that are poorly probed by experimental and computational structural methods alike. However, I argue here that the preponderance of data indicates that force acts on an interdomain region which regulates the conformation of a distal ligand-binding site, in a process closely related to mechanochemistry and allosteric regulation.
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Affiliation(s)
- Wendy E Thomas
- Department of Bioengineering, University of Washington, 1705 NE Pacific Street, Foege N430P, Box 355061, Seattle, WA 98195-5061, United States.
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62
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Kerby MB, Urban JC, Mouallem L, Tripathi A. Circulating IgSF Proteins Inhibit Adhesion of Antibody Targeted Microspheres to Endothelial Inflammatory Ligands. Appl Biochem Biotechnol 2009; 159:208-20. [DOI: 10.1007/s12010-008-8474-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2008] [Accepted: 12/03/2008] [Indexed: 02/07/2023]
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63
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Atomic Force Microscopy: A Versatile Tool for Studying Cell Morphology, Adhesion and Mechanics. Cell Mol Bioeng 2008. [DOI: 10.1007/s12195-008-0037-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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64
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Helenius J, Heisenberg CP, Gaub HE, Muller DJ. Single-cell force spectroscopy. J Cell Sci 2008; 121:1785-91. [PMID: 18492792 DOI: 10.1242/jcs.030999] [Citation(s) in RCA: 336] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The controlled adhesion of cells to each other and to the extracellular matrix is crucial for tissue development and maintenance. Numerous assays have been developed to quantify cell adhesion. Among these, the use of atomic force microscopy (AFM) for single-cell force spectroscopy (SCFS) has recently been established. This assay permits the adhesion of living cells to be studied in near-physiological conditions. This implementation of AFM allows unrivaled spatial and temporal control of cells, as well as highly quantitative force actuation and force measurement that is sufficiently sensitive to characterize the interaction of single molecules. Therefore, not only overall cell adhesion but also the properties of single adhesion-receptor-ligand interactions can be studied. Here we describe current implementations and applications of SCFS, as well as potential pitfalls, and outline how developments will provide insight into the forces, energetics and kinetics of cell-adhesion processes.
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Affiliation(s)
- Jonne Helenius
- Biotechnology Center, University of Technology Dresden, Germany.
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65
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Hu M, Wang J, Cai J, Wu Y, Wang X. Nanostructure and force spectroscopy analysis of human peripheral blood CD4+ T cells using atomic force microscopy. Biochem Biophys Res Commun 2008; 374:90-4. [DOI: 10.1016/j.bbrc.2008.06.107] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Accepted: 06/25/2008] [Indexed: 11/28/2022]
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66
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Schmitz J, Gottschalk KE. Mechanical regulation of cell adhesion. SOFT MATTER 2008; 4:1373-1387. [PMID: 32907100 DOI: 10.1039/b716805p] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Cellular adhesion against external forces is governed by both the equilibrium affinity of the involved receptor-ligand bonds and the mechanics of the cell. Certain receptors like integrins change their affinity as well as the mechanics of their anchorage to tune the adhesiveness. Whereas in the last few years the focus of integrin research has lain on the affinity regulation of the adhesion receptors, more recently the importance of cellular mechanics became apparent. Here, we focus on different aspects of the mechanical regulation of the cellular adhesiveness.
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Affiliation(s)
- Julia Schmitz
- Applied Physics, LMU München, Amalienstr. 54, 80799 München, Germany.
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67
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Riethmuller C, Nasdala I, Vestweber D. Nano-surgery at the leukocyte-endothelial docking site. Pflugers Arch 2007; 456:71-81. [PMID: 18094992 PMCID: PMC2756369 DOI: 10.1007/s00424-007-0412-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Accepted: 11/20/2007] [Indexed: 01/13/2023]
Abstract
The endothelium has an important role in controlling the extravasation of leukocytes from blood to tissues. Endothelial permeability for leukocytes is influenced by transmembrane proteins that control inter-endothelial adhesion, as well as steps of the leukocyte transmigration process. In a cascade consisting of leukocyte rolling, adhesion, firm adhesion, and diapedesis, a new step was recently introduced, the formation of a docking structure or “transmigratory cup.” Both terms describe a structure formed by endothelial pseudopods embracing the leukocyte. It has been found associated with both para- and transcellular diapedesis. The aim of this study was to characterize the leukocyte–endothelial contact area in terms of morphology and cell mechanics to investigate how the endothelial cytoskeleton reorganizes to engulf the leukocyte. We used atomic force microscopy (AFM) to selectively remove the leukocyte and then analyze the underlying cell at this specific spot. Firmly attached leukocytes could be removed by AFM nanomanipulation. In few cases, this exposed 8–12 μm wide and 1 μm deep footprints, representing the cup-like docking structure. Some of them were located near endothelial cell junctions. The interaction area did not exhibit significant alterations neither morphologically nor mechanically as compared to the surrounding cell surface. In conclusion, the endothelial invagination is formed without a net depolymerization of f-actin, as endothelial softening at the site of adhesion does not seem to be involved. Moreover, there were no cases of phagocytotic engulfment, but instead the formation of a transmigratory channel could be observed.
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Affiliation(s)
- Christoph Riethmuller
- Institute of Physiology II, University of Münster, Robert-Koch-Strasse 27 b, 48149 Münster, Germany.
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68
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Mitchell G, Lamontagne CA, Lebel R, Grandbois M, Malouin F. Single-molecule dynamic force spectroscopy of the fibronectin-heparin interaction. Biochem Biophys Res Commun 2007; 364:595-600. [PMID: 17959151 DOI: 10.1016/j.bbrc.2007.10.034] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Accepted: 10/09/2007] [Indexed: 11/26/2022]
Abstract
The integrity of cohesive tissues strongly depends on the presence of the extracellular matrix, which provides support and anchorage for cells. The fibronectin protein and the heparin-like glycosaminoglycans are key components of this dynamic structural network. In this report, atomic force spectroscopy was used to gain insight into the compliance and the resistance of the fibronectin-heparin interaction. We found that this interaction can be described by an energetic barrier width of 3.1+/-0.2A and an off-rate of 0.2+/-0.1s(-1). These dissociation parameters are similar to those of other carbohydrate-protein interactions and to off-rate values reported for more complex interactions between cells and extracellular matrix components. Our results indicate that the function of the fibronectin-heparin interaction is supported by its capacity to sustain significant deformations and considerable external mechanical forces.
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Affiliation(s)
- Gabriel Mitchell
- Centre d'Etude et de Valorisation de la Diversité Microbienne (CEVDM), Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, Que., Canada J1K 2R1
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69
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Lewis NT, Hussain MA, Mao JJ. Investigation of nano-mechanical properties of annulus fibrosus using atomic force microscopy. Micron 2007; 39:1008-19. [PMID: 17977735 DOI: 10.1016/j.micron.2007.08.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Revised: 08/20/2007] [Accepted: 08/20/2007] [Indexed: 11/28/2022]
Abstract
We describe the use of atomic force microscopy (AFM) to investigate the nanomechanical properties of annulus fibrosus (AF)-the outer fibrous layer of an intervertebral disc (IVD) encapsulating the inner jelly-like mass known as the nucleus pulposus (NP). Disk disease, degenerated discs, slipped discs, and herniated discs are common terms often linked to back pain and are caused due to degeneration of IVD. Due to the variations in the structure and biochemical composition of the IVD, studies of macromechanical properties in the motion segment or AF may lack all significant nanomechanical responses or behaviors. Existing studies do not report the micro or nano level of mechanics of IVD components and whether the nanomechanics of this tissue mimic its macromechanical behavior is not known. Our studies used AFM to investigate the regional micromechanical properties of the AF that have been otherwise difficult due to small sample size of the tissue. Five different zones including peripheral and central were tested mechanically as well as biochemically. Qualitative biochemical staining and quantitative values of nanomechanical properties of different zones are compared and discussed in detail. The results of nanomechanical investigations described in this study not only reveal its mimic at macroscopic level, they represent an important step towards establishing a framework for testing and comparing tissue engineered IVD replacements with native tissues.
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Affiliation(s)
- Naama T Lewis
- Department of Bioengineering, University of Illinois at Chicago, Science and Engineering Offices (SEO), room 218, 815 S. Morgan Street (m/c 063), Chicago, IL 60607-7052, USA.
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70
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Sumagin R, Sarelius IH. A role for ICAM-1 in maintenance of leukocyte-endothelial cell rolling interactions in inflamed arterioles. Am J Physiol Heart Circ Physiol 2007; 293:H2786-98. [PMID: 17704289 DOI: 10.1152/ajpheart.00720.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
A key endothelial receptor in leukocyte-endothelial cell (EC) interactions is ICAM-1. ICAM-1 is constitutively expressed at low levels on vascular ECs, and its levels significantly increase following stimulation with many proinflammatory agents. This study provides evidence that in inflamed arterioles of anesthetized mice (65 mg/kg ip Nembutal), ICAM-1 mediates leukocyte rolling, in contrast to its expected role of mediating firm adhesion in venules. The number of leukocytes rolling on arteriolar ECs is decreased in ICAM-1 knockout (KO) compared with wild-type (WT) mice (KO, 6.0 +/- 0.9; WT, 12.0 +/- 1.0 leukocytes/40 s; P < 0.05), whereas the leukocyte-rolling number in venules remains unaffected (KO, 5.6 +/- 0.9; WT, 7.0 +/- 0.7 leukocytes/40 s; n = 13-15 sites). We also show that the fraction of leukocytes that is rolling on arteriolar ECs does so with a higher characteristic velocity (>70 microm/s), and, furthermore, that the distance over which rolling contacts with the arteriolar wall are maintained is ICAM-1 dependent. In ICAM-1 KO animals or in WT mice in the presence of ICAM-1-blocking antibody, leukocytes rolled significantly shorter distances over the sampled 200-microm vessel length compared with WT (68 +/- 6.7 and 55 +/- 9.4 vs. 85 +/- 12.9% total, respectively, n = 4 sites, P < 0.05). We also found evidence that in ICAM-1 KO mice, a significant fraction of leukocyte rolling and adhesive interactions with arteriolar ECs could be accounted for by upregulation of another adhesion molecule, VCAM-1, providing an important illustration of how expression of related proteins can be altered following genetic ablatement of a target molecule (in this case ICAM-1).
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Affiliation(s)
- Ronen Sumagin
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
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71
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Abramovitch DY, Andersson SB, Pao LY, Schitter G. A Tutorial on the Mechanisms, Dynamics, and Control of Atomic Force Microscopes. ACTA ACUST UNITED AC 2007. [DOI: 10.1109/acc.2007.4282300] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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72
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Abstract
Molecular interactions between receptors and ligands can be characterized by their free energy landscape. In its simplest representation, the energy landscape is described by a barrier of certain height and width that determines the dissociation rate of the complex, as well as its dynamic strength. Some interactions, however, require a more complex landscape with additional barriers and roughness along the reaction coordinate. This roughness slows down the dissociation kinetics of the interaction and contributes to its dynamic strength. The streptavidin-biotin complex has been extensively studied due to its remarkably low dissociation kinetics. However, single molecule measurements from independent experiments showed scattered and disparate results. In this work, the energy landscape roughness of the streptavidin-biotin interaction was estimated to be in the range of 5-8kBT using dynamic force spectroscopy (DFS) measurements at three different temperatures. These results can be used to explain both its slow dissociation kinetics and the discrepancies in the reported force measurements.
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Affiliation(s)
- Félix Rico
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, 1600 N.W. 10th Avenue, Miami, FL 33136, USA.
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