Elsevier

Journal of Biomechanics

Volume 46, Issue 2, 18 January 2013, Pages 307-313
Journal of Biomechanics

Force distribution on multiple bonds controls the kinetics of adhesion in stretched cells

https://doi.org/10.1016/j.jbiomech.2012.10.039Get rights and content

Abstract

We show herein how mechanical forces at macro or micro scales may affect the biological response at the nanoscale. The reason resides in the intimate link between chemistry and mechanics at the molecular level. These interactions occur under dynamic conditions such as the shear stress induced by flowing blood or the intracellular tension. Thus, resisting removal by mechanical forces, e.g., shear stresses, is a general property of cells provided by cellular adhesion. Using classical models issued from theoretical physics, we review the force regulation phenomena of the single bond. However, to understand the force regulation of cellular adhesion sites, we need to consider the collective behavior of receptor–ligand bonds. We discuss the applicability of single bond theories to describe collective bond behavior. Depending on bond configuration, e.g., presently “parallel” and “zipper”, the number of bonds and dissociation forces variably affect the kinetics of multiple bonds. We reveal a marked efficiency of the collective organization to stabilize multiple bonds by sharply increasing bond lifetime compared to single bond. These theoretical predictions are then compared to experimental results of the literature concerning the kinetic parameters of bonds measured by atomic force microscopy and by shear flow. These comparisons reveal that the force-control of bonds strongly depends on whether the force distribution on multiple bonds is homogeneous, e.g., in AFM experiments, or heterogeneous, e.g., in shear flow experiments. This reinforces the need of calculating the stress/strain fields exerted on living tissues or cells at various scales and certainly down to the molecular scale.

Introduction

It is widely accepted that mechanical forces control normal biological processes and their pathological alterations through cell–environment interactions (Discher et al., 2005). These interactions occur under dynamic conditions, e.g., the flowing blood; the internal tension, through adhesion sites which are protein assemblies through clusters which link the cytoskeleton to the extracellular environment (Geiger and Bershadsky, 2001). In particular, receptor–ligand bond anchoring cells in the presence of flowing liquids are stretched by tensile mechanical forces that balance the drag force on the bound cell. Therefore, stabilization under force and resisting removal to shear stresses – and to intra/extracellular stretching forces–are fundamental properties of cellular adhesion. Moreover, weakening or strengthening adhesion by mechanical force remains an opened question if one wants to understand flow-controlled key cellular interactions such as: macrophage–epithelium , leukocyte–endothelium or bacteria–host cell (Thomas, 2008, Thomas et al., 2008).

A fundamental aspect to consider is the stochastic nature of molecular adhesion and the subsequent bond detachment under force which are extensively described in the literature (Bongrand and Golstein, 1983, Evans, 1998). A less considered aspect deals with the complexity of adhesion structures since cellular adhesion involves not only one but several bonds, which stabilize and resist mechanical forces through different strategies of association and reinforcement (Evans, 2001, Evans and Ritchie, 1994, Leckband et al., 1992). These strategies are most likely influenced by forces generated through the intracellular structure or transiting through the extracellular environment (Féréol et al., 2009) and a number of biochemical and biomechanical processes implicating many signaling pathways (Vogel and Sheetz, 2009). From initial adhesion to focal complex and beyond the mature focal adhesion, the adhesion site configuration changes and the maximal force supported by adhesion sites varies by six orders of magnitude (pN-μN) (Bruinsma, 2005). Although these adhesion sites are made of similar weak bond units – i .e., a non covalent molecular link given to support forces up to the pN – their collective organization allows them supporting a huge range of stress (Geiger and Bershadsky, 2001). The structural changes associated to stabilization and strengthening include: (i) increase in cell–substrate contact area (spreading) (Capo et al., 1981), (ii) recruitment of receptors to anchoring sites including their lateral association (clustering) (Andre et al., 1990, Bell et al., 1984, Cluzel et al., 2005), (iii) interaction with cytoskeleton elements that lead to enhanced force distribution among bound receptors via local cytoskeleton stiffening (focal adhesion assembly) (Pasternak and Elson, 1985). These mechanisms of adhesion strengthening are supported by numerous observations from various cellular systems (Balaban et al., 2001, Choquet et al., 1997, Galbraith et al., 2002, Giannone et al., 2003, Zhu et al., 2008). Trying to understand these mechanisms of adhesion stabilization or reinforcement, and how they are regulated by force, remains challenging questions which require new theoretical knowledge and pertinent analysis of data.

Recognizing the need to expose actions at the submicroscopic level, many research groups have employed ultrasensitive force techniques to probe extremely small regions of adhesive contact between surfaces functionalized by biological molecules (Evans and Ritchie, 1994, Leckband et al., 1992). Most direct measurements of single bond strength have been performed with three types of ultrasensitive probes: the Atomic Force Microscope (AFM) where force is sensed by deflection of a thin silicon nitride cantilever (Binnig et al., 1986), the Biomembrane Force Probe (BFP) where force is sensed by a glass microsphere glued to the pole of a micropipette-pressurized membrane capsule (Evans et al., 1995, Simson et al., 1998); and the laser optical tweezers where force is sensed by displacement of a microsphere trapped in a narrowly focused beam of laser light (Ashkin, 1992, Ashkin et al., 1990). Common limitations associated with these techniques deal with thermal fluctuations, hydrodynamic interactions, and noteworthy the difficulty of controlling the number and the configuration of bonds implicated.

Since most of adhesive interactions are initiated and then sustained under flow conditions (in priority blood but not only), cell resistance to removing by fluid shear stress using a “laminar flow chamber” has become a relevant method to measure the kinetics of receptor-ligand adhesion (Bongrand and Golstein, 1983, Pierres et al., 1996a, Pierres et al., 1996b). Basically, particles or circulating cells covered by receptors are flowing near a surface coated by a ligand and arrested by the formation of limited number of adhesion bonds, e.g., one per cell in many experiments, as far as hydrodynamic forces do not exceed a few pNs (Kaplanski et al., 1993, Pierres et al., 1996a, Smith et al., 1999). The relationship between the number of arrested particles and the duration of their arrest allows (i) determining detachment curves whose initial slope provides the dissociation rate (Chang and Hammer, 1999, Smith et al., 1999, Tissot et al., 1992) and moreover (ii) studying the mechanisms of flow-enhanced cell adhesion (Zhu et al., 2008).

The present paper concerns some under considered aspects of the regulation by mechanical force of collective bond organization implicated in the structuration of different adhesion sites. We purposely apply theories of bond dissociation – issued from stochastic approaches – to different types of bond configurations, e.g., parallel or zipper bonds, on which dissociation forces are exerted. The experimental data purposely used are issued from two different methods: the atomic force microscopy (AFM) and the laminar (viscous) shear flow. It appears that force-control of multiple bonds strongly depends on whether the force distribution on multiple bonds is homogeneous, such as during certain AFM experiments, or heterogeneous, such as during shear flow experiments. Thus, to understand the cell adhesion response to stretch, the knowledge of force distribution is needed down to the smallest scale possible. This reinforces the need of calculating the stress/strain fields exerted on living tissues or cells at various scales and certainly down to the molecular scale.

Section snippets

Single bond

Weak noncovalent interactions between large molecules mediate many of life's functions in cells (Evans, 2001). The strength of interaction is the level of force to disrupt a bond on a particular time scale, knowing that these molecular interactions have limited lifetimes and thus fail under any level of force if pulled on for modest period of time (Evans, 1998). For instance, an isolated bond has no strength on times scales longer than its natural lifetime for spontaneous dissociation

Theoretical aspects

Fig. 2 summarizes the theoretical predictions for lifetimes of multiple uncooperative bonds dissociating randomly (Eqs. (10), (11), (12)). The lifetime of multiple bond (n=N) normalized by the bond lifetime of a single and isolated bond (n=1) is plotted versus the number N of identical bonds constituting the parallel and “zipper” configurations. The main message is that although the lifetime of the collective bonds still decreases with increasing force (as shown by Eqs. (11), (12)), bonds

Conflict of interest

All authors report no actual or potential conflict of interest for the work reported in this paper.

Acknowledgment

For this work, we acknowledge receipt of a grant from Agence Nationale de la Recherche (ANR-09-PIRI-002-03).

References (57)

  • E. Evans et al.

    Sensitive force technique to probe molecular adhesion and structural linkages at biological interfaces

    Biophysical Journal

    (1995)
  • E.A. Evans

    Detailed mechanics of membrane-membrane adhesion and separation II. Discrete kinetically trapped molecular cross-bridges

    Biophysical Journal

    (1985)
  • S. Féréol et al.

    Prestress and adhesion site dynamics control cell sensitivity to extracellular stiffness

    Biophysical Journal

    (2009)
  • A. Gefen et al.

    Analysis of stress distribution in the alveolar septa of normal and simulated emphysematic lungs

    Journal of Biomechanics

    (1999)
  • B. Geiger et al.

    Assembly and mechanosensory function of focal contacts

    Current Opinion in Cell Biology

    (2001)
  • D.A. Hammer et al.

    Simulation of cell rolling and adhesion on surfaces in shear flow: general results and analysis of selectin-mediated neutrophil adhesion

    Biophysical Journal

    (1992)
  • G. Kaplanski et al.

    Granulocyte–endothelium initial adhesion. Analysis of transient binding events mediated by E-selectin in a laminar shear flow

    Biophysical Journal

    (1993)
  • S.H. Lo

    Focal adhesions: what's new inside

    Developmental Biology

    (2006)
  • A. Pierres et al.

    Measuring bonds between surface-associated molecules

    Journal of Immunological Methods

    (1996)
  • D.A. Simson et al.

    Micropipet-based pico force transducer: in depth analysis and experimental verification

    Faraday Discussions of the Chemical Society

    (1998)
  • M.J. Smith et al.

    A direct comparison of selectin-mediated transient, adhesive events using high temporal resolution

    Biophysical Journal

    (1999)
  • E.V. Sokurenko et al.

    Catch-bond mechanism of force-enhanced adhesion: counterintuitive, elusive, but ... widespread?

    Cell Host Microbe

    (2008)
  • B. Suki et al.

    Extracellular matrix mechanics in lung parenchymal diseases

    Respiratory Physiology & Neurobiology

    (2008)
  • T. Sulchek et al.

    Strength of multiple parallel biological bonds

    Biophysical Journal

    (2006)
  • O. Tissot et al.

    Motion of cells sedimenting on a solid surface in a laminar shear flow

    Biophysical Journal

    (1992)
  • Y. Tsukasaki et al.

    Role of multiple bonds between the single cell adhesion molecules, nectin and cadherin, revealed by high sensitive force measurements

    Journal of Molecular Biology

    (2007)
  • V. Vogel et al.

    Cell fate regulation by coupling mechanical cycles to biochemical signaling pathways

    Current Opinion in Cell Biology

    (2009)
  • M.D. Ward et al.

    A theoretical analysis for the effect of focal contact formation on cell-substrate attachment strength

    Biophysical Journal

    (1993)
  • View full text