The state diagram for cell adhesion under flow: Leukocyte rolling and firm adhesion

103

C ell-protein adhesion regulates essential processes in multicellular organisms and provides signals that affect the morphology, motility, gene expression, and survival of cells (1). Fibronectin (Fn) is an extracellular matrix protein that is widely distributed in the tissues of all vertebrates and is a potential ligand for most cell types (2). Fn is also an important mediator of bacterial invasions and of persistent infections like that of Staphylococcus epidermidis (3). Until now, S. epidermidis was considered a mere saprophyte, usually harboring on the skin and mucosae. Recently, this organism has been shown to also act as a pathogen, mainly in association with surgical applications of biomaterials (4).Like many other cell-protein adhesions, the binding between Fn and staphylococci takes place under physiological shear rates (5). It has been reported that the high shear stress characteristic of the turbulent flow at blood vessel entrances and bifurcations can prevent Fn-mediated adhesion of Staphylococcus aureus to the endothelial cells lining the vessel, reducing, in this way, the chances of bacterial invasion (6). Thus, a thorough characterization of the binding͞unbinding dynamics of these interactions is necessary to better understand the molecular mechanisms of Fn-mediated pathogenesis. Moreover, specific cell-protein interactions have been selected by nature to mediate different dynamic processes of adhesion of a cell under hydrodynamic flow, as in the case of the rolling adhesion of leukocytes whose velocity in the blood vessels is controlled by transient binding events to the inner walls. It is of interest to understand how different cell͞protein adhesions are optimized in their functions through the details of the interactions at the molecular level. In this article, we address this issue by comparing the interaction dynamics of three different adhesion processes: firm adhesion mediated by the biotin͞avidin pair, rolling adhesion, which is mediated by the L-selectin͞P-selectin glycoprotein ligand 1 (PSGL-1) system, and cell͞bacterium adhesion mediated by Fn͞adhesin binding.Traditionally, adhesion interactions have been studied in reversible equilibrium conditions. However, in vivo, these interactions take place under significant shear forces with pulling rates that are much faster than the relaxation rates of the binding pair, and thus, the binding͞unbinding process occurs under nonequilibrium, irreversible conditions. The development of single-molecule manipulation methods, such as scanning force microscopy (SFM) and optical tweezers, has made it possible to investigate the dynamics of these processes under nonequilibrium conditions, and to measure their force-dependent dissociation kinetics. Here, we investigate the dynamics of the interactions between individual living S. epidermidis cells and single Fn molecules, map the energy landscape of the binding͞ unbinding process, and measure the association and dissociation rate constants of the binding pair by using SFM. In particular, we show that two p...

“…5). These parameters are consistent with the function of avidin-biotin known to mediate firm adhesion under flow (33).…”

Section: Mapping the Deadhesion Energy Landscape Under A Mechanical Fsupporting

confidence: 84%

Section: Mapping the Deadhesion Energy Landscape Under A Mechanical Fmentioning

confidence: 75%

Dynamics of the interaction between a fibronectin molecule and a living bacterium under mechanical force

Bustanji

Arciola

Conti

et al. 2003

103

“…A key molecule in this process is L-selectin, a leukocyte-expressed adhesion receptor that is localized to tips of microvilli and binds to glycosylated ligands on the endothelium. Its properties are optimized for initial capture and rolling under physiological shear (2,3), as confirmed by recent experimental data and computer simulations (4,5). In contrast to tethering through other receptor systems like P-selectin, E-selectin, or integrins, appreciable tethering through L-selectin and subsequent rolling occurs only above a threshold in shear (6), even in cell-free systems (7,8).…”

mentioning

confidence: 75%

L-selectin-mediated leukocyte tethering in shear flow is controlled by multiple contacts and cytoskeletal anchorage facilitating fast rebinding events

Schwarz

Alon

2004

L-selectin-mediated tethers result in leukocyte rolling only above a threshold in shear. Here we present biophysical modeling based on recently published data from flow chamber experiments, which supports the interpretation that L-selectin-mediated tethers below the shear threshold correspond to single L-selectin carbohydrate bonds dissociating on the time scale of milliseconds, whereas L-selectin-mediated tethers above the shear threshold are stabilized by multiple bonds and fast rebinding of broken bonds, resulting in tether lifetimes on the time scale of 10 ؊1 seconds. Our calculations for cluster dissociation suggest that the single molecule rebinding rate is of the order of 10 4 Hz. A similar estimate results if increased tether dissociation for tail-truncated L-selectin mutants above the shear threshold is modeled as diffusive escape of single receptors from the rebinding region due to increased mobility. Using computer simulations, we show that our model yields first-order dissociation kinetics and exponential dependence of tether dissociation rates on shear stress. Our results suggest that multiple contacts, cytoskeletal anchorage of L-selectin, and local rebinding of ligand play important roles in L-selectin tether stabilization and progression of tethers into persistent rolling on endothelial surfaces. L eukocyte trafficking plays a central role in the immune response of vertebrates. Leukocytes constantly circulate in the cardiovascular system and enter into tissue and lymph through a multistep process involving rolling on the endothelium, activation by chemokines, arrest, and transendothelial migration (1). A key molecule in this process is L-selectin, a leukocyte-expressed adhesion receptor that is localized to tips of microvilli and binds to glycosylated ligands on the endothelium. Its properties are optimized for initial capture and rolling under physiological shear (2, 3), as confirmed by recent experimental data and computer simulations (4, 5). In contrast to tethering through other receptor systems like P-selectin, E-selectin, or integrins, appreciable tethering through L-selectin and subsequent rolling occurs only above a threshold in shear (6), even in cell-free systems (7,8). Down-regulation by low shear is unique for L-selectin tethers and might be necessary because L-selectin ligands are constitutively expressed on circulating leukocytes, platelets, and subsets of blood vessels (9).The dissociation rate of single molecular bonds is expected to depend exponentially on an externally applied steady force (Bell equation) (10). Quantitative analysis with a regular video camera (time resolution of 30 ms) of L-selectin tether kinetics in flow chambers above the shear threshold resulted in first-order dissociation kinetics, with a force dependence that could be fit well to the Bell equation, resulting in a force-free dissociation constant of 6.6 Hz (2-4, 11). These findings have been interpreted as signatures of single L-selectin carbohydrate bonds. However, recent experimental evidence suggests th...

“…Adhesive dynamics has been used extensively to investigate the biophysics of cell adhesion (28,29), and we recently demonstrated that integrating catch-slip mechanochemistry can account for shear-promoted rolling behavior (30). We first evaluated the ability of each parameter set to accurately predict the rolling dynamics of human neutrophils on a PSGL-1 substrate observed from 0 to 2 dynes/cm 2 wall shear stress.…”

Section: Predicting Selectin-mediated Adhesion Dynamicsmentioning

confidence: 99%

Selectin catch–slip kinetics encode shear threshold adhesive behavior of rolling leukocytes

Beste¹,

Hammer

2008

Self Cite

The selectin family of leukocyte adhesion receptors is principally recognized for mediating transient rolling interactions during the inflammatory response. Recent studies using ultrasensitive force probes to characterize the force-lifetime relationship between Pand L-selectin and their endogenous ligands have underscored the ability of increasing levels of force to initially extend the lifetime of these complexes before disrupting bond integrity. This so-called ''catch-slip'' transition has provided an appealing explanation for shear threshold phenomena in which increasing levels of shear stress stabilize leukocyte rolling under flow. We recently incorporated catch-slip kinetics into a mechanical model for cell adhesion and corroborated this hypothesis for neutrophils adhering via L-selectin. Here, using adhesive dynamics simulations, we demonstrate that biomembrane force probe measurements of various Pand L-selectin catch bonds faithfully predict differences in cell adhesion patterns that have been described extensively in vitro. Using phenomenological parameters to characterize the dominant features of molecular force spectra, we construct a generalized phase map that reveals that robust shear-threshold behavior is possible only when an applied force very efficiently stabilizes the bound receptor complex. This criteria explains why only a subset of selectin catch bonds exhibit a shear threshold and leads to a quantitative relationship that may be used to predict the magnitude of the shear threshold for families of catch-slip bonds directly from their force spectra. Collectively, our results extend the conceptual framework of adhesive dynamics as a means to translate complex single-molecule biophysics to macroscopic cell behavior.force spectroscopy ͉ inflammation ͉ nanomechanics B y associating with cognate ligands on apposed surfaces, selectins expressed inducibly on the endothelial lumen (Eand P-selectin) and constitutively on the microvillar tips of peripheral blood leukocytes (L-selectin) mediate cell tethering and rolling adhesion (1). Stable rolling through L-selectin requires a threshold level of fluid shear stress, an unexpected but important consequence that prevents homotypic aggregation and inappropriate adhesion in low-shear environments (2-4). Much attention has focused on the underlying molecular kinetics to understand this behavior, with particular emphasis on the role of convective transport (5-8) and the molecular response to mechanical strain (9, 10). Several studies have now firmly established that fluid shear rate controls the tethering rate at which cells initially adhere to the substrate (6-8). Although a rate-controlled model of rolling adhesion does account for observed changes in adherent cell flux to a surface above and below the shear threshold, it does not provide a satisfactory explanation for why rolling cells in continuous contact with the surface roll progressively slower as the optimal level of fluid shear is approached. Rather, the favored hypothesis for the shear threshold po...