Adhesion Cascade Research Articles

Metabolic innovations towards the human lineage

BackgroundWe describe a function-driven approach to the analysis of metabolism which takes into account the phylogenetic origin of biochemical reactions to reveal subtle lineage-specific metabolic innovations, undetectable by more traditional methods based on sequence comparison. The origins of reactions and thus entire pathways are inferred using a simple taxonomic classification scheme that describes the evolutionary course of events towards the lineage of interest. We investigate the evolutionary history of the human metabolic network extracted from a metabolic database, construct a network of interconnected pathways and classify this network according to the taxonomic categories representing eukaryotes, metazoa and vertebrates.ResultsIt is demonstrated that lineage-specific innovations correspond to reactions and pathways associated with key phenotypic changes during evolution, such as the emergence of cellular organelles in eukaryotes, cell adhesion cascades in metazoa and the biosynthesis of complex cell-specific biomolecules in vertebrates.ConclusionThis phylogenetic view of metabolic networks puts gene innovations within an evolutionary context, demonstrating how the emergence of a phenotype in a lineage provides a platform for the development of specialized traits.

VAP-1 and CD73, Endothelial Cell Surface Enzymes in Leukocyte Extravasation

Leukocyte extravasation from the blood into tissues is crucial for normal immune surveillance and in inflammation. Traditionally molecules belonging to selectin, chemokine, integrin, and immunoglobulin super families are thought to mediate the multiple adhesive and activation events needed for a successful emigration cascade. Recently, emerging evidence suggests that enzymes expressed on the surface of endothelial cells and leukocytes also contribute to the leukocyte extravasation cascade. Here we briefly review the role of vascular adhesion protein-1 (VAP-1) and CD73, 2 cell surface enzymes, in leukocyte migration form the blood into the tissues. Importantly, specific enzyme inhibitors, gene-deficient mice, and recombinant enzymes have recently unambiguously shown that the catalytic activity of these enzymes regulates the leukocyte traffic. The concept of enzymatic regulation of leukocyte extravasation provides new insight into the multi-step adhesion cascade and opens new possibilities for inhibiting inappropriate inflammatory reaction through the use of small molecule enzyme inhibitors.

Metalloproteinase-9 deficiency protects against hepatic ischemia/reperfusion injury

Leukocyte transmigration across endothelial and extracellular matrix protein barriers is dependent on adhesion and focal matrix degradation events. In the present study we investigated the role of metalloproteinase-9 (MMP-9/gelatinase B) in liver ischemia/reperfusion (I/R) injury using MMP-9-deficient (MMP-9(-/-)) animals and mice treated with a specific anti-MMP-9 neutralizing antibody or with a broad gelatinase inhibitor for both MMP-9 and metalloproteinase-2 (MMP-2/gelatinase A). Compared to wild-type mice, MMP-9(-/-) mice and mice treated with an anti-MMP-9 antibody showed significantly reduced liver damage. In contrast, mice treated with a broad gelatinase inhibitor showed rather inferior protection against I/R injury and were characterized by persistent ongoing liver inflammation, suggesting that MMP-2 and MMP-9 may have distinct roles in this type of injury. MMP-9 was mostly detected in Ly-6G and macrophage antigen-1 leukocytes adherent to the vessel walls and infiltrating the damaged livers of wild-type mice after liver I/R injury. Leukocyte traffic and cytokine expression were markedly impaired in livers of MMP-9(-/-) animals and in livers of mice treated with anti-MMP-9 antibody after I/R injury; however, initiation of the endothelial adhesion cascades was similar in both MMP-9(-/-) and control livers. We also showed that MMP-9-specific inhibition disrupted neutrophil migration across fibronectin in transwell filters and depressed myeloperoxidase (MPO) activation in vitro. These results support critical functions for MMP-9 in leukocyte recruitment and activation leading to liver damage. Moreover, they provide the rationale for identifying inhibitors to specifically target MMP-9 in vivo as a potential therapeutic approach in liver I/R injury.

Getting to the site of inflammation: the leukocyte adhesion cascade updated

Neutrophil recruitment, lymphocyte recirculation and monocyte trafficking all require adhesion and transmigration through blood-vessel walls. The traditional three steps of rolling, activation and firm adhesion have recently been augmented and refined. Slow rolling, adhesion strengthening, intraluminal crawling and paracellular and transcellular migration are now recognized as separate, additional steps. In neutrophils, a second activation pathway has been discovered that does not require signalling through G-protein-coupled receptors and the signalling steps leading to integrin activation are beginning to emerge. This Review focuses on new aspects of one of the central paradigms of inflammation and immunity--the leukocyte adhesion cascade.

Stabilin-2 is involved in lymphocyte adhesion to the hepatic sinusoidal endothelium via the interaction with αMβ2 integrin

Although lymphocyte recirculation to the endothelium plays a critical role in the movement of immune cells from the blood into tissues and sites of inflammation, the mechanisms involved in lymphocyte trafficking via the hepatic circulation have yet to be elucidated fully. In this study, we investigated the role of stabilin-2, which is expressed specifically in the sinusoidal endothelium, in the adhesion of lymphocytes to the hepatic endothelium. Stabilin-2-expressing cells mediate the adhesion of PBLs. This interaction was attributed specifically to the interaction of stabilin-2 with alphaMbeta2 integrin. Using mutant stabilin-2 molecules with deletions in the extracellular domain, we mapped the binding site for alphaMbeta2 integrin to the fasciclin 1 (FAS1) domains of stabilin-2. The specificity of the interaction between alphaMbeta2 integrin and the FAS1 domain was confirmed further by binding assays using neutralizing antibodies. More physiologically, we showed that the down-regulation of stabilin-2 results in the defective binding of lymphocytes to hepatic sinusoidal endothelial cells under conditions of static and physiological flow. Together, these data show that stabilin-2 can reconstitute the lymphocyte-endothelial adhesion cascade under physiological shear stress. We propose a critical role for stabilin-2 in lymphocyte adhesion to specialized endothelia, such as that of the hepatic sinusoid.

The Neutrophil Specific CD177 Is a Novel Counter-Receptor for Endothelial PECAM-1.

CD177 is a glycosyl-phosphatidylinositol-linked member of the Ly-6 superfamily that is expressed on approximately 50% of human neutrophils, though 3–5% of Caucasians and African Americans are CD177 null. CD177 carries the clinically-important neutrophil antigen, HNA-2a - alloantibodies to which can result in profound neutropenia. Although the role of CD177 in neutrophil function is not known, it has been found to be aberrantly expressed on the neutrophils of most patients suffering from polycythemia vera, and in approximately half of patients with essential thrombocythemia. To further elucidate the function of CD177, we produced a CD177/IgG Fc fusion protein, and used it identify its binding partner on endothelial cells. Flow cytometric analysis revealed that CD177/Fc bound tightly and specifically to human umbilical vein endothelial cells, and an antigen-capture ELISA screen employing a panel of monoclonal antibodies (mAbs) to endothelial cell surface proteins further revealed the target antigen to be the endothelial cell junctional protein, PECAM-1. Surface plasmon resonance analysis showed tight binding between PECAM-1 and CD177, having a Kd of 8.17 x 10−7 M. U937 cells stably transfected with CD177 bound immobilized PECAM-1, and this heterophilic interaction could be blocked by mAbs specific for Ig domains 5 or 6 of the PECAM-1 extracellular domain, or by mAbs specific for CD177. In contrast, no inhibition was observed when mAbs against Ig domains 1 and 2 were applied. The same mAbs were also found to be effective inhibitors of neutrophil transendothelial migration. Taken together, these data establish PECAM-1/CD177 as a previously unrecognized heterophilic receptor/counter-receptor pair that functions in the multi-step adhesion and signaling cascade of events that take place during the inflammatory response.

PECAM‐1, a key player in neuroinflammation

Platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) is a 130-kDa protein, which plays a significant role in the adhesion cascade. It is therefore involved in leucocyte endothelium interaction and in leucocyte transendothelial migration during inflammation. As neuroinflammation and subsequent blood brain barrier disruption are integral processes in many neurological disorders, PECAM-1 and its soluble form (sPECAM-1) have been investigated in a number of conditions, rising hopes as a potential marker of disease activity, a possible target in treatment and a prognostic factor. It has been shown that serum and CSF levels of PECAM-1 and sPECAM-1 are increased in patients in active stages of multiple sclerosis. Similarly, they rise in individuals after ischaemic stroke. PECAM-1 has also been shown to be involved in the pathogenesis of Abeta-related cerebral vascular disorders, such as Alzheimer disease. It participates in the pathomechanism of paraneoplastic neurological disorders and in neuroinflammation in NeuroAIDS. A number of experiments on animal models were carried out in order to investigate PECAM-1 role in the above-mentioned conditions and more, including brain trauma and nerve root injury. In this review most recent investigations on PECAM-1 biology and its role in neuroinflammation have been described and discussed from a multidisciplinary point of view.

Leukocyte–endothelial cell interactions

Leukocytes constantly patrol the vascular system in order to react promptly to infections when and where it is necessary. To fulfil this task, the cells have to enter secondary lymphoid organs and to emigrate into inflamed tissues, which requires them to cross the barrier of endothelial cells that line blood vessels. Transendothelial migration into inflamed tissues is preceded by a sequence of leukocyte–endothelial cell interactions, generally referred to as the ‘multistep adhesion cascade’ (Fig. 1). The cascade is initiated by inflammatory signals that cause local activation of vascular endothelium. Activated endothelial cells express Eand P-selectin molecules that capture leukocytes from the bloodstream and mediate rolling of the cells by binding to glycoconjugate ligands on the leukocyte surface. Homing to secondary lymphoid organs is initiated by interactions of L-selectin (expressed by leukocytes) with glycoconjugates on high endothelial venules. Rolling allows the leukocytes to perceive and accumulate signals that are mediated by the binding of endothelial-bound chemokines to their leukocyte receptors. These signals lead to leukocyte activation, resulting in a transfer of leukocyte integrins into a high affinity conformation. The integrins now allow the leukocytes to adhere firmly to the endothelium by interactions with intercellular adhesion molecule-1 and ⁄or vascular cell adhesion molecule-1. The leukocytes then migrate to sites where they can cross the endothelial layer, using either a paracellular pathway through intercellular junctions, or a transcellular pathway through the endothelial cell body. This minireview series comprises five reviews that cover important aspects of leukocyte–endothelial cell interactions (indicated in Fig. 1). In the first review, Markus Sperandio considers in vivo results on selectinmediated leukocyte rolling. He describes the requirements for rolling interactions and reviews the current knowledge of the functional relevance of the various known selectin ligands. This review focuses in particular on the glycosyland sulfotransferases that are required for the post-translational modification of selectin ligands and for which a series of knockout animals is available. The second review, by Sviatlana Yakubenia & Martin K. Wild, deals with leukocyte adhesion deficiency II, a human congenital disease in which hypofucosylation prevents selectin binding and leukocyte capture ⁄ rolling, thus inducing an immunodeficiency. The review describes recent advances on the genetic defects in patients with leukocyte adhesion deficiency II. It also focuses on open questions concerning the molecular basis of the therapy for leukocyte adhesion deficiency II and the mechanisms of the developmental defects that accompany the immunodeficiency in this disease. The third review, by Bjorn Petri & Gabriele Bixel, discusses current knowledge on the interaction of cell adhesion molecules during leukocyte transendothelial migration. In contrast to leukocyte rolling and firm adhesion, leukocyte diapedesis, and the routes taken by migrating leukocytes, are less well understood. The article focuses on cell adhesion molecules that are known to participate in the process of leukocyte extravasation, including cell surface molecules such as platelet ⁄ endothelial cell adhesion molecule-1, members of the junctional adhesion molecule family and CD99. Junctional cell adhesion molecules are believed to be important for paracellular transmigration, with leukocytes squeezing through between adjacent endothelial cells. In addition, leukocytes can cross the endothelium via an alternative pathway whereby they migrate through the body of an endothelial cell. To date, not much is known about the molecular players involved in the latter pathway. However, endothelial components, such as intermediate filaments and caveolae, seem to be important for this process. The fourth review, by Peter Hordijk, summarizes recent progress made towards an understanding of the signaling pathways that are induced in endothelial cells during leukocyte extravasation. A series of studies clearly shows that endothelial cells play an active role in this process, allowing leukocytes to cross the vascular endothelium via the paracellular or the transcellular pathway. Adhesion of leukocytes to the luminal surface of the vascular endothelium induces the formation of a docking structure that is associated with the clustering of adhesion and signaling molecules. This local concentration of cell adhesion molecules, such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, is believed to be required for the initiation of endothelial signaling. Both intracellular calcium and the actin cytoskeleton, but also small GTPases, reactive oxygen species and protein kinases, are involved in these signaling events. doi: 10.1111/j.1742-4658.2006.05436.x

Clonal deletion of thymocytes by circulating dendritic cells homing to the thymus

Dendritic cell (DC) presentation of self antigen to thymocytes is essential to the establishment of central tolerance. We show here that circulating DCs were recruited to the thymic medulla through a three-step adhesion cascade involving P-selectin, interactions of the integrin VLA-4 with its ligand VCAM-1, and pertussis toxin-sensitive chemoattractant signaling. Ovalbumin-specific OT-II thymocytes were selectively deleted after intravenous injection of antigen-loaded exogenous DCs. We documented migration of endogenous DCs to the thymus in parabiotic mice and after painting mouse skin with fluorescein isothiocyanate. Antibody to VLA-4 blocked the accumulation of peripheral tissue-derived DCs in the thymus and also inhibited the deletion of OT-II thymocytes in mice expressing membrane-bound ovalbumin in cardiac myocytes. These findings identify a migratory route by which peripheral DCs may contribute to central tolerance.

Different expression of adhesion molecules and tetraspanins of monocytes of patients with atopic eczema

Atopic eczema (AE) and psoriasis vulgaris (Pso) represent the most frequent chronic inflammatory skin diseases, which have a high number of characteristics in common but differ in their clinical picture and immunological background. A shared feature of both AE and Pso is a high recruitment of distinct proinflammatory cells from the blood into the skin at the initiation of the disease. A multistep adhesion cascade via different adhesion receptors consisting of 'tethering' and 'rolling' mediated by selectins, alpha-integrins and beta-integrins and the 'arrest' of the cells is initiated during this process. To evaluate the expression of adhesion molecules and tetraspanins of monocytes of patients with AE and Pso in comparison with healthy controls. We analysed the expression of adhesion molecules and tetraspanins on monocytes freshly isolated from the peripheral blood of patients with AE (n = 40) and Pso (n = 65) during exacerbation of their disease in comparison with healthy, non-atopic controls (n = 50). A high number of similarities between monocytes of patients with AE and patients with Pso, and disease-related differences in the expression of CD62L, CD62P, CD11a, CD11b, CD11c, CD49b, CD49d, CD49e and CD18 and the tetraspanins CD9, CD53, CD63 and CD151, which were elevated on monocytes of patients with AE could be observed. A distinct expression pattern of adhesion molecules and tetraspanins on monocytes of patients with AE and Pso might influence the recruitment process of inflammatory precursor cells and facilitate new approaches for therapeutic strategies aimed at interrupting the very earliest steps of the fateful recruitment process.

Intracellular heterogeneity in adhesiveness of endothelium affects early steps in leukocyte adhesion

Endothelial cell junctions are thought to be preferential sites for transmigration. However, the factors that determine the site of transmigration are not well defined. Our data show that the preferential role of endothelial cell junctions is not limited to transmigration but extends to earlier steps of leukocyte recruitment, such as rolling and arrest. We used primary mouse neutrophils and mouse aortic endothelium in a flow chamber system to compare adhesive interactions near endothelial cell junctions to interactions over endothelial cell centers. We found differences in both rolling velocity and arrest frequency for neutrophils at endothelial cell junctions vs. more central areas of endothelial cells. Differences were governed by adhesion molecule interactions, not local topography. Interestingly, the role of particular adhesion molecules depended on their location on the endothelial cell surface. Although ICAM-1 stabilized and slowed rolling over central areas of the cell, it did not influence rolling velocity over endothelial cell junctions. P-selectin and VCAM-1 were more important for rolling near endothelial cell junctions than E-selectin. This demonstrates that adhesive properties of endothelial cell junctions influence early events in the adhesion cascade, which may help explain how leukocytes are localized to sites of eventual transmigration.

Leukocyte Recruitment to the Inflamed Glomerulus: A Critical Role for Platelet-Derived P-Selectin in the Absence of Rolling

The renal glomerulus is one of the few sites within the microvasculature in which leukocyte recruitment occurs in capillaries. However, due to the difficulty of directly visualizing the glomerulus, the mechanisms of leukocyte recruitment to glomerular capillaries are poorly understood. To overcome this, we rendered murine kidneys hydronephrotic to allow the visualization of the functional glomerular microvasculature during an inflammatory response. These experiments demonstrated that following infusion of anti-glomerular basement membrane (GBM) Ab, leukocytes became adherent in glomerular capillaries via a process of immediate arrest, without undergoing prior detectable rolling. However, despite the absence of rolling, this recruitment involved nonredundant roles for the P-selectin/P-selectin glycoprotein ligand-1 and beta2 integrin/ICAM-1 pathways, suggesting that a novel form of the multistep leukocyte adhesion cascade occurs in these vessels. Anti-GBM Ab also increased glomerular P-selectin expression and induced a P-selectin-independent increase in platelet accumulation. Moreover, platelet depletion prevented both the increase in glomerular P-selectin, and the leukocyte recruitment induced by anti-GBM Ab. Furthermore, depletion of neutrophils and platelets also prevented the increase in urinary protein excretion induced by anti-GBM Ab, indicating that their accumulation in glomeruli contributed to the development of renal injury. Finally, infusion of wild-type platelets into P-selectin-deficient mice restored the ability of glomeruli in these mice to support leukocyte adhesion. Together, these data indicate that anti-GBM Ab-induced leukocyte adhesion in glomeruli occurs via a novel pathway involving a nonrolling interaction mediated by platelet-derived P-selectin.

Rolling Adhesion of α L I Domain Mutants Decorrelated from Binding Affinity

Activated lymphocyte function-associated antigen-1 (LFA-1, α Lβ 2 integrin) found on leukocytes facilitates firm adhesion to endothelial cell layers by binding to intercellular adhesion molecule-1 (ICAM-1), which is up-regulated on endothelial cells at sites of inflammation. Recent work has shown that LFA-1 in a pre-activation, low-affinity state may also be involved in the initial tethering and rolling phase of the adhesion cascade. The inserted (I) domain of LFA-1 contains the ligand-binding epitope of the molecule, and a conformational change in this region during activation increases ligand affinity. We have displayed wild-type I domain on the surface of yeast and validated expression using I domain specific antibodies and flow cytometry. Surface display of I domain supports yeast rolling on ICAM-1-coated surfaces under shear flow. Expression of a locked open, high-affinity I domain mutant supports firm adhesion of yeast, while yeast displaying intermediate-affinity I domain mutants exhibit a range of rolling phenotypes. We find that rolling behavior for these mutants fails to correlate with ligand binding affinity. These results indicate that unstressed binding affinity is not the only molecular property that determines adhesive behavior under shear flow.

A multistep adhesion cascade for lymphoid progenitor cell homing to the thymus.

Homing of bone marrow (BM)-derived progenitors to the thymus is essential for T cell development. We have previously reported that two subpopulations of common lymphoid progenitors, CLP-1 and CLP-2, coexist in the BM and give rise to lymphocytes. We demonstrate that CLP-2 migrate to the thymus more efficiently than any other BM-derived progenitors. Short-term adoptive transfer experiments revealed that CLP-2 homing involves P-selectin/P-selectin glycoprotein ligand 1 interactions, pertussis toxin-sensitive chemoattractant signaling by CC chemokine ligand 25 through CC chemokine receptor 9, and binding of the integrins alpha4beta1 and alphaLbeta2 to their respective ligands, vascular cell adhesion molecule 1 and intercellular adhesion molecule 1. Preferential thymus-tropism of CLP-2 correlated with higher chemokine receptor 9 expression than on other BM progenitors. Thus, CLP access to the thymus is controlled by a tissue-specific and subset-selective multistep adhesion cascade.

Nano-to-Microscale Mechanical Switches and Fuses Mediate Adhesive Contacts between Leukocytes and the Endothelium

As a vital part of the inflammatory response, the leukocyte adhesion cascade involves the capture of white blood cells at the vascular endothelium, a progressively slowing, “rolling” motion of cells along the vessel walls, firm cell adhesion at target sites, and eventually, the transmigration of activated cells into the inflamed tissue1-4 (for an instructive overview see also http://bme.virginia.edu/ley/). Studies aiming to reveal the biophysical mechanisms underlying these processes face the difficult challenge of covering a large range of relevant scales: nanoscale interactions between adhesive molecules, local deformations of subcellular structures under point loads, and whole-cell activation and motion. Yet multiscale approaches also offer particularly rewarding insights, for example, by providing an understanding of single-molecule interactions within their natural, larger-scale biological context and, conversely, by tracing macroscopically observed cellular phenomena directly to their molecular origins. The present work focuses on nano-to-microscale regulatory aspects that mediate the initial stages of the adhesion cascade. Early events, such as the capture of leukocytes and their initial rolling exploration at the endothelium, occur usually too fast to be regulated biologically, i.e., through the expression of proteins. We thus expected that most mechanisms governing initial leukocyte adhesion under a broad range of blood-flow conditions had to be “preprogrammed” into molecular-to-subcellular structures and that they had to be primarily mechanical. Accordingly, our experimental approach was to study in vitro the nano-to-micromechanical response of individual leukocytes that were loaded at a point with a rapidly increasing force. The adhesion bond between P-selectin (expressed in vivo on the endothelium and on activated platelets), and its ligand PSGL-1 (resident in the leukocyte membrane) is a key player in the initial adhesion stages.4,5 We exploited this bond to form point attachments between polymorphonuclear leukocytes (PMNs) and functionalized microspheres that had been coated with P-selectin. To distinguish the dynamic properties of an individual P-selectin:PSGL-1 bond from mechanisms governed by other cellular structures, we also tested this bond on its own using isolated PSGL-1 that had been immobilized on a second batch of microspheres. Both types of interaction, i.e., P-selectin:PSGL-1 as well as P-selectin:PMN, were characterized by dynamic force spectroscopy6,7 over exceptionally wide ranges of forceloading rates. Complementary test surfaces were first brought into soft, feedback-controlled contact to allow for the formation of bonds between immobilized, reactive molecules. Then, while moving the surfaces apart at preset velocities, we recorded the force experienced by attachments between them. Piconewton forces were reported by the biomembrane force probe,8,9 a prototypical biophysical tool that is uniquely suited to study the dynamics of biologically relevant, ultraweak interactions. This approach enabled us to inspect in detail two possible candidates for principal regulatory mechanisms in early leukocyte adhesion. One is a serial molecular attachment consisting of (i) the extracellular P-selectin:PSGL-1 bond and (ii) a putative, weak biochemical link that anchors the intracellular tail domain of the transmembrane PSGL-1 to the cortical cytostructure.10 The other is a hierarchy of rheological cell responses to point loads: from slow viscoelastic deformation of the whole cell, and a soft-elastic displacement of the cell cortex, to the extrusion of thin membrane tubes (“tethers”) that can easily growsat quasiconstant pulling forcessto several micrometers in length. The formation of tethers from fluid membranes under point loads is a ubiquitous phenomenon, as evidenced by a large body of work on lipid vesicles11-14 and on various types of biological cells.15-18 A number of pioneering studies also investigated the mechanical properties of PMN tethers19-21 and their importance in leukocyte rolling.22,23 Perhaps even more interesting than these regulatory mechanisms by themselves is the intriguing interplay between them. For example, the lifetime of weak attachments under stress depends critically on the history of force application. In the present case where the leukocyte itself links adhesive molecules to rigid surfaces, any subcellular soft structures will act to dampen the sudden impact of force and thus modulate the force history experienced by the actual adhesion bonds. Therefore, the lifetime, or strength, of adhesive attachments is directly affected by the rheology of cell deformation under point loads. On the other hand, the extrusion of tethers from PMNs appears to commence only * Corresponding author e-mail: vheinrich@ucdavis.edu. † Boston University. # Current address: Department of Biomedical Engineering, University of California, Davis, 451 East Health Sciences Drive, Davis, CA 95616. ‡ Department of Pathology, University of British Columbia. § Department of Physics and Astronomy, University of British Columbia. 1482 J. Chem. Inf. Model. 2005, 45, 1482-1490

Anti-Inflammatory Effects of Inhibiting the Amine Oxidase Activity of Semicarbazide-Sensitive Amine Oxidase

Human semicarbazide-sensitive amine oxidase (SSAO) or vascular adhesion protein-1 (VAP-1) is a copper-containing amine oxidase (AOC3, EC 1.4.3.6) that has both enzymatic and adhesive function. SSAO catalyzes the oxidative deamination of primary amines, resulting in the formation of the corresponding aldehyde and release of hydrogen peroxide and ammonia. Membrane-bound SSAO is an inflammation-inducible endothelial cell adhesion molecule that mediates the interaction between leukocytes and activated endothelial cells in inflamed vessels. Both the direct adhesive and enzymatic functions seem to be involved in the adhesion cascade. LJP 1207 [N'-(2-phenyl-allyl)-hydrazine hydrochloride] is a potent (human SSAO IC(50) = 17 nM), selective, and orally available SSAO inhibitor that blocks both the enzymatic and adhesion functions of SSAO/VAP-1. In a mouse model of ulcerative colitis, LJP 1207 significantly reduces mortality, loss of body weight, and colonic cytokine levels. Quantitative histopathological assessment of colitis activity in this model showed a highly significant suppression of inflammation, injury, and ulceration scores in the animals treated with the SSAO/VAP-1 inhibitor. LJP 1207 also reduced serum levels of tumor necrosis factor-alpha and interleukin 6 in lipopolysaccharide (LPS)-challenged mice and prolonged survival post-LPS-induced endotoxemia. Therapeutic and prophylactic administration of LJP 1207 in the rat carrageenan footpad model also markedly inhibited swelling and inflammation. Overall, the data suggest that small molecule SSAO/VAP-1 inhibitors may provide clinical benefit in the treatment of acute and chronic inflammatory diseases.

Effect of Microvillus Deformability on Leukocyte Adhesion Explored Using Adhesive Dynamics Simulations

Leukocyte rolling on the endothelium via selectin molecules is an important step in the adhesion cascade, which allows leukocytes in the bloodstream to reach sites of infection. We improve upon Adhesive Dynamics simulations by incorporating deformable microvilli on which adhesion molecules are clustered. As determined in micropipette experiments, microvilli deform like an elastic spring at small forces and a combination of yield and viscous dissipation at high forces. First, we create a modified version of the state diagram for adhesion which includes microvillus deformation, and find four adhesion states—firmly bound; landing; rolling; and no-adhesion. Then, we simulate the effects of receptor clustering on the tips of microvilli, number of adhesion molecules on the cell, and the spring constant of the bonds, within the context of deformable microvilli. We also explore how the microvillus rheology itself controls the dynamics of adhesion. A minimum in rolling velocity occurs at an intermediate value of the microvillus membrane viscosity, remarkably close to the reported physiological value, suggesting that the mechanics of microvilli have evolved ideally for rolling and adhesion of leukocytes. We find that a larger degree of association between the membrane and cytoskeleton leads to slower rolling, and stiffer microvilli result in faster rolling. Decreasing the overall deformability of the microvilli greatly reduces a simulated cell's ability to roll. A comparison to experimental results of in vitro cell rolling agrees with the simulation at low shear rates. Furthermore, simulated rolling trajectories of cells with deformable microvilli display periods of rolling interdispersed with pauses, consistent with that seen in experiments where microvilli were observed to stretch.

L-selectin: Adhesion, signalling and its importance in pathologic posttraumatic endotoxemia and non-septic inflammation

The leucocyte expressed surface-bound L-selectin belongs to the selectin family of adhesion molecules. It exhibits adhesive as well as signalling functions. Mainly, it is of importance in lymphocyte homing and in the extravasation of leucocytes into the surrounding tissue during inflammation. Acting in the initial step of the cell adhesion cascade, L-selectin is responsible for the rolling of leucocytes on endothelial layers. Therefore, L-selectin is thought to be an adequate target for pharmacological interventions. Beneath the discussion of the molecules’ general features like molecule structure and its regulation, the review focuses firstly on L-selectin in the context of posttraumatic inflammatory disorders, and secondly on the importance of L-selectin specific signalling events.

Junctional Adhesion Molecule-C Regulates the Early Influx of Leukocytes into Tissues during Inflammation

Leukocyte recruitment from blood to inflammatory sites occurs in a multistep process that involves discrete molecular interactions between circulating and endothelial cells. Junctional adhesion molecule (JAM)-C is expressed at different levels on endothelial cells of lymphoid organs and peripheral tissues and has been proposed to regulate neutrophil migration by its interaction with the leukocyte integrin Mac-1. In the present study, we show that the accumulation of leukocytes in alveoli during acute pulmonary inflammation in mice is partially blocked using neutralizing Abs against JAM-C. To confirm the function of JAM-C in regulating leukocyte migration in vivo, we then generated a strain of transgenic mice overexpressing JAM-C under the control of the endothelial specific promotor Tie2. The transgenic animals accumulate more leukocytes to inflammatory sites compared with littermate control mice. Intravital microscopy shows that this is the result of increased leukocyte adhesion and transmigration, whereas rolling of leukocytes is not significantly affected in transgenic mice compared with littermates. Thus, JAM-C participates in the later steps of the leukoendothelial adhesion cascade.

Systemic Inflammatory Response and Adhesion Molecules

The lecture presents the materials of foreign studies on the mechanisms responsible for the formation of a systemic inflammatory response syndrome (SIRS). The hypotheses accounting for the occurrence of SIRS in emergencies are described. Adhesion molecules (AM) and endothelial dysfunction are apparent to be involved in the inflammatory process, no matter what the causes of SIRS are. The current classification of AM and adhesion cascades with altered blood flow is presented. There are two lines in the studies of AM. One line is to measure the concentration of AM in the plasma of patients with emergencies of various etiology. The other is to study the impact of antiadhesion therapy on the alleviation of the severity of terminal state and its outcome. The studies provide evidence for that an adhesive process is a peculiar prelude to a systemic inflammatory response.