Physiology and Pathophysiology of Selectins,Integrins, and IgSf Cell Adhesion Molecules Focusing on Inflammation. A Paradigm Model on Infectious Endocarditis

Abstract

The development of adhesion bonds, either among cells or among cells and components of the extracellular matrix, is a crucial process. These interactions are mediated by some molecules collectively known as adhesion molecules (CAMs). CAMs are ubiquitously expressed proteins playing a central role in controlling cell migration, proliferation, survival, and apoptosis. Besides their key function in physiological maintenance of tissue integrity, CAMs play an eminent role in various pathological processes such as cardiovascular disorders, atherogenesis, atherosclerotic plaque progression and regulation of the inflammatory response. CAMs such as selectins, integrins, and immunoglobulin superfamily take part in interactions between leukocyte and vascular endothelium (leukocyte rolling, arrest, firm adhesion, migration). Experimental data and pathologic observations support the assumption that pathogenic microorganisms attach to vascular endothelial cells or sites of vascular injury initiating intravascular infections. In this review a paradigm focusing on cell adhesion molecules pathophysiology and infective endocarditis development is given.     

Molecular events during leukocyte diapedesis

The recruitment of leukocytes from the circulation into tissues requires leukocyte migration through the vascular endothelium. The mechanisms by which leukocytes attach and firmly adhere to the endothelial cell surface have been studied in detail. However, much less is known about the last step in this process, the diapedesis of leukocytes through the vascular endothelium. This minireview focuses on the interactions between leukocyte and endothelial cell adhesion molecules that are important during leukocyte extravasation. In the past few years a series of endothelial cell surface and adhesion molecules have been identified that are located at endothelial cell contacts and found to participate in leukocyte diapedesis. These junctional cell adhesion molecules are believed to have an active role in controlling the opening and closure of endothelial cell contacts to allow the passage of leukocytes between adjacent endothelial cells. Alternatively, leukocytes can cross the endothelium at nonjunctional locations, with leukocytes migrating through a single endothelial cell. Further work is clearly needed to understand, in greater detail, the molecular mechanisms that allow leukocytes to cross the endothelium via either the paracellular or the transcellular pathway.     

CELL ADHESION MOLECULES: A UNIFYING APPROACH TO TOPOGRAPHIC BIOLOGY

Cell adhesion molecules are pivotal to the development and maintenance of tissue structure in metazoan organisms. In mammals, several families of proteins are involved in cell-cell and cell-matrix adhesion. The cadherins are homophilic, primary CAMs, involved in the establishment of boundaries between cell collectives early in embryogenesis. The Ig gene superfamily have diversified widely, with homophilic and heterophilic CAMs and antigen recognition molecules amongst the members. The Integrin family play an important role in binding to extracellular matrix, as well as counter-receptors on the surface of other cells. The Selectin family and HCAM are carbohydrate-binding proteins, and play a prominent role in the circulation of lymphocytes and neoplastic cells. CAMs are fundamental to development of tissue structure in metazoan organisms. Cellular differentiation dictates adherence to a specific microenvironment, through the pattern of surface CAM expression. Conversely, CAM binding can affect gene expression within the cell itself. Cell differentiation and cell adhesion are interdependent processes. In the adult, CAM are crucial to tissue maintenance. Cells frequently change their adhesive properties in response to physiological or pathological processes. The integrity of the vascular system is maintained by circulating platelets which are capable of rapid upregulation of cell adhesion and profound changes in metabolism, on contact with subendothelial matrix. Both endothelial cells and neutrophils undergo changes in CAM expression in response to inflammatory mediators, permitting rapid and appropriate recruitment of phagocytes to damaged tissue. Tissue repair is dependent on phenotypic changes in normally static cells, allowing increased motility and replication. The immune system requires constitutive cells to undergo multiple complex adhesion and detachment events over short periods of time, and is capable of discriminating normal self from aberrant-self or non-self, through antigen specific recognition and adhesion molecules. The pathophysiology of processes such as infection and neoplasia are profoundly affected by cellular CAM expression. CAMs and related molecules are fundamental to the development, maintenance and surveillance of tissue structure.     

Activated leukocyte cell adhesion molecule is a component of the endothelial junction involved in transendothelial monocyte migration

Transendothelial leukocyte migration is a major aspect of the innate immune response. It is essential in repair and regeneration of damaged tissues and is regulated by multiple cell adhesion molecules (CAMs) including members of the immunoglobulin (Ig) superfamily. Activated leukocyte cell adhesion molecule (ALCAM/CD166) is an Ig CAM expressed by activated monocytes and endothelial cells. Hitherto, the functional relevance of ALCAM expression by endothelial cells and activated monocytes remained unknown. In this report, we demonstrate soluble recombinant human ALCAM significantly inhibited the rate of transendothelial migration of monocyte cell lines. Direct involvement of ALCAM in transendothelial migration was evident from the robust inhibition of this process by ALCAM blocking antibodies. However, soluble recombinant ALCAM had no impact on monocyte migration or adhesion to endothelium. Localization of ALCAM specifically at cell-cell junctions in endothelial cells supported its role in transendothelial migration. This study is the first to localize ALCAM to endothelial cell junctions and demonstrate a functional relevance for co-expression of ALCAM by activated monocytes and endothelial cells.     

Visfatin enhances ICAM-1 and VCAM-1 expression through ROS-dependent NF-kappaB activation in endothelial cells

Visfatin has recently been identified as a novel visceral adipokine which may be involved in obesity-related vascular disorders. However, it is not known whether visfatin directly contributes to endothelial dysfunction. Here, we investigated the effect of visfatin on vascular inflammation, a key step in a variety of vascular diseases. Visfatin induced leukocyte adhesion to endothelial cells and the aortic endothelium by induction of the cell adhesion molecules, ICAM-1 and VCAM-1. Promoter analysis revealed that visfatin-mediated induction of CAMs is mainly regulated by nuclear factor-kappaB (NF-kappaB). Visfatin stimulated IkappaBalpha phosphorylation, nuclear translocation of the p65 subunit of NF-kappaB, and NF-kappaB DNA binding activity in HMECs. Furthermore, visfatin increased ROS generation, and visfatin-induced CAMs expression and NF-kappaB activation were abrogated in the presence of the direct scavenger of ROS. Taken together, our results demonstrate that visfatin is a vascular inflammatory molecule that increases expression of the inflammatory CAMs, ICAM-1 and VCAM-1, through ROS-dependent NF-kappaB activation in endothelial cells.     

New aspects of integrin-mediated leukocyte adhesion in inflammation: regulation by haemostatic factors and bacterial products

Leukocyte recruitment to sites of inflammation, infection or vascular injury is a complex event, depending on a tightly coordinated sequence of leukocyte-endothelial- and leukocyte-platelet interactions, which are controlled by the expression and activation of various adhesion receptors and protease systems. The present review will focus on novel aspects of the regulation of integrin-dependent leukocyte adhesion by haemostatic factors and bacterial products. In particular, after a short overview of leukocyte recruitment, the review (i) will focus on the crosstalk between haemostatic factors and adhesion molecules with respect to leukocyte extravasation based on the paradigms of the urokinase receptor and high molecular weight kininogen, (ii) will provide information on novel mechanisms for the regulation of leukocyte recruitment by bacterial proteins, on the basis of the anti-inflammatory role of Staphylococcus aureus extracellular adhesive protein and (iii) will draw attention to the junctional adhesion molecules, a novel family of adhesive receptors that are counter-receptors for leukocyte integrins and mediate vascular cell interactions. The better understanding of the interactions between vascular cells and particularly of integrin-dependent leukocyte adhesion may lead to the development of novel therapeutical concepts in inflammatory vascular disorders.     

West Nile Virus-Induced Cell Adhesion Molecules on Human Brain Microvascular Endothelial Cells Regulate Leukocyte Adhesion and Modulate Permeability of the In Vitro Blood-Brain Barrier Model

Characterizing the mechanisms by which West Nile virus (WNV) causes blood-brain barrier (BBB) disruption, leukocyte infiltration into the brain and neuroinflammation is important to understand the pathogenesis of WNV encephalitis. Here, we examined the role of endothelial cell adhesion molecules (CAMs) in mediating the adhesion and transendothelial migration of leukocytes across human brain microvascular endothelial cells (HBMVE). Infection with WNV (NY99 strain) significantly induced ICAM-1, VCAM-1, and E-selectin in human endothelial cells and infected mice brain, although the levels of their ligands on leukocytes (VLA-4, LFA-1and MAC-1) did not alter. The permeability of the in vitro BBB model increased dramatically following the transmigration of monocytes and lymphocytes across the models infected with WNV, which was reversed in the presence of a cocktail of blocking antibodies against ICAM-1, VCAM-1, and E-selectin. Further, WNV infection of HBMVE significantly increased leukocyte adhesion to the HBMVE monolayer and transmigration across the infected BBB model. The blockade of these CAMs reduced the adhesion and transmigration of leukocytes across the infected BBB model. Further, comparison of infection with highly neuroinvasive NY99 and non-lethal (Eg101) strain of WNV demonstrated similar level of virus replication and fold-increase of CAMs in HBMVE cells suggesting that the non-neuropathogenic response of Eg101 is not because of its inability to infect HBMVE cells. Collectively, these results suggest that increased expression of specific CAMs is a pathological event associated with WNV infection and may contribute to leukocyte infiltration and BBB disruption in vivo. Our data further implicate that strategies to block CAMs to reduce BBB disruption may limit neuroinflammation and virus-CNS entry via ‘Trojan horse’ route, and improve WNV disease outcome.     

Role of the extracellular matrix in lymphocyte migration

The extracellular matrix (ECM) exists in various biochemical and structural forms that can act either as a barrier to migrating leukocytes, in the case of basement membranes, or provide a physical scaffold supporting or guiding migration (interstitial matrix). This review focuses on basement membranes and our current knowledge of the way that leukocytes transmigrate this protein barrier, with emphasis on T lymphocytes. Recent data suggest that the classical concept of cell-matrix adhesion requires revision with respect to leukocyte-ECM interactions. Whereas specific receptors may be required for leukocyte recognition of ECM molecules or three-dimensional structural domains, the role of adhesion in migration as perceived from the traditional studies of adherent cell-ECM interactions is less clear. Further, the indirect effects of ECM such as the binding and presentation of cytokines or chemotactic factors may more profoundly influence the directed migration of normally non-adherent leukocytes than the migration of adherent cells such as epithelial cells or fibroblasts. Proteases (in particular matrix metalloproteinases) released at sites of inflammation can selectively process ECM, cell surface molecules or soluble factors, which may result in the release of bioactive fragments that can function as chemoattractants for different leukocyte subsets or may modulate the activity/function of resident mesenchymal and immune cells. Current findings suggest that different leukocyte types employ different mechanisms to migrate across or through the ECM; this might be determined by the composition and organization of the ECM itself.     

Significance of cell adhesion molecules, CD56/NCAM in particular, in human tumor growth and spreading

Cell adhesion molecules (CAM) represent a large group of cell surface protein moieties with distinctive biological functions. In physiological terms they ascertain cell to cell contact such as cell cohesion of epithelia, condition cell migration and transmigration via biological membranes such as blood vessel walls, provide means for homing cells in a new microenvironment etc. These features of CAM are exploited by tumor cells to grow and spread in a tumor bearing host. CD56/N-CAM antigen is 140 kD isoform of neural cell adhesion molecule. N-CAM belongs to the large Ig superfamily of CAMs. CD56 can be traced at various sites, including nervous tissue, neuro-muscular junctions, neuroendocrine and endocrine organs. It is well known as a differentiation antigen of natural killer (NK) cells. Its role and function are far from clear, but its adhesion properties are evident in cell-cell (homophilic) interactions. CD56 has been, however, demonstrated the cells various human malignancies. Tumors of the nervous system such as neuroblastoma, are well known to express this marker. Malignant lymphomas of T-NK cell origin bear CD56, as well as multiple myeloma, melanoma and some cancers of epithelial origin. These data suggest that CD56/N-CAM antigen is, in some unknown manner involved in tumor biology.     

L1 and NCAM adhesion molecules as signaling coreceptors in neuronal migration and process outgrowth

Neural cell adhesion molecules (CAMs) of the immunoglobulin superfamily engage in multiple neuronal interactions that influence cell migration, axonal and dendritic projection, and synaptic targeting. Their downstream signal transduction events specify whether a cell moves or projects axons and dendrites to targets in the brain. Many of the diverse functions of CAMs are brought about through homophilic and heterophilic interactions with other cell surface receptors. An emerging concept is that CAMs act as coreceptors to assist in intracellular signal transduction, and to provide cytoskeletal linkage necessary for cell and growth cone motility. Here we will focus on new discoveries that have revealed novel coreceptor functions for the best-understood CAMs--L1, CHL1, and NCAM--important for neuronal migration and axon guidance. We will also discuss how dysregulation of CAMs may also bear on neuropsychiatric disease and cancer.     

神经粘附分子CHL1在神经系统中的研究进展

粘附分子通过介导细胞间相互作用发挥其在发育、再生和突触修饰等方面的重要作用.神经细胞粘附分子CHL1(close homologue of L1)是近年发现的粘附分子,属于粘附分子免疫球蛋白超家族,集中表达于神经系统,通过亲异性作用(heterophilic interaction)介导细胞与细胞、细胞与胞外基质的相互作用,进而参与神经系统的发育、轴突的生长、迁移及导向等过程.     

Role of E-cadherin and other cell adhesion molecules in survival and differentiation of human pluripotent stem cells

The survival, proliferation, self-renewal and differentiation of human pluripotent stem cells (hPSCs, including human embryonic stem cells and human induced pluripotent stem cells) involve a number of processes that require cell-cell and cell-matrix interactions. The cell adhesion molecules (CAMs), a group of cell surface proteins play a pivotal role in mediating such interactions. Recent studies have provided insights into the essential roles and mechanisms of CAMs in the regulation of hPSC fate decisions. Here, we review the latest research progress in this field and focus on how E-cadherin and several other important CAMs including classic cadherins, Ig-superfamily CAMs, integrins and heparin sulfate proteoglycans control survival and differentiation of hPSCs     

Role of E-cadherin and other cell adhesion molecules in survival and differentiation of human pluripotent stem cells

The survival, proliferation, self-renewal and differentiation of human pluripotent stem cells (hPSCs, including human embryonic stem cells and human induced pluripotent stem cells) involve a number of processes that require cell-cell and cell-matrix interactions. The cell adhesion molecules (CAMs), a group of cell surface proteins play a pivotal role in mediating such interactions. Recent studies have provided insights into the essential roles and mechanisms of CAMs in the regulation of hPSC fate decisions. Here, we review the latest research progress in this field and focus on how E-cadherin and several other important CAMs including classic cadherins, Ig-superfamily CAMs, integrins and heparin sulfate proteoglycans control survival and differentiation of hPSCs     

EndoCAM: a novel endothelial cell-cell adhesion molecule

Cell-cell adhesion is controlled by many molecules found on the cell surface. In addition to the constituents of well-defined junctional structures, there are the molecules that are thought to play a role in the initial interactions of cells and that appear at precise times during development. These include the cadherins and cell adhesion molecules (CAMs). Representatives of these families of adhesion molecules have been isolated from most of the major tissues. The notable exception is the vascular endothelium. Here we report the identification of a cell surface molecule designated "endoCAM" (endothelial Cell Adhesion Molecule), which may function as an endothelial cell-cell adhesion molecule. EndoCAM is a 130-kD glycoprotein expressed on the surface of endothelial cells both in culture and in situ. It is localized to the borders of contiguous endothelial cells. It is also present on platelets and white blood cells. Antibodies against endoCAM prevent the initial formation of endothelial cell-cell contacts. Despite similarities in size and intercellular location, endoCAM does not appear to be a member of the cadherin family of adhesion receptors. The serologic and protease susceptibility characteristics of endoCAM are different from those of the known cadherins, including an endogenous endothelial cadherin. Although the precise biologic function of endoCAM has not been determined, it appears to be one of the molecules responsible for regulating endothelial cell-cell adhesion processes and may be involved in platelet and white blood cell interactions with the endothelium.     

The junctional adhesion molecule-C promotes neutrophil transendothelial migration in vitro and in vivo

The third member of the family of junctional adhesion molecules (JAMs), JAM-3, also called JAM-C, was recently shown to be a novel counter-receptor on platelets for the leukocyte beta(2)-integrin Mac-1 (alphaMbeta(2), CD11b/CD18). Here, new functional aspects of the role of endothelial cell JAM-C were investigated. Endothelial cells express JAM-C, which is predominantly localized within junctions at interendothelial contacts, since it codistributes with a tight junction component, zonula occludens-1. Whereas JAM-C does not participate in neutrophil adhesion to endothelial cells, it mediates neutrophil transmigration in a Mac-1-dependent manner. In particular, inhibition of JAM-C significantly reduced neutrophil transendothelial migration, and the combination of JAM-C and platelet/endothelial cell adhesion molecule-1 blockade almost completely abolished neutrophil transendothelial migration in vitro. In vivo, inhibition of JAM-C with soluble mouse JAM-C resulted in a 50% reduction of neutrophil emigration in the mouse model of acute thioglycollate-induced peritonitis. Thus, JAM-C participates in neutrophil transmigration and thereby provides a novel molecular target for antagonizing interactions between vascular cells that promote inflammatory vascular pathologies.     

Role of Cell Adhesion Molecules and Immune-Cell Migration in the Initiation,Onset and Development of Atherosclerosis

Atherosclerosis is currently the leading factor of death in developed countries. It is now recognized as a chronic immune-inflammatory disease, whose initial stages involve the interaction of leukocytes with the endothelial monolayer. The initial stage of atherosclerosis requires the interplay of various cell adhesion molecules and immune cells to trigger leukocyte and lymphocyte migration from the circulating blood into the arterial intima. Studies have unveiled the role of inflammatory mediators in the initiation, onset and progression of the disease. During the last few years we have gained a greater understanding of the mechanism that modulates monocyte, macrophage and T cell infiltration, the role these cells play in the atherosclerotic lesion, in the formation of the fibrous plaque formation with the consequent narrowing of the arteries and the mechanisms that lead to plaque rupture and the formation of thrombi and emboli. This review talks about the leukocyte recruitment in early atherosclerosis, the formation of the plaque, and the mechanisms that lead to thrombosis in advanced atherosclerosis. Finally, we discuss the potential for novel therapies to treat this disease.Key Words: CAMs, leukocyte, lymphocyte, migration, atherosclerosis, extravasation     

Genetic evidence for functional redundancy of Platelet/Endothelial cell adhesion molecule-1 (PECAM-1): CD31-deficient mice reveal PECAM-1-dependent and PECAM-1-independent functions

Platelet/endothelial cell adhesion molecule-1 (PECAM-1; CD31), a member of the Ig superfamily, is expressed strongly at endothelial cell-cell junctions, on platelets, and on most leukocytes. CD31 has been postulated to play a role in vasculogenesis and angiogenesis, and has been implicated as a key mediator of the transendothelial migration of leukocytes. To further define the physiologic role of CD31, we used targeted gene disruption of the CD31 gene in embryonic stem cells to generate CD31-deficient mice. CD31-deficient mice (CD31KO) are viable and born at the expected Mendelian frequency, remain healthy, and exhibit no obvious vascular developmental defects. In response to inflammatory challenge, polymorphonuclear leukocytes of CD31KO mice are arrested between the vascular endothelium and the basement membrane of inflammatory site mesenteric microvessels, confirming a role for CD31 in the migration of neutrophils through the subendothelial extracellular matrix. Normal numbers of leukocytes are recovered from inflammatory sites in CD31KO mice, however, suggesting that the defect in leukocyte migration across basal lamina observed in the absence of CD31 may be compensated for by the use of other adhesion molecules, or possibly an increased rate of migration. Homing of T lymphocytes in vivo is normal, and CD31KO mice are able to mount a cutaneous hypersensitivity response normally. In addition, CD31-mediated homophilic adhesion does not appear to play a role in platelet aggregation in vitro. This study provides genetic evidence that CD31 is involved in transbasement membrane migration, but does not play an obligatory role in either vascular development or leukocyte migration.     

Surface engineering of quantum dots for in vivo vascular imaging

Quantum dot-antibody bioconjugates (QD-mAb) were synthesized incorporating PEG cross-linkers and Fc-shielding mAb fragments to increase in vivo circulation times and targeting efficiency. Microscopy of endothelial cell cultures incubated with QD-mAb directed against cell adhesion molecules (CAMs), when shielded to reduce Fc-mediated interactions, were more specific for their molecular targets. In vitro flow cytometry indicated that surface engineered QD-mAb labeled leukocyte subsets with minimal Fc-mediated binding. Nontargeted QD-mAb nanoparticles with Fc-blockade featured 64% (endothelial cells) and 53% (leukocytes) lower nonspecific binding than non-Fc-blocked nanoparticles. Spectrally distinct QD-mAb targeted to the cell adhesion molecules (CAMs) PECAM-1, ICAM-1, and VCAM-1 on the retinal endothelium in a rat model of diabetes were imaged in vivo using fluorescence angiography. Endogenously labeled circulating and adherent leukocyte subsets were imaged in rat models of diabetes and uveitis using QD-mAb targeted to RP-1 and CD45. Diabetic rats exhibited increased fluorescence in the retinal vasculature from QD bioconjugates to ICAM-1 and VCAM-1 but not PECAM-1. Both animal models exhibited leukocyte rolling and leukostasis in capillaries. Examination of retinal whole mounts prepared after in vivo imaging confirmed the fluorescence patterns seen in vivo. Comparison of the timecourse of retinal fluorescence from Fc-shielded and non-Fc-shielded bioconjugates indicated nonspecific uptake and increased clearance of the non-Fc-shielded QD-mAb. This combination of QD surface design elements offers a promising new in vivo approach to specifically label vascular cells and biomolecules of interest.     

突触细胞黏附分子在应激中作用的研究进展

突触细胞黏附分子是一类介导突触前、后膜结构和功能互作的膜表面糖蛋白,可以动态调节突触活动和可塑性,其表达与功能受到环境因素调控。突触细胞黏附分子亦是应激反应重要的效应分子之一,可介导应激对认知和情绪的不良影响。本文综述近年来突触细胞黏附分子在应激中作用的研究进展,旨在为应激相关障碍的分子机制研究和药物研发提供思路。     

Should I stay or should I go? Shedding of RPTPs in cancer cells switches signals from stabilizing cell-cell adhesion to driving cell migration

Dissolution of cell-cell adhesive contacts and increased cell-extracellular matrix adhesion are hallmarks of the migratory and invasive phenotype of cancer cells. These changes are facilitated by growth factor binding to receptor protein tyrosine kinases (RTKs). In normal cells, cell-cell adhesion molecules (CAMs), including some receptor protein tyrosine phosphatases (RPTPs), antagonize RTK signaling by promoting adhesion over migration. In cancer, RTK signaling is constitutive due to mutated or amplified RTKs, which leads to growth factor independence, or autonomy. An alternative route for a tumor cell to achieve autonomy is to inactivate cell-cell CAMs such as RPTPs. RPTPs directly mediate cell adhesion and regulate both cadherin-dependent adhesion and signaling. In addition, RPTPs antagonize RTK signaling by dephosphorylating molecules activated following ligand binding. Both RPTPs and cadherins are downregulated in tumor cells by cleavage at the cell surface. This results in shedding of the extracellular, adhesive segment and displacement of the intracellular segment, altering its subcellular localization and access to substrates or binding partners. In this commentary we discuss the signals that are altered following RPTP and cadherin cleavage to promote cell migration. Tumor cells both step on the gas (RTKs) and disconnect the brakes (RPTPs and cadherins) during their invasive and metastatic journey.